Search

Background Although specific interventions previously demonstrated benefit in patients with ARDS, use of these interventions is inconsistent, and patient mortality remains high. The impact of variability in center management practices on ARDS mortality rates remains unknown. Research Question What is the impact of treatment variability on mortality in patients with moderate to severe ARDS in the United States? Study Design and Methods We conducted a multicenter, observational cohort study of mechanically ventilated adults with ARDS and Pa o 2 to F io 2 ratio of ≤ 150 with positive end-expiratory pressure of ≥ 5 cm H2O, who were admitted to 29 US centers between October 1, 2016, and April 30, 2017. The primary outcome was 28-day in-hospital mortality. Center variation in ventilator management, adjunctive therapy use, and mortality also were assessed. Results A total of 2,466 patients were enrolled. Median baseline Pa o 2 to F io 2 ratio was 105 (interquartile range, 78.0-129.0). In-hospital 28-day mortality was 40.7%. Initial adherence to lung protective ventilation (LPV; tidal volume, ≤ 6.5 mL/kg predicted body weight; plateau pressure, or when unavailable, peak inspiratory pressure, ≤ 30 mm H2O) was 31.4% and varied between centers (0%-65%), as did rates of adjunctive therapy use (27.1%-96.4%), methods used (neuromuscular blockade, prone positioning, systemic steroids, pulmonary vasodilators, and extracorporeal support), and mortality (16.7%-73.3%). Center standardized mortality ratios (SMRs), calculated using baseline patient-level characteristics to derive expected mortality rate, ranged from 0.33 to 1.98. Of the treatment-level factors explored, only center adherence to early LPV was correlated with SMR. Interpretation Substantial center-to-center variability exists in ARDS management, suggesting that further opportunities for improving ARDS outcomes exist. Early adherence to LPV was associated with lower center mortality and may be a surrogate for overall quality of care processes. Future collaboration is needed to identify additional treatment-level factors influencing center-level outcomes. Trial Registry ClinicalTrials.gov; No.: NCT03021824; URL: www.clinicaltrials.gov

In emphysema airway resistance can exceed collateral airflow resistance, causing air to flow preferentially through collateral pathways. In severe emphysema ventilation through openings directly through the chest wall into the parenchyma (spiracles) could bypass airway obstruction and increase alveolar ventilation via transpleural expiration. During lung transplant operations, spiracles occasionally can occur inadvertently. We observed transpleural expiration via spiracles in three subjects undergoing lung transplant for emphysema. During transpleural spiracle ventilation, inspiratory tidal volumes (TV) were unchanged; however, expiration was entirely transpleural in two patients whereas the expired TV to the ventilator circuit was reduced to 25% of the inspired TV in one. At baseline, mean PCO2 was 61 ± 5 mm Hg, which decreased to a mean PCO2 of 49 ± 5 mm Hg (P = .05) within minutes after transpleural spiracle ventilation and further decreased at 1 to 2 h (36 ± 4 mm Hg; P = .002 compared with baseline) on unchanged ventilator settings. This observation of increased alveolar ventilation supports further studies of spiracles as a possible therapy for advanced emphysema.

SESSION TITLE: Disorders of the Pleura Posters SESSION TYPE: Original Investigation Posters PRESENTED ON: October 18-21, 2020 PURPOSE: Spontaneous pneumothorax is a relatively common complication in critically ill patients with severe acute respiratory distress syndrome (ARDS) Limited data exists regarding pneumothorax in severe acute respiratory coronavirus 2 (SARS-CoV-2) patients This study depicts cases of spontaneous pneumothorax in critically ill SARS-CoV-2 patients and explores the potential underlying mechanisms METHODS: This is a retrospective cohort study of SARS-CoV-2 patients with severe ARDS admitted to a tertiary care center between March 9, 2020 to April 5, 2020 SARS-CoV-2 was diagnosed via polymerase chain reaction Only patients on mechanical ventilation were analyzed RESULTS: A total of 22 patients with confirmed SARS-CoV-2 infection on mechanical ventilation were identified and analyzed Out of these, 7 patients developed a spontaneous pneumothorax The patients were predominantly male (86%) with an age range between 67 and 82 years old Cough (100%) and shortness of breath (71%) were the most common presenting symptoms Chronic obstructive pulmonary disease was not present in any of the patients Pneumothoraxes were diagnosed 6 to 33 days after hospital admission All 7 patients had subclavian central lines that were placed by 4 different providers with more than 15 years of critical care experience All 7 patients had right sided pneumothoraxes of varying sizes but only 42% had right-sided lines Remarkably, the mean peak inspiratory pressure (Ppeak) for these patients was 25 cm H2O and the mean positive end expiratory pressure (PEEP) was 11 cm H2O Prone positioning was utilized in 57% of patients and 42% of patients received convalescent plasma The mortality rate was 71% and the 2 patients who survived were discharged to long term acute care hospitals CONCLUSIONS: Traditionally, ventilator associated pneumothorax is associated with a Ppeak greater than 40 cm H2O, which contrasts with the mean Ppeak of 25 cm H2O observed in this study While iatrogenic pneumothoraces are common following subclavian central line placement, the majority of the pneumothoraces in this study occurred on the opposite side of the procedure ARDS secondary to SARS-CoV-2 infection appears to have a completely different pathophysiology than that of traditional ARDS, which is typically managed with low PEEP and Ppeak Utilizing the ARDSnet protocol in patients with ARDS secondary to SARS-CoV-2 may be deleterious Further investigation is needed to evaluate this hypothesis CLINICAL IMPLICATIONS: ARDS secondary to SARS-CoV-2 appears to be distinct from ARDS caused by other disease processes and may have a different risk of pneumothorax development As elderly, critically ill SARS-CoV-2 patients with ARDS have been found to have increased risk of death, identifying modifiable risks associated with the development of a spontaneous pneumothorax could help mitigate morbidity and mortality in this population DISCLOSURES: No relevant relationships by Andres Chacon Martinez, source=Web Response No relevant relationships by robert chait, source=Web Response No relevant relationships by Kai Chen, source=Web Response No relevant relationships by Nakeya Dewaswala, source=Web Response No relevant relationships by Katherine Hodgin, source=Web Response no disclosure on file for Jesus Pino;No relevant relationships by Fergie Ramos Tuarez, source=Web Response No relevant relationships by Renuka Reddy, source=Web Response

BACKGROUND Mechanical ventilation is a cornerstone in the management of acute respiratory failure. Both volume-targeted and pressure-targeted ventilations are used, the latter modes being increasingly used. We provide a narrative review of the physiologic principles of these two types of breath delivery, performed a literature search, and analyzed published comparisons between modes. METHODS We performed a systematic review and meta-analysis to determine whether pressure control-continuous mandatory ventilation (PC-CMV) or pressure control-inverse ratio ventilation (PC-IRV) has demonstrated advantages over volume control-continuous mandatory ventilation (VC-CMV). The Cochrane tool for risk of bias was used for methodologic quality. We also introduced physiologic criteria as quality indicators for selecting the studies. Outcomes included compliance, gas exchange, hemodynamics, work of breathing, and clinical outcomes. Analyses were completed with RevMan5 using random effects models. RESULTS Thirty-four studies met inclusion criteria, many being at high risk of bias. Comparisons of PC-CMV/PC-IRV and VC-CMV did not show any difference for compliance or gas exchange, even when looking at PC-IRV. Calculating the oxygenation index suggested a poorer effect for PC-IRV. There was no difference between modes in terms of hemodynamics, work of breathing, or clinical outcomes. CONCLUSIONS The two modes have different working principles but clinical available data do not suggest any difference in the outcomes. We included all identified trials, enhancing generalizability, and attempted to include only sufficient quality physiologic studies. However, included trials were small and varied considerably in quality. These data should help to open the choice of ventilation of patients with acute respiratory failure.

