Definitions
Anaesthesia (αυαισθεσια = Without Perception):
1. a partial or complete loss of all forms of sensation caused by pathology in the nervous system; 2. a technique using drugs (inhalational, intravenous or local) that renders the whole or part of the organism insensible for variable periods of time. Analgesia: the loss of pain sensation. Hypnotic agent: a sleep-inducing drug. Muscle relaxant: a drug that reduces muscle tension by affecting the nerves that supply the muscles or the myoneuronal junction (e.g curare, succinylcholine). Sedation: the production of a calm and restful state by the administration of a drug.
General Anaesthesia:
relies upon generalized suppression of some functions of the cerebral cortex to induce a generalized state of insensibility.
Regional Anaesthesia:
relies upon blockage of nerve impulses or spinal transmission of impulses to induce analgesia and immobility.
- Fasting – while food should be avoided for several hours preoperatively, water may be given freely to most patients up to 2 hours before operation.
- Pre-operative assessment and risk is based on the ASA classification and the urgency and complexity of surgery.
- General anaesthesia comprises safe induction, active maintenance of anaesthesia and safe recovery.
- Regional anaesthesia is preferred for many procedures, e.g. obstetrics, eye surgery, orthopaedics.
- Spinal/epidural anaesthesia is contraindicated in the anticoagulated patients.
Pre-Operative Assessment
Prior to an operation the anaesthetist will assess the patient and devise a plan for anaesthesia based on the following:
- The condition of the patient (ASA classification) determined by:
- The complexity of the surgery to be performed.
- The urgency of the procedure (emergency or elective).
| Class | ASA pre-operative physical status classification |
| Class I | Fit and healthy |
| Class II | Mild systemic disease |
| Class III | Severe systemic disease that is not incapacitating |
| Class IV | Incapacitating systemic disease that is constantly life-threatening |
| Class V | Moribund – not expected to survive >24 hours without surgery |
ASA = American Society of Anesthesiologists.
General Anaesthesia
Pre-Operative Fasting
- Rationale:
- Adults:
- Children:
- Emergency surgery:
Aims and Technique
- To induce a loss of consciousness using hypnotic drugs which may be administered intravenously (e.g. propofol) or by inhalation (e.g. sevoflurane).
- To provide adequate operating conditions for the duration of the surgical procedure using balanced anaesthesia, i.e. a combination of hypnotic drugs to maintain anaesthesia (e.g. propofol, sevoflurane), analgesics for pain (e.g. opiates, NSAIDs) and, if indicated, muscle relaxants (e.g. suxamethonium, tubocurarine) or regional anaesthesia.
- To maintain essential physiological function by:
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