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Objective: To define the magnitude of spontaneous cardiac output variability over time in sedated medical intensive care unit patients attached to a continuous cardiac output monitor, and to determine whether high level positive end-expiratory pressure or inverse inspiratory-to-expiratory (I:E) ratio ventilation resulted in greater variability over time than low positive end-expiratory pressure with conventional I:E ratio ventilation. Design: Prospective study. Setting: Medical intensive care unit in a tertiary medical center. Patients: A total of 22 hemodynamically stable acute respiratory failure patients with a pulmonary artery catheter inserted for hemodynamic monitoring Interventions: After being sedated, patients were randomized alternately to receive pressure control ventilation first at setting A (high positive end-expiratory pressure [15 cm H 2 O] with conventional I:E ratio [1:2]) and then at setting B (low positive end-expiratory pressure [5 cm H 2 O] with inverse I:E ratio [2:1]), or vice versa, and then at setting C (low positive end-expiratory pressure [5 cm H 2 O] with conventional I:E ratio [1:2]). Each ventilation setting period lasted 1 hr. Measurements and Main Results: Cardiac output (CO) was measured continuously. The continuous CO value displayed was updated every 30-60 secs. The updated value reflected an average of the previous 3-6 mins. The coefficient of variation (CV) of CO for each setting in each patient was calculated to represent the spontaneous variability. The mean CO ± so and CV of each setting was 5.7 ± 1.8 Umin and 4.4% for setting A, 5.6 ± 1.5 Umin and 4.6% for setting B, and 5.9 ± 1.7 Umin and 4.8% for setting C. Analysis of variance revealed no significant differences between the CVs of the three settings. The 95% confidence interval for the COs for each setting was approximately the mean CO ± 0.1 x mean CO measured. Conclusions: In critically ill sedated medical intensive care unit patients with stable hemodynamics, the spontaneous variability of cardiac output over time was not significant. High positive end-expiratory pressure (15 cm H 2 O) and inverse ratio ventilation (2:1) did not contribute to increased spontaneous variability of cardiac output.

Continuous as well as cyclic (with each expiration) lung collapse in acute respiratory failure can be reduced by positive end-expiratory pressure (PEEP) or short expiration times, as in inverse ratio ventilation (IRV). In 20 pigs with oleic acid-induced lung edema, we compared the effects of a PEEP of 20 cm H(2)O with IRV, using an inspiratory-to-expiratory ratio of 3:1 without external PEEP. During IRV, expiration times of 0.5 or 1.0 s were obtained with respiratory rates of 30 breaths/min or 15 breaths/min, respectively. In 15 animals, ventilation-perfusion relationships were studied through the multiple inert gas elimination technique, and lung morphology was studied with computed tomography. In another five pigs, blood flow distribution was studied with perfusion scintigraphy. All three ventilatory modes had similar effects on mean arterial blood pressure, cardiac output, oxygen delivery, and mean airway pressure. PEEP reduced shunt and improved oxygenation to a greater extent than the two modes of IRV, although there was a large variation within each group. The improvement, irrespective of which ventilatory mode was superior in a particular pig, was caused by greater and more even aeration of the lung, whereas the perfusion distribution with PEEP was the same as with IRV. Thus, the strategy of stabilizing the lungs through short expiration times, as in IRV, did not offer any advantages in our lung injury model.

In 1982, Pepe and Marini [1] pointed out the clinical importance of dynamic increase in end-expiratory lung volume and positive end-expiratory alveolar pressure in mechanically ventilated patients with airflow obstruction. This end-expiratory pressure was termed “occult, auto or intrinsic PEEP” (PEEPi) and is due to the positive end-expiratory elastic recoil pressure of the total respiratory system consequent to incomplete lung emptying. In patients with severe airflow obstruction, because the rate of the lung emptying is slow relative to the available expiratory duration, the expiration is interrupted by the subsequent breath before the relaxation volume of the respiratory system (Vr) is reached. The increase in end expiratory lung volume above Vr is termed dynamic pulmonary hyperinflation. Dynamic hyperinflation and PEEPi were detected not only in ventilated patients with airway obstruction but also in ventilated patients with other disorders [2–4] and in all ventilatory conditions in which a short expiratory time is used, as inverse ratio ventilation (5, 6].

