What are the causes of hypotension and how should it be managed?

Causes and Treatment of Hypotension

The management of hypotension depends critically on identifying the underlying cause—whether it's volume depletion, vasodilation, cardiac dysfunction, or autonomic failure—and treatment must be tailored to the specific mechanism while prioritizing organ perfusion over arbitrary blood pressure targets.

Major Causes of Hypotension

Acute Hypotension

• Volume depletion: Blood loss, dehydration from diarrhea/fever, excessive diuretic use
• Vasodilation: Anaphylaxis, sepsis, medications (vasodilators, calcium channel blockers, alpha-blockers)
• Cardiac causes: Bradycardia, low cardiac output from myocardial dysfunction
• Increased compartment pressures: Elevated intraabdominal pressure, pneumothorax reducing effective perfusion pressure 1

Chronic Hypotension

• Orthostatic hypotension: Drug-induced (most common—diuretics, vasodilators, antihypertensives), autonomic failure (neurogenic), volume depletion, deconditioning 2, 3
• Neurally-mediated syncope: Vasovagal, situational (cough, micturition, defecation), carotid sinus syndrome 2
• Heart failure with reduced ejection fraction: Particularly when on guideline-directed medical therapy 4

Treatment Approach

Immediate Management of Acute Severe Hypotension

For life-threatening hypotension (systolic BP <80 mmHg) with inadequate organ perfusion:

1. Assess airway, breathing, circulation, and mental status 5

2. Identify and treat the underlying mechanism 1:

   • Anaphylaxis: Epinephrine 0.3-0.5 mg IM (0.01 mg/kg in children, max 0.3 mg) into deltoid or anterolateral thigh every 5 minutes as needed 5
   • Vasodilation: Noradrenaline infusion if restricted volume replacement fails to achieve target pressure 6
   • Hypovolemia: Rapid crystalloid infusion (normal saline or balanced crystalloid 1-2 L in adults at 5-10 mL/kg in first 5 minutes; up to 30 mL/kg in first hour for children) 5, 6
   • Bradycardia: Atropine or glycopyrronium; epinephrine if refractory 1
   • Low cardiac output: Dobutamine for myocardial dysfunction 5, 6

3. Supportive measures:

   • Place patient recumbent with legs elevated 5
   • Administer oxygen 6-8 L/min 5
   • Establish IV access 5

Critical pitfall: Intravenous epinephrine should only be used in cardiac arrest or profound hypotension unresponsive to multiple IM doses and volume replacement, as it carries risk of lethal arrhythmias 5

Management of Orthostatic Hypotension

Orthostatic hypotension is defined as a drop of ≥20 mmHg systolic or ≥10 mmHg diastolic within 3 minutes of standing 3, 7, 8

Step 1: Confirm diagnosis and assess symptoms

• Measure BP supine/seated and after standing for 1-3 minutes 4, 9
• If symptoms don't correlate with standing BP drops, use ambulatory BP monitoring to capture hypotensive episodes 4
• Assess for symptoms: dizziness, lightheadedness, blurred vision, weakness, syncope, falls 3, 7

Step 2: Identify and eliminate reversible causes

• Discontinue or reduce offending medications: Diuretics, vasodilators, calcium channel blockers, alpha-blockers, centrally acting antihypertensives 4, 2, 9
• Treat transient conditions: Dehydration, fever, diarrhea, overdiuresis 4
• Avoid alcohol (causes autonomic neuropathy and volume depletion) 2

Step 3: Non-pharmacological interventions (first-line for all patients)

• Volume expansion: Increase salt intake (6-10 g/day), adequate fluid intake (2-2.5 L/day) 2, 10
• Physical countermaneuvers: Leg crossing, squatting, muscle tensing before standing 3, 10, 8
• Postural modifications: Rise slowly, sit rather than stand when possible, sleep with head elevated >10° 2, 10
• Compression garments: Waist-high compression stockings (30-40 mmHg) or abdominal binders 10, 8
• Water bolus treatment: Drink 500 mL water rapidly before orthostatic stress 10
• Exercise program: To prevent deconditioning 2, 11

Step 4: Pharmacological treatment (if non-pharmacological measures insufficient)

For persistent symptomatic orthostatic hypotension:

1. Fludrocortisone 0.1-0.2 mg daily (mineralocorticoid; increases sodium retention and blood volume) 10, 7, 12, 8

2. Midodrine 2.5-10 mg three times daily (alpha-1 agonist; increases vascular tone) - FDA approved 11, 10, 7, 8

3. Droxidopa (norepinephrine precursor) - FDA approved 11, 8

4. Pyridostigmine 30-60 mg three times daily (acetylcholinesterase inhibitor) 7

Important caveat: The goal is to improve symptoms and functional status, NOT to normalize standing BP. Attempting to fully correct standing BP will cause excessive supine hypertension 4, 10, 12, 8

Management in Heart Failure with Reduced Ejection Fraction

For patients with HFrEF and low BP (systolic <80 mmHg or causing major symptoms) 4:

1. Verify BP readings and confirm adequate organ perfusion (absence of cardiogenic shock)
2. Assess for orthostatic component as above
3. Remove non-HF hypotensive drugs (calcium channel blockers, alpha-blockers)
4. If treatment-naïve: Start SGLT2 inhibitors and mineralocorticoid receptor antagonists first (least BP effect), then low-dose beta-blocker or sacubitril/valsartan 4
5. If on GDMT with minor symptoms: Do NOT reduce guideline-directed medical therapy 4
6. If major symptoms or SBP <80 mmHg: Re-evaluate and potentially adjust GDMT 4

Special Populations

Older/frail patients 9:

• Screen for frailty before intensifying BP treatment
• If BP drops with progressing frailty, consider deprescribing BP-lowering medications and sedatives
• Use long-acting dihydropyridine calcium channel blockers or RAS inhibitors, avoid beta-blockers and alpha-blockers unless compelling indication

Diabetic autonomic neuropathy 11:

• Ensure adequate salt intake
• Avoid medications that worsen orthostatic hypotension
• Use compression garments
• Midodrine and droxidopa are FDA-approved options

Perioperative hypotension 1, 13:

• Treat based on underlying cause (vasodilation, hypovolemia, bradycardia, low cardiac output)
• Use passive leg raise test to assess fluid responsiveness (only ~50% of hypotensive postoperative patients respond to fluids) 13
• Phenylephrine appropriate when hypotension accompanied by tachycardia 13
• Compensate for increased compartment pressures (e.g., if intraabdominal pressure is 15 mmHg and target organ perfusion is 65 mmHg, maintain MAP >80 mmHg) 1

Vasovagal syncope 2:

• Patient education and reassurance about benign prognosis (Class I recommendation)
• Avoid triggers when possible
• Volume expansion, tilt training
• Single episode without high-risk setting requires no treatment
• Cardiac pacing for cardioinhibitory carotid sinus syndrome