What are the causes and management of hypotension?

Causes and Management of Hypotension

Definition and Critical Thresholds

Hypotension should be assessed primarily by symptoms and organ perfusion status rather than absolute blood pressure numbers alone, though systolic BP <90 mmHg or mean arterial pressure <65 mmHg generally defines hypotension. 1, 2 Severe hypotension with systolic BP <80 mmHg or any hypotension causing major symptoms (altered mental status, chest pain, oliguria) requires immediate intervention and potential hospitalization. 3, 1

Major Causes of Hypotension

Volume Depletion (Most Common)

• Acute fluid losses from diarrhea, vomiting, fever, or excessive diuresis represent the most frequent cause of hypotension in clinical practice. 1, 2, 4
• Excessive diuretic therapy can precipitate volume depletion, electrolyte abnormalities, and acute renal failure, particularly in heart failure patients. 1, 2
• Look specifically for: recent gastrointestinal illness, fever, increased urinary output, or recent diuretic dose escalation. 3

Medication-Induced Hypotension

• Antihypertensive medications are a leading cause, especially in older adults with polypharmacy. 1, 4
• High-risk medications include: 1, 2, 4
  • ACE inhibitors and ARBs (especially with concurrent volume depletion)
  • Calcium channel blockers (not recommended in heart failure)
  • Alpha-blockers
  • Centrally acting antihypertensives
  • Beta-blockers (particularly those with alpha-blocking properties like carvedilol)
• Tricyclic antidepressants, phenothiazines, and MAO inhibitors carry significant risk. 5

Cardiac Causes

• Cardiogenic shock is defined by systolic BP <90 mmHg with central filling pressure >20 mmHg or cardiac index <1.8 L/min/m². 1, 4
• Poor left ventricular function, acute myocardial infarction, and congestive heart failure are high-risk conditions. 3
• Physical examination findings of heart failure indicate higher risk of sudden death. 3

Orthostatic Hypotension

• Defined as a drop of ≥20 mmHg systolic and/or ≥10 mmHg diastolic BP within 3 minutes of standing. 3, 1, 2, 4
• Causes include: 2, 4, 6
  • Medication effects (most common)
  • Autonomic dysfunction (diabetic neuropathy, Parkinson's disease, Shy-Drager syndrome)
  • Volume depletion
  • Age-related changes (present in up to 40% of asymptomatic patients >70 years) 3

Endocrine Causes

• Adrenal insufficiency (primary or secondary) presents with hypotension, hyponatremia, and hyperkalemia. 7
• Isolated hypoaldosteronism from diabetes, renal failure, or medications. 7
• Pheochromocytoma (paradoxically can cause hypotension, especially during surgical removal). 7

Septic Shock

• Defined as sepsis requiring vasopressors to maintain MAP ≥65 mmHg with serum lactate >2 mmol/L despite adequate volume resuscitation. 1

Diagnostic Approach

Immediate Assessment

1. Measure BP in both supine/sitting and standing positions to identify orthostatic component. 3, 2
2. Assess for end-organ hypoperfusion: 1, 2
   • Altered mental status
   • Oliguria or worsening renal function
   • Cardiac ischemia (chest pain, ECG changes)
   • Cool extremities, delayed capillary refill
3. Verify BP readings are accurate (proper cuff size, technique). 3

Correlation with Symptoms

• Establish temporal relationship between symptoms (dizziness, fatigue, lightheadedness) and documented low BP readings. 3
• Recurrence of symptoms on standing is more significant than numeric BP changes alone. 3
• If orthostatic hypotension not confirmed initially, use ambulatory BP monitoring to identify hypotensive episodes correlating with symptoms. 3

Identify Reversible Causes

• Review all medications, particularly antihypertensives, diuretics, and psychotropic drugs. 3, 1
• Assess for transient medical conditions: fever, diarrhea, vomiting, urinary retention. 3
• Check volume status: orthostatic vital signs, mucous membranes, skin turgor, urine output. 3
• Obtain ECG to identify arrhythmias, ischemia, or conduction abnormalities. 3