Objective: To assess the magnitude of spontaneous variability of arterial oxygenation and oxygen tension-based indices over time in medical intensive care unit (ICU) patients and to study whether high positive end-expiratory pressure (PEEP) or inverse inspiratory-to-expiratory (I:E) ratio ventilation (IRV) results in a greater variability than low PEEP with conventiona l I:E ratio ventilation. Design: Prospective study. Setting: Medical ICU in a tertiary medical center. Participants: 23 patients requiring a pulmonary artery floating catheter for hemodynamic monitoring. Intervention: After being completely sedated, patients were randomized to receive pressure-control ventilation at setting A: high PEEP (15 cmH2O) with conventional I:E ratio (1:2) and setting B: inverse I:E ratio (2:1) with low PEEP (5 cmH2O) alternately, and then at setting C: low PEEP (5 cmH2O) with conventional I:E ratio (1:2). Each ventilation setting lasted 1 h. Measurements and results: The arterial and mixed venous blood samples were measured simultaneously at baseline (time 0), and at 15, 30, 45, and 60 min thereafter. The coefficient of variation (CV) of arterial oxygen tension (PaO2) over time was 5.9 % for setting A, 7.2 % for setting B, and 6.9 % for setting C. ANOVA showed no significant differences in CVs of PaO2 between the three settings. Oxygen tension-based indices, alveolar-arterial oxygen difference (A-aDO2) and PaO2/PAO2 (alveolar oxygen tension), displayed CV s equal to that of PaO2; the CV of A-aDO2/PaO2 was significantly greater than that of PaO2. Conclusions: In critically ill medical ICU patients, despite sedation, the spontaneous variability in PaO2 over time is substantial. A high PEEP or IRV does not contribute to the increased variation in PaO2.

When conventional respiratory strategies fail to maintain adequate oxygenation treatment of severe ARDS is largely empirical. Modern techniques such as inverse ratio ventilation, permissive hypercapnia, NO inhalation and lowering tidal volumes/pressures are advocated. We report on a patient with severe ARDS who showed all the complications of the disease. The risks and benefits of (non)conventional ventilatory strategies are discussed and illustrated.

When conventional respiratory strategies fail to maintain adequate oxygenation treatment of severe ARDS is largely empirical. Modern techniques such as inverse ratio ventilation, permissive hypercapnia, NO inhalation and lowering tidal volumes/pressures are advocated. We report on a patient with severe ARDS who showed all the complications of the disease. The risks and benefits of (non)conventional ventilatory strategies are discussed and illustrated. (C) 1998 Elsevier Science B.V. All rights reserved.

OBJECTIVE: To quantify the current practice patterns of mechanical ventilation for respiratory failure in pediatric patients. DESIGN: Mail survey using 2 hypothetical case studies sent to pediatric critical care physicians. MEASUREMENTS AND MAIN RESULTS: The required arterial blood gas (ABG) on conventional mechanical ventilation (CMV) is pH = 7.25 to 7.29, PO 2 = 50 to 59 torr, O 2 saturation = 0.85 to 0.89. Most of our survey participants will treat a patient failing conventional mechanical ventilation in their pediatric intensive care units (PICUs) with inverse ratio ventilation (IRV) (95%) and with high-frequency oscillatory ventilation (HFOV)(92%). CONCLUSION: Most of the surveyed pediatric critical care physicians practice permissive hypercapnia in the treatment of their patients who receive ventilatory assistance. More than 90% of surveyed pediatric critical care physicians are presently using inverse ratio ventilation and high-frequency oscillatory ventilation. These data suggest that these innovative modes of therapy are already accepted as part of the standard therapeutic spectrum by the surveyed group of physicians.

Pressure controlled ventilation (PCV) has been used extensively in the ventilation of neonates, but only over the last decade has it taken off as an alternative mode of mechanical ventilation for intensivists in adult intensive care units (ICU). PCV (often linked synonymously with inverse ratio ventilation as PC-IRV) was introduced to many as a mode of last resort when problems were occurring with more traditional forms of ventilation. PCV offers a mode of ventilation suited to the most complex ventilatory challenges, including severe acute respiratory distress syndrome (ARDS), extremes of airflow obstruction and synchrony with a difficult to wean patient.

To assess the cardiorespiratory effects of a prolonged application of inverse ratio ventilation (IRV), we compared IRV (I/E = 2) with conventional ventilation (CV) (I/E = 0.5), applied for 6 h each in a randomized order, with constant tidal volume (VT) and total positive end-expiratory pressure (PEEP(tot)) in eight patients with acute respiratory distress syndrome (ARDS). After 1 h, IRV resulted in a lower peak inspiratory pressure (PIP) (28.2 +/- 1.5 versus 35.6 +/- 1.7 cm H2O, p0.05), an unchanged plateau pressure, and a higher mean airway pressure (MAP) (17.8 +/- 0.8 versus 15.6 +/- 0.5 cm H2O, p0.05) than CV. No significant difference in Pa(O2) and shunt fraction (QS/QT) was observed (83 +/- 7 mm Hg and 40 +/- 4% in CV versus 92 +/- 14 mm Hg and 35 +/- 3% in IRV, respectively). The Pa(CO2) was lower in IRV (48 +/- 3 versus 55 +/- 5 mm Hg, p0.05). Cardiac index (CI) and oxygen delivery (D(O2)) were lower in IRV (3.7 +/- 0.4 L/min/m2 and 500 +/- 61 ml/min/m2 versus 4.6 +/- 0.5 L/min/m2 and 617 +/- 80 ml/min/m2, respectively, p = 0.05 for both). Regardless of the considered parameter, no significant difference was observed between results after 1, 2, 4, and 6 h in each mode. We conclude that IRV at a ratio that results in a significant intrinsic PEEP does not improve Pa(O2), enhances CO2 elimination, decreases cardiac output (CO), and does not exert any time-dependent effect.

