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 ® 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.
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).
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.
This pilot study illustrated the feasibility of measuring cutaneous mitoPO 2 using the COMET ® 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.