Anaesthesia
Local anaesthetic agents:
| doses are for regional anaesthetic only | |
|---|---|
| amide LA's - metabolised in liver Ester LA's - metab by hydrolysis (plasma esterases) |
|
| Lignocaine | amide LA duration:30-120mins 3-5mg/kg, max.200 mg |
| Bupivacaine | amide LA duration:120-240mins Slower onset (up to 30mins for full effect) but longer duration of action than other local anaesthetics. 2mg/kg, to 150 mg, using a 2.5 mg/mL (0.25%) solution |
| Levobupivacaine | amide LA bupivacaine isomer with fewer adverse effects Up to 150 mg, using a 2.5 mg/mL (0.25%) solution |
| Prilocaine | amide LA duration:30-120mins least toxicity of the amides 3mg/kg using 0.5% solution usually used for IV regional anaesthesia (Bier's block) Methaemoglobinaemia is specific toxicity of prilocaine but at much higher doses |
| Ropivacaine | amide-type derived from bupivacaine, less cardiotoxic but also less potent 3mg/kg, to 200 mg, using 2 mg/mL (0.2%) solution |
| Tetracaine | para-aminobenzoic acid ester, effective LA for topical use |
| Toxicity of all - dose dependent CNS effects from tingling to seizures. Vasodilation and vasoconstriction at higher doses, -ve inotropy. Hypersensitivity - rare but more so with Esters |
Sedation and Analgesia
| Adult | Paediatric | |
|---|---|---|
| Midazolam | • Binds to α/γ interface of the receptor, increasing affinity of the receptor for GABA (GABAA&B) • Sedation/Amnesia • may have slightly more muscle relaxant effect than propofol because if it's broader GABA rec activity • side effects - reduced Tidal Vol, tachypnoea, respiratory depression (occ apnoea), hypotension. • Dose: ≤2.5mg and titrate 1mg every few minutes to effect • Half life ~ 1/24 | • May cause agitation in children • Dose:≤2mg and titrate 1mg every few minutes to effect, max 10mg |
| Propofol | • Sedation/Amnesia • potentiates GABA (GABAA) mediated inhibitory tone in the CNS by decreasing the rate of dissociation of GABA from the receptor • side effects - hypotension, resp depression, pain with injection • pre-oxygenation is probably appropriate, esp in children • was considered unsafe in patients with egg, soy allergies - no longer • propofol infusion syndrome - in setting of prolonged and high dose infusion, acute refractory brady progressing to asystole in setting of metabolic acidosis, rhabdomyolysis,hyperlipidemia, and liver disease • Dose: 0.5-1mg/kg (≤20mg in elderly) & titrate 0.25-0.5mg/kg to effect • Half life for initial dose - 40mins | • Dose: >2yr old - 0.5-2mg/kg then titrate 0.5mg/kg every minutes to effect, max 3mg/kg |
| Ketamine | • Sedation/Amnesia/Analgesia • dose response is not linear and dissociation usually appears at a threshold which is then maintained with further doses • side effects - tachycardia, hypertension, laryngospasm, unpleasant hallucinations (reduced by pre-medication with a benzodiazepine), nausea and vomiting • Contraindications - schizophrenia, resp and CVS disease • Dose: 1mg/kg (≤30mg in elderly) & titrate 0.25-0.5mg/kg every few minutes to effect | • Dose: >3/12 only, 1.5-2mg/kg then 0.5-1mg/kg after 5-10mins |
| Nitrous Oxide | • still some debate about mode of action • analgesia - opioid in nature (possibly by inducing release of endogenous opioid peptides) and may involve a number of spinal neuromodulators. • anxiolytic - similar to benzodiazepines (possibly by activating BZ binding) & may involve GABA receptors. • anaesthesic - may involve GABA and possibly N-methyl-D-aspartate receptors. •contraindications - patients with likely air-filled cavities, including pneumothorax, pulmonary blebs, air embolism, bowel obstruction, and those undergoing surgery of the middle ear. | |
References include:
BJ anaesthesia article
http://www.partone.lifeinthefastlane.com/local_anaesthetics.html
https://www.scottishintensivecare.org.uk/uploads/2014-07-08-00-14-41-RSIbrochurepdf-76814.pdf
UK EM college guidelines - sedation and analgesia
ACEP propofol guidelines 2018
https://www.openanesthesia.org/
Muscle relaxant comparison - propofol and Midazolam
Emed Nitrous
Advances in understanding N2O