Anaesthesia

• "Without feeling"

Principles of Anaesthesia

1. Sleep (hypnosis)
   • Occurs at induction - propofol (short half-life, quick onset +/- combination with fentanyl), inhalational agents (halothane/isoflurane/desflurane)
2. Analgesia
   • Administered via premedication and during procedure
   • Short acting - alfentanyl
   • Long acting - morphine
   • Paracetamol
   • NSAIDs
3. Muscle relaxation
   • Neuromuscular blocking agents - profound muscle relaxation
   • Faciliates ETT intubation, intraoperatively aids surgeon
   • Non-depolarising agents (atracurium, vencuronium) quick onset, reversed by anticholinesterase neostigmine
   • Depolarizing agents: suxamethonium (cannot be reversed - just have to wait until it wears off)

Crash Induction - Thio / Sux / Tube

• Rapid sequence: used when patient not adequately starved prior to surgery
• Stomach assumed to be full - apply cricoid pressure as anasthetic being given (prevents regurgitation): thiopentone used (less hypotensive effect than propofol)

Stages of Anaesthesia

1. Stage 1: Analgesia
   • Normal reflexes remain intact
   • Stage ends with loss of eyelash reflex
2. Stage 2: Excitement
   • Pupils dilate, divergent gaze
   • Irregular breathing
   • Stage ends with onset of automatic breathing and loss of eyelid reflex
3. Stage 3: Surgical anaesthesia
   • Plane 1 - pupils normal, small, lacrimation increased
   • Plane 2 - until onset of intercostal paralysis. Loss of corneal reflex
   • Plane 3 - ideal surgical anaesthesia
   • Plane 4 - includes diaphragmatic paralysis and depression of cranial nerves
4. Stage 4: Overdose
   • Seen with dilation of pupils and apnoea

Complications of Anaesthesia

• Malignant hyperpyrexia: triggered by all inhalational anaesthetics (except nitrous oxide); familial disorder Autosomal dominant - appears to be rapid influx of Ca into muscle cells resulting in actin/myosin activation and muscle rigidity
• Treated with dantrolene (binds to ryanodine receptor - decreasing intracellular calcium concentration and results in muscle relaxation), surface cooling, iv fluids in ITU

Premedication

1. Analgesics
   • Opiods - analegesic and sedative
2. Antiemetics / prokinetics / antacids
   • Antacids - cimetidine, ranitidine: prevent aspiration of gastric contents in patients at risk - pregnancy, trauma patients not starved, obese, hiatus hernia
   • Metoclopramide
   • Erythromycin: pro-kinetic
3. Amnesics
4. Sedatives
   • Benzodiazepines (midazolam)
   • Temazepam 10-20mg pre surgery
   • Diazepam:
5. Anti-secretions
   • Anticholinergics (acetylcholine antagonists)
   • Hyoscine
   • Glycopyrronium
   • Hyoscine
6. Antibiotics