Hypotension

Hypotension is a blood pressure low enough to cause symptoms or end organ hypoperfusion. In adults this means systolic blood pressure under 90 mmHg, mean arterial pressure under 65 mmHg, or a fall of over 40 mmHg from baseline.

Low readings without symptoms (for example 85/55 in a fit young woman) can be normal. Hypotension is a manifestation of shock when it is accompanied by signs of poor tissue perfusion (altered mental state, oliguria, cold clammy skin, lactate over 2 mmol/L).

Clinical relevance. Acute hypotension is a medical emergency until shown otherwise. The type of shock (hypovolaemic, cardiogenic, distributive, obstructive) must be found and treated at once. Chronic or intermittent hypotension is often due to drugs, volume depletion, autonomic failure or endocrine disease.

Classification by mechanism.

• Hypovolaemic: haemorrhage (trauma, gastrointestinal, ruptured aneurysm or ectopic), dehydration, burns, third space loss.
• Cardiogenic: myocardial infarction, severe heart failure, arrhythmia, acute valve failure, myocarditis, cardiomyopathy.
• Distributive: sepsis, anaphylaxis, neurogenic shock (spinal injury), adrenal crisis, drugs, liver failure, toxic shock.
• Obstructive: pulmonary embolism, tension pneumothorax, cardiac tamponade, aortic dissection, severe aortic stenosis.
• Chronic or constitutional: physiological low pressure, orthostatic hypotension, drugs, endocrine (adrenal insufficiency, hypothyroidism), malnutrition, anorexia nervosa, heart failure.

Shock stages. Compensated (tachycardia, cool peripheries, normal pressure), decompensated (hypotension, oliguria, confusion), refractory.

Mean arterial pressure equals diastolic pressure plus one third of pulse pressure; target 65 mmHg or more in shock.

History.

• Onset and time course, symptoms (dizziness, weakness, confusion, nausea, sweating, palpitations, chest pain, breathlessness, thirst, reduced urine).
• Bleeding, trauma, vomiting, diarrhoea, poor intake, burns, heat exposure, fever, infection, rash, wheeze, swelling, allergen exposure (food, drug, sting), recent surgery or procedure, spinal injury.
• Cardiac history, chest pain, syncope, orthopnoea, leg swelling, recent infarction.
• Endocrine: adrenal disease, steroid use or withdrawal, weight loss, pigmentation.
• Drugs: antihypertensives, diuretics, nitrates, alpha blockers, beta blockers, calcium channel blockers, ACE inhibitors, sacubitril, sildenafil, antidepressants, antipsychotics, opioids, sedatives, insulin, anaesthetics, overdoses (calcium channel blockers, beta blockers, tricyclics, clonidine).
• Pregnancy, menstrual history, abdominal or pelvic pain.

Examination.

• ABCDE; heart rate, blood pressure, respiratory rate, temperature, oxygen saturation, capillary glucose, urine output, capillary refill (over 3 seconds is abnormal), mental state (Glasgow Coma Scale).
• Skin: warm and flushed (distributive early), cold and clammy (hypovolaemic, cardiogenic), mottling, rash, urticaria, petechiae, purpura.
• Cardiac: jugular venous pressure (low in hypovolaemia, high in cardiogenic and obstructive shock), heart sounds, murmurs, muffled sounds, pulsus paradoxus.
• Chest: wheeze, crackles, absent breath sounds, tracheal deviation.
• Abdomen: tenderness, rigidity, distension, pulsatile mass, rectal examination for melaena.
• Limbs: pulses, swelling, injection sites; pregnancy signs; pigmentation.
• Neck and spine for injury.

Red flags.

• Systolic pressure under 90 mmHg with heart rate over 100 (shock index heart rate to systolic pressure over 0.9).
• Altered consciousness, oliguria (under 0.5 mL/kg/hour), cold mottled skin, lactate over 2 mmol/L.
• Chest pain, breathlessness, tachyarrhythmia, bradycardia under 40.
• Bleeding, haematemesis, melaena, abdominal pain with rigidity.
• Fever with rash or known infection source (sepsis).
• Wheeze, stridor, urticaria (anaphylaxis).
• Known adrenal disease or steroid withdrawal.

Hypovolaemic shock. Gastrointestinal bleeding, trauma, ruptured abdominal aortic aneurysm, ruptured ectopic pregnancy, postpartum haemorrhage, dehydration (gastroenteritis, cholera, diabetic ketoacidosis, hyperosmolar state), burns, pancreatitis, intestinal obstruction.

