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O presente estudo buscou identificar dificuldades de manejo ou déficit de conhecimento quanto à utilização do dispositivo bolsa-válvula-máscara (BVM), entre os profissionais intensivistas. O processo ocorreu em quatro etapas, a primeira com a aplicação de um questionário estruturado que abordou questões básicas, como o conhecimento do dispositivo, a segunda através de um teste prático, onde os participantes simularam um atendimento rotineiro, para avaliar a pressão e o volume corrente realizado pelos mesmo, em seguida a terceira fase ocorre com uma educação continuada embasada nas dificuldades apresentadas pelos voluntários durante a execução dos testes, a quarta e última, consistiu em um pós teste teórico, para análise da fixação do aprendizados. Os intensivistas apresentam, em sua grande maioria, bom domínio prático sobre equipamento, observa-se isso devido gerarem pressões em níveis seguros, volume corrente com média de 7,57±2,95ml, ficando dentro do recomendado em um estudo realizado por Holte, em 2020. Quanto à frequência respiratória a média foi de 40,87±15,78 incursões por minuto, também conforme recomendações. Na avaliação teórica foi possível indicar poucas dificuldades, a que mais se destaca é 48,4% diz não saber a pressão ideal a ser realizada em um neonato estável. É válido ressaltar a importância dos treinamentos contínuos teóricos e práticos em qualquer espaço hospitalar. O profissional preparado evita danos ao paciente, exerce sua função e presta um serviço com segurança, proporcionando um atendimento humanizado, reduzindo gastos e período de hospitalização. The present study sought to identify management difficulties or a lack of knowledge regarding the use of the bag-valve-mask (BVM) device among intensive care professionals. The process took place in four stages, the first with the application of a structured questionnaire that addressed basic questions, such as knowledge of the device, the second through a practical test, where participants simulated a routine care, to assess pressure and volume. carried out by the same, then the third phase occurs with a continuing education based on the difficulties presented by the volunteers during the execution of the tests, the fourth and last, consists of a theoretical post test, for analysis of the learning fixation. Intensivists have, for the most part, practical mastery over equipment, this is observed because they generate pressures at safe levels, tidal volume with an average of 7.57±2.95 ml, being within the estimated ideal and respiratory rate of 40.87 ±15.78 incursions per minute, also as recommended. In the theoretical evaluation, it was possible to indicate few difficulties, the one that stands out the most is 48.4% say they do not know the ideal pressure to be performed on a stable neonate. It is worth emphasizing the importance of continuous theoretical and practical training in any hospital setting. The prepared professional avoids harm to the patient, performs his function and provides a service safely, providing humanized care, reducing expenses and hospitalization period. El presente estudio buscó identificar dificultades de manejo o desconocimiento sobre el uso del dispositivo bolsa-válvula-mascarilla (BVM) entre los profesionales de cuidados intensivos. El proceso se desarrolló en cuatro etapas, la primera con la aplicación de un cuestionario estructurado que abordó cuestiones básicas, como el conocimiento del aparato, la segunda a través de una prueba práctica, donde los participantes simularon un cuidado de rutina, para evaluar la presión y el volumen llevados a cabo. por el mismo, luego se da la tercera fase con una educación continúa basada en las dificultades presentadas por los voluntarios durante la ejecución de las pruebas, la cuarta y última, consta de un post test teórico, para el análisis de la fijación del aprendizaje. Los intensivistas tienen, en su mayoría, dominio práctico sobre los equipos, esto se observa porque generan presiones a niveles seguros, volumen corriente con un promedio de 7,57±2,95 ml, estando dentro del ideal estimado y frecuencia respiratoria de 40,87±15,78 incursiones por minuto, también como se recomienda. En la evaluación teórica fue posible señalar pocas dificultades, la que más se destaca es que el 48,4% dice desconocer la presión ideal a realizar en un neonato estable. Cabe destacar la importancia de la formación teórica y práctica continua en cualquier ámbito hospitalario. El profesional preparado evita el daño al paciente, cumple su función y presta un servicio con seguridad, brindando una atención humanizada, reduciendo gastos y tiempo de hospitalización.

BACKGROUND: Brain damage can affect several functions related to speech production leading to dysphonia and dysarthria. Most rehabilitation treatments focus on articulation training rather than on pneumophonic coordination and respiratory muscle strength. Respiratory training using an intermitted positive pressure breathing (IPPB) ventilator can be used for this last purpose; no agreement on a standard protocol has been reached to date. AIM: To evaluate the feasibility and the effectiveness of a standardized incremental protocol of respiratory training using IPPB to treat dysphonia and dysarthria. DESIGN: Case series study. SETTING: Neuropsychological Rehabilitation Unit in an Italian Neurorehabilitation Division. POPULATION: Thirty-two subjects with dysphonia and dysarthria resulting from neurological lesion. METHODS: Participants were assessed using clinical evaluation scales (GIRBAS scale of dysphonia, Robertson dysarthria profile), respiratory function test, and arterial blood gas analysis in air. The evaluations were performed at baseline and after 20 sessions of respiratory training with IPPB. The protocol provided a default increment of ventilator parameters. All subjects also underwent a standard speech and language therapy treatment. A satisfaction survey to assess acceptability and the Goal Attainment Scale were applied. RESULTS: All participants fulfilled the protocol. No complications or discomfort were reported. Subjects' satisfaction at survey was 97.7%. After respiratory training, all respiratory function parameters increased, but only maximal voluntary ventilation (MVV), maximum inspiratory pressure (MIP), and maximum expiratory pressure (MEP) were statistically significant (P

Transfusion-associated acute lung injury (TRALI) is one of the complications seen due to transfusion. Hypoxemia and bilateral pulmonary infiltration in posteroanterior chest roentgenogram is seen in all cases during transfusion or within the first 6 hours; fever, hypotension, and pink frothy bleeding from endotracheal tube may also be seen. It can be seen following the administration of any blood product. The management strategies for TRALI include withholding the transfusion, positive pressure breathing support, and diuretics. There are few reported cases of TRALI occurring following donor granulocyte transfusion (DGT). In this article, we discuss two cases of TRALI following DGT transfusion.

Introduction: Positive pressure breathing air-fed protective suits from three vendors are commonly used in biosafety level 4 (BSL-4) laboratories: they are Dover Chemturion suits (ILC Dover, DE), Delta suits (Honeywell Safety, NC), and HVO suits (HVO-ISSI-Deutschland GmbH, Germany). To address the potential risk of infectious agents being introduced through the supplied breathing air stream, some suit manufacturers incorporate protective filters on the suits themselves. However, these integrated filters are not amenable to in situ testing for efficacy verification. We have been using external filters from Matheson USA on the positive pressure suits since our BSL-4 laboratories were commissioned two decades ago. As part of our BSL-4 protective suit management program, we test these filters before them being put into use, and annually thereafter. In the past few years, we have observed these filters failing at a higher rate, as high as two out of three of the new filters tested at one point. Objective: The purpose of this study was to procure personal protective filters from other sources and validate their efficacy long-term. Methods: Filters from Respirex, HVO, and Honeywell were validated for filter integrity and filter loading. Results: Respirex filters performed well during the initial testing and periodic testing thereafter. Regular testing of the Respirex filters has now been ongoing for 30 months with continued successful performance. Conclusion: Filters from Respirex are a suitable option to protect personnel wearing positive pressure suits in BSL-4 laboratories.

A respiratory mechanics model of the human lung is developed for studying pressure-compensated breathing through a respiration mask in low-ambient pressure environments encountered during high-altitude flight. The model formulation is described using a bond graph (BG) approach to convey the key elements used to capture critical effects in lung airways and effects of dissipative and energy storing processes. Specific extensions to constitutive relations are described, along with derivation and solution of system state equations via simulation. Gas exchange effects are not incorporated in the model, with emphasis placed on developing and assessing a respiratory mechanics model for integration with breathing support systems. Results from several case studies with variations in the lung characteristics and operational conditions are presented to demonstrate the effectiveness of the model in predicting key physiological measures, reported in the form of flow-volume loops and work of breathing (WoB). Favorable comparisons with the past results reported in the literature confirm the suitability of this model as part of a system-level model capable of guiding modifications and explaining anomalous behavior in these critical systems.

