Common Anesthesia Medications

Question 1

Discuss determinants of cardiac status and ways to affect it

Answer 1

Preload
- Decrease with venous vasodilators (nitroglycerine, nitroprusside) or diuretics (furosemide)
- increase with IV fluids
Heart Rate
- decrease with beta blockers (metoprolol, esmolol) or calcium channel blockers (diltiazem, verapmil)
- increase with anticholinergics (atropine), beta agonist (ephedrine, epinephrine) or pacemaker
Contractility
- decrease with general anesthetic or beta blocker (labetalol) or CCB
- increase with beta agonist (ephedrine, epinephrine, dobutamine) or aortic balloon pump
Afterload
- decrease with arterial vasodilators (nitroprusside, hydralazine) or ACE inhibitor
- increase with alpha agonist (phenylephrine, norepinephrine) or IV fluids

Question 2

Discuss general principles for vasoactive and vasodepressive medications

Answer 2

Vasoactive
- bradycardia without hypotension: atropine
- hypotension and bradycardia: ephedrine
- hypotension without bradycardia: phenylephrine
- hypotensive shock: phenylephrine or norepinephrine
- cardiac arrest: epinephrine
Vasodepressive
- hypertension and tachycardia in response to surgery: opioid or increase inhaled analgesia
- hypertensive crisis: labetalol

Question 3

Discuss the mechanism of action of each of the vasoactive agents

Answer 3

Ephedrine
- indirect stimulation of adrenergic receptors (alpha 1, beta 1&2) leading to vasoconstriction (alpha 1), increased HR and contractility (beta 1)
Phenylephrine
- selective alpha-1 adrenergic receptor agonist leading to vasoconstriction
Epinephrine
- non-selective agonist of all adrenergic receptors (alpha 1&2, beta 1&2&3) leading to vasoconstriction, increased HR and contractility
Norepinephrine
- mostly alpha 1 and 2 adrenergic receptor agonist
Atropine
- anticholinergic by competitive antagonism of muscarinic receptor which increase HR
Vasopressin
- ADH bind to ADH receptor leading to vasoconstriction

Question 4

Discuss the mechanism of action of vasodepressive agents

Answer 4

Hydralazine
- alpha 1 antagonist leading to peripheral vasodilation and decrease BP
Labetalol
- alpha 1 and beta 1&2 antagonist resulting in vasodilation, decrease HR and decrease contractility

Question 5

Discuss the mechanism, indication and contraindications for benzodiazepines

Answer 5

Mechanism
- Inhibit GABA
Indication
- anxiolytic
- hypnotic
- alcohol withdrawal
- anticonvulsant
- general anesthesia
Contraindication
- Hx of substance disorder
- fall risk
- cognitive disorder
- narrow angle, glaucoma, OSA, myasthenia gravis, liver disease
- pregnancy
- use of CNS depressant

Question 6

Discuss the risk factors for post-operative nausea and vomiting

Answer 6

Patient
- young
- female
- prior hx
- motion sickness
- non-smoker
Surgical
- longer surgery
- gynecological, urology, breast or middle ear surgery
Anesthetic
- general anesthesia
- peri- or post-op opioids

Question 7

Discuss the mechanism and dose of ondansetron

Answer 7

• 4-8mg IV Q6H after surgery
  Mechanism
• antagonist to 5HT3 receptor in chemoreceptor trigger zone and GI tract

Question 8

Discuss the mechanism and dose of dexamethasone for PONV

Answer 8

• 8-10mg IV before induction

- unknown mechanism

Question 9

Discuss mechanism and dose for haloperidol and prochlorperazine

Answer 9

• haloperidol 0.5-4mg IV at end of surgery
• prochlorperazine 5-10mg IV at end of surgery
• metoclopramide option post-operative
  Mechanism
• D2 receptor antagonist in chemoreceptor trigger zone

Question 10

Discuss mechanism and dose of diphenhydramine

Answer 10

• 25-50mg PO/IV Q6H
  Mechanism
• H1 receptor antagonist at vomiting centre and vestibular system

Question 11

Discuss when to give anti-emetic prophylaxis

Answer 11

Low Risk
- Hx of PONV or 2 risk factors
- single antiemetic
Moderate Risk
- Hx of PONV and 1 risk factor or 3 risk factors
- 2 agents with one being ondansetron
High Risk
- Hx of PONV on more than 1 occasion plus 1 risk factor
- all anti-emetics

