Body position and the effectiveness of mask ventilation in anaesthetised paralysed obese patients: A randomised cross-over study.

Background: Airway management is more challenging in the obese. Compared with the supine position, the sitting position can decrease the collapsibility of the upper airway and improve respiratory mechanics.

Objective: The aim of this study was to evaluate the 25° semisitting position on the effectiveness of mask ventilation in anaesthetised paralysed obese patients.

Design: A randomised, cross-over study.

Setting: Medical centre managed by a university tertiary hospital.

Patients: Thirty-eight obese adults scheduled for general anaesthesia.

Methods: After anaesthesia and paralysis, two-handed mask ventilation was performed in the supine and 25° semi-sitting positions with a cross-over, in a randomised order. During mask ventilation, mechanical ventilation was delivered with a pressure-controlled mode with a peak inspiratory pressure of 15 cmH2O, a respiratory rate of 15 bpm, and no positive end-expiratory pressure. Ventilatory outcomes were based upon lean body weight.

Main Outcomes: Exhaled tidal volume (ml kg-1), respiratory minute volume (ml kg-1 min-1), and the occurrence of inadequate ventilation, defined as an exhaled tidal volume less than 4 ml kg-1, or absence of end-tidal CO2 recording.

Results: Exhaled tidal volume (mean ± SD) in the 25° semi-sitting position was higher than in the supine position, 9.3 ± 2.7 vs. 7.6 ± 2.4 ml kg-1; P less than 0.001. Respiratory minute volume was improved in the 25° semisitting position compared with that in the supine position, 139.6 ± 40.7 vs. 113.4 ± 35.7 ml kg-1 min-1; P less than 0.001.

Conclusion: The 25° semisitting position improved mask ventilation compared with the supine position in anaesthetised paralysed obese patients.

Trial Registry Number: ClinicalTrials.gov (NCT03996161).