BACKGROUND: Spontaneous pneumothorax (PTX) is a diagnostic challenge in aviators given the common occurrence of musculoskeletal pain after flight and notorious underreporting of symptoms of other diseases in this group.CASE REPORT: A 24-yr-old active duty F/A-18 Weapon Systems Officer performed an anti-G straining maneuver (AGSM) in response to a 6.5-g warm-up turn during a training flight at 16,000 ft (4876.8 m) above sea level. He immediately developed right-sided thoracic back pain. The flight was terminated, he landed, and the pain improved. Over the next 5 d, he noticed the insidious development of pleuritic chest pain and dyspnea. His symptoms prompted presentation to an aviation medicine clinic where a large right sided PTX was identified. After transfer to a local emergency department, a large bore chest tube was placed. A CT scan showed bilateral apical blebs requiring right and subsequently left video assisted thoracoscopy (VATS) with chemical/mechanical pleurodesis and apical wedge resection. Pulmonary function testing (PFT) showed a mild restriction defect 2-1/2 mo after surgery. The patient also completed cardiopulmonary exercise testing (CPET), performing better than his predicted reference range. After a high resolution CT showed no remaining signs of bleb or cyst disease and another month of healing he was returned to flight.DISCUSSION: PTX should be considered in aviators with perithoracic pain after flight as several aspects of flight in high performance aircraft may increase the risk for PTX. These include positive pressure breathing through a facemask, repeated use of the AGSM, and the possibility of bleb expansion at altitude.DeYoung H, Ahmed Y, Buckley J. F/A-18 aviator successfully returned to flight after an in-flight spontaneous pneumothorax. Aerosp Med Hum Perform. 2018; 89(11):1008-1012.

The hemodynamic effects of ventilation can be grouped into three concepts: 1) Spontaneous ventilation is exercise; 2) changes in lung volume alter autonomic tone and pulmonary vascular resistance and can compress the heart in the cardiac fossa; and 3) spontaneous inspiratory efforts decrease intrathoracic pressure, increasing venous return and impeding left ventricular ejection, whereas positive-pressure ventilation decreases venous return and unloads left ventricular ejection. Spontaneous inspiratory efforts may induce acute left ventricular failure and cardiogenic pulmonary edema. Reversing the associated negative intrathoracic pressure swings by using noninvasive continuous positive airway pressure rapidly reverses acute cardiogenic pulmonary edema and improves survival. Additionally, in congestive heart failure, states increasing intrathoracic pressure may augment left ventricular ejection and improve cardiac output. Using the obligatory changes in venous return induced by positive pressure breathing, one can quantify the magnitude of associated decreases in venous flow and left ventricular ejection using various parameters, including vena caval diameter changes, left ventricular stroke volume variation, and arterial pulse pressure variation. These parameters vary in proportion to the level of cardiac preload reserve present, thus accurately predicting which critically ill patients will increase their cardiac output in response to fluid infusions and which will not. Common parameters include arterial pulse pressure variation and left ventricular stroke volume variation. This functional hemodynamic monitoring approach reflects a practical clinical application of heart-lung interactions.

Background Immersion pulmonary edema is potentially a catastrophic condition; however, the pathophysiological mechanisms are ill-defined. This study assessed the individual and combined effects of exertion and negative pressure breathing on the cardiovascular system during the development of pulmonary edema in SCUBA divers. Methods Sixteen male professional SCUBA divers performed four SCUBA dives in a freshwater pool at 1 m depth while breathing air at either a positive or negative pressure both at rest or with exercise. Echocardiography and lung ultrasound were used to assess the cardiovascular changes and lung comet score (a measure of interstitial pulmonary edema). Results The ultrasound lung comet score was 0 following both the dives at rest regardless of breathing pressure. Following exercise, the mean comet score rose to 4.2 with positive pressure breathing and increased to 15.1 with negative pressure breathing. The development of interstitial pulmonary edema was significantly related to inferior vena cava diameter, right atrial area, tricuspid annular plane systolic excursion, right ventricular fractional area change, and pulmonary artery pressure. Exercise combined with negative pressure breathing induced the greatest changes in these cardiovascular indices and lung comet score. Conclusions A diver using negative pressure breathing while exercising is at greatest risk of developing interstitial pulmonary edema. The development of immersion pulmonary edema is closely related to hemodynamic changes in the right but not the left ventricle. Our findings have important implications for divers and understanding the mechanisms of pulmonary edema in other clinical settings.

The National Institutes of Health (NIH)-National Heart, Lung, and Blood Institute’s (NHLBI) Division of Lung Diseases is celebrating its 50(th) anniversary. On this occasion, we are reviewing the major landmark clinical trials that were initiated by the NHLBI’s Division of Lung Disease and that have had substantial impact on our understanding of chronic obstructive pulmonary disease (COPD) and how it is best treated. Although some of these trials did not show hypothesized treatment benefits for COPD, they have enabled clinicians to provide care for individuals with COPD relying on the most rigorous evidence. The 5 trials that are reviewed here are: the Intermittent Positive Pressure Breathing Trial, the Nocturnal Oxygen Treatment Trial, the Lung Health Study, the National Emphysema Treatment Trial, and the Long-term Oxygen Treatment Trial. These clinical trials have not only set the standards for COPD care but have served as models for the state-of-the-art conduct of clinical research in COPD.

Purpose Children have few small alveoli, which reduce lung compliance; in contrast, their cartilaginous rib cage makes their chest wall highly compliant. This combination promotes lung collapse. Prolonged inspiratory to expiratory (I:E) ratio ventilation is used to optimize gas exchange and respiratory mechanics in surgery. However, the optimal ratio is unclear in children. We hypothesized that, compared to a 1:2 I:E ratio, a 1:1 I:E ratio would improve dynamic compliance and oxygenation, and affect the peak airway pressure in pediatric patients undergoing surgery. Materials and methods Forty-eight patients aged ≤6 years who were scheduled to undergo surgery under general anesthesia with an arterial line were randomly allocated to receive 1:1 (group 1:1) or 1:2 (group 1:2) I:E ratio ventilation. Airway pressure, respiratory system compliance, and arterial blood gas analyses were compared between groups immediately after induction (T0), 30 min after induction (T1), 60 min after induction (T2), immediately after surgery (T3), and on arrival at the post-anesthesia care unit (T4). Results Peak and plateau airway pressures were significantly lower in group 1:1 than in group 1:2 at T1 (p=0.044 and 0.048, respectively). The dynamic and static compliances were significantly higher in group 1:1 than in group 1:2 at T1 (p=0.044 and 0.045, respectively). However, the partial pressure of oxygen did not significantly differ between groups. Conclusion Compared to a 1:2 I:E ratio, a 1:1 I:E ratio improved dynamic compliance and lowered the peak airway pressure without complications in pediatric patients. Nevertheless, our results do not support its use solely for improving oxygenation.

