IV Anesthesia Flashcards by Rachael Petry

What is special about induction agents?

they have a short onset of action

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List the induction agents used in IV anesthetics.

Thiopental
Propofol
Etomidate

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List the additional agents (with longer onset of actions) used in IV anesthetics.

Ketamine
Diazepam, Lorazepam, Midazolam
Morphine, Meperidine, Fentanyl, Remifentanil

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What are the 4 components of achieving balanced anesthesia?

Relieve Anxiety
Relax Muscles
Induce unconsciousness
Prevent secretions

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How does balanced anesthesia contrast with “neurolept” analgesia?

Use of neurolept analgesia produces pain relief and provides a state of indifference (patient is responsive to command but is not compromised by situational anxiety)

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What agents are used for neurolept analgesia?

Droperidol

Fentanyl

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What does droperidol do to the patient?

state of indifference, anti-emetic, anti-convulsant

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What does fentanyl do for the patient?

analgesia

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What do you add to droperidol and fentanyl to get neurolept ANESTHESIA?

N2O

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What other combination can you use for neurolept analgesia in preparation for surgery (dry secretions + provide analgesia)?

Atropine

- Opiate (morphine or meperidine)

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What problem does the high level of lipid solubility pose for lipophillic (IV) anesthetics?

difficult to formulate them for injection

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What are two “tricks” for making lipophillic anesthetics more soluble for injection?

Adjust pH
Use surfactant like propylene glycol or glycerol
Use 2nd generation pro-drugs that yield same pharmacologically active product only once they are inside the body

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What problems may adding surfactant to a lipophillic anesthetic pose?

can sometimes give rise to a direct toxicity to the lining of the vein into which it is being administered; this can sometimes be avoided by diluting the drug and giving it more slowly

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What is the main MOA for IV anesthetics?

reinforcing the inhibitory action of GABA and glycine

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Which two IV anesthetics also have aneffect on the NMDA receptor for glutamate?

Ketamine (major inhibition)

Propofol (minor inhibition)

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List the IV anesthetics that are major inhibitors of GABA.

Barbiturates
Propofol
Etomidate

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List the IV anesthetics that are major inhibitors of glycine.

Propofol

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MOA of barbiturates.

prolong the binding of GABA to the receptor (increases the strength of the inhibitory effects of endogenous GABA, so increase efficacy)

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MOA of benzodiazepines.

Produce only an allosteric change in receptor activity, that is to say, they shift the dose response curve for GABA binding to the left, the increase potency but not efficacy.

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True or false: barbiturates and benzodiazepines both have a “ceiling effect”

FALSE: With increasing dose barbiturates produce greater and greater CNS depression, ultimately leading to coma and death.

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True or false: it is just as easy to overdose on barbiturates as it is on benzodiazepines.

FALSE: benzodiazepines are much safer and difficult to overdose with unless combined with drugs or alcohol (CNS depressants).

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What is the benzodiazepine antagonist that can rapidly reverse acute toxicities if they occur?

flumazenil

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What neurotransmitter is used in the consciousness pathway that activates the thalamus?

Ach

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What part of the brain is activated by Histamine, Serotonin, and GABA in the consciousness pathway?

cortex

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How do inhaled anesthetics compare to IV induction agents in terms of onset?

When compared with the onset of anesthesia with an inhaled anesthetic, the effects of an IV induction agent are almost instantaneous.

Where do IV anesthetics distribute to in the body?

Out of plasma into high flow organs then re-distributes to other organs (eventually adipose tissue if dosage is high enough)

What is happening when a patient awakens after IV anesthetia?

Awakening of the patient is due only to drug re-distribution, the timescale is far too short for metabolism or excretion to have had a meaningful impact upon drug load in the body.

What is the rate-limiting step in final elimination of the drug following surgery?

release of drug from adipose tissue

What two IV anesthetics have half lives that increase dramatically with the duration of drug administration (due to accumulation and release from fat, metabolism and elimination)?

Diazepam | Thiopental

What is the barbiturate used in IV anesthesia?

Thiopental

MOA: Reinforce the inhibitory effects produced by endogenous GABA binding to its receptor system.

Etomidate

MOA: Reinforce the inhibitory effects produced by endogenous GABA binding to its receptor system (can function like GABA at high concentrations). Also can block the binding of glutamate to its receptor

Propofol

TOXICITY: - Depress cerebral blood flow, cerebral O2 consumption and ICP. - Slight increase in HR, inhibition of cardiac output. - Inhibit respiratory rate and minute volume. - Porphyria*

Thiopental

What affect does thiopental have on CYPs?

induction

TOXICITY: - Depress cerebral blood flow, cerebral O2 consumption and ICP. - Slight increase in HR, inhibition of cardiac output. - Inhibit respiratory rate and minute volume. - Anti-emetic*

Propofol

What is propofol infusion syndrome?

fatal cardiovascular and organ-systems failure of unknown etiology with protracted use

TOXICITY: - Depress cerebral blood flow, cerebral O2 consumption and ICP. - NO side effects with heart* - Inhibit respiratory rate and minute volume. - Inhibition of Steroidogenesis→ fatalities in elderly

Etomidate

Which IV anesthetic is NOT used in the ICU?

