What are the causes of acute severe hypotension?

Causes of Acute Severe Hypotension

The primary causes of acute severe hypotension include hypovolemia, cardiogenic shock, distributive shock, obstructive shock, and endocrine disorders, with hypovolemia being the most common cause requiring immediate fluid resuscitation.

Classification of Causes by Pathophysiologic Mechanism

1. Hypovolemic Causes

• Hemorrhage
  • Trauma with blood loss
  • Gastrointestinal bleeding
  • Ruptured aneurysm
  • Postpartum hemorrhage
• Non-hemorrhagic fluid losses
  • Severe vomiting/diarrhea
  • Excessive diuresis
  • Burns
  • Third-spacing (pancreatitis, bowel obstruction)
  • Inadequate fluid intake

2. Cardiogenic Causes

• Pump failure
  • Acute myocardial infarction
  • Acute heart failure/cardiogenic pulmonary edema 1
  • Cardiomyopathy
  • Myocarditis
  • Severe arrhythmias (bradycardia, tachycardia)
• Valvular dysfunction
  • Acute valvular regurgitation
  • Mechanical valve failure

3. Distributive Causes

• Sepsis/septic shock
  • Most common cause of distributive shock 1
• Anaphylaxis
  • Medication reactions
  • Food allergies
  • Insect stings/bites
• Neurogenic shock
  • Spinal cord injury
  • Spinal anesthesia 2
• Drug-induced vasodilation
  • Antihypertensive overdose
  • Vasodilators
  • Anesthetic agents

4. Obstructive Causes

• Pulmonary embolism 1
• Cardiac tamponade
• Tension pneumothorax
• Aortic dissection 1, 3

5. Endocrine Causes

• Adrenal insufficiency/crisis 4
• Pheochromocytoma (paradoxical hypotension) 2, 4
• Myxedema coma
• Diabetic dysautonomia 4

6. Neurological Causes

• Autonomic dysfunction
  • Primary autonomic failure (Bradbury-Eggleston syndrome) 5
  • Secondary autonomic neuropathies (Shy-Drager syndrome) 5
• Baroreceptor dysfunction 5
• Vasovagal syncope

7. Medication-Related Causes

• Antihypertensive overdose
• Rapid intravenous administration of medications
• Drug interactions
• Dopamine-beta-hydroxylase deficiency 5

Clinical Assessment and Diagnostic Approach

Severity Assessment

• Hypotension severity correlates with outcomes - SBP <80 mmHg associated with 50% adverse outcomes versus 17% with SBP >89 mmHg 6
• Sustained hypotension (SBP <100 mmHg for ≥60 minutes) is the strongest predictor of adverse hospital outcomes (OR 3.1) 6

Key Diagnostic Elements

1. Vital signs pattern

   • Heart rate (tachycardia in hypovolemia, bradycardia in neurogenic shock)
   • Respiratory rate and pattern
   • Temperature (fever suggests sepsis)

2. Volume status assessment

   • Skin turgor, mucous membranes
   • Jugular venous distension (elevated in cardiogenic/obstructive, flat in hypovolemic)
   • Peripheral edema

3. Cardiac evaluation

   • Heart sounds (murmurs, gallops)
   • ECG findings
   • Point-of-care ultrasound if available

4. Laboratory tests

   • Complete blood count (anemia, infection)
   • Electrolytes (sodium, potassium abnormalities)
   • Renal and liver function
   • Cardiac enzymes
   • Lactate (marker of tissue hypoperfusion)
   • Cortisol level if adrenal insufficiency suspected

Management Considerations

Immediate Interventions

• Secure airway if compromised
• Provide supplemental oxygen for SaO₂ <90% 1
• Establish IV access
• Initiate appropriate fluid resuscitation for suspected hypovolemia 1
• Consider vasopressors (norepinephrine) if fluid resuscitation inadequate 1, 2

Cautions

• Avoid excessive fluid administration in cardiogenic shock 1
• In traumatic brain injury with polytrauma, balance cerebral perfusion needs against bleeding risk 1
• In acute ischemic stroke, avoid aggressive BP lowering unless extremely elevated (>220/120 mmHg) 1
• Consider underlying causes like pheochromocytoma before initiating treatment 2, 4

Special Considerations

Hypovolemic Shock

• Most common cause of early death in trauma patients 1
• Initial crystalloid bolus (balanced solution preferred over 0.9% saline) 1
• Blood products for hemorrhagic shock

Cardiogenic Shock

• Cautious volume loading only if central venous pressure is low 1
• Inotropic support with dobutamine if myocardial dysfunction present 1

Distributive Shock

• Norepinephrine is first-line vasopressor for septic shock 1
• Consider hydrocortisone if adrenal insufficiency suspected

Endocrine Emergencies

• Adrenal crisis requires immediate hydrocortisone administration
• Thyroid storm/myxedema require specific endocrine interventions

By systematically evaluating the patient's clinical presentation and understanding these pathophysiologic mechanisms, clinicians can rapidly identify and address the underlying cause of acute severe hypotension, potentially improving patient outcomes.