Hypotension

Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Clinically significant complications may occur when blood pressure falls enough for crucial organs to become insufficiently perfused. Diagnostic studies and treatment depend on the clinical presentation and underlying conditions.

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Overview

Definition

Hypotension is defined as blood pressure below 90/60 mm Hg. If blood pressure decreases enough, shock may develop. Shock is most commonly defined as the life-threatening failure of adequate oxygen delivery to the tissues and may be due to decreased blood perfusion of vital organs (e.g., brain, heart, kidneys, lungs).

Etiology

  • Cardiovascular: 
    • Hypovolemia:
      • Most common cause
      • Hemorrhage (e.g., acute GI bleeding, vaginal bleeding, epistaxis, etc.)
      • Dehydration
    • Impaired cardiac output:  
      • Myocardial infarction
      • Heart failure 
      • Aortic stenosis 
      • Arrhythmias
      • Constrictive pericarditis, pericardial effusion, or cardiac tamponade
      • Aortic dissection
  • Infectious:  
    • Sepsis or septic shock
    • Staphylococcal toxic shock syndrome
  • Neurologic: 
    • Central: 
      • Multiple system atrophy
      • Parkinson’s disease
      • Multiple strokes
      • Tabes dorsalis
      • Transverse myelitis
    • Peripheral: 
      • Amyloidosis
      • Diabetic, alcoholic, or nutritional neuropathy
      • Familial dysautonomia (Riley-Day syndrome)
      • Guillain-Barré syndrome
      • Paraneoplastic syndromes
      • Pure autonomic failure
      • Surgical sympathectomy
  • Endocrine: 
    • Adrenal insufficiency 
    • Hyperaldosteronism
  • Drug induced:
    • Anti-hypertensives (especially alpha- and beta-blockers, centrally acting agents)
    • Antipsychotics, tricyclic antidepressants, and monoamine oxidase inhibitors (MAOIs) 
    • Theophylline
  • Miscellaneous:
    • Anaphylaxis caused by medications, food, and arthropod or animal bites
    • Pregnancy (physiologic)
    • Hypo- or hyperthermia
    • Air embolism
    • Pneumothorax
    • Intradialytic hypotension
    • Postprandial hypotension
    • Orthostatic hypotension: a fall of at least 20 mm Hg in systolic blood pressure or of at least 10 mm Hg in diastolic pressure within 2–5 minutes of standing
    • Postural orthostatic tachycardia syndrome (POTS): chronic orthostatic intolerance defined by a heart rate of ≥ 120/min or an increase of ≥ 30/min when a patient stands up

Pathophysiology and Clinical Presentation

Pathophysiology

  • In the case of hypovolemia, compensatory changes occur as a response to the decreased intravascular volume:
    • RAAS activation → fluid retention and vasoconstriction
    • Sympathetic nervous system activation → vasoconstriction and increased heart rate/contractility
    • B1 receptor activation → renin release
    • Increased antidiuretic hormone release → retention of free water and increased intravascular volume
    • When these compensatory mechanisms fail to maintain normal blood pressure, hypotension results in clinical manifestations.
  • In the case of septic shock and anaphylaxis, hypotension is caused by an increased release of cytokines that produce vasodilation → decrease in peripheral vascular resistance → decrease in blood pressure
    • Massive inflammation and release of cytokines also cause contraction of endothelial cells → leakage of intravascular volume into the interstitium (“3rd spacing”) → lower circulating intravascular volume → hypotension
  • Heart failure and myocardial infarction cause hypotension due to decreased cardiac output → less circulating intravascular volume → hypotension
  • Medications can cause hypotension by:
    • Decreasing the peripheral vascular resistance (e.g., alpha-blockers)
    • Causing volume depletion (e.g., thiazide diuretics)
  • Damage to the nervous system can also cause hypotension by decreasing systemic vascular resistance due to the loss of sympathetic outflow and/or central control of blood pressure regulation.
  • Hypotension is common in pregnancy due to:
    • Hormonal changes
    • The gravid uterus compressing the inferior vena cava (reducing the venous return and cardiac output)

Clinical presentation

  • Lightheadedness or dizziness
  • Syncope (temporary loss of consciousness)
  • Nausea
  • Fatigue
  • Diaphoresis (excessive sweating) or clammy skin
  • Confusion
  • Blurred vision

Diagnosis

Urgent/emergent evaluation

History: 

  • Bleeding  
  • Trauma 
  • Medications
  • Chest pain 
  • Insect or animal bites
  • Respiratory distress  
  • Pregnant or possible pregnancy 
  • Other history relating to presentation

Physical examination:

  • If in shock, assess airway, breathing, and circulation (ABCs)
  • Blood pressure < 90/60 mm Hg
  • Mental status
  • Skin turgor
  • Cardiac exam

Laboratory tests:

  • CBC
  • CMP: glucose, electrolytes, BUN/creatinine
  • Urinalysis 
  • Blood and urine cultures
  • Cardiac enzymes

Additional tests:

  • ECG
  • Imaging of the suspected organ/region (e.g., brain, abdomen, kidneys)
  • Endoscopy or colonoscopy if GI bleed is suspected

Outpatient/non-urgent evaluation

  • Detailed history
  • Pertinent physical examination
  • Laboratory tests as indicated
  • Additional tests as necessary/according to clinical suspicion:
    • Stress test and/or echocardiogram if history is consistent with a possible cardiac cause
    • Holter monitor if symptoms are intermittent or if history is consistent with possible arrhythmia
    • Imaging as pertinent to the history
    • Tilt-table test for diagnosis of orthostatic hypotension
  • Referral to cardiologist, neurologist, gastroenterologist, or other specialists as applicable

Management

The main goal of the management of hypotension is to reverse the etiology. Thus, identifying and treating the cause appropriately, either medically or surgically, is most important.

