What causes hypotension (low blood pressure)?

Causes of Low Blood Pressure (Hypotension)

Low blood pressure results from multiple mechanisms including volume depletion (dehydration, hemorrhage, excessive diuresis), cardiac dysfunction (heart failure, valvular disease, arrhythmias), medication effects (especially antihypertensives), autonomic dysfunction (orthostatic hypotension, diabetic neuropathy), and distributive shock states (sepsis). 1, 2, 3

Volume-Related Causes

Hypovolemia is among the most common causes of hypotension in clinical practice. 2

• Dehydration from diarrhea, fever, or vomiting represents a frequent and readily reversible cause 1, 2
• Hemorrhage or blood loss leads to acute hypovolemia and subsequent hypotension 2
• Excessive diuretic use can cause volume depletion, electrolyte abnormalities, and acute renal failure, particularly problematic in heart failure patients 1, 2, 3

Cardiac Causes

Heart failure is a common cause, occurring in 3-4% of outpatients with HFrEF and up to 25% of hospitalized patients. 1, 2

• Cardiogenic shock is characterized by SBP <90 mmHg, central filling pressure >20 mmHg, or cardiac index <1.8 L/min/m² 2, 3
• Valvular dysfunction can impair cardiac performance and contribute to hypotension 2, 3
• Arrhythmias can compromise cardiac output and provoke hypotension 2
• Bradycardia-hypotension syndrome presents with "warm hypotension," bradycardia, venodilatation, normal jugular venous pressure, and decreased tissue perfusion, commonly seen in inferior myocardial infarction 3
• Right ventricular infarction presents with high jugular venous pressure, poor tissue perfusion, bradycardia, and hypotension 3

Medication-Related Causes

Antihypertensive medications are a leading cause, especially when multiple agents are used or in elderly patients with polypharmacy. 2

• ACE inhibitors, ARBs, calcium channel blockers, and alpha-blockers are particularly problematic in older adults and should be reduced or discontinued in HFrEF patients with hypotension 1, 2
• Beta-blockers, especially those with alpha-blocking properties like carvedilol, can cause hypotension typically within 24-48 hours of initiation or dose increase 2
• Vasodilators such as nitrates can cause excessive vasodilation leading to low diastolic pressures 2, 3
• Angiotensin receptor-neprilysin inhibitors (ARNi) cause the most significant BP decreases among HF medications 1
• Centrally acting antihypertensive drugs not recommended for HFrEF should be discontinued 1

Autonomic and Neurogenic Causes

Orthostatic hypotension is defined as a drop of ≥20 mmHg systolic or ≥10 mmHg diastolic BP within 3 minutes of standing. 1, 2, 4

• Diabetic dysautonomia represents a common cause of autonomic dysfunction leading to hypotension 5, 6
• Peripheral autonomic impairment (Bradbury-Eggleston syndrome) causes isolated peripheral autonomic failure 6
• Central autonomic impairment (Shy-Drager syndrome) involves central nervous system degeneration 6
• Dopamine-beta-hydroxylase deficiency is a rare genetic defect causing absence of norepinephrine with dopamine accumulation 6
• Baroreceptor dysfunction causes wide swings in blood pressure unrelated to posture 6

Endocrine Causes

Adrenal insufficiency from primary or secondary causes represents an important endocrine etiology. 5

• Primary adrenal failure (including congenital 21-hydroxylase deficiency) presents with hyperreninism 5
• Secondary adrenal insufficiency from hypopituitarism presents with hyporeninism 5
• Isolated hypoaldosteronism (primary with hyperreninism or secondary with hyporeninism) associates low sodium and high potassium levels 5
• Pseudohypoaldosteronism involves congenital or acquired resistance to aldosterone 5
• Pheochromocytoma rarely causes hypotension, especially during surgical removal without adequate calcium channel blocker preparation 5

Distributive Shock

Septic shock is characterized by vasodilation, increased capillary permeability, and requires vasopressors to maintain MAP ≥65 mmHg. 2, 3

• Carcinoid crisis presents with flushing and hypotension, highly sensitive to subcutaneous somatostatin analogs 5

Clinical Context and Severity

The prevalence of hypotension increases with severity of heart failure, ranging from 3-4% in outpatients to 9-25% in hospitalized patients depending on the threshold used. 1

• SBP <80 mmHg represents a critical threshold that warrants careful attention and may necessitate re-evaluation of medical treatment 1
• Low BP does not always correlate with impaired perfusion, so assessment should focus on symptoms and organ perfusion rather than BP metrics alone 1
• Persistent poor organ perfusion (possibly accompanied by severe worsening renal function) should trigger comprehensive evaluation and possible hospitalization 1

Common Pitfalls to Avoid

• Failing to measure BP in both supine/sitting AND standing positions misses orthostatic hypotension in up to 30% of cases 1, 2, 4
• Focusing only on BP numbers without assessing symptoms and perfusion can lead to inappropriate interventions 2, 4
• Not considering ambulatory BP monitoring (ABPM) when office measurements don't correlate with symptoms 1, 4
• Overlooking transient medical conditions like diarrhea or fever that lead to dehydration 1
• Missing cardiovascular treatments not recommended for HFrEF (calcium channel blockers, centrally acting antihypertensives, alpha-blockers) that should be discontinued 1