Anaesthesia

Anaesthesia

General
1. Loss of consciousness and sensitivity to pain
2. Either IV or inhalation
  1. IV: Induction with propofol, thiopental or etomidate. Pt is pre-oxygenated and monitored. Maintenance with oxygen + nitrous oxide + continuous propofol with additional muscle relaxants when required.
  2. Inhalation: Either for induction or maintenance. Potency calculated by MAC (minimum alveolar concentration): the amount of gas required in the lungs to prevent 50% of humans moving when given a painful stimulus. Isoflurane, sevoflurane, desflurane. For maintenance they are given with O2, muscle relaxants and analgesia.
  3. Preferably IV for induction and inhaled for maintenance.
3. Rapid sequence induction
  1. For emergency situation: rapidly acting muscle relaxant given immediately after induction agent. Risk of inability to intubate and ventilate pt.
4. Acts on the brain
5. Effect on cardio and respiratory systems: CVS: reduced myocardial contractility, reduced cardiac output, hypotension, arrythmias, increased myocardial sensitivity to catecholamines. RS: reduced ventilation, laryngospasm/airway obstruction, reduced ventilatory response to hypoxia and hypercapnia, bronchodilation.
6. Risks: PONV, acid aspiration syndrome, allergic reactions, respiratory arrest, pt awareness, slow recovery
Regional
1. Epidural
  1. Local anaesthetic into epidural space either via single dose, intermittent top-up or continuously via a pump. Unlike a spinal it can be topped-up so prolongued action, but slower onset (up to 45 mins). Can also be used as a PCA system. Must monitor ECG, BP, RR & O2 sats. May become hypotensive.
  2. Risks: respiratory depression, toxicity, failure, total spinal effect from dural puncture, CSF/dural puncture causing spinal headache
2. Caudal
  1. Blocks sacral and lumbar nerve roots. Mainly in children.
3. Spinal
  1. Solution directly into CSF. Complete sensory block, may also be loss of power. Usually lower body, can extend from nipples (T10) to toes. Level measured using ice/light touch. Fast onset lasting 1-4 hrs. Must monitor ECG, BP, RR & O2 sats. May become hypotensive (sympathetic blockade) so may need fluid.
  2. Effect on cardio and respiratory systems: reduced ventilation (if opiates) , bradycardia, hypotension (vasodilation caused by anaesthetic blocking sympathetic nerves to blood vessels)
  3. Risks: Failure, localised bruising/pain, infection, respiratory depression with opiates, PONV, bladder distension, bradycardia, hypotension, high spinal block (depression of cervical spine and brainstem, spinal headache.
Local
1. Blocks conduction of nerve impulses along nerve axons
2. Topical (skin/mucous membranes ie before injection), local infiltration (for minor procedures ie suturing), regional/conductional anaesthesia (minor/major nerve blockade ie ulnar/brachial plexus). Can also be used for treatment of pain in combi with opioids, NSAIDS etc.
3. Vasodilator effect so often given with vasoconstrictor to increase potency. But do not use adrenaline around end-arteries (ie penis/finger ring-block) - can cause ischaemia
4. Risks: Toxicity - coma, circulatory collapse, cardiac arrest, apnoea

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