Impact of depth of propofol anaesthesia on functional residual capacity and ventilation distribution in healthy preschool children

Background: Propofol is commonly used in children undergoing diagnosticinterventions under anaesthesia or deep sedation. Because hypoxaemiais the most common cause of critical deterioration during anaesthesiaand sedation, improved understanding of the effects of anaestheticson pulmonary function is essential. The aim of this study wasto determine the effect of different levels of propofol anaesthesiaon functional residual capacity (FRC) and ventilation distribution. Methods: In 20 children without cardiopulmonary disease mean age (SD)49.75 (13.3) months and mean weight (SD) 17.5 (3.9) kg,anaesthesia was induced by a bolus of i.v. propofol 2 mg kg^–1followed by an infusion of propofol 120 µg kg^–1 min^–1(level I). Then, a bolus of propofol 1 mg kg^–1was given followed by a propofol infusion at 240 µg kg^–1 min^–1(level II). FRC and lung clearance index (LCI) were calculatedat each level of anaesthesia using multibreath analysis. Results: The FRC mean (SD) decreased from 20.7 (3.3) ml kg^–1at anaesthesia level I to 17.7 (3.9) ml kg^–1at level II (P < 0.0001). At the same time, mean (SD) LCIincreased from 10.4 (1.1) to 11.9 (2.2) (P = 0.0038), whereasbispectral index score values decreased from mean (SD) 57.5(7.2) to 35.5 (5.9) (P < 0.0001). Conclusions: Propofol elicited a deeper level of anaesthesia that led toa significant decrease of the FRC whereas at the same time theLCI, an index for ventilation distribution, increased indicatingan increased vulnerability to hypoxaemia.