Etomidate/Propofol/Ketamine Flashcards
In a perfect world
drugs are stable in aqueous solution; water soluble
minimal CV or respiratory depression
Lack of hypersensitivity reactions
rapid and smooth onset of action
rapidly metabolized
produce a steep dose-response relationship
quick return to baseline mental status
Propofol
insoluble; requires a lipid vehicle for emulsification 10% soybean oil 2.25% glycerol 1.2% lecithin supports bacterial growht not chiral pain on injection no antagonist a rapid return to consciousness with minimal residual side effects is one of the most important advantages
pH of Diprivan
7-8.5
pKa of Diprivan
11
Diprivan contains
0.05% EDTA- ethylenediaminetetraacetic acid
pH of propofol
4.5-6.4
pKa of propofol
11
Propofol contains
0.025% sodium metabisulfite or benzyl alcohol
MOA of Propofol
Selective modulator of GABAa Receptor
GABA is major inhibitory transmitter in CNS
spinal motor neuron excitability not altered
Pharmacokinetics of Propofol
Clearance exceeds hepatic BF
context sensitive half-time infusions less than 40 mins
Not influenced by hepatic or renal dysfunction
decreased rate of plasma clearance in patients older then 60
Active metabolite of Propofol
4-hydroxypropofol
What do propofol reversibly bind to
erythrocytes and plasma proteins (50%)
plasma albumin (48%)
Free (2%)
Increase in free fraction of Propofol seen in
severe hepatic and renal disease
pregnancy
PD of Propofol (CNS)
rapid and pleasant loss and return to conciousness
may induce myoclonus secondary to disinhibition of subcortical centers (less then etomidate)
neuro protectant
PD of Propofol (CV)
may cause mild to moderate decrease in BP secondary to
- decrease in sympathetic tone and vasodilation (primarily)
- CNS cardiac and baroreceptor depression
PD of Propofol (Resp)
respiratory depression common in induction doses
DD with induction secondary to decreased sensitivity of respiratory center to O2
minimal bronchodilation
Propofol Induction Dose
Adult dose: 1.5-2.5 mg/kg
decrease dose in elderly
increase dose in pediatrics
effects exaggerated with CV disease
Continuous Infusion of Propofol
IV sedation
prompt recovery without residual sedation- great for endoscope
25-100ug/kg/min
minimial/ no analgesic properties
can be used in conjuction with anxiolytic and opioid
Maintenance of Anesthesia (Propofol)
associated with minimal PONV
100-300ug/kg/min
used in conjuction with a short acting opioid
Other applications of Propofol
antiemetic 10-15mg IV; followed by 10 ug/kg/min infusion Antipruritic 10 mg IV related to intrathecal opioids, cholestasis Anticonvulsant 1mg/kg Attenuate bronchoconstricction* effects intracellular Ca++ homeostasis Analgesic (neuropathic pain)
Contraindications of Propofol
Hypersensitivity (maybe lechithin allergy)
lipid metabolism disorder
sulfate allergy (more common in asthmatics)
use caution in elderly, debilitated and cardiac-compromised patients
PRIS
propofol infusion Syndrome
not seen in long term, high dose infusions of propofol
not seen in anesthesia
associated with significant morbidity and mortality
exact mechanism of action unknown
more common in adults, but children as well
Risk Factors of PRIS
> 4mg/kg/hr > 48 hours critical illness high fat low carb intake concmitant catecholamine infusion steroid administeration and inborn errors of mitchondrail fatty acid oxidation
Signs of PRIS
high anion gap metabolic acidosis cardiac failure persistent bradycarida refractory to treatment fever severe hepatic and renal disturbances
Clinical Features of PRIS (CV)
hypotension, bradycardia, widening QRS, VTACH or FIB, asystole, ischemic EKG, arrhythmia, heart failure
Clinical Features of PRIS (Resp)
hypoxia, pulmonary edema
Clinical Features of PRIS (Renal)
acute kidney injury, hyperkalemia
Clinical Features of PRIS (musculoskeletal)
rhabdomyolysis
Clinical Features of PRIS (metabolic)
hyperthermia, high anion gap metabolic acidosis, urine discoloration
Clinical Features of PRIS (hepatic)
hepatomegaly, abnormal LFTs, steatosis, lipidemia, hypertryceridemia
Propofol Abuse
addictive properties
well-being on emergence, develop a tolerance
incidence markedly increased over past ten years
18% of academic centers reported incidence of abuse or diversion
significant mortality rate among anesthesia providers
not a controlled substance (facility dependent)
Etomidate
Carboxylated Imidazole
Viewed as an alternative to propofol for IV induction, esp in the presence of an unstable cardiac patient
Ph and Pka of Etomidate
water soluble in an acidic pH and lipid soluble in physiologic
ph 8.1
pka 4.2
MOA of Etomidate
administered as a single Isomer
R+ isomer 5x more potent
selective modulator of GABAa receptors
Pharmacokinetics of Etomidate
Large Vd suggest significant tissue uptake
moderate lipid solubility as a weak base
75% bound to plasma albumin
prompt emergence secondary to redistribution to tissues and rapid metabolism
metabolized by hydrolysis (plasma esterases and mircrosomal enzymes in liver)
Pharmacodynamics of Etomidate
onset occurs rapidly; within one arm to brain circulation
return to consciousness 5-15 mins
CBF and CMRO2 both decreased (decreased toin ICP while maintain CPP)
involuntary myoclonic movements common (can involve a single muscle or groups, so severe can be mistaken for seizures… secondary to distribution to deep cerebral and brainstem
decreases amplitude and increases latency
maintain hemodynamic stability (advantage over propofol) - acts on alpha2 B adrenergic receptors which mediates increases in BP
minute volume decreases but RR increases