Cause-specific therapy

Table: Cause-specific therapy
Cause of hypertensionSpecific management
Acute hemorrhage with hypovolemiaBlood transfusion
Infection with hypovolemiaIV fluids or plasma
Cardiogenic shockIntra-aortic balloon pump (IABP)
Sepsis or septic shockIV antibiotics
Vomiting combined with hypotensionHospitalization and IV fluids
Ruptured arteryEmergency surgical repair
Drug-induced hypotensionDiscontinue or decrease the dose of the offending medications.
Heart failure
  • Increase water and salt intake.
  • Dobutamine is used to increase cardiac output in refractory cases.
Inferior vena cava (IVC) compression by gravid uterus in pregnancyLeft lateral repositioning and avoidance of supine position
Acute myocardial infarction
  • Depends on many factors (e.g., time from onset, comorbidities, symptoms)
  • IV fluids are often used to increase preload and maintain cardiac output.

Medical therapy

Table: Medical therapy
IndicationMedical therapy
Hypotensive emergencies for anaphylaxis or shockIV epinephrine (nonselective beta-agonist), dobutamine (beta-1 adrenergic receptor agonist), or dopamine
Severe cases of arrhythmiaAntiarrhythmics and/or cardioversion (management depends on the specific subtype)
Orthostatic hypotensionFludrocortisone to promote fluid and salt retention
Adrenal insufficiencyReplacement of mineralocorticoids and glucocorticoids

Clinical Relevance

The following conditions are the most common causes of hypotension: 

  • Heart failure: the inability of the heart to supply the body with normal cardiac output to meet its metabolic needs and to provide sufficient oxygenation to the organs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Treatment is directed at the removal of excess fluid and decreasing oxygen demand of the heart. 
  • Tachyarrhythmias: a rhythm in which the heart rate exceeds 100/min, which may result in poor perfusion. Can be physiologic, without symptoms of hemodynamic change, or pathologic, resulting in hemodynamic instability and possibly related to intrinsic cardiac abnormalities, systemic diseases, or medication toxicity. 
  • Bradyarrhythmias: a rhythm in which the heart rate is < 60/min. Can be physiologic, without symptoms or hemodynamic change, or pathologic, resulting in reduced cardiac output and hemodynamic instability. May present as syncope, dizziness, or dyspnea.
  • Sepsis: an organ dysfunction resulting from a dysregulated systemic host response to infection. The etiology is mainly bacterial and pneumonia is the most commonly known source. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation.
  • Adrenal insufficiency: the inadequate production of adrenocortical hormones (glucocorticoids, mineralocorticoids, and adrenal androgens). The condition can be primary or secondary. Primary adrenal insufficiency (Addison’s disease) is related to disease in the gland itself; the most common cause is autoimmune adrenalitis. Secondary adrenal insufficiency occurs due to decreased production of adrenocorticotropic hormone (ACTH) either from prolonged glucocorticoid therapy or disease in the pituitary or hypothalamic glands.
  • Hypothermia: prolonged or severe cold exposure that causes peripheral vasoconstriction when the mean body temperature drops below 34°C (93.2°F). Hypotension can result when compensatory mechanisms fail.
  • Heatstroke: an illness characterized as a core body temperature exceeding 40°C (104°F) with accompanying neurological symptoms including ataxia, seizures, and/or delirium. Usually due to the body’s inability to regulate its temperature when challenged with an elevated heat load, causing peripheral vasodilatation and resultant hypotension.
  • Dehydration: refers to a loss of water volume in the body. Dehydration may be caused by GI losses (e.g., diarrhea), renal losses (e.g., diuretics), bleeding, poor sodium intake, and/or 3rd spacing of fluids. The body also loses fluid through normal physiologic processes including respiration, urination, and sweating. Dehydration occurs when fluid loss from the body exceeds fluid intake.
  • Myocardial infarction: ischemia of the myocardial tissue due to a complete obstruction or drastic constriction of the coronary arteries. This condition is usually accompanied by an increase in cardiac enzymes, typical ECG changes, and chest pain. The subsequent decreased cardiac output often results in hypotension.

References

  1. Gaieski DF, Mikkelsen ME. (2021). Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock. UpToDate. Retrieved on March 20, 2021, from https://www.uptodate.com/contents/evaluation-of-and-initial-approach-to-the-adult-patient-with-undifferentiated-hypotension-and-shock
  2. Procter LD. (2020). Shock. Merck Manual Professional Version. https://www.merckmanuals.com/professional/critical-care-medicine/shock-and-fluid-resuscitation/shock
  3. Thompson AD, Shea MJ. (2020). Orthostatic Hypotension. Merck Manual Professional Version. https://www.merckmanuals.com/professional/cardiovascular-disorders/symptoms-of-cardiovascular-disorders/orthostatic-hypotension
  4. American Heart Association. (2021). Syncope. Retrieved on March 20, 2021, from https://www.heart.org/en/health-topics/arrhythmia/symptoms-diagnosis–monitoring-of-arrhythmia/syncope-fainting

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