Effect of forced deflation maneuvers upon measurements of respiratory mechanics in ventilated infants

Abstract

Objective: To determine the effect of forced deflation maneuvers on respiratory mechanics and to assess the reproducibility of such measurements in intubated infants with lung disease. Design and setting: Prospective study in the pediatric intensive care unit of a university children's hospital. Patients: Ten clinically stable infants requiring mechanically assisted ventilation for acute pulmonary disease, mean age 5.9 months (1-18), mean weight 5.8 kg (3.2-13). Interventions: Two sets of measurements of compliance (Crs) and resistance (Rrs) were obtained at 20-min intervals both before and after +40/ -40 cmH2O forced deflation maneuvers. Forced deflation measurements were repeated at the end of the study. Results: Forced deflation caused a significant increase in Crs from 0.53±0.09 and 0.58±0.11 ml/cmH2O/kg to 0.71± 0.11 and 0.68±0.11 ml/cmH 2O/kg. Rrs measurements did not differ. The low coefficients of variation for repeated measures of the baseline measurements (Crs 4.2±0.5%, RTS 7.1±0.8%, for forced vital capacity 8.6±2.5%, maximum expiratory flows at 25% vital capacity 16.0%±3.3%) confirmed the good reproducibility during stable conditions. Conclusions: Inflation and deflation maneuvers affect subsequent measurements of respiratory system compliance but not measurements of maximum expiratory flow-volume relationships in intubated infants, probably through recruitment of lung volume. Careful interpretation and planning of the sequence of infant pulmonary function testing is necessary to reassure that changes are not related to short-term alterations in volume history.