Chronic kidney disease is both a cause and consequence of hypertension. In patients with both conditions, accurate evaluation and a tailored treatment program are essential for successful hypertension management.
Blood circulates through the body at a certain pressure within the arteries. This pressure changes depending on activity levels– elevating during exercise, to increase the blood flow to the heart, muscles and brain, and lower at rest. In some people, the range of blood pressure levels is raised above normal; this is called “hypertension”. People who have hypertension are at an increased risk of heart disease, stroke and kidney failure. The causes of hypertension are complex – it can be related to an underlying disease, but in the majority of people no underlying cause is found.
The kidneys have several important functions. They filter the blood to balance fluids and electrolytes (such as sodium and potassium) and remove waste products. Excess water and waste products are excreted in the urine. The kidneys are also important for blood pressure control, both by controlling fluid-electrolyte balance and by stimulating a group of hormones that cause blood vessels to constrict and increase sodium re-absorption. These hormones are part of the renin-angiotensin-aldosterone system (RAAS). Diseased kidneys can lead to hypertension, but conversely, hypertension can damage the kidneys and cause chronic kidney disease (CKD).
The current management practices for treating hypertension in patients with CKD were recently reviewed in the journal Current Hypertension Reports.
How does CKD lead to hypertension?
Several interlinked mechanisms can lead to hypertension in patients with CKD.
- Poor sodium regulation
In CKD, the inability to excrete sodium properly causes sodium and fluid retention, resulting in volume-related hypertension. This situation can be made worse by a high-sodium diet. Excessive salt intake has been shown to reduce the effects of most types of antihypertensive drugs. On the other hand, low salt intake can help the action of some types of anti-hypertensives.
- Increased sympathetic nervous system activity
The sympathetic nervous system is involved in the body’s “fight or flight” response. Sympathetic nervous system activity is increased in CKD and this is thought to activate the hormonal RAAS. This, in turn, results in increased sodium reabsorption, fluid retention and vasoconstriction – all of which increase blood pressure.
- Protein in the urine
The presence of protein in the urine (proteinuria)is commonly seen in CKD. This may cause raised blood pressure by a pathway that increases sodium retention.
CKD is more common in patients with obesity. There is a well-described relationship between obesity and hypertension, although the mechanism for this is not fully understood.
- Other factors
Some medications can interfere with blood pressure control in patients with CKD – these include anti-inflammatory drugs, some decongestants and diet medications, oral contraceptives and herbal preparations containing ephedra.
How should we evaluate blood pressure in CKD?
Careful assessment is essential for developing a successful hypertension management plan for CKD patients. Accurate blood pressure (BP) measurements are key. Taking careful BP readings in a clinic or at home provides useful information; however, a 24-hour continuous ambulatory blood pressure monitoring (ABPM) test provides a more complete information on how the patient’s BP varies during their usual activity. In particular, patients with CKD often lose the normal nighttime dip in BP, and in advanced CKD might even have a rise. Nighttime BP rise is linked to a higher risk of damage to organs, heart attack and stroke. ABPM can also exclude patients who appear to have hypertension based on raised readings in the clinic setting (“white-coat” hypertension) or unmask patients who have normal readings in the clinic, but a raised reading when monitored over a longer period.
What is the optimal target BP in CKD?
Despite much research, the optimal BP level in treating hypertension in CKD patients remains a matter of debate. The goal is to prevent cardiovascular problems and the progression of kidney disease. However, it is important to balance the benefits of antihypertensive treatment against drug-related side effects. In addition, patients with CKD often have diseased blood vessels, and treating BP too intensively may have serious consequences because of insufficient blood flow to the heart or brain.
The current guidelines for patients with CKD is a target BP of <140/90 mmHg in those without proteinuria, and <130/80 in those with proteinuria. Although some trials have looked at a more intensive BP treatment in CKD, the benefits are not clear and this may lead to increased drug side effects and other adverse events, and have a higher treatment cost.
How should the treatment program be tailored?
Achieving good BP control in CKD patients is often challenging. An important first step is to educate and encourage patients to make any necessary lifestyle modifications including restricting dietary salt, losing weight, taking regular exercise, decreasing alcohol consumption and stopping any potentially interfering substances such as anti-inflammatory drugs or certain herbal remedies.
Drug treatment should be tailored for an individual patient to take into account coexisting diseases, their cardiovascular disease risk status, age, gender and ethnicity. The number of drugs and frequency of dosing should be kept as simple as possible. This helps patients to comply with treatment and is also less expensive.
Different types, or classes, of antihypertensive drugs have different mechanisms of action. Diuretics increase sodium excretion, and drugs such as ACE inhibitors and Angiotensin II Receptor blockers inhibit the RAAS hormonal system. These drugs are useful in the treatment of hypertension in CKD. In addition, calcium channel blockers, aldosterone antagonists and beta-blockers maybe other options in some patients.
Prescribing a combination of drugs from different classes can work in an additive way to reduce hypertension. There is strong evidence that a combination of different antihypertensive drugs reduces cardiovascular events and this is currently the standard recommendation. In particular, adding a diuretic to a drug regimen can improve BP control.
Another important factor in hypertension management in CKD is the timing of drug dosage. Bedtime administration of a least one of the antihypertensive drugs gives a better 24 hour mean BP control. It could also produce a nocturnal BP dip in patients who have lost this phenomenon. Frequent home BP monitoring by patients can help them to take their medication regularly.
The interaction between hypertension and CKD is complex. When the conditions occur together there is an increased risk of heart disease and stroke, particularly if the hypertension is difficult to control. ABPM is important to get a clear picture of the BP pattern. Loss of sodium regulation increased SNS activity and alterations in RAAS are some of the mechanisms of hypertension in CKD. A tailored treatment program, including lifestyle modifications and combination drug therapy including an appropriate diuretic, is currently the recommended practice.
Written by: Julie McShane, Medical Writer
Hamrahian SM. Management of hypertension in patients with chronic kidney disease. CurrHypertens Rep (2017) 19.43. DOI: 10.1007/s11906-017-0739-9.