PURPOSE: The purpose of this review was to investigate the effect of respiratory physiotherapy after lung resection on mortality, postoperative pulmonary complications (PPC), length of stay, lung volumes, and adverse events.MATERIAL AND METHODS: Randomized or quasi-randomized controlled trials were searched in CENTRAL, PubMed, EMBASE, Cinahl, PEDro, and hand searching of related studies. Various respiratory physiotherapy interventions were compared to standard care, sham treatment, or no treatment. Two reviewers assessed eligibility and quality of studies using Cochrane guidelines. Meta-analyses were undertaken on subgroups of intervention.RESULTS: Various types of positive pressure breathing, deep breathing exercises, and strength and aerobic exercises as a supplement to standard care did not show any significant effect over standard care in preventing mortality or PPC, reducing length of stay, or improving lung volumes.CONCLUSION: Prophylactic continuous positive airway pressure does not seem to affect rate of mortality and PPC, when compared with standard care embodying respiratory physiotherapy such as airway clearance techniques and assistance with early ambulation. However, further research is still needed to make a final conclusion. The effect of standard respiratory physiotherapy as a package is still unknown, and may or may not be effective in preventing PPC among patients undergoing lung resection.

BACKGROUND: Internal jugular phlebectasia (IJP) is an uncommon entity with only about 100 reported cases and with very few available cases in the literature. The current case study is about a male trainee fighter pilot incidentally diagnosed to have IJP. With limited literary evidence, it was a complex task to predict the prognosis of IJP and its implications on fighter flying.CASE REPORT: In order to confirm the diagnosis, a preliminary study was carried out to find out the normal and expanded area of the internal jugular vein (IJV) of 30 volunteers. The expanded area of the right IJV of the trainee pilot fell beyond 1 SD of the study population, confirming the diagnosis of IJP in the trainee pilot.DISCUSSION: Aeromedical concerns were the anti-G straining maneuver, positive pressure breathing for G, negative Gz, modified Valsalva maneuver, and rapid decompression. Considering the potential progression of IJP by repeated exposure to aviation stresses, the trainee pilot was re-assigned to helicopters.Khatua SS, Sannigrahi P, Dahiya M, Rastogi P, Raheem A. Aeromedical decision making in internal jugular phlebectasia. Aerosp Med Hum Perform. 2019; 90(2):132-134.

Mechanical ventilation is central to critical care and came into routine practice after the polio outbreaks in the mid-20th century. A contemporary mechanical ventilator is a device made to deliver breaths using positive pressure (pressure above atmospheric level). The technology has become increasingly sophisticated in efforts to improve patient comfort and synchrony, as well to enhance ease of use. It is used for many indications, mainly for respiratory failure either from pulmonary or extrapulmonary sources, as well as to provide anesthesia. The most frequently used invasive modes in pediatric populations are synchronized pressure control ventilation with/without volume limitation and pressure support ventilation. While in special circumstances, such as congenital diaphragmatic hernia and severe hypoxemic respiratory failure, high frequency oscillatory ventilation may be a first choice, in most cases noninvasive ventilation and humidified high flow are increasingly used. However, positive pressure breathing can cause direct injury to lungs and has deleterious effects on hemodynamics. The overall goal therefore is to optimize patient needs and minimize risk of harm, while tailoring the ventilation strategy to the patient need. Hence, selection of right mode and strategy, optimization of respiratory mechanics and gas exchange, and provision of expert care are central to management of mechanical ventilation in critically ill children. These are addressed in this chapter.

Glossopharyngeal breathing (GPB), also called “frog breathing”, is a positive pressure breathing technique that uses muscles of the mouth and pharynx to propel small volumes of air (“gulps”) into the lungs. It consists of three phases: 1) mouth opening so that air enters the oral and pharyngeal cavities; 2) mouth closure with tongue and pharyngeal muscles propelling a gulp of air through the open glottis, that raises; 3) glottis closure to ensure the air trapped into the lungs [1, 2]. These three phases are repeated several times until a comfortable lung expansion is reached. GPB is known to be able to increase lung volumes above physiological total lung capacity (TLC) therefore increasing vital capacity [2–5]. This is the consequence of an increase in lung volume, but also of intrapulmonary gas compression. The physiological factors limiting TLC are the effect of the inspiratory muscles that rapidly decreases and the elastic expiratory (inward) recoil of lungs and chest wall that increase. By contrast, TLC during GPB seems to be limited by sensation rather than by respiratory muscles and/or the mechanics of the respiratory system [3]. GPB is largely used by divers because it increases the amount of oxygen/carbon dioxide stored in the body therefore prolonging their breath-hold duration [3, 6, 7]. GPB can also be used as lung inflation therapy to assist the ventilatory pump when it becomes weak or impaired, as in the case of cervical spinal cord injury and/or neuromuscular diseases [8]. Footnotes This manuscript has recently been accepted for publication in the European Respiratory Journal . It is published here in its accepted form prior to copyediting and typesetting by our production team. After these production processes are complete and the authors have approved the resulting proofs, the article will move to the latest issue of the ERJ online. Please open or download the PDF to view this article. Conflict of interest: Dr. LoMauro has nothing to disclose. Conflict of interest: Dr. Banfi has nothing to disclose. Conflict of interest: Dr. Aliverti has nothing to disclose. Conflict of interest: Dr. D'Angelo has nothing to disclose.

This book provides a unique, authoritative and detailed examination of the physiological and clinical consequences of human exposure to high G forces. Pilots of military fast jets, civilian aerobatic pilots and astronauts during the launch and re-entry phases of spaceflight are frequently and repetitively exposed to high G forces, for which the human body is not fundamentally designed. The book examines not only the nature of the high G environment, but the physiological effects of exposure to high G on the various systems of the human body. In particular, the susceptibility of the human cardiovascular system to high G is considered in detail, since G-Induced Loss of Consciousness (G-LOC) is a serious hazard for high G pilots. Additionally, the factors that influence tolerance to G and the emerging scientific evidence of physiological adaptation to high G are examined, as are the various countermeasures and techniques that have been developed over the years to protect pilots from the potentially adverse consequences of high G flight, such as the G-suit and positive pressure breathing. The accumulated knowledge of human exposure to high G is drawn together within High G Flight, resulting in a definitive volume on the physiological effects of high G and their countermeasures.

Purpose. Following corrective surgery for tetralogy of Fallot (TOF), approximately one-third of these patients develop low cardiac output (CO) due to right ventricular (RV) diastolic heart failure. Extubation is beneficial in these patients because the fall in intrathoracic pressure that occurs with conversion from positive pressure breathing to spontaneous breathing improves venous return, RV filling and CO. We hypothesized that if CO were to increase but remain limited following extubation, the obligatory increase in perfusion to the respiratory pump that occurs with loading of the respiratory musculature may occur at the expense of other vital organs, including the brain. Materials and Methods. We conducted a retrospective analysis of all patients undergoing repair of TOF and monitoring of cerebral oxygenation using near infrared spectroscopy. We evaluated the following parameters two hours prior to and following extubation: mean and systolic arterial blood pressure (MBP, SBP), right atrial pressure (RAP), heart rate (HR) and cerebral oxygenation. Results. The study included 22 patients. With extubation, MBP and SBP increased significantly from 67.3 ± 6.5 to 71.1 ± 8.4 mm Hg (P= 0.004) and from 87.2 ± 8.6 to 95.9 ± 10.9 mm Hg (P= 0.001), respectively, while the HR remained unchanged (145 vs. 146 bpm). The RAP remained unchanged following extubation (11.9 vs. 12.0 mm Hg). Following extubation, cerebral oxygen saturations increased significantly from 68.5 ± 8.4 to 74.2 ± 7.9% (P < 0.0001). Cerebral oxygen saturations increased by ≥5% in 11 of 22 patients and by ≥10% in 5 of 22 patients. Conclusion. We conclude that converting from positive pressure ventilation to spontaneous negative pressure breathing following repair of TOF significantly improves arterial blood pressure and cerebral oxygenation.

