Page 50 - TNFlipTest

A16 Anesthesia
Solubility of Volatile
Anesthetics in Blood
Least Soluble to Most Soluble
Nitrous oxide < desflurane < sevoflurane < isoflurane < halothane
Table 8. Intravenous Induction Agents
Induction Toronto Notes 2019 Induction Agents
• inductioningeneralanesthesiamaybeachievedwithintravenousagents,volatileinhalationagents,or both
Intravenous Agents
• IVinductionagentsarenon-opioiddrugsusedtoprovidehypnosis,amnesiaandbluntreflexes
• theseareinitiallyusedtodrawthepatientintothemaintenancephaseofgeneralanesthesiarapidly,
smoothly and with minimal adverse effects
■ most commonly used is propofol or ketamine
■ a continuous propofol infusion may also be used for the maintenance phase of GA
Class Action
Indications
Caution
Dosing
Special Considerations
Propofol (Diprivan®)
Alkylphenol – hypnotic
Inhibitory at GABA synapse
Decreased cerebral metabolic rate and blood flow, decreased ICP, decreased SVR, decreased BP, and decreased SV
Induction Maintenance Total intravenous anesthesia (TIVA)
Patients who cannot tolerate sudden decreased BP (e.g fixed cardiac output or shock)
IV induction: 2.5-3.0 mg/ kg (less with opioids) Unconscious <1 min Lasts 4-6 min
t1/2 = 55 min Decreased post- operative sedation, recovery time, N/V
0-30% decreased BP due to vasodilation
Reduce burning at IV site by mixing with lidocaine
Thiopental (sodium thiopental, sodium thiopentone)*
Ultra-short acting thiobarbiturate – hypnotic
Inhibitory at GABA synapse Decreased cerebral metabolism and blood flow, decreased CPP, decreased CO, decreased BP, decreased reflex tachycardia, decreased respiration
Induction
Control of convulsive states, obstetric patients
Allergy to barbiturates Uncontrolled hypotension, shock, cardiac failure Porphyria, liver disease, status asthmaticus, myxedema
IV induction: 3-5 mg/kg Unconscious about 30 s Lasts 5 min
Accumulation with repeat dosing – not for maintenance t1/2 = 5-10 h
Post-operative sedation lasts hours
Combining with rocuronium causes precipitates to form
Ketamine (Ketalar®, Ketaject®)
Phencyclidine (PCP) derivative – dissociative
May act on NMDA (antagonistically), opiate, and other receptors Increased HR, increased BP, increased SVR, increased coronary flow, increased myocardial O2 uptake CNS and respiratory depression, bronchial smooth muscle relaxation
Major trauma, hypovolemia, obstetric bleeding, severe asthma because sympathomimetic
Ketamine allergy
TCA medication (interaction causes HTN and dysrhythmias)
History of psychosis
Patients who cannot tolerate HTN (e.g. CHF, increased ICP, aneurysm)
IV induction 1-2 mg/kg Dissociation in 15 s, analgesia, amnesia, and unconsciousness in 45-60 s
Unconscious for 10-15 min, analgesia for 40 min, amnesia for 1-2 h
t1/2 = ~3 h
High incidence of emergence reactions (vivid dreaming, out-of- body sensation, illusions) Pretreat with glycopyrrolate to decrease salivation
Benzodiazepines (midazolam [Versed®], diazepam [Valium®], lorazepam [Ativan®])
Benzodiazepines – anxiolytic
Inhibitory at GABA synapse Produces antianxiety and skeletal muscle relaxant effects Minimal cardiac depression
Used for sedation, amnesia, and anxiolysis
Marked respiratory depression
Onset less than 5 min if given IV Duration of action long
but variable/somewhat unpredictable
Antagonist: flumazenil (Anexate®) competitive inhibitor, 0.2 mg IV over 15 s, repeat with 0.1 mg/min (max of 2 mg), t1/2 of 60 min
Midazolam also has amnestic (antegrade) effect and decreased risk of thrombophlebitis
Etomidate
Imadazole derivative - hypnotic
Decreases concentration of GABA required to activate receptor
CNS depression Minimal cardiac or respiratory depression
Induction
Poor cardiac function, severe valve
lesions, uncontrolled hypertension
Post-operative nausea and vomiting
Venous irritation
IV induction 0.3 mg/kg Onset 30-60 seconds Lasts 4-8 minutes
Adrenal suppression after first dose, cannot repeat dose or use as infusion
Myoclonic movements during induction
*As of 2011, Thiopental has been discontinued from production for North America
Volatile Inhalational Agents
• examplesincludesevoflurane,desflurane,isoflurane,enflurane,halothane,andnitrousoxide • seeTable9