What are the causes and management of hypotension?

Causes of Hypotension

Definition and Clinical Assessment

Hypotension should be assessed based on symptoms and organ perfusion rather than absolute blood pressure values alone, though systolic BP <90 mmHg or mean arterial pressure <65 mmHg generally defines hypotension. 1, 2 Severe hypotension (systolic BP <80 mmHg) or any hypotension causing major symptoms requires immediate intervention. 1, 2

Major Categories of Hypotension

Volume Depletion (Most Common)

• Acute fluid losses from diarrhea, vomiting, fever, or excessive diuresis are the most common causes of hypotension 1, 2
• Excessive diuretic therapy can lead to volume depletion, electrolyte abnormalities, and acute renal failure, particularly in heart failure patients 3, 1
• Hemorrhage and dehydration manifest along a spectrum from compensated tachycardia to frank shock 2

Clinical Pearl: Volume depletion should always be corrected as fully as possible before administering vasopressors. 4

Medication-Induced Hypotension

• Antihypertensive medications (ACE inhibitors, ARBs, calcium channel blockers, alpha-blockers) are particularly problematic in older adults with polypharmacy 1, 2
• Beta-blockers can cause hypotension, especially those with alpha-blocking properties like carvedilol, typically within 24-48 hours of initiation or dose increase 3
• Diuretics when used aggressively can precipitate hypotension and renal dysfunction 3, 1
• Sedatives and prostate-specific alpha-blockers should be considered as potential culprits 3

Management Approach: Administer beta-blockers and ACE inhibitors at different times of day to minimize hypotensive effects; reduce diuretic dose in volume-depleted patients rather than discontinuing the beta-blocker. 3

Cardiac Causes

• Cardiogenic shock: Defined by systolic BP <90 mmHg, central filling pressure >20 mmHg, or cardiac index <1.8 L/min/m² 2, 5
• Acute myocardial infarction: Particularly inferior MI causing bradycardia-hypotension syndrome (warm hypotension with venodilatation) 5, 4
• Right ventricular infarction: Presents with elevated jugular venous pressure, bradycardia, and hypotension 5
• Heart failure: Advanced cases show hypotension in 3-4% of outpatients and up to 25% of hospitalized patients 5
• Valvular dysfunction and arrhythmias (both brady- and tachyarrhythmias) 2

Septic Shock

• Septic shock is defined as sepsis requiring vasopressors to maintain MAP ≥65 mmHg and serum lactate >2 mmol/L despite adequate volume resuscitation 3
• Norepinephrine is the first-line vasopressor for septic shock, more efficacious than dopamine 3, 4
• Early identification and prompt fluid resuscitation within 3 hours is critical, targeting MAP 65-70 mmHg 3

Orthostatic Hypotension

• Definition: Drop of ≥20 mmHg systolic and/or ≥10 mmHg diastolic BP within 3 minutes of standing 3, 1, 2
• Causes include:
  • Medication effects (most common) 3, 2
  • Autonomic neuropathy (diabetic, Shy-Drager syndrome, Bradbury-Eggleston syndrome) 6, 7
  • Volume depletion 1, 2
  • Age-related autonomic dysfunction 8

Testing Protocol: Have patient sit or lie for 5 minutes, then measure BP at 1 and/or 3 minutes after standing. 3

Endocrine Causes

• Adrenal insufficiency (primary or secondary) with hyperkalemia and hyponatremia 6
• Hypoaldosteronism (isolated or with glucocorticoid deficiency) 6
• Diabetic autonomic neuropathy 1, 6
• Pheochromocytoma (rare presentation, especially during surgical removal) 6

Neurogenic/Reflex-Mediated

• Vasovagal syncope triggered by emotional upset, pain, or specific situations (micturition, coughing, defecation) 2
• Carotid sinus hypersensitivity 7
• Autonomic failure (central or peripheral) 7, 8

Critical Management Principles

Immediate Assessment

1. Confirm BP reading in both supine/sitting and standing positions 2
2. Assess for end-organ hypoperfusion: altered mental status, oliguria, worsening renal function, cardiac ischemia 1, 2
3. Check vital signs: heart rate, respiratory rate, oxygen saturation, temperature 2
4. Perform passive leg raise test to assess fluid responsiveness 2

Treatment Algorithm

For Fluid-Responsive Hypotension:

• Administer IV crystalloid solutions rapidly 3, 2
• Target MAP 65-70 mmHg initially 3
• Avoid fluid overload, which can worsen outcomes (particularly in peritonitis/sepsis) 3

For Non-Fluid-Responsive Hypotension:

• Norepinephrine is first-line vasopressor 3, 4
  • Dilute 4 mg in 1000 mL of 5% dextrose (4 mcg/mL) 4
  • Start at 8-12 mcg/minute, titrate to maintain MAP 65-70 mmHg 4
  • Average maintenance: 2-4 mcg/minute 4
• For cardiogenic shock: Consider inotropes like dobutamine 2

For Orthostatic Hypotension:

• Non-pharmacologic measures first: adequate salt intake, compression garments, physical activity, avoid aggravating medications 1
• FDA-approved medications: Midodrine or droxidopa 1
• Goal: Minimize postural symptoms, not necessarily restore normotension 1

Special Population Considerations

Older/Frail Patients:

• Screen for orthostatic hypotension before starting or intensifying BP medications 3
• Switch medications that worsen orthostatic hypotension rather than simply de-intensifying therapy 3
• Consider deprescribing if BP drops with progressing frailty 3

Heart Failure Patients:

• Assess organ perfusion rather than relying solely on BP values 1, 2
• Start guideline-directed medical therapy at low doses with medications having minimal BP-lowering effects 2
• Reduce diuretics if volume depleted, but avoid in euvolemic patients as this increases fluid retention risk 3

Critical Pitfalls to Avoid

• Do not rely solely on absolute BP values without assessing symptoms and organ perfusion 1, 2
• Do not administer vasopressors before correcting volume depletion when possible 4
• Do not abruptly withdraw vasopressor infusions; taper gradually 4
• Do not overlook medication-induced hypotension in older adults with polypharmacy 2
• Do not use saline alone for norepinephrine infusion; always use dextrose-containing solutions 4
• Only 54% of postoperative hypotension responds to fluid boluses, suggesting vascular tone or cardiac issues in the remainder 1