Correlates of thenar near-infrared spectroscopy-derived tissue O2 saturation after cardiac surgery

We studied the significance of near-infrared spectroscopy (NIRS), for measuring tissue oxygenation (S(t)O(2)) and perfusion adequacy, and thus for haemodynamic monitoring of patients after cardiac surgery. We compared NIRS-derived S(t)O(2) of the thenar muscle to haemodynamic variables, oxygenation indices, temperature, lactate levels and urinary output, in 23 patients in the course of time after cardiac surgery and admission into the intensive care unit. Clinical variables, global haemodynamics and NIRS% total haemoglobin (%HT) and S(t)O(2) in the thenar for up to 18-22 h after admission were measured. The S(t)O(2) declined concomitantly with a rise in the body-finger temperature difference. Cardiac output did not change but mean arterial pressure rose, concomitantly with tapering doses of nitroglycerine, indicative of an increase in vascular tone during recovery from surgery. From all variables, changes in body-finger temperature difference best correlated to changes in S(t)O(2) (r(s)=-0.48, P<0.001). As judged from clinical and haemodynamic correlates, thenar NIRS S(t)O(2) is a non-invasive measure of peripheral rather than global perfusion adequacy, after cardiac surgery. This may help to define the role of thenar NIRS monitoring after cardiac surgery in future studies.