Shock

Shock is life threatening circulatory failure in which oxygen delivery does not meet tissue demand, leading to cellular dysfunction and organ failure.

Definition. Clinically: systolic pressure under 90 mmHg, mean arterial pressure under 65 mmHg, or a fall of over 40 mmHg from baseline, with evidence of hypoperfusion. Evidence of hypoperfusion is lactate over 2 mmol/L, mottled or cold skin, capillary refill over 3 seconds, urine output under 0.5 mL/kg/hour, or altered mental state. Hypotension without hypoperfusion is not shock, and shock can occur with a normal pressure when compensation is active.

Classification.

Haemorrhage classes. Class I: under 15% blood volume loss, usually normal vital signs. Class II: 15 to 30%, tachycardia, normal pressure. Class III: 30 to 40%, hypotension, confusion. Class IV: over 40%, collapse.

Mechanisms. Hypoperfusion causes anaerobic metabolism, lactic acidosis, endothelial injury, coagulopathy and multiple organ failure. Prolonged shock becomes refractory to treatment.

Key distinctions. Shock index (heart rate divided by systolic pressure) over 0.9 is abnormal and over 1.0 indicates high risk, including in pregnancy. Beta blockers, older age and pacemakers blunt tachycardia. Children keep pressure until late, then collapse.

History (fast, from patient or others). Ask about:

• Bleeding (trauma, melaena, vaginal bleeding, pregnancy), vomiting and diarrhoea.
• Fever and infection source, chest pain, breathlessness.
• Leg swelling or recent surgery or travel, allergen exposure and rash.
• Drugs (antihypertensives, beta blockers, anticoagulants, steroids, insulin, overdose), steroid use and adrenal disease.
• Spinal injury, comorbidity, pregnancy and the last menstrual period.

Examination.

• Vital signs including temperature, capillary refill, mottling, peripheral temperature, urine output, Glasgow Coma Scale and capillary glucose.
• Jugular venous pressure (raised in cardiogenic and obstructive shock, flat in hypovolaemic and distributive shock), heart sounds (muffled in tamponade), new murmurs, pulse volume, pulsus paradoxus.
• Chest: crackles, silent or hyper-resonant hemithorax, tracheal shift. Abdomen: distension, rigidity, pulsatile mass, rectal examination for melaena. Skin: rash (purpura, urticaria, erythema), cellulitis, injection sites. Legs for swelling and spine for neurological level.
• Warm shock (bounding pulses, wide pulse pressure) points to early sepsis, anaphylaxis, neurogenic or liver failure. Cold shock (narrow pulse pressure, cool peripheries) points to hypovolaemic, cardiogenic and obstructive causes.

Red flags.

• Systolic pressure under 90 mmHg, lactate over 4 mmol/L, heart rate over 130 or under 40 beats/min, anuria, Glasgow Coma Scale under 13.
• Purpuric rash with fever, stridor or swollen face with hypotension, ST elevation, tearing chest or back pain, rigid abdomen, and unilateral absent breath sounds with hypotension.

Special groups.

• Pregnancy: blood volume is expanded 40 to 50%, so hypotension is a late sign; use left lateral tilt after 20 weeks; consider haemorrhage, ectopic pregnancy, abruption, embolism, sepsis and eclampsia.
• Children: tachycardia, prolonged capillary refill and cool peripheries come first; hypotension is late and pre-arrest (systolic pressure under 70 mmHg plus twice the age in years from 1 to 10 years).
• Older adults: beta blockers and pacemakers mask tachycardia; any sepsis presents with confusion.
• Region specific: consider dengue shock syndrome, severe malaria, cholera and other severe dehydrating diarrhoea, typhoid perforation, viral haemorrhagic fevers, severe acute malnutrition, sickle cell splenic sequestration, tuberculous pericarditis and tamponade, and HIV related sepsis.

Hypovolaemic.

• Haemorrhagic: trauma, gastrointestinal bleeding, ruptured abdominal aortic aneurysm, ruptured ectopic pregnancy, placental abruption, placenta praevia, postpartum haemorrhage, ruptured spleen, retroperitoneal bleeding.
• Non-haemorrhagic: gastroenteritis, cholera, diabetic ketoacidosis, hyperosmolar hyperglycaemic state, burns, acute pancreatitis, bowel obstruction, heat stroke, diuretic excess, adrenal crisis, diabetes insipidus.

Cardiogenic.

• Acute myocardial infarction, papillary muscle rupture, ventricular septal rupture, free wall rupture.
• Ventricular tachycardia, rapid atrial fibrillation, complete heart block.
• Myocarditis, dilated cardiomyopathy decompensation, takotsubo cardiomyopathy.
• Aortic stenosis, prosthetic valve thrombosis, infective endocarditis with valve destruction.
• Beta blocker poisoning, calcium channel blocker poisoning, tricyclic antidepressant poisoning.

Obstructive. Massive pulmonary embolism, tension pneumothorax, cardiac tamponade, aortic dissection, constrictive pericarditis, severe aortic stenosis, auto-PEEP in ventilated asthma, abdominal compartment syndrome, caval compression in late pregnancy.