Objectives To directly measure airway pressures proximal and distal to endotracheal tubes during conventional synchronized intermittent mandatory ventilation (SIMV) and pressure controlled-inverse ratio ventilation (PC-IRV), and to compare them with these values measured by the ventilator. Design Prospective, nonrandomized study. Setting Surgical intensive care unit at a trauma center. Patients Group 1: Eight intubated adult patients connected to mechanical ventilators in the SIMV mode were studied. All patients required mechanical ventilation following traumatic injuries. Group 2: Five intubated adult patients with adult respiratory distress syndrome connected to mechanical ventilators were studied. Interventions A small polyethylene catheter was threaded through each endotracheal tube such that it could be positioned to measure pressures proximal and distal to the tubes. Measurements and main results During SIMV, a significant pressure gradient exists across endotracheal tubes. In addition, although initiation of PC-IRV did lead to a lower peak airway pressure measured proximally, intratracheal peak airway pressure was unchanged. Conclusions A pressure gradient exists during inspiration from the ventilator to the trachea in mechanically ventilated patients. Tracheal pressures cannot be predicted from proximal airway pressure monitors because of marked variation in endotracheal tube resistance in vivo. Initiation of PC-IRV does not result in a decrease in peak airway pressure when measured intratracheally.

In adult respiratory distress syndrome (ARDS), whilst a great fraction of the lung is affected by the disease, some parts, still function normally creating a non-homogeneous distribution of lung pathology. This unequal distribution results in increased differences in time constants of different lung units (1–3). Conventional volume controlled ventilation (VCV) with positive end expiratory pressure (PEEP) with a standard inspiration/expiration (I/E) ratio of 1:2 may be inadequate to ventilate these affected lung units equally, as they tend to open later and close earlier compared to healthy alveoli due to high retractive forces. Prolonging the inspiration time of the respiratory cycle is suggested to overcome these time-constant inequalities within the ARDS lungs, ventilate all alveoli despite different retraction forces in the airways and improve the gas exchange (4,5). Furthermore, the application of pressure controlled inverse ratio ventilation (PC-IRV) is shown to provide better gas exchange with significantly lower peak inspiratory pressures (PIP) (4).

Numerous approaches to the provision of mechanical ventilation during acute lung injury are currently available. Of these, pressure control inverse ratio ventilation has been considered superior to volume control ventilation with PEEP with respect to improving gas exchange and minimizing cardiovascular compromise. However, no study systematically compares volume-controlled (VC) and pressure-controlled (PC) ventilation while maintaining mean airway pressure (MAP) constant at varying I/E ratios. We studied the effect of VC and PC with PEEP at normal (1:2) and inverse I/E ratios (2:1 and 4:1) on gas exchange, lung mechanics, and hemodynamics in a sheep lung injury model. Severe lung injury was induced in 12 sheep with bilateral lung lavages using normal saline; prelavage PO2 230 +/- 50 mm Hg, PEEP 5 cm H2O and postlavage, pretreatment PO2 70 +/- 20 mm Hg, PEEP 10 cm H2O, both at FIO2 0.50. MAP was kept constant throughout the study at 25 +/- 2 cm H2O while ventilating all animals with a VT of 10 ml/kg and a rate of 20/min by randomized application of VC and PC with I/E ratios of 1:2, 2:1, and 4:1. Despite liberal fluid administration, all ventilatory modes depressed cardiac output compared with preinjury values. However, gas exchange and hemodynamics did not differ among ventilation modes or I/E ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