Background Protective ventilation strategy has been shown to reduce ventilator-induced lung injury in patients with ARDS. In this study, we questioned whether protective ventilatory settings would attenuate lung impairment during one-lung ventilation (OLV) compared with conventional ventilation in patients undergoing lung resection surgery. Methods One hundred patients with American Society of Anesthesiology physical status 1 to 2 who were scheduled for an elective lobectomy were enrolled in the study. During OLV, two different ventilation strategies were compared. The conventional strategy (CV group, n = 50) consisted of F io 2 1.0, tidal volume (V t ) 10 mL/kg, zero end-expiratory pressure, and volume-controlled ventilation, whereas the protective strategy (PV group, n = 50) consisted of F io 2 0.5, V t 6 mL/kg, positive end-expiratory pressure 5 cm H2O, and pressure-controlled ventilation. The composite primary end point included Pa o 2/F io 2 o 2), Pa co 2, and peak inspiratory pressure (PIP) were repeatedly measured. Results During OLV, although 58% of the PV group needed elevated F io 2 to maintain an Sp o 2 > 95%, PIP was significantly lower than in the CV group, whereas the mean Pa co 2 values remained at 35 to 40 mm Hg in both groups. Importantly, in the PV group, the incidence of the primary end point of pulmonary dysfunction was significantly lower than in the CV group (incidence of Pa o 2/F io 2 Conclusion Compared with the traditional large V t and volume-controlled ventilation, the application of small V t and PEEP through pressure-controlled ventilation was associated with a lower incidence of postoperative lung dysfunction and satisfactory gas exchange. Trial registry Australian New Zealand Clinical Trials Registry; No.: ACTRN12609000861257; URL: www.anzctr.org.au

To compare pressure characteristics of mechanical ventilation and their impact on pediatric patients with severe ARDS in the pre-protective lung strategy (PLS) and post-PLS eras.Medical records of 33 patients admitted to our pediatric ICU with ARDS from 1992 through 1994 (pre-PLS) and 52 patients with ARDS admitted from 2000 through 2003 (post-PLS) were retrospectively reviewed.Patient age and gender distribution were identical in both eras. Fifty-five percent of the patients in the pre-PLS era had pneumothorax, compared to 17% in the post-PLS era (p0.05). Overall mortality rates for patients in the pre-PLS and post-PLS eras were 42% and 25%, respectively (p = 0.09; not significant). Mean duration of exposure to peak inspiratory pressure (PIP) values40 cm H2O was significantly longer in the pre-PLS era than in the post-PLS era. Pre-PLS patients with pneumothorax received mean maximum PIP of 72 +/- 17 cm H2O, mean maximum positive end-expiratory pressure (PEEP) of 20 +/- 5 cm H2O, and maximum mean airway pressure (MAP) of 46 +/- 8 cm H2O, while patients in the post-PLS era required mean maximum PIP of 42 +/- 2 cm H2O, mean maximum PEEP of 14 +/- 2 cm H2O, and maximum MAP of 30 +/- 6 cm H2O, respectively (p0.05 for all pressure parameters). There were no significant differences in mechanical ventilation pressure characteristics among patients who did not have pneumothorax during their course of management in both eras.A significantly more aggressive use of ventilator pressure characteristics distinguished the pre-PLS era from the post-PLS era, and was found to be associated with a markedly higher incidence of pneumothorax. Outcome in both eras did not differ significantly, presumably due to insufficient statistical power.

Background Low tidal volume (Vt) ventilation for ARDS is a well-accepted concept. However, controversy persists regarding the optimal ventilator settings for patients without ARDS receiving mechanical ventilation. This study tested the hypothesis that ventilator settings influence the development of new ARDS. Methods Retrospective analysis of patients from the Multi Parameter Intelligent Monitoring of Intensive Care-II project database who received mechanical ventilation for ≥ 48 h between 2001 and 2005. Results A total of 2,583 patients required > 48 h of ventilation. Of 789 patients who did not have ARDS at hospital admission, ARDS developed in 152 patients (19%). Univariate analysis revealed high peak inspiratory pressure (odds ratio [OR], 1.53 per SD; 95% confidence interval [CI], 1.28 to 1.84), increasing positive end-expiratory pressure (OR, 1.35 per SD; 95% CI, 1.15 to 1.58), and Vt (OR, 1.36 per SD; 95% CI, 1.12 to 1.64) to be significant risk factors. Major nonventilator risk factors for ARDS included sepsis, low pH, elevated lactate, low albumin, transfusion of packed RBCs, transfusion of plasma, high net fluid balance, and low respiratory compliance. Multivariable logistic regression showed that peak pressure (OR, 1.31 per SD; 95% CI, 1.08 to 1.59), high net fluid balance (OR, 1.3 per SD; 95% CI, 1.09 to 1.56), transfusion of plasma (OR, 1.26 per SD; 95% CI, 1.07 to 1.49), sepsis (OR, 1.57; 95% CI, 1.00 to 2.45), and Vt (OR, 1.29 per SD; 95% CI, 1.02 to 1.52) were significantly associated with the development of ARDS. Conclusions The associations between the development of ARDS and clinical interventions, including high airway pressures, high Vt, positive fluid balance, and transfusion of blood products, suggests that ARDS may be a preventable complication in some cases.

Background Average volume-assured pressure support (AVAPS) has been introduced as a new additional mode for a bilevel pressure ventilation (BPV) device (BiPAP; Respironics; Murrysville, PA), but studies on the physiologic and clinical effects have not yet been performed. There is a particular need to better define the most efficient ventilatory treatment modality for patients with obesity hypoventilation syndrome (OHS). Methods In OHS patients who did not respond to therapy with continuous positive airway pressure, the effects of BPV with the spontaneous/timed (S/T) ventilation mode with and without AVAPS over 6 weeks on ventilation pattern, gas exchange, sleep quality, and health-related quality of life (HRQL) assessed by the severe respiratory insufficiency questionnaire (SRI) were prospectively investigated in a randomized crossover trial. Results Ten patients (mean [± SD] age, 53.5 ± 11.7 years; mean body mass index, 41.6 ± 12.1 kg/m 2 ; mean FEV 1 /FVC ratio, 79.4 ± 6.5%; mean transcutaneous P co 2 [Ptc co 2 ], 58 ± 12 mm Hg) were studied. Ptc co 2 nonsignificantly decreased during nocturnal BPV-S/T by −5.6 ± 11.8 mm Hg (95% confidence interval [CI], −14.7 to 3.4 mm Hg; p = 0.188), but significantly decreased during BPV-S/T-AVAPS by −12.6 ± 12.2 mm Hg (95% CI, −22.0 to −3.2 mm Hg; p = 0.015). Pneumotachographic measurements revealed a higher individual variance of peak inspiratory pressure (p Conclusion BPV-S/T substantially improved oxygenation, sleep quality, and HRQL in patients with OHS. AVAPS provided additional benefits on ventilation quality, thus resulting in a more efficient decrease of Ptc co 2 . However, this did not provide further clinical benefits regarding sleep quality and HRQL.