Question 12

Discuss the indications and contraindications for muscle relaxants

Answer 12

Indications
- induction
- mechanical ventilation
- during surgery
- prior to ECT
- emergency treatment for laryngospasm
Contraindications
- Inability to maintain airway
- lack of resuscitation equipment
- known hypersensitivity
- positive history of malignant hyperthermia

Question 13

Discuss the two types of muscle relaxants

Answer 13

• Competitive non-depolarizing muscle relaxant that can be antagonized
  
  • Mivacurium, Rocuronium
• Non-competitive depolarizing muscle relaxant that cannot be antagonized
  
  • Succinylcholine

Question 14

Discuss the mechanism, dose and reversal of rocuronium

Answer 14

• 4-16mcg/kg/min
  Mechanism
• competitive antagonist to cholinergic nicotinic receptor
• onset in 60sec but last 40 minute
  Reversal
• Atropine 0.01mg/kg with Edrophonium 0.5-1mg/kg

Question 15

Discuss the mechanism and dose for succinylcholine

Answer 15

• 1mg/kg
• infusion of 50-150mcg/kg/min
  Mechanism
• binds nicotinic receptor and depolarizes motor plate so that post-synaptic membrane remains depolarized and unresponsive to ACh
• onset of 60 sec and lasts 5-10 minutes

Question 16

Discuss the ascending sensory nociceptive pathway

Answer 16

Transduction
- noxious stimuli activate nociceptor on free nerve endings
Transmission
- primary afferent sensory neuron transmit signal from periphery to spinal cord
- Delta fiber are myelinated mechanoreceptor and thermoreceptors so have fast somatotopically organized pain
- sharp/pricking pain
- C-fiber have polymodal receptor and are unmyelinated and less somatopically organized
Transmission
- primary afferent neuron synapse with secondary afferent neuron in substantio gelitanosa within dorsal horn
- secondary afferent cross spinal cord and travel in contra-lateral lateral spinothalamic tract to thalamus
- thalamus intergrate and sort according to region
- in ventral posterior lateral nucleus of thalamus synapse on tertiary neuron which goes to parietal lobe
Perception
- interpretation of pain

Question 17

Discuss the descending modulating pathway

Answer 17

Origin in Brainstem
- peri-aqueductal grey matter and locus ceruleus
- can be controlled by higher cerebral areas
Descending
- Descending nerve fibers travel in spinal cord to synapse on primary and secondary afferent neuron
- descending fiber secrete enkephalin, serotonin and norepinephrine to inhibit primary and secondary afferent neuron

Question 18

Differentiate between acute and chronic pain

Answer 18

• Acute pain serves a purpose

- Chronic pain when lasts longer than 3-6 months or persisting beyond resonable amount of time of tissue healing

Question 19

Discuss analgesia at each of the ascending and descending pain pathways

Answer 19

Ascending Nociceptive Pathway
- Foundational analgesia block nociception, transduction or transmission by decreasing inflammation
- local anesthetic block Na channel to prevent transmission
Descending Anti-Nociceptive Pathway
- pro-antinociceptive which activate descending pathway
- opioid activate endogenous receptors
- tramadol activate endogenous opioid receptors, alpha 2- adrenergic and serotonin
Descending Pro-Nociceptive Modulation
- inhibit descending pro-nociceptive signal
- NMDA antagonist (ketamine)
- anti-convulsants block voltage gated Ca channel

Question 20

Discuss the mechanism of action of acetaminophen

Answer 20

• inhibit central COX enzyme and spinal serotonergic pathway as well as decrease inflammation

Question 21

Discuss the mechanism of action of NSAID

Answer 21

Reversible COX-1 and COX-2 inhibitors
- inhibit COX-1 leading to increased gastric secretion and disruption of platelet homeostasis
- inhibit COX-2 to inhibit inflammation and acute pain
COXib is irreversible inhibitor of COX-2 Only
- decreased risk of PUD
- preserved platelet homeostasis which improves tissue healing
- COX-2 inhibition only
- has increased risk of cardiovascular disease
- contraindicated in those with sulfa allergy

Question 22

Discuss the mechanism of action for opioids

Answer 22

Mechanism
- activate mu receptor resulting in analgesia, sedation and respiratory depression
- activate kappa receptor resulting in weak analgesia, sedation and psychomimetric side effect
- activate delta receptor resulting in weak analgesia and respiratory depression
Work at 4 Levels
- suppression of limbic and cerebral cortex so not aware of pain
- activation of peri-aqueductal grey in brainstem to activate anti-nociceptive pathway
- inhibit neurotransmission at synapse between primary and secondary afferent neuron
- activate peripheral opioid receptors to decrease pro-inflammatory neuropeptides