Anesthesia Adjuncts (Exam IV) Flashcards
β agonism results in activation of _____ which then produces _______.
Adenylyl Cyclase (AC)
cAMP
Does Ca⁺⁺ influx or efflux during β agonism?
Influx
What type of receptors are β receptors?
GPCR
What types of β receptors are there and where are they primarily located?
- β1 - Heart
- β2 - Lungs
- β3 - Fat/Muscle
Chronic administration of β blockers results in what effect on receptors?
Receptor upregulation (aka ↑ # of receptors)
After β receptor desensitization from prolonged catecholamine exposure, what drug class can restore receptor responsiveness?
β-blockers
How do β blockers protect myocytes from perioperative ischemia?
By ↓O₂ demand on the heart
T/F. β blockers will potentiate renin release.
false. β blockers will inhibit renin release
How will β blockers affect the cardiac foci action potential?
Prolong Phase 4
↓ dysrhythmias during ischemia and reperfusion.
How will β blockers affect diastolic perfusion time?
β blockers will increase diastolic perfusion time.
What type of HTN is a possible indication for β blocker therapy?
Essential Hypertension
What is SCIP?
Describe the protocol and its goals.
- Surgical Care Improvement Protocol
- β-blockers must be given within 24 hrs of surgery for patients at risk for cardiac ischemia and ones already on β-blocker therapy.
What were the three β1 selective agents discussed in lecture?
- Atenolol
- Metoprolol
- Esmolol
What percentage of β receptors in the myocardium are β1 ?
75%
Do cardio-selective β-blockers cause vasodilation?
No
What non-selective β-blocker has active metabolites and is generally shitty for anesthesia?
Propanolol
Differentiate the clearance mechanisms of metoprolol and esmolol.
- Metoprolol = Hepatic
- Esmolol = Plasma cholinesterases
Differentiate the E½ of metoprolol and esmolol.
Metoprolol E½ = 3-4 hours
Esmolol E½ = 9 minutes (0.15 hr)
When propanolol is given, what effect lasts longer, negative inotropy or negative chronotropy?
Negative chronotropy (bradycardia) lasts longer
What is a possible reason why the heart rate slowing effects of propanolol last longer than the negative inotropic effects?
Possible β1 sub-receptor types (ex. β1A, β1B, etc.)
Propanolol will decrease the clearance of which two important anesthetic drug classes?
- Opioids
- Amide LA’s
What drug is the most selective β1 antagonist?
Atenolol (Tenormin)
What are the three benefits of Atenolol?
- Good for non-cardiac sx CAD patients (↓ complications for 2 years)
- No insulin-induced hypoglycemia
- Does not cross the BBB (no fatigue)
What is the dose for Atenolol?
5mg q10min IV
What is the dose of metoprolol (Lopressor)?
1mg q5min (Given in 5mg “blocks”)
What two formulations of metoprolol are there?
- Tartrate = E1/2 2-3hr (bid - qid)
- Succinate = E1/2 5-7hr (qd)
What β blocker would be used for treat intubation stimuli?
Esmolol (Brevibloc)
What are the onset and offset of esmolol?
Onset: 5 min
Offset: 10-30min
What is the initial dose for esmolol?
20-30mg IV
Caution should be taken when giving esmolol with which two conditions?
Why?
- Cocaine and/or epinephrine
- Can cause pulmonary edema and cardiac collapse
Are the effects of CCBs and β-blockers additive?
No, synergistic
What two scenarios were given in class for a β1 indication over a non-selective β blocker?
- DM: β2 can cause hypoglycemia by insulin potentiation
- Airway: blocking β2 potentiates bronchospasm
What volatile anesthetic will cause the greatest additive depression when combined with a β blocker?
The least?
Why does this not matter?
- Enflurane = greatest additive depression
- Isoflurane = least additive depression
- Not significant between 1-2 MAC
What 2ⁿᵈ messengers are potentiated by α1 agonism?
IP₃ → Ca⁺⁺ release from SR
What occurs with α2 agonism?
↓ release of NE in the brainstem
Is phenylephrine primarily a venoconstrictor or an arterioconstrictor?
Venous constriction > arterial constriction
Phenylephrine clinically mimics norepinephrine but is….
less potent and longer lasting
What is the normal dosing of phenylephrine?
50-100mcg/mL IV push
What adverse effect results from phenylephrine?
How is it resolved?
