General anaesthesia is now an uncommon anaesthetic technique for C-section and other obstetric procedures due to the benefits and reduced risk associated with a neuraxial technique. However, there are still scenarios where it is required.
Urgency - Cat 1 sections often done as a GA, though regional technique can sometimes be just as quick
Neuraxial technique contraindicated e.g. coagulopathy
Failed neuraxial technique
As noted, in many cases the indication for a GA is the urgency of the delivery, and so some aspects of the optimal approach may be difficult to fully achieve e.g. full informed consent. The balance of risk vs benefit must be maintained though, and this will clearly vary on the specific clinical scenario.
A full anaesthetist assessment is important. Particular attention to the airway assessment is required, with close attention to features that may indicate difficulty. Blood results (if available) should be checked. A valid group and screen is essential.
Prophylaxis against regurgitation is important. Whilst this is usually given prophylactically in all anticipated C-section cases, there is special importance prior to GA. Traditionally this involves:
Ranitidine - 150mg orally 2 and 12 hours preop (50mg IV in emergency)
30ml 0.3M sodium citrate immediately before induction
Metoclopramide - 10mg orally 2 hours preop (10mg IV in emergency)
Induction will usually take place on the operating table. Full AAGBI standard monitoring is essential. The patient should have large bore IV access (16g) with fluid running. They should be positioned supine with left tilt to improve aortocaval compression. Appropriate positioning to optimise airway management is essential e.g. ramped. Head up tilt may help with this, and also help with oxygenation and regurgitation risk. Full, meticulous preoxygenation is essential. The reduced FRC of pregnant women can result in rapid desaturation. In emergency settings, the patient will often be draped and prepped during preoxygenation to minimise time to delivery.
A ‘classic’ RSI will commonly be the technique of choice:
Thiopentone 5-7 mg/kg
Suxamethonium 1.5 mg/kg
Ensuring adequate dosing of both induction agent and relaxant are important to optimise intubation conditions and minimise the risk of awareness. Opioids are traditionally avoided due to the sedating effect on the foetus. Some maternal conditions may require them e.g. preeclampsia, to avoid adverse effects from the sympathetic stimulation of laryngoscopy e.g. alfentanil.
Intubation with a 7.0 ID oral ETT can provide adequate ventilation and may also be easier to pass if there is mucosal engorgement.
Anaesthesia should be maintained with a volatile agent and nitrous oxide/oxygen mix. Nitrous oxide has the theoretical benefits of a faster onset and some analgesic properties which are useful prior to administration of other analgesia. A MAC of at least 0.75 should be rapidly achieved to minimise the risk of awareness. It is important to remember that patients have an increased sensitivity to volatile anaesthetic agents, and MAC can be reduced by up to 40%. Further muscle relaxation will likely be needed. However, the effect of suxamethonium can be more prolonged (due to reduced cholinesterase levels) and thus its resolution should first be observed.
Oxytocin (5 units) is given at the time of delivery. Additional uterotonics may be requested by the obstetrician. Once the cord has been clamped, additional analgesia in the form of opioids can be given e.g. morphine.
Patients remain at high risk of aspiration postoperatively. Extubation should be performed awake and in the left lateral position. In patients who are very high risk e.g. have just eaten, insertion of an orogastric tube (not NG) may be used to try and reduce the volume of stomach contents.
Analgesia is less satisfactory than following neuraxial anaesthesia. A clear analgesia plan prior to extubation needs to be in place. This will usually require a multimodal approach:
Intraoperative NSAID (if tolerated) e.g. diclofenac 100 mg PR
IV opioids e.g. Morphine 0.1mg/kg
Regional anaesthesia e.g. TAP blocks
Regular analgesia should be prescribed with breakthrough analgesia available. A morphine PCA may be required.
Antiemetics may be required due the emetogenic effects of GA. Intraoperative administration and PRN prescription is suitable.
Ensuring adequate VTE prophylaxis is essential sue the high risk nature of these patients. Mechanical prophylaxis e.g. TED stockings, should be in place for all patients without contraindications. Prophylactic dose LMWH is very commonly indicated if there are no contraindications.
Difficulty in intubation in obstetric patients is a well recognised problem, and a contributing factor to the strong preference for regional anaesthesia. Adverse factors include:
Urgency of surgery (often)
Rapid desaturation (reduced FRC)
Increased adiposity/breast tissue
Some of these relate more to the environmental and human factors than just anatomical/physiological changes of pregnancy and thus may explain some of the variation in rates described.
Failed intubation has a quoted incidence of about 1 in 250 cases. The DAS has produced some excellent guidance on an algorithm approach to managing these cases. This provides an overview to challenges that may arise. The key management plans to have prepared include considerations of the following questions:
What is the plan for failed intubation?
Will surgery need to proceed if ventilation possible but unable to intubate?