Induction Agents (Week 1) Flashcards
What are characteristics of the ideal IV Anesthetic?
1) Rapid, smooth onset of hypnosis
2) Stable in solution
3) Drug compatibility
4) Lack of CV or respiratory depression
5) Decreased cerebral metabolism and ICP
6) Low/no histamine release
7) Rapid metabolism to inactive metabolites
8) Steep dose/response curve
9) Rapid return to consciousness with analgesia
10) No adverse post-op effects
What is the chemical structure of propofol?
2,6 – diisopropylphenol
What drug class is Propofol? Uses?
Class: Hypnotic
Uses: May be used for the induction and maintenance of general anesthesia; and for monitored anesthesia care. Also, may be used as an anticonvulsant and antiemetic.
Mechanism of Action of Propofol
MOA: Mimics GABA at the receptor, directly activating chloride channels, which hyperpolarizes the postsynaptic membrane.
Dosing of Propofol… GA? Maintenance? Sedation?
Dosed adjusted to the individual: body weight, age and premedication
Induction of GA: 1-2.5 mg/kg
Maintenance of GA: 25-300 mcg/kg/min IV
Sedation: 25-100 mcg/kg/min
Dosing of Propofol for antiemetic purposes?
Antiemetic 10-20 mg can repeat every 5-10 minutes, or start infusion of 10 mcg/kg/min
Onset and duration of Propofol during induction?
Onset after induction dose: 30 seconds
Duration after induction dose: 5 – 15 minutes
Metabolism and Excretion of Propofol
Metabolized via hepatic and extrahepatic metabolism (mostly lungs), no active metabolite
Excreted by the kidney
*Propofol has the potential to change urine color (green or cloudy)
Discuss the progression of Propofol through the body from entry
Initially, all intravenously administered propofol resides in the blood
Then, there is a rapid redistribution to the vessel rich organs
Peak concentration of propofol in the brain occurs in 1 minute
Then, there is a redistribution from vessel rich organs to muscle and fat
Then redistribution of propofol out of the brain results in patient awareness
CNS Effects of Propofol
Rapid onset and emergence
Raises seizure threshold
Reduces cerebral blood flow, CMRO2, ICP and IOP
No analgesia
Myoclonus may occur
Pulmonary Effects of Propofol
Dose dependent respiratory depression
Infusion will decrease TV and increase RR
Decrease reflexes
Shifts CO2 response curve to the right
Bronchodilation
Cardiovascular Effects of Propofol
Decreases BP r/t decrease SNS and vasodilation
Decrease myocardial contractility and SVR
Decrease venous tone - > lower preload
Metabolism & Elimination Effects of Propofol
Hepatic and extra hepatic metabolism
Renally excreted
Propofol has the potential to change urine color (green or cloudy)
Effects of Propofol on Muscles
Does not prolong neuromuscular blockade but can offer adequate intubation conditions
Additional Considerations with Propofol Usage
There is no evidence that propofol should be avoided in egg or soy allergic patients
Contains sulfites
Painful on injection
Thrombophlebitis
Bacterial infection risk
What is Propofol Infusion Syndrome?
Long-term high dose propofol infusions may result in metabolic derangements and organ system failures
Suggested etiology: Propofol inhibits oxidative phosphorylation
Risk Factors for Developing Propofol Infusion Syndrome
Risk factors include:
doses greater than 4 mg/kg/hour
duration greater than 48 hours
critical illness
concurrent catecholamine infusion
steroid administration
high-fat and low carbohydrate diet
Symptoms of Propofol Infusion Syndrome
metabolic acidosis, persistent bradycardia, cardiac failure, fever and severe hepatic and renal disturbances
What is Ketamine? Uses?
Chemical name: 2-(o-chlorophenyl)-2(methylamino) cyclohexanone hydrochloride
Class: phencyclidine derivative
Clinical Uses: May be used for GA induction and maintenance, and monitored anesthesia care
Used as an anesthetic, analgesic and antidepressant
Mechanism of Action of Ketamine
MOA: Non-competitive antagonist at NMDA receptor ion channels. Blocks the open channel, inhibiting the excitatory response to glutamate. It also binds with opioid, MAO, serotonin, NE, muscarinic and sodium channels
Provides amnesic and potent analgesia. DISSOCIATIVE STATE.