Cardiogenic shock. Acute myocardial infarction, decompensated heart failure, acute mitral regurgitation, ventricular septal rupture, arrhythmia (ventricular tachycardia, rapid atrial fibrillation, bradycardia), myocarditis, Takotsubo syndrome, peripartum cardiomyopathy, beta blocker or calcium channel blocker overdose.

Obstructive shock. Massive pulmonary embolism, tension pneumothorax, cardiac tamponade, aortic dissection, severe aortic stenosis, constrictive pericarditis.

Distributive shock. Sepsis and septic shock, toxic shock syndrome, anaphylaxis, neurogenic shock, adrenal crisis, myxoedema coma, liver failure, pancreatitis, drug reactions, vasodilators, malaria, dengue shock syndrome.

Chronic and drug related. Antihypertensive excess, diuretics, alpha blockers, antidepressants, constitutionally low pressure, adrenal insufficiency, hypothyroidism, hypopituitarism, anorexia nervosa, malnutrition, autonomic failure, heart failure with low output, severe anaemia, chronic liver disease.

Pseudo hypotension. Wrong cuff size, arterial disease (subclavian stenosis, aortic dissection, Takayasu arteritis) causing unequal arm pressures, measurement error.

1. Treat while assessing. Check airway, breathing, circulation; attach monitor; 12 lead ECG; capillary glucose; intravenous access (two large bore cannulas); blood tests; lactate.
2. Blood tests: full blood count, urea, creatinine, electrolytes, glucose, liver function tests, lactate, arterial or venous gas (acidosis), coagulation screen, group and crossmatch, troponin, blood cultures (before antibiotics but without delay), C reactive protein or procalcitonin, cortisol (random cortisol under 400 nmol/L during illness suggests insufficiency), thyroid stimulating hormone, amylase or lipase, pregnancy test, drug levels and toxicology as indicated.
3. Bedside ultrasound (point of care): inferior vena cava collapse (hypovolaemia), cardiac function, pericardial effusion, right ventricular dilatation, lung sliding, free abdominal fluid, aortic aneurysm.
4. Chest radiograph; echocardiography for cardiogenic or obstructive shock; CT pulmonary angiography; CT abdomen; CT aortography; endoscopy; focused assessment with sonography in trauma.
5. Urinalysis and culture, pregnancy test, lumbar puncture only when safe.
6. Haemodynamic monitoring: arterial line, central venous pressure, urine output, cardiac output estimation, passive leg raise test (increase in stroke volume or pulse pressure of 10% to 15% predicts fluid responsiveness).
7. For chronic hypotension: lying and standing pressures, ambulatory blood pressure monitoring, review of drugs, cortisol and short synacthen test, thyroid function, full blood count, glucose, B12, electrolytes, ECG, echocardiography, autonomic testing.

Limits. Blood pressure may be preserved in early shock, especially in young patients and pregnant women; older adults and those on beta blockers lack tachycardia. Cuff readings are unreliable in shock. Lactate may be raised by metformin, liver failure and seizures.

Immediate (all with shock).

• Oxygen to keep saturation 94% to 98%.
• Lie flat with legs raised (unless pulmonary oedema).
• Two large bore intravenous or intraosseous accesses, monitoring, urinary catheter.
• Treat the cause; involve senior and critical care staff early.
• Targets: mean arterial pressure 65 mmHg or more, urine output over 0.5 mL/kg/hour, normalising lactate, and capillary refill under 3 seconds.

Fluid resuscitation. For hypovolaemic, distributive and many obstructive causes:

• Balanced crystalloid (Ringer lactate or Plasma-Lyte) or 0.9% sodium chloride 500 mL over 15 minutes (250 mL in heart failure, older adults, renal impairment). Reassess after each bolus.
• In sepsis give 30 mL/kg over the first 3 hours.
• Stop when no longer fluid responsive or when signs of overload appear.
• Albumin 4% to 5% may be added in sepsis requiring large volumes.

Haemorrhagic shock.

• Control the source (pressure, tourniquet, surgery, endoscopy, angioembolisation).
• Permissive hypotension (systolic 80 to 90 mmHg) in penetrating trauma without head injury.
• Blood products in a 1:1:1 ratio (red cells, plasma, platelets) with massive transfusion activation.
• Tranexamic acid 1 g intravenously over 10 minutes within 3 hours of injury, then 1 g over 8 hours.
• Calcium chloride 10% 10 mL for each 4 units transfused.
• Prothrombin complex concentrate for anticoagulant reversal. Keep the patient warm.
• Ectopic pregnancy or aortic rupture: immediate surgery.

Septic shock.

