Please see Bibliography of References for a list of abstracts, manuscripts and posters.
Sanders J, Toor I, Yurik T, Smith A, Keogh BE, Montgomery HE, Mythen M. ACTA Spring Meeting; June 6, 2008; London, England.
Near Infra-Red Spectroscopy is a novel method for rapid and non-invasive assessment of tissue oxygen saturation (StO2). An association between StO2 and oxygen delivery has been demonstrated during shock, trauma and resuscitation. We sought to explore StO2 during anaesthesia and surgery and its association with outcome.
Methods: 74 adult patients undergoing first-time, elective, single procedure cardiac surgery requiring cardiopulmonary bypass (CPB) were studied. StO2 was measured from the thenar eminence (Inspectra Tissue Spectrometer Model 325, Hutchinson Technology Inc, USA) through anaesthesia, surgery and intensive care unit (ICU) care for a maximum of 24hours. Clinical details and haemodynamic variables (blood pressure and heart rate) were prospectively collected. Outcome was defined as duration of ventilation and of ICU stay.
Results: StO2 rose from baseline during induction of anaesthesia (81.70 to 88.52, p<0.001). This rise was 5.70 lower in those patients suffering haemodynamic change requiring treatment (p=0.0055). StO2 then fell during surgery (mean 78.89) with a significant change in minimum StO2 during CPB (75.88 to 68.16 p<0.0001). During this time, StO2 was associated with CPB temperature (every one point increase in temperature was associated with a 1.14 increase in StO2, p<0.001) ) and CPB flow rate (every one point increase in flow rate was associated with a 2.39 increase in StO2, p=0.02), and inversely with FiO2 (every one point increase in FiO2 was associated with a 1.95 decrease in StO2, p=0.04). Minimum StO2 during surgery was also associated with pre-operative Hb (correlation coefficient 0.22, p=0.054) but not minimum intra-op Hb (correlation coefficient 0.001, p=0.84). There was no association between any StO2 measure and length of ventilation or length of stay on ICU. Using a StO2 cut-off of 75 for the mean during surgery, there was a trend for StO2 <75 to be associated with longer CPB duration (105.0 v 86.7, p0.22) and longer ventilation time (8.2 v 6.2, p=0.06) than those with StO2 >75.
Discussion: We have shown that StO2 is easily and non-invasively measured in cardiac surgical patients. StO2 increased as CPB temperature rose, an effect perhaps attributable to muscle bed vasodilatation. Similarly, the rise in StO2 with increased CPB flow may reflect increased oxygen delivery. The fall in StO2 with rise in FIO2 is harder to explain, but may reflect a confounding effect, with clinical variables associated with lower StO2 themselves triggering an increase in FIO2 as an intervention. Such hypotheses are worthy of further interrogation. Our data also support expanded studies relating StO2 to CPB duration.
Acknowledgement: This work was supported by an unrestricted educational grant from Hutchinson Technology Inc.