Ketamine inhibits neuronal sodium channels (producing a modest local anesthetic action) and calcium channels (causing cerebral vasodilatation).
DOES NOT WORK ON GABA
What can be used to premedicate a patient before giving Ketamine?
*IF THE PATIENT CONDITION ALLOWS,
benzodiazepine and antisaligogue (e.g. glycopyrrolate)
Ketamine dosage for IV Induction
IV Induction 1-2 mg/kg
Onset: 2-5 minute
DOA: 10-20 minutes (may require an hour for full orientation)
Ketamine dosage for IM Induction
IM Induction 4-6 mg/kg
Onset: 20 minutes
Ketamine dosage for sedation and multimodal infusions
Also, what concentrations are available?
Sedation 1-3 mcg/kg/min or 0.5-1 mg/kg boluses as needed
Multimodal infusion – 3-5 mcg/kg/minute
Caution: 3 dilutions: 10, 50 or 100 mg/cc
________ is the least protein bound of induction agents
ketamine
How is ketamine metabolized and excreted?
P450 enzymes in the liver
Chronic ketamine use induces enzymes that metabolize it
Active metabolite: norketamine is 1/3 as potent as ketamine and is renally excreted
Induction Agents and Protein Binding
Propofol – 98% Diazepam – 98%
Midazolam – 94% Dexmedetomidine – 94%
Lorazepam – 90%
Etomidate – 75%
Ketamine – 12%
Effects of Ketamine on the CNS
Increased CMRO2 (cerebral metabolic rate of oxygen (CMRO2) is the rate of oxygen consumption by the brain), Increased CBF, Increased ICP
Dissociative
Analgesic
Depression
Associated with emergence delirium, nightmares and hallucinations
- Benzodiazepines are an effective means of prevention
- Risk factors: age > 15, female gender, personality disorder, dose > 2mg/kg
Cardiovascular Effects of Ketamine
SNS stimulant
Increased SVR, HR, myocardial O2 consumption, PVR
Mild myocardial depression (in trauma patients)
Respiratory Effects of Ketamine
Bronchodilator
Maintains respiratory rate
Preserves reflexes at low dose
Increased secretions, often paired with an antisialagogue like glycopyrrolate
Occular Effects of Ketamine
Nystagmus
Caution Ketamine Usage in patients with a history of which medical condition(s)?
Hypertension
Angina
CHF
Increased intracranial pressure
Increased ocular pressure
Auditory/Visual hallucinations
Airway problems d/t increase secretions
Emergence reactions – vivid dreams, hallucinations (lasts 1-3 hours) and can be reduced with propofol and/or benzodiazepines
What is Etomidate?
R-1-methyl-1-(a-methylbenzyl) imidazole-5-carboxylate
Carboxylated imidazole derivate
Class: Hypnotic
Uses: May be used for induction of anesthesia. Considered for CV stability and trauma
Mechanism of Action of Etomidate
Binds to the GABA-a receptor
Lower doses: potentiates GABA at its receptors
Higher doses: directly stimulates the GABA receptor
Etomidate dosing
Induction Dose: 0.3 mg/kg
Onset: 1 minute
Duration: 5 -15 minutes
Metabolism & Excretion of Etomidate
Metabolism: Hepatic P450 enzymes and plasma esterases
Excreted by kidneys and in bile
No active metabolite
CNS Effects of Etomidate
Reduces intracranial pressure, cerebral blood flow, CMO2
Myoclonia likely related to an imbalance of excitatory and inhibitory pathways in the thalamacortical tract and can induce EEG seizure foci
No analgesia
Cardiovascular Effects of Etomidate
Hemodynamically stable
Minimal/no cardiac depression
Does not blunt sympathetic response to laryngoscopy
Pulmonary Effects of Etomidate
Brief hyperventilation followed by apnea
Mild respiratory depression (less than propofol)
No histamine release
Endocrine & GI Effects of Etomidate
Endocrine: inhibits cortisol; adrenal suppression via suppression of 11-beta hydroxylase
GI: N/V in 30-40% of patients
Hematologic Effects of Etomidate
May induce acute intermittent porphyria
What are porphyrias?
Porphyrias are a set of autosomally inherited metabolic disorders that are the result various defects in heme synthesis. Broadly, they can be classified into inducible, and non-inducible forms.
