Vasodilators Flashcards
SV is determined by?
- Preload
- Afterload
- Contractility
What effect will an increase of B1 receptors do?
Where is it located?
B1 receptors are located on the heart
and activation of this receptor results in INCREASED CO
What does the activation of ALPHA 1 receptors do? where is it located?
Activation of alpha 1 receptors on the peripheral vasculature results in an increase in SVR
Causes of systemic hypertension
- renal artery stenosis
- Pheochromocytoma
- withdrawal from alcohol
- sympathomimetics
- rebound
How do you manage hypertension?
- Inhibit RAAS
- direct peripheral vasodilation
- effects of autonomic receptor
The patient population that should be started on B BLOCKERS as long as there is not overt HF
Acute Coronary Syndrome
–> as long as there is no exacerbation of HF or BB could cause worsening hypotension
When do you use B blockers as first-line agents for the management of hypertension
ACS [w/o HF]
Cardiac Dysrhythmias
Receptos sites where B- blockers may act upon (competitive inhibition)
B1 sites and effects
B1 - CARDIAC
- Decrease heart rate (negative chronotropic effects)
- Decrease cardiac output (negative inotropic effects)
- Inhibit the release of renin from the kidneys
Where can we find B2 receptors?
B2 found in the vascular and bronchial smooth muscle, metabolic
- B2 agonist –> albuterol will cause bronchial relaxation
Where can we find Alpha 1 receptors?
what do we get when we block alpha 1 receptors?
Alpha 1 is found in the vasculature
– decrease in peripheral resistance when blocked
Which ones are beta selective among the beta-blockers
MEAN
Metoprolol
Esmolol
Atenolol
Nebivolol
beta-blockers consideration / special population
beta 1 selectivity is overcome with large doses
–> if we give massive doses of metoprolol sometime we will hit the beta 2 receptors ;
- COPD patients on high dose beta-blockers may end up with blocked beta 2 receptors and this may cause vasoconstriction
What is the ratio of beta:alpha blockade on IV Labetalol
how about oral?
Beta:alpha (IV) = 7:1
Oral: 3:1
ratio of Metoprolol oral:iv
2.5 mg oral: 1 mg IV
When do you use Beta-blockers that are cardioselective??
- May be more preferable in patients with
- asthma/COPD,
- peripheral vascular disease, vulnerable to hypoglycemia
- Tachyarrhythmias
- Decrease risk of postoperative myocardial ischemia in patients at high risk for cardiovascular disease with perioperative administration
-
Prophylaxis against tachycardia/hypertension around procedures (e.g., laryngoscopy, tracheal intubation)
- Esmolol
Common adverse effects of Beta-blockers
- Hypotension
- Bronchospasm
- Bradycardia/heart block
- Possible worsening CHF
- masking of hypoglycemia (tremors and tachycardia)
- Angina and MI –> HIGHER RISK PATIENTS upon abrupt discontinuation
How can poorly controlled diabetes management be affected by B- blockers?
- May block the release of insulin from pancreatic β cells –> hyperglycemia
- Initial signs of hypoglycemia (tremors, tachycardia) can be masked
If a patient has known CAD and at risk for MI what should you do with the beta-blocker?
Perioperative management of β-blockers
-
Continue in patients at risk for myocardial infarction (e.g., known CAD, perioperative stress tests, diabetes treated with insulin, LV hypertrophy) during high-risk surgery (e.g., vascular, thoracic, intraperitoneal surgery, large blood loss)
- Pre- and post- non-cardiac surgery shown to decrease mortality, CV complications, myocardial ischemia
- Consider baseline blood pressure, possible intraoperative complications and start low dose postoperatively
What are the common selective alpha 1 blockers?
“zosin”
- Prazosin
- Terazosin
- Doxazosin
- Tamsulosin
what is the MOA of selective alpha 1 blockers
what is the downside?
Mechanism of action
- Post-synaptic α1 blockade: vasodilation of arterial and venous vessels
- downside: Usually long/longer half-lives
- common uses: hypertension, benign prostatic hyperplasia
- prazosin, terazosin, doxazosin, tamsulosin
MOA of non-selective alpha-blockers
when is it commonly used?
- Phenoxybenzamine, phentolamine
Mechanism of action
- Post-synaptic α1 blockade: vasodilation of arterial and venous vessels
- Pre-synaptic synaptic competitive α2 blockade–> release of presynaptic norepinephrine
Common uses: *pheochromocytoma management*
Adverse effects of alpha receptors blockers
- orthostatic hypotension
- Hypotension
- exaggeration of hypotension during epidural anesthesia –> alpha 1 receptor blockers tend to have a longer half-life [mind prolong hypotension even more] but can really happen to any antihypertensive
How do you overcome the effects of alpha-receptor blockers in the OR?
use vasoactive agents with alpha1 agonist activity
—> PHENYLEPHRINE [POTENT], NOREPINEPHRINE
Other atypical agents could include (not recommended as first line): epinephrine, angiotensin II, vasopressin
Alpha 2 receptor agonist
Clonidine
Dexmedetomidine
MOA of Clonidine compared to Dexmedetomidine
Mechanism of action
Clonidine
- Selective partial α2 agonist
- 220:1 (α2: α1 activity) –> reason for potent BP management
- The decreased sympathetic output from the central nervous system to peripheral tissues peripheral —-> vasodilation, decreased systemic blood pressure, heart rate and cardiac output
Dexmedetomidine
- Selective partial α2 agonist
- 1,600:1 α2 to α1 activity –> reason for more sedation
- alpha 2 receptors are in the locus coeruleus of brain stem
If you have a patient that is bradycardic and is on clonidine what should you do?
take clonidine off. it may cause a decrease in HR and CO
alpha 2 receptor agonist
Adverse SE
CAUTIONS?
big deal with Clonidine
- sedation
- Fever –> case report; really high close to 40 C . It starts within hours to dex then a day
- temporal, if dex is taken off usually it subsides
-
CAUTION:
-
REBOUND HYPERTENSION –> BIG DEAL WITH CLONIDINE
- Abrupt dc can result in rebound hypertension 8-36 hours after last dose
- most likely to occur in pts taking >- 1.2 mg/day
-
REBOUND HYPERTENSION –> BIG DEAL WITH CLONIDINE
What can rebound clonidine discontinuation cause?
-
tachycardia but predominantly hypertension
-
Beta 1 selective blockers can only control the HR but not the unopposed alpha-receptor
- Beta adrenergic blockade may worsen hypertension due to unopposed alpha receptors
-
Beta 1 selective blockers can only control the HR but not the unopposed alpha-receptor
- Tricyclic antidepressants may exaggerate the hypertensive response
How do you manage rebound hypertension with abrupt d/c of clonidine?
- Reinitiating clonidine
- Initiate vasodilators
- β- adrenergic blockade with concurrent α blockade [HR and BP control!!]
- Gradually taper (e.g., 7 days or longer)
MOA of ACE Inhibitor
prevents ACE then we will prevent angiotensin I conversion to angiotensin II