Clinical Uses of Etomidate
differs from most IV anesthetics in that cardiac depressive effects are minimial in doses required to produce anesthesoa
NOT AN INFUSION
induction doses up to 0.3mg/kg result in minimal changes in: HR, SV, CO
doses >0.45mg/kg results in decreased B/P and CO, apnea may occur with rapid injection
Induction Dose of Etomidate
Adult Induction Dose-
0.2-0.4mg/kg
involuntary myoclonic movements common
no analgesic properties
Side Effects and complications of Etomidate
spontaneous myoclonus due to disinhibitation of subcortical structures; administration of fentanyl or benzo can decrease incidence
causes adrenocortial suppression
Increased incidence of postoperative nausea and vomitting
incidence of allergic reaction is very low
minimal pain on injection
may activate seizure foci in specific populations; however has been shown to terminate status epilecpticus
What enzyme is inhibited with etomidate administration
11B-hydroxylase- inhibits conversion of cholesterol to cortisol
Etomidate is Contraindicated in what patient population
porphyrias
Ketamine
Phencyclidine
produces “dissociative anesthesia”
potent amnestic and analgesic
does not produce significant respiratory depression
does not require a lipid vehicle for dissolution
ph and Pka of ketamine
ph 3.5 to 5.5
pka 7.5
Pharmacokinetics of Ketamine
not significantly bound to plasma proteins (12% ) rapid distribution to tissues
highly lipid soluble, rapid transfer to BBB
demethlyation of ____ by CYP 450 microenzymes
elimination half-life 2-3 hours
MOA of Ketamine
binds non-competitely to the phenylcyclidine site of N-methyl-D apartate (NMDA) receptors (antagonist-glutatmate) resulting in depressive effect on the medial thalmic nuclei
Weak actions on GABAa receptors
Pharmacodynamics of Ketamine
produces a “dissociative state” patient is cataleptic
increased CBF CMRO2 and ICP increased
produces nystagmus increase IOP
increases HR BP and SVR (SNS nervous activation)
maintain spontaneous respirations
bronchodilator, not effective as sole agent
Ketamine as an Induction Agent
Best for : hypovolemic patients (trauma),
Adult induction Doses (induction 2-3 minutes IV)
1-2.5mg/kg IV
4-8 mg/kg IM (<10 minutes)
10 mg/kg orally (<10 minutes)
does not produce pain or irritation in injection
bronchodilation useful for patients in asthma
induction of anesthesia in patients with CAD is complicated
Clinical Uses of Ketamine
trauma patients benefit from favorable cardiovascular effects
provides analgesic effects at sub anesthetic doses
0.2-0.5mg/kg (somatic > visceral)
OB anesthesia without neonatal depression
chronic pain syndromes
used for burn patients
Ketamine Dart
good for pediatric patients with asthma
Ketamine Side Effects and Complications
produces effects similar to sympathetic nervous system stimulation
potent cerebral dilator; patients with intracranial pathology are considered vulnerable to sustained increase ICP
tolerance may develop
pulmonary arterial blood pressure, heart rate , CO and cardiac work and myocardial oxygen requirements all increased
apnea after administeration of succinylcholine prolonged
enhancement of nondeplorizing neuromuscular blocking agents
in patients are risk for MI during periop period, medications that block preconditioning should be avoided
increased oral secretions
Ketamine and Emergence Delirium
incidence 5-30%; Partially dose dependent
emergence associated with visual, auditory, proprioceptive and confusional illusions
frequently have morbid content and vivid color
factors: age > 15 female history of personality problems or frequent dreams
occurs less frequently with repeated doses
adminstering with benzos five minutes prior to surgery can decrease incidence (midazolam > diazepam)
atropine can increase incidence
Dextromethorpan
low affinity NMDA antagonist
commonly found in cough medicines as an antitussve
psychoactive effects increase abuse potential
Dextromethorpan (chemical structure)
D-isomer of the opioid agonist levomethorphan
Excessive intake of Dextromethorpan
hypertension, tachycardia, somnolence, agitation, slurred speech, ataxia, diaphoresis, skeletal muscle rigidity, seizures, coma
Dexmedetomidine
alpha2 adrenergic agonist
alpha2 antagonist (shorter then acting than clonidine) more selective for alpha2 then alpha1
differs from GABA drugs in that it produces sedation by decreasing sympathetic nervous system activity (inhibits NE release)
Where are highest density of dexmedetomidine receptor?
pontine locus cerulus
Atipamezole
is the specific and selective reversal agent of dexmedetomidine
Dexmedetomidine Pharmacokinetics
highly protein bound
undergoes extensive hepatic metabolism
half life 2-3 hours
Dexmedetomidine Clinical Uses
pre-treatment: attenuates hemodynamic response to tracheal intubation, decreases MAC and opioid requirements, increases hypotension
TIVA- 0.5-1ug/kg bolus over 15 minutes
0.2-0.7 ug/kg/hr infusion
severe bradycardia/asystole may follow administration
intranasal preop anxiolysis in peds patietnts
Scopolamine
anticholinergic
only anticholinergic drug for sedation
decreases activity of the reticular activating system
preop sedation (0.3-0.5mg IV/IM)
enhances effects of concomitantly administered (opioids and benzos)
strong antisialagogue effect
less lilkely to produce cardiac effects
commonly administered transdermal for N/V
Side effects of Scopolamine
mydriasis
cycloplegia
central anticholinergic symptom
overdose- characteristics of muscarinic cholinergic blockade
Scopoloimine reversal
physostigmine (anticholinesterase)
15-60ug/kg IV
repeat as required
