USE OF A VITAL CAPACITY MANEUVER TO PREVENT ATELECTASIS AFTER CARDIOPULMONARY BYPASS - AN EXPERIMENTAL-STUDY

Background: Respiratory failure secondary to cardiopulmonary bypass (C PB) remains a major complication after cardiac surgery. The authors pr eviously found that the increase in intrapulmonary shunt was well corr elated with the amount of atelectasis. They tested the hypothesis that post-CPB atelectasis can be prevented by a vital capacity maneuver (V IM) performed before termination of the bypass. Methods: Eighteen pigs received standard hypothermic CPB (no ventilation during bypass). The VCM was performed in two groups and consisted of inflating the lungs during 15 s to 40 cmH(2)O at the end of the bypass. hn one group, the inspired oxygen fraction (FIO2) was then increased is, 1.0. In the sec ond group, the FIO2 was left at 0.4. In the third group, no VCM was pe rformed (control group). Ventilation-perfusion distribution mas measur ed with the inert gas technique and atelectasis by computed tomographi c scanning. Results: Intrapulmonary shunt increased after bypass in th e control group (from 4.9 +/- 4% to 20.8 +/- 11.7%; P < 0.05) and was also increased in the vital capacity group ventilated with 100% oxygen (from 2.2 +/- 1.3% to 6.9 = 2.9%; P < 0.01) but was unaffected in the vital capacity group ventilated with 40% oxygen. The control pigs sho wed extensive atelectasis (21.3 +/- 15.8% of total lung area), which w as significantly larger (P < 0.01) than the proportion of atelectasis found in the two vital capacity groups (5.7 +/- 5.7% for the vital cap acity group ventilated with 100% oxygen and 2.3 +/- 2.1% for the vital capacity group ventilated with 40% oxygen. Conclusion: In this pig mo del, postcardiopulmonary bypass atelectasis was effectively prevented by a VCM.