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Arterial versus venous lactate – a pediatric study
Summarized from Samaraweera S, Gibbons B, Gour A et al. Arterial versus venous lactate: a measure of sepsis in children. Eur J Pediatr 2017; 176:1055-60
As a blood marker of tissue hypoxia, lactate is frequently measured to assess and monitor acutely and critically ill patients. The gold standard sample for lactate measurement is arterial blood, but since this is often difficult to obtain, there is ongoing interest in investigating the validity of using venous rather than arterial blood.
Clearly, if there is acceptably close agreement between arterial and venous lactate concentration, it is immaterial which sample is used. A number of studies have addressed this issue but these have for the most part focused on adult patients. The focus of this most recently published study is critically ill children with sepsis.
Investigators working at a UK pediatric intensive care unit retrospectively identified all 220 babies, infants or children who had been admitted to their unit with sepsis (either sepsis, neutropenic sepsis or septic shock) during a 3-year period. Interrogation of these patients’ records revealed that for 60 of the 220 patients lactate had been measured on both arterial and venous blood.
In each case the two samples were obtained within an hour of each other. These 60 paired venous and arterial lactate results were extracted for statistical analysis to determine the level of agreement.
Median venous-blood lactate was 1.9 mmol/L (interquartile range 1.4 to 4.7 mmol/L) and median arterial-blood lactate was 1.6 mmol/L (interquartile range 1.1 to 3.2 mmol/L). Bland-Altman plot analysis revealed that the overall mean difference between the paired results (venous – arterial) was 0.77 mmol/L and the overall 95 % limits of agreement were wide (–1.2 mmol/L to +2.7 mmol/L), indicating poor agreement. However, visual examination of the Bland-Altman plot clearly shows much lower mean difference and much narrower (better) level of agreement for values <2.0 mmol/L.
The authors of this study were able to conclude that a venous-blood lactate <2.0 mmol/L (i.e. essentially a normal result) is a reliable indicator of arterial lactate. However, they find increasingly less agreement between arterial and venous lactate as levels rise above 2.0 mmol/L. If venous blood lactate is found to be greater than 2.0 mmol/L, the authors recommend that arterial blood be sampled to confirm lactate value.
In discussion of their study the authors highlight other adult studies with similar results and conclusions. They also speculate that the disparity between venous and arterial lactate at higher concentration is to be expected in the light of the reduced peripheral diffusion (hemodynamic compromise) associated with worsening sepsis.
This study contributes to a growing body of evidence that venous blood is a suitable sample for lactate measurement so long as lactate is within normal limits but does not accurately reflect arterial lactate at higher, abnormal values.
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