Antihypertensives (Alpha Agents) - Week 2

Question 1

Effects of Alpha 2 receptor activation

Answer 1

Inhibits neuronal firing in CNS and PeriphNS
- HoTN
- Bradycardia
- Sedation
- Analgesia 
Other organ functions
- Decreased salivation and secretions
- Decreased GI motility
- Inhibits renin release
- Inc GFR
- Inc Na and H2O secretion
- Dec insulin release

Question 2

What type of drug is Phenoxybenzamine?

Answer 2

Nonselective alpha antagonist

Question 3

Does Phenoxybenzamine bind reversibly to the receptor?

Answer 3

NO. It binds irreversibly and has a half-life of several days.

Question 4

Uses of Phenoxybenzamine

Answer 4

• long-term pre-op tx t control the effects of pheochromocytoma (chemical sympathectomy)
• Relieve ischemia in PVD
• Improve flow for BPH (flomax, papaflo, hytrin are now used more)

Question 5

T/F Phenoxybenzamine reduces BP by reducing PVR.

Answer 5

True

Question 6

Secondary increases in NE due to alpha 2 blocked can:

Answer 6

inc HR and CO

Question 7

Does Phenoxybenzamine cross the BBB?

Answer 7

Yes

Question 8

Side effects of Pehnoxybenzamine

Answer 8

Sedation
Depression
Tiredness
Lethargy
HA
N/V
Postural HoTN
Tachycardia
Arrhythmias

Question 9

What are the half life and duration of Phenoxybenzamine, and how is it administered?

Answer 9

Half-life: 24 hrs
Duration of action: 4 days
Route of admin: PO

Question 10

What is Phentolamine?

Answer 10

mixed a1 and a2 antagonist

Question 11

What is phentolamine used for?

Answer 11

• HTN from pheochromocytoma
• HTN from clonidine w/d
• Erectile dysfunction
• Tx extravasation of catecholamines

Question 12

Half-life and onset of Phentolamine (IV and IM)

Answer 12

Half-life: 19 min
Onset IM: 15-20 min
Onset IV: immediate

Question 13

Oral Alpha 1 antagonists

Answer 13

“-osin’s”
Prazosin, Terazosin, Doxazosin, Tamsulosin, Silodosin, Alfuzosin

Primarily used for BPH; only used for HTN if everything else has failed

Question 14

Uses for Alpha agonists in anesthesia

Answer 14

Premedication
Sedation
Anesthetic sparing effect
Regional anesthesia
Intrathecal, epidural, or caudal admin
Periph nerve block
Post-op analgesia
Analgesia of labor
Chronic pain
Prevent/tx drug w/d
Prevent/tx post-op shivering

Question 15

T/F: According to the Cochrane Review, A2 agonists decrease overall mortality, cardiac mortality, and MI and are esp beneficial in vasc surg.

Answer 15

True

Question 16

When using A2 agonists, the anesthetist should monitor for:

Answer 16

Excessive HoTN and bradycardia

Question 17

How does clonidine work?

Answer 17

Central acting Alpha 2 agonist that decreases the release of symp NT’s and inhibits renin release; has a much greater affinity for a2 than a1 (220:1)

Question 18

CV effects of Clonidine:

How does it affect the baroreceptors?

Answer 18

dec HR, BP, CO, and SVR

barorecptor reflexes are preserved

Question 19

Abrupt cessation of clonidine may lead to:

Answer 19

Rebound HTN

Question 20

From what do the s/s of clonidine w/d occur, and what are the s/s?

Answer 20

s/s are d/t NE

• excessive HTN
• Tachycardia
• restlessness
• Insomnia
• HA
• Severe nausea

Question 21

A pt is at risk for clonidine w/d if using clonidine for at least _____.

Answer 21

6 days

Because NE release has been inhibited, the body has increased the number of B1 and A1 receptors all over the body to catch any available NE. When the NE comes rushing back in, it attaches to all the receptors it can find.

Question 22

disadvantageous s/e of clonidine

Answer 22

• drowsiness
• dizziness
• dry mouth
• orthostasis

Question 23

What are cautions to consider w clonidine?

Answer 23

• Severe coronary insufficiency
• Conduction disturbances
• Recent MI/CVA
• CKD

Question 24

Why is epidural clonidine not recommended for preoperative period?

Answer 24

it creates HoTN

Question 25

Clonidine effects on anesthesia

Answer 25

- dec prop requirements - alternative to N2O to - shorten induct time - attenuate adrenergic response to intub during inh anes - supplement regional blocks

Question 26

T/F: Dexmedetomidine is more selective to A2 over A1 than clonidine is.

Answer 26

True. Precedes has a 1620:1 affinity for a2:a1

Question 27

T/F: Precedex maintains resp stability in intub or extub pts and allows pts to be arousable and alert when stimulated because its sedation is a more natural sleep-like state.

Answer 27

True

Question 28

5 reasons Precedex is good for procedural sedation such as FOI and regional anesthesia administration

Answer 28

- maintains spontaneous resp - sedation more like natural sleep - some analgesic effects - no amnesic effects - safe for non-anesthesia providers to use

Question 29

T/F: Although no studies have been conducted for safety of Precedex in children, it is useful in children who were inadequately sedated for procedures w other techinques.

Answer 29

True.

Question 30

Intra-op advantages of Precedex:

Answer 30

- dec stress response - improved respirations - hemodynamic stability - improved efficacy of anes - inc recovery time - need fewer pain meds

Question 31

Post-op advantages of Precedex:

Answer 31

- cuts opiate use in half | - dec post-op shivering

Question 32

Adverse effects of Precedex - Overall - Bolus - Infusion

Answer 32

``` Over all - N/V - Fever - Hypoxia Bolus - HTN - bradycardia infusion - HoTN ```

Question 33

Precedex can cause clinically significant bradycardia and sinus arrest in what pt population?

Answer 33

Young, healthy pts w high vagal tone (or w rapid bolus)

Question 34

Do not give continuous precedex infusion to pts for > ______

Answer 34

24 hrs

Question 35

When using Precedex, exercise caution should be used in pts w:

Answer 35

- advanced heart block | - severe ventricular dysfunction

Question 36

How does Methyldopa work?

Answer 36

It is metabolized to alpha-methylepinephrine in the CNS which acts at A2 receptors to decrease symp outflow

Question 37

Methyldopa is commonly used to treat HTN in what pt population?

Answer 37

Pregnant pts (usually in 3rd trimester)

Question 38

S/e of methyldopa

Answer 38

- Sedation, HA, dizzy - Fluid retention (compounds fluid retention they already have) - orthostasis, bradycardia - hepatic necrosis - dry mouth, diarrhea, N/V - positive Coombs test, hemolytic anemia, bone marrow suppression (when used long term), impotence, rash