Background

Inadequate oxygen perfusion during cardiac surgery increases risk of postoperative complications. In order to optimize perfusion strategies, the aim of this exploratory study was to investigate oxygen delivery, consumption and extraction during hypothermic circulatory arrest and their association with postoperative hyperlactatemia.

Method

A consecutive sample of 44 adult patients scheduled for total aortic arch replacement under cardiopulmonary bypass and hypothermic circulatory arrest were prospectively enrolled during the study period. Oxygen delivery index, oxygen consumption index and oxygen extraction rate were measured during cooling from 36 to 24 ℃ and rewarming from 24 to 36 ℃. The primary outcome was the association between intraoperative oxygen metabolism parameter and postoperative hyperlactatemia. Hyperlactatemia was defined as peak lactate ≥ 4 mmol/L within 24 h after surgery.

Results

A total of 41 patients were enrolled in the final analysis. Serum lactate rose slightly from 1.5 (1.3–2.2) mmol/L at baseline to 2.0 (1.5–2.6) mmol/L before hypothermic circulatory arrest and again to 4.0 (3.6–5.1) mmol/L after 29.17 ± 5.87 min of arrest, finally peaking at 5.0 (2.9–7.1) mmol/L within 24 h after surgery. The three oxygen parameters decreased progressively during cooling and increased gradually during rewarming. All three parameters at a given temperature were obviously higher during rewarming than cooling. Oxygen extraction rate at 24 ℃ during cooling correlated positively with peak lactate concentration within 24 h after surgery (Spearman’s ρ = 0.67, p = 0.001). Hyperlactatemia occurred in 24 patients (58.54%), whose oxygen extraction rate and oxygen consumption index at 24 ℃ during cooling were significantly higher than in those who did not suffer hyperlactatemia. In fact, these two parameters discriminated hyperlactatemia with respective areas under the receiver operating characteristic (AUC) curves of 0.83 and 0.80.

Conclusion

In this exploratory study, a relatively higher oxygen extraction rate at 24 °C during cooling appeared to be associated with postoperative hyperlactatemia (AUC 0.83, cut-off > 0.102). This preliminary finding warrants validation in larger prospective studies.