• Antibiotics within 1 hour after cultures. For example, ceftriaxone 2 g intravenously daily, or piperacillin-tazobactam 4.5 g every 6 hours.
• Add vancomycin 15 to 20 mg/kg every 8 to 12 hours if MRSA risk. Add gentamicin or meropenem 1 g every 8 hours for resistant organisms. Add clindamycin 600 to 900 mg every 8 hours for toxic shock.
• Source control.
• Noradrenaline infusion 0.05 to 0.5 micrograms/kg/minute (start at 0.05 and titrate to mean arterial pressure 65 mmHg) via central or large peripheral vein.
• Add vasopressin 0.03 units/minute if the dose rises. Give hydrocortisone 50 mg intravenously every 6 hours if requirements persist.
• Lactate directed resuscitation.

Anaphylaxis.

• Adrenaline 0.5 mg (0.5 mL of 1 in 1,000) intramuscularly into the anterolateral thigh, repeated every 5 minutes if no improvement.
• Intravenous adrenaline infusion 0.05 to 0.1 micrograms/kg/minute if refractory.
• Crystalloid 1 to 2 litres; oxygen.
• Chlorphenamine 10 mg intravenously; hydrocortisone 200 mg intravenously.
• Salbutamol for bronchospasm. Glucagon 1 to 5 mg for patients on beta blockers.

Cardiogenic shock.

• Reperfusion for infarction (percutaneous coronary intervention).
• Noradrenaline to maintain pressure. Dobutamine 2.5 to 10 micrograms/kg/minute for low output with adequate pressure.
• Avoid large fluid volumes.
• Treat arrhythmia (cardioversion, pacing).
• Mechanical circulatory support (intra aortic balloon pump, Impella, extracorporeal membrane oxygenation).
• Diuretics only when congested and not hypotensive.

Obstructive shock.

• Pulmonary embolism: alteplase 100 mg over 2 hours or catheter therapy.
• Tension pneumothorax: needle decompression then chest drain.
• Tamponade: pericardiocentesis.
• Dissection: surgery and blood pressure control.

Neurogenic shock. Fluids 1 to 2 litres, then noradrenaline or phenylephrine. Atropine 500 micrograms for bradycardia. Spinal immobilisation.

Adrenal crisis.

• Hydrocortisone 100 mg intravenously at once, then 200 mg over 24 hours (or 50 mg every 6 hours).
• 0.9% sodium chloride 1 litre over 1 hour, then 4 to 6 litres over 24 hours.
• 10% glucose 150 to 200 mL for hypoglycaemia.
• Search for the precipitant.
• Continue steroid for chronic management (hydrocortisone 15 to 25 mg daily with fludrocortisone 50 to 100 micrograms daily). Give a steroid emergency card and advise double dosing during illness.

Myxoedema coma. Levothyroxine 200 to 400 micrograms intravenously, then 1.6 micrograms/kg daily, and hydrocortisone 100 mg every 8 hours. Warming and ventilation as needed.

Drug related. Stop culprit drugs.

• Beta blocker overdose: glucagon 5 to 10 mg intravenously then 2 to 5 mg/hour, high dose insulin therapy, calcium.
• Calcium channel blocker overdose: calcium chloride 10% 10 to 20 mL, high dose insulin, vasopressors.
• Tricyclic overdose: sodium bicarbonate 50 to 100 mmol.

Dengue shock. Cautious crystalloid 5 to 10 mL/kg over 1 hour, reassess, avoid excess. Blood transfusion for bleeding.

Chronic or constitutional hypotension. Reassure if asymptomatic. Remove contributing drugs. Advise fluids, salt and compression. For symptomatic cases, give fludrocortisone 100 to 300 micrograms daily or midodrine 2.5 to 10 mg three times daily, with fluids, salt and compression.

Monitoring. Continuous ECG, blood pressure (arterial line in shock), urine output hourly, lactate every 2 to 4 hours until normal, electrolytes, glucose, and haemoglobin. Reassess for fluid overload.

Referral and escalation. Critical care for shock; surgery for haemorrhage and obstruction; cardiology for cardiogenic shock; endocrinology for adrenal and thyroid emergencies; poison centre for overdose.

Admission. All with shock or symptomatic hypotension not rapidly reversible; sepsis; bleeding; cardiac or arrhythmic causes; electrolyte or endocrine emergencies; elderly with falls.

Safety netting. Return for fainting, confusion, reduced urine, chest pain, breathlessness, bleeding or black stool, fever with rigors, or inability to drink.

Special groups.

• Pregnancy: supine hypotension (left lateral tilt), haemorrhage, amniotic fluid embolism, sepsis; resuscitate the mother first.
• Children: hypotension is a late sign (heart rate, capillary refill and mental state first).
• Older adults: drug effects and dehydration; lower target pressures may be unsafe.
• Endemic regions: malaria, dengue, cholera, sepsis, severe anaemia, and HIV.