- Reflex bradycardia
- Stopping the drug
What is the ratio of β to α blockade for Labetalol?
7:1
Is Labetalol a selective β antagonist?
No: non-selective β and selective α1 antagonist
Which of the following receptors does Labetalol antagonize?
A. α1
B. α2
C. β1
D. β2
A, C, and D
What is the dose for labetalol?
2.5 - 5mg IV; 10mg max
Which of the following drugs would you utilize for a post-carotid endarterectomy with a BP of 214/62 ?
Labetalol
Esmolol
Esmolol
Labetolol could drop the dBP too much due to alpha effect.
Which drug is an indirect acting sympathomimetic?
Ephedrine
Releases NE
What is the IV push dose of epinephrine?
How long does it last?
- 2-8mcg IVpush
- 1-5 min
What is the infusion dose of epinephrine for β2 effects?
1-2 mcg/min
What is the infusion dose of epinephrine for β1 effects?
4 mcg/min
What is the infusion dose of epinephrine for predominantly α effects?
10-20 mcg/min
What catecholamine will have the greatest effect on heart rate and cardiac output?
Epinephrine
What catecholamine will have the greatest effect on SVR?
Phenylephrine
Which SNS agonist can be given IM?
Why would this be done?
- Ephedrine IM 50mg
- Long lasting increase in BP for OB patients.
Why does tachyphylaxis occur with ephedrine?
Ephedrine depletes NE stores
What is the preferred sympathomimetic for parturient patients?
Why?
Ephedrine (It doesn’t effect uterine blood flow)
How does phenylephrine compare to ephedrine in parturient patients?
Phenylephrine has similar effects but has the additional benefit of a higher umbilical pH in neonates.
What is the mechanism of action of vasopressin?
Stimulation of vascular V1 receptors → arterial vasoconstriction
What drug would be utilized for catecholamine-resistant hypotension?
Vasopressin
What drug would be used for ACE-Inhibitor induced resistant hypotension?
Vasopressin
Resistant hypotension can occur with both ACEi and ARBs.
How does Nitric Oxide cause vasodilation?
In broad terms.
NO → GC → cGMP → Ca⁺⁺ inhibition and increased uptake.
How can vasodilators alleviate pulmonary congestion?
By decreasing venous return via venodilation
What does Nitroprusside dissociate on contact with?
What is the result?
Dissociates on contact with oxyhemoglobin → methemoglobin, NO, and cyanide released.
What does nitroprusside vasodilate?
Arterial and venous vasculature
What vasodilator absolutely requires arterial line monitoring?
Nitroprusside.
What is the dose of Nitroprusside?
0.3 - 2 mcg/kg/min
When is nitroprusside used?
- Hypotensive necessary surgeries (aortic, spine, etc.)
- Hypertensive emergencies (post CEA’s)
What drug is used to treat cyanide toxicity?
Methylene blue
What signs would tip you off to possible cyanide toxicity secondary to nitroprusside administration?
- ↑ need for nitroprusside
- ↑ SvO₂
- Metabolic acidosis
- LOC changes
Where does nitroglycerin work?
- Coronary arteries
- Venous capacitance vessels
Would nitroglycerin increase or decrease preload?
↓ preload
Does nitroprusside or nitroglycerin exhibit tachyphylaxis?
Nitroglycerin
What is the nitroglycerin dose?
5 - 10 mcg/min
What is the firstline treatment for sphincter of Oddi spasm?
What is second?
- Glucagon
- Nitroglycerin
What are the indications for nitroglycerin?
- Acute MI
- Controlled Hypotension
- Sphincter of Oddi spasm
- Retained placenta
How does hydralazine work?
(ITP?)↓ Ca⁺⁺ release and systemic arterial vasodilation
When does hydralazine peak?
What is it’s half-life?
- Peak: 1 hour
- ½-life: 3-7 hours
What is the initial dose of hydralazine?
2.5mg
What are the three categories of CCBs?
Where do each interact?
- AV Node (Phenylalkylamines & Benzothiazepines)
- Vasculature (Dihydropyridines)
How do CCBs generally work?
Bind and block L-type VG-Ca⁺⁺ channels thus ↓ Ca⁺⁺ influx.
CCBs will ______ blood pressure and ________ coronary blood flow.
decrease; increase
Which CCB has the greatest coronary artery dilation and least myocardial depression?
Nicardipine
What is the dose of nicardipine?
5mg/hr (2.5mg titration) max 15mg
