Vasodilators Flashcards
Idiopathic HTN
- overactivity of the ANS and an interaction with RASS and factors related to Na homeostasis and intravascular volume
causes of perioperative HTN
- hypercarbia
- hypoxia
- aortic cross clamp
- hypervolemia
- hypothermia
- pain
- airway manipulation
primary cause of peri-op HTN
- increased sympathetic discharge with sympathetic vasoconstriction
prevalence of peri-op HTN
~ 80% of cardiac surgery patients
~ 25% of non-cardiac surgery patients
- does not have to be a diagnosis of HTN
vasodilators MOA
- direct smooth muscle dilation (production of smooth muscle NO)
types of vasodilators
- alpha 1 antagonists (prazosin and labetalol)
- alpha 2 agonists (clonidine, alpha methyldopa)
- ACE inhibitors (captopril, enalapril)
how vasodilators are classified according to their predominate site of action
- arterial dilators
- venodilators
- balanced vasodilators
hemodynamic effects of vasodilators
- pure arteriole dilators cause minimal effects of preload
- pure venodilators do not exist
- balanced vasodilators decrease afterload and preload
reflex response to vasodilators
- reflex increase in HR (baroreceptors)
- redistribution of coronary blood flow (may improve or cause coronary steal)
coronary steal
- narrowed coronaries are already max dilated. Dilating other arteries may cause blood to be shunted away from the coronary vessels
SNP effect on coronary steal
- dilates both epicardial conductance and intramyocardial resistance vessels and in the presence of CAD, shunts blood away from the ischemic zone
NGT and coronary steal
- preferentially dilates conductance vessels and directs more blood toward ischemic zones
hydralazine effects and reflex response
- direct acting arterial vasodilator (alters Ca movement and metabolism)
- has its own receptor
- decreases BP (diastolic > systolic) and SVR
- reflex = (increase HR, contractility, renin activity, fluid retention, CO, SV)
who to avoid hydralazine in
- avoid with CAD, increased ICP, lupus
- increases myocardial O2 demand leading to ischemia (from reflex tachycardia)
side effects of hydralazine
- 5-10% of patients on hydralazine will have a positive ANA (lupus) titer (butterfly rash, joint pain)
- headache, dizziness, tremor, angina, tachycardia, flushing, palpitations, anorexia, agranulocytosis congestion, muscle cramps, edema
pharmacokinetics of hydralazine
- metabolized in the liver
- excreted in kidney
- highly protein bound
- onset 30 min
how nitroglycerine works and what it does to the body
- causes a release of nitric oxide for non-specific relaxation of the vascular smooth muscle
- dilates veins > arteries
- decreases PVR, venous return, myocardial O2 consumption
- relaxes coronary vessels and relieves spasms
nitroglycerin non-cardiac effects
- dilates meningeal vessels (caution with ICP) (causes headaches)
- decreases renal blood flow with decreased BP
- dilates pulmonary vessels
pharmacokinetics of nitroglycerine
- onset 1 min
- duration 3-5 min
nitroglycerine metabolism
- metabolized by glutathione nitrate reductase in the liver
- nitrite ion oxidizes Hgb to methemoglobin
- arterial vessels can build tolerance but not venous vessels
nitroglycerin warnings/ contraindications
- PDE 5 inhibitors (Viagra, Cialis) (usually end in “fil”)
- narrow angle glaucoma
- head trauma / cerebral hemorrhage
- severe anemia
- hypotension
advantages of nitroglycerine
- rapid onset
- coronary vasodilator
- dec myocardial O2 consumption
- no toxicities
- no coronary steal
- reduced PVR
disadvantages of nitroglycerin
- decreased diastolic BP
- reflex tachycardia
- possible hypotension
- tachyphylaxis
- methemoglobinemia
- intrapulmonary shunting
- prolonged bleeding time
sodium nitroprusside actions and effects on the body
- directly vasodilates arteries and veins
- decease BP and HR
