Respiratory mechanics with volume-controlled auto-flow ventilation mode in cardiac surgery

We aimed to investigate the changes in respiratory mechanics in adult patients undergoing open heart surgery (OHS) while using volume-controlled auto-flow (VCAF) ventilation mode.

After obtaining ethics committee's approval and informed consent, 30 patients (17 males and 13 females; mean age: 57.3 ± 17.0 years; mean weight; 74.9 ± 13.6 kg) scheduled for OHS were enrolled. Mechanical ventilation was carried out using VCAF mode (V_T: 5-8 mL/kg, I/E: 1/2, 10 ± 2 fr/min). Values of dynamic compliance (C_dyn) and resistance (R) were obtained at six time points (TPs). Normally distributed variables were analyzed with repeated measure of analysis of variance and Bonferroni tests. For abnormally distributed variables, Friedman variance analysis and Wilcoxon signed-rank tests were used. Values were expressed as mean ± standard deviation. P value <0.05 was considered significant.

C_dyn (mL/mbar) and R (mbar/L/s) values were as follows - (1) before sternotomy (S): 49.9 ± 17.1 and 7.8 ± 3.6; (2) after S: 56.7 ± 18.3 and 7.1 ± 3.7; (3) after S and after sternal retractor placement: 48.7 ± 16.1 and 8.3 ± 4.4; (4) after weaning from cardiopulmonary bypass and following decannulation while retractor was in place: 49.6 ± 16.5 and 8.1 ± 4.0; (5) after retractor removal: 56.5 ± 19.6 and 7.4 ± 3.7; and (6) after sternal closure: 43.1 ± 14.2 and 9.6 ± 9.1, respectively. Significant differences were observed in C_dyn and R between; first and second TPs, second and third TPs, fourth and fifth TPs, and fifth and sixth TPs. Also, significant difference in C_dyn was found between first and sixth TPs, but it was not found in R.

C_dyn decreases, but R remains the same in cardiac surgical patients when mechanical ventilation is performed with VCAF ventilation mode. Additionally, C_dyn is negatively affected by the presence of sternal retractor and the sternal closure in OHS.