Hypotension (low blood pressure) refers to inadequate intravascular pressure to maintain tissue oxygenation. While often associated with shock, it may also arise from cardiovascular, respiratory, neurologic, or metabolic disorders. Hypoperfusion particularly affects vital organs such as:

• Kidneys → Renal failure

• Brain → Altered level of consciousness (LOC)

• Heart → Myocardial ischemia

Other causes include medications, diagnostic tests (especially those involving contrast media), stress, and positional changes (e.g., orthostatic hypotension).

Clinical Threshold

• Blood pressure <90/60 mm Hg or

• A drop of ≥30 mm Hg from baseline

Note: Consider baseline variability—what is low for one patient may be normal for another.

Pathophysiological Mechanisms

Hypotension may result from:

1. Expanded intravascular space – e.g., in sepsis, anaphylaxis, adrenal insufficiency

2. Reduced intravascular volume – e.g., in dehydration, hemorrhage

3. Decreased cardiac output – e.g., due to poor myocardial contractility

Often, these mechanisms overlap due to the interrelated nature of blood pressure regulation.

Emergency Interventions

If systolic BP <80 mm Hg or >30 mm Hg below baseline, suspect shock.

Immediate Actions:

• Assess LOC, pulse (apical for tachycardia), respirations (for tachypnea)

• Check for cool, clammy skin

• Positioning: Leg elevation or Trendelenburg position

• Initiate IV access with a large-bore needle

• Administer fluids, blood, or vasopressors as needed

• Start oxygen therapy; be prepared for mechanical ventilation

• Insert urinary catheter for accurate output monitoring

• Consider central venous or pulmonary artery catheter

• Initiate cardiac monitoring

• Insert nasogastric tube if comatose to prevent aspiration

• Maintain spinal precautions until spinal cord injury is ruled out

History and Physical Examination

History:

Ask about:

• Fatigue, weakness

• Nausea, vomiting, GI bleeding

• Blurred vision, unsteady gait

• Palpitations, chest/abdominal pain

• Dizziness, fainting

• Postural symptoms → check for orthostatic hypotension:

  • Drop in systolic/diastolic BP by 10–20 mm Hg

  • HR increase >15 bpm on standing

Physical Exam:

• Skin: Pallor, sweating, clammy

• Peripheral pulses: Assess presence and strength

• Paradoxical pulse: Indicates pericardial tamponade

• Heart: Gallops, murmurs, brady/tachycardia

• Lungs: Crackles, diminished sounds, abnormal rhythm

• Signs of hemorrhage: Bruising, tenderness, masses

• Abdomen: Rigidity, rebound tenderness, bowel sounds

• Infection sources: Open wounds, IV sites

Normal Pediatric Blood Pressure Ranges

Medical causes of hypotension

1. Acute Adrenal Insufficiency

• Orthostatic hypotension

• Fatigue, weakness, nausea, vomiting

• Hyperpigmentation of skin, nails, scars

• Tachycardia, clammy skin, coma

2. Alcohol Toxicity

• Rare hypotension

• Tachycardia, bradypnea, seizures

• Staggering gait, nausea, stertorous breathing

3. Anaphylactic Shock

• Rapid BP drop, narrowed pulse pressure

• Anxiety, itching, nasal congestion

• Respiratory distress, GI symptoms, seizures

4. Anthrax (Inhalation)

• Caused by Bacillus anthracis

• Initial: Flu-like symptoms

• Later: Stridor, hypotension, mediastinitis

5. Cardiac Arrhythmias

• BP fluctuations, dizziness, chest pain

• Irregular rhythm; HR >100 or <60 bpm

6. Cardiac Contusion

• Hypotension with tachycardia, anginal pain

7. Cardiac Tamponade

• Paradoxical pulse, muffled heart sounds

• JVD, cyanosis, Kussmaul’s sign

8. Cardiogenic Shock

• Systolic BP <80 mm Hg

• Narrowed pulse pressure, restlessness

• Peripheral cyanosis, JVD, weak pulse

9. Cholera

• Vibrio cholerae infection

• Profuse diarrhea, dehydration, muscle cramps

10. Diabetic Ketoacidosis (DKA)

• Hypovolemia, dehydration

• Fruity breath, Kussmaul’s respirations, coma

11. Heart Failure

• BP may drop suddenly

• Orthopnea, fatigue, edema, JVD

12. HHNS (Type 2 Diabetes)

• Severe dehydration from hyperglycemia

• Confusion, seizures, hypotension

13. Hypovolemic Shock

• BP <80 mm Hg

• Rapid weak pulse, clammy skin, anxiety

14. Hypoxemia

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14. Hypoxemia

• Low oxygen levels impair myocardial function

• Causes vasodilation and reduced vascular tone

• Symptoms: confusion, dyspnea, cyanosis, tachycardia, and hypotension

• May lead to shock if severe and prolonged

15. Myocardial Infarction (MI)

• Hypotension occurs with:

  • Large infarct area

  • Involvement of left ventricle or right ventricle

  • Bradyarrhythmias or tachyarrhythmias

• Clinical features:

  • Chest pain (may radiate)

  • Diaphoresis, nausea

  • Weakness, dizziness, hypotension

  • Possible signs of cardiogenic shock

16. Neurogenic Shock

• Loss of sympathetic tone (e.g., spinal cord injury, anesthesia)

• Causes:

  • Bradycardia

  • Hypotension

  • Warm, dry skin (due to vasodilation)

• Absence of tachycardia distinguishes it from other types of shock

17. Orthostatic (Postural) Hypotension

• Drop in BP upon standing:

  • Systolic ↓ ≥20 mm Hg

  • Diastolic ↓ ≥10 mm Hg

  • HR ↑ ≥15 bpm

• Common in:

  • Elderly

  • Patients on diuretics, antihypertensives

  • Dehydrated individuals

• May cause dizziness, fainting

18. Sepsis and Septic Shock

• Sepsis = life-threatening organ dysfunction from infection

• Septic shock:

  • Persistent hypotension despite fluid resuscitation

  • Elevated lactate levels

  • Warm peripheries early; cold and clammy later

  • High output but low perfusion state

19. Spinal Cord Injury

• Especially injuries above T6

• Disrupts sympathetic pathways

• Features:

  • Hypotension

  • Bradycardia

  • Flaccid paralysis

  • Loss of sensation and reflexes

20. Trauma (Hemorrhagic Shock)

• Common cause of hypovolemic shock

• Blood loss leads to decreased preload and cardiac output

• Clinical signs:

  • Tachycardia, hypotension

  • Cold, clammy skin

  • Decreased urine output

  • Altered mental status

• May involve internal bleeding

21. Vasovagal Syncope

• Reflex-mediated drop in BP and HR

• Triggered by:

  • Emotional stress

  • Pain

  • Prolonged standing

• Preceded by:

  • Nausea, sweating

  • Lightheadedness

• Self-limiting; recovery is usually spontaneous

22. Medication-Induced Hypotension

• Common culprits:

  • Diuretics (volume depletion)

  • Antihypertensives (ACE inhibitors, beta-blockers, nitrates)

  • Psychotropics (antipsychotics, antidepressants)

  • Anesthetics

• Monitor closely when starting new medications or adjusting doses

23. Adrenal Crisis (Addisonian Crisis)

• Acute worsening of chronic adrenal insufficiency

• Features:

  • Hypotension unresponsive to fluids

  • Vomiting, abdominal pain

  • Hyperpigmentation

  • Hyponatremia, hyperkalemia

  • Requires urgent steroid replacement

Summary Table: Causes and Key Features

Conclusion

Hypotension is a clinical sign—not a disease. A detailed history, physical examination, and timely interventions are crucial to identify and manage the underlying cause effectively. Persistent hypotension, especially in the setting of end-organ damage, should raise concern for shock and prompt urgent resuscitative efforts.

References

1. Here is a list of Vancouver-style references for the content on Hypotension (Low Blood Pressure), based on standard textbooks and peer-reviewed sources that cover emergency medicine, internal medicine, and pathophysiology of shock and hypotension:

2. McCance KL, Huether SE. Pathophysiology: The Biologic Basis for Disease in Adults and Children. 8th ed. St. Louis: Elsevier; 2019.

3. Tintinalli JE, Stapczynski JS, Ma OJ, Yealy DM, Meckler GD, Cline DM. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 9th ed. New York: McGraw-Hill Education; 2020.

4. Kumar P, Clark M. Kumar and Clark’s Clinical Medicine. 10th ed. Philadelphia: Elsevier; 2020.

5. Guyton AC, Hall JE. Textbook of Medical Physiology. 14th ed. Philadelphia: Elsevier; 2021.

6. American Diabetes Association. Hyperglycemic crises in diabetes: standards of medical care in diabetes—2022. Diabetes Care. 2022 Jan;45(Suppl 1):S109–14.Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, editors. Harrison’s Principles of Internal Medicine. 20th ed. New York: McGraw-Hill Education; 2018.

7. Levy MM, Evans LE, Rhodes A. The surviving sepsis campaign bundle: 2018 update. Intensive Care Med. 2018 Jun;44(6):925–8.

8. Centers for Disease Control and Prevention (CDC). Anthrax: Information for Health Professionals. 2021 [cited 2025 May 15]. Available from: https://www.cdc.gov/anthrax

9. Ropper AH, Samuels MA, Klein JP. Adams and Victor's Principles of Neurology. 11th ed. New York: McGraw-Hill Education; 2019.

10. Marik PE. The diagnosis and management of hypotension in the critically ill patient. Crit Care. 2021;25(1):197.