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Flashcards in Anesthesia Adjuncts Deck (23):
1

Volume of distribution: half life

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

2

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

3

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

4

Opioid side effects

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

5

Meperidine unique effects

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

6

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)

7

Which two properties of opioids is resistant to tolerance?

Constipation and myosis

8

Which opioids inhibit serotonin reuptake?

-meperidine
-methadone
-tramadol

9

How does sufentanil compare to fentanyl?

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

10

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

11

Baclofen receptor and location in body

GABA-B receptor found in CNS and ANS

12

Dexmedetomidine
-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)

13

Dextromethorphan

-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)

14

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)

15

NMDA antagonists

-ketamine
-dextromethorphan
-methadone

16

Methylnaltrexone

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

17

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

18

Opioid elimination half-life
-short
-intermediate
-long

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

19

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)

20

Relative potency of opioids:
-meperidine
-morphine
-alfentanil
-fentanyl
-remifentanil
-sufentanil

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

21

Largest patient factor that prolongs opioid clearance

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

22

Partial opioid agonists

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

23

Efficacious applications of 0.04 mg naloxone

-N/V
-sedation
-pruritus (including neuraxial opioids)