Pulmonary mechanics in infants after cardiac surgery.

Objective: To determine pulmonary mechanical characteristics in neonates after cardiac surgery.

Design: A prospective study.

Setting: A 23-bed, pediatric ICU in a 280-bed children's hospital.

Patients: Twenty-six infants on the first post-operative day after cardiac surgery.

Methods: Pulmonary 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).

Results: Spontaneous 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 greater than 75 cm H2O/L.sec exhibited respiratory failure (resistance greater than 75 cm H2O/L.sec correlated with respiratory failure, r2 = .73, odds ratio of 70 [confidence interval, 4.4 to 3240], p less than .001).

Conclusions: Increased lung resistance identifies neonates with respiratory failure after cardiac surgery. Pulmonary mechanics testing may be useful in timing withdrawal of mechanical ventilation.