Tissue oxygen saturation does not correlate with the oxygen delivery index during major abdominal surgery

Introduction

Tissue oxygenation (STO₂) measured by near-infrared spectroscopy (NIRS) has been shown to correlate with the global oxygen delivery index (DO₂I) in both humans and animals during haemorrhagic shock and its fluid resuscitation [1]. This is a pilot study to determine whether STO₂ can be used as a surrogate marker of DO₂I with a view to utilising this simple noninvasive technique to guide intraoperative haemodynamic therapy.

Methods

Eighteen patients undergoing major abdominal surgery were recruited from a London teaching hospital. All patients received the same induction and maintenance anaesthesia. Ten patients were actively haemodynamically optimised to a DO₂I >600 ml/min/kg with fluid resuscitation. The DO₂I was determined using an oesophageal Doppler probe cardiac output monitor (CardioQ; Deltex Medical, UK). The STO₂ of the thenar muscle was determined using the InSpectra STO₂ (Hutchinson Technology, USA). Paired measurements of the DO₂I and STO₂ were taken every 20 minutes from the start of surgery.

Results

The average patient age was 67 (30–84) years; seven (39%) were female. A total of 173 paired observations were made. The median (IQR) for the DO₂I and STO₂ were 454 (332.5–595.5) and 88 (83–93), respectively. There was no correlation between the DO₂I and STO₂ (Figure 1; r = 0.1, P > 0.1). In addition there is no statistically significant difference in STO₂ when the DO₂I > 600 ml/min/m² (paired t test, P = 0.6). STO₂ did not track the changes in DO₂I.

Figure 1

Conclusion

There is no clear relationship between STO₂ and the DO₂I during major abdominal surgery. STO₂ in the intraoperative period cannot currently be used as a surrogate marker for oxygen delivery in this group of patients.