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EFFECTS OFMANUAL HYPERINFLATION (MHI) OF THE LUNGS IN CARDIAC SURGERY.

Division of Cardiac Anesthesia & Intensive Care, Toronto General Hospital, University of Toronto, Toronto, Ontario, Canada.

INTRODUCTION

Postoperative atelectasis and hypoxia are common complications in cardiac surgery. Although the use of hyperinflation maneuver has been shown to reduce intrapulmonary shunt in an animal model [1], evidence to support clinical use of such a maneuver is largely anecdotal. This prospective, randomized, controlled trial investigates the effects of MHI on hypoxia and intrapulmonary shunt in cardiac surgical patients.

METHODS

Following IRB approval and informed consent, we recruited 106 elective cardiac surgical patients who underwent cardiopulmonary bypass (CPB). Subjects were randomly assigned either to receive two MHIs (one prior to separation from CPB and one on arrival to the ICU) or to act as a control group. The MHI group received a sustained lung inflation of 35cmH₂O for 15 seconds in the operating room and of 30cm H₂O for 5 seconds in the ICU. Anesthesia technique and mechanical ventilation were standardized for all patients. Intrapulmonary shunt fractions were compared between both groups at baseline, post CPB, on ICU arrival and post tracheal extubation. Results are expressed as mean ± 95% confidence intervals.

RESULTS

Completed data were collated on 97 subjects representing a dropout of 9 patients (8.5%). Demographic data were comparable for both groups, as were duration of aortic cross-clamping and CPB. Immediately following CPB there was a significant reduction in intrapulmonary shunt in the MHI group (p= 0.002), however this improvement in gas exchange was not maintained into the postoperative period.

MHI failed to produce any sustained improvement of intrapulmonary shunt in cardiac surgical patients who underwent CPB. Nine subjects were withdrawn from completing the study in the ICU phase, due to relative hypotension, which was noticeably worsened by the application of MHIs. Furthermore, application of the maneuver immediately following CPB was associated with significant stretching of mammary arterial grafts. We conclude that manual lung hyperinflation in cardiac surgical patients is of no benefit to gas exchange and may actually worsen hemodynamic instability and endanger the integrity of mammary arterial grafts.

REFERENCES

1 British Journal of Anesthesia 1998; 80: 682–684

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