Study objective The clinical usefulness of varying inspiratory flow waveforms during mechanical ventilation has not been adequately studied. The aim of this study was to compare the effects of three different respiratory waveforms on the pulmonary mechanics, gas exchange, and respiratory metabolism of ventilated patients with COPD. Design A randomized and comparative trial of consecutive patients. Setting Medical ICUs of a 2,000-bed university hospital. Patients Fifty-four patients with COPD were enrolled. Interventions Constant, decelerating, and sine waveforms were applied to each patient in a random order. Measurements and results With tidal volume, inspiratory time, and inspiratory frequency being kept constant, the decelerating waveform produced statistically significant reductions of peak inspiratory pressure, mean airway resistance, physiologic dead space ventilation (V d /V t ), Pa co 2 , and symptom score. There was also a significant increase in alveolar-arterial oxygen pressure difference with the decelerating flow waveform, but there were no significant changes in mean airway pressure, arterial oxygenation, heart rate, mean BP, and other hemodynamic measurements. In addition, assessment on the work of breathing (WOB) revealed that ventilator WOB values were reduced with the decelerating waveform. Oxygen consumption and carbon dioxide output were virtually not affected by changing inspiratory flow waveforms. Except for V d /V t , the effects of constant square and sine waveforms were similar to each other and could not be separated statistically. Conclusions The most favorable flow pattern for ventilated patients with COPD appeared to be the decelerating waveform. There are possibilities for the improvement of ventilation in these patients by selecting an appropriate inspiratory flow.

Lung transplantation reduces mortality in patients with end-stage lung disease; however, only approximately 21% of lungs from potential donor patients undergo transplantation. A large number of donor lungs become categorized as unsuitable for lung transplantation as a result of lung injury around the time of brain death. Limiting this injury is key to increasing the number of successful lung procurements and subsequent transplants. This narrative review by a working group of pulmonologists, respiratory therapists, and lung transplant specialists elucidates principles of mechanical ventilatory support that can be used to limit lung injury in potential lung donor patients and examines the implementation of protocolized strategies in enhancing the procurement of donor lungs for transplantation.

The aim of this study was to measure inspiratory pressure-generating capacity in patients presenting with acute asthma, as it has been suggested that inspiratory muscle fatigue may contribute to breathlessness and acute respiratory failure.Descriptive study.Emergency departments of two inner-city hospitals.Fifty-one patients with acute asthma, and 45 patients without respiratory disease who served as control subjects.Maximum inspiratory pressure-generating capacity was measured soon after presentation by the sniff nasal inspiratory pressure (SNIP) method. The mean (SD) SNIP was 110 cm H(2)O (23 cm H(2)O) in men with asthma (mean for control subjects, 126 cm H(2)O [25 cm H(2)O]; p0.05) and 80 cm H(2)O [24 cm H(2)O] in women with asthma (mean for control subjects, 105 cm H(2)O (26 cm H(2)O); p0.01). In a second study of simultaneous SNIP and intrathoracic pressure measurements in a group of patients with acute asthma (n = 10) and control subjects (n = 11), the effect of airways obstruction on SNIP was assessed. The measurement of sniff esophageal pressure was more negative than SNIP by approximately 16% in asthmatic patients and by 4% in control subjects. Taking account of the likely effect of airways obstruction on SNIP, the reduction in inspiratory pressure-generating capacity that was observed in these patients with moderately severe acute asthma was minor and was consistent with the modest hyperinflation observed.This study did not find evidence of inspiratory muscle weakness or fatigue in patients with moderately severe acute asthma presenting to the emergency department.

Objective: To identify parameters thatindicate retained secretions and the need for tracheal suctioning (TS)in patients receiving mechanical ventilation (MV). Design: Prospective observational study. Setting: A 14-bed medical ICU in a 946-bed universityhospital. Patients: Sixty-six consecutive patientsreceiving MV. Interventions: Two successive trachealsuctions, TS1 and TS2, performed at a 2-h interval as usual patientcare. Retained secretions were considered significant if the volume of secretions removed by TS2 was > 0.5 mL. Measurementsand results: Variations between TS1 and TS2 of pulse oximetricsaturation (Sp o 2 ), peak inspiratory pressure(Ppeak), tidal volume (V t ), and Ramsay score were comparedbetween patients with TS2 ≤ 0.5 mL (group 1; n = 27) and patientswith TS2 > 0.5 mL (group 2; n = 39). The presence of a sawtoothpattern on flow-volume loop displayed on the monitor screen of theventilator and of respiratory sounds heard over the trachea before TS2were compared between the two groups. Variations of Ppeak, V t , Sp o 2 , and Ramsay score betweenTS1 and TS2 did not differ between the two groups. However, group 2 hada sawtooth pattern (82% vs 29.6%; p = 0.0001) and respiratorysounds (66.6% vs 25.9%; p = 0.001) more frequently than group 1before TS2. For the sawtooth pattern, the likelihood ratio (LR) of apositive test was 2.70 and the LR of a negative test was 0.25, whilefor respiratory sounds it was 2.50 and 0.45, respectively. When thepresence of a sawtooth pattern and of respiratory sounds was combined, the LR of a positive test rose to 14.7 and the LR of a negative testwas 0.42. Conclusions: A sawtooth pattern and/orrespiratory sounds over the trachea are good indicators of retainedsecretions in patients receiving MV and may indicate the need for TS. Conversely, the absence of a sawtooth pattern may rule out retainedsecretions.

Study objectives To evaluate changes in respiratory and hemodynamic function of patients with ARDS and requiring high-frequency percussive ventilation (HFPV) after failure of conventional ventilation (CV). Design Retrospective case series. Setting Surgical ICU (SICU) and medical ICU (MICU) of an academic county facility. Measurements and results Thirty-two consecutive patients with ARDS (20 from SICU, 12 from MICU) who were unresponsive to at least 48 h of CV and were switched to HFPV were studied. Data on respiratory and hemodynamic parameters were collected during the 48 h preceding and the 48 h after institution of HFPV and compared. Between the period of CV and the period of HFPV, the ratio of Pa o 2 to the fraction of inspired oxygen (F io 2 ) increased ([mean ± SE] 130 ± 8 vs 172 ± 17; p = 0.027), peak inspiratory pressure (PIP) decreased (39.5 ± 1.7 vs 32.5 ± 1.9 mm Hg; p = 0.002), and mean airway pressure (MAP) increased (19.2 ± 1.2 vs 27.5 ± 1.4 mm Hg; p o 2 /F io 2 per hour was also significantly improved between the two periods. The same changes in Pa o 2 /F io 2 , PIP, and MAP were observed when the last value recorded while the patients were on CV was compared with the first value recorded after 1 h of HFPV. This improvement was sustained but not amplified during the hours of HFPV. The patterns of improvement in these three parameters were similar in SICU and MICU patients as well as in volume-control and pressure-control patients. There were no changes in hemodynamic parameters. Conclusion The HFPV improves oxygenation by increasing MAP and decreasing PIP. This improvement is achieved soon after institution of HFPV and is maintained without affecting hemodynamics.

