Decrease of functional residual capacity and ventilation homogeneity after neuromuscular blockade in anesthetized young infants and preschool children.

BACKGROUND: Based on age-dependent differences in pulmonary mechanics, the effect of neuromuscular blockade may differ in infants compared with older children. The aim of this study was to determine the impact of neuromuscular blockade and its reversal by positive end-expiratory pressure (PEEP) on functional residual capacity (FRC) and ventilation distribution in young infants and preschool children. METHODS: The authors studied 14 infants (aged 0-6 months) and 25 preschool children (aged 2-6 yr). FRC and lung clearance index were calculated. Measurements were taken (1) after intubation, (2) during neuromuscular blockade, and (3) during neuromuscular blockade plus application of PEEP (3 cm H2O). RESULTS: Functional residual capacity (mean +/- SD) decreased from 21.3 +/- 4.7 ml/kg to 12.2 +/- 4.8 ml/kg (P < 0.001) during neuromuscular blockade in infants and from 25.6 +/- 5.9 ml/kg to 23.0 +/- 5.3 ml/kg (P < 0.001) in preschool children. With the application of PEEP, FRC increased to 22.3 +/- 5.9 ml/kg (P = 0.4829, compared with baseline) in infants and 28.2 +/- 5.8 ml/kg (P < 0.001) in children. The lung clearance index increased after neuromuscular blockade, whereas baseline values were regained after the application of PEEP. The changes induced by neuromuscular blockade were significantly greater in infants compared with preschool children (P < 0.001). CONCLUSIONS: Although the use of neuromuscular blockade decreased FRC and ventilation distribution substantially in both groups, the changes were more pronounced in young infants. With PEEP, FRC increased and ventilation homogeneity was restored. These results provide a rationale to use PEEP in anesthetized, paralyzed infants and children.