To assess the cardiorespiratory effects of pressure-controlled ventilation (PCV) and pressure-controlled inverse ratio ventilation (PC-IRV), we compared pressure-controlled ventilation with an inspiratory-to-expiratory time ratio (I/E) of 1/2 (PCV) and of 2/1 (PC-IRV) to volume-controlled ventilation (VCV) with an I/E of 1/2 in 10 patients suffering from the adult respiratory distress syndrome. In all modes, the inspiratory oxygen fraction, tidal volume, respiratory rate, and total positive end-expiratory pressure (PEEPt = applied PEEP + intrinsic PEEP) were kept constant. Each ventilatory mode was applied for 1 h in a randomized order. No significant differences in PaO2 were observed among the three modes. The PaCO2 was lower (p0.05) in PC-IRV (39 +/- 4 mm Hg) than in PCV (43 +/- 5 mm Hg) and in VCV (45 +/- 5 mm Hg). The peak airway pressure was significantly lower in PC-IRV than in PCV (p0.05) and in PCV than in VCV (p0.05), but plateau pressure was not different in the 3 modes. The mean airway pressure (mPaw) was significantly higher (p0.05) in PC-IRV (21.4 +/- 0.7 cm H2O) than in PCV (17.1 +/- 0.7 cm H2O) and VCV (16.4 +/- 0.5 cm H2O). As a consequence of this increased mPaw, PC-IRV induced a decrease in cardiac index (CI) (3.3 +/- 0.2 vs 3.7 +/- 0.2 L/min/m2 in VCV; p0.05) and hence in oxygen delivery (DO2) (424 +/- 28 vs 469 +/- 38 ml/min/m2 in VCV; p0.05). Our results suggest that neither PCV nor PC-IRV bring any benefit over VCV in terms of arterial oxygenation. Moreover, the increase in mPaw induced by PC-IRV may be deleterious to the CI and DO2.

Although pressure controlled-inverse ratio ventilation (PC-IRV) has been used successfully in the treatment of respiratory failure, it has not been applied to the treatment of respiratory dysfunction during anaesthesia. With PC-IRV the inspiratory wave form is fundamentally altered so that inspiratory time is prolonged (inverse I:E), inspiratory flow rate is low, and the peak inspiratory pressure is limited. Positive end-expiratory pressure (PEEP) can be applied and the mean airway pressure is higher than with conventional ventilation. To assess the clinical efficacy of this new mode of ventilation we studied ten patients having lower abdominal gynaecologic surgery in the Trendelenburg position under general anaesthesia. Pulmonary O2 exchange was determined during four steady states: awake control(AC), after 30 and 60 min of PC-IRV during surgery, and at the end of surgery. Patients’ lungs were ventilated with air/O2 by a Siemens 900C servo ventilator in the PC-IRV mode with an I:E ratio of 2:1 and 5 cm H2O of PEEP. TheFiO2 was controlled at 0.5 and arterial blood gases were used to calculate the oxygen tension-based indices of gas exchange. There were significant increases of(A-a) DO2 at 30 and 60 min (41 and 43%). These changes were less than those reported in a previous study using conventional tidal volume ventilation (7.5 ml · kg−1) and were similar to those in patients whose lungs were ventilated with high tidal volumes (12.7 ml · kg−1). Thus, in this clinical model of compromised gas exchange, arterial oxygenation was better with PC-IRV than with conventional ventilation, but not better than with large tidal volume ventilation.

Inverse ratio ventilation, with prolonged inspiratory times, appears to improve gas exchange and arterial oxygenation in patients with severe respiratory failure; however, in previous studies, pressure-controlled inverse ratio ventilation (PC-IRV), which uses a rapidly decelerating inspiratory flow pattern, was compared to conventional volume-controlled ventilation, which uses a constant inspiratory flow rate. Pressure-controlled ventilation (PCV), with a decelerating inspiratory flow pattern and conventional inspiratory-to-expiratory (I/E) ratios, also has been shown to produce improvement in PaO2 when compared to volume-controlled ventilation. It therefore is unknown if the potentially beneficial effects of PC-IRV are due to the reversal of I/E ratios or to the use of the rapidly decelerating inspiratory flow pattern. In order to investigate this issue, cardiorespiratory values were measured in ten patients with severe respiratory failure ventilated first with PCV, then PC-IRV, and finally with a second period of PCV. Tidal volume, respiratory rate, end-expiratory pressure, and fraction of oxygen in inspired gas (FIo2) were maintained at the same value for both ventilatory modalities. The PC-IRV was associated with significant increases in PaO2, arterial pH, and mean airway pressure. Significant decreases in pulmonary shunt fraction, PaCO2, and cardiac index were found with PC-IRV. No significant changes in tissue oxygen delivery or consumption occurred with either PCV or PC-IRV. These results demonstrate that inversion of conventional I/E ratios produces no significant improvement in the overall cardiorespiratory profile of critically ill patients. This study also suggests that the clinical utility of PC-IRV is limited except in the setting of the adult respiratory distress syndrome with hypoxemia or hypercapnia refractory to other therapeutic options.

