Obesity, PEEP and Postoperative Oxygenation

Positive end-expiratory pressure (PEEP) is often used during mechanical ventilation to preserve end-expiratory lung volume. After emergence and extubation, this volume will diminish instantly. Some patients will have difficulties to restore functional residual capacity (FRC) during the early phase of recovery. If routine high FIO2 is being delivered together with maintained PEEP prior to extubation, several important prerequisites are established for the development of postoperative atelectasis. The investigators hypothesize that establishing zero positive end-expiratory pressure (ZEEP) immediately prior to emergence preoxygenation, will prevent gas with high oxygen concentration from entering dorso-basal areas of the lungs, and thereby diminishing postoperative atelectasis formation and improve oxygenation.

This randomized controlled study will study overweight patients undergoing general anesthesia for laparoscopic surgery. The patients in the two study groups will receive mechanical ventilation with identical settings, comprising low TV, PEEP, and no RM. Randomization will occur at the end of surgery, before awakening. The patients will be allocated to zero PEEP (ZEEP) or maintained PEEP during emergence preoxygenation and extubation. Importantly, the intervention group will have ZEEP established while still having low ETO2 levels, prior to any preoxygenation. Arterial blood gases will be collected before, during and after anaesthesia. Primary endpoint measure will be change in oxygenation from before awakening to after awakening.

Inclusion criteria

• Obese patients scheduled for elective laparocopic surgery.
• American Society of Anesthesiologists functional class I-III
• Body Mass Index 35-50 kg/m2

Exclusion criteria

• Body Mass Index ≥50 kg/m2
• Peripheral oxygen saturation (SpO2) breathing air <94 %
• Symtomatic asthma, COPD or heart failure
• Ischemic heart disease
• Hemoglobin < 100g/l
• Smokers and ex-smokers that stopped smoking < 9 months ago
• Need for peroperative RM and PEEP higher than in study protocol, as indicated by SpO2 <92% despite the stipulated FiO2 0.30-0.35.
• Obstructive sleep apnea syndrome on home-CPAP