IntroductionPoint of care (POC) ultrasound brings another powerful dimension to the physical examination of the critically ill. A contemporary challenge for all care providers, however, is how to best incorporate ultrasound into contemporary algorithms of care. When POC ultrasound corroborates pre-examination clinical suspicion, incorporation of the findings into decision-making is easier. When POC ultrasound generates new or unexpected findings, decision-making may be more difficult, especially with conditions that were previously not appreciated with older diagnostic technologies. Pneumothoraces (PTXs), previously seen only on computed tomography and not on supine chest radiographs known as occult pneumothoraces (OPTXs), which are now increasingly appreciated on POC ultrasound, are such an example.MethodsThe relevant literature concerning POC ultrasound and PTXs was reviewed after an electronic search using PubMed supplemented by ongoing research by the Canadian Trauma Trials Collaborative of the Trauma Association of Canada.ResultsOPTXs are frequently encountered in the critically injured who often require mechanical ventilation with positive pressure breathing (PPB). Standard recommendations for post-traumatic PTXs and the setting of PPB mandate chest drainage, recognizing a significant rate of complications related to this procedure itself. Whether these standard recommendations generated in response to obvious overt PTXs apply to these more subtle OPTXs is currently unknown, and evidence-based recommendations regarding appropriate therapy are impossible due to the lack of clinical studies.ConclusionsOPTXs are a condition that illustrates how incorporation of POC ultrasound findings brings further responsibilities to critically appraise the significance of these findings in terms of patient outcomes and overall care. Adequately powered and adequately followed-up clinical trials addressing the treatment are required.

The Royal Australian Air Force (RAAF) mimics emergency aircraft decompression and hypoxia in a chamber decompressed over two to six minutes to a simulated altitude of 25,000 feet (7500m). Air crews in the chamber are trained to use oxygen apparatus including positive pressure breathing systems under these conditions. Over a seven year period, the RAAF has performed approximately 2500 subject decompressions and the Alfred Hospital Hyperbaric Service has treated 11 patients suffering decompression sickness (DCS) following this hypobaric exposure. The 11 patients (eight males, three females, mean age 26±4 years) presented with typical DCS, with joint pains (9), paraesthesiae (7) and concentration and memory deficits (6). One had major neurological deficits including ataxia and dysarthria. Patients required a mean of seven treatments (range 2–25) to a depth of 18m on 100% oxygen. Two patients with refractory symptoms were recompressed with a 50: 50 mix of helium and oxygen and the patient with severe neurological deficit required recompression to 30m. Nine patients had complete resolution of DCS with treatment, one patient resolved fully by one month after treatment, the patient with more severe neurologic deficit recovered completely by 12 months and one patient with persistent mild sensory deficits was lost to follow-up by the Alfred Hospital. There were no major differences in presenting symptoms, number of treatments, or outcome between these patients and 422 treated patients suffering DCS following diving over the same time period. DCS may occur with exposure to high altitude. The severity and treatment is similar to that occurring following diving. Resolution of symptoms and signs may be achieved by recompression therapy.

Background: Positive pressure breathing (PPB) is commonly used in modern fighter aircraft as part of the anti-G ensemble. PPB is combined with a chest counterpressure bladder which is pressurized to the same magnitude as the breathing mask (balanced PPB). The chest counterpressure is expected to reduce the expiratory work of breathing, reduce the risk for lung rupture, and increase G tolerance. In a previous study we did not find any effect from chest counterpressure on G tolerance or G endurance. The aim of this study was to investigate the effects of chest counterpressure on the work of breathing and the risk for lung rupture. Methods: Eight male test subjects were exposed to 20-s periods of PPB at +1.0, 5.0, 6.0, 7.0, and 8.0 G z . Each G z level was accomplished twice, with and without pressurization of the chest bladder. Inspiratory and expiratory flows were measured and esophageal pressures were measured in the lower and upper third of the thorax. Subsequently, work and power of breathing and apical transpulmonary pressure were estimated. Results: The apical transpulmonary pressure was slightly larger without than with chest counterpressure at 1.0 G z , while chest counterpressure did not affect apical transpulmonary pressure at increased G z load. Nor did the chest counterpressure affect work or power of breathing at any G z load. Conclusion: Inflation of the chest bladder does not seem to have any effects on work or power of breathing or risk for lung rupture during PPB at high G z loads.

Background It is unknown to what extent therapeutic continuous positive airway pressure (CPAP) levels obtained by various methods for the treatment of obstructive sleep apnea syndrome (OSAS) differ. This study aimed to explore the relationships among pressures titrated by an automatic CPAP (APAP) device and those calculated using different predictive equations, and to compare different ranges of calculated pressures with pressure values titrated by APAP. Methods In 140 OSAS patients, the 95th percentile pressure delivered by an APAP device (AutoSet T; ResMed; Sydney, NSW, Australia) during polysomnography, and pressures calculated by three equations ( equation 1 , Hoffstein and Miljetig [1994]; equation 2 , Series et al [2000]; and equation 3 , Stradling et al [2004]) were compared. Results Titrated and calculated pressures were weakly correlated. Significant differences were found between the mean (± SD) pressures (11.1 ± 1.6, 8.3 ± 1.8, 10.5 ± 1.6, and 10.3 ± 1.3 cm H 2 O, respectively) for 95th percentile APAP, and pressures calculated by equations 1 , 2 , and 3 , except between values calculated by equations 2 and 3 . Differences between the calculated and APAP-derived pressures were negative for the low calculated values, and were progressively attenuated, or became positive, for the high values. The differences were smallest for calculated pressures from 11 to > 13 cm H 2 O, which were represented to a greater extent among the values calculated by equations 2 and 3 than by those calculated by equation 1 . Conclusions Considerably different therapeutic CPAP levels may be determined using various methods. The differences between the calculated and APAP-derived pressures are largest for calculated values of 15 cm H 2 O. The clinical consequences of these findings deserve further evaluation. Caution is still required before treating OSAS patients with calculated pressures.

Using simultaneous nitric oxide and carbon monoxide lung transfer measurements (TLNO and TLCO), the membrane transfer capacity (Dm) and capillary lung volume (Vc) as well as the dimensionless ratio TLNO/TLCO can be calculated. The significance of this ratio is yet unclear. Theoretically, the TLNO/TLCO ratio should be inversely related to the product of both lung alveolar capillary membrane (μ) and blood sheet thicknesses (K). NO and CO transfers were measured in healthy subjects in various conditions likely to be associated with changes in K and/or μ. Experimentally, deflation of the lung from 7.4 to 4.8 l decreased the TLNO/TLCO ratio from 4.9 to 4.2 (n= 25) which was consistent mainly with a thickening of the blood sheet. Compared with continuous negative pressure breathing, continuous positive pressure breathing increased this ratio suggesting a thinning of the capillary sheet. It was also observed with 12 healthy subjects that slight haemodilution that may thicken the blood sheet decreased the TLNO/TLCO ratio from 4.85 to 4.52. In conclusion, the TLNO/TLCO ratio is related to the thickness of the alveolar blood barrier. This ratio provides novel information for the analysis of the diffusion properties.

Forearm pain occurring during high +Gz exposure has been linked with vascular distension from elevated transmural pressure of hydrostatic origin and is exacerbated by positive pressure breathing (PBG). We postulated that at high vascular transmural pressure vascular autoregulation might be overcome and be associated with worsened pain. Six volunteers were studied at +4, +5, +6, and +7 Gz on a human centrifuge. Forearm vascular resistance (FVR) was assessed by Doppler ultrasound resistive index (RI), and superficial forearm venous pressure (FVP) was measured via an indwelling catheter. Pain rating was assessed by numerical scale. The left arm was located at heart level (control position), or on the throttle (test position). Runs were completed with and without positive pressure breathing for G protection (PBG); subjects wore full coverage anti-G trousers and chest counter-pressure. In the test position, pain increased with increasing acceleration (P < 0.0001), and was more severe with PBG at +5 Gz and +7 Gz (P < 0.05). FVP rose substantially more in the test than control position (238 ± 17 mmHg vs. 61 ± 8 mmHg at +7 Gz, P < 0.0001) but the presence or absence of PBG had no effect on the FVP increase during acceleration in either position. In the test position, RI fell with increasing acceleration above +5 Gz (P < 0.0001), and the fall was greater with PBG (P < 0.05). Forearm pain was thus associated with a decrease in FVR and an increase in vascular transmural pressure. PBG exacerbated forearm pain and prompted a greater fall in RI, but had no effect on FVP response. These findings support FVR but not forearm venous distension in the aetiology of +Gz arm pain.