Objectives: To characterize different modes of pressure- or volume-controlled mechanical ventilation with respect to their short-term effects on oxygen delivery (DO2). Furthermore to investigate whether such differences are caused by differences in pulmonary gas exchange or by airway-pressure-mediated effects on the central hemodynamics.Design: After inducing severe respiratory distress in piglets by removing surfactant, 5 ventilatory modes were randomly and sequentially applied to each animal.Setting: Experimental laboratory of a university department of Anesthesiology and Intensive Care.Animals: 15 piglets after repeated bronchoalveolar lavage.Interventions: Volume-controlled intermittent positive-pressure ventilation (IPPV) with either 8 or 15 cmH2O PEEP; pressure-controlled inverse ratio ventilation (IRV); pressure-controlled high-frequency positive-pressure ventilation (HFPPV) and pressure-controlled high frequency ventilation with inspiratory pulses superimposed (combined high frequency ventilation, CHFV). The prefix (L) indicates that lavage has been performed.Measurements and results: Measurements of gas exchange, airway pressures, hemodynamics, functional residual capacity (using the SF6 method), intrathoracic fluid volumes (using a double-indicator dilution technique) and metabolism were performed during ventilatory and hemodynamic steady state. The peak inspiratory pressures (PIP) were significantly higher in the volume-controlled low frequency modes (43 cmH2O for L-IPPV-8 and L-IPPV-15) than in the pressure-controlled modes (39 cmH2O for L-IRV, 35 cmH2O for L-HFPPV and 33 cmH2O for L-CHFV, with PIP in the high-frequency modes being significantly lower than in inverse ratio ventilation). The mean airway pressure (MPAW) after lavage was highest with L-IRV (26 cmH2O). In the ventilatory modes with a PEEP>8 cmH2O PaO2 did not differ significantly and beyond this “opening threshold” MPAW did not further improve PaO2. Central hemodynamics were depressed by increasing airway pressures. This is especially true for L-IRV in which we found the highest MAPW and at the same time the lowest stroke index (74% of IPPV).Conclusions: In this model, as far as oxygenation is concerned, it does not matter in which specific way the airway pressures are produced. As far as oxygen transport is concerned, i.e. aiming at increasing DO2, we conclude that optimizing the circulatory status must take into account the circulatory influence of different modes of positive pressure ventilation.

A key element in the treatment of Adult Respiratory Distress Syndrome (ARDS) is improvement in oxygen delivery to match metabolic demands. Conventional modes of ventilation have decreased mortality (50%) very little. We have done a retrospective analysis of 30 surgical patients who were treated with pressure-controlled inverse ratio ventilation. Mortality was 10%. Arterial oxygenation improved from 40.8 +/- 12.2 mm Hg to 138 +/- 47.2 mm Hg, while PCO2 decreased from 37.8 +/- 7.6 mm Hg to 31.1 +/- 5.9 mm Hg. Simultaneously, with the use of pressure-controlled inverse ratio ventilation, minute ventilation could be decreased by 30%, which may be secondary to increased O2 delivery to the tissue. Our data indicate that pressure-controlled inverse ratio ventilation may be beneficial to surgical patients with ARDS.

Since the earliest use of mechanical ventilation for respiratory insufficiency the search has been on for optimal ventilation attuned to different degrees of pulmonary involvement. Pressure controlled inverse ratio ventilation is a recently described ventilatory modality, in which the conventional inspiratory to expiratory ratio is reversed. This method of ventilation allows for stabilization of pulmonary units and diffusion of gases.

Inverse ratio ventilation (IRV) has been reported to improve oxygenation at lower peak airway pressures in patients with respiratory failure. Therefore we hypothesised that IRV might also improve oxygen exchange during anaesthesia. Conventional ratio ventilation (CRV) and IRV were compared in 24 low-risk surgical patients who were paralysed and whose lungs were ventilated with air/O2 by a non-rebreathing circuit and a Siemens 900-C servo ventilator. Two levels of time-cycled IRV (I:E ratios of 60/40 and 77/23) were bracketed by control periods with CRV (I:E ratio of 35/65). Inspired O2 fraction, O2 uptake and CO2 elimination, arterial blood gases, pulmonary ventilation and mechanics, heart rate and blood pressure were measured. From these data alveolar and dead space ventilation and four oxygen tension-based indices of gas exchange were calculated. During IRV, mean airway pressure (mean AWP) was increased but there were no changes in oxygen exchange indices, pulmonary mechanics, HR or BP. A sub-set of the sample with moderately impaired oxygen exchange, defined as the upper quartile for (A-a)DO2, was examined separately with identical results. Multivariate models were tested to identify variables which predicted O2 exchange during CRV. Patient age was the only predictor consistently significant in all models. We conclude that age is an important determinant of impaired pulmonary oxygen exchange during anaesthesia, and that increasing mean AWP by TC-IRV has no beneficial effects on pulmonary mechanics or gas exchange.

Recent interest in newer ventilatory support modes has been stimulated by the fact that the only thing we can offer the patient with severe acute respiratory failure (ARF) is to buy time and allow the lung to heal by itself. The mortality from acute adult respiratory distress syndrome (ARDS) has changed little since the first description in 1967 by Ashbaugh et al. However, there seems to be mounting evidence that high peak pressures (Ppeak) and high fractions of inspired oxygen (FiO2) should be avoided as this would add further injury to an already compromised lung (Taghizadeh and Reynolds 1976; Kolobow et al. 1987; Denek and Fanburg 1980; Pratt et al. 1979).

