Nephrology — L6: Hypertension & The Kidney

📚 Lecture Overview

This lecture explores the critical intersection of nephrology and hypertension, highlighting epidemiology, pathophysiology, and hypertension-mediated organ damage (HMOD). It details the diagnosis and management of both primary hypertension and secondary causes, with a strong focus on the bidirectional relationship between hypertension and chronic kidney disease (CKD).

🎯 Key Concepts & Definitions

Essential (Primary) Hypertension: High blood pressure where the exact underlying cause remains unknown; accounts for the vast majority of cases.
Secondary Hypertension: High blood pressure with an identifiable underlying cause, such as renovascular disease or endocrine disorders.
Hypertension-Mediated Organ Damage (HMOD): Structural or functional damage to organs (heart, brain, kidneys, eyes, vessels) caused by long-standing elevated blood pressure.
Renovascular Hypertension (RVH): A condition where renal artery stenosis or occlusion decreases renal perfusion, activating the renin-angiotensin-aldosterone system (RAAS) to raise blood pressure.
Fibromuscular Dysplasia (FMD): A systemic non-atherosclerotic vascular disease of medium-sized muscular arteries that can cause renovascular hypertension, particularly in younger women and children.
Resistant Hypertension: Blood pressure that remains above target despite the concurrent use of three appropriately chosen and dosed antihypertensive agents (including a diuretic).

📖 Main Content

Epidemiology & Pathophysiology

Approximately 1.4 billion adults worldwide have hypertension, with two-thirds residing in low- and middle-income countries.
Around 44% of adults with hypertension are unaware they have it, and only 23% have it under control.
Pathophysiology involves complex interactions between genes, environment, hormonal networks, vascular mechanisms, and immune pathways.
The 2024 ESC Guidelines define hypertension as a confirmed office systolic BP of ≥140 mmHg or diastolic BP of ≥90 mmHg.

Assessment & Renal HMOD

Routine work-up for hypertension includes serum creatinine, eGFR, and urine albumin:creatinine ratio (ACR) to detect kidney involvement.
CKD is defined as abnormalities of kidney structure or function present for at least 3 months.
Renal ultrasound and Doppler examination help assess kidney structure, determine CKD causes, and exclude renovascular hypertension.
For patients with moderate-to-severe CKD, eGFR and urine ACR should be repeated at least annually.

Secondary Hypertension & Renovascular Disease

Secondary hypertension accounts for 10%–35% of all cases and up to 50% of resistant hypertension.
Atherosclerosis is the most common cause of RVH in older adults, while fibromuscular dysplasia (FMD) is more common in children and younger women.
Indications for renal artery angioplasty and stenting include:
Recurrent heart failure, unstable angina, or flash pulmonary edema
Resistant hypertension
Unexplained unilaterally small kidney or CKD
Bilateral renal artery stenosis or unilateral stenosis in a solitary kidney
Open surgical revascularization is considered if angioplasty/stenting is technically unfeasible or fails.

Hypertension in Chronic Kidney Disease (CKD)

Over 80% of patients with CKD are hypertensive, and the two conditions are closely entwined.
ACE inhibitors or ARBs are the foundational therapies as they provide superior protection against adverse kidney outcomes and reduce albuminuria.
Combination therapy is usually required (RAS inhibitor combined with a calcium channel blocker or diuretic).
In CKD with eGFR >30 mL/min/1.73 m2, target systolic BP is 120–129 mmHg if tolerated.
SGLT2 inhibitors are recommended for hypertensive patients with CKD (eGFR >20 mL/min/1.73 m2) to improve outcomes and provide modest blood pressure-lowering properties.
Never combine an ACE inhibitor and an ARB due to increased risk of adverse events without added clinical benefit.

Catheter-Based Renal Denervation

Targets afferent and efferent sympathetic nerves in the adventitia of renal arteries to combat sympathetic overactivity.
Provides a modest blood pressure-lowering effect (placebo-corrected systolic drop of ~6 mmHg on office BP).
Attractive for patients with suboptimal medication adherence ("always on" effect).
Not recommended for patients with moderate-to-severe renal impairment (eGFR <40 mL/min/1.73 m2) or secondary hypertension.

📊 Visual Learning

flowchart TD A[Elevated BP] --> B{Initial Screening} B -->|Normal Risk| C[Lifestyle Changes] B -->|High CVD Risk| D[Start Meds and Lifestyle] D --> E{Check Renal Function} E -->|Normal CKD| F[Target BP 120-129] E -->|Resistant HTN| G[Add Diuretic or Evaluate RVH]

mindmap root("Renovascular Hypertension Causes") "Atherosclerosis" "Older adults" "Most common cause" "Stenosis 50 to 99 percent" "Fibromuscular Dysplasia" "Younger women and children" "Systemic vascular disease" "Treat with angioplasty without stenting"

graph LR A[Renal Artery Stenosis] --> B[Decreased Renal Perfusion] B --> C[RAAS Activation] C --> D[Increased Blood Pressure] D --> E[Renal Damage and HMOD]

💡 Important Points to Remember

Definition Threshold: Hypertension is defined as office BP ≥140/90 mmHg.
First-Line CKD Protection: ACE inhibitors and ARBs are mandatory for reducing proteinuria and preserving kidney function.
The Dual Blockade Rule: Never combine an ACE inhibitor with an ARB—this causes hyperkalemia and acute kidney injury without clinical benefit.
Renal Denervation Limit: Do not perform renal denervation if eGFR is <40 mL/min/1.73 m2.
Diagnostic Markers: Always measure serum creatinine, eGFR, and urine ACR to evaluate renal HMOD.
FMD vs. Atherosclerosis: FMD affects younger women and is treated with angioplasty without stenting; atherosclerosis affects older adults and may require stenting.
Resistant HTN Definition: BP uncontrolled despite three agents, including a diuretic (loop diuretic required if eGFR <30).
Target BP in CKD: Aim for a systolic BP of 120–129 mmHg for patients with eGFR >30 mL/min/1.73 m2, if tolerated.
SGLT2 Inhibitors: Recommended in CKD (eGFR >20) for organ protection and modest BP lowering.
Common Confusion: Do not confuse the general office diagnostic threshold (140/90) with CKD treatment triggers and targets (≥130/80 threshold, 120-129 target).

⚠️ Common Exam Questions

Examiners frequently test students by presenting clinical scenarios where a patient with CKD or resistant hypertension is prescribed both an ACE inhibitor and an ARB, testing whether the student recognizes this as a contraindication. Another common trap is confusing the indications for renal artery stenting in atherosclerotic disease versus angioplasty alone in fibromuscular dysplasia. MCQs often try to trick students into performing renal denervation on patients with low eGFR (<40 mL/min/1.73 m2) or secondary hypertension, ignoring strict contraindications.

📝 Quick Review Checklist

I can explain the pathophysiology and diagnostic criteria for primary hypertension
I understand the bidirectional relationship between hypertension and CKD
I can define HMOD and list the routine renal screening tests (creatinine, eGFR, urine ACR)
I know the key differences between atherosclerotic RVH and fibromuscular dysplasia
I understand why ACE inhibitors and ARBs are crucial in CKD management
I know the contraindication of combining ACE inhibitors and ARBs
I can identify the indications and restrictions for renal denervation
I know the target blood pressure ranges for patients with moderate-to-severe CKD

📚 Nephrology — L6: Hypertension & The Kidney