Abstract 14757: Prognostic Significance of Tissue Oxygen Saturation Using Near Infrared Spectroscopy in Patients Undergoing Therapeutic Hypothermia After Cardiac Arrest

Abstract

Background: Near infrared spectroscopy is a noninvasive method for assessing regional tissue oxygenation (StO2), a parameter influenced by microvascular perfusion. Normal StO2 values recorded from the thenar eminance are 87% ± 6%. In critically ill patients, low StO2 levels (<70%) have been associated with a poor prognosis. We evaluated the prognostic significance of StO2 in patients undergoing therapeutic hypothermia (TH) after cardiac arrest (CA). Hypothesis: After resuscitation from CA, an initial StO2 ≥70%, or an initial StO2 <70% followed by an upward trend, is associated with a good neurologic outcome. Methods: We conducted a retrospective analysis of CA patients who underwent TH between August, 2005 and June, 2013. StO2 levels at the thenar eminence were collected at the onset and hourly during TH. Neurological outcome was assessed by the Cerebral Performance Category (CPC) at hospital discharge. Good outcome was defined as survival to hospital discharge with a CPC ≤2. Univariate and multivariate analyses were performed. Results: Among 160 patients, 18% (n=29) survived with a CPC ≤2. Survival with a CPC ≤2 was associated with witnessed CA (p=0.04; OR 11.6; 95% CI 1.1-118.0), shockable rhythm (p=0.02; OR 3.4; 95% CI 1.2-9.3), time to return of spontaneous circulation (ROSC) ≤15 minutes (p=0.02; OR 4.5; 95% CI 1.2-16.6) and age <65 (p=0.001; OR 7.6; 95% CI 2.3-25.5). However, an initial StO2 ≥70% was not associated with a CPC ≤2 (P=0.7; OR 0.82; 95% CI 0.29-2.2). For patients with an initial St02 <70%, there was no difference in outcome between those with an upward trend vs downward trend in St02 (p=0.98). Conclusions: Similar to previous trials documenting the value of TH witnessed CA, shockable rhythm, short time to ROSC, and younger age were associated with a good neurologic outcome. StO2 levels recorded from the thenar eminence were not associated with neurologic outcome. These StO2 levels are influenced by regional perfusion and tissue oxygenation but may not reflect cerebral microvascular perfusion. Identifying alternative technologies to assess cerebral microvascular perfusion may help determine patients for whom a good neurologic outcome can be predicted.