IV anesthetics Flashcards
IVAA which has intrinsic analgesic property
Ketamine
IVAA which has antiemetic and appetite stimulating property
Propofol
IVAA with amnestic and anxiolytic property
Midazolam
Adjuvants for IVAA to produce TIVA
Opioid
LAA
MoA of Barbiturates
Depress RAS
Inhibit ACh
Enhance GABA
First barbiturate used
Hexobarbital
Gold standard of IV anesthetic inductional agent
Thiopental
Advantages of thiopental
Fast induction time
Fast recovery time
Fast elimination time
Disadvantages of thiopental
Localized pain on injection
Excitatory side effect
Induce tachycardia
IVAA widely used in dental anesthesia and day-case surgery
Thiopental
Effect of replacing Oxygen (oxybarbs) by Sulfur (thiobarb)
Increase lipid solubility
Barbiturate available for rectal administration
Thiopental
Methohexital
Barbiturate available for IM
Pentobarbital
Secobarbital
Property of Thiopental
High PPB
High lipid solubility
High non-ionized fraction
Redistribution time of thiopental
20-30 min
Effect of repeated dosage on redistribution
Peripheral compartment saturates
DOA becomes dependent on elimination
What does awakening depend upon?
Redistribution
What does recovery of psychomotor function depend upon?
Metabolism
More rapidly metabolized barbiturate
Methohexital (3-4X)
Factors that determine elimination of drug and recovery time
Elimination of drug from central compartment
Amount of drug present in the peripheral compartment
Rate of redistribution from peripheral into central compartment
Effect of high PPB on elimination
Decreases glomerular filtration
Effect of Barbiturate on CVS
Fall in BP
Rise in HR
Maintained CO
Sympathetic induced vasoconstriction (Increased PVR)
Factors that determine CVS effects of barbiturates
Volume status
Baseline autonomic tone
Pre-existing CVS disease
Rate of injection
Effect of Intra-arterial injection of barbiturate
Crystal formation in artery and capillary
Intense vasoconstriction
Thrombosis
Tissue necrosis
Remedy for Intra-arterial injection of barbiturate
IA injection of lidocaine Regional sympathectomy (brachial plexus block) Heparinization
Effect of Barbiturate on Respiratory system
Decrease response to hypercapnia and hypoxia
Does not completely depress airway reflex
Apnea
UAW obstruction (sedation)
Barbiturate more commonly associated with laryngospasm and hiccup
Methohexital
Cause for Bronchospasm after induction of thiopental + Remedy
Cholinergic nerve stimulation
Histamine release
Direct bronchial smooth muscle stimulation
Remedy
Atropine pre-treatment
Effect of Barbiturate on CNS
Decrease CBF + CMRO2
Decrease ICP
Increased CPP (drop in ICP exceede drop in MAP)
Which barbiturate relates a sense of taste of garlic/onion during induction
Thiopental
Which group of IVAA has an anti-analgesic effect (lower the pain threshold)
Barbiturates
Which IVAA are known to develop tolerance and dependence
Barbiturate
Ketamine (partial tolerance)
Which barbiturate induces involuntary muscle contraction)
Methohexital
What is the effect of Barbiturate on Renal system
Reduce RBF and GFR proportional to fall in BP
What is the effect of Barbiturate on Liver
Reduced Hepatic BF
Liver enzyme induction upon chronic exposure
Increase metabolic rate of some drugs (digitoxin)
Which group of barbiturates evoke mast cell histamine release
Thiopental (Sulfur containing barbiturate)
What are drugs that could increase/potentiate barbiturates?
