What are the causes of hypotension (low blood pressure)?

Causes of Hypotension

Hypotension is defined as a systolic blood pressure (SBP) <90 mmHg or mean arterial pressure (MAP) <65 mmHg in resting conditions, with multiple etiologies ranging from cardiac dysfunction to medication effects. 1

Primary Categories of Hypotension

Cardiac Causes

• Cardiogenic shock - characterized by SBP <90 mmHg, central filling pressure >20 mmHg, or cardiac index <1.8 L/min/m², typically associated with extensive left ventricular damage 2
• Heart failure - a common cause of hypotension, especially in advanced cases (3-4% in outpatients, up to 25% in hospitalized patients) 1
• Arrhythmias - can compromise cardiac output and lead to hypotension 1
• Valvular dysfunction - can impair cardiac performance and contribute to hypotension 2

Volume-Related Causes

• Hypovolemia - from dehydration, hemorrhage, or excessive diuresis 1
• Diarrhea and fever - common causes of volume depletion leading to hypotension 1
• Excessive diuretic use - can cause volume depletion and electrolyte abnormalities 1, 3

Neurogenic/Autonomic Causes

• Orthostatic hypotension - defined as a drop in SBP >20 mmHg or diastolic BP >10 mmHg within 3 minutes of standing 1, 4
• Autonomic neuropathies - including those secondary to diabetes, peripheral autonomic impairment (Bradbury-Eggleston syndrome), or central autonomic impairment (Shy-Drager syndrome) 5
• Dopamine-beta-hydroxylase deficiency - genetic defect causing absence of norepinephrine with accumulation of dopamine 5
• Sleep apnea - commonly encountered in patients with resistant and refractory hypertension 2

Endocrine Causes

• Adrenal insufficiency - from primary adrenal failure or central (pituitary) origin 6
• Isolated hypoaldosteronism - associated with low blood sodium and high potassium levels 6
• Pheochromocytoma - rarely causes hypotension, more commonly during surgical removal when not properly prepared with calcium channel blockers 6
• Carcinoid syndrome - can cause flushing with hypotension, responsive to somatostatin analogs 6
• Diabetic dysautonomia - can lead to secondary hypoaldosteronism and orthostatic hypotension 6

Medication-Related Causes

• Antihypertensive medications - especially when multiple agents are used 3
• Diuretics - particularly when causing volume depletion 1, 3
• Vasodilators - such as nitrates can cause excessive vasodilation 2
• MAO inhibitors - can potentiate the effects of endogenous catecholamines 7
• Anesthetic agents - particularly cyclopropane or halogenated hydrocarbons can cause hypotension 7

Special Considerations

• Bradycardia-hypotension syndrome - characterized by "warm hypotension," bradycardia, venodilatation, normal jugular venous pressure, and decreased tissue perfusion; commonly seen in inferior myocardial infarction 2
• Right ventricular infarction - presents with high jugular venous pressure, poor tissue perfusion, bradycardia, and hypotension 2
• Septic shock - characterized by vasodilation and increased capillary permeability 8

Clinical Evaluation of Hypotension

Initial Assessment

• Confirm the blood pressure reading and assess for symptoms of hypoperfusion (dizziness, lightheadedness, altered mental status) 8
• Check other vital signs including heart rate, respiratory rate, oxygen saturation, and temperature 8
• Perform passive leg raise test to assess fluid responsiveness 8

Diagnostic Approach

• Measure BP in both supine/sitting and standing positions to assess for orthostatic hypotension 3
• Consider ambulatory blood pressure monitoring (ABPM) if office measurements don't correlate with symptoms 3
• Assess for subtle signs of hypoperfusion even in apparently asymptomatic patients 3

Critical Thresholds

• SBP <80 mmHg is considered a critical threshold requiring intervention 3
• In children, hypotension thresholds are age-specific: 70 mmHg for 1 month to 1 year, (70 mmHg plus twice the age) for 1-10 years, and 90 mmHg for 11-17 years 1

Management Considerations

• For fluid-responsive hypotension, administer intravenous crystalloid solutions 8
• For non-fluid-responsive hypotension, consider vasopressors such as norepinephrine 8
• In cardiogenic shock, inotropic agents like dobutamine may be beneficial 2
• For patients with heart failure and hypotension, maintain guideline-directed medical therapy unless symptomatic or severe hypotension persists 9
• When discontinuing vasopressors like dopamine, gradually decrease the dose while expanding blood volume with intravenous fluids to prevent sudden hypotension 7