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Sepsis

Can near infrared spectroscopy detect functional microcirculation abnormalities in septic patients?

Georger JF, Chaari A, Richard C, Teboul JL. Int Care Med. 2007;33(Supp 2):S254. Abstract 0987.

Introduction: The near infrared spectrometry (NIRS) assesses the haemoglobin saturation in the tissue (StO₂). Performance of a dynamic test resulting in a transient regional ischemia can provide additional information on the functional integrity of the local microcirculation (washout effect) through the analysis of the slope of the StO₂ re-ascension after occlusion release.

Objective: To examine whether 1) baseline StO₂ and the StO₂ re-ascension slope are altered in severe sepsis and septic shock patients in comparison with healthy volunteers, and 2) these new regional perfusion variables correlate with classical systemic perfusion variables.

Methods: We included 27 patients in severe sepsis (n=3) and septic shock (n=24) within the first 48 hours after ICU admission. Cardiac index (CI) was obtained from a transpulmonary thermodilution device (PiCCO™, Pulsion Germany). The thenar muscle StO₂ was continuously measured whit Inspectra™ StO₂ model 640 (Hutchinson Technology) and after transient forearm ischemia induced by pneumatic cuff inflation (220 mmHg) until StO₂ went down to 40%. The rate of StO₂ re-ascension after cuff deflation was calculated. We also compared the first measurements of StO₂ and the rate of StO₂ re-ascension in the septic patients with those collected in 9 healthy volunteers.

Results: Overall, 115 sets of measurements were obtained in the 27 patients. The mean SAPS2, CI and MAP were 57 ± 21, 3.48 ± 1.31L/min/m² and 76 ± 18mmHg, respectively. In comparison with healthy subjects StO₂was not different in septic patients (79 ± 5%) and in healthy subjects (80 ± 12%). In contrast, the StO₂re-ascension slope was lower in septic patients (0.77 ± 0.91%.sec^-1) than in controls (1.95 ± 0.34%.sec^-1) (p=0.004). StO₂ weakly correlated with CI (r²=0.13, p<0.001) and with MAP (r²=0.05, p<0.005 ). StO₂ re-ascension slope weakly correlated with CI (r²=0.15, p<0.001) and with MAP (r²=0.21, p<001). However, CI was lower (p< 0.0001) in cases of StO₂<70 % (n=28) (CI= 2.58 ± 1.01 L/min. m2) than in cases of StO₂>70 % (n=87) (CI= 3.76 ± 1.23 L/min.m2).

Conclusion: On average, septic patients are not characterized by lower than normal StO₂. Low values of StO₂ are generally associated with low CI. Slow StO₂ re-ascension slopes after inducing transient regional using forearm cuff inflation seem to better detect functional microcirculation abnormalities in particular when StO₂ is in the normal range.