Noninvasive ventilation (NIV) in preterm infants is currently applied using intermittent positive pressure (2 positive-pressure levels) or in a conventional manner (one pressure level). However, there are no studies in the literature comparing the chances of failure of these NIV methods. The aim of this study was to evaluate the occurrence of failure of 2 noninvasive ventilatory support systems in preterm neonates over a period of 48 h.A randomized, prospective, clinical study was conducted on 80 newborns (gestational age37 weeks, birthweight2,500 g). The infants were randomized into 2 groups: 40 infants were treated with nasal CPAP and 40 infants with nasal intermittent positive-pressure ventilation (NIPPV). The occurrence of apnea, progression of respiratory distress, nose bleeding, and agitation was defined as ventilation failure. The need for intubation and re-intubation after failure was also observed.There were no significant differences in birth characteristics between groups. Ventilatory support failure was observed in 25 (62.5%) newborns treated with nasal CPAP and in 12 (30%) newborns treated with NIPPV, indicating an association between NIV failure and the absence of intermittent positive pressure (odds ratio [OR] 1.22, P.05). Apnea (32.5%) was the main reason for nasal CPAP failure. After failure, 25% (OR 0.33) of the newborns receiving nasal CPAP and 12.5% (OR 0.14) receiving NIPPV required invasive mechanical ventilation.Ventilatory support failure was significantly more frequent when nasal CPAP was used.

BACKGROUND On August 14, 2003, the United States and Canada suffered the largest power failure in history. We report the effects of this blackout on New York City's healthcare system by examining the following: 1) citywide 911 emergency medical service (EMS) calls and ambulance responses; and 2) emergency department (ED) visits and hospital admissions to one of New York City's largest hospitals. METHODS Citywide EMS calls and ambulance responses were categorized by 911 call type. Montefiore Medical Center (MMC) ED visits and hospital admissions were categorized by diagnosis and physician-reviewed for relationship to the blackout. Comparisons were made to the week pre- and postblackout. RESULTS Citywide EMS calls numbered 5,299 on August 14, 2003, and 5,021 on August 15, 2003, a 58% increase (p < .001). During the blackout, there were increases in "respiratory" (189%; p < .001), "cardiac" (68%; p = .016), and "other" (40%; p < .001) EMS call categories, but when expressed as a percent of daily totals, "cardiac" was no longer significant. The MMC-ED reflected this surge with only "respiratory" visits significantly increased (expressed as percent of daily total visits; p < .001). Respiratory device failure (mechanical ventilators, positive pressure breathing assist devices, nebulizers, and oxygen compressors) was responsible for the greatest burden (65 MMC-ED visits, with 37 admissions) as compared with 0 pre- and postblackout. CONCLUSIONS The blackout dramatically increased EMS and hospital activity, with unexpected increases resulting from respiratory device failures in community-based patients. Our findings suggest that current capacity to respond to public health emergencies could be easily overwhelmed by widespread/prolonged power failure(s). Disaster preparedness planning would be greatly enhanced if fully operational, backup power systems were mandated, not only for acute care facilities, but also for community-based patients dependent on electrically powered lifesaving devices.

Due to more stringent requirements to protect personnel against hazardous gasses, the inspiratory resistance of the present generation of respiratory protective devices tends to increase. Therefore an important question is to what extent inspiratory resistance may increase without giving problems during physical work. In this study the effects of three levels (0.24; 1.4 and 8.3 kPa s l(-1)) of inspiratory resistance were tested on maximal voluntary performance. Nine male subjects performed a graded exercise test on a cycle ergometer with and without these three levels of inspiratory resistance. Oxygen consumption, heart rate, time to exhaustion and external work were measured. The results of these experiments showed that increasing inspiratory resistance led to a reduction of time to exhaustion (TTE) on a graded exercise test(GXT). Without inspiratory resistance the mean TTE was 11.9 min, the three levels of resistance gave the following mean TTE's: 10.7, 7.8 and 2.7 min. This study showed that TTE on a GXT can be predicted when physical fitness (VO2-max) of the subject and inspiratory resistance are known. The metabolic rate of the subjects was higher with inspiratory resistance, but no differences were found between the three selected inspiratory loads. Other breathing parameters as minute ventilation, tidal volume, expiration time and breathing frequency showed no or minor differences between the inspiratory resistances. The most important conclusion of these experiments is that the overall workload increases due to an increase in inspiratory resistance by wearing respiratory protective devices.

Inhaled nitric oxide (iNO) is routinely used for hypoxic respiratory failure and persistent pulmonary hypertension of the newborn, and investigation of its new indications requiring various levels of iNO is underway. Cumulated exposure of high level of iNO may exert adverse effects on lung function and morphology, which may be confounded with ventilator-associated lung injury. Sixteen healthy piglets (5.5-11 kg) were anaesthetised, intubated and mechanically ventilated at low FiO(2) on continuous positive airway pressure and pressure support mode. The animals were randomly allocated to receive 40 ppm iNO (NO group, n=8) or no iNO (Control group, n=8). In both groups at 24 and 48 h, mild to moderate lung injury was observed, with mean values of PaO(2)/FiO(2)300 mmHg. Compared to the Control, iNO at 40 ppm for 24-48 h did not adversely affect dynamic compliance or resistance of respiratory system, oxygenation, pulmonary and systemic hemodynamics. Neither did it affect composition and surface activity of surfactant phospholipids and white cell counts in bronchoalveolar lavage fluid. Inhaled NO resulted in elevated total serum nitrite/nitrate to 352+/-90 micromol/l and methemoglobin (MetHb) to 5.0+/-3.4%, in contrast to 88+/-38 micromol/l and 0.88+/-0.52% in the Control; 50% of the iNO animals having MetHb3%. The lung injury scores as well as alveolar expansion were similar between the two groups at 24 h. At 48 h, low wet/dry lung weight ratio and lung injury score were found in the NO group. We conclude that no significant adverse effects on lung physiology and structure were found in the piglets receiving 40 ppm iNO for 24 or 48 h, on the contrary lung injury was moderately alleviated. The significantly impaired gas exchange over time associated with discrete morphological changes suggests adverse effects of prolonged positive pressure breathing and not necessarily exposure to oxides of nitrogen.

Functional haemodynamic monitoring is the assessment of the dynamic interactions of haemodynamic variables in response to a defined perturbation.Fluid responsiveness can be predicted during positive pressure breathing by variations in venous return or left ventricular output using numerous surrogate markers, such as arterial pulse pressure variation (PPV), left ventricular stroke volume variation (SVV), aortic velocity variation, inferior and superior vena cavae diameter changes and pulse oximeter pleth signal variability. Similarly, dynamic changes in cardiac output to a passive leg raising manoeuvre can be used in any patient and measured invasively or noninvasively. However, volume responsiveness, though important, reflects only part of the overall spectrum of functional physiological variables that can be measured to define physiologic state and monitor response to therapy. The ratio of PPV to SVV defines central arterial elastance and can be used to identify those hypotensive patients who will not increase their blood pressure in response to a fluid challenge despite increasing cardiac output. Dynamic tissue O2 saturation (StO2) responses to complete stop flow conditions, as can be created by measuring hand StO2 and occluding flow with a blood pressure cuff, assesses cardiovascular sufficiency and micro-circulatory blood flow distribution. They can be used to identify those ventilator-dependent individuals who will fail a spontaneous breathing trial or trauma patients in need of life-saving interventions.Functional haemodynamic monitoring approaches are increasing in numbers, conditions in which they are useful and resuscitation protocol applications. This is a rapidly evolving field whose pluripotential is just now being realized.

