[Effect of respiratory care on pulmonary function in patients after cardiopulmonary bypass].

BACKGROUND

Respiratory failure after cardiopulmonary bypass (CPB) remains one of the major complications after cardiac surgery. This study was designed to evaluate effects of respiratory care after CPB on pulmonary function.

METHODS

Eighteen patients scheduled for cardiac surgery were investigated. Preoperative respiratory functions (%VC, FEV1.0%, V25/Ht, FRC-CC, deltaN2) were measured in all the patients. Both induction and maintenance of anesthesia were performed using propofol, midazolam, fentanyl, and vecuronium bromide. All the patients were ventilated using volume controlled ventilation by setting FIO2 at 0.5, the respiratory frequency at 15 x min(-1), the tidal volume at 6-10 ml x kg(-1) adjusted to maintain PaCO2 between 30 to 40 mmHg, and the peak airway pressures below 40 cmH2O, PEEP of 0 cmH2O. From 1 hour after the operation, the patients were randomly divided into 2 groups: group A, ventilated artificially with PEEP of 5 cmH2O and group B, ventilated with PEEP adjusted to the patient's lower inflection point (LIP) obtained by the pressure-volume curve. PaO2, Qs/Qt and FRC were measured after induction of anesthesia, just after surgery, 1 hour after surgery and 1 hour after artificial ventilation with PEEP. The values of the LIP were obtained from the P-V curves with the constant-flow methods before and after surgery.

RESULTS

PaO2 and FRC decreased and Qs/Qt increased significantly after the surgery in all the patients. One hour after artificial ventilation with PEEP, PaO2 increased and Qs/Qt decreased significantly compared with the values after operation. However, there was no significant difference in the magnitude of these changes among the different groups. The changes in PaO2 and Qs/Qt were not correlated with the changes in FRC and preoperative respiratory functions. The LIP tended to increase after surgery in 2 groups.

CONCLUSIONS

Although pulmonary function deteriorated after CPB. PEEP could improve oxygenation in all the patients. There were no significant differences in the degree of these improvements between patients receiving PEEP of 5 cmH2O and patients with PEEP adjusted to their LIP. There was no significant relationship between preoperative pulmonary function and changes in oxygenation after CPB.