Inducible porphyrias
(i.e. Acute Intermittent Porphyria) can present with acute neurological and/or GI symptoms.
Patients may have anxiety, confusion, autonomic instability (manifested as hypertension or tachycardia), emesis, and severe abdominal pain.
Acute attacks of porphria can be precipitated by _______
stress, fasting, dehydration, sepsis, and certain medications, including some meds commonly used in the perioperative period.
What are examples of triggering agents for porphyria? What drugs are safe to use?
potential triggering agents = barbiturates, etomidate, diazepam, ketorolac, phenytoin and sulfonamides.
Drugs that are safe to use in the perioperative period include propofol, ketamine, succinylcholine, atropine, neostigmine, nitrous oxide, fentanyl and morphine.
What is dexmedetomidine?
Class: Selective alpha2 adrenergic agonist
Use: May be used for monitored anesthesia care, induction, analgesia and prevention of emergence delirium
Mechanism of Action for Dexmedetomidine?
Centrally and peripherally alpha 2 adrenergic receptor agonist. Acts on alpha 2 receptors thereby producing sedation by decreasing sympathetic nervous system activity and the level of arousal.
How does it regulate the cardiac system? by inhibiting norepinephrine release.
How does it regulate HR & BP? by decreasing the tonic levels of sympathetic outflow from the CNS and augmenting cardiac vagal activity.
Dosing for Dexmedetomidine
For procedural sedation: start at 1 mcg/kg over 10 minutes, followed by a maintenance infusion from 0.2 to 1 mcg/kg/hr.
Cardiac & Respiratory Effects of Dexmedetomidate
Cardiovascular: Hypotension and bradycardia
Respiratory: Minimal respiratory depression
Pain Effects of Dexmedetomidine and Miscellaneous
Pain: Analgesic properties, Enhance neuraxial blockade
Other: Reduces emergence delirium in pediatric patients, reduces inhalational agent requirements
Pharmacokinetics of Dexmedetomidine
Metabolized by the P450 system in the liver
Cleared by the liver
Inactive metabolites
Medication class & use of benzodiazepines
Class: Hypnotic
Clinical Use: Sedative, anxiolytic, amnestic, anticonvulsant (increases seizure threshold), muscle relaxant
MOA of Benzodiazepines
Enhances the response to the GABA A receptor
Provides anterograde amnesia, not retrograde amnesia
_______ is added to diazepam and lorazepam to enhance water solubility.
Propylene glycol
*Propylene glycol can cause venous irritation
Midazolam does not require propylene glycol , because it contains an imidazole ring
Absorption & Distribution of Benzodiazepines
Absorption: Oral, IV, IM, intranasal
Distribution
DOA: midazolam < lorazepam < diazepam
Determined by redistribution
Potency: Lorazepam > midazolam > diazepam
Highly protein bound
Metabolism and Excretion of Benzodiazepines
Metabolized by the liver
Excreted by the kidneys
Midazolam Dosing
Premed: titrated 0.5-2 mg IV (adult) or .2-.6 mg/kg PO (pedi)
Induction dose: 0.1 - 0.3 mg/kg
Onset, Peak and DOA of Midazolam
Onset: 1 minute
Peak: 2 – 5 minutes
DOA of induction dose: 6-15 minutes
Highly protein bound (95%)
Metabolism & Excretion of Midazolam
Metabolized by the CYP 450 system in the liver
Active metabolite: 1-hydroxymidazolam
Excreted by the kidneys
* Caution: May be related to post operative delirium in the elderly
Cardiovsacular Effects of Midazolam
Sedation dose: Minimal effects
Induction dose: decrease BP and decrease SVR
Respiratory Effects of Midazolam
Reduce muscular tone in upper airway
Decrease CO2 and hypoxia response
Patients with COPD are more sensitive depressant effects
CNS Effects of Midazolam
Anterograde amnesia
Anticonvulsant
Anxiolysis
Antispasmodic
No analgesia
Lorazepam… premedication dosing and metab/excretion
Premed: 2 - 4 mg PO or 0.25 – 1 mg IV
Risk for venous irritation and thrombophlebitis
Metabolized in the liver to an inactive metabolite
Excreted by the kidneys
Remimazolam
Acts on GABA receptors like midazolam and has organ-independent metabolism (plasma esterases) like remifentanil
In preliminary phase II trial
What is Flumazenil?
