Fetal monitoring is a recurring theme in perinatal morbidity and mortality reports,
highlighting the limitations of cardiotocography and current adjunctive technologies,
such as fetal blood sampling (FBS). There is an unmet need for more robust methods
of intrapartum fetal assessment. Microdialysis may help to detect babies at risk of
hypoxia by monitoring trends in lactate and related metabolites from fetal scalp
interstitial fluid in a minimally invasive manner. However, its clinical value remains
unproven because there is limited evidence on the relationship between interstitial and
arterial lactate. Translating advances in fetal monitoring technology into improved
clinical outcomes also depends on how obstetricians use such technology in their
practice, which few past studies have explored in depth.
This research comprised two components. The first part aimed (1) to develop a
neonatal piglet model of hyperlactataemia; and, using this model, (2) to investigate the
relationship between interstitial and arterial lactate; and (3) to explore the feasibility of
using subcutaneous microdialysis to monitor the metabolic response to hypoxia in vivo.
Eight neonatal piglets were monitored under non-recovery general anaesthesia.
Hyperlactataemia was achieved by means of alveolar hypoxia and/or intravenous
sodium L-lactate infusion, with target lactate concentrations above 12 mmol/L.
Microdialysate from two subcutaneous microdialysis catheters inserted into the scalp
of each piglet was analysed for interstitial lactate, pyruvate, glucose and glutamate
concentrations, which were compared to arterial blood gas measurements. A subset
of dialysate samples underwent secondary analyses with the StatStrip Xpress® pointof-
care lactate meter to assess its performance.
In total, 432 dialysate samples were collected from seven piglets. There was variation
in the piglets’ response to hypoxia therefore two piglets received lactate infusions, with
four overall achieving target hyperlactataemia. Interstitial lactate, pyruvate and glucose
concentrations were not affected by microdialysis catheter insertion. There was a
strong positive correlation between arterial lactate and interstitial lactate, and weaker
positive correlations with interstitial lactate-to-pyruvate and lactate-to-glucose ratios.
Interstitial lactate mirrored trends in arterial lactate with an approximate time lag of 10
v
to 20 min, although the closeness of agreement varied between piglets. StatStrip
Xpress® lactate values showed a proportional negative bias relative to the reference
microdialysis analyser, but trend data and assay precision were comparable.
The second part of this research sought to understand how UK obstetricians use
adjunctive fetal monitoring technologies and what factors influence their practice, as
well as exploring attitudes towards new technology and other areas for improving
practice. Data were collected through semi-structured telephone interviews with 16
obstetricians of varying career grade from nine maternity units across the UK, prior to
thematic analysis. Most obstetricians reported performing FBS but attitudes towards it
varied. The use of fetal monitoring technology was influenced by obstetricians’
individual clinical autonomy, the socio-cultural norms of their unit, and wider external
factors, such as guidelines. Obstetricians recognised the limitations of current methods
of monitoring, but enthusiasm towards new technology was checked by a scepticism
of ‘computerisation’ and perceived barriers to changing practice; hence, better staff
training was seen as the immediate priority for improving outcomes.
In summary, the work presented in this thesis provides new insight into the current role
of adjunctive technologies in UK obstetric practice and demonstrates proof of concept
for subcutaneous microdialysis as a novel approach to monitoring metabolic wellbeing
in the fetus and neonate. Although interstitial lactate reflected trends in arterial lactate
in response to hypoxia and lactate infusion in neonatal piglets, further research is
required to fully characterise this relationship, including standardisation of the
hyperlactataemia model described here.
This research has also identified a range of individual and contextual factors that
influence how obstetricians use fetal monitoring technology and highlights the urgent
need for future qualitative studies to improve understanding of this complex process,
alongside efforts to develop new technology