In 19 anesthetized piglets 3 ventilatory modes were studied after inducing pulmonary insufficiency by bronchoalveolar lavage by the method of Lachmann. The lavage model was considered suitable for reproduction of severe respiratory distress. This model was reproducible and stable with respect to alveolar collapse, decrease in static chest-lung compliance and increase in extravascular lung water. The ventilatory modes studied were volume-controlled intermittent positive-pressure ventilation (IPPV), pressure-controlled inverse ratio ventilation (IRV), and pressure-controlled high-frequency positive-pressure ventilation (HFPPV). The 3 ventilatory modes were used in random sequence for at least 30 min to produce a ventilatory steady state. Ventilation with no PEEP, permitting alveolar collapse, was interposed between each experimental mode. The ability to open collapsed alveoli, i.e. alveolar recruitment, was different. The recruitment rate for IPPV was 74%, but for IRV and HFPPV it was 95%, respectively. Although IRV provided the best PaO2, this was at the expense of high airway pressures with circulatory interference and reduced oxygen transport. In contrast to this, HFPPV provided lower airway pressures, less circulatory interference and improved oxygen transport. In the clinical setting there might be negative effects on vital organs and functions unless the ventilatory modes are continuously and cautiously adapted to the individual requirements in different phases of severe respiratory distress. Therefore, one ventilatory strategy could be to “open the airways” with IRV, but then switch to HFPPV in an attempt to maintain the airways open with lesser risk of barotrauma and with improved oxygen transport.

Cardiopulmonary Critical Care is a conveniently small textbook that discusses clinically relevant physiology and treatment of cardiac and pulmonary derangements in intensve care unit patients. I appreciate the compact size of this textbook because my stamina for lifting heavy, more comprehensive textbooks is yielding to the electronic medium. By restricting discussions to cardiac and pulmonary areas, I found that this compact textbook comprehensively covered topics such as advanced ventilator modes and techniques, the variety of new drugs available to treat cardiac and hypertensive disorders, and the unique problems encountered in cardiac and thoracic surgical and trauma patients. As pointed out by its editors, the book is designed for '... clinicians with intermittent responsibilities for critically ill patients in a world of competing demands.' With this goal in mind, I wonder whether this type of clinician will spend much time with the discussions of respiratory and cardiac physiology that are found at the beginning of the textbook. Some of these discussions are quite basic and are readily found in surgical, internal medicine, and anesthesiology textbooks, as well as in most critical care textbooks. Examples include discussions of acid–base abnormalities, oxygen transport, and lung mechanics. I am convinced, however, that intermittent critical care physicians will find the discussions of newer and increasingly popular medications and treatment approaches very practical. When, for example, should vasopressin be used for hypotension? When should a patient with acute lung injury be placed in the prone position? Should lipid-lowering therapy be used in the immediate period after a patient presents with an acute coronary syndrome? The discussions of these topics are well referenced. The authors clearly state when there is controversy and when supporting literature is lacking. Critical care medicine has seen an explosion in new ventilator technologies. With the exception of pulmonary and critical care specialists, it is not unusual for physicians to be overwhelmed with advanced ventilator terminology and techniques. I found that the chapters on mechanical ventilation, including modes of ventilation, weaning from mechanical ventilation, and the use of noninvasive ventilation, were lucidly written and well referenced. The serious reader of these chapters will find the basics of volume and pressure targeted modes (traditional and untraditional), auto-PEEP (auto positive end-expiratory pressure), and weaning techniques clearly presented with clarifying illustrations. Discussions of advanced ventilator management including lung protective strategies, airway pressure release ventilation, and pressure control inverse ratio ventilation will be useful to the advanced critical care practitioner. I appreciated the sections on postoperative care of cardiac and thoracic surgical and trauma patients. Although the physiology of these patients' derangements is well understood by most practitioners of critical care medicine, the unique problems with these perioperative patients and practice preferences of cardiothoracic surgeons and anesthesiologists may be poorly understood by physicians whose training did not span these disciplines. The chapters discuss the basics of care for these patients but they also include unique issues such as the use of independent lung ventilation, epidural and intrathecal narcotic administration, and management of injury to the recurrent laryngeal nerve. A table outlining complications of common and unusual thoracic surgical procedures will be useful to nonsurgical physicians who care for these patients. A small section is dedicated to the use of portable ultrasonography to assist vascular access to the internal jugular vein – a cutting edge technology that is experiencing increasing application. Unfortunately, more studies documenting the safety and efficacy of portable ultrasound for vascular procedures are needed, but I believe that this technology will become standard soon. I hope that future editions of this book will provide even more detailed information to validate and describe this important adjunct to vascular catheterization.

