Assessment of disease severity in patients with septic shock (SS) is crucial in determining optimal level of care. In both pre- and in-hospital settings, blood lactate measurement is broadly used in combination with the clinical evaluation of patients as the clinical picture alone is not sufficient for assessing disease severity and outcomes.

From 15th April 2017 to 15th April 2019, patients with SS requiring prehospital mobile Intensive Care Unit intervention (mICU) were prospectively included in this observational study. Prehospital blood lactate clearance was estimated by the difference between prehospital (time of first contact between the patients and the mICU prior to any treatment) and in-hospital (at hospital admission) blood lactate levels divided by prehospital blood lactate.

Among the 185 patients included in this study, lactate measurement was missing for six (3%) in the prehospital setting and for four (2%) at hospital admission, thus 175 (95%) were analysed for prehospital blood lactate clearance (mean age 70 ± 14 years). Pulmonary, digestive and urinary infections were probably the cause of the SS in respectively 56%, 22% and 10% of the cases. The 30-day overall mortality was 32%.

Mean prehospital blood lactate clearance was significantly different between patients who died and those who survived (respectively 0.41 ± 2.50 mmol.l⁻¹ vs 1.65 ± 2.88 mmol.l⁻¹, p = 0.007).

Cox regression analysis showed that 30-day mortality was associated with prehospital blood lactate clearance > 10% (HRa [CI95] = 0.49 [0.26–0.92], p = 0.028) and prehospital blood lactate clearance < 10% (HRa [CI95] = 2.04 [1.08–3.84], p = 0.028).

A prehospital blood lactate clearance < 10% is associated with 30-day mortality increase in patients with SS handled by the prehospital mICU. Further studies will be needed to evaluate if prehospital blood lactate clearance alone or combined with clinical scores could affected the triage decision-making process for those patients.