Hypertension and Antihypertensive Drugs

Hypertension Study Notes

• Primary hypertension is idiopathic and accounts for 90-95% of cases.
• Secondary hypertension accounts for 5-10% of cases and results from conditions like pheochromocytoma, pre-eclampsia, renal artery disease, or sleep apnea.
• Malignant hypertension is a medical emergency indicated by a blood pressure above 180/120.
• Blood pressure is calculated as cardiac output multiplied by systemic vascular resistance (BP = CO × SVR).
• High-normal blood pressure is a systolic reading of 130–139 mm Hg or a diastolic reading of 85–89 mm Hg.
• Hypertension impacts roughly 7.5 million Canadians.

Antihypertensive Drugs

• Medications used to treat hypertension are categorized as adrenergic drugs, ACE inhibitors, ARBs, calcium channel blockers and diuretics.

Adrenergic Drugs

• Includes adrenergic neuron blockers (central and peripheral).
• Includes α2-receptor agonists (central).
• Includes α1-receptor blockers (peripheral).
• Includes β-receptor blockers (peripheral).
• Includes combination α1- and β-receptor blockers (peripheral).

Centrally Acting Adrenergic Drugs

• Clonidine and methyldopa are centrally acting.
• They reduce norepinephrine production.
• They stimulate α2-adrenergic receptors.
• Renin activity in the kidneys is reduced.
• Blood pressure reduction results.

Peripherally Acting Adrenergic Drugs

• Block α1-adrenergic receptors and dilate arteries and veins.
• Blood pressure decreases when α1-adrenergic receptors are blocked.

A2-Adrenergic Receptor Stimulators (Agonists)

• Clonidine and methyldopa belongs to this class.
• They are not typically the first choice for antihypertensive treatment.
• They have a high incidence of adverse effects like orthostatic hypotension, fatigue, and dizziness.
• These drugs are used as adjuncts when other treatments for hypertension have been unsuccessful.
• They can be used with other antihypertensives, such as diuretics.

Beta-Blockers

• Blocks beta 1 receptors, which causes reduced heart rate.
• Atenolol, metroprolol, and propranolol are beta-blockers.
• Causes reduced secretion of renin.
• Long-term use of beta-blockers results in reduced peripheral vascular resistance.

Adrenergic Drugs: Adverse Effects

• Orthostatic hypotension has a high incidence.
• Common effects are bradycardia with reflex tachycardia and dry mouth.
• Other common effects include drowsiness, sedation, constipation, depression, edema, and sexual dysfunction.
• Further adverse effects include sleep disturbances, nausea, rash, headaches and cardiac disturbances such as palpitations.

Angiotensin-Converting Enzyme (ACE) Inhibitors

• Effective for hypertension and heart failure, ACE inhibitors are safe and often used as first-line medications.
• ACE inhibitors include ramipril, captopril, enalapril, perindopril, and quinapril.
• Thiazide diuretics or calcium channel blockers may be used in combination with them.
• ACE is inhibited which stops conversion of angiotensin I to angiotensin II.
• Angiotensin II is a potent vasoconstrictor stimulating aldosterone secretion in the adrenal glands.
• ACE inhibitors can be prescribed to treat hypertension and heart failure.
• They slow the progression of left ventricular hypertrophy post-MI (cardioprotective).
• Useful due to their renal protective effects in patients with diabetes.
• They reduce blood pressure.
• They reduce blood pressure by decreasing SVR.
• They prevent sodium and water resorption, by inhibiting aldosterone secretion.
• Diuresis results as blood volume and return to the heart decreases.
• Preload is decreased.
• The heart is required to do less work.
• They reduce glomerular filtration pressure, and proteinuria.
• Considered drugs of choice for treating cardiovascular issues in patients with diabetes, and prevent diabetic nephropathy progression.
• Adverse effects include fatigue, dizziness, headache, taste impairment, mood changes, a first-dose hypotensive effect, hyperkalemia, dry cough and angioedema which is rare but potentially fatal.

Angiotensin II Receptor Blockers

• Block vasoconstriction and the secretion of aldosterone.
• ARBs are also called angiotensin II blockers, which are well-tolerated and do not cause a dry cough.
• ARBs such as losartan and valsartan selectively block angiotensin II binding to type 1 receptors in vascular smooth muscle and the adrenal gland.
• ARBs are beneficial for patients with hypertension and HF, but should be used cautiously in those with renal or hepatic dysfunction or renal artery stenosis, and are not to be taken while breastfeeding.
• Commonly include headaches and upper respiratory infections.
• Dizziness and insomnia are potential side effects.
• Further adverse effects include diarrhea, heartburn, nasal congestion, back pain and fatigue.
• Hyperkalemia is less likely than with ACE inhibitors.

