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

Hammer, Jürg
Patel, Neal
Newth, Christopher J.L.

¹1Division of Pediatric Intensive Care and Pulmonology, University Children's Hospital, Römergasse 8, 4005 Basel, Switzerland
²Division of Critical Care, Children's Hospital Los Angeles, University of Southern California, Los Angeles, Calif., USA

Received: 27 September 2002/Accepted: 3 June 2003/Published online: 25 July 2003

Intensive Care Medicine 29(11):p 2004-2008, November 2003. | DOI: 10.1007/s00134-003-1895-8

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/cmH₂O/kg. Rrs measurements did not differ. The low coefficients of variation for repeated measures of the baseline measurements (Crs 4.2±0.5%, Rrs 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.