Tissue oxygen saturation is predictive of lactate clearance in patients with circulatory shock

BackgroundTissue oxygen saturation (StO(2)) decrease could appear earlier than lactate alteration. However, the correlation between StO(2) and lactate clearance was unknown.MethodsThis was a prospective observational study. All consecutive patients with circulatory shock and lactate over 3 mmol/L were included. Based on the rule of nines, a BSA (body surface area) weighted StO(2) was calculated from four sites of StO(2) (masseter, deltoid, thenar and knee). The formulation was as follows: masseter StO(2) x 9% + (deltoid StO(2) + thenar StO(2)) x (18% + 27%)/ 2 + knee StO(2) x 46%. Vital signs, blood lactate, arterial and central venous blood gas were measured simultaneously within 48 h of ICU admission. The predictive value of BSA-weighted StO(2) on 6-hour lactate clearance > 10% since StO(2) initially monitored was assessed.ResultsA total of 34 patients were included, of whom 19 (55.9%) had a lactate clearance higher than 10%. The mean SOFA score was lower in cLac >= 10% group compared with cLac < 10% group (11 +/- 3 vs. 15 +/- 4, p = 0.007). Other baseline characteristics were comparable between groups. Compared to non-clearance group, StO(2) in deltoid, thenar and knee were significantly higher in clearance group. The area under the receiver operating curves (AUROC) of BSA-weighted StO(2) for prediction of lactate clearance (0.92, 95% CI [Confidence Interval] 0.82-1.00) was significantly higher than StO(2) of masseter (0.65, 95% CI 0.45-0.84; p < 0.01), deltoid (0.77, 95% CI 0.60-0.94; p = 0.04), thenar (0.72, 95% CI 0.55-0.90; p = 0.01), and similar to knee (0.87, 0.73-1.00; p = 0.40), mean StO(2) (0.85, 0.73-0.98; p = 0.09). Additionally, BSA-weighted StO(2) model had continuous net reclassification improvement (NRI) over the knee StO(2) and mean StO(2) model (continuous NRI 48.1% and 90.2%, respectively). The AUROC of BSA-weighted StO(2) was 0.91(95% CI 0.75-1.0) adjusted by mean arterial pressure and norepinephrine dose.ConclusionsOur results suggested that BSA-weighted StO(2) was a strong predictor of 6-hour lactate clearance in patients with shock.

Automated summary

This study found that tissue oxygen saturation (StO(2)) decrease may occur earlier than lactate alteration, and body surface area (BSA)-weighted StO(2) is a strong predictor of 6-hour lactate clearance in patients with shock.