Advanced Testing When Indicated

• Passive leg raise (PLR) test predicts fluid responsiveness: increase in cardiac output after PLR strongly predicts response to fluids (positive likelihood ratio = 11), while no increase suggests fluids will not help (negative likelihood ratio = 0.13). 3
• Laboratory studies: complete blood count, electrolytes, renal function, lactate (if sepsis suspected). 3
• Consider cortisol/ACTH if adrenal insufficiency suspected. 7

Management Algorithm

Step 1: Address Life-Threatening Hypotension

• If systolic BP <80 mmHg or signs of shock (altered mental status, oliguria, lactate >2 mmol/L), initiate immediate resuscitation. 1
• Establish large-bore IV access. 3
• Administer rapid IV crystalloid bolus (500-1000 mL). 3
• If no response to fluids or PLR test negative, start norepinephrine as first-line vasopressor (more efficacious than dopamine for septic shock). 1, 8
• Target MAP ≥65 mmHg initially. 1

Step 2: Correct Reversible Causes

• Discontinue or reduce non-essential hypotensive medications: calcium channel blockers, alpha-blockers, centrally acting antihypertensives. 3, 1
• Treat underlying conditions: 3
  • Supplemental oxygen for hypoxemia
  • Warming for hypothermia
  • Catheterization for urinary retention
  • Anxiolytics for severe anxiety
• For volume depletion, administer IV fluids targeting euvolemia. 3, 1

Step 3: Manage Orthostatic Hypotension

Non-pharmacologic measures (first-line): 2

• Ensure adequate salt intake (unless contraindicated)
• Increase fluid intake to 2-2.5 L daily
• Use compression stockings (waist-high, 30-40 mmHg)
• Elevate head of bed 10-20 degrees at night
• Rise slowly from supine/sitting positions
• Encourage physical activity and reconditioning

Pharmacologic therapy (if non-pharmacologic measures fail): 2

• Midodrine (FDA-approved): start 2.5-5 mg three times daily, titrate to maximum 10 mg three times daily. 2
• Droxidopa (FDA-approved): start 100 mg three times daily, titrate to maximum 600 mg three times daily. 2

Step 4: Special Considerations for Heart Failure Patients

• In chronic heart failure with hypotension, assess organ perfusion rather than relying solely on BP values. 3, 1, 2
• Hypotension with minor symptoms is NOT a reason to withhold or reduce guideline-directed medical therapy (GDMT). 3
• If starting GDMT in hypotensive heart failure patients, initiate SGLT2 inhibitors and mineralocorticoid receptor antagonists first (least BP-lowering effect), followed by low-dose beta-blockers if heart rate >70 bpm. 3
• Avoid abrupt withdrawal of beta-blockers as this can cause clinical deterioration. 3

Step 5: Perioperative Hypotension

• Only 54% of postoperative hypotensive patients respond to fluid boluses; the remainder require vasopressor or inotropic support. 3, 2
• Use PLR test to guide fluid versus vasopressor therapy. 3
• For phenylephrine use, ensure patient is not bradycardic as it can cause reflex bradycardia. 3

Critical Pitfalls to Avoid

• Do not rely on absolute BP numbers alone without assessing symptoms and organ perfusion. 3, 1, 4
• Do not automatically give fluids for all hypotension—approximately half of hypotensive patients are not fluid-responsive and require vasopressors or inotropes. 3, 2
• Do not discontinue GDMT in heart failure patients with asymptomatic or mildly symptomatic hypotension. 3
• Do not miss medication-induced hypotension, especially in elderly patients with polypharmacy. 1, 4
• Do not use dopamine as first-line vasopressor in septic shock—norepinephrine is superior. 1
• Do not administer beta-blockers to patients on MAO inhibitors without dose reduction to 1/10 usual dose. 9
• Orthostatic hypotension is present in up to 40% of asymptomatic elderly patients, so correlation with symptoms is essential. 3