Respiratory mechanics in cardiac surgery with volume controlled autoflow ventilation mode

Aim of the Study: The effects of open heart surgery (OHS) on respiratory mechanics were investigated while using volume controlled AutoFlow (VCAF) ventilation mode.Materials and Methods: After obtaining ethics committee approval and informed consent, thirty patients (sex; 17 male/13 female; mean age: 57.3±17.0 year; mean weight; 74.9±13.6 kg) scheduled for OHS were enrolled. Mechanical ventilation was carried out using VCAF mode (VT: 5-8 mL/kg, I/E: 1/2, FiO2: 0.5-1.0; PEEP: Ø, RR: 10±2 fr/min) under closed system with autocontrol. The values of dynamic compliance (Cdyn) and resistance (R) were obtained at 6 different intraoperative time points (TPs). Data distributions were assessed with Shapiro-Wilk test. Repeated Measure of Anova and Bonferroni tests (Cdyn), and Friedman Varyans Analysis and Wilcoxon Signed Rank tests (R) were used. Data were given as mean±SD and/or number and p <0.05 was considered significant.Results: Cdyn (mL/mbar) and R (mbar/L/s) values were as follows: (1) before sternotomy; 49.9±17.1 and 7.8±3.6, (2) after sternotomy and before retractor placement; 56.7±18.3 and 7.1±3.7, (3) after retractor placement; 48.7±16.1 and 8.3±4.4, (4) after weaning from cardiopulmonary bypass (CPB) while retractor was in place; 49.6±16.5 and 8.1±4.0, (5) after retractor removement (5); 56.5±19.6 ve 7.4±3.7, and (6) after sternal closure; 43.1±14.2 and 9.6±9.1, respectively. Significant differences were found in regard to Cdyn (p<0.001) and R (p<0.001) in these TPs. Differences were observed in Cdyn and R between; 1th and 2nd TPs ([p<0.001], [p=0.002], respectively), 2nd and 3rd TPs ([p=0.001], [p<0.001], respectively), 4th and 5th TPs ([p<0.001], [p<0.001], respectively), and 5th and 6th TPs ([p<0.001], [p<0.001], respectively). Significant difference in Cdyn (p=0.001) was found between 1st and 6th TPs, but not in R (p=0.10).Conclusion: Cdyn is mainly affected by sternal closure intraoperatively during OHS when VCAF mode is chosen for mechanical ventilation, not by CPB itself. Besides, the presence of sternal retractor isimportant when respiratory mechanics are obtained intraoperatively, a condition which has not been mentioned previously.