ASSOCIATION BETWEEN BLOOD LACTATE AND ACID-BASE STATUS AND MORTALITY IN VENTILATED BABIES

Aim-To investigate the relation between common acid-base parameters an d blood lactate concentrations and their prognostic importance in sick , ventilated neonates. Methods-Two hundred and seventy eight serial si multaneous measurements of arterial acid-base status and blood lactate concentrations were carried out in 75 mechanically ventilated neonate s with indwelling arterial catheters (gestational age and birthweight, median (range) - 29 (23-40) weeks, and 1340 (550-4080) g, respectivel y). Results-There were no correlations between arterial blood lactate and pH and base excess within subjects (r=0.07 and r= -0.06, respectiv ely) and only weakly positive but clinically irrelevant positive corre lations between subjects (r=0.28 and r=0.27) in this group. Even in th ose infants who had not received any bicarbonate before their initial measurements (n=48), there were no correlations between initial blood lactate concentrations and pH (r=0.27), base excess (r=0.17), or serum bicarbonate concentrations (r=-0.18). There was no relation between p eak lactate concentration (PLC) and base excess (r=0.16), and only a w eak correlation between peak lactate concentration (PLC) and pH (r=0.2 8). Negative base excess was an insensitive indicator of raised lactat e concentrations. Only two out of 33 (6%) instances of hyperlactataemi a (lactate >2.5 mmol/l) would have been identified with a base excess <-10 mmol/l as a cutoff. Lower cutoff values of base excess or pH perf ormed no better. Raised lactate concentrations were associated with in creased mortality at all levels. While six of 53 (11%) infants with a PLC <2.5 mmol/l died, this proportion increased to four of 15 (27%) wi th a PLC between 2.5-5.0 mmol/l, and four of seven (57%) with a PLC >5 .0 mmol/l. Infants showing little rise or a substantial fall in blood lactate fared better than those with persistently raised values. A cli nically important increase in blood lactate preceded the development o f clinical markers of deterioration and complications in six infants. Conclusions-Contrary to popular belief, pH or base excess cannot be us ed as proxy measures for blood lactate concentration, and independent measurements of the latter are needed. Blood lactate concentrations ma y provide an early warning signal and important prognostic information in ill, ventilated neonates. In this regard, serial measurements of b lood lactate are more useful than a single value.