Incidence of a low tissue oxygen saturation in a mixed population of critically ill patients

Introduction

Tissue oxygen saturation (StO₂; normal value 87 ± 6% [1]) measured with NIRS has been associated with disease severity in trauma [1]. The incidence of StO₂ <75% that has been associated with organ failure [2] and its clinical consequences for ICU patients are unknown.

Methods

StO₂ was measured on the thenar eminence (InSpectra StO₂ Monitor Model 650; Hutchinson Technology) of all patients present in the ICU during 1 week. All patients were measured only once (on Monday when already admitted, or on the day of admission). Data are presented as mean ± SD unless otherwise specified.

Results

Forty-one patients (age 53 ± 19 years; 63% males) were included. Fifty-nine percent of the patients were admitted following surgery. Median StO₂ was 83% (IQR: 75 to 88) (Figure 1). No relationship was found between day of admission and measured StO₂ (Figure 2). Thirty-one patients (76%) had StO₂ below normal (Figure 2, top line). Twelve (29%) patients had StO₂ ≤75% (Figure 2, dotted line). Seven patients had StO₂ <70; mortality of these patients was 29% vs 9% in patients with StO₂ >70% (NS).

Figure 1

Frequency distribution of StO ₂ .

Figure 2

Day of admission at time of measurement vs StO ₂ .

Conclusions

The incidence of an abnormal StO₂ in critically ill patients is high. Also very low StO₂ values are frequently found and may be associated with increased mortality.