Distributive. Septic shock, anaphylaxis, neurogenic shock, adrenal crisis, toxic shock syndrome, dengue shock syndrome, severe malaria, acute liver failure, severe pancreatitis, vasodilator and sedative overdose, post cardiac arrest syndrome, thyroid storm, myxoedema coma.

Resuscitation and diagnosis run together.

Immediate tests.

• 12 lead ECG, capillary glucose
• blood gas with lactate (over 2 mmol/L abnormal, over 4 mmol/L severe, repeat at 2 hours)
• full blood count, urea, creatinine, electrolytes, corrected calcium, liver tests
• coagulation with fibrinogen, group and crossmatch
• troponin, CRP
• blood cultures (before antimicrobials if no delay of more than 45 minutes)
• urinalysis, pregnancy test, creatine kinase
• mast cell tryptase if anaphylaxis is possible
• malaria test and dengue test where relevant, HIV test
• a random cortisol if adrenal crisis is suspected (never delay hydrocortisone)

Bedside ultrasound (pump, tank, pipes, lungs, abdomen).

• Left ventricle function and pericardial effusion, right ventricle dilatation, inferior vena cava size and collapse (under 2 cm with over 50% collapse suggests low filling; unreliable in ventilated patients).
• Aorta (aneurysm), free fluid in the abdomen and chest, lung sliding (absent in pneumothorax), B-lines (pulmonary oedema), and leg veins for thrombosis.

Imaging. Chest radiograph. When stable enough: CT pulmonary angiography, CT aorta, CT abdomen and pelvis, and CT or MRI for neurogenic shock.

Haemodynamic assessment. Passive leg raise with a rise of 10% or more in stroke volume or cardiac output predicts fluid responsiveness in spontaneously breathing patients. Arterial line for mean pressure. Central venous oxygen saturation under 70% suggests inadequate delivery.

Targets. Mean arterial pressure 65 mmHg or more, falling lactate, capillary refill under 3 seconds, urine output 0.5 mL/kg/hour or more, and improved mentation.

Limitations. Blood pressure is normal in early compensated shock. Lactate is raised by adrenaline, seizures, liver failure and metformin, and may be normal in early shock. Ultrasound findings depend on the operator.

Common measures. Oxygen to saturation 94 to 98%, two large bore cannulae (14 to 16 G) or intraosseous access, monitoring with arterial line, urinary catheter, control of source, warmth, and early senior and critical care review. Do not delay vasopressors where pressure is critically low.

Hypovolaemia and haemorrhage.

• Control bleeding: direct pressure, tourniquet, pelvic binder, surgery, endoscopy or interventional radiology. Activate massive transfusion with red cells, plasma and platelets in near equal proportions.
• Tranexamic acid 1 g IV over 10 minutes within 3 hours of injury or obstetric haemorrhage, then 1 g over 8 hours; monitor for thrombosis and seizures; reduce in kidney impairment.
• Permissive hypotension (systolic 80 to 90 mmHg) until bleeding is controlled in penetrating torso injury; avoid in head or spinal injury, where a systolic pressure over 110 mmHg is wanted.
• Calcium chloride 10% 10 mL IV after every 4 units of red cells. Fibrinogen under 1.5 g/L: fibrinogen concentrate 2 to 4 g IV or cryoprecipitate. Platelets over 50 x 10^9/L (over 100 x 10^9/L in head injury or ongoing bleeding). Warm all fluids.
• Reverse anticoagulants: warfarin with 4 factor prothrombin complex concentrate 25 to 50 units/kg IV and vitamin K 5 to 10 mg IV. Dabigatran with idarucizumab 5 g IV. Factor Xa inhibitors with prothrombin complex concentrate 50 units/kg IV or the specific antidote from the product label.
• Non-haemorrhagic loss: balanced crystalloid 500 mL IV over 15 minutes, then reassess; repeat only while the patient responds; monitor for pulmonary oedema.
• Children: isotonic crystalloid 10 to 20 mL/kg over 10 to 20 minutes with reassessment. In severe febrile illness without ventilatory support, use 10 mL/kg and reassess, since large boluses have been associated with harm. In severe acute malnutrition, 10 to 15 mL/kg over 1 hour then reassess; blood if no improvement.

Septic shock.

