Where can I find this paper?

http://www.ncbi.nlm.nih.gov/pubmed/23167859

What is this paper about (what is the research question)?

Does an ED measurement of hyperlactataemia (serum lactate ≥ 4.0mmol/L) predict increased risk of organ dysfunction within 24h?

Summary of the Paper

Design: single-centre prospective observational cohort study

Objective: to ascertain whether an ED serum lactate of ≥4.0mmol/L predicts risk of organ dysfunction within 24h in paediatric patients presenting with systemic inflammatory response syndrome (SIRS)

Intervention: point-of-care venous lactate measurement

Primary outcome: organ dysfunction within 24h of triage time, classified following International Paediatric Sepsis Consensus Conference definitions.

Population: convenience sample of patients presenting to ED of tertiary children’s hospital over 1 year (recruitment occurring 17/24h per day)

• Inclusion: patients <19 years old with temperature >38.5 or <36 and HR>2 standard deviations above normal for age, undergoing phlebotomy or CVC access as part of their care
• Exclusion: patients transferred from other institutions, patients with known inborn errors of metabolism, lactate not measured within 15mins of IV therapy initiation.

Results: 239 eligible subjects enrolled (missed eligible rate 36%), of whom 8% were admitted to an intensive care unit.

Mean lactate was 2.0 (+/- 1.2) mmol/L. 8% of subjects had hyperlactataemia. 5% of subjects had organ dysfunction within 24h; 4% of the low lactate population, 22% of the hyperlactataemic population.

Hyperlactataemia had an LR+ of 5.0 (95% CI 1.9-13.0) for organ dysfunction within 24h, sensitivity 31% (95% CI 13-58%), specificity 94% (95% CI 90-96%).

The relative risk of lactate ≥ 4.0mmol/L was 5.5 for 24-hr organ dysfunction

Authors’ Conclusions:

Serum lactate measurement identifies a population at higher risk for severe outcomes than the broader Paediatric ED population with fever and tachycardia and would be a useful addition to clinical assessment in paediatric sepsis clinical and research protocols.

On the study design

As with so many papers, the convenience sampling presents a potential problem in extrapolating this data to our own EDs. While convenience sampling is common, practical and understandable, it does impact the external validity.

To their credit, the authors have been honest about this, giving us a “missed inclusion” rate of 36%. This suggests that greater than 1/3 paediatric patients presenting with two SIRS criteria do so in 29% of the 24h period. We can only imagine how including these patients would affect the results.

The inclusion criteria are interesting too; I would suspect that many more than 239 patients present to an average PED with fever and tachycardia in 12/12 (particularly as we know that the annual attendance is around 80,000). This means that a large number of these patients did NOT have blood tests. This, of course, represents our standard practice (we don’t bleed every child with a temp and tachycardia), but it means we can only really consider the value of lactate measurement in those children whom we already deem to be systemically unwell. It would also be useful to know if a capillary lactate could help to identify those patients for whom we are not sure whether blood tests are necessary.

What were the results and what does this mean?

Despite small numbers, the study was adequately powered by their own calculation. The relative risk of lactate ≥4.0mmol/L for 24-hr organ dysfunction means that patients with an initial lactate above 4.0mmol/L have 5.5 times the risk of 24-hr organ dysfunction as those with a lactate below 4.0mmol/L. They also had 2.2 times the risk of serious bacterial infection, 4.6 times the risk of positive culture and 4.4 times the risk of ICU admission.

The low sensitivity sensitivity (31% (95% CI 13-58%)) tells us that we cannot be reassured by an initial normal lactate (we are unable to use it to “rule out” serious illness), but the specificity is  reasonable at 94% (95% CI 90-96%) – raised lactate should raise our concern. Clinically, a high specificity is more useful to us as arguably it is more important to reliably rule-in serious illness.

What can we take from this paper into clinical practice?

If we are taking bloods in children in the ED because they have signs of SIRS, a venous lactate may help with risk stratification by predicting those more likely to require antibiotics and organ support. It is probably worth taking one if you are taking bloods, but a normal lactate is not reassuring. It is not yet clear how this applies to children about whom we are unsure as to the need for blood tests.

More questions to ask

• How would the results differ if we obtained a venous (or capillary) lactate from  all paediatric patients meeting the two SIRS criteria used in this paper (temperature and heart rate)?
• How would results be affected  if we included children recruited around the clock rather than a convenience sample?

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