Anaesthetic drug Flashcards
Halothane
INHALED anaesthetic (GA)
- First modern INHALED anaesthetic, standard for comparison
- VOLATILE liquid, non-flammable and non-irritating
- Potent (MAC 0.75%)
- MEDIUM rate of onset and recovery
- Little or NO analgesia until unconsciousness supervenes
• Causes RESPIRATORY DEPRESSION dose-dependently
• DECREASE B.P. due to DEPRESSION of CARDIAC OUTPUT
BRADYCARDIA and ARRHYTHMIA may also occur leading to hypotension and dysarrhythmia
• RELAXES skeletal muscle and potentiates skeletal muscle relaxants
• May lead to halothane-associated HEPATITIS
Isoflurane
Isoflurane (Inhaled GA)
- Pungent smell
- Potent (MAC 1.4%)
- MEDIUM rate of onset and recovery
- Similar to halothane with less hypotension and arrhythmia
- Causes RESPIRATORY DEPRESSION dose-dependently
- Decreases B.P. due mainly to decrease in systemic vascular resistance
Sevoflurane
Sevoflurane (inhaled GA)
- Potent (MAC 2%)
- More RAPID rate of onset and recovery
- Metabolized in the LIVER to release inorganic fluoride, also NEPHROTOXIC
- UNSTABLE when exposed to carbon dioxide absorbents in anaesthetic machines, degrading to a compound that is potentially nephrotoxic
Nitrous oxide
Nitrous oxide (N2O) (GAS GA)
- Odourless gas
- Non-flammable
- RAPID onset and recovery but LACK POTENCY (MAC 105%)
• Nitrous oxide alone gives ANALGESIA and AMNESIA but NOT complete unconsciousness or surgical anaesthesia
- Patients undergoing GA receive nitrous oxide to SUPPLEMENT the analgesic effects of primary anaesthetic
- When used alone: as analgesic agent (eg. dentistry, during delivery*)
• Major concern: postoperative nausea and vomiting
Thiopentone (sodium thiopental) + MOA
IV GA
- A barbiturate with extremely high lipid solubility
- Enters the brain easily and rapidly - rapid onset of action (unconsciousness occurs 10-20sec after IV)
• Single Dose: Re-distributes to less vascularized tissues – ultra-short duration of action
(Injected alone & w/o inhale agents, patients wake up ~10min)
- Multiple doses/infusions: duration of action depends on clearance
- Slow elimination, large Vd, active metabolite (PENTOBARBITAL), liver cirrhosis –> can result in prolongation of clinical action.
• Extensively bound to plasma protein
- small amount of free drug can be excreted by glomerular filtration + reabsorption in tubules.
• Less than 1% excreted unchanged
MOA
• Cause CNS depression by potentiating the action of the neurotransmitter GABA on the GABAA receptor-gated chloride ion channels
Propofol
IV GA
Propofol*
• the most common IV anaesthetic used in Singapore – (ready made in injectable form, no need to re-constitute (unlike thiopentone)
- Induction rate is similar to thiopentone, and recovery is more rapid (patients move sooner and feel better)
- Used both for induction and maintenance
- Rapid onset (unconsciousness develops within ~60sec) • Short duration of action (~3-5min following single injection) because rapid redistribution from brain to other tissues
- Extensively used in “day surgery”
- needs continuous, low-dose infusion for extended effects
- Reduced postoperative vomiting (may be related to an antiemetic action)
- Significant cardiovascular effect during induction (decrease b.p. and negative inotropic) – HYPOTENSION
- To be used with caution in elderly patients, patients with compromised cardiac function, hypovolemic patients
Ketamine
IV GA
Ketamine
- racemic (potency: S- > R+); I/M, oral, rectal routes
- Produces a state known as dissociative anaesthesia ie. patient feels dissociated from environment
- Can cause SEDATION, IMMOBILITY, ANALGESIA, and AMNESIA
- Rapid induction; Responsiveness to pain is lost
- Metabolized in LIVER to LESS active metabolite, excreted in urine & bile
- Large Vd, rapid clearance –> suitable for continuous infusion without the lengthening in duration of action
- Unpleasant psychologic reactions (HALLUCINATION DISTURBING DREAM, DELIRIUM) may occur during recovery from ketamine
- Risks of psychologic adverse reactions may be reduced with premedication of diazepam or midazolam
• It is the ONLY IV anaesthetic that possess ANALGESIC property
hence very popular in 3rd world country as the only anaesthetic, due to the lack of other anaesthetic agents
Benzodiazepine: Midazolam (I/V) AS adjunct
Used for ANXIOLYSIS , AMNESIA and SEDATION prior to induction of anaesthesia (perioperative period) or Used for sedation during procedures not requiring GA
- Rapid onset (unconsciousness develops in 80sec; peak ~2min; sedates ~30min)
- Metabolized in liver (elderly, alcoholic, liver cirhosis tend to be more sensitive, slower recovery)
- Midazolam (benzodiazepine group of drugs) usually has a high therapeutic index –> it has relatively lesser cardiovascular & respiratory depressing effect compare to other IV anaesthetics.
- Side effects are compounded by concurrent usage of other agents
- Adverse effects can be minimized by injecting midazolam SLOWLY (over 2 or more minutes) and by waiting another 2 or more minutes for full effects to develop before dosing again
α2 Adrenergics: Dexmedetomidine (I/V)
as adjunct
- Highly selective α2 adrenergic receptor agonist
- Short term sedation (<24hrs)
- Sedation and analgesic effects (doesn’t produce reliable GA even at maximal doses)
• Little respiratory depression
- Tolerable decrease in blood pressure and heart rate
- Undesirable side effects: nausea, dry mouth, hypotension, bradycardia
Analgesics:
as adjunct
• Minor surgical procedures –> COX-2 inhibitors and paracetamol
- Opioids (Fentanyl, morphine) – perioperative period
- Agonist activity at µ-opioid receptors
• Relative potency to morphine [duration of action]: sufentanil (1000x) [intermediate ~15min]
remifentanil ( 300x) [ultra-short ~10min]
fentanyl ( 80x) [intermediate ~30min]
alfentanil ( 15x) [intermediate ~20min]
- Choice – based primarily on duration of action
- Metabolized in liver (except remifentanil is hydrolyzed by tissue & plasma esterases)
• Excretion: urine, bile
Neuromuscular Blockers as adjunct
Neuromuscular Blockers
• Depolarizing: Succinylcholine
• Non-depolarizing (eg. vecuronium)
- Administered during induction of anaesthesia to relax muscles of jaw, neck, airway –> facilitate laryngoscopy and endotracheal intubation
- Aids many surgical procedures and provide additional insurance of immobility
• Note: barbiturates will precipitate when mixed with muscle relaxants –> should be allowed to clear from the IV line prior to injection of muscle relaxant
Cocaine
(2) M
ester LA
Procaine
procaine (1) S
ester LA
tetracaine
tetracaine (16) L
ester LA
benzocaine
benzocaine (surface only)
ester LA
