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

Abstract

Background: Tissue oxygen saturation (StO₂) decrease could appear earlier than lactate alteration. However, the correlation between StO₂ and lactate clearance was unknown.

Methods: This 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 StO₂ was calculated from four sites of StO₂ (masseter, deltoid, thenar and knee). The formulation was as follows: masseter StO₂ × 9% + (deltoid StO₂ + thenar StO₂) × (18% + 27%)/ 2 + knee StO₂ × 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 StO₂ on 6-hour lactate clearance > 10% since StO₂ initially monitored was assessed.

Results: A 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, StO₂ in deltoid, thenar and knee were significantly higher in clearance group. The area under the receiver operating curves (AUROC) of BSA-weighted StO₂ for prediction of lactate clearance (0.92, 95% CI [Confidence Interval] 0.82-1.00) was significantly higher than StO₂ 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 StO₂ (0.85, 0.73-0.98; p = 0.09). Additionally, BSA-weighted StO₂ model had continuous net reclassification improvement (NRI) over the knee StO₂ and mean StO₂ model (continuous NRI 48.1% and 90.2%, respectively). The AUROC of BSA-weighted StO₂ was 0.91(95% CI 0.75-1.0) adjusted by mean arterial pressure and norepinephrine dose.

Conclusions: Our results suggested that BSA-weighted StO₂ was a strong predictor of 6-hour lactate clearance in patients with shock.

Keywords: Diagnostic accuracy; Lactate clearance; Shock; Tissue oxygen saturation.