Reperfusion injury is one of the major causes of early morbidity and mortality after lung transplantation. Features of thi s syndrome are pulmonary edema, reduction of compliance, and impaired gas exchange, and these occur in about 20% of all lung transplant recipients. Usual treatment includes prolonged mechanical ventilation with elevated positive end-expiratory airway pressure (PEEP), enhanced mean airway pressure with high oxygen content (Fio2), and, in severe cases, inverse ratio ventilation and extracorporeal membrane oxygenation. We report on the successful treatment with nebulized synthetic surfactant (Exosurf; Wellcome, Burgwedel, Germany) of a patient in whom reperfusion injury developed 5 hours after right lung transplantation. Right lung transplantation was done in a 26-year-old woman who had sarcoidosis with terminal interstitial lung disease and recurrent failure of the right side of the heart. The patient had been dependent on continuous oxygen insufllation for 30 months before transplantation. Pulmonary hypertension was present with a mean pulmonary artery pressure of 50 mm Hg.

Inverse ratio ventilation and related ventilatory modes (eg, pressure release ventilation) have been applied to patients with the adult respiratory distress syndrome (ARDS) with apparent beneficial effects on arterial oxyhemoglobin saturation. While several mechanisms of improved gas exchange have been postulated, many intensive care physicians believe that the development of occult PEEP (autoPEEP; intrinsic PEEP) leads to the observed rise in oxygen saturation. We report here our findings in a patient whose improved oxygenation on inverse ratio ventilation could not be attributed to autoPEEP.

Pressure controlled inverse ratio ventilation (PCIRV) is often used as the initial therapeutic manoeuvre to improve oxygenation in severe adult respiratory distress syndrome (ARDS). When this alone fails, however, there is no consensus as to which therapy to resort to. We have used combined high frequency ventilation (CHFV) along with kinetic therapy (KT) to treat three patients with ARDS and resistant hypoxia. The basis for this treatment was our previous clinical observation that the two techniques together produced a greater improvement in oxygenation than either used alone. In CHFV a Monsoon jet ventilator was used to superimpose high frequency jet ventilation (rate 300 cycles min−1, inspiratory time 0.3, driving pressure 1 bar) on pressure controlled ventilation (rate 10 breaths min−1, inspiratory pressure 30 mbar). At the same time patients were positioned on a kinetic therapy pressure relief low air-loss bed (KCI) and rotated through a total angle of 90°. ThreePaO2/FIO2 values for each patient are shown in Table 14 and these correspond to (a) PCIRV alone (b) after 1 h of combined therapy and (c) after 24 h of combined therapy. The combination of CHFV with kinetic therapy produced improvement in oxygenation in all patients. Each of these individual therapies is believed to act through a different physiological mechanism.1 2 It is possible that the two together may, therefore, produce greater improvement than either therapy applied on its own. The number of such cases that present to one institution limits our small study, but we believe the significant improvement in oxygenation warrants further investigation.

In acute respiratory distress syndrome (ARDS) change from supine (SP) to prone position can improve gas exchange by recruiting alveoli situated in dorsal dependent regions and by alteration of ventilation/perfusion ratio. The aim of this study was to investigate the effect of prone position (PP) after application of high fractional inspired oxygen (hFiO2), inverse ratio ventilation (IRV), positive end exspiratory pressure (PEEP)as well as kinetic therapy (KT) and hemofiltration (HF) did not lead to a breakthrough in treatment of severe ARDS.

The approach to mechanical ventilation has been revolutionized by new insights into the pathogenesis of respiratory failure in acute respiratory distress syndrome (ARDS). Concepts such as low-volume ventilation, permissive hypercapnia, inverse ratio ventilation, best and intrinsic positive end-expiratory pressure, airway shear, pressure volume curves, inflection points, and prone positioning have radically transformed thinking about ventilator management. Since 1966, more than 8000 ARDS-related publications have appeared. Studies highlighting the experimental basis for innovations in mechanical ventilation are presented. Selected clinical series that exemplify the use of these new strategies are reviewed, to demonstrate how key experimental and clinical research has altered our understanding about what works, and why. Mismanagement of mechanical ventilation causes lung injury and increases mortality. The strategy of protective ventilation has provided the first substantial reduction of mortality in the history of ARDS.