The initiation of mechanical ventilation and selection of initial ventilator settings is a complex process that must address the underlying pathophysiology and the change in clinical status which may follow intubation and the implementation of positive pressure breathing. The initial ventilator settings must be instituted to target a patient’s specific clinical indication(s) for mechanical ventilation. Due to the substantial variation in disease processes, no single ventilator strategy can be successfully applied to all patients. The strategy used for a patient with acute respiratory distress syndrome (ARDS) will vary greatly from that for status asthmaticus or a chronic neuromuscular disorder. An additional factor in the approach to mechanical ventilation in the pediatric critical care setting is the tremendous variation in both patient age and size. These considerations are important elements in the development of an approach to mechanical ventilation of the pediatric patient.

Our objective was to determine if the magnitude of the Y descent in the central venous pressure tracing could be used to determine which patients have restrictive hemodynamics. To better understand the determinants of the Y descent, we also examined the effects of changes in blood volume, changes in pleural pressure, and respiratory maneuvers on its magnitude. Studies were performed in both humans and dogs. In six anesthetized dogs, we examined the effect on the Y descent in central venous pressure (CVP) of an infusion of normal saline, a decrease in pleural pressure produced by having animals perform a Mueller maneuver, and the combination of a Mueller maneuver and volume loading. Observations were made with the chest closed, chest open, and chest and pericardium open. The state of the chest did not effect the Y descent. The Y descent was only significantly increased when a Mueller maneuver was combined with volume loading. There was a significant inverse relationship between the magnitude of the decrease in esophageal pressure and the Y descent. There was also a linear relationship between the CVP and Y descent. For the human studies, we examined patients undergoing routine cardiac surgery. They were examined during spontaneous breathing before intubation, with positive pressure breathing and closed chest, with positive pressure breathing and open chest, with an open pericardium, with a closed chest and positive pressure breathing postsurgery, and with spontaneous breathing after extubation following surgery. The Y descent was greater in spontaneous breaths postsurgery compared to before surgery, and this was associated with an increase in CVP. However, the magnitude of CVP did not correlate with the magnitude of the Y descent. A restrictive pattern in cardiac filling was identified by a lack of respiratory variation in right atrial pressure during spontaneous breaths. All patients with large Y descents had a restrictive pattern, but many patients with restrictive filling patterns did not have a large Y descent. The magnitude of the Y descent is affected by the volume status, the magnitude and direction of the changes in pleural pressure, and the compliance of the pericardial compartment. A large Y descent indicates a restrictive cardiac state, but a small Y descent does not rule out a restrictive condition because of the many interacting variables.

We assessed the influence of cranial-to-caudal inertial force (+G z ) and the countermeasures of anti-G suit and positive pressure breathing during G (PBG), specifically during +G z , on regional pulmonary blood flow distribution. Unanesthetized swine were exposed randomly to 0 G z (resting), +3 G z , +6 G z , and +9 G z , with and without anti-G suit and PBG with the use of the Air Force Research Laboratory centrifuge at Brooks Air Force Base (the gravitational force of the Earth, that is, the dorsal-to-ventral inertial force, was present for all runs). Fluorescent microspheres were injected into the pulmonary vasculature as a marker of regional pulmonary blood flow. Lungs were excised, dried, and diced into ∼2-cm3 pieces, and the fluorescence of each piece was measured. As +G z was increased from 0 to +3 G z , blood flow shifted from cranial and hilar regions toward caudal and peripheral regions of the lung. This redistribution shifted back toward cranial and hilar regions as anti-G suit inflation pressure increased at +6 and +9 G z . Perfusion heterogeneity increased with +G z stress and decreased at the higher anti-G suit pressures. The distribution of pulmonary blood flow was not affected by PBG. ANOVA indicated anatomic structure as the major determinant of pulmonary blood flow.

Objective: To evaluate whether the application of bilevel positive airway pressure in the postoperative period of bariatric surgery might be more effective in restoring lung volume and capacity and thoracic mobility than the separate application of expiratory and inspiratory positive pressure. Method: Sixty morbidly obese adult subjects who were hospitalized for bariatric surgery and met the predefined inclusion criteria were evaluated. The pulmonary function and thoracic mobility were preoperatively assessed by spirometry and cirtometry and reevaluated on the 1st postoperative day. After preoperative evaluation, the subjects were randomized and allocated into groups: EPAP Group (n=20), IPPB Group (n=20) and BIPAP Group (n=20), then received the corresponding intervention: positive expiratory pressure (EPAP), inspiratory positive pressure breathing (IPPB) or bilevel inspiratory positive airway pressure (BIPAP), in 6 sets of 15 breaths or 30 minutes twice a day in the immediate postoperative period and on the 1st postoperative day, in addition to conventional physical therapy. Results: There was a significant postoperative reduction in spirometric variables (p0.05). Thoracic mobility was preserved only in group BIPAP (p>0.05), but no significant difference was found in the comparison among groups (p>0.05). Conclusion: The application of positive pressure does not seem to be effective in restoring lung function after bariatric surgery, but the use of bilevel positive pressure can preserve thoracic mobility, although this technique was not superior to the other techniques. Objetivo: Avaliar se a aplicação de dois níveis de pressão positiva nas vias aéreas no pós-operatório de cirurgia bariátrica pode ser mais efetiva do que quando aplicadas pressões positivas expiratória e inspiratória separadamente na restauração dos volumes e capacidades pulmonares e na mobilidade torácica. Método: Foram avaliadas 60 voluntárias adultas, obesas mórbidas, internadas para realização da cirurgia bariátrica. Afunção pulmonar e a mobilidade torácica foram avaliadas por meio da espirometria e da cirtometria no pré-operatório e reavaliadas no primeiro pós-operatório. Após a avaliação pré-operatória, as voluntárias foram randomizadas e alocadas nos grupos G EPAP (n=20), G RPPI (n=20) e G BIPAP (n=20) e então receberam a intervenção proposta, pressão positiva expiratória nas vias aéreas (EPAP), respiração por pressão positiva inspiratória (RPPI) ou pressão positiva binível nas vias aéreas (BIPAP), em sessões de seis séries de 15 respirações ou de 30 minutos, duas vezes ao dia no pós-operatório imediato e no primeiro pós-operatório, além do tratamento fisioterapêutico convencional. Resultados: Houve redução significativa das variáveis espirométricas no pós-operatório (p0,05), e preservação da mobilidade torácica somente nas voluntárias do grupo BIPAP (p>0,05), porém sem diferença nas comparações entre os grupos (p>0,05). Conclusão: A aplicação de pressão positiva parece não ser efetiva na restauração da função pulmonar no pós-operatório de cirurgia bariátrica, porém a aplicação de dois níveis de pressão positiva pode preservar a mobilidade torácica, embora não tenha demonstrado superioridade em relação às outras técnicas.

Positive pressure breathing (PPB) is a survival system that delivers high-pressure oxygen and body counterpressure in the event of cockpit depressurization at high altitude, but the ability of aircrew to perform an emergency "get-me-down" maneuver with this system is unknown. To address this question, a serial choice reaction time (RT) task was administered to six participants, who were sustained with PPB after rapid decompression to 60000 feet (18 288 m) or 72 000 feet (21946 m) in a hypobaric chamber (Experiment 1). Hypoxia was monitored by blood oxygen saturation (SaO2). Experiment 2 assessed the effects of PPB alone on performance. In Experiment 3, performance was measured while the rate of decrease of Sao2 observed in Experiment 1 was replicated with low oxygen mixtures at ground level. During the first 60 s at 72 000 feet, RT increased by 79 ms because of a shift of the whole distribution to the right. PPB at ground level did not increase RT. Decreasing Sao2 at ground level increased RT, but only after a delay. We conclude that inattention to the task, PPB alone, or, surprisingly, hypoxia cannot explain the majority of the impairment observed in Experiment 1. Rather, PPB and low pressure at high altitude interacted to exacerbate lacrimation, thereby degrading vision. Implications for the design of get-me-down maneuvers are discussed.

