Research concerning cardiopulmonary bypass (CPB) management during minimally invasive cardiac surgery (MICS) is scarce. We investigated the effect of CPB parameters such as pump flow, haemoglobin concentration and oxygen delivery on clinical outcome and renal function in a propensity matched comparison between MICS and median sternotomy (MS) for atrioventricular valve surgery.

A total of 356 patients undergoing MICS or MS for atrioventricular valve surgery between 2006 and 2017 were analysed retrospectively. Propensity score analysis matched 90 patients in the MS group with 143 in the MICS group. Logistic regression analysis was performed to investigate independent predictors of cardiac surgery-associated acute kidney injury in patients having MICS.

In MICS, CPB (142.9 ± 39.4 vs 101.0 ± 38.3 min; P < 0.001) and aortic cross-clamp duration (89.9 ± 30.6 vs 63.5 ± 23.0 min; P < 0.001) were significantly prolonged although no differences in clinical outcomes were detected. The pump flow index was lower [2.2 ± 0.2 vs 2.4 ± 0.1 l⋅(min⋅m²)⁻¹; P < 0.001] whereas intraoperative haemoglobin levels were higher (9.25 ± 1.1 vs 8.8 ± 1.2; P = 0.004) and the nadir oxygen delivery was lower [260.8 ± 43.5 vs 273.7 ± 43.7 ml⋅(min⋅m²)⁻¹; P = 0.029] during MICS. Regression analysis revealed that the nadir haemoglobin concentration during CPB was the sole independent predictor of cardiac surgery-associated acute kidney injury (odds ratio 0.67, 95% confidence interval 0.46–0.96; P = 0.029) in MICS but not in MS.

Specific cannulation-related issues lead to CPB management during MICS being confronted with flow restrictions because an average pump flow index ≤2.2 l/min/m² is achieved in 40% of patients who have MICS compared to those who have a conventional MS. This study showed that increasing the haemoglobin level might be helpful to reduce the incidence of cardiac surgery-associated acute kidney injury after minimally invasive mitral valve surgery.