Low blood pressure (hypotension)

Definition
Hypotension refers to an abnormally low blood pressure that may cause symptoms or lead to inadequate tissue perfusion. In adults, it is often defined as a systolic blood pressure below 90 mmHg or a mean arterial pressure (MAP) below 65 mmHg, though the clinical significance depends on baseline blood pressure, rate of decline, and patient symptoms.

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Types of Hypotension

1. Orthostatic (Postural) Hypotension

   • A fall in systolic BP of ≥20 mmHg or diastolic BP of ≥10 mmHg within 3 minutes of standing.

   • Common in elderly patients, those on antihypertensive medications, and in autonomic dysfunction.

2. Postprandial Hypotension

   • Blood pressure drop after meals due to splanchnic vasodilation.

3. Neurally Mediated Hypotension

   • Vasovagal episodes triggered by pain, emotional distress, or prolonged standing.

4. Severe Hypotension / Shock

   • Life-threatening fall in BP leading to hypoperfusion of vital organs (septic, cardiogenic, hypovolemic, anaphylactic shock).

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Causes

1. Non-emergency causes

• Dehydration.

• Medication-induced (antihypertensives, diuretics, nitrates, alpha-blockers, beta-blockers, tricyclic antidepressants).

• Endocrine disorders (adrenal insufficiency, hypothyroidism).

• Prolonged bed rest.

• Nutritional deficiencies (B12, folate).

2. Emergency causes

• Massive blood loss.

• Severe infection (sepsis).

• Myocardial infarction or heart failure.

• Pulmonary embolism.

• Anaphylaxis.

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Clinical Features

Symptoms

• Dizziness or lightheadedness.

• Syncope (fainting).

• Blurred vision.

• Nausea.

• Fatigue.

• Difficulty concentrating.

Signs

• Low BP on measurement.

• Tachycardia (in compensatory states).

• Cool extremities, weak pulse (in shock).

• Reduced urine output (in severe hypotension).

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Diagnosis

Assessment

• Detailed history: symptom onset, triggers, medication review, fluid intake.

• Physical examination: orthostatic BP measurement, pulse, cardiovascular and neurological exam.

Investigations

• Complete blood count, electrolytes, renal function.

• Blood glucose.

• ECG, echocardiography if cardiac cause suspected.

• Cortisol levels (if adrenal insufficiency suspected).

• Tilt-table testing (for unexplained recurrent episodes).

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Management

General Principles

• Identify and treat underlying cause.

• Correct reversible factors such as dehydration, medication side effects, or acute bleeding.

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Non-Pharmacologic Measures

• Adequate hydration: 2–3 liters of fluids daily unless contraindicated.

• Increased salt intake (6–10 g/day) in chronic orthostatic hypotension if not contraindicated by cardiac/renal disease.

• Small, frequent meals for postprandial hypotension.

• Gradual position changes from lying to standing.

• Compression stockings to reduce venous pooling.

• Elevating head of bed to reduce nocturnal diuresis.

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Pharmacologic Treatment (for chronic symptomatic hypotension)

Midodrine

• Generic name: midodrine hydrochloride.

• Dose: 2.5–10 mg orally three times daily (last dose at least 4 hours before bedtime to avoid supine hypertension).

• Alpha-1 adrenergic agonist causing peripheral vasoconstriction.

Fludrocortisone

• Generic name: fludrocortisone acetate.

• Dose: 0.1–0.2 mg orally once daily.

• Synthetic mineralocorticoid increasing sodium and water retention to expand plasma volume.

Droxidopa

• Generic name: droxidopa.

• Dose: 100–600 mg orally three times daily.

• Synthetic norepinephrine precursor used in neurogenic orthostatic hypotension.

Other options (specialist use)

• Pyridostigmine: 30–60 mg orally two to three times daily to enhance autonomic neurotransmission.

• Octreotide: 25–100 mcg subcutaneously before meals in severe postprandial hypotension.

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Acute Severe Hypotension / Shock

• Immediate airway, breathing, and circulation (ABC) support.

• Intravenous fluids (e.g., isotonic saline or lactated Ringer’s).

• Vasopressors if hypotension persists despite fluids:

  • Norepinephrine: 0.05–1 mcg/kg/min IV infusion (first-line in septic shock).

  • Epinephrine: 0.05–2 mcg/kg/min IV infusion (anaphylaxis-related shock).

  • Dopamine: 5–20 mcg/kg/min IV infusion (selected cardiogenic shock cases).

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Complications

• Falls and injuries from syncope.

• Organ hypoperfusion leading to acute kidney injury, myocardial ischemia, or cerebral hypoxia.

• Progression to shock and death if untreated in severe cases.

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Prognosis

• Generally good in mild or situational hypotension with lifestyle adjustment.

• Prognosis depends on underlying cause in severe hypotension; early treatment significantly improves outcomes.