Prone positioning in patients with moderate and severe acute respiratory distress syndrome: a randomized controlled trial.

CONTEXT: Post hoc analysis of a previous trial has suggested that prone positioning may improve survival in patients with severe hypoxemia and with acute respiratory distress syndrome (ARDS). OBJECTIVE: To assess possible outcome benefits of prone positioning in patients with moderate and severe hypoxemia who are affected by ARDS. DESIGN, SETTING, AND PATIENTS: The Prone-Supine II Study, a multicenter, unblinded, randomized controlled trial conducted in 23 centers in Italy and 2 in Spain. Patients were 342 adults with ARDS receiving mechanical ventilation, enrolled from February 2004 through June 2008 and prospectively stratified into subgroups with moderate (n = 192) and severe (n = 150) hypoxemia. INTERVENTIONS: Patients were randomized to undergo supine (n = 174) or prone (20 hours per day; n = 168) positioning during ventilation. MAIN OUTCOME MEASURES: The primary outcome was 28-day all-cause mortality. Secondary outcomes were 6-month mortality and mortality at intensive care unit discharge, organ dysfunctions, and the complication rate related to prone positioning. RESULTS: Prone and supine patients from the entire study population had similar 28-day (31.0% vs 32.8%; relative risk [RR], 0.97; 95% confidence interval [CI], 0.84-1.13; P = .72) and 6-month (47.0% vs 52.3%; RR, 0.90; 95% CI, 0.73-1.11; P = .33) mortality rates, despite significantly higher complication rates in the prone group. Outcomes were also similar for patients with moderate hypoxemia in the prone and supine groups at 28 days (25.5% vs 22.5%; RR, 1.04; 95% CI, 0.89-1.22; P = .62) and at 6 months (42.6% vs 43.9%; RR, 0.98; 95% CI, 0.76-1.25; P = .85). The 28-day mortality of patients with severe hypoxemia was 37.8% in the prone and 46.1% in the supine group (RR, 0.87; 95% CI, 0.66-1.14; P = .31), while their 6-month mortality was 52.7% and 63.2%, respectively (RR, 0.78; 95% CI, 0.53-1.14; P = .19). CONCLUSION: Data from this study indicate that prone positioning does not provide significant survival benefit in patients with ARDS or in subgroups of patients with moderate and severe hypoxemia. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00159939.

Effects of the beach chair position, positive end-expiratory pressure, and pneumoperitoneum on respiratory function in morbidly obese patients during anesthesia and paralysis.

BACKGROUND: The authors studied the effects of the beach chair (BC) position, 10 cm H2O positive end-expiratory pressure (PEEP), and pneumoperitoneum on respiratory function in morbidly obese patients undergoing laparoscopic gastric banding. METHODS: The authors studied 20 patients (body mass index 42 +/- 5 kg/m2) during the supine and BC positions, before and after pneumoperitoneum was instituted (13.6 +/- 1.2 mmHg). PEEP was applied during each combination of position and pneumoperitoneum. The authors measured elastance (E,rs) of the respiratory system, end-expiratory lung volume (helium technique), and arterial oxygen tension. Pressure-volume curves were also taken (occlusion technique). Patients were paralyzed during total intravenous anesthesia. Tidal volume (10.5 +/- 1 ml/kg ideal body weight) and respiratory rate (11 +/- 1 breaths/min) were kept constant throughout. RESULTS: In the supine position, respiratory function was abnormal: E,rs was 21.71 +/- 5.26 cm H2O/l, and end-expiratory lung volume was 0.46 +/- 0.1 l. Both the BC position and PEEP improved E,rs (P < 0.01). End-expiratory lung volume almost doubled (0.83 +/- 0.3 and 0.85 +/- 0.3 l, BC and PEEP, respectively; P < 0.01 vs. supine zero end-expiratory pressure), with no evidence of lung recruitment (0.04 +/- 0.1 l in the supine and 0.07 +/- 0.2 in the BC position). PEEP was associated with higher airway pressures than the BC position (22.1 +/- 2.01 vs. 13.8 +/- 1.8 cm H2O; P < 0.01). Pneumoperitoneum further worsened E,rs (31.59 +/- 6.73; P < 0.01) and end-expiratory lung volume (0.35 +/- 0.1 l; P < 0.01). Changes of lung volume correlated with changes of oxygenation (linear regression, R2 = 0.524, P < 0.001) so that during pneumoperitoneum, only the combination of the BC position and PEEP improved oxygenation. CONCLUSIONS: The BC position and PEEP counteracted the major derangements of respiratory function produced by anesthesia and paralysis. During pneumoperitoneum, only the combination of the two maneuvers improved oxygenation.

