Capillary lactate as a tool for the triage nurse among patients with SIRS at emergency department presentation: a preliminary report

The main result of this study is that a high capillary lactate concentration measured by the triage nurse at ED presentation among patients with clinical criteria of SIRS is associated with a high risk of death. This study reinforces the role of the triage nurse.

To the best of our knowledge, this is the largest study evaluating the prognostic value of capillary lactate concentration at ED presentation in terms of the number of patients included. Only one study has specifically studied the prognostic value of capillary lactate at ED admission. Seoane et al., in their prospective study of 79 patients with critical illness, identified that a capillary lactate concentration of >2.35 mmol.L⁻¹ was associated with mortality [20]. In the present study, we identified a cutoff of 3.6 mmol.L⁻¹ that best predicted 28-day mortality (OR = 3.8 [1.6 to .1], p = 0.003). This cutoff is close to the cutoff of 4 mmol.L⁻¹ recommended to identify patients with severe sepsis [2].

Measuring capillary lactate concentration may help to identify patients with altered microcirculation. Indeed, in our study, 90% of patients presented to the ED without hypotension but with increased capillary lactate concentration. Among the variables collected by the triage nurse, we found that the capillary refilling time was associated with 28-day mortality, with an optimal cutoff of 2 s (OR = 18.9 [5.4 to 66.7], p < 0.0001). However, only 8% of patients had a capillary refilling time >2 s. Intuitively, one could imagine that an elevated capillary refilling time provides the same information as the presence of mottling or increased lactate concentration. However, interestingly, presence of mottling, capillary lactate concentration >3.6 mmol.L⁻¹, and capillary refilling time >2 s were independent of each other for the identification of 28-day non-survivors.

A score integrating capillary lactate concentration with a cutoff of 3.6 mmol.L⁻¹, and presence or absence of mottling, appears to be a useful tool for determining severity of disease in these patients. Mortality at 28 days was 6%, 19%, and 67% among patients with a score 0, 1, or 2, respectively (p < 0.0001). This nurse hypoperfusion score presents several advantages.

Firstly, it can be calculated by a nurse and not necessarily by a doctor. Secondly, it can be obtained immediately at patient presentation, avoiding the time delay engendered by admission procedures, arterial or venous blood puncture, and the time required for laboratory analyses. Indeed, it has been demonstrated that the time required for capillary lactate assessment was significantly shorter than that needed for arterial or venous lactate assessment [20]. Thirdly, this score does not take into account variables that are clearly associated with patient’s severity. Indeed, coma, hypotension, or acute respiratory failure are clinically obvious, and these patients are immediately oriented towards a medical doctor. On the contrary, our score takes into account variables that could reflect occult tissue hypoperfusion, even in patients with normal vital signs. Indeed, the score was strongly associated with 28-day mortality, even after restricting the analysis to patients presenting to the ED without hypotension (Table 5). Analysis of the patient’s characteristics at ED presentation according to the three classes of the score showed that the median systolic or mean arterial pressure, the median SaO₂, and the median Glasgow Coma Score were all within normal range (Table 6). Since all the patients had clinical criteria of SIRS, it can be observed that median heart and ventilatory rates were increased. Furthermore, a recent study showed that some patients do not have increased plasma lactate concentration despite an unfavorable outcome including vasopressor-dependant septic shock [22]. There is thus a likely benefit to be gained from using such a composite score that integrates both capillary lactate dosage and clinical signs of hypoperfusion. Although promising, these results are preliminary, in view of the sample size. The utility of such a score needs to be evaluated prospectively in a large cohort of patients.

The MEDS score is the most validated prognostic score among patients admitted to the ED with sepsis or SIRS [7,8,23]. Its calculation requires the intervention of a medical doctor for the evaluation of fatal disease and diagnoses of pneumonia and septic shock, and it is also necessary to wait for the results of biological analyses for leucocyte and platelet counts. Therefore, the MEDS score cannot be calculated by a nurse and cannot be calculated immediately at patient presentation. Two findings of the present study deserve to be underlined. Firstly, the AUC for our microcirculatory dysfunction score was similar to the AUC of the MEDS score for predicting 28-day mortality (0.75 and 0.79, respectively), suggesting that our score is efficient for discriminating the most severe patients. Secondly, multiple logistic regression analysis showed that the two scores were independent of each other for the prediction of 28-day mortality, suggesting that they give different information regarding prognosis (AUC of the global model 0.87). Finally, these two scores could be complementary, with one performed by the triage nurse at patient presentation and the second calculated by the doctor after admission and evaluation of the patient.

Improving patient triage is a matter of importance, in particular, in case of high affluence to the ED, a situation where there is a risk of underestimating severity due to lack of time and means. In this setting, reinforcing the role and the performance of the triage nurse may help the medical doctor to allocate the appropriate care to the patients. In the present study, the nurse did not inform the medical doctor of capillary lactate concentration. However, the score calculated by the triage nurse at presentation was associated with care intensity in the ED. It remains to be evaluated whether taking the results of the nurse hypoperfusion score into account might improve the patient’s prognosis. For example, patients presenting to the ED with a score of 0, with an expected 28-day mortality risk of 6%, could be oriented to usual care. On the contrary, those with a score of 1 or 2, with an expected 28-day mortality risk ranging between 19% and 67%, should be immediately evaluated by an intensive care specialist and oriented towards an ICU. By avoiding delay in the first precious hours of care, for example, the golden hour for initiation of antibiotic therapy, such a strategy could considerably improve the prognosis of patients presenting to the ED.

This study has several limitations. First, this was a monocentric study. It is necessary to evaluate the interest and limits of the nurse hypoperfusion score in a large multicentric study, and in particular, to compare it with the MEDS score. Second, during the study period, consecutive patients presenting to the ED were not all included. Indeed, triage nurses who did not participate to the short educational program did not participate to the study. Third, arterial or venous lactate concentration was not measured in all patients, and therefore, a correlation between capillary and plasma lactate concentration was not available. However, a recent study has found a good correlation between capillary and plasma lactate concentrations [20].