Renin Angiotensin Aldosterone System (RAAS)

The renin angiotensin aldosterone system, or RAAS for short, helps regulate blood pressure in the body through vasoconstriction and increased blood volume. Now, when blood pressure falls, the kidneys release the enzyme renin, which converts angiotensinogen into angiotensin I. Angiotensin I is then converted into angiotensin II by angiotensin-converting enzyme, or ACE for short. Angiotensin II is a potent vasoconstrictor that causes the muscular walls of small arteries to constrict, increasing blood pressure. It also triggers the release of the hormone aldosterone from the adrenal cortex, as well as vasopressin, also known as antidiuretic hormone, from the pituitary gland, prompting the kidneys to retain sodium and excrete potassium. The increased sodium causes water to be retained, thereby increasing blood volume and blood pressure.

Medications that impact RAAS include ACE inhibitors and angiotensin II receptor blockers, or ARBs for short. ACE inhibitors and ARBs are typically used to treat hypertension and heart failure, while ACE inhibitors are also used for patients who have had a myocardial infarction. Now, ACE inhibitors usually end in “-pril”, and include enalapril, lisinopril, ramipril, benazepril, and captopril. Whereas ARBs usually end in “-sartan,” like candesartan, valsartan, irbesartan and losartan. ACE inhibitors and ARBs are taken orally except one ACE inhibitor called enalaprilat that can be administered intravenously for hypertension when oral treatment isn’t practical.

Alright, both ACE inhibitors and ARBs lower BP by inhibiting angiotensin II, but in different ways. ACE inhibitors prevent the conversion of angiotensin I to angiotensin II. In contrast, ARBs block the actions of angiotensin II. Both actions prevent the vasoconstricting effects of angiotensin II as well as the volume expanding effects of aldosterone.

Now, the most common side effects of ACE inhibitors and ARBs are mild and nonspecific, such as a headache, dizziness, and fatigue. Other side effects include tachycardia, as well as hypotension, which tends to occur with the first few doses.

Since ACE inhibitors and ARBs decrease potassium excretion in the urine, this could lead to hyperkalemia; so it’s important for patients who are taking ARBs and ACE inhibitors to avoid taking potassium supplements and salt substitutes that contain potassium.

A common side effect of ACE inhibitors is a persistent, dry, irritating cough. That’s because ACE also breaks down bradykinin, so when the patient takes ACE inhibitors, bradykinins accumulate, which induces the cough reflex. In fact, this is a common reason for quitting ACE inhibitors and switching to another medication. Less frequently, bradykinin accumulation may lead to increased capillary permeability, which results in fluid accumulation and swelling of the eyes, lips, tongue, pharynx, and glottis, called angioedema, and can be life threatening. These side effects are much less common with ARBs.

As far as contraindications go, ACE inhibitors and ARBs should be avoided in patients who also take potassium sparing diuretics like spironolactone or have another underlying cause of hyperkalemia. Also, they should be given with caution in patients with renal stenosis, since they can cause kidney injury.

Finally, all medications like ACE inhibitors and ARBs that act on the RAAS have a Black Box warning for causing fetal injury or death, so they should not be used during pregnancy.

Alright, if your patient is prescribed an ARB or ACE inhibitor, perform a baseline assessment, including vital signs; and review diagnostic tests like CBC, sodium, potassium, creatinine, BUN, and urinalysis. For patients of childbearing age, obtain a negative pregnancy test.

Then, ensure your patient understands why the medication has been prescribed. Emphasize the importance of taking the medication exactly as directed, and to not discontinue the medication abruptly because of the risk of rebound hypertension. Also, talk to them about the importance of avoiding potassium supplements and salt substitutes that contain potassium while taking an ACE inhibitor or ARB; and advise them to avoid taking NSAIDs, since this will reduce the antihypertensive effect of their medication.

Next, let them know that hypotension can often occur with the first few doses, so remind them to make position changes slowly until they adjust to their medication. Also teach them to recognize other possible adverse effects that require immediate medical attention like angioedema. Also, assist your patient by teaching them about lifestyle modifications such as weight loss, smoking cessation, decreased alcohol intake, increased physical activity, and following a low sodium diet. Also teach them how to take their blood pressure at home, and explain blood pressure readings that warrant the need to seek medical attention.

While caring for a patient taking an ARB or ACE inhibitor, periodically monitor their blood pressure and laboratory test results. Evaluate for the therapeutic effect of their medication, such as reduced blood pressure or a decrease in symptoms of heart failure. Finally, for patients of childbearing age, stress the importance of using an effective birth control method when taking these medications, and instruct your patient to inform their healthcare provider if they think they might be pregnant.

Alright, as a quick recap… The renin angiotensin aldosterone system, or RAAS helps regulate BP in the body through vasoconstriction and increased blood volume. Medications that impact RAAS include ACE inhibitors and ARBs. These medications work by preventing the vasoconstrictive effects of angiotensin II and the volume expanding effects of aldosterone. Important side effects include hypotension, hyperkalemia, and angioedema. ARBs and ACE inhibitors are contraindicated during pregnancy and in patients who are at risk of hyperkalemia. Nursing considerations include safe medication administration, monitoring for side effects and the patient’s response to treatment; and providing patient education.