Comparison of capillary and arterial lactate levels in patients with shock

Abstract

Objective: Several guidelines recommend point-of-care lactate measurements for therapeutic decision-making in patients with shock. The aim of the study was to validate capillary lactate measurements with a bedside micromethod in patients with shock.

Study design: Prospective observational study.

Patients and measurements: Capillary lactate levels measured by a micromethod (CAPI) and arterial lactate levels measured by a standard laboratory method (ARTs) were simultaneously and repeatedly assayed in consecutive ICU patients with shock. The validity and clinical acceptability of the CAPI method was assessed from its reproducibility, the arterio-capillary lactate difference (ACLD) and conventional diagnostic indicators.

Main results: Lactate measurements were available for 139 time-points in 37 patients. CAPI values correlated well with ARTs values (intraclass coefficient correlation: r²=0.92, P<0.001). CAPI had a sensitivity of 98%, a specificity of 36%, an accuracy of 88% and a positive predictive value of 89% to detect lactate values≥2mmol/L (P<0.0001). The mean bias between the two methods (ACLD: 0.56±2.21mmol/L) was mainly due to higher lactate concentration in capillary blood.

Conclusion: CAPI was correctly correlated to ARTs. The bias between the two methods is probably acceptable for triage purpose. Patients with elevated capillary lactate or in shock should be monitored with atrial-based lactate.

Keywords: Lactate; Point-of-care testing; Shock; Triage.