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General anaesthesia is the advanced full body anaesthesia needed before most major surgery. It may help you to read the page on stages of anaesthesia before you move on.
Principles Of Anaesthesia
The principles of anaesthesia underly everything that you will encounter when considering how to deal with patients before and during operations:
- Analgesia - your main aim is to control pain, otherwise operations would be torture.
- Sedation - usually, the patient needs to be asleep, and so sedation is rather important for making this a reality.
- Muscle Relaxation - in some situations it is important to use muscle relaxants; for example tense rectus muscles do not help abdominal surgery.
Anaesthesia is all about altering the physiology of the body to achieve these things without killing the patient.
Planning general anaesthesia
There are four things to consider: induction, maintenance, airway and breathing. Let's take them one at a time.
Standard choice: IV propofol
Firstly, you need to knock 'em out and there's two choices: IV or inhaled. Intravenous drugs are hence first-line. However, sometimes it's not possible to get IV access meaning you just end up rubbing drugs on the patient's skin. Which does little except mildly annoy them. Needlephobia, children, difficult access and difficult airway are all reasons to use inhaled agents to induce anaesthesia in a patient. The following are the drugs we use:
- IV - propofol; etidomote where CVS risks are present; and thiopenthal sodium
- Inhaled - sevoflurane (never isoflurane)
Standard choice: N2O (nitrous oxide), O2, Isoflurane
Again, the choice is between inhaled or IV. It is very rare that TIVA (total intravenous anaesthesia) is actually used but if it is, the choice is generally thiopenthal sodium. Otherwise, it's done by gas. Basically, it's done with:
N2O + O2 + Inhalation agent
Essentially, you need to ask the question: does the patient need an endotracheal tube?.
- Yes - because
- No -
There's basically a choice between IPPV (intermittent positive-pressure ventilation) or Spontaneous (i.e. no help).