What are the causes of hypotension?

Causes of Hypotension

Hypotension has multiple etiologies including cardiac dysfunction, volume depletion, medication effects, autonomic dysfunction, and endocrine disorders, which should be systematically evaluated for appropriate management. 1

Definition

• Clinically significant hypotension should be assessed based on symptoms and organ perfusion rather than absolute blood pressure values alone 1
• Severe hypotension (systolic blood pressure <80 mmHg) or hypotension causing major symptoms requires immediate attention 1

Major Causes of Hypotension

Volume Depletion and Dehydration

• Fluid volume depletion from acute causes (diarrhea, vomiting, fever, excessive diuresis) is a common cause of hypotension 1
• Diuretic therapy, especially when aggressive, can lead to acute renal failure and hypotension in patients with heart failure 2
• Volume depletion manifests along a spectrum from tachycardia to shock, depending on whether compensation is adequate 1

Cardiac Causes

• Poor cardiac output due to heart failure, myocardial infarction, or cardiomyopathy 2
• Cardiogenic shock characterized by systolic pressure <90 mmHg, central filling pressure >20 mmHg, or cardiac index <1.8 L/min/m² 1
• Bradyarrhythmias and tachyarrhythmias can cause hypotension through reduced cardiac output 1

Medication-Induced Hypotension

• Antihypertensive medications, particularly ACE inhibitors, can cause hypotension, especially when initiating therapy 2
• Drug-induced hypotension is particularly prevalent in older adults with multiple comorbidities and polypharmacy 1, 3
• Common culprit medications include:
  • Antihypertensives (ACE inhibitors, calcium channel blockers, beta-blockers) 3
  • Psychiatric medications (phenothiazines, tricyclic antidepressants, MAO inhibitors) 4
  • Vasodilators and nitrates 3
  • Anti-Parkinsonian drugs 3
  • Dopamine agonists and other cardiovascular drugs 4

Orthostatic Hypotension

• Defined as a drop of ≥20 mmHg in systolic BP and/or ≥10 mmHg in diastolic BP within 3 minutes of standing 2, 1
• Occurs in 10-30% of elderly patients and is linked to recurrent falls and syncope 3
• Secondary orthostatic hypotension can be caused by medication effects, volume depletion, or other medical conditions 1
• Diabetic autonomic neuropathy can lead to orthostatic hypotension 2, 5

Autonomic Dysfunction

• Reduced baroreflex sensitivity and cardiac vagal function can contribute to hypotension 1
• Autonomic neuropathies include those secondary to diabetes (diabetic dysautonomia), peripheral autonomic impairment (Bradbury-Eggleston syndrome), and central autonomic impairment (Shy-Drager syndrome) 5
• Dopamine-beta-hydroxylase deficiency causes absence of norepinephrine with accumulation of dopamine, leading to hypotension 5

Endocrine Causes

• Adrenal failure (primary or secondary) can cause hypotension due to cortisol and/or aldosterone deficiency 6
• Isolated hypoaldosteronism can present with hypotension, hyponatremia, and hyperkalemia 6
• Pheochromocytoma can paradoxically cause hypotension, especially during surgical removal when not properly prepared with calcium channel blockers 6
• Carcinoid syndrome can present with flushing and hypotension during carcinoid crisis 6

Situational and Reflex-Mediated Hypotension

• Vasovagal syncope triggered by emotional upset, pain, or specific scenarios 1
• Situational syncope associated with specific activities such as micturition, coughing, or defecation 1

Perioperative Hypotension

• Common after anesthetic induction, especially in older individuals with higher baseline sympathetic drive 1
• Anesthetic agents can impair baroreflex sensitivity, removing key blood pressure control mechanisms 1
• Only about 54% of patients with postoperative hypotension respond to fluid boluses, suggesting that vascular tone or inotropy issues may be responsible in the remaining cases 2

Special Considerations

Hypotension in Heart Failure

• Low blood pressure in heart failure patients requires careful assessment of organ perfusion rather than relying solely on BP values 1
• ACE inhibitors commonly lead to acute renal failure in patients who are volume depleted from diuretic therapy 2

Orthostatic Hypotension Management

• Treatment should focus on minimizing postural symptoms rather than restoring normotension 2
• Non-pharmacologic measures include ensuring adequate salt intake, avoiding medications that aggravate hypotension, using compressive garments, and encouraging physical activity 2
• Midodrine and droxidopa are FDA-approved for the treatment of orthostatic hypotension 2

Pitfalls and Caveats

• Relying solely on absolute BP values rather than assessing symptoms and organ perfusion can lead to inappropriate management 1
• Failing to identify medication-induced hypotension, especially in older adults with polypharmacy, can have significant consequences 1, 3
• Inappropriate use of vasopressors may correct hypotension but potentially at the expense of multi-organ cellular injury 1
• When treating hypotension with vasopressors like dopamine, be aware of potential side effects including arrhythmias, tissue necrosis with extravasation, and drug interactions 7