Continuous measurement of cerebral oxygen saturation (rSO2) for assessment of cardiovascular status during hemorrhagic shock in a swine model

BACKGROUND: Early trauma care is dependent on subjective assessments and sporadic vital sign assessments. We hypothesized that near-infrared spectroscopy-measured cerebral oxygenation (regional oxygen saturation [rSO2]) would provide a tool to detect cardiovascular compromise during active hemorrhage. We compared rSO(2) with invasively measured mixed venous oxygen saturation (SvO(2)), mean arterial pressure (MAP), cardiac output, heart rate, and calculated pulse pressure. METHODS: Six propofol-anesthetized instrumented swine were subjected to a fixed-rate hemorrhage until cardiovascular collapse. rSO(2) was monitored with noninvasively measured cerebral oximetry; SvO(2) was measured with a fiber optic pulmonary arterial catheter. As an assessment of the time responsiveness of each variable, we recorded minutes from start of the hemorrhage for each variable achieving a 5%, 10%, 15%, and 20% change compared with baseline. RESULTS: Mean time to cardiovascular collapse was 35 minutes +/- 11 minutes (54 +/- 17% total blood volume). Cerebral rSO(2) began a steady decline at an average MAP of 78 mm Hg +/- 17 mm Hg, well above the expected autoregulatory threshold of cerebral blood flow. The 5%, 10%, and 15% decreases in rSO(2) during hemorrhage occurred at a similar times to SvO(2), but rSO(2) lagged 6 minutes behind the equivalent percentage decreases in MAP. There was a higher correlation between rSO(2) versus MAP (R-2 = 0.72) than SvO(2) versus MAP (R-2 = 0.55). CONCLUSIONS: Near-infrared spectroscopy-measured rSO(2) provided reproducible decreases during hemorrhage that were similar in time course to invasively measured cardiac output and SvO(2) but delayed 5 to 9 minutes compared with MAP and pulse pressure. rSO(2) may provide an earlier warning of worsening hemorrhagic shock for prompt interventions in patients with trauma when continuous arterial BP measurements are unavailable. (J Trauma Acute Care Surg. 2012; 73: S140-S146. Copyright (C) 2012 by LippincottWilliams & Wilkins)