Competitive antagonist for benzodiazepines (reversal agent)
Short half life – risk for rebound effect
Flumazenil Dosing
Initial dose is 0.2 mg IV and titrated in 0.1 mg increments to prevent rebound effect
Onset: 1-3 minutes
DOA: 3 – 30 minutes
Caution for those on chronic benzodiazepines, may cause acute withdrawal
Chemical Composition of Barbituates
Urea + malonic acid -> barbituric acid
Your 2nd carbon is replaced by either oxygen or sulfa.
If its oxygen… = oxy barb
If its Sulfa = Thio barb – increases solubility
Clinical Use and MOA of Barbituates
Clinical Use: Phenobarbital is an anticonvulsant
Thiopental and Methohexital are anesthetic agents
MOA: Binds to the GABA A receptor resulting in increase Cl- conduction into the cell causing hyperpolarization
Lower doses – enhances GABA effect
Higher doses – directly stimulates GABA receptors
Absorption & Distribution of Barbituates
Absorption: IV, rectal methohexital
Distribution:
Onset ~ 1 minute
DOA ~ 20 minutes and is determined by redistribution
Metabolism & Excretion of Barbituates
Metabolism: Most barbiturates are metabolized in the liver
Excretion: Most barbiturates are excreted by the kidneys
Methohexital is excreted in feces
Cardiac Effects of Barbituates
Tachycardia r/t central vagolytic effect and decrease BP
CO is maintained r/t baroreceptor reflex (resulting in increase HR and contractility)
This process may be inhibited in the setting of hypovolemia, CHF & beta-adrenergic blockade
Respiratory Effects of Barbituates
Depression of the medullar ventilatory center decreases ventilatory response to hypercapnia and hypoxia
Induction doses often result in apnea
Airway reflexes are not completely depressed
CNS Effects of Barbiturates
Constriction of cerebral vasculature may result in decrease cerebral blood flow, cerebral blood volume, and intracranial pressure
Cerebral perfusion pressure increases Decreased CBF (vasoconstriction)
Decreased cerebral oxygen consumption
Renal & Hepatic Effects of Barbiturates
Renal: Reduction in renal blood flow and glomerular filtration, both in proportion to decrease systemic BP
Hepatic: Hepatic blood flow is decreased
Chronic barbiturate use often results in an increased metabolism of the CYP450
Stimulates the formation of porphyrin and should be avoided in individuals with porphyria
Thiopental
rapid-onset short-acting barbiturate general anesthetic
Thio barbiturate
Alkaline; pH ~10
Ultra short acting because of redistribution
Elimination half life: >11 hours
Onset: 30 seconds
Dose: Induction 3-6 mg/kg
Special considerations for Thiopental
Rapid onset
Painful injection
Highly alkaline making infiltration or inadvertent arterial injection serious.
Long half life means residual sedation post op
Cumulative with repeat doses as storage depots get filled.
Not currently available in US but used worldwide.
Methohexital: Brevital
Oxybarbiturate
Induction 1-2 mg/kg
Shorter half life than thiopental
CNS excitation
Phenobarbital
PO, IM, PR, IV
Oxybarbiturate
Sometimes used for procedural sedation
Brain protection; induced coma
ECT therapy
ECT is a treatment option for medication-resistant depression, mania, catatonia, suicidal ideation and forms of schizophrenia
Initial response: Increased PNS activity during the tonic phase
decreased heart rate (r/f asystole) and hypotension
Secondary response: Increased SNS activity during the clonic phase
increased heart rate (r/f SVT and atrial fibrillation) and hypertension
Drugs that increase seizure duration = _____
Etomidate
Ketamine
Alfentanil + Propofol (?together)
Aminophylline
Drugs that decrease seizure duration = _____
Propofol
Midazolam
Lorazepam
Fentanyl
Lidocaine
Drugs that have no effect on seizue duration = ______
Methohexital
Dexmedetomidine
Clonidine
Esmolol
Conditions that decrease seizure duration = _____
Hypoventilation, Hypercarbia, Hypoxia
Conditions that increase seizure duration = _____
Hyperventilation & Hypocapnia
Describe HOW Ketamine produces a dissociative state?
by depressing the cerebral cortex and thalamus and stimulating the hippocampus.
