Indications for Uterine Relaxation:
Uterine relaxation may be required if there is:
1. an obstruction to an after-coming shoulders or head during assisted breech delivery (Figure 14.1),
2. a placenta retained within the uterus which needs to be removed manually,
3. a uterine constriction ring which has to be relieved,
4. a transverse-lying second twin who needs to be operatively delivered, and
5. an inverted uterus that requires correction.
Techniques Available:
If adequate analgesia in the form of epidural or other major regional block (subarachnoid, caudal, combined-spinal-epidural) is already present and uterine relaxation is required, this can be achieved using:
1. minibolus intravenous nitroglycerine (GTN/NTG), (Chapter 52).
2. inhalational agent (eg. isoflurane, enflurane, halothane) (1),
3. beta-adrenergic agonists (salbutamol, ritodrine, terbutaline), or
4. amyl nitrate.
Precautions:
a.Hypovolaemia
1. The parturient must be euvolaemic before the GTN or the inhalational agent is administered.
2. If there is significant blood loss or hypovolaemia this should be treated aggressively with colloid or crystalloid as appropriate before uterine relaxation is undertaken.
3. While hypotension is uncommon in euvolaemic patients, if it ensues, the blood pressure fall should be treated aggressively with volume expansion and pressor agent (eg. incremental doses of ephedrine 3mg/ml) as appropriate.
b. Loss of laryngeal protective reflexes
1.Inhalational agents must be titrated carefully to effect without rendering the mother unconscious.
2. Care must be exercised where other agents (narcotics, tranquillisers, ketamine, N20), which may obtund pharyngo-laryngeal reflexes, are already in use. In these situations, manoeuvres aimed at securing the airway (eg. rapid sequence induction and intubation) may need to take precedence over the uterine relaxation.
c. Heart Disease
In patients with severe valvular heart disease or cardiomyopathy the use of minibolus GTN, tocolytic beta-agonist or inhalational agent may be deleterious and the therapeutic benefit must be weighed against the potential risk (2).
d.Monitoring
1. Maternal systemic arterial pressure should be monitored frequently or continuously.
2. Maternal electrocardiogram and/or Sa02 (oximetry) should be displayed continuously when appropriate.
3. If the uterine relaxation is required antepartum, fetal heart rate monitoring may be necessary.
References:
1. Marx G, Kim Y, Lin C, Halvey S, Schulman H. Postpartum Uterine Pressures under Halothane or Enflurane Anesthesia. Obstet Gynecol 51:695, 1978.
2. Benedetti T. Maternal Complications of Parenteral Beta-sympathomimetic Therapy for Premature Labor. Am J Ob Gyn 145:1-6, 1983.