Preparation. Caesarean sections are frequently performed as emergencies in unprepared patients. The procedure may be complicated by an unfasted patient, fetal distress, severe haemorrhage, pre-eclampsia etc. Prepare and check equipment for obstetric anesthesia in advance, so that your apparatus and drugs are immediately to hand. This saves valuable time in an urgent case. Particular attention should be paid to the function of the laryngoscopes, the endotracheal tube and cuff, and the suction apparatus. As intubation may be difficult, it is a wise precaution to have an introducer and a smaller size of endotracheal tube ready. A trained assistant must be available at induction.

A relevant anaesthetic history is obtained from the patient and clinical examination carried out paying particular attention to the cardiovascular and respiratory systems. Any likely intubation problems should be identified. The blood pressure is measured and the haemoglobin result checked. It should be confirmed that blood has been sent for crossmatch and will be available for emergency transfusion if required.

The patient should be pre-oxygenated with 100% oxygen via a close fitting face mask for 3 minutes before induction. Thlopentone 3-5mg/kg or ketamine 2mg/kg is then injected, followed by suxamethonlum 1.5mg/kg. Cricoid pressure is applied by the assistant as consciousness is lost and must be maintained until the anaesthetist is satisfied that the airway is secure. When the patient is fully relaxed intubation is performed. The lungs are not normally inflated by face mask prior to intubation as this may force gas into the stomach, raise the intragastric pressure and promote regurgitation. Only when the anaesthetist has confirmed the placement of the endotracheal tube and the cuff has been inflated is cricoid pressure released. If intubation cannot be performed, however, facemask ventilation will be necessary to maintain oxygenation. This situation is termed "failed intubation". Always have a plan available in case this happens -a suitable plan is discussed at the end of this article.
 
Maintenance of anaesthesia.

Anaesthesia can be maintained with a 50% mixture of nitrous oxide and oxygen, supplemented with a low concentration of a volatile agent in order to avoid the possibility of awareness. Halothane 0.5% is suitable. High concentrations of volatile agents should be avoided as they may decrease uterine tone increasing bleeding at operation and they may depress the neonate.

Further relaxation can be achieved by increments of suxamethonium (remember to give atropine before a second dose of suxamethonium) or the use of a non-depolarising relaxant. Most non-depolarising relaxants do not cross the placenta to any great extent, except gallamine which should be avoided until after the cord is clamped. After delivery oxytocin 10 units or ergometrine 500 micrograms is injected intravenously to contract the uterus. Ergometrine should be avoided in the presence of hypertension as it causes a rise in blood pressure. Once the umbilical cord is clamped an opioid such as morphine (5-15mg) can safely be given slowly intravenously. At this point the inspired oxygen concentration can be reduced to 30-35%.

In situations where no nitrous oxide is available an increased concentration of halothane (around 1%) should be given in oxygen until delivery. After the cord has been clamped an intravenous opioid should be administered and the concentration of halothane reduced to minimise relaxation of the uterus.

In many places diethyl ether is the main anaesthetic agent available, and it is also suitable for caesarean section. The patient may be paralysed and ventilated with a mixture of air, oxygen and 2-3% ether. Where muscle relaxants are in short supply many anaesthetists allow the patient to breathe air, oxygen and ether spontaneously following intubation. 4-6% ether is required for this purpose, although a higher concentration is needed initially until the patient is settled. If a spontaneously breathing technique is used it is wise to assist ventilation to improve the efficiency of respiration.

At the conclusion of surgery muscle relaxation is reversed, (or in the case of suxamethonium allowed to wear off), and the patient turned on to her left side in the head down position. The endotracheal tube is removed only when laryngeal reflexes have returned and spontaneous respiration has resumed. Oxygen is administered by face mask for at least 30 minutes following surgery, during which time the patient should remain on her side. The intravenous infusion is continued into the post-operative period to ensure adequate hydration and to retain venous access. Analgesia is prescribed, usually in the form of an opiate such as morphine or pethidine.
 
In extremely difficult circumstances.

In some countries there are many anaesthetists working without oxygen or endotracheal tubes. However they are still faced with the challenge of providing anaesthesia for caesarean sections. People working in these difficult environments recommend the use of local infiltration anaesthesia or regional block (both of which will be covered in a future edition). Some anaesthetists attest to the use of ketamine by intravenous bolus injections, and others administer ether via a facemask. It is likely that techniques using local anaesthesia are the safest, providing proper precautions are taken, and the anaesthetists and surgeons are skilled in their use. Although several of these techniques are unconventional, careful attention to basic anaesthetic principles, such as airway care, monitoring of the colour and circulation, will ensure the safest anaesthetic available under the circumstances.
 
Failed intubation drill.

A clear plan must be available in the event of failed intubation. There is a serious risk of hypoxia if the situation is mishandled. An appropriate course of action is as follows:

1. Maintain cricoid pressure.

2. Oxygenate using the facemask.

3. Turn the patient on to the left side into a head down position and allow her to wake up. Proceed with local anaesthetic block when the patient has regained consciousness.

4. If the operation is needed very urgently (eg for fetal distress or an antepartum haemorrhage), re-establish spontaneous respiration after the suxamethonlum has worn off, and continue the anaesthetic under a facemask using nitrous oxide, oxygen and halothane or an ether based technique. If possible maintain cricold pressure during the anaesthetic. If problems are encountered with the airway, it may be necessary to wake the patient up and use a regional technique.

5. At all times ensure that the patient is well oxygenated.

If available a laryngeal mask may be useful for maintaining the airway in the event of a failed intubation. If severe airway obstruction develops during a failed intubation and none of the usual airway manoeuvers regains the airway, a cricothyroidotomy should be performed using a large intravenous cannula (at least 16 gauge). This should be connected to the anaesthetic circuit (use a Portex 3.5mm connector or other similar connector) and 100% oxygen delivered directly into the trachea, until the patient wakes up. This equipment should always be available for this event.

This article contained links to the following additional information:

Figures 2 & 3 - Applying Cricoid Pressure During Induction of Anaesthesia
Letters to the Editor Issue 5 - General anaesthesia for caesarean section
Letters to the Editor Issue 6 - Low spinal anaesthesia for Caesarean section
Letters to the Editor Issue 7 - Low spinal anaesthesia for Caesarean section

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