In 1992, Dreyfuss and Saumon coined the term “volutrauma” to emphasize that the choice of tidal volume is the single most important risk factor of mechanical ventilation–associated lung injury (1). In doing so, Dreyfuss and Saumon underscored that tidal volume is a better measure of lung parenchymal stress than airway pressure because the latter is often dominated by the elastic properties of the chest wall (2). It is now well established that mechanical ventilation with large tidal volumes can damage the lung by distinct biophysical injury mechanisms (3). These include tensile stress associated with so-called alveolar overstretch, interfacial stress associated with surfactant dysfunction, accumulation of liquid and foam in airspaces, cyclic recruitment and derecruitment of unstable lung units, and shear stress between interdependent units with different mechanical properties. Although research on biophysical lung injury mechanisms is clearly motivated by concerns for complications of positive pressure ventilation, one may reasonably ask if the same mechanisms would not operate in spontaneously breathing patients as well. In other words, assuming similar tidal volumes, is the topographical distribution of parenchymal stress fundamentally different between the modes of breathing? This question has occupied respiratory physiologists during the latter half of the 20th century and has now reemerged in a clinical context in the article by Yoshida and colleagues (pp. 1420–1427) in this issue of the Journal (4). Yoshida and colleagues compared the vertical distributions of inspired gas between assisted and controlled mechanical ventilation in a patient using electrical impedance tomography (EIT). To their surprise, they observed a significant translocation of alveolar gas from nondependent to dependent regions of diaphragm-apposed lung during the patient’s assisted positive pressure breathing. They characterized the phenomenon as pendelluft (derived from the German words for pendulum and air), noted its absence during paralysis and controlled mechanical ventilation, and hypothesized that it was caused by a nonuniform change in lung surface pressure (pleural pressure) during diaphragm contraction. This interpretation is qualitatively consistent with prior observations in normal recumbent anesthetized humans, in whom muscle paralysis and mechanical ventilation was shown to be associated with a different ventilation distribution than spontaneous breathing (5). These changes in regional ventilation were attributed to different deformations of the chest wall and different motion of the diaphragm between the modes of breathing (6). Under normal circumstances, that is, in individuals with normal lungs and respiratory drive, these differences are modest at best, because the shear modulus of normal lungs (their resistance to an isovolumic shape change) approaches that of liquids (7), because mode-related differences in thoracic cavity shape are relatively small and because the sliding motions of lung lobes minimize parenchymal distortions (8). In comparison, the changes in regional ventilation and hence in parenchymal stress and strain in patients and animals with injured lungs as reported by Yoshida and colleagues were huge and are therefore of potential clinical and biologic significance (4). To validate the patient findings and explore responsible mechanisms, Yoshida and colleagues measured the effects of breathing modality on regional volumes and pressures (parenchymal stress) in a porcine model subjected to lung injury by saline lavage. Topographical volume and ventilation distributions were inferred from density maps of EIT and high-speed computer tomography–derived images. Not only did these experiments confirm the presence of “occult” pendelluft during spontaneous pressure assisted breathing, but, more importantly, they revealed a very large effect size. For example, to achieve comparable tidal inflations of diaphragm-apposed dependent lung regions, the airway pressure amplitude of spontaneously breathing animals had to be increased from 10 cm H2O to 28 cm H2O after neuromuscular blockade. This resulted in a corresponding increase in global tidal volumes from 6 to 15 ml/kg. On that basis, Yoshida and colleagues conclude that spontaneous breathing in mechanically ventilated patients can cause unsuspected, transient overstretching of dependent lung regions with concurrent deflation of nondependent lung. Notwithstanding the need to confirm these observations in different lung injury models and clinical settings, the pendelluft hypothesis challenges some firmly held beliefs. For example, proponents of assisted pressure release ventilation have long argued that the maintenance of diaphragm activity preserves the aeration of dependent lung and thereby leads to superior patient outcomes (9). Although clinical benefit of assisted pressure release ventilation remains to be established (10), Yoshida and colleagues’ observations suggest that the prevention of dependent lung atelectasis by virtue of cyclic diaphragm contractions could come at considerable long-term cost. In fact, proponents of early neuromuscular blockade for patients with the adult respiratory distress syndrome (ARDS) will likely embrace the pendelluft hypothesis as one mechanistic explanation of the survival benefit associated with this intervention (11). The proposed mechanism of overstretch injury requires that dependent diaphragm near lung regions remain recruitable at the prevailing local inflation pressures. This was clearly the case in lavage-injured pigs, but may not be the case in patients with established ARDS (12). Moreover, the presence of pleural fluid could serve to dissipate the heterogeneity in lung surface pressure, which drives the pendelluft phenomenon. It should be noted that Yoshida and colleagues’ examples of “occult” pendelluft were generally observed under conditions of increased respiratory drive. This tends to magnify muscular chest wall distortions and may have biased the size of the pendelluft estimate. Aside from the postulated effect of lavage injury on the shear modulus and hence deformability of the lungs, the much lower respiratory drive of anesthetized uninjured pigs probably explains why pendelluft was not seen in animals with healthy lungs. In fact, inspiratory efforts against an occluded airway of a magnitude comparable to that reported in injured pigs had previously been shown to produce pendelluft between apical and caudal lobes in normal dogs (13). Finally, neither EIT nor computer tomography provides accurate information on the locations of distinct anatomic lung regions in time. As a result, it is not possible to assess the effects of diaphragm motion on rigid body displacement and rotation of a lobe or lung region. This could lead to the erroneous impression of recruitment as a neighboring region fills the space vacated by consolidated lung. Notwithstanding these minor caveats, Yoshida and colleagues’ observations are important. They emphasize that patients who breathe with seemingly lung-protective tidal volumes could still suffer biophysical lung trauma unless their respiratory drive and diaphragm motor output are carefully manipulated. If refined and confirmed, the pendelluft hypothesis has serious implications for the use of noninvasive mechanical ventilation in patients with impending or established ARDS. Mask ventilation imposes limits on the use of sedatives and narcotics, so its prolonged use may inappropriately delay intubation and lung-protective support (14). It took decades before the critical care community accepted low tidal volume mechanical ventilation as the standard of care. Yoshida and colleagues may have just added another important “wrinkle” to this story.

Positive pressure breathing produced by mechanical ventilation with an expiratory threshold load (ETL) may modify electrocardiogram (ECG) complexes independently of any recording artefact due to lung volume changes. Anaesthetized, paralyzed rabbits were treated for about 2 h, then killed. In intact then vagotomized animals two situations were studied successively. Firstly, positive inspiratory pressure breathing, and secondly, positive inspiratory plus expiratory pressure breathing by adding ETL to mechanical ventilation. Arterial blood gases were measured and held constant throughout the challenge. Oesophageal pressure, giving indirect measurement of intrathoracic pressure, arterial blood pressure, blood flows in abdominal aorta and inferior vena cava and standard ECG recordings were made at baseline condition during mechanical ventilation, then at the end of a 10-min period of ETL breathing. The ETL breathing decreased arterial blood pressure significantly and reduced arterial and venous blood flows in the same proportion. No change in the duration of ECG complexes was noticed. However, ETL markedly reduced the amplitude of P- and T-waves, but not that of R-wave, an effect significantly accentuated after vagotomy. The ETL breathing increased the T-vector angle, with no associated change in QRS vector angle. The present animal investigations revealed that positive pressure breathing modifies the ECG independently of the consequences of ETL-induced lung volume changes. We speculate that the changes in P- and T-wave amplitude may have resulted from a reduced transmural pressure gradient between the epicardium and endocardium.

