Chest wall motion during halothane anaesthesia in infants and young children.

Chest wall motion during anaesthesia may differ from the awake state because of the effect of anaesthetic agents on the muscles of respiration. The purpose of this study was twofold (1) to describe the pattern of chest wall motion in infants and children during halothane anaesthesia (HA) using respiratory inductive plethysmography (RIP) and (2) to calibrate the voltage output of RIP in units of volume. Seven infants (2.3 +/- 1.7 mo, 5.9 +/- 0.7 kg) and five children (2.9 +/- 1.1 yr, 15.5 +/- 1.5 kg) were studied. Since results in both age groups were qualitatively similar they are presented as a single group. Respiratory excursions of the rib cage (RC) and abdomen (ABD) were measured using RIP. Airflow was measured with a pneumotachograph. During spontaneous breathing the analogue signals of airflow, pressure, RC and ABD were recorded. Measurements were taken during (1) halothane anaesthesia and (2) during emergence from anaesthesia. The XY plots of the RC and ABD signals were plotted for each period. In addition the voltage output of the respiratory excursions of the RC and ABD signals was converted to units of volume using the simultaneous solution of equation method. The accuracy of conversion factors was validated by regression analysis of the predicted and measured tidal volume using breaths sampled at random throughout the entire period of study. Regression analysis of this relationship gave a slope between 0.85 and 1.15 (r2 value greater than 0.7) in five of the twelve patients. The pattern of chest wall motion in the XY plots showed synchronous motion between RC and ABD signals during HA in nine of the twelve patients.(ABSTRACT TRUNCATED AT 250 WORDS)