Abstract
Evidence is accumulating for the adverse pulmonary consequences of cardiopulmonary bypass (CPB), its effects on the airway and lung tissue mechanics, ventilation heterogeneities, and dead space parameters have not been characterized.
Anaesthetized, mechanically ventilated patients (n=46) undergoing elective cardiac surgery were studied in open-chest condition before and 5 min after weaning from CPB. Airway resistance (Raw), inertance (Iaw), tissue damping (G) and elastance (H) were derived from the lung impedance spectra. The third phase slope of the expired CO2 concentration (SIII) and the respiratory dead space indices were determined by using mainstream capnography. Fowler's dead space (VDF) reflecting the volume of the conductive airways, Bohr's dead space (VDB) including also the unperfused alveolar volume, and Enghoff's dead space (VDE)comprising additionally the volume of the perfused but not ventilated alveoli were assessed. VDE-VDB reflects the intrapulmonary shunt.
Raw significantly increased (143±15[SE]%) while Iaw (-178±25%) and VDF (-10±0.1%) decreased after CPB. SIII (38±17%), G (130±6%) and H (7±0.5%, p=0.024) elevated post-CPB. The lowering in VDB (-12±0.1%) was associated with increased VDE-VDB (38±0.6%) following CPB (p<0.001 for all).
The rise of Raw with concomitant drops of Iaw and VDF implies that the airway narrowing was associated with their shortening after CPB. The changes in SIII, G and H suggest the development of ventilation heterogeneities. The increased VDE-VDB indicates enhanced intrapulmonary shunting. Bedside volumetric capnography may serve as a good indicator for loss of alveoli and ventilation/perfusion mismatch.
Grant: OTKA K81179 and TÁMOP-4.2.4.A/2-11/1-2012-0001.
- © 2014 ERS
