Pulmonary mechanics in infants after cardiac surgery

OBJECTIVETo determine pulmonary mechanical characteristics in neonates after cardiac surgery. DESIGNA prospective study. SETTINGA 23-bed, pediatric ICU in a 280-bed childrenʼs hospital. PATIENTSTwenty-six infants on the first post-operative day after cardiac surgery. METHODSPulmonary mechanics measurements were made during spontaneous breathing, using the esophageal balloon technique and a pneumotachometer. The least mean square method of analysis was used to calculate mechanics. Infants who tolerated withdrawal of mechanical ventilation (group 1) were compared with those infants with respiratory failure (group 2). RESULTSSpontaneous respiratory rate, tidal volume, and minute ventilation were similar in groups 1 and 2. Lung compliance was decreased, with no difference between groups. Total lung resistance (34.3 ± 21.6 cm H2O/L·sec in group 1 vs. 136.8 ± 105.8 cm H2O/L·sec in group 2, p = .002) and resistive work of breathing (33.4 ± 29.9 g·cm/kg in group 1 vs. 212.9 ± 173.8 g·cm/kg in group 2, p = .001) were significantly higher in group 2. All infants with a total lung resistance >75 cm H2O/L·sec exhibited respiratory failure (resistance >75 cm H2O/L·sec correlated with respiratory failure, r = .73, odds ratio of 70 [confidence interval, 4.4 to 3240], p < .001). CONCLUSIONSIncreased lung resistance identifies neonates with respiratory failure after cardiac surgery. Pulmonary mechanics testing may be useful in timing withdrawal of mechanical ventilation. (Crit Care Med 1992; 20:22)