Hemorrhagic Shock

Hemorrhagic shock is circulatory failure from acute blood loss, with loss of oxygen-carrying capacity and volume. The cause is trauma in most cases, and others are gastrointestinal bleeding, ruptured aortic aneurysm, obstetric hemorrhage, ruptured ectopic pregnancy and surgery. It is the leading preventable cause of death after injury.

Severity classes by estimated blood volume lost (adult blood volume about 70 mL/kg):

• Class I: under 15% (under 750 mL), minimal signs
• Class II: 15 to 30% (750 to 1500 mL), tachycardia, narrowed pulse pressure, normal pressure
• Class III: 30 to 40% (1500 to 2000 mL), hypotension, heart rate over 120 beats a minute, confusion, oliguria
• Class IV: over 40% (over 2000 mL), imminent arrest

Mechanisms: hypoperfusion produces lactic acidosis, and the lethal triad of hypothermia, acidosis and coagulopathy sets in.

Trauma-induced coagulopathy begins early, from endothelial injury, fibrinolysis and protein C activation, before any fluid is given. Large volumes of crystalloid worsen dilution, acidosis and bleeding.

Time to bleeding control drives survival, and each 10 minutes of delay in a hypotensive trauma patient raises mortality.

Complications: acute kidney injury, acute respiratory distress syndrome, abdominal compartment syndrome, infection and multiorgan failure.

• Pallor, cold clammy skin, thirst, anxiety and agitation, then drowsiness
• Tachycardia (but beta-blocked patients, athletes and elderly may not mount it), weak pulse and delayed capillary refill
• Hypotension as a late sign
• External bleeding, distended or tender abdomen, unstable pelvis, long bone deformity, and signs of hematemesis, melena or vaginal bleeding
• Red flags: systolic pressure under 90 mmHg, heart rate over 120 beats a minute, shock index (heart rate divided by systolic pressure) over 1.0, falling consciousness and ongoing bleeding

1. Primary survey by airway, breathing, circulation with external hemorrhage control.
2. Extended focused ultrasound for trauma: free fluid in the abdomen, pericardium or chest. Chest and pelvis radiographs.
3. Laboratory tests drawn with initial access: hemoglobin (an unreliable early marker), lactate, base deficit, blood group and crossmatch, coagulation studies, fibrinogen, platelet count, ionized calcium, blood gases, and viscoelastic testing where available.
4. CT with contrast once stable enough, to find the bleeding site, and angiography for suspected arterial bleeding.
5. Source-specific tests: urgent endoscopy for upper gastrointestinal bleeding, and a pregnancy test in women of reproductive age.

Differentials: obstructive shock (tamponade, tension pneumothorax), neurogenic shock, cardiogenic shock and other forms of hypovolemia.

1. Control bleeding first: direct pressure, tourniquet for limb hemorrhage, pelvic binder, wound packing and hemostatic dressings, and rapid surgical or interventional control (damage control laparotomy, angioembolization, balloon occlusion of the aorta). Do not delay transfer to definitive care.
2. Access and warming: two large-bore IV lines or intraosseous access, warmed products and fluids, and active warming to keep temperature above 36 degrees Celsius.
3. Limit crystalloid: no more than 1 L initially.
4. Permissive hypotension: target systolic pressure 80 to 90 mmHg (mean 50 to 60 mmHg) until bleeding is controlled in penetrating torso trauma. In brain injury keep systolic pressure at 110 mmHg or higher and mean arterial pressure at 80 mmHg or higher. Avoid permissive hypotension in the elderly with hypertension, in spinal injury and in pregnancy.
5. Balanced blood products: red cells, plasma and platelets in a 1:1:1 ratio (or low-titer whole blood) through a massive transfusion protocol activated for ongoing bleeding (for example, 4 units in an hour or a high shock index).
6. Tranexamic acid: 1 g IV over 10 minutes within 3 hours of injury, then 1 g IV over 8 hours (children 15 mg/kg bolus, maximum 1 g, then 2 mg/kg/h for 8 hours). Reduce in severe renal impairment.
7. Calcium chloride 1 g IV (or calcium gluconate 3 g) after each 4 units of blood, maintaining ionized calcium over 1.1 mmol/L.
8. Fibrinogen replacement: cryoprecipitate 10 units or fibrinogen concentrate 3 to 4 g IV when fibrinogen is under 1.5 g/L.
9. Anticoagulant reversal: four-factor prothrombin complex concentrate 25 to 50 units/kg IV with phytomenadione 5 to 10 mg IV for warfarin, and idarucizumab 5 g IV for dabigatran.
10. Vasopressors only as a bridge when hypotension persists during hemorrhage control: norepinephrine 0.05 to 0.5 micrograms/kg/min IV, and vasopressin 0.04 units/min IV.
11. Obstetric hemorrhage: uterine massage, oxytocin 10 units IV, tranexamic acid, and surgical measures.
12. Upper gastrointestinal bleeding: omeprazole 80 mg IV bolus, then 8 mg/h, urgent endoscopy within 24 hours. Variceal bleeding: terlipressin 2 mg IV every 4 hours and ceftriaxone 1 g IV daily.

Transfusion triggers once stable: hemoglobin under 70 g/L (under 80 g/L with cardiac disease). Give enoxaparin 40 mg SC daily from 24 to 48 hours after bleeding is controlled. Counsel on recovery, and on iron replacement (ferric carboxymaltose 1000 mg IV once, or ferrous sulfate 200 mg orally daily).