Although some authorities recommend that patients undergoing general anaesthesia for a Caesarean section should be warned about the risk of awareness, this is not generally advocated. The low incidence with modern anaesthetic techniques, coupled with the risk of raising anxiety and actually increasing the likelihood of awareness, means that most practitioners would eschew such a warning. Because of the advisability of waking the mother before tracheal extubation after Caesarean section, it is wise to mention the possibility of waking up with 'a tube in the throat' to ensure that she does not mistake this for intraoperative awareness.
Most incidents of awareness in recent years can be clearly traced back to a technical problem with the anaesthetic apparatus, vaporiser faults being the most common. When checking the anaesthetic machine, correct seating of the chosen vaporiser on its mount and adequate filling should be ensured. The anaesthetist should be familiar with the breathing system and ventilator and understand how air or oxygen can be entrained into the system (e.g. a gas piston ventilator) and how the inspired concentration of volatile agent can be lower than that set on the vaporiser
(e.g. a circle system). A volatile agent monitor is invaluable and it is rapidly becoming indefensible to be without one.
There is no guaranteed 'sleep' dose of an induction agent, and the drug must be titrated against the patient's response, bearing in mind that it will be responsible for maintaining anaesthesia throughout the onset of muscle relaxation and tracheal intubation. Thiopental is probably still the drug of choice for induction, and the anaesthetist should have 6 mg/kg available in the syringe. Suxamethonium has a very rapid onset of action and should not be given until after the eyelash reflex has been lost.
Volatile agents with a low lipid solubility will achieve alveolar-inspired equilibrium most quickly. Isoflurane is the best of the 'established' agents, but the rapid onset times of desflurane and sevoflurane suggest that they are particularly appropriate for Caesarean section. Concentrations representing at least 0.5 MAC should be used during the procedure and this should be higher if the inspired nitrous oxide concentration is to be less than 60%. An overpressure of 1.5-2 MAC should be employed in the first 2-3 minutes if a more soluble agent is being used.
The patient should be closely watched for signs of lightening anaesthesia (tears, sweating), and the monitors should be observed frequently for evidence of sympathetic overactivity (tachycardia, hypertension). Some practitioners advocate the use of specific monitors of anaesthetic depth, but none has so far been shown to be any more effective than simply watching vital signs (Table 57.1). A meticulous record should be kept, which should include vaporiser settings and end-tidal volatile concentrations, if available.
A generous dose of a suitable opioid drug should be given directly after cord clamping and the volatile agent left on until the skin is being sutured. It is better to wait a few minutes at the end of the operation rather than risk awareness.
All mothers undergoing general anaesthesia for Caesarean section should be followed up within 24 hours of delivery and questioned about dreaming or sensation during the operation. The psychological sequelae of awareness can be minimised by a sympathetic approach. Many such patients complain that the medical staff do not believe them when they first report that they have memories of the operation; this can exacerbate the degree of trauma, so all such complaints should be taken seriously and handled at a senior level. Midwives should be alert
Table 57.1. Methods for monitoring depth of anaesthesia
Clinical signs - PRST score (pressure, rate, sweating, tears) Isolated forearm technique Lower oesophageal contractility Skin resistance
Evoked auditory/somatosensory potentials Electroencephalogram
Cerebral function analysing monitor and derivations thereof (e.g. Bispectral Index; BIS)
to the possibility of awareness and ensure early referral to an anaesthetist. Early referral to a psychologist with experience of post-traumatic stress disorder is desirable.
Some patients will mistake their memory of awake extubation for true intraoperative awareness. This risk can be minimised by careful preoperative explanation, but any markers as to the timing of such memory should be sought in order to reassure the patient if possible. Just because true awareness did not occur does not mean that the patient will not be traumatised.
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