Etomidate

MOA: physical occulsion of the glutamate channel

Ketamine

What are the major ways in which ketamine's toxicity differs from the other IV anesthetics?

- INCREASE in cerebral blood flow, NO EFFECT on cerebral O2 consumption, and INCREASE in ICP - INCREASE HR, CO and MAP - NO effect on respiratory system - Analgesic - Bronchodilatory - Hallucinations

What does it mean when you call ketamine a "dissociative anesthetic"?

Analgesic that preserves pharyngeal and laryngeal reflexes (patients can be unconscious with eyes open)

How do you treat ketamine hallucinations?

benzodiazepine

Why aren't benzodiazepines used to produce unconsciousness?

they have a long onset of effect

What do benzodiazepines do to a patient?

- Anticonvulsant - Antiemetic - NO ANALGESIA

What are the 3 most commonly used benzodizapeines in IV anesthesia?

Diazpeam Lorazepam Midazolam

Metabolism of midazolam.

Rapidly inactivated (halflife is 2-4 hours)

Metabolism of diazepam.

3 active metabolites (halflife is 20-40 hours)

Metabolism of lorazepam.

conugated for elimination

What happens when venodilation (decreased venous return) or reduced CO occur with administration of a benzodiazepine?

immediate compensation by increasing HR and myocardial contractility. Also, blood is shunted from the spleen and intestines into the portal system to increase venous return

When would the net effect of benzodiazepines be a depressant?

When compensatory reactions to venodilation and reduced CO cannot occur due to things like cardio-active drug preventing increases in HR or contractility or hemorrhage preventing blood mobilization from the periphery

List some advantages of opioid therapy.

- Absence of direct effects on the heart - Maintenance of regional blood flow autoregulation - Decreased airway reflexes (facilitates intubation) - Pain relieved but patient arousable - Non-organotoxic (no malignant hyperthermia)

List some disadvantages of opioid therapy.

- Incomplete amnesia - Histamine-related reactions - Increased blood requirements - Prolonged respiratory depression in ICU - CV instability (bradycardia, hypo- or hypertension; addition of N2O results in CV depression)

Which opioid is favored for a 20 minute procedure?

fentanyl (short duration of action, onset in seconds, no N/V)

Which opioid is favored for long lasting analgesia?

Morphine (poor BBB penetration but longer duration of action)

List the CV effects of opiates.

Dependent on speed of injection and presence of other CV agents. - Hypotension (secondary to histamine release) - Hypertension (reflex with light analgesia) - R-A-A effect - Intense pressor effect with naloxone

List the respiratory effects of opiates.

dose dependent respiratory depression due to unresponsiveness to CO2 in carotid bodies (reversible with naloxone or nalmefene)

List the other toxicities of IV opiates.

- Muscle rigidity (wooden chest) - Increased ICP - N/V, constipation, miosis

What is the overdose triad for opiates?

Pinpoint pupils Decreased respiration Coma

How does remifentanil differ from other opioid agents?

Remifentanil is an ultra-short acting drug that must be given by IV infusion. AND you must give analgesic coverage prior to terminating remifentanil infusion

True or false: effects of remifentanil are cumulative.

FALSE

What causes malignant hyperthermia?

Succinylcholine and volatile anesthetics leads to intracellular calcium release from the SR

Who gets malignant hyperthermia?

most commonly in young men as a result of genetic predisposition

What genetic predisposition exists for malignant hyperthermia?

Several genetic loci are implicated, most especially that of the ryanodine receptor (RYR1)

What is the presentation of a patient with malignant hyperthermia?

heat generation, increase (X 2-3) in end tidal CO2, total body rigidity, unexpected tachycardia and tachypnea, respiratory and metabolic acidosis OR unexpected cardiac arrest

How do you treat malignant hyperthermia?

- Stop giving trigger agent - Cool patient - Acid-base support (hyperventilate with O2) - Dantrolene

MOA of dantrolene.

permits the calcium to be repackaged back into the sarcoplasmic reticulum

DDI of dantrolene

CCBs (which interfere with calcium entry at the cell surface)

Prognosis for malignant hyperthermia.

in young males with undiagnosed cardiomyopathy (50% mortality)