Identifying traumatic significant haemorrhage is challenging for patient with low and intermediate risk, not when bleeding is obvious

Dear Editor,

We have read with great interest the original article of Griggs et al. on the predictive clinical utility of pre-hospital point of care lactate (P-LACT) for transfusion of blood products in patients with suspected traumatic haemorrhage [1]. Their work has led to the development of an algorithm aiming to identify the need for pre-hospital transfusion. We would like to address a few comments on their work.

Griggs and al consider a major haemorrhage unlikely with a P-LACT < 2.5 mmol/L. However, with a sensitivity of around 80%, almost 20% of their patients have an underestimated risk of Major Haemorrhage as assessed by their algorithm. A negative likelihood ratio of 0.37 is inappropriate to exclude a major haemorrhage as it represents a small decrease of the probability of major haemorrhage. Considering that 50% of the cohort had a P-LACT < 2.5 mmol/L, the conclusion should probably be: “Low probability of Major Haemorrhage” instead of “Major Haemorrhage unlikely”.

Given the high specificity and positive likelihood ratio of P-LACT > 6 mmol/L, it seems reasonable to conclude that pre-hospital transfusion needs to be considered. However, the proportion of patients representing this range of P-LACT is lacking to allow the reader judge the pertinence of the decision support tool. As we suspected that patients with P-LACT > 6 mmol/l are very few, the challenge for pre-hospital clinician is to identify major haemorrhage among patients with a P-LACT between 2.5 and 6 for whom P-LACT seems useless. We believe that the use of P-LACT in addition to clinical prehospital score might be useful and allows to improve clinical decision-making in the possible major haemorrhage group.

Furthermore, Griggs et al.. assessed the prediction of P-LACT on the in-hospital transfusion (requirement or continuation). As clinicians were not blinded from the P-LACT result, there is a high risk of circularity and false prediction. Patients with high P-LACT were probably more transfused in-hospital independently of their risk of death from bleeding. Recently, Costa et al. showed that clinical scores predicting massive transfusion were weak to predict life-threatening bleeding represented by early death and haemorrhagic death [2]. The assessment of P-LACT predicting early death within 24 h might be considered to avoid this bias.