• Broad spectrum antimicrobials within 1 hour of recognition, for example ceftriaxone 2 g IV once daily (maximum 4 g daily) for community acquired infection.
• Piperacillin with tazobactam 4.5 g IV every 6 hours (maximum 18 g piperacillin daily; 4.5 g every 8 hours for CrCl 20 to 40 mL/min; 4.5 g every 12 hours for CrCl under 20 mL/min) for hospital acquired or intra-abdominal sepsis.
• Meropenem 1 g IV every 8 hours if resistant organisms are likely (1 g every 12 hours for CrCl 26 to 50 mL/min; 500 mg every 12 hours for CrCl 10 to 25 mL/min; 500 mg every 24 hours under 10 mL/min).
• Adjust to local resistance, monitor creatinine, and narrow when cultures return. Source control within 6 to 12 hours.
• Fluids: balanced crystalloid up to 30 mL/kg within 3 hours, in 500 mL boluses with reassessment after each (evidence for this volume is limited).
• Noradrenaline 0.05 to 0.5 micrograms/kg/min IV titrated to mean arterial pressure 65 mmHg or more; start early through a large peripheral vein if central access is delayed; monitor arterial pressure continuously, limb perfusion and extravasation; doses over 0.5 micrograms/kg/min need critical care direction.
• Vasopressin 0.03 units/min IV fixed rate added when noradrenaline reaches 0.25 to 0.5 micrograms/kg/min; maximum 0.04 units/min; monitor for digital ischaemia and hyponatraemia.
• Hydrocortisone 50 mg IV every 6 hours (or 200 mg over 24 hours) when noradrenaline is over 0.25 micrograms/kg/min for at least 4 hours; monitor glucose and sodium; stop when vasopressors are weaned.
• Adrenaline 0.05 to 0.5 micrograms/kg/min IV as the second vasopressor; dobutamine 2.5 to 20 micrograms/kg/min IV for persistent hypoperfusion with low cardiac output (monitor arrhythmia and pressure).

Cardiogenic shock.

• Avoid fluid unless clearly hypovolaemic (250 mL boluses with reassessment).
• Noradrenaline 0.05 to 0.5 micrograms/kg/min IV titrated to mean arterial pressure 65 mmHg or more for hypotension; dobutamine 2.5 to 20 micrograms/kg/min IV for low output with a mean pressure of 65 mmHg or more; monitor arrhythmia, lactate and urine output.
• Revascularisation: urgent angiography and percutaneous coronary intervention, or fibrinolysis if not available within the time window. Mechanical circulatory support by specialist teams.
• Unstable tachyarrhythmia: synchronised cardioversion at 120 to 150 J biphasic, escalating. Bradycardia: atropine 500 micrograms IV every 3 to 5 minutes (maximum 3 mg), then adrenaline infusion 2 to 10 micrograms/min or transcutaneous pacing.
• Furosemide 40 mg IV for pulmonary oedema only if blood pressure allows. Avoid nitrates and morphine when hypotensive.

Obstructive shock.

• Tension pneumothorax: immediate decompression and chest drain.
• Tamponade: pericardiocentesis under ultrasound direction or surgical drainage.
• Massive pulmonary embolism: alteplase 100 mg IV over 2 hours (peri-arrest: 0.6 mg/kg over 15 minutes, maximum 50 mg), then unfractionated heparin 80 units/kg IV bolus and 18 units/kg/hour; monitor aPTT, bleeding, and neurological status.
• Absolute contraindications include previous intracranial haemorrhage, ischaemic stroke in the last 3 months, intracranial tumour, recent major surgery, trauma or head injury, and active bleeding.

Other distributive shock.

• Anaphylaxis: adrenaline 0.5 mg IM (repeated every 5 minutes), crystalloid 500 to 1000 mL IV, adrenaline infusion 0.05 to 0.5 micrograms/kg/min if refractory; in patients on beta blockers add glucagon 1 to 5 mg IV over 5 minutes then 5 to 15 micrograms/min.
• Neurogenic shock: exclude haemorrhage, restore volume, noradrenaline to mean pressure 85 to 90 mmHg for up to 5 to 7 days after cord injury (evidence is limited), atropine 500 micrograms IV for bradycardia.
• Adrenal crisis: hydrocortisone 100 mg IV immediately, then 50 mg IV every 6 hours (or 200 mg over 24 hours); isotonic saline 1 L over the first hour; monitor sodium, potassium and glucose.
• Toxic causes: poison centre direction for beta blocker and calcium channel blocker overdose.

Blood transfusion outside haemorrhage. Transfuse red cells at haemoglobin under 70 g/L (target 70 to 90 g/L).

Monitoring. Continuous ECG, saturation and arterial pressure, hourly urine output, lactate every 2 hours until falling, glucose, electrolytes and blood gas every 4 to 6 hours, repeat bedside ultrasound after interventions, and daily creatinine.

Referral and escalation. Critical care for all shock needing vasopressors or persisting hypotension. Surgery or interventional radiology for haemorrhage. Cardiology for cardiogenic shock. Obstetrics for obstetric causes. Infectious diseases for refractory sepsis. Palliative care when treatment goals are limited.

Admission criteria. All patients with shock are admitted, to critical care when vasopressors, ventilation or organ support are needed. After anaphylaxis, observe for at least 6 to 12 hours (longer after severe reactions).

Discharge and safety netting. Discharge only after resolution, a clear cause and a safe follow up plan. After anaphylaxis, give two adrenaline auto-injectors with training, a written action plan and allergy referral. Patients are told to return for dizziness, fainting, black stools, bleeding, fever with rigors, breathlessness or reduced urine.