Near-infrared spectroscopy in post-cardiac arrest patients undergoing therapeutic hypothermia.

Aims: To investigate the relationship between tissue oxygen saturation during a vascular occlusion test with systemic hemodynamics, central and peripheral skin temperature in patients resuscitated from cardiac arrest.

Methods: This prospective, observational study included a convenience sample of 30 patients hospitalized in a multidisciplinary intensive care unit in a university hospital and treated with therapeutic hypothermia. Near infrared spectroscopy (NIRS) was used to measure thenar tissue oxygen saturation, desaturation rate and saturation recovery rate after the vascular occlusion test, conducted within 24h of hospital admission and within 12h of initiating re-warming. Measurements included heart rate (HR), mean arterial blood pressure (MAP), oxygen saturation, use of vasopressors and sedatives, core body (esophageal) and peripheral skin temperature and sequential organ failure assessment (SOFA) score.

Results: Peripheral skin temperature was found to have a significant effect on StO(2) deoxygenation and recovery slopes, resulting in lower rates at colder temperatures. This effect was independent of MAP, HR, and core temperature. NIRS-derived variables were not associated with SOFA score or use of vasopressors and did not predict mortality.

Discussion: Colder peripheral skin temperatures resulting in lower StO(2) desaturation rates may be explained by slower aerobic metabolism, thus lower extraction rate of oxygen, in the tissue beds. Lower recovery slopes at colder local temperatures may result from peripheral vasoconstriction during reactive hyperemia.

Conclusion: We found that peripheral skin temperature in post-arrest critically ill patients undergoing TH strongly influences tissue oxygen desaturation and reoxygenation rates. In additional, changes in NIRS derived variables were independent of measures of shock, vasopressor use or illness severity.