Background: Increased intra-abdominal pressure during laparoscopy induces atelectasis. Positive end-expiratory pressure (PEEP) can alleviate atelectasis but may cause hyperinflation. Cyclic opening of collapsed alveoli and hyperinflation can lead to ventilator-induced lung injury and postoperative pulmonary complications. We aimed to study the effect of PEEP on atelectasis, lung stress, and hyperinflation during laparoscopy in the head-down (Trendelenburg) position.
Methods: An open-label, repeated-measures, interventional, physiological cohort trial was designed. All participants were recruited from a single tertiary Belgian university hospital. Twenty-three nonobese patients scheduled for laparoscopy in the Trendelenburg position were recruited.We applied a decremental PEEP protocol: 15 (high), 10 and 5 (low) cm H 2 O. Atelectasis was studied with the lung ultrasound score, the end-expiratory transpulmonary pressure, the arterial oxygen partial pressure to fraction of inspired oxygen concentration (P ao2 /Fi o2 ) ratio, and the dynamic respiratory system compliance. Global hyperinflation was evaluated by dead space volume, and regional ventilation was evaluated by lung ultrasound. Lung stress was estimated using the transpulmonary driving pressure and dynamic compliance. Data are reported as medians (25th-75th percentile).
Results: At 15, 10, and 5 cm H 2 O PEEP, the respective measurements were: lung ultrasound scores (%) 11 (0-22), 27 (11-39), and 53 (42-61) ( P < .001); end-expiratory transpulmonary pressures (cm H 2 O) 0.9 (-0.6 to 1.7), -0.3 (-2.0 to 0.7), and -1.9 (-4.6 to -0.9) ( P < .001); P ao2 /Fi o2 ratios (mm Hg) 471 (435-538), 458 (410-537), and 431 (358-492) ( P < .001); dynamic respiratory system compliances (mL/cm H 2 O) 32 (26-36), 30 (25-34), and 27 (22-30) ( P < .001); driving pressures (cm H 2 O) 8.2 (7.5-9.5), 9.3 (8.5-11.1), and 11.0 (10.3-12.2) ( P < .001); and alveolar dead space ventilation fractions (%) 10 (9-12), 10 (9-12), and 9 (8-12) ( P = .23). The lung ultrasound score was similar between apical and basal lung regions at each PEEP level ( P = .76, .37, and .76, respectively).
Conclusions: Higher PEEP levels during laparoscopy in the head-down position facilitate lung-protective ventilation. Atelectasis and lung stress are reduced in the absence of global alveolar hyperinflation.
Trial registration: ClinicalTrials.gov NCT04900714.
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