Although a high inspired oxygen fraction (FiO 2) is commonly used in paediatric anaesthesia, the impact on postoperative lung function is unclear. We compared lung volume, ventilation heterogeneity, and respiratory mechanics in anaesthetised children randomised to receive low or high FiO 2 intraoperatively.
In a double-blind randomised controlled trial, children scheduled for elective surgery were randomly assigned FiO 2 100% ( n=29) or FiO 2 80% ( n=29) during anaesthesia induction and emergence. During maintenance of anaesthesia, participants assigned FiO 2=100% at induction/emergence received FiO 2=80% (FiO 2>0.8 group); those randomised to FiO 2=80% at induction/emergence received FiO 2=35% intraoperatively (FiO 2 [0.8→0.35 group]). During spontaneous breathing, we measured the (i) functional residual capacity (FRC) and lung clearance index (ventilation inhomogeneity) by multiple-breath nitrogen washout; and (ii) airway resistance and respiratory tissue elastance by forced oscillations, before operation, after discharge from the recovery room, and 24 h after operation. Mean (95% confidence intervals) are reported.
Fifty eight children (12.9 [12.3–13.5] yr) were randomised; 22/29 (high group) and 21/29 (low group) children completed serial multiple-breath nitrogen washout measurements. FRC decreased in the FiO 2>0.8 group after discharge from recovery (–12.0 [–18.5 to –5.5]%; P=0.01), but normalised 24 h later. Ventilation inhomogeneity increased in both groups after discharge from recovery, but persisted in the FiO 2>0.8 group 24 h after surgery (6.1 [2.5–9.8%]%; P=0.02). Airway resistance and respiratory elastance did not differ between the groups at any time point.
FiO 2>0.8 decreases lung volume in the immediate postoperative period, accompanied by persistent ventilation inhomogeneity. These data suggest that FiO 2>0.8 should be avoided in anaesthetised children with normal lungs.