Article Text

Lactate and anion gap in asphyxiated neonates
  1. D ORIOT,
  2. A NASIMI,
  4. S MARLIN,
  5. A HUBERT,
  1. Neonatal Intensive Care Unit
  2. Univeristy Hospital of Poitiers
  3. France F-86000

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    Editor—We read with interest the article by Deshpande about blood lactate and acid base status in neonates. We agree with the authors about the lack of correlation between blood pH and lactate. Nevertheless, in a retrospective study we found that the anion gap [(Na+K) - (Cl+HCO3)] was a reliable marker, and correlated well with blood lactate for at least 36 hours.

    From January 1990 until December 1992, 155 asphyxiated neonates were admitted after acute fetal distress. All were mechanically ventilated and none had received bicarbonate. Mean gestational age was 36 weeks (range 26–42), (57% preterm; 20% small for gestational age). Sixteen per cent died and 12% had an abnormal neurological examination on discharge. We measured: umbilical arterial pH at birth and arterial pH, bicarbonate, anion gap and lactate at time 1 (T1) (mean 4 hours after birth), and in the sickest, at T2 (mean 14 hours) and T3 (mean 37 hours). We used the Spearman Rank test for correlations.

    Lactate correlated with the anion gap throughout, but not with arterial pH. There was a decreasing correlation with bicarbonate over time (table 1). Umbilical pH correlated with lactate at T1 (p=0.0041). The blood lactate concentration at T1 did not seem to influence mortality or morbidity. Interestingly, an anion gap above 20 mmol/l at T1 was associated with an increased neonatal mortality (19% vs9%) and neurological abnormalities detected on discharge (18%vs 4%). Nevertheless, the positive predictive values (PPV) of death at T1 was very poor: 20% for lactate > 2 mmol/l, and 13% for anion gap > 20 mmol/l. The negative predictive values were, respectively, 70% and 63%. The best PPV was obtained by either lactate > 2 mmol/l or anion gap > 20 mmol/l, associated with an Apgar score < 4 at l and 5 minutes (66% in both cases).

    Table 1

    Correlation (Spearman test) between blood lactate values and anion gap, arterial pH and bicarbonate at Tl (4 hours), T2 (14 hours) and T3 (37 hours)

    Metabolic acidosis is a marker of birth asphyxia,2 but is poorly correlated with outcome.3 To our knowledge, correlation of blood lactate with the anion gap has not been studied before in neonates. Although lactate was not correlated with anion gap in adults,4 we speculate that the excretion of lactate in case of lactacidemia5 might be immature in neonates, then avoiding the reabsorption of chloride.

    Our results suggest that the anion gap is a useful and easily performed biological reflection of neonatal asphyxia.


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