In asthmatic patients with acute respiratory failure (ARF), placing an endotracheal tube is associated with a high rate of complications and results in increased airway resistance. In acute asthma, mask-continuous positive airway pressure (CPAP) decreases airway resistance and the work of breathing (WOB), but does not improve gas exchange. In COPD with ARF, adding intermittent positive pressure ventilation to mask-CPAP results in an additional improvement in WOB and is highly effective in correcting gas exchange abnormalities. In our medical ICU, noninvasive positive pressure ventilation (NPPV) is used as first-line interventional therapy in eligible patients with hypercapnic ARF. We report our experience with NPPV in 17 episodes of asthma and ARF over a 3-year period.A face mask was secured with head straps, avoiding a tight fit, and connected to a ventilator (PB-7200). Initial ventilatory settings included CPAP at 4 +/- 2 cm H2O to offset intrinsic positive end-expiratory pressure and pressure support ventilation (PSV) at 14 +/- 5 cm H2O aiming at a respiratory rate less than 25 breaths/min and an exhaled tidal volume of 7 mL/kg or more. PSV was then adjusted following arterial blood gas results.Mean age was 35.4 +/- 11.3 years; 10 patients were female. The mean (+/- SE) for different physiologic values are reported at initiation, less than 2 h, 2 to 6 h, and 12 to 24 h into NPPV. pH was 7.25 +/- 0.01, 7.32 +/- 0.02 (p = 0.0012), 7.36 +/- 0.02 (p0.0001), and 7.38 +/- 0.02; PaCO2 was 65 +/- 2, 52 +/- 3(p = 0.002), 45 +/- 3(p0.0001), and 45 +/- 4; PaO2 fraction of inspired oxygen was 315 +/- 41, 403 +/- 47, 367 +/- 47, and 472 +/- 67 (p = 0.06); and respiratory rate was: 29.1 +/- 1, 22 +/- 1 (p0.0001), 20 +/- 1, and 17 +/- 1. NPPV was well tolerated, and only two patients required sedation. Initial delivered minute ventilation was 16 +/- 4 L/min. The mean (+/- SD) peak inspiratory pressure to ventilate in the NPPV-treated patients was 18 +/- 5 cm H2O and always less than 25 cm H2O. There was no complication or problem with expectorating of secretions. Oral intake (liquid diet) was preserved. Two patients required intubation (35 min and 89 h into NPPV) for worsening PaCO2. Duration of NPPV was 16 +/- 21 h. All patients survived. Length of hospital stay was 5 +/- 4 days.In asthmatic patients with ARF, NPPV via a face mask appears highly effective in correcting gas exchange abnormalities using a low inspiratory pressure (25 cm H2O). A randomized study is in progress to assess fully the role of NPPV in status asthmaticus.

Objective To estimate mortality risk in pediatric patients with acute hypoxemic respiratory failure (AHRF). Design Retrospective chart review. Setting Forty-one pediatric ICUs. Subjects Four hundred seventy children with AHRF. We defined AHRF as mechanical ventilation with positive end-expiratory pressure ≥6 cm H 2 O and fraction of inspired oxygen greater than or equal to 0.5 for 12 or more hours. Measurements Physiologic and treatment variables were recorded every 12 h for 14 days. Cases were randomly assigned to score development and score validation subsets. Variables were assessed for their association with mortality in the development subset by logistic regression analysis. The analysis generated a series of logistic equations, which we called the Pediatric Respiratory Failure (PeRF) score, to estimate mortality risk at 12-h intervals over the first 7 days of treatment for AHRF. The predictive ability of the score was assessed in the validation subset by receiver operating characteristic curve area and goodness-of-fit χ 2 . Results Mortality of the collected cases was 43%. The PeRF score included age, operative status, Pediatric Risk of Mortality score, fraction of inspired oxygen, respiratory rate, peak inspiratory pressure, positive end-expiratory pressure, PaO 2 , and PaCO 2 . Area under the receiver operating characteristic curve was 0.769 at entry and increased to greater than 0.8 after 36 h. When the score was applied to the validation subset of patients, goodness-of-fit χ 2 showed no significant difference between estimated and actual mortality between 0 and 96 h. Conclusions The PeRF Score accurately estimated mortality risk in this retrospectively sampled group of high-risk pediatric patients with AHRF. This score may be useful in studies of newer therapies for pediatric AHRF, though prospective validation is necessary before it could be used to make clinical decisions.

Independent lung ventilation using two ventilators has been attempted in the treatment of acute respiratory failure due to unilateral lung disease. However, this method has been found to be cumbersome and difficult to use. We reasoned that a bifurcated endotracheal tube with a variable resistance valve may enable us to change the inspiratory airway pressures and, hence, the inspired tidal volume to one lung using a single ventilator. We tested this hypothesis in eight anesthetized sheep and created a bronchopleural fistula in one lung as a model of unilateral lung disease. A bifurcated endotracheal tube was placed to separate the ventilation to each lung and, through a "Y" connector, both right and left lungs were ventilated simultaneously with a single ventilator. A variable resistance valve was placed between the "Y" connector and the tube ventilating the experimental lung with bronchopleural fistula. With a ventilator-generated peak inspiratory pressure of 31 +/- 2 cm H2O, the airway pressure distal to the valve was randomly changed from 31 cm H2O to 23 +/- 2, 15 +/- 1, 8 +/- 1, and 0 cm H2O. This resulted in progressive diversion of tidal volume from the experimental lung to the control lung and an increase in exhaled tidal volume due to a decrease in air leak from the bronchopleural fistula. These data suggest that a variable resistance valve may be used for independent lung ventilation using a single ventilator.

Background Intraabdominal hypertension (IAH) and abdominal compartment syndrome (ACS) traditionally have been treated surgically through emergent laparotomy. Intensivist-performed bedside drainage of free intraperitoneal fluid or blood (percutaneous catheter decompression [PCD]) has been advocated as a less-invasive alternative to open abdominal decompression (OAD). Methods A single-center disease and severity of illness-matched case-control comparison of 62 patients with IAH/ACS treated with PCD vs traditional OAD was performed. The relative efficacy of each treatment in reducing elevated intraabdominal pressure (IAP) and improving organ dysfunction was assessed. Physiologic and demographic predictors of successful PCD therapy were determined. Results PCD and OAD both were effective in significantly decreasing IAP and peak inspiratory pressure as well as in increasing abdominal perfusion pressure. PCD potentially avoided the need for subsequent OAD in 25 of 31 patients (81%) treated. Successful PCD therapy was associated with fluid drainage of > 1,000 mL or a decrease in IAP of > 9 mm Hg in the first 4 h postdecompression. Conclusions Intensivist-performed PCD is an effective and less-invasive technique for treating patients with IAH/ACS where free intraperitoneal fluid or blood is present as determined by bedside ultrasonography. Failure to drain at least 1,000 mL of fluid and decrease IAP by at least 9 mm Hg in the first 4 h postdecompression is associated with PCD failure and should prompt urgent OAD.

Continuous irrigation-suction catheter (Irri-cath) is a double-lumen device that allows for simultaneous saline solution infusion and aspiration. This system may theoretically be more effective than conventional dry intermittent suction due to its vortex principle. To test this hypothesis, we performed 200 suction maneuvers in 20 ventilated patients. Identically shaped catheters were used in a randomized sequence. For the same individual, we used equal instilled saline solution volume (40 ml), vacuum pressure (-180 cm H2O), and ventilatory parameters. Effectiveness of suction was determined by measuring the total aspirated volume, the dry lyophilized weight of secretion, the corrected dry weight (dry weight-weight of instilled salt), and protein concentration. No difference in heart rate, respiratory frequency, O2 saturation, systemic blood pressure, peak inspiratory pressure, or patient discomfort was found when the two modalities were compared; however, the total volume of secretions collected, the dry weight, the corrected dry weight, and the protein concentration were significantly higher with continuous irrigation suction catheter when compared with the conventional method (p0.05). The suction time was shorter with the Irri-cath (p0.05). We conclude that the Irri-Cath is more effective than conventional intermittent suction catheter in clearing bronchial secretions in patients on mechanical ventilation.

Pneumopericardium in newborns is most often a complication of mechanical ventilation and frequently results in fatal cardiac tamponade. We report the case of a mechanically ventilated 33-day-old full-term gestation infant with interstitial pneumonitis who developed tension pneumopericardium. Treatment includes lowering peak inspiratory pressure and decompressing the pericardial space with tube drainage following pericardiocentesis.

