Prehospital Blood Lactate Measurements in Ambulances and Associations with Outcomes: A Cohort Study.

Objectives: The prehospital use of blood lactate measurements is increasing. The blood lactate level is a well-recognized biomarker of poor outcomes, mainly investigated in potentially critically ill patients or patients with specific illnesses. However, evidence of a correlation in a broad prehospital setting with undifferentiated patients is lacking. This study aimed to investigate the correlation between prehospital blood lactate levels and the risks of poor outcomes in undifferentiated prehospital patients with apparent non-life-threatening conditions.

Methods: This was a large cohort study of undifferentiated prehospital patients aged ≥18 years old who required intravascular accesses during prehospital care from February 3 to June 14, 2020. StatStrip Xpress Lactate Meter analyzed the lactate levels. The primary outcome was the risk of 7-day mortality. Follow-up was 90 days. The categorical secondary outcomes were 30-day and 90-day mortality risks and risks of mechanical ventilation, vasopressor treatment, or acute renal replacement therapy. Other secondary outcomes were the number of days alive within 30 days outside the hospital, outside the intensive care unit, and without mechanical ventilation. The primary analyses were uni- and multivariate logistic regressions presented as odds ratios (OR) with 95% confidence intervals (CI) and p-values.

Results: The study included 11,515 patients. The overall 7-day mortality rate was 3.1%. The 7-day mortality rates were 2.0%, 3.6%, and 12.8% in patients with lactate levels of <2.0mmol/L, 2.0-3.9mmol/L and ≥4.0mmol/L, respectively. The risk of 7-day mortality increased with elevated lactate level, OR = 1.43 (95% CI: 1.36-1.51), p < 0.001. The ORs were similar in all prespecified diagnostic subgroups except for patients receiving diagnoses within the nervous system. Patients with elevated lactate levels had increased risks of all categorical secondary outcomes. They stayed longer in the hospital, in the intensive care unit, and on mechanical ventilation than the patients with normal prehospital lactate levels.

Conclusions: This study found evidence of correlations between elevated lactate levels and poor outcomes in all acute prehospital patients except patients receiving diagnoses within the nervous system. Implementing prehospital lactate measurements is useful if knowledge of the patient's lactate levels adds to existing parameters in the prehospital setting.