Comparison of ACE Inhibitors and Angiotensin II Receptor Blockers

• Appear to be equally effective for treating hypertension and are well tolerated.
• ARBs do not cause a cough and may be better tolerated with lower post-MI mortality than ACE inhibitors.

Calcium Channel Blockers

• Blocks binding of calcium which prevents muscle contraction for primary use for hypertension and angina
• Leads to decreased SVR, peripheral smooth muscle tone, and blood pressure.
• Amlodipine, diltiazem, nifedipine, and verapamil are useful.
• Treat angina, hypertension, and antidysrhythmias
• May treat migraine headaches, Raynaud's disease, and cerebral artery spasms after subarachnoid hemorrhage may be treated.

Diuretics

• Considered first-line antihypertensives.
• Decreases plasma and extracellular fluid volumes.
• Leads to reduction in preload, cardiac output, total peripheral resistance, workload of the heart and blood pressure.

Classifications of Diuretics

• Loop diuretics like furosemide/Lasix.
• Osmotic diuretics like mannitol.
• Potassium-sparing diuretics like spironolactone.
• Thiazides diuretics include hydrochlorothiazide.
• Side effects of diuretics include hypotension, hypokalemia, dizziness, headaches, dehydration and muscle cramps.

Fluid Balance

• Total body water makes up 60% of body weight and includes intracellular fluid (67%), interstitial fluid (25%) and plasma volume (8%).

Fluids

• Crystalloids contain fluids and electrolytes, which are solutions normally found in the body.
• May be used as maintenance fluids for AKI, Burns, Hyponatremia, Sock.
• They might cause peripheral or pulmonary edema and reduce colloid oncotic pressure by diluting plasma proteins.
• Colloids contain protein substances that increase colloid oncotic pressure.
• These move fluid from the interstitial compartment to the plasma compartment when plasma protein levels are low.
• Adverse effects are usually safe but may cause altered coagulation or, rarely, anaphylaxis or kidney failure with dextran therapy.
• Colloids are substances that are often safer than crystalloids.
• Albumin (5% and 25% from human donors).
• Dextran (40 or 70 available in sodium chloride and 5% dextrose).
• Hetastarch (synthetic).

Colloids: Albumin

• A natural protein created by the liver, responsible for approximately 70% of the colloid oncotic pressure.
• Prepared from pooled blood, plasma, serum, or placentas from healthy human donors, then pasteurized to destroy contaminants.
• Blood products are the only fluid type used for carrying oxygen.
• They increase tissue oxygenation and plasma volume.
• They are the most expensive and least readily available due to the requirement for human donors

IV Solutions

• Refer to IV fluids document for further details.
• Isotonic solutions, examples, indications, contraindications, assessments.
• Hypertonic solutions, examples, indications, contraindications, assessments.
• Hypotonic solutions, examples, indications, contraindications, assessments.
• Differentiate between electrolyte imbalances for sodium, potassium, and calcium, including hyper and hypo.

Sodium

• This drug is indicated if sodium depletion occurs when dietary measures are inadequate.
• Sodium should be administered orally or intravenously, depending on symptoms.
• Adverse effects from oral administration can cause nausea, vomiting and cramps.
• Adverse effects from IV administration can cause venous phlebitis.
• Potassium is indicated for preventing or treating potassium depletion when dietary means are inadequate.
• Potassium has other therapeutic uses for stopping irregular heartbeats and managing tachydysrhythmias post cardiac surgery.
• Oral administrations can cause diarrhea, vomiting, nausea, gastrointestinal bleeding and ulceration as adverse effects.
• IV administrations can result in pain at the injection site and phlebitis can occur.
• Excessive administration can cause hyperkalemia, toxic effects and cardiac arrest.

Nursing Implications

• Parenteral infusions of potassium must be closely monitored.
• IV potassium should not be administered faster than 10 mmol/hr to patients without cardiac monitors; rates of 20 mmol/hr may be used if cardiac monitors are used for ill patients.
• Potassium should never be administered as an IV bolus or undiluted.
• Oral forms of potassium must be diluted in water or fruit juice and taken with food or immediately after meals to minimize gastrointestinal distress or irritation and to prevent rapid potassium absorption.
• Nurses should monitor and report any symptoms of nausea, vomiting, gastrointestinal pain, or bleeding
• Recognize the nursing implications for these anti-hypertensives; adrenergic drugs, ACE inhibitors, ARBs, calcium channel blockers and diuretics.