Maintenance and reversal of General Anaesthesia
Effects of IV drugs used for induction of anaesthesia wears off after a few minutes and unconsciousness must still be maintained. This is achieved either through inhalational anaesthesia or IV infusion of a drug. i) Inhalational Anaesthesia
Patient must receive a sufficient concentration of oxygen to prevent hypoxia, sufficient concentration of anaesthetic drug to ensure consciousness and sufficient flow of fresh gases to prevent hypercarbia. The anaesthetic drug used is maintained at an appropriate end-tidal concentration depending upon the patient, the surgical stimulus and concurrent use of analgesic drugs. In spontaneously breathing patients, inadequate anaesthesia for the intensity of the surgical stimulus results in an increased respiratory rate, reflex activity, increase in heart rate and blood pressure. This results in an increment of the anaesthetic drug concentration. In patients who are given neuromuscular blocking drugs and is ventilated, anaesthetists must anticipate the need for changes in the depth of anaesthesia as there might be a possibility that the depth of anaesthesia is inadequate and the patient is aware but unable to communicate this.
ii) TIVA using propofol
In this technique, appropriate brain concentration of propofol must be achieved and maintained to prevent awareness and respond to the surgery. This is done by giving the usual IV induction dose, followed by maintenance using a microprocessor controlled infusion pump. This is more reliable as it calculates the rate of infusion required to achieve a constant plasma concentration. Propofol can be used alone but it is always combined with IV opioids to prevent cardiovascular side-effects. Advantages of TIVA is the toxic effect of inhalational anaesthetics are avoided and better quality of recovery is claimed. Disadvantage is it may cause profound hypotension.
Reversal of General Anaesthesia
The two main priorities of reversal...
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