Tissue oxygen saturation and the rate of tissue deoxygenation during stagnant ischemia in the medical emergency department

Hypothesis

Tissue oxygen saturation (StO₂) and the rate of tissue deoxygenation during stagnant ischemia can early and reliably detect inadequate tissue oxygenation and assess prognosis in medical emergency room patients.

Introduction

Early recognition of patients with inadequate tissue oxygenation facilitates early diagnostic evaluation and treatment that was correlated with improved outcome. Near-infrared spectroscopy is noninvasive and in the emergency setting is a rapidly appliable method for measuring StO₂.

Methods

In a prospective observational study we included 340 consecutive medical emergency room patients. On admission, StO₂ and the rate of tissue deoxygenation during stagnant ischemia were measured by the near-infrared spectroscopy method (InSpectra tissue spectrometer; Hutchinson Technology Inc., The Netherlands) and correlated with clinical signs of shock, lactate and outcome.

Results

Three hundred and forty patients were included. Of 137 patients admitted, 16 (11.7%) were admitted to the ICU and 14 (10.2%) died in the hospital. The StO₂ was higher in patients who were not admitted compared with patients with LOS > 7 days (80.2 ± 8.7% vs 76.9 ± 9.2%, P = 0.009). Tissue deoxygenation was faster (16.7 ± 7.0%/min vs 12.9 ± 5.6%/min, P = 0.014) in survivors. Tissue deoxygenation was slower in the group of patients with clinical signs of shock compared with all patients (11.8 ± 6.0%/min vs 16.5 ± 7.0%/min, P < 0,05). Age, lactate and rate of tissue deoxygenation but not StO₂ were significant predictors of death (Table 1). There was weak but significant correlation between StO₂ and age (P < 0.0001, r = -0.28), StO₂ and lactate (P = 0.035, r = -0.12) and StO₂ and systolic blood pressure (P < 0.0001, r = 0.26).

Table 1 Predictors of survival

Conclusion

StO₂ and the rate of tissue deoxygenation during stagnant ischemia are promising additional variables, which can be measured rapidly and noninvasively in the emergency room setting. The rate of deoxygenation rather than StO₂ may be helpful for early detection of patients with inadequate tissue perfusion and worse prognosis.