Prognostic relevance of serum lactate kinetics should be approached with caution

Abstract

Dear Editor, We read with interest the article recently published by Masyuk et al. in Intensive Care Medicine [1]. By coincidence, we also recently analyzed blood lactate kinetics in our ICU patients. The methodology of lactate measurements in our study and the Masyuk et al. study was largely similar. All consecutive patients treated in our general ICU between 2012 and 2016 were included in the analysis (n = 639). Maximum lactate concentrations on day 1 and day 2 were identified by manual retrieval of medical records (information coming from point of care devices are not entered into our hospital information system). Patients who died or were discharged from the ICU within 24 h following admission, and those with incomplete data on lactate concentrations on day 1, day 2 or both, were excluded (n = 210). Finally, 429 patients were included in the analysis. Lactate concentrations were linked to the hospital database containing detailed information on each patient, including ICU mortality and all-cause mortality during the follow-up period. Due to the retrospective and anonymous nature of the study, the Ethics Committee at the Medical University of Silesia in Katowice waived the need for consent of patients to be enrolled in the study. Among the 429 patients analyzed, there were 192 patients (44.8%) with a lactate concentration above 2.0 mmol/L on day 1 (admission day). ICU mortality in this group was 49.5%. 114 patients (59.4%) were assessed according to the APACHE II on admission with a mean score of 26.5 ± 5.6 points. Cardiovascular system disorder was the principal reason for admission in the majority of patients. Mean lactate concentration on day 1 was 5.3 ± 4.5 mmol/L in survivors and 6.3 ± 7.4 mmol/L in non-survivors (p = 0.295). On day 2, mean lactate concentrations significantly declined in both groups: to 3.2 ± 2.8 mmol/L (p < 0.001) and 3.7 ± 3.0 mmol/L (p < 0.001), respectively. Mean decrease in lactate concentration was 28.5% ± 59.3% in survivors vs 20.4% ± 54.9% in non-survivors (p = 0.228). According to the cutoff proposed by Masyuk et al. 170 of our patients had a Δ24Lac ≤ 19%, while the remaining 22 patients had a Δ24Lac > 19%. ICU mortality was significantly lower in patients with lower Δ24Lac (45.9% vs 77.3%, p = 0.005). Data on long-term mortality were available but were not assessed due to small sample size (only five survivors among patients with Δ24Lac > 19%). The ROC curve was computed, and our optimal cutoff point (Δ24Lac 17.5%) was calculated by means of the Youden’s index (Fig. 1). We would like to comment on these findings. Generally, ICU mortality in our study was higher compared to the study of Masyuk et al. [1]. This was not a surprise since the available data clearly indicate that mortality in Polish intensive care units is high [2], but appropriate for the patient’s condition on ICU admission, assessed with the use of the APACHE II and SAPS III scoring systems [3]. Observation of a better outcome associated with decreasing blood lactate concentrations seems to be consistent throughout published clinical studies [4]. Therefore, our results are not in line with these findings. Additionally, a few serious methodological issues should be discussed. The area under the ROC curve in our study was only 0.55 (95% CI 0.47–0.63) and the cutoff point was 17.5%. *Correspondence: [email protected]; [email protected] 1 Department of Anaesthesiology, Intensive Therapy and Emergency Medicine, Silesian Centre for Heart Diseases, Medical University of Silesia, Curie-Skłodowskiej 9 Str, 41-800 Zabrze, Poland Full author information is available at the end of the article