OO I a/ PF ratio of 8.7 provides an approximate indication of the problems with oxygen transfer in these patients, the pic- ture is incomplete. First, it would be helpful to know how long the problems persisted at this level before extracorporeal sup- port was started; was it one or more hours or was the mean cal- culated from the single worst value for each patient and so based in each case on a single blood-gas result? Second, apart from the Murray score which includes positive end-expiratory pressure (PEEP) as one component, we are given little clue as to mean airway pressure at this time, despite the fact that this is accepted as being a major determinant of arterial oxygena- tion. 3 As long ago as the 1970s the importance of at least some ref- erence to airway pressure was recognized and the American ECMO study entry criteria reflected this by referring to specific levels of PEEP together with defined requirements for 2 O I F and 2 O a. P 4 At the time, this was reasonable in that PEEP was the only commonly used means of increasing mean airway pressure. It is, of course, still used extensively and is one of the components of the Murray score. However, today, particularly in the most severe forms of acute lung injury, the extensive use of inverse ratio ventilation to maximize mean airway pressure means that its relationship to the level of PEEP is less pre- dictable. It would be helpful, therefore, if future descriptions of severity of lung injury in patients undergoing ventilation could include data on the mean airway pressure being used.

The respective roles of high pressure and high tidal volume to promote high airway pressure pulmonary edema are unclear. Positive end-expiratory pressure (PEEP) was shown to reduce lung water content in this type of edema, but its possible effects on cellular lesions were not documented. We compared the consequences of normal tidal volume ventilation in mechanically ventilated rats at a high airway pressure (HiP-LoV) with those of high tidal volume ventilation at a high (HiP-HiV) or low (LoP-HiV) airway pressure and the effects of PEEP (10 cm H2O) on both edema and lung ultrastructure. Pulmonary edema was assessed by extravascular lung water content and microvascular permeability by the drug lung weight and the distribution space of 125I-labeled albumin. HiP-LoV rat lungs were not different from those of controls (7 cm H2O peak pressure ventilation). By contrast, the lungs from the groups submitted to high volume ventilation had significant permeability type edema. This edema was more pronounced in LoP-HiV rats. It was markedly reduced by PEEP, which, in addition, preserved the normal ultrastructural aspect of the alveolar epithelium. This was in striking contrast to the diffuse alveolar damage usually encountered in this type of edema. To our knowledge, this constitutes the first example of a protective effect of PEEP during permeability edema.

Conventional modes of mechanical ventilation provide patients with ventilatory support during episodes of acute respiratory failure. Problems with these methodologies include ventilation-perfusion mismatching, difficulty in stabilization of alveolar units, airway pressure complications, and lack of synchronization of the patient-mechanical ventilator system. New modes of mechanical ventilation have been developed to address these specific problems. These include pressure support ventilation, high frequency ventilation, inverse ratio ventilation, airway pressure release ventilation, and mandatory minute ventilation. Independent lung ventilation is a technique of ventilation that addresses the problem of mechanical ventilation in unilateral lung disease.

Cardiorespiratory values were measured in nine patients with severe respiratory failure before and following initiation of pressure controlled inverse ratio ventilation (PC-IRV) at an inspiratory to expiratory ratio of 2:1. All patients showed increases in PaO2, with the mean PaO2 rising from 63 +/- 4 (mean +/- SEM) to 76 +/- 8 mm Hg. Peak inspiratory pressure fell from 44 +/- 4 to 39 +/- 2 cm H2O. There were no significant changes in any hemodynamic or oxygen metabolism variable associated with the institution of PC-IRV. In particular, no significant alteration in cardiac index, pulmonary artery pressures, oxygen delivery, oxygen consumption, or oxygen extraction ratio occurred with the use of PC-IRV. These results suggest that PC-IRV may be a useful ventilatory modality in the treatment of severe respiratory failure since it results in improvement in arterial oxygenation without any deterioration in hemodynamic or tissue oxygen metabolism parameters.

The respiratory-distress syndrome in 12 patients was manifested by acute onset of tachypnœa, hypoxaemia, and loss of compliance after a variety of stimuli; the syndrome did not respond to usual and ordinary methods of respiratory therapy. The clinical and pathological features closely resembled those seen in infants with respiratory distress and to conditions in congestive atelectasis and postperfusion lung. The theoretical relationship of this syndrome to alveolar surface active agent is postulated. Positive end-expiratory pressure was most helpful in combating atelectasis and hypoxaemia. Corticosteroids appeared to have value in the treatment of patients with fat-embolism and possibly viral pneumonia.

The effect of altering peak airway pressure, respiratory frequency, and inspiration: expiration ratio on arterial blood gas tensions, blood pressure, and calculated right-to-left shunt was investigated in 6 infants undergoing mechanical ventilation for hyaline membrane disease with a Bennet ventilator. The use of a very long inspiratory phase resulted in a large increase in Pao2 and fall in right-to-left shunt without affecting mean arterial blood pressure.

Mechanical ventilation with different ratios of inspiratory to expiratory times (I:E ratio) and levels of positive end-expiratory pressure (PEEP) were applied to 9 dogs after the aspiration of fresh water and then were compared. The dogs were ventilated with an I:E ratio of 2:1 with 0 PEEP; an I:E r