The incidence of mediastinal emphysema (ME) and pneumothorax (PTX) was analyzed to determine the roentgenographic patterns and risk factors for the development of barotrauma in a population of mechanically ventilated patients. The roentgenograms of 139 intubated patients admitted to our medical intensive care unit over a ten-month period were evaluated for the presence of ME and PTX. Barotrauma was diagnosed in 34 of these patients, and ME was the initial manifestation in 24 patients. Of these patients with initial ME, ten subsequently developed PTX, a positive predictive value of 42 percent. The adult respiratory distress syndrome (ARDS) patient population was at highest risk for barotrauma, with an intermediate risk seen in those admitted with COPD or pneumonia. Values of peak inspiratory pressure, positive end-expiratory pressure level, respiratory rate, tidal volume, and minute ventilation were significantly elevated in patients who developed barotrauma as compared with patients who did not develop barotrauma. However, these elevations in part reflect the high incidence of barotrauma in the ARDS population, a patient group in which all of the above parameters were elevated.

Uncuffed tracheostomy tubes are used for long-term mechanical ventilation in children. However, upper airway mechanics differ between sleep and wakefulness; this may affect air leak around tracheostomies. We studied 19 children with high cervical spinal cord injury on portable positive pressure ventilators, age range birth to 19 years. Ventilator settings were adjusted while awake to achieve PaCO2 less than 45 mm Hg and PO2 greater than 90 mm Hg. Clinically several children with uncuffed tracheostomies became unstable at night with seizures and sleep disruption. Nine of 11 children on volume controlled systems were found to be inadequately ventilated during sleep. Substitution with a cuffed tracheostomy allowed adequate ventilation both awake and asleep, suggesting that inadequate ventilation during sleep was due to an uncompensated leak around the uncuffed tracheostomy. To avoid cuffed tracheostomies, eight children received pressure controlled ventilation. Gas exchange was adequate throughout the day and night. We conclude that children receiving volume controlled mechanical ventilation via uncuffed tracheostomy tubes can exhibit hypoventilation due to uncompensated air leak. Pressure controlled ventilation improves adequacy of gas exchange during sleep and wakefulness.

Study Objective : To determine the epidemiology of multiple organ failure (MOF) in patients with the adult respiratory distress syndrome. Patients : We followed up 50 patients with serial determinations of respiratory and nonrespiratory organ function for seven days after diagnosis. Design : Data were stratified between patients who died and those who survived (defined as hospital discharge). Measurements and Results : Values that did not differ at any time between the two groups of patients included oxygen availability, oxygen consumption, oxygen extraction, PaCO 2 , respiratory rate, heart rate, systolic blood pressure, cardiac output, stroke index, systemic vascular resistance, and temperature. Patients who died had greater defects in oxygenation (from day 1 through day 7). They also exhibited decreased arterial oxygen content (from day 1 to day 4), decreased mixed venous oxygen content (day 1), increased peak inspiratory pressure (present on day 2, persisted to day 5, reappeared on day 7), decreased diastolic blood pressure (seen on days 1 through 3, reappeared on day 7), and increased mean pulmonary artery pressure (seen on days 2 and 3). Nonsurvivors also exhibited greater degrees of thrombocytopenia (from day 1 to day 4). Decreases in pH (seen on day 1, reappeared from days 4 to 7), abnormalities in liver function (seen only on day 1), and increases in serum creatinine levels (appeared on day 7) were also observed. Conclusions : Multiorgan dysfunction (MOD) was frequently observed in both groups of patients. Alterations in organ function and the pattern of abnormalities were often subtle and would not be characterized as significant organ dysfunction by most available organ scoring systems. Adult respiratory distress syndrome is a manifestation of systemic disease produced by widespread increases in endothelial permeability; lung dysfunction dominates the early clinical course. When respiratory function is supported, it becomes evident that alterations occur in other organs. Multiorgan failure is really a misnomer; the term emphasizes end-stage changes. Multiorgan dysfunction is common and often resolves without progressing to MOF. Alternatively, MOD can progress to MOF. (Chest 1992; 101:320-26)

Background Flexible bronchoscopy performed through endotracheal tubes (ETTs) in children receiving mechanical ventilation can significantly impact ventilation, but the magnitude of this impact has not been established. We used a lung model to simulate mechanical ventilation in a range of child sizes in order to determine how the insertion of pediatric flexible bronchoscopes into ETTs alters ventilatory parameters, especially tidal volume (V t ) and peak inspiratory pressure (PIP), in both healthy and diseased lungs. Methods We simulated five child sizes based on weight, and evaluated 22 bronchoscope/ETT combinations, first in pressure control (PC) ventilation mode and then in volume control (VC) ventilation mode. The combinations ranged from the 2.2-mm (bronchoscope outer diameter)/3.0-mm (ETT inner diameter) to 5.0-mm bronchoscope/8.0-mm ETT. The primary outcome measures were decrease in V t after bronchoscope insertion during PC ventilation and increase in PIP during VC ventilation. Results In the PC ventilator mode, V t decreased by > 50% with nine of the combinations, while during VC ventilation, PIP increased by ≥ 20 cm H 2 O with seven combinations. The 2.2-mm bronchoscope/3.0-mm ETT, 2.8-mm bronchoscope/5.0-mm ETT, and 3.6-mm bronchoscope/5.0-mm ETT combinations severely impaired ventilation, while the 3.6-mm bronchoscope/4.5-mm ETT, 5.0-mm bronchoscope/6.5-mm ETT, and 5.0-mm bronchoscope/7.0-mm ETT combinations were incompatible with adequate ventilation. Conclusions The insertion of bronchoscopes into ETTs can lead to clinically relevant decreases in V t when in the PC ventilator mode and large increases in PIP during VC ventilation. The minimum bronchoscope/ETT diameter difference required to maintain adequate ventilation increases with child size.

Background: Respiratory muscle weakness may contribute to dyspnea and exercise limitation in patients with significant COPD. In an attempt to reduce the severity of breathlessness and to improve exercise tolerance, inspiratory muscle training has been applied in many COPD patients. On the other hand, there is a paucity of data related to expiratory muscle performance and training in COPD. Methods: Thirty-two patients with significant COPD (ie, mean FEV1, 37% of predicted) were recruited for the study. The patients were randomized into four groups: eight patients were assigned to receive specific expiratory muscle training (SEMT); eight patients received specific inspiratory muscle training (SIMT); eight patients received SEMT and SIMT (ie, the SEMT SIMT group); and eight patients who were assigned to a control group received training with very low load. All patients trained daily, six times a week, with each session consisting of one half hour of training, for 3 months. Spirometry, respiratory muscle strength and endurance, 6-min walk test distance, the perception of dyspnea, and the Mahler baseline dyspnea index (BDI) were measured before and following training. Results: Training caused a statistically significant specific increase in the expiratory muscle strength and endurance (in the SEMT and SEMT SIMT groups) and in the inspiratory muscle strength and endurance (in the SIMT and SEMT SIMT groups). There was significant increase in the distance walked in 6 min in the SEMT, SIMT, and SEMT SIMT groups. However, the increase in the SIMT and SEMT SIMT groups was significantly greater than that in the SEMT group. There was a statistically significant increase in the BDI, and a decrease in the mean Borg score during breathing against resistance in the SIMT and SEMT SIMT groups, with no changes in the SEMT and control groups. Conclusions: The inspiratory and expiratory muscles can be specifically trained with improvement of both muscle strength and endurance. The improvement in the inspiratory muscle performance is associated with an increase in the 6-min walk test distance and the sensation of dyspnea. There is no additional benefit gained by combining SIMT with SEMT, compared to using SIMT alone. (CHEST 2003; 124:1357–1364)

