The effect of positive pressure ventilatory patterns on post-bypass lung functions.

BACKGROUND This study aimed at evaluating the effect of application of different patterns of positive ventilatory pressure either during or after cardiopulmonary bypass (CPB), on lung functions. METHODS 30 patients undergoing coronary artery revascularisation under the management of CPB were randomly allocated into 3 groups. Group I (VCM) 10 patients were subjected to manual vital capacity manoeuvre (VCM) before weaning off the CPB. Group II (CPAP) 10 patients were subjected to continuous positive airway pressure (CPAP) of 10 cmH2O during CPB. Group III (PEEP) 10 patients were subjected to positive end expiratory pressure (PEEP) of 7 cmH2O after weaning off the CPB. Measurements included the PO2, PCO2, together with derived calculated parameters as the alveolar-arterial oxygen difference [P (A-a) DO2] and shunt fraction, as well as the dynamic lung compliance being recorded directly from the anesthetic and ventilatory equipments. All readings were taken on closed chest and on FiO2 of 0.5. Intraoperative anesthetic and surgical data as well as postoperative extubation time and length of ICU stay were also evaluated. RESULTS Statistical analysis of ventilatory parameters showed no significant differences for both PO2 and PCO2 in between the studied groups. Alveolar-Arterial oxygen difference mean values were comparable in the 3 studied groups. The mean values of intrapulmonary shunt fraction showed a significant difference in relation to the baseline values in Group I (VCM) and Group III (PEEP) at 30 minutes after ICU admission and 4 hours post CPB with estimated P value < 0.01 and < 0.05 respectively, while in Group II (CPAP) mean values started to be significant after chest closure with a P value < 0.05, but there was no significant intergroup differences with a P value > 0.01. Dynamic lung compliance mean values showed no intergroup statistical significance. CONCLUSION Maintenance of ventilatory parameters was achieved in all the positive pressure ventilatory methods applied, either being applied during or after CPB.