Does Intraoperative Tidal Volume Affect Lung Injury after Cardiac Surgery?

Background: During surgery, tidal volumes (TV) between 10-12 ml/kg were advocated to ensure adequate gas exchange and avoid atelectasis. However, recent research suggests that high TV is injurious to both damaged and normal lungs, and studies in non-cardiac surgery have shown that ventilation with lower TV reduces postoperative pulmonary complications. Not much, however, is known about the effect of intraoperative TV on lung injury after cardiac surgery.

Objective: To test the influence of intraoperative TV on pulmonary function after cardiac surgery.

Methods: The electronic medical records of patients who underwent cardiac surgery using cardiopulmonary bypass at Assuta Medical Center between 2009-2015 were queried. The primary endpoint was the PF ratio (p_aO₂/F_iO₂) two hours after ICU admission, and was analyzed both as a continuous variable using linear regression, and as a dichotomous variable (above and below 300) using logistic regression. A secondary endpoint was time to extubation in patients admitted to the ICU during the day shift. The main independent variable was intraoperative TV normalized to ideal body weight (IBW). p

Results: 3347 patients were included in the analysis (age 63.8±10.3 years, 24.4% females). Mean intraoperative TV was 8.45±1.73 ml/kg IBW, and was not correlated with the PF ratio neither by multiple linear regression or by logistic regression. Median (IQR) time to extubation was 579 (356-814) minutes, and was weakly correlated with intraoperative TV (p=0.002, r=0.078 by Spearman`s correlation).

Conclusion: Intraoperative TV did not affect lung injury after cardiac surgery, but was weakly associated with time to extubation.