There are several reports showing that expiratory muscle strength and endurance can be impaired in patients with COPD. This muscle weakness may have clinically relevant implications. Expiratory muscle training tended to improve cough and to reduce the sensation of respiratory effort during exercise in patients other than those with COPD.Twenty-six patients with COPD (FEV(1) 38% predicted) were recruited for the study. The patients were randomized into two groups: group 1, 13 patients were assigned to receive specific expiratory muscle training (SEMT) daily, six times a week, each session consisting of 1/2 h of training, for 3 months; and group 2, 13 patients were assigned to be a control group and received training with very low load. Spirometry, respiratory muscle strength and endurance, 6-min walk test, Mahler baseline dyspnea index (before), and the transitional dyspnea index (after) were measured before and after training.The training-induced changes were significantly greater in the SEMT group than in the control group for the following variables: expiratory muscle strength (from 86 +/- 4.1 to 104 +/- 4.9 cm H(2)O, p0.005; mean difference from the control group, 24%; 95% confidence interval, 18 to 32%), expiratory muscle endurance (from 57 +/- 2.9% to 76 +/- 4.0%, p0.001; mean difference from the control group, 29%; 95% confidence interval, 21 to 39%), and in the distance walked in 6 min (from 262 +/- 38 to 312 +/- 47 m, p0.05; mean difference from the control group, 14%; 95% confidence interval, 9 to 20%). There was also a small but not significant increase (from 5.1 +/- 0.9 to 5.6 +/- 0.7, p = 0.14) in the dyspnea index.The expiratory muscles can be specifically trained with improvement of both strength and endurance in patients with COPD. This improvement is associated with increase in exercise performance and no significant change in the sensation of dyspnea in daily activities.

Study objective In children with acute lung injury, there is an increase in minute ventilation ( V ˙ e ) and inefficient gas exchange due to a high level of physiologic dead space ventilation (V d /V t) . Mechanical ventilation with positive end-expiratory pressure, when used in critically ill patients to correct hypoxemia, may contribute to increased V d /V t . The purpose of this study was to measure metabolic parameters and V d /V t in critically ill children. Design A cross-sectional study. Setting Pediatric ICU of a university hospital. Patients A total of 45 mechanically intubated children (mean age, 5.5 years). Interventions Indirect calorimetry was used to measure metabolic parameters. V d /V t parameters were calculated using the modified Bohr-Enghoff equation. ARDS was defined based on criteria by The American-European Consensus Conference. Measurements and results The group mean (± SD) ventilatory equivalent for oxygen (VeqO 2 ) and ventilatory equivalent for carbon dioxide (VeqCO 2 ) were 2.9 ± 1 and 3.3 ± 1 L per 100 mL, respectively. The group mean V d /V t was 0.48 ± 0.2. When compared to non-ARDS patients (33 patients), the patients with ARDS (12 patients) had a significantly higher VeqO 2 (3.3 ± 1 vs 2.8 ± 1 L per 100 mL, respectively; p 2 (3.7 ± 1 L/100 vs 3.1 ± 1 L per 100 mL, respectively; p d /V t (0.62 ± 0.14 vs 0.43 ± 0.15, respectively; p Conclusions Critically ill children with ARDS have increased V d /V t . Increased V d /V t was the main cause of the excess of V ˙ e demand in these patients. Increased metabolic demands, as shown by the VeqO 2 , VeqCO 2 , and ventilatory support, are the major determinants of V ˙ e requirements in children with ARDS.

Background: Positive-pressure ventilators are equipped with low-inspiratory-pressure alarms to protect patients from hypoventilation. Small uncuffed tracheostomy tubes have a high resistance, and may not trigger these alarms during decannulation. Study objective: To determine whether ventilator low-inspiratory-pressure alarms are effective in detecting tracheostomy decannulation. Design: We connected tracheostomy tubes of varying inner diameters (3.0 to 6.0 mm) to a home ventilator and simulated decannulation using low (tidal volume [VT], 600 mL; peak inspiratory pressure [PIP], 25 cm H2O), medium (VT, 800 mL; PIP, 30 cm H2O), and high (VT, 1,000 mL; PIP, 35 cm H2O) ventilator settings. Results: When the ventilator low-inspiratory-pressure alarm was set at 4 cm H2O below the desired PIP, it failed to alarm for simulated decannulation of tracheostomy tubes < 4.5 mm on low and medium settings, and < 4.0 mm on high settings. When the ventilator low-inspiratorypressure alarm was set at 10 cm H2O below the desired PIP, it failed to alarm with tracheostomy tubes < 6.0 mm. Conclusion: We conclude that ventilator low-inspiratory-pressure alarms fail to alarm during simulated decannulation with small tracheostomy tubes commonly used in children. We speculate that low-inspiratory-pressure alarms set at 4 cm H2O below the desired PIP will detect more decannulation than when set at 10 cm H2O below the desired PIP. (CHEST 2001; 119:562‐564)

Study objectives To evaluate the effects of fiberopticbronchoscopy (FOB) on delivered volumes and pressures during mechanicalventilation, utilizing a lung model. Design Benchstudy. Setting Laboratory. Materials and methods Using varying-sized endotracheal tubes (ETTs), weventilated a lung model at two levels of compliance utilizing differentmodes and parameters of ventilation. After establishing baselinemeasurements, the bronchoscope was inserted and measurementsrepeated. Measurements and results During controlledmechanical ventilation (CMV) with a preset high-pressure limit (HPL),tidal volumes (V t s) were reduced from 700 m, L to 0 to 500 m, Lfollowing insertion of the bronchoscope. Increasing the HPL to 120 cm, H 2 O resulted in a V t of 40 to 680 m, L. Changingfrom square to decelerating flow waveform resulted in no consistentdifference in V t . Auto-positive end-expiratory pressure(auto-PEEP) of 0 to 41 cm H 2 O was present under mostconditions. Higher rates and lower peak inspiratory flows wereassociated with higher levels of auto-PEEP. In the pressure-control(PC) mode, using a preset inspiratory pressure level (IP),V t was reduced from 700 m, L to 40 to 280 m, L followinginsertion of the bronchoscope. Maximum IP (100 cm H 2 O)increased V t to 260 to 700 m, L. Auto-PEEP was less in the PCmode. Conclusions Extreme care must be taken whenbronchoscopy is performed on a patient receiving mechanicalventilation. Extremely low V t and significant auto-PEEP maydevelop unless flow, respiratory rate, mode, and ETT size are carefullyselected. The PC mode delivered more volume than did the CMV mode. Whenperforming FOB during mechanical ventilation, the inside diameter ofthe ETT should be ≥ 2.0-mm larger than the outside diameter of thebronchoscope to maintain volume delivery and minimize the developmentof auto-PEEP.

Monitoring data in critical care and anesthesiology should be displayed to present a rapid and easily comprehensible definition of the patient's clinical status. A graphic computer display of the analog output of gas flow rates and the O 2 and CO 2 concentrations of respiratory gases profiles the expired breath for an estimation of pulmonary function and gas exchange. An estimate of pulmonary perfusion, cardiac output, and the general adequacy of cardiovascular circulation is obtained from the computer calculation of O 2 uptake and CO 2 elimination, dead space, and alveolar ventilation. Adjunctive data from the spirometric measurements of airway pressures, volumes, and compliance, supplemented by hemodynamic monitoring, aids in the diagnosis of physiologic changes. For > 10 years, we have used this system to monitor patients who are anesthetized, sedated, and receiving mechanical ventilation during anesthesia and surgery, and recently have extended the technique to intensive care areas. Our experience has shown good correlation of changes in the computer-assisted expired breath analysis with coinciding clinical events, including upper airway obstruction, bronchospasm, and alveolar volume/pulmonary capillary blood flow impairment. To demonstrate the use of this system, we describe the ventilator management for a patient with severe ARDS. In this patient, changes in ventilator management, including pressure control ventilation, improved pulmonary O 2 uptake (mean, 18.7 vs 8.5 mL/breath), CO 2 elimination (mean, 17 vs 13 mL/breath), and compliance (mean, 29.7 vs 19.0 mL/cm H 2 O), were compared with intermittent mandatory ventilation.

