Background The effects of prone positioning on esophageal pressures have not been investigated in mechanically ventilated patients. Our objective was to characterize effects of prone positioning on esophageal pressures, transpulmonary pressure, and lung volume, thereby assessing the potential utility of esophageal pressure measurements in setting positive end-expiratory pressure (PEEP) in prone patients. Methods We studied 16 patients undergoing spine surgery during general anesthesia and neuromuscular blockade. We measured airway pressure, esophageal pressures, airflow, and volume, and calculated the expiratory reserve volume and the elastances of the lung and chest wall in supine and prone positions. Results Esophageal pressures at end expiration with 0 cm H 2 O PEEP decreased from supine to prone by 5.64 cm H 2 O (95% CI, 3.37 to 7.90; P < 0.0001). Expiratory reserve volume measured at relaxation volume increased from supine to prone by 0.15 l (interquartile range, 0.25, 0.10; P = 0.003). Chest wall elastance increased from supine to prone by 7.32 (95% CI, 4.77 to 9.87) cm H 2 O/l at PEEP 0 ( P < 0.0001) and 6.66 cm H 2 O/l (95% CI, 3.91 to 9.41) at PEEP 7 ( P = 0.0002). Median driving pressure, the change in airway pressure from end expiration to end-inspiratory plateau, increased in the prone position at PEEP 0 (3.70 cm H 2 O; 95% CI, 1.74 to 5.66; P = 0.001) and PEEP 7 (3.90 cm H 2 O; 95% CI, 2.72 to 5.09; P < 0.0001). Conclusions End-expiratory esophageal pressure decreases, and end-expiratory transpulmonary pressure and expiratory reserve volume increase, when patients are moved from supine to prone position. Mean respiratory system driving pressure increases in the prone position due to increased chest wall elastance. The increase in end-expiratory transpulmonary pressure and expiratory reserve volume may be one mechanism for the observed clinical benefit with prone positioning.

Background: Recent studies show that intraoperative mechanical ventilation using low tidal volumes ( V T ) can prevent postoperative pulmonary complications (PPCs). The aim of this individual patient data meta-analysis is to evaluate the individual associations between V T size and positive end–expiratory pressure (PEEP) level and occurrence of PPC. Methods: Randomized controlled trials comparing protective ventilation (low V T with or without high levels of PEEP) and conventional ventilation (high V T with low PEEP) in patients undergoing general surgery. The primary outcome was development of PPC. Predefined prognostic factors were tested using multivariate logistic regression. Results: Fifteen randomized controlled trials were included (2,127 patients). There were 97 cases of PPC in 1,118 patients (8.7%) assigned to protective ventilation and 148 cases in 1,009 patients (14.7%) assigned to conventional ventilation (adjusted relative risk, 0.64; 95% CI, 0.46 to 0.88; P < 0.01). There were 85 cases of PPC in 957 patients (8.9%) assigned to ventilation with low V T and high PEEP levels and 63 cases in 525 patients (12%) assigned to ventilation with low V T and low PEEP levels (adjusted relative risk, 0.93; 95% CI, 0.64 to 1.37; P = 0.72). A dose–response relationship was found between the appearance of PPC and V T size ( R 2 = 0.39) but not between the appearance of PPC and PEEP level ( R 2 = 0.08). Conclusions: These data support the beneficial effects of ventilation with use of low V T in patients undergoing surgery. Further trials are necessary to define the role of intraoperative higher PEEP to prevent PPC during nonopen abdominal surgery. Abstract This individual patient meta-analysis of 2,127 patients ventilated under general anesthesia for surgery from 15 randomized controlled trials shows that intraoperative ventilation with low tidal volume protects against postoperative pulmonary complications, but further trials are necessary to define the role of intraoperative higher positive end–expiratory pressure to prevent postoperative pulmonary complications after major abdominal surgery.

Background Low tidal volumes have been associated with improved outcomes in patients with established acute lung injury. The role of low tidal volume ventilation in patients without lung injury is still unresolved. We hypothesized that such a strategy in patients undergoing elective surgery would reduce ventilator-associated lung injury and that this improvement would lead to a shortened time to extubation Methods A single-center randomized controlled trial was undertaken in 149 patients undergoing elective cardiac surgery. Ventilation with 6 versus 10 ml/kg tidal volume was compared. Ventilator settings were applied immediately after anesthesia induction and continued throughout surgery and the subsequent intensive care unit stay. The primary endpoint of the study was time to extubation. Secondary endpoints included the proportion of patients extubated at 6 h and indices of lung mechanics and gas exchange as well as patient clinical outcomes. Results Median ventilation time was not significantly different in the low tidal volume group; a median (interquartile range) of 450 (264-1,044) min was achieved compared with 643 (417-1,032) min in the control group (P = 0.10). However, a higher proportion of patients in the low tidal volume group was free of any ventilation at 6 h: 37.3% compared with 20.3% in the control group (P = 0.02). In addition, fewer patients in the low tidal volume group required reintubation (1.3 vs. 9.5%; P = 0.03). Conclusions Although reduction of tidal volume in mechanically ventilated patients undergoing elective cardiac surgery did not significantly shorten time to extubation, several improvements were observed in secondary outcomes. When these data are combined with a lack of observed complications, a strategy of reduced tidal volume could still be beneficial in this patient population.