- inc cerebral blood flow and ICP
- renal blood flow maintains
- overall reduction in myocardial O2 demand
- with abrupt discontinuation = reflex tachycardia and hypertension
warnings / contraindications w/ sodium nitroprusside
- congenital optic atrophy
- hypovolemia
- compensatory HTN (AV shunting, aortic coarctation)
- increased ICP
- severe renal/ hepatic impairment
presentation of cyanide toxicity w/ sodium nitroprusside
- hypotension, blurred vision, fatigue
- metabolic acidosis
- pink skin
- absence of reflexes
- faint heart sounds
toxic thiocyanide and cyanide levels
- thiocyanate (toxic >30)
- cyanide (toxic >2) (normal 0.2 smoker 0.4)
treatment of cyanide toxicity
- 100% O2
- correct acidosis
- 3% Na nitrate 4-6 mg/kg slow
- sodium thiosulfate
- hydroxocobalamin
phenoxybenzamine (dibenzyline) binding and uses
- nonselective alpha antagonist
- irreversibly binds to receptor (must wait for new receptors to be made)
- long-term preop control of pheochromocytoma
- relieve ischemia in PVD
- BPH to improve flow
phenoxybenzamine (dibenzyline) effects on body
- reduced PVR to reduce BP
- secondary increases in NE due to alpha 2 blockade can increase HR and CO
- crosses the BBB
oral alpha 1 antagonists
- prazosin
- terazosin
- doxazosin
- tamsulosin
- silodosin
- alfuzosin
clonidine receptor and effects
- central acting alpha 2 agonist
- decreases release of sympathetic neurotransmitters
- inhibits renin
clonidine actions
- decrease HR, BP, CO, SVR
- abrupt cessation may lead to rebound HTN
clonidine withdraw
- from sudden discontinuation, due to NE
- manifests with sudden HTN, tachycardia, restlessness, insomnia, headache, nausea
- at risk after 6 days of use
caution with clonidine
- severe coronary insufficiency, conduction disturbances, recent MI/CVA, CKD
clonidine and anesthesia
- reduced propofol and thiopental requirements
- alternative to N2O for shortening induction time and attenuating the adrenergic response to intubation during inhaled anesthesia
methyldopa (aldomet)
- acts as a false neurotransmitter in the periphery (alpha-methyl-NE is almost as potent as NE)
- in the CNS its metabolized to alpha-methylepinephrine (acts at alpha-2 to decrease sympathetic outflow)
- treats HTN during pregnancy
why hyperkalemia from ACE inhibitors
- prevents angiotensin II from causing K+ excretion
RASS pathway
- angiotensinogen from the liver forms with renin from the kidney to make angiotensin 1 which forms with ACE from the lungs to make angiotensin II
ACE inhibitors primary function and use
- predominantly arterial vasodilators
- treat CHF and MR by afterload reduction
- used post MI
- improves outcomes in DM
renal function and ACE inhibitors
- with HTN: decreased renal vascular resistance improves RBF and GFR
- with hypotension: if BP is decreased renal function may deteriorate b/c compensatory constriction is blocked
- avoid in pts with significant renal dysfunction or renal artery stenosis
side effects of ACE inhibitors
- cough, congestion, rhinorrhea
- angioedema from increased bradykinin
- do not use in pregnancy
peri-op issues with ACE inhibitors
- prolonged hypotension can occur
- risk of ARF
ACE inhibitor med interactions
- increased hypotensive effects with diuretics, vasodilators and anesthetics
- NSAIDs and ASA interaction: reduce antihypertensive effect, increased risk of hyperK and ARF
primary action of CCB
- negative inotropic effect
- negative dromotropic effect (AV conduction block)
- vasodilation of systemic, splanchnic, coronary and pulmonary beds
dihydropyridines
- nifedipine
- nicardipine
- amlodipine
- pure arterial dilators, minimal reflex tachycardia
- minimal negative inotropic and dromotropic effects
nicardipine
- potent vasodilator of systemic, coronary, and cerebral circulations
- arteriole specific vasodilator
