Asian Intensive Care: problems & solutions
International Intensive Care conference, Hong Kong, November 28th-30th 2007
Click here for details

The fetus in utero is at risk of hypoxia, acidosis, meconium aspiration, infection and trauma. All fetuses are hypoxic relative to the adult, with a PO₂ of 3-4 Kpa antenatally and 2.5-3 Kpa in labour due to the effect of contractions on placental blood flow.

Labour imposes repetitive stress period on all fetuses. Uterine contractions interrupt uterine blood flow and provoke transient period of hypoxaemia in the fetus.

The normally oxygenated fetus can cope with such stress. However, the fetus with suboptimal oxygenation reacts to the hypoxic stresses by depression of fetal heart rate.

Within the fetal cells, energy production is maintained by aerobic catabolism of glucose. As long as fetal oxygenation is adequate, glucose is fully oxidised to water and carbon dioxide to generate the large amounts of energy required by the fetus. Whenever oxygenation is suboptimal, lactic acid is produced with a drop in pH due to reduction in bicarbonate reserves.

Fetal heart rate monitoring

Cardiotocography

Spontaneous or induced uterine contractions are recorded and the fetal heart rate observed to detect pathological heart rate patterns such as late decelerations, bradycardia or tachycardia with absent variability. This may be an early warning sign of fetal hypoxia and utero-placental insufficiency.

Normal recording shows no change, accelerations, early decelerations or mild variable decelerations.

Continuous electronic fetal heart rate monitoring has not been shown in randomised trials to reduce the overall rates of stillbirth, neonatal death or cerebral palsy but it does appear to detect acidosis reasonably well and halve the incidence of neonatal convulsions. Meta-analysis shows that it does produce a significant reduction in stillbirth attributable to hypoxia.

Fetal movements and biophysical profile

Qualitative assessment of amniotic fluid volume by ultrasound is correlated positively with the fetal outcome.

The profile combines assessment of fetal breathing, fetal tone, gross body movement, amniotic fluid volume and fetal heart rate.

Fetal scalp blood monitoring

The fetal scalp blood sampling values usually fall between those of the umbilical artery and vein i.e. between 7.20-7.25. it is used to determine fetal acid base balance.

If blood gas value indicate a metabolic component, operative delivery is indicated.

Clinical condition at birth as assessed by the Apgar score, correlates poorly with heart rate and fetal blood pH values; factors such as meconium aspiration, infection and trauma are also important and these relate only weakly to hypoxia.

Fetal distress in labour

Causes:

• Intrinsic fetal disease
• placental disease
• cord compression
• maternal disease
• drug administration for analgesia/anaesthesia
• maternal hypotension from supine position, regional anaesthesia or both.

Treatment:

• Change the parturient position to avoid cord compression and relieve supine hypotension
• Administration of oxygen by mask
• Discontinuation of oxytocin

If no improvement

• scalp blood sampling is recommended

If blood gas values indicate a metabolic component, operative delivery is indicated.

Forthcoming BASIC courses: February - London, Kuala Lumpur; March - Hawkes Bay, Sun City; April - Beijing, Brisbane
Click here for details

©Charles Gomersall, March, 2007 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
Copyright policy    Contributors