PERIOPERATIVE CHANGES IN FUNCTIONAL RESIDUAL CAPACITY IN MORBIDLY OBESE PATIENTS

A reduction in FRC following induction of anaesthesia occurs in normal subjects [1]. How-ever, little is known of variations in FRC in morbidly obese patients undergoing general anaesthesia. Don and colleagues [2] described a negative relationship between FRC during anaes-thesia (expressed as percent of preanaesthesia values) and the weight: height ratio. This re-lationship predicts a marked decrease in FRC for obese patients, but in morbidly obese patients investigated before and after induction of gen-eral anaesthesia a reduction in FRC was found lower than that observed in patients of normal weight [3]. The present study has investigated the effect of general anaesthesia and muscle paralysis on FRC (as measured by the helium dilution technique) in obese patients; FRC changes produced by lapar-otomy were also investigated. PATIENTS AND METHODS Eighteen normocapnic morbidly obese patients (group A) of mean weight 152 kg (table I) undergoing jejunoileal bypass surgery were studied after informed consent had been obtained. The day before anaesthesia respiratory function tests were performed, including FRC, RV, VC and FEVi, m the supine position. Measurement of FRC was also undertaken at 5 min before and after induction of anaesthesia and after the laparotomy incision (approxi-mately 20 min after induction of anaesthesia). FRC was measured also in seven of these patients during anaesthesia, full muscle paralysis and mechanical ventilation, after the skin incision wa