European Journal of Cardio-Thoracic Surgery, Vol 5, 253-257, Copyright © 1991 by European Association for Cardio-thoracic Surgery
Lung mechanics and airway pressure transmission in infants after open heart surgery
J Rasanen, K Peltola and M Leijala
Department of Anesthesiology, University of South Florida College of Medicine, Tampa.
To evaluate the effects of positive airway pressure on lung mechanics and
airway pressure transmission into the intrathoracic space, airway and
intrathoracic pressure were recorded during stepwise lung inflation in 17
infants undergoing open heart surgery during the first year of life. Eleven
of the 17 patients had cuffed tracheal tubes allowing calculation of lung
and chest wall compliance. In 7 of these 11 patients, lung inflation to 2.5
ml/kg above functional residual capacity produced an improvement in
initially low lung compliance. This volume increment required elevation of
airway pressure by 4-11 cm H2O above ambient. Further lung inflation to 10
ml/kg did not effect an improvement in lung mechanics. In the remaining
patients, initial lung compliance was high and remained unchanged
throughout the range of lung inflation. Transmission of pressure into the
intrathoracic space averaged 47 +/- 9% (mean +/- SD) and ranged from 33% to
61% when airway pressure was 10-15 cm H2O. The results indicate that the
use of moderately elevated airway pressure is required to optimize lung
distensibility in most infants immediately after open heart surgery. When
evaluating circulatory effects of elevated airway pressure, assumption of a
50% pressure transmission is appropriate for clinical purposes. However,
the observed wide range of pressure transmission warrants careful
hemodynamic monitoring during continuous positive pressure breathing.