Sulfonamide Ethanol Opioids Antihistamine Other sedatives
Propofol (Vs Thiopental)
Higher lipid solubility
Faster onset
Rapid recovery
Less hangover
Adjuvants of Propofol
10% soybean oil
- 25% glycerol
- 2% egg Lecithin
Remedy of pain on injection of propofol
Using larger veins
Prior administration of LAA or opioid (fentanyl, remifentanil)
Sodium metabisulfite in propofol
Newer formulations
Antimicrobial additive
Less pain on injection
Concentration and Dose of Thiopental induction
2.5-5%
3-6 mg/kg
Concentration and Dose of Thiopental sedation
- 5%
0. 5-1.5 mg/kg
Concentration and Dose of Methohexital induction
1%
1-2 mg/kg
Concentration and Dose of Methohexital sedation
1%
0.2-0.4 mg/kg
Dose of Propofol induction
1.5-2.5 mg/kg
Reasons for higher induction and maintenance dose for children for propofol
Large central distribution volume
Higher clearance rate
IVAA with a subjective feeling of well-being (euphoria)
Propofol
Metabolism of propofol
10X clearance rate of thiopental
Clearance exceeds hepatic BF (extrahepatic metabolism)
Conjugation in liver results in inactive metabolite
Elimination of propofol
Eliminated by renal clearance
Effect of moderate cirrhosis and chronic renal failure on propofol
Not much effect on its pharmacokinetic property
Infusion of propofol for long-term sedation of children or neurosurgical patient
Lipemia
Metabolic acidosis
Death
Effect of Propofol on CVS
Drop in SVR Drop in contractility Drop in preload Vagally mediated reflex bradycardia More pronounced hypotension Coronary steal syndrome
Effect of Propofol on Respiratory system
Profound depressant Apnea at induction Depress UAR Laryngeal placement without paralysis Histamine release
Effect of Propofol on CNS
Decrease CBF Decrease ICP Decrease IOP Anticonvulsant No tolerance development
Drugs that are potentiated by Propofol
NDMRs
MoA of Propofol
Facilitate GABA
MoA of Etomidate
Depress RAS
Disinhibitory effect on extrapyramidal motor activity
Dosage of Etomidate for Induction
0.2-0.5 mg/kg
Metabolism of Etomidate
Hepatic microsomal enzyme
Plasma esterase
Fast metabolism (5X of thiopental)
Excretion of Etomidate
Primarily excreted in urine
Which IVAA has minimal effect on CVS
Etomidate
Effect of Etomidate on Respiratory system
Less respiratory depression (unless combined with opioid)
Effect of Etomidate on CNS
Decrease CBF, CMRO2
Decrease ICP
CPP well maintained
Postoperative nausea and vomiting
Which IVAA leads to adrenocortical suppression
Etomidate
Which drug prolongs the half-life of Etomidate
Fentanyl
MoA of Ketamine
NMDA antagonist
Blocks polysynaptic reflexes in the SC
Inhibits excitatory NT
Which IVAA produces dissociative anesthesia
Ketamine
Two isomers of Ketamine
S+ and R-
S+ more potent anesthetic and analgesic
Dosage of Ketamine Induction IV
1-2 mg/kg
Dosage of Ketamine Induction IM
3-5 mg/kg
Dosage of Ketamine Sedation IV
0.1-0.5 mg/kg
Dosage of Ketamine Sedation IM
1-1.5 mg/kg
Property of Ketamine
More lipid soluble
Less protein bound
Equally ionized
Vs thiopental
Metabolism of Ketamine
Hepatic microsomal CP450
Metabolite of Ketamine
Nor-ketamine
Excretion of Ketamine
Excreted Renally
High hepatic clearance rate
Effect of Ketamine on CVS
Increase BP, HR and CO
Counter-indication for Ketamine
CAD Uncontrolled HTN CHF Aneurysms Space occupying intracranial lesion
Effect of Ketamine on Respiratory system
Minimally affect at induction dose
Rapid/Repeated/Opioid coadmin causes apnea
Potent bronchodilator (for asthmatic patient)
Intact UAR
Effect of Ketamine on CNS
Increases CMRO2
Increases CBF
Increases ICP
Psychomimetic effect
What drugs does Ketamine potentiate
Non-depolarizing muscle relaxants
What two drugs mixture would form dangerous precipitation that would occlude IV line
Ketamine
Thiopental
MoA of BDZ
Enhance inhibitory NT
Increase conductance of Cl-
Receptor occupancy required to achieve anxiolysis, amnesia-sedation, hypnosis?
20%
30-50%
60%
Hydrophobic BDZ
Diazepam (Valium)
Lorazepam (Ativan)
Water soluble BDZ
Midazolam
acidified (3.5) aqueous formulation
minimal irritation
Physiologic pH
Change of physico-chemical property (lipid soluble)
BDZ specific receptor antagonist
Flumazenil
BDZ that are well absorbed from GIT + peak plasma level
Diazepam (1hr)
Lorazepam (2hr)
BDZ available in Intranasal, buccal and sublingual for children
Midazolam
Redistribution and Property of BDZ
Rapid redistribution
Can’t match rapid onset and offset of thiopental
Lorazepam Vd, half life and duration
Vd limited by lower lipid solubility
Shorter half life (15 hrs)
Prolonged duration due to high receptor affinity
Midazolam Vd, half life and duration
Large Vd
Small half life (2hrs)
Shortest duration due to high hepatic extraction
Excretion of BDZ
Renal
Excretion of Midazolam in Renal failure patient
Prolonged sedation
Accumulation of conjugated metabolite (a-hydroxymidazolam)
Effect of BDZ on CVS
Minimal CVS depressant at induction dose
Masked by laryngoscopic stimulation
More marked in hypovolemic patient
Midazolam vs Diazepam (CVS)
Midazolam reduces BP, PVR more
Drug induced vagolysis by Midazolam
Effect of BDZ on Respiration
Depress ventilatory response to CO2
Apnea uncommon
Depress swallowing reflex
Reduce UAR
Effect of BDZ on CNS
Reduce CMRO2, CBF, ICP less than barbs
Slower hypnosis
Longer recovery
Treatment of Status epilepticus
Drug that binds to CP450 and reduce diazepam metabolism
Cimetidine
Drug that inhibit midazolam metabolism and cause 2-3 increased intensity
Erythromycine
Displaces diazepam from protein-binding site and increase free drug concentration
Heparin
Metabolism and excretion of Flumazenil
Rapid metabolism in Liver
Excreted in urine as glucuronide conjugate