- no coronary steal, favorable myocardial O2 supply/ demand
- onset < 5 min
clevidipine
- IV CCB (dihydropyridine)
- vasodilation reduces PVR, arteriole specific
- onset <5min, half life 1 min
- reduces gastric emptying
verapamil
- phenylalkylamine
- potent negative inotrope, dromotrope, and vasodilator
- for aortic stenosis, conversion of atrial re-entry tacyarrhythmias, coronary artery vasospasms
diltiazem
- benzothiazine
- used for rate control in a-fib and atrial tach
- moderate CYP3A4 inhibitor, weak CYP2D6 inhibitor, weak P-gp inhibitor (tons of drug interactions)
verapamil and diltiazem effect on myocardial O2 balance
- enhance myocardial O2 balance (decrease myocardial O2 consumption by afterload reduction and or negative inotrope effect and increased o2 delivery through coronary vasodilation
dihydropyridine vasodilators effect on myocardial O2 balance
- may worsen MvO2 by causing diastolic hypotension and reflex tachycardia (except nicardipine)
- decrease reperfusion injury after ischemia
CCB effect on renal perfusion
- increase RBF and GFR and induce naturesis
- benefits reversed in they induce hypotension
- reflex catecholamine release and angiotensin activation lead to decreased RBF and GFR
recommendations with CCB
- continue up to surgery without risk of significant drug interactions
- may potentiate NMB
- primarily block L type Ca channels in CV system (causing NDNMB to bind to P-type channels that effect Ach release)
BB actions
- decrease CO (HR and contractility)
- decrease renin release
- do not vasodilate
BB advantages over vasodilators
- no reflex tachycardia or widening pulse pressure
- improve MvO2
- antiarrhythmic activity
beta 1 selective BB
- metoprolol
- atenolol
- acebutolol
- bisoprolol
- esmolol
- decrease velocity of A-V conduction, HR, contractility, renin release, lipolysis
non-selective BB
- propranolol
- nadolol
- timolol
- pindolol
- carteolol
- block beta 1 and beta 2 (bronchoconstriction, peripheral vasoconstriction)
combined alpha 1 and non selective beta
- carvedilol
- labetalol
short acting BB elimination
- red cell esterases (esmolol)
adverse effects of BB
- non-selective blockade of beta 2 = vasoconstriction and worsening PVD, bronchospasm
- myocardial depression
- life threatening bradycardia asystole
- hyperkalemia in renal failure
BB contraindications and cautions
- bradycardia, heart block
- cardiogenic shock
- raynauds disease
- caution with asthma, COPD, diabetes, HF
propranolol
- non-selective BB
- lipid soluble (can penetrate CNS)
- undergoes 1st pass (70%)
esmolol
- beta 1 selective
- blunts cardiovascular response to intubation
- control SVT a-fib
- rapid onset and off
- red cell esterase metabolism
metoprolol
- beta 1 selective
- approved for treatment of angina and acute MI
- antihypertensive
- longer DOA
Labetalol
- combines a weak alpha blockade with weak non-selective beta blockade
- negative inotrope and chronotrope with vasodilation, providing antihypertensive action
- for aortic dissection
- treatment of tachyphylaxis with SNP
- intercranial HTN (does not increase ICP)
adverse effects of labetalol
- unwanted negative inotropy
- prolonged DOA with higher dose
- bronchospasm in high doses
- hyperkalemia in renal failure
- caution in hypothermic pt ( may exacerbate rewarming hypotension)
BB warnings
- negative inotropic effects and conduction delays are potentiated by general anesthetics
- rebound HTN and tachycardia with abrupt cessation
- mask hypoglycemia and hyperthyroidism
- anticholinesterases may increase bradycardia
treatment of BB overdose
- glucagon
- atropine
- beta 1 agonists
- high dose insulin
- IV lipids
- ca and bicarb
antihypertensives and pregnancy
- alpha-methyldopa is favored
- labetalol can be used in 2nd and 3rd trimester
- hydralazine during delivery
- nifedipine PO