Study objectives Investigating the effect of low-volume pressure-limited ventilation and repeated prone positioning on the short-term course and outcome in patients with severe ARDS. Setting Level 1 trauma center of a university hospital. Patients Twenty-five patients suffering from ARDS with a lung injury score (LIS) ≥2.5 admitted consecutively to our ICU from January 1992 to December 1994. Methods Mechanical ventilation with peak inspiratory pressure limitation to 35 mbar, irrespective of hypercapnia and prone positioning to achieve adequate oxygenation. Scoring and measurements Patient assessment with LIS, APACHE (acute physiology and chronic health evaluation) II score, injury severity score, and multiple organ failure score. Blood gas analyses and estimation of static compliance were repeated at least every 4 h during the treatment period. PaO 2 /FIo 2 (fraction of inspired oxygen) ratio, alveolo-arterial oxygen difference, and intrapulmonary shunt were calculated according to standard equations. The best values taken from each 4-h period during the investigation were used to evaluate the best possible performance of the lung within this interval and to investigate the entire course. Results Mean predicted mortality based on the APACHE II score was 35.4±15.2%. Three of the 25 patients (12%) died. However, none was related to respiratory failure. No pneumothorax occurred. Sixteen patients, lacking any contraindication for prone positioning, responded positively to this change in position, each to a different individual degree. Conclusion We assume that our low mortality in patients with severe ARDS might be due mainly to low-volume pressure-limited ventilation and prone positioning. This simple strategy seems to allow successful treatment for patients with severe ARDS.

Study objective To characterize the physiologic response to, and safety of, intravenacaval membrane oxygenation and carbon dioxide removal. Design Interventional before-after study. Setting University teaching hospital ICU. Patients Twenty-two patients with severe acute respiratory distress syndrome (ARDS). Interventions Implantation of a hollow-fiber membrane oxygenator (IVOX; CardioPulmonics; Salt Lake City, Utah) into the superior and inferior venae cavae by venotomy of the right femoral or right internal jugular vein for a duration of up to 20 days. Measurements Hemodynamic measurements using pulmonary artery and systemic artery catheters, ventilator settings (FIo 2 , minute ventilation, peak inspiratory pressure, and positive end-expiratory pressure), arterial and mixed venous blood gases (pH, Pco 2 , Po 2 , and measured saturation), and clinical laboratory determinations (CBC, fibrinogen, plasma hemoglobin, complement C3 and C5) were obtained. Calculations of PaO 2 /FIo 2 ratio and PaCo 2 -V E product were used to assess gas exchange efficacy. Microbiologic cultures were obtained from the device and wound following explantation. Survival to ICU discharge and hospital discharge were recorded. Results Implantation was successful in 20 of 22 patients. Gas exchange rates averaged 50.4 ± 15.8 mL-min −1 for carbon dioxide and 71.1 ± 20.2 mL-min −1 for oxygen. A reduction in FIo 2 from 0.78 ± 0.16 to 0.63 ± 0.21 and in V E from 177 ± 94 mL·kg −1 ·min −1 to 127 ± 58 mL·kg −1 ·min −1 was possible within 4 h postimplantation. By 12 h, FIo 2 was reduced to 0.57 ± 0.18. Indices of gas exchange improved significantly after implantation, with PaO 2 /FIo 2 ratio increasing from 79 ± 20 to 112 ± 47 and PaCO 2 -V E product decreasing from 7.6 ± 4.2 to 4.9 ± 2.5 within 4 h. A significant reduction in peak inspiratory pressure was achieved (45 ± 10 to 38 ± 9 cm H 2 O). Major complications were blood loss during implantation requiring transfusion in 11 patients, a retroperitoneal bleed in 1 patient, and femoral deep venous thrombosis in 4 patients, but there were no long-term sequelae or IVOX-related deaths. The ICU and hospital survival were 10/20 (50%) and 8/20 (40%), respectively. Conclusions Intravenacaval membrane oxygen and carbon dioxide removal can provide partial respiratory support during severe respiratory failure and permit reductions in the level of mechanical ventilator support, with an acceptable safety profile.

Subject objective To assess the hemodynamic effects of manual lung hyperinflation in mechanically ventilated patients and to measure the different inspiratory pressures and tidal volumes generated by different operators. Design Measurements of aortic blood flow (by esophageal Doppler ultrasonography), systemic blood pressure, tidal volumes (by respirometry), and inspiratory pressures in the ventilator circuit were measured on the ventilator, during six intended manual hyperinflations (tidal volume > 150% that delivered by ventilator) using a 2-L rebreathing bag, and at 1,5,10, and 15 min after reconnection to the ventilator. Setting Intensive care unit. Patients Eighteen mechanically ventilated patients with normovolemia and stable circulatory status were assessed on a total of 20 occasions. Interventions Patients were disconnected from the ventilator to enable six manual hyperinflations to be given. Measurements were made before and at 5-min intervals until no further hemodynamic changes were seen. Measurements and results: Hyperinflation (50% increase in tidal volume) was achieved only in 10 of 20 studies. Large variations were seen in percentage change in peak inspiratory pressure (—30% to +250%) and tidal volume (—33% to +127%) generated. Falls in cardiac output correlated to the increase in tidal volume but not to the increase in peak inspiratory pressure and took up to 15 min to recover to baseline values. Changes in cardiac output were independent of lung compliance and concurrent vasoactive drug support. No consistent change was noted in either blood pressure or heart rate. Conclusions Lung hyperinflation is frequently not achieved by the manual technique. Significant changes in cardiac output can occur and appear to be related to the tidal volume rather than pressure generated.

Whether nebulized ipratropium bromide is of benefit to mechanically ventilated patients with chronic bronchitis is not well defined. The objective of the study was to determine the effect of ipratropium bromide as a nebulized solution on ventilatory function in patients with severe airflow limitation and under ventilator treatment because of respiratory failure. The design was a randomized, double-blind, controlled trial. Forty-two ventilated patients (43 to 83 years old) with acute airflow obstruction and wheezing or coughing were chosen. The patients were randomly allocated to treatment every 6 h with either 500 micrograms of nebulized ipratropium bromide or 0.9 percent saline solution. Comparison was made between ipratropium bromide and placebo. Their responses were assessed in terms of arterial blood gas analysis, pulmonary mechanics, and respiratory symptoms. No significant differences in oxygenation, arterial CO2 tension, or static lung compliance attributable to ipratropium were found. However, a significant tendency to decreased mean airway resistance, peak inspiratory pressure, mean airway pressure, and improved symptom status 24 h after giving ipratropium was observed. We conclude that ventilated patients with obstructive lung disease could obtain incremental benefit from adding nebulized ipratropium to aminophylline. Their responses may be explained by the bronchodilating effect of ipratropium that resulted in a reduced airway resistance and a lower mean airway pressure.

