Mitochondrial oxygenation during cardiopulmonary bypass: a pilot study

Objective: Adequate oxygenation is essential for the preservation of organ function during cardiac surgery and cardiopulmonary bypass (CPB). Both hypoxia and hyperoxia result in undesired outcomes, and a narrow window for optimal oxygenation exists. Current perioperative monitoring techniques are not always sufficient to monitor adequate oxygenation. The non-invasive COMET (R) monitor could be a tool to monitor oxygenation by measuring the cutaneous mitochondrial oxygen tension (mitoPO(2)). This pilot study examines the feasibility of cutaneous mitoPO(2) measurements during cardiothoracic procedures. Cutaneous mitoPO(2) will be compared to tissue oxygenation (StO(2)) as measured by near-infrared spectroscopy. Design and Method: This single-center observational study examined 41 cardiac surgery patients requiring CPB. Preoperatively, patients received a 5-aminolevulinic acid plaster on the upper arm to enable mitoPO(2) measurements. After induction of anesthesia, both cutaneous mitoPO(2) and StO(2) were measured throughout the procedure. The patients were observed until discharge for the development of acute kidney insufficiency (AKI). Results: Cutaneous mitoPO(2) was successfully measured in all patients and was 63.5 [40.0-74.8] mmHg at the surgery start and decreased significantly (p < 0.01) to 36.4 [18.4-56.0] mmHg by the end of the CPB run. StO(2) at the surgery start was 80.5 [76.8-84.3]% and did not change significantly. Cross-clamping of the aorta and the switch to non-pulsatile flow resulted in a median cutaneous mitoPO(2) decrease of 7 mmHg (p < 0.01). The cessation of the aortic cross-clamping period resulted in an increase of 4 mmHg (p < 0.01). Totally, four patients developed AKI and had a lower preoperative eGFR of 52 vs. 81 ml/min in the non-AKI group. The AKI group spent 32% of the operation time with a cutaneous mitoPO(2) value under 20 mmHg as compared to 8% in the non-AKI group. Conclusion: This pilot study illustrated the feasibility of measuring cutaneous mitoPO(2) using the COMET (R) monitor during cardiothoracic procedures. Moreover, in contrast to StO(2), mitoPO(2) decreased significantly with the increasing CPB run time. Cutaneous mitoPO(2) also significantly decreased during the aortic cross-clamping period and increased upon the release of the clamp, but StO(2) did not. This emphasized the sensitivity of cutaneous mitoPO(2) to detect circulatory and microvascular changes.