18.2 Obstetric anaesthesia

Anaesthesia is often the most dangerous part of a difficult delivery. In most district hospitals general anaesthesia is best avoided in obstetrics, except for Caesarean section, when the patient is bleeding, or is already hypovolaemic, or is very ill. It should be expert, and she must be intubated. It is dangerous in the circumstances of most labour wards, and the theatre may take dangerously long to get ready.

Most Caesarean sections can be done under subarachnoid (spinal) anaesthesia, provided you take the necessary precautions (A 16.6). You can also use local anaesthesia (A 6.9). For a vacuum extraction and outlet forceps, use a pudendal block, with local infiltration anaesthesia for the episiotomy. For a destructive operation, other than a transverse lie, use a pudendal block combined with intravenous pethidine and diazepam (A 8.8). For a transverse lie, she must have a general anaesthetic. For manual removal of the placenta, use intravenous pethidine and diazepam. Epidural anasthesia is excellent, but is probably impractical, except in specialized well-staffed obstetric units. The routine aseptic prcedures in your wards may not be reliable enough to justify its routine use, and you will probably not have the staff to monitor it.

LOCAL ANAESTHESIA FOR AN OPERATIVE VAGINAL DELIVERY

Primary Anaesthesia describes transvaginal pudendal block, but not the alternative perineal pudendal block, nor any method of local infiltration. These are described here. Use a total of 50 ml of 0.5% lignocaine or 1% procaine, both with adrenalin (A 5-1).

Transvaginal pudendal block: see Section A 6.13.

Perineal pudendal block: raise a skin wheal half way between the patient’s vaginal opening and her ischial tuberosities, as in C, Fig. 18-1. Use a 12 cm1 mm needle to reach her ischial spines. Inject about 12.5 ml of solution on each side.

Local infiltration anaesthesia is needed to supplement a pudendal block for most operative vaginal deliveries. For a low forceps delivery or episiotomy local infiltration alone may be enough. Keep the needle moving while you inject 25 ml of solution.

Figure 18.1: LOCAL ANAESTHESIA FOR AN OPERATIVE VAGINAL DELIVRY. A, feeling for a patient’s ischial spine for a transvaginal pudendal block. B, injecting for a transvaginal pudendal block. C, the injection site for doing a pudendal block through her perineal skin. D, local anaesthesia after a pudendal block. E, local infiltration alone from a single central puncture site.1, her ischial spine. 2, her ischial tuberosity. 3, the site of injection for pudendal block through her perineum and for local infiltration anaesthesia after a pudendal block. After Howie, Beryl. ’High Risk Obstetrics’ Fig. 14-6 and 14-7. Macmillan Publishers, with kind permission.

After a perineal pudendal block, use the same needle to puncture and infiltrate, as in D, 18-1. After a transvaginal one make fresh punctures.

For local infiltration alone, inject radially from a single central puncture site (E). CAUTION! (1) Premedicate her with pethidine and diazepam. (2) Distinguish her ischial spines from her ischial tuberosities. (3) ALWAYS withdraw the plunger before you inject. If you withdraw blood, move the needle, or you will inject the anaesthetic solution intravenously. (4) Give the anaesthetic enough time to act (at least 3 minutes).