Study Objective: To determine if reducing respiratory muscle load or increasing tidal volume (V T ) with pressure support (PS) would improve ventilatory efficiency by reducing respiratory rate (RR) and resting PaCO 2 . Design: Prospective, and patient-controlled, with randomized treatment crossover. Setting: University cancer center and research institute. Patients: ASA status I and II patients scheduled to undergo inhalation anesthesia for operations in which neuromuscular relaxation is undesirable. Interventions: Propofol and succinylcholine were used to induce anesthesia and facilitate tracheal intubation. General anesthesia was maintained with desflurane, nitrous oxide, and oxygen. Patients breathed spontaneously at atmospheric pressure for 15 minutes and then randomly received alternate 15-minute trials of PS adjusted to provide either 5 cmH 2 O or a level titrated to produce V T of 8 ml/kg body weight. Then patients breathed spontaneously at atmospheric pressure for 15 minutes. Measurements and Main Results: In 20 patients aged 52 ± 11 years and weighing 72 ± 18kg, airway gas flow and pressure, esophageal pressure, arterial blood gas tensions and pH, and mean arterial pressure (MAP) were measured. Heart rate (HR), V T , RR, minute ventilation (V E ), carbon dioxide production (VCO 2 ), ratio of dead space to (V T ) (VD(VT), and inspiratory work of breathing (W I ) were calculated. End-tidal desflurane (6.7 ±0.4 %), VCO 2 (142 ± 39 ml/min), HR, and MAP were unchanged throughout the study. W I , RR, V E , VD(VT, and PaCO 2 were reduced significantly when PS was titrated to produce a (V T ) of 8 ml/kg and spontaneous breathing before and after PS trials ( p Conclusions: PS titrated to produce a near normal V T improves the efficiency of spontaneous breathing by lowering RR and PaCO 2 while preserving hemodynamic homeostasis in patients undergoing inhalation anesthesia. Lesser PS levels will unload the respiratory muscles, but have no effect on RR or PaCO 2 .

Background Incentive spirometry (IS) is a treatment technique that uses a mechanical device to reduce pulmonary complications during postoperative care. This is an update of a Cochrane review first published in 2007. Objectives Update the previously published systematic review to compare the effects of IS for preventing postoperative pulmonary complications in adults undergoing coronary artery bypass graft (CABG). Search methods We searched CENTRAL and DARE on The Cochrane Library (Issue 2 of 4 2011), MEDLINE OVID (1948 to May 2011), EMBASE (1980 to Week 20 2011), LILACS (1982 to July 2011) , the Physiotherapy Evidence Database (PEDro) (1980 to July 2011), Allied & Complementary Medicine (AMED) (1985 to May 2011), CINAHL (1982 to May 2011). Selection criteria Randomised controlled trials comparing IS with any type of prophylactic physiotherapy for prevention of postoperative pulmonary complications in adults undergoing CABG. Data collection and analysis Two reviewers independently evaluated trial quality using the guidelines of the Cochrane Handbook for Systematic Reviews and extracted data from included trials. For continuous outcomes, we used the generic inverse variance method for meta-analysis and for dichotomous data we used the Peto Odds Ratio. Main results This update included 592 participants from seven studies (two new and one that had been excluded in the previous review in 2007. There was no evidence of a difference between groups in the incidence of any pulmonary complications and functional capacity between treatment with IS and treatment with physical therapy, positive pressure breathing techniques (including continuous positive airway pressure (CPAP), bilevel positive airway pressure (BiPAP) and intermittent positive pressure breathing (IPPB), active cycle of breathing techniques (ACBT) or preoperative patient education. Patients treated with IS had worse pulmonary function and arterial oxygenation compared with positive pressure breathing. Based on these studies there was no improvement in the muscle strength between groups who received IS demonstrated by maximal inspiratory pressure and maximal expiratory pressure. Authors' conclusions Our update review suggests there is no evidence of benefit from IS in reducing pulmonary complications and in decreasing the negative effects on pulmonary function in patients undergoing CABG. In view of the modest number of patients studied, methodological shortcomings and poor reporting of the included trials, these results should still be interpreted cautiously. An appropriately powered trial of high methodological rigour is needed to determine if there are patients who may derive benefit from IS following CABG.

Background. The prone position is applied to facilitate surgery of the back and to improve oxygenation in the respirator-treated patient. In particular, with positive pressure ventilation the prone position reduces venous return to the heart and in turn cardiac output (CO) with consequences for cerebral blood flow. We tested in healthy subjects the hypothesis that rotating the head in the prone position reduces cerebral blood flow.Methods. Mean arterial blood pressure (MAP), stroke volume (SV), and CO were determined, together with the middle cerebral artery mean blood velocity (MCAVmean) and jugular vein diameters bilaterally in 22 healthy subjects in the prone position with the head centered, respectively, rotated sideways, with and without positive pressure breathing (10 cmH2O).Results. The prone position reduced SV (by5.4±1.5%;P<0.05) and CO (by2.3±1.9%), and slightly increased MAP (from78±3to80±2 mmHg) as well as bilateral jugular vein diameters, leaving MCAVmeanunchanged. Positive pressure breathing in the prone position increased MAP (by3.6±0.8 mmHg) but further reduced SV and CO (by9.3±1.3% and7.2±2.4% below baseline) while MCAVmeanwas maintained. The head-rotated prone position with positive pressure breathing augmented MAP further (87±2 mmHg) but not CO, narrowed both jugular vein diameters, and reduced MCAVmean(by8.6±3.2%).Conclusion. During positive pressure breathing the prone position with sideways rotated head reduces MCAVmean~10% in spite of an elevated MAP. Prone positioning with rotated head affects both CBF and cerebrovenous drainage indicating that optimal brain perfusion requires head centering.

OBJECTIVES To test whether perfluorocarbon-associated gas exchange (gas ventilation of the perfluorocarbon-liquid filled lung) could support oxygenation better than conventional positive pressure breathing in a piglet model of gastric aspiration-induced adult respiratory distress syndrome (ARDS). DESIGN Prospective, randomized, blinded, controlled study. SETTING A critical care research laboratory in a university medical school. SUBJECTS Fourteen healthy piglets. INTERVENTIONS Under alpha-chloralose anesthesia and metocurine iodide neuromuscular blockade, 14 piglets underwent tracheostomy; central venous, systemic and pulmonary arterial catheterizations; and volume-regulated continuous positive-pressure breathing. Homogenized gastric aspirate (1 mL/kg) titrated to pH of 1.0 was instilled into the tracheostomy tube of each subject at 0 min to induce ARDS. Hemodynamics, lung mechanics, and gas exchange were evaluated every 30 mins for 6 hrs. Seven piglets were treated at 60 mins by tracheal instillation of perflubron, a volume selected to approximate normal functional residual capacity, and were supported by perfluorocarbon-associated gas exchange without modifying ventilatory settings. Perflubron was added to the trachea every hour to replace evaporative losses. MEASUREMENTS AND MAIN RESULTS There was a significant difference in oxygenation over time when tested by repeated-measures analysis of variance (F test = 8.78, p < .01). On further analysis, the differences were not significant from baseline to 2.5 hrs but became increasingly significant from 2.5 to 6 hrs after injury (p < .05) in the inflammatory phase of gastric aspiration-induced ARDS. Histologic evidence for ARDS in the treated group 6 hrs after injury was lacking. CONCLUSIONS In the piglet model, perfluorocarbon-associated gas exchange with perflubron facilitates oxygenation in the acute phase of gastric aspiration-induced inflammatory ARDS when compared with conventional positive-pressure breathing. Histologic and physiologic data suggest that perfluorocarbon-associated gas exchange with perflubron might prevent ARDS if instituted after aspiration in the time window before the acute inflammatory process is manifest.