Anesthesia Adjuncts Flashcards Preview

Anesthesia > Anesthesia Adjuncts > Flashcards

Flashcards in Anesthesia Adjuncts Deck (23):

Volume of distribution: half life

Inversely proportional
*bigger Vd-->longer t1/2 (same rate of clearance)


Mechanism of opioids

-All opioid receptors couple to G proteins; binding of an agonist to an opioid receptor causes membrane hyper polarization
-Acute opioid effects are mediated by inhibition of adenylyl cyclase (reductions in intracellular cAMP) and activation of phospholipase C
-Inhibit voltage-gated calcium channels and activate inwardly rectifying potassium channels (increase K and decrease Ca conductance)-->decrease release of neurotransmitters


Opioid Receptors

Mu 1: supraspinal analgesia, muscle rigidity, euphoria, miosis, bradycardia
Mu 2: resp depression, constipation, sedation
Kappa: spinal analgesia, stops shivering, sedation, miosis
Delta: resp depression (maybe), constipation
Sigma: hallucinations/dysphoria


Opioid side effects

-interruption of sympathetic tone
-parasympathetic-like effects
-decrease preload


Meperidine unique effects

-decreases myocardial contractility
-atropine like structure (increase HR, mydriasis)
-histamine release (like morphine)-->decreased SVR and preload


Opioid effects on respiratory system

-increased apnea threshold
-increase PaCO2 (acidosis)
-shifts CO2 response curve downward and to the right
-decreases hypoxic drive
-decreases A-a gradient and P/F ratios (but only at extremely high PaCO2s, especially at low FiO2s)


Which two properties of opioids is resistant to tolerance?

Constipation and myosis


Which opioids inhibit serotonin reuptake?



How does sufentanil compare to fentanyl?

-more potent
-greater tendency to depress ventilation and cause bradycardia
-context sensitive half time increases to a lesser extent w/long infusions (>2hrs)


Benzodiazepine receptor and effect

-Alpha subunit of GABA-A receptor (sedative, anxiolytic, hypnotic, amnestic, anticonvulsant) in cerebral cortex
-Gamma subunit of GABA-A receptor in the spinal cord (muscle relaxation)
-Enhanced chloride conductivity across (into cell) the membrane leading to hyperpolarization and reduced excitability of post-synaptic neurons in cerebral cortex
-changes the Nernst potential- the potential difference between EC and IC side of cell


Baclofen receptor and location in body

GABA-B receptor found in CNS and ANS


-side effects at high doses
-compared to clonidine
-effect of discontinuation

-at high doses, cross reactivity with alpha-1 receptor (HTN w/baroreceptor mediated bradycardia)
-more selective for alpha-2 receptor than clonidine
-discontinuation of prolonged use can lead to rebound HTN (like clonidine)



-primarily used as antitussive agent
-NMDA antagonist (like ketamine and methadone- local anesthetic)
-local anesthetic effects
-SSRI qualities- like methadone (so should be used w/MAOIs)


Prolonged exposure to opioids and hyperalgesia

-fewer opiod receptors: down regulation and internalization of opioid receptors, leading to less membrane hyper polarization (of pain fibers/pathways)
-reduced response of opioid receptors: "decoupling" of secondary messaging systems (G-proteins)
-down-regulation of glutamate receptors in the spinal cord leading to wind up(opioids also have weak NMDA agonistic properties)


NMDA antagonists




Peripheral opioid antagonist that cannot pass the BBB
-used for reversal of GI side effects of opioids


Opioid side effects

GI: decrease motility, gastric secretions, and pancreatic secretions; decreased LES tone and increased GERD; increased sphincter of Oddi; increased amylase and lipase
CNS: directly stimulate CTZ, decreased sympathetic outflow
Airway: decreased cough reflex
Respiratory: decreased CO2 responsiveness, increased OSA sxs
CV: histamine release (morphine, meperidine)
MSK: muscle rigidity


Opioid elimination half-life

-short: remifentanil (10min)
-intermediate: morphine-long: methadone (34 hrs)


Elimination half-life and duration of action: fentanyl v morphine

-fentanyl has longer elimination half-life but shorter duration of action
-fentanyl is very lipophilic and distributes from central compartment to muscle and fat, thus terminating its effects (large volume of distribution)


Relative potency of opioids:

Meperidine: 0.1
Morphine: 1.0
Alfentanil: 10
Fentanyl: 100
Remifentanil: 300
Sufentanil: 1,000


Largest patient factor that prolongs opioid clearance

Advanced age
-morphine half-life almost doubles in the elderly


Partial opioid agonists

Nalbuphine and butorphanol
-less resp depression
-very sedating
-less GI effects (esp butorphanol)
-precipitate withdrawal sxs in dependent patients (nalbuphine)


Efficacious applications of 0.04 mg naloxone

-pruritus (including neuraxial opioids)