Physiologic rationale for ventilator setting in acute lung injury/acute respiratory distress syndrome patients.

OBJECTIVES: To review the physiologic approach to setting mechanical ventilation in acute lung injury/acute respiratory distress syndrome. DATA SOURCES: MEDLINE search from 1979 to the present. DATA SELECTION: Personal selection of some articles we believe relevant for understanding acute lung injury/acute respiratory distress syndrome physiopathology and its physiologic management. DATA SUMMARY: Knowing the underlying pathology is key to estimating the potential for recruitment. The potential for recruitment is rather low when the consolidation of pulmonary units exceeds collapse, as in diffuse pneumonia. In contrast, when pulmonary unit collapse exceeds consolidation, as in acute lung injury/acute respiratory distress syndrome from extrapulmonary origin, the potential for recruitment may be high. To exploit the potential for recruitment, a transpulmonary pressure greater than the opening pressure must be applied to the lung. To do so, chest wall elastance must be measured or estimated. To avoid collapse after recruitment, a positive end-expiratory pressure greater than the compressive forces operating on the lung and an alveolar ventilation sufficient to prevent absorption atelectasis must be provided. Indeed, avoidance of stretch (low airway plateau pressure) and prevention of cyclic collapse and reopening (adequate positive end-expiratory pressure and alveolar ventilation) are the physiologic cornerstones of mechanical ventilation in acute lung injury/acute respiratory distress syndrome. When considering all the randomized clinical trials reported so far, it is tempting to speculate that transpulmonary pressure and stresses, rather than tidal volume per se, are the key factors that may have an impact on mortality. CONCLUSIONS: The majority of physiologic, experimental, and clinical trial data converge on one simple concept: treat the lung gently.

Decrease in PaCO2 with prone position is predictive of improved outcome in acute respiratory distress syndrome.

OBJECTIVE: To determine whether gas exchange improvement in response to the prone position is associated with an improved outcome in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). DESIGN: Retrospective analysis of patients in the pronation arm of a controlled randomized trial on prone positioning and patients enrolled in a previous pilot study of the prone position. SETTING: Twenty-eight Italian and two Swiss intensive care units. PATIENTS: We studied 225 patients meeting the criteria for ALI or ARDS. INTERVENTIONS: Patients were in prone position for 10 days for 6 hrs/day if they met ALI/ARDS criteria when assessed each morning. Respiratory variables were recorded before and after 6 hrs of pronation with unchanged ventilatory settings. MEASUREMENTS AND MAIN RESULTS: We measured arterial blood gas alterations to the first pronation and the 28-day mortality rate. The independent risk factors for death in the general population were the Pao2/Fio2 ratio (odds ratio, 0.992; confidence interval, 0.986-0.998), the minute ventilation/Paco2 ratio (odds ratio, 1.003; confidence interval, 1.000-1.006), and the concentration of plasma creatinine (odds ratio, 1.385; confidence interval, 1.116-1.720). Pao2 responders (defined as the patients who increased their Pao2/Fio2 by > or =20 mm Hg, 150 patients, mean increase of 100.6 +/- 61.6 mm Hg [13.4 +/- 8.2 kPa]) had an outcome similar to the nonresponders (59 patients, mean decrease -6.3 +/- 23.7 mm Hg [-0.8 +/- 3.2 kPa]; mortality rate 44% and 46%, respectively; relative risk, 1.04; confidence interval, 0.74-1.45, p =.65). The Paco2 responders (defined as patients whose Paco2 decreased by > or =1 mm Hg, 94 patients, mean decrease -6.0 +/- 6 mm Hg [-0.8 +/- 0.8 kPa]) had an improved survival when compared with nonresponders (115 patients, mean increase 6 +/- 6 mm Hg [0.8 +/- 0.8 kPa]; mortality rate 35.1% and 52.2%, respectively; relative risk, 1.48; confidence interval, 1.07-2.05, p =.01). CONCLUSION: ALI/ARDS patients who respond to prone positioning with reduction of their Paco2 show an increased survival at 28 days. Improved efficiency of alveolar ventilation (decreased physiologic deadspace ratio) is an important marker of patients who will survive acute respiratory failure.