Learning objectives
- Definition and causes of fetal distress
- Fetal monitoring
- Treatment and anesthetic management of fetal distress
Definition and mechanisms
- Fetal distress is a broad terminology to define a compromised fetus due to hypoxia
- Subclassification of fetal distress are:
- Fetal asphyxia: a non-reassuring fetal status due to a diminished but persisting gas exchange
- Fetal anoxia: complete cessation of gas exchange, which can be lethal in less than ten minutes
Causes of asphyxia
- Inadequate perfusion on the maternal side
- Maternal hypotension
- Aortocaval compression
- Interruption of gas exchange across the placenta
- Interruption of umbilical blood flow
- Cord compression
- Transient intermittent hypoxia caused by uterine contractions of normal labor
Fetal monitoring
- Fetal monitoring aids in detecting fetal distress through alterations in the fetal heart rate or scalp blood gases
- Modalities of fetal monitoring are:
- External heart rate monitoring
- Ultrasound scanning
- Doppler ultrasound
- Cardiotocography
- Internal heart rate monitoring
- Fetal scalp electrodes
- Fetal acid-base status
- External heart rate monitoring
- Fetal heart rate, baseline variability, and decelerations are used to assess characteristic and pattern changes in the fetal heart rate
- The normal fetal heart rate is between 110 and 160 beats per minute
- Persistent fetal tachycardia and bradycardia can be associated with fetal hypoxia, however, fetal bradycardia is the most common cause
- Possible causes of tachycardia are fever, chorioamnionitis, anticholinergic agents, beta-sympathomimetics, or fetal anemia
- Possible causes of bradycardia are congenital heart block or beta-adrenergic blocking agents
- Early decelerations occur simultaneously with uterine contractions and usually are less than 20 bpm below the baseline
- Early decelerations are not ominous
- Late decelerations begin 10 to 30 seconds after the beginning of a uterine contraction and end 10-30 seconds after the end of the uterine contraction
- Late decelerations represent a response to hypoxia
- The normal fetal heart rate is between 110 and 160 beats per minute
- Fetal acid-base status can be obtained from the scalp
- It is used to exclude or confirm fetal acidosis
- A pH of 7.2 is considered abnormal and urgent delivery should be arranged
- Relative contra-indications for fetal scalp blood pH sampling are intact membranes, infections (HIV, herpes, herpes simplex), and fetal coagulopathy
Signs of fetal distress
- A Nonreasurring fetal heart rate pattern
- Repetitive late decelerations
- Loss of fetal beat-to-beat variability
- Sustained fetal heart rate < 80/min
- Fetal scalp pH < 7.0
- Meconium-stained amniotic fluid
- Intrauterine growth restriction
Anesthetic management
- 4 categories were defined to classify an emergency caesarean section:
| Category | Risk to mother and/ or baby | Indication | Target time for decision to delivery interval (DDI) |
|---|---|---|---|
| 1. Emergency | An immediate threat to life | An immediate threat to the life of the woman or fetus (e.g. severe foetal bradycardia, cord prolapse, uterine rupture, foetal blood sample pH ≤7.2) | ≤30 minutes |
| 2. Urgent | Maternal or fetal compromise | No immediate threat to life of woman or baby (e.g. APH, failure to progress) | ≤75 minutes |
| 3. Scheduled | Time for procedure to be scheduled | Requires early delivery (e.g. intrauterine growth retardation, failed induction of labor) | In the interests of mother and baby |
| 4. Elective (Management see above) | No maternal or fetal compromise | At a time to suit the woman and maternity services (breech, previous CD) | Usually after 39 weeks of gestation if possible |
- General anesthesia is the preferred anesthetic technique for life-threatening conditions (category 1) unless epidural anesthesia can be established by using a pre-existing epidural catheter
- Regional anesthesia is preferred if there is an urgent but non-life-threatening condition (category 2-4)
- See also caesarean delivery
Suggested reading
- Morgan and Mikhail’s clinical anesthesiology (2022). McGraw Hill Medical. Chapter 41.
- Caesarean birth NICE guidelines (2021). Available at: https://www.nice.org.uk/guidance/ng192.
- Omotayo, Rotimi & Akinsowon, OR & Bello, EO & Olumide, Akadiri & Akintan, AL & Omotayo, SE. (2019). Fetal distress, options of anesthesia, and immediate postdelivery outcome at state specialist hospital Akure. Tropical Journal of Obstetrics and Gynaecology. 36. 424.
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