Hypertension and renal disease
Hypertension is important in renal disease for three reasons:
- Renal disease often causes hypertension
- Hypertension can cause further damage to impaired kidneys – it accelerates deterioration of renal function
- Hypertension with renal disease strongly predisposes to cardiovascular disease
Hypertension occurs in about 80% of patients with chronic renal failure, due to sodium (and therefore fluid) retention and often hypersecretion of renin. If there is renovascular disease, reduced renal perfusion may exacerbate the hypertension.
Randomized controlled trials in patients with renal disease show that lowering blood pressure can protect renal function, especially in patients with proteinuria. Blood pressure targets are set lower than for many other patients, especially if there is proteinuria. The target should be individual to the patient depending on circumstance, but guideline levels are as follows:
- 140/90 max (130-139 systolic target) in patients with CKD, unless they justify lower targets:
- 130/80 max (120-129 target) if proteinuric: ACR>30 or PCR>50
- Children with proteinuria: below 50th centile for age (BP in children)
(These targets are 2009 NICE/SIGN and other limits. The second blood pressure limit is slightly higher than previously, but the threshold for applying it has been lowered)
ACE inhibitors are more effective than other agents in patients with proteinuria. Angiotensin receptor blockers (ARBs) are probably equally effective. In diabetics (and arguably other patients with CKD) with increased albumin excretion, ACEI/ARB should be titrated up to maximal dose regardless of blood pressure.
Presents with headache, impaired vision, and features of HUS. Very high blood pressure is associated with changes to small blood vessels in the retina causing haemorrhages and exudates, and with swelling of the optic disc. Similar changes in the kidney lead to glomerular capillary occlusion and thrombosis and rapid deterioration in renal function. Treatment of hypertension can reverse some of the damage. Malignant hypertension is more likely to occur in secondary hypertension than in primary, but primary hypertension is more common, so a cause may not be apparent.
Benign hypertensive nephrosclerosis
Although hypertension is often used as an explanation for renal disease, there is little evidence that it is often a primary cause. The histological changes labelled as benign hypertensive nephrosclerosis correlate poorly with blood pressure and may have other aetiologies.
- Patient info on high blood pressure and the kidney – edren/info
- Hypertension in adults – Edren handbook
- Blood pressures in children – Edren handbook
- High blood pressure is linked to kidney disease; and the discovery of Renin – History of Nephrology blog