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.