The common chemical warfare protective masks impose an excessive respiratory load on the wearer due to elevated breathing resistance and increased dead space. For patients with severe respiratory disease, the excessive respiratory effort may be intolerable. Besides, the substantial negative pressure created within the mask during inspiration may result in an inward leakage in individuals having difficulties with proper facial fitting of the mask. The purpose of the current investigation was to evaluate the effects of a blower, actively driving air, through the mask's filter, at a flow (mean +/- SD) of 42 +/- 2 L/min, on respiratory parameters during rest and moderate exercise. Ten healthy subjects of either sex participated in two experimental sessions, wearing the mask with and without the blower. Each session included 6 min of sitting at rest and 6 min of walking on a treadmill (3.2 mph, and 10 percent grade). In nine of the subjects, the active air supply produced a positive inspiratory pressure at rest (5 +/- 4 vs -24 +/- 9 mm H2O peak inspiratory pressure with and without the blower, respectively, p0.0001). Inspiratory carbon dioxide concentration (FICO2) at rest was diminished (0.4 +/- 0.4 vs 1.3 +/- 0.7 percent with and without the blower, respectively; p0.01) while FIO2 increased from 19.5 +/- 0.7 percent to 20.6 +/- 0.4 percent with the device (p0.01). These changes were associated with a significant decrease in respiratory rate (15 +/- 2 vs 18 +/- 3 per minute, p0.01). During exercise the blower barely decreased the negative inspiratory pressures, had no effect on other respiratory parameters measured, but significantly shortened the inspiratory/cycle-length time ratio (0.46 +/- 0.03 vs 0.53 +/- 0.03, p0.005). The effects of active air supply were not different between male and female subjects. We conclude that the blower is expected to be a useful accessory to respiratory protective devices for patients with pulmonary disease.

We evaluated the airway occlusion maneuver as a method to estimate respiratory resistance, respiratory elastance and the pressure generated by respiratory muscles in ICU patients breathing in the PSV mode. The airflow was interrupted at selected flows or volumes during inspiration by a computer-driven rapid occlusion pneumatic valve. The airway occlusion was maintained for 2 to 3 s. From the airway pressure tracing we obtained various measurements of pressure. We then computed the pressure generated by the patient's inspiratory muscles. The method was validated by two different approaches in two groups of patients: the Pes and the CMV protocols. We conclude that the airflow interruption method can be used to measure basic respiratory mechanical parameters in PSV patients. The method also offers an opportunity to evaluate Pmusc, aw and the respiratory work performed by the patient.

Cardiorespiratory values were measured in ten patients with severe respiratory failure on volume controlled and pressure controlled ventilation. Tidal volume, respiratory rate, PEEP, auto-PEEP, inspiratory:expiratory ratio (1:2) and FIo 2 were maintained at the same value for both ventilatory modalities. Changing from VCV to PCV was associated with significant improvements in PaO 2 , oxygen delivery, and tissue oxygen consumption. Peak inspiratory pressure fell. There were no significant changes in other cardiorespiratory values, such as arterial blood pressure, nor in ventilatory measurements, such as mean airway pressure, associated with the use of PCV. These results suggest that PCV may be a beneficial ventilatory modality in the treatment of severe respiratory failure since it results in improvement in arterial oxygenation, tissue oxygen delivery and utilization without any concomitant adverse effects on other hemodynamic or ventilatory factors.

High peak inspiratory pressure (PIP) during mechanical ventilation is associated with increased risk of barotrauma. High frequency jet ventilation (HFJV) and pressure control ventilation (PCV) have been advocated for the reduction of PIP. The Food and Drug Administration has approved HFJV, respiratory frequency as high as 150 breaths per minute (bpm); however, bpm greater than 150 are still considered for experimental use. At less than 40 bpm, the point where HFJV is no longer considered to be high frequency, PCV is substituted which then becomes the mode of choice because of the ability to control ventilating pressures by setting the PIP. We present a case in which we used these two forms of ventilation for reducing the risk of stump blowout and barotrauma following pneumonectomy.

To determine the frequency of pulmonary function abnormalities in mixed connective tissue disease (MCTD), we studied 16 consecutive patients. Spirometry, total lung capacity (TLC), diffusing capacity (Dco), static lung compliance (Cst), and tests of respiratory muscle function (peak inspiratory pressure [PIP] and the maximum change in transdiaphragmatic pressure [delta PDI] during a diaphragmatic Müeller maneuver) were obtained. Airway resistance (RAW) and frequency dependence of compliance were also measured. Static lung compliance was less than 0.2 L/cm H2O in four of nine patients. The PIP was less than 75 cm H2O in only one patient and delta PDI was greater than 45 cm H2O in all ten patients evaluated. Frequency dependence of compliance was abnormal in seven of ten patients, whereas RAW was increased in only three of eight patients. The TLC and DCO were less than 80 percent of the predicted values in ten of 16 and 14 of 16 patients respectively. There was no correlation between the level of extractable nuclear antigen and pulmonary function abnormalities. The study did not identify significant abnormalities in respiratory muscle function.

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.

Thirty-one patients with severe respiratory failure who were failing volume controlled conventional ratio ventilation were placed on pressure controlled inverse ratio ventilation (PC-IRV) for a total of 4,426 patient-hours. The PC-IRV resulted in a reduction of minute ventilation from 22 ± 1.0 L/min (mean ± SEM) to 15 ± 0.7 L/min. Peak inspiratory pressure (PEP) was reduced from 66 ± 2.3 cm H2O to 46 ± 1.6 cm H2O and positive end expiratory pressures (PEEP) from 15 ± 1.0 cm H2O to 2.5 ± 0.5 cm H2O. Mean airway pressure increased from 30 ± 1.7 cm H2O to 35 ± 1.7 cm H2O. Oxygenation (PaO2) improved from 69 ± 4.0 mm Hg to 80 ± 4.5 mm Hg. The FaCO2 and arterial pH were not significantly changed. There were no significant changes in mean hemodynamic pressures. A lung compromise index (FIO2·PIP·10/PaO2) retrospectively distinguished between successful and unsuccessful PC-IRV episodes. These data suggest that PC-IRV can be successfully and safely implemented in critically ill patients with severe respiratory failure over prolonged periods of time resulting in significant improvement in oxygenation at lower minute volume, peak airway pressure and PEEP requirements. (Chest 1988; 94:755-62)

Patients with chronic airflow obstruction (CAO) often develop impairment of respiratory muscle function. We hypothesized that inspiratory muscle strength, as assessed by resting, peak inspiratory pressure (PIP) may be an important determinant of maximum exercise capacity in patients with CAO. Twenty ambulatory male patients (mean age, 56 ± 3 years [± SE]) with CAO (FEV 1 , 1.72 ± 0.21 L) comprised the studied population. Oxygen consumption at incremental cycle ergometry to tolerance ( V ˙ o 2 max , 1.80 ± 0.20 L/min) served as the dependent variable for regression vs measures of resting pulmonary function. Significant correlations with V ˙ o 2 max included power output in watts (r=0.951), V ˙ E max (r = 0.858), Dsb (r = 0.841), PIP (r = 0.816), age (r = – 0.809), FEV 1 (r = 0.763), and FVC (r = 0.663). The FEV 1 , Dsb, and PIP each entered into a multiple linear regression relationship describing V ˙ o 2 max . Also, when paired with V ˙ E max as independent variables in multiple regression, PIP and Dsb each improved description of V ˙ o 2 max over V ˙ E max alone (p 1 and FVC did not (p>0.05). We conclude that factors other than ventilatory capacity also have a quantitative effect on V ˙ o 2 max and that PIP constitutes a determinant of maximum exercise capacity in patients with CAO. (Chest 1989; 96:267–71)

Nineteen patients with ARDS or pneumonia who were ventilated with PcIRV on the Siemens-Elema Servo 900 C were retrospectively reviewed. The PcIRV reduced peak airway pressure, PEEP, increased Paw, and improved ventilation and oxygenation in these patients. When these patients were compared with themselves on prior conventional IPPV, all had a decrease in PIP, an increase in Paw and most had a decrease in VE, with no change in PaCO2 and an increase in PaO2. The increase in Paw may have contributed to this improved arterial oxygenation. High levels of PIP and PEEP during IPPV have been identified as risk factors in the development of barotrauma and residual parenchymal pulmonary damage. We propose that PcIRV allows for adequate ventilation and oxygenation with decreases in PIP, extrinsically added PEEP and inspired O2 concentration. This mode of ventilation may decrease the morbidity associated with IPPV utilizing high PIP and PEEP.