Use of Lactate Pro2 for measurement of fetal scalp blood lactate during labor - proposing new cutoffs for normality, preacidemia and acidemia: a cross-sectional study

OBJECTIVE: Measurement of fetal scalp blood lactate is a supplementary tool to cardiotocography in the case of a non-reassuring tracing. Several hand-held lactate meters have been launched, all with differentials in absolute values. Therefore, the reference intervals must be calculated for each device. The internationally accepted reference interval is based on measurement with Lactate ProTM with recently got out of production. The aim of this study was to propose cutoffs for normality, preacidemia, and acidemia in fetal scalp blood for Lactate ProTM2 based on the comparison of lactate values measured with Lactate ProTM and Lactate ProTM2.

DESIGN: Seven hundred one fetal scalp blood samples were analyzed simultaneously. The conversion equations were retrieved from the linear regression model. On the basis of the cutoffs for Lactate ProTM cutoffs for Lactate ProTM2 were calculated.

RESULTS: The conversion equations obtained were Lactate ProTM = -0.02 + 0.68 × Lactate ProTM2 (SD: -0.09-0.07 × Lactate ProTM2) and Lactate proTM2 (LP2) = 0.03 + 1.48 × Lactate ProTM (SD: 0.16 + 0.17 × Lactate ProTM). The correlation to umbilical arterial pH was identical for the two devices (r = -0.18), whereas the correlation to umbilical arterial lactate was better for Lactate ProTM than for Lactate ProTM2 (r = 0.38, respectively, r = 0.33). The correlation to umbilical arterial lactate was dependent on time from sampling to delivery.

CONCLUSION: Proposed reference values for Lactate ProTM2: scalp lactate <6.3 mmol/L = normal, no indication for intervention; 6.3-7.1 mmol/L = preacidemia, repeated testing has to be considered; > 7.1 mmol/L = acidemia, expedite delivery.