Introduction
The aim of intrapartum fetal surveillance is to ensure fetal wellbeing. Cardiotocography (CTG), the most recognized method, has a low positive predictive value so a secondary tool is often needed to detect those fetuses who are at risk for hypoxia (1–4). Point of care measurement of scalp lactate is recognized as a such a tool. Analysis of fetal scalp blood by a standardized method was initially with a suggested reference interval for pH, published by Saling et al. in the 1960s (5). Later, in the 1990s a Swedish research team proposed cut-offs for lactate measured by the POC LactateProTM (LP), Arkray, Japan (6,7). The advantages of analysing lactate include discrimination between respiratory and metabolic acidosis, bedside analysis with the result available in 60 seconds, and reduced failure rate from over 16% to approximately 1% (1,8). Two randomized trials comparing pH and lactate analysis revealed no significant differences in neonatal outcomes (8,9).
POC-lactate-meters were originally designed for physical performance assessment in professional athletes. There are several lactate-meters on the market, of which only StatstripLactate® and StatStripXpress® (SSLX) Lactate system, Nova Biomedical, US, are exclusively designed for hospital use. They are equally calibrated but the StatstripLactate meter has the advantage of being able to transfer data in real time to an electronic medical record system. The performance and accuracy in fetal and adult blood for several POC lactate meters have been published, with SSLX performing with better accuracy and agreement to the stationary blood gas machines (6,10–14). It is important to recognize that lactate values vary depending on the POC-lactate-meter used (1,6). Since the production of LP has ceased, there is an urgent need for evaluation of a new POC-lactate-meter, with assessment of a safe interventional cut-off for fetal acidosis. Various interventional cut-offs for SSLX have been suggested. However, all are based on a small number of participants and on conversion equations from the existing accepted cut-offs of LP or pH and not on neonatal outcome (12–14).
The aim of this study was to establish a clinically useful cut-off for fetal scalp blood lactate measured by SSLX when used as a second line tool to CTG in intrapartum fetal surveillance, based on neonatal outcome.