Hemorrhagic Shock

Aka: Hemorrhagic Shock, Hemorrhage Evaluation, Hemorrhage, Hemorrhage Management, Hemorrhage Control, Exsanguination, Massive Hemorrhage, Large Volume Hemorrhage, Traumatic Coagulopathy

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II. Epidemiology

  1. Hemorrhage is the leading cause of Trauma related death (typically within hours of presentation)
    1. Accounts for 40% of all Trauma deaths (esp. multi-system Trauma)
    2. Two thirds of Hemorrhage deaths occur in first 6 hours

III. Pathophysiology

  1. Significant Blood Volume loss causes impaired Oxygen Delivery
  2. With Hypoxemia, cellular metabolism relies on anaerobic Glycolysis; Lactic Acid is produced with Metabolic Acidosis
  3. Tissue swelling and cell death result from proinflammatory mediator release, vascular endothelial cell injury
  4. Compensatory endogenous Catecholamines result in Tachycardia, increased Cardiac Output, and Vasoconstriction
  5. Compensation ultimately fails leading to cardiovascular collapse

IV. Precautions

  1. Recognize and definitively manage signs of shock early (see above)
    1. Most cases are Hemorrhagic Shock in the Trauma patient
    2. Paramount to locate and stop the source of bleeding (and replace losses)
  2. Comprehensive examination of the patient may be best evaluation tool in Hemorrhagic Shock
    1. Check distal extremity warmth and pulses
    2. Continue to assess occult bleeding sites (see causes of below)
  3. Hemorrhage Classification is a documentation and coding tool (not a Hemorrhage Management tool)
    1. Degree of Hemorrhage is often difficult to quantify or grade until retrospect
    2. Do not delay definitive management before patient meets a precise classification
  4. Vital Signs are a poor predictor of degree of Hemorrhage
    1. Shock Index (by contrast with Vital Signs) does correlate with degree of Hemorrhage
      1. Mutschler (2013) Crit Care 17(4): R172 [PubMed]
    2. Blood Pressure is unreliable for reassurance in a Trauma patient
      1. Frequently repeat Blood Pressure readings during Resuscitation
      2. Blood Pressure is the last hemodynamic marker to fall
        1. Vasoconstriction and Tachycardia are earlier compensation
      3. Hypotension in Trauma suggests Class III Hemorrhage or worse (>30% blood loss)
      4. Narrow Pulse Pressure is a better marker in shock (Vasoconstriction increased DBP)
    3. Narrow Pulse Pressure
      1. May predict circulatory collapse in Trauma with Hemorrhage
      2. Prehospital Narrow Pulse Pressure predicts severe Trauma and need for aggressive Resuscitation
      3. Interpret in combination with Trauma Evaluation and other markers (Hypotension, Shock Index)
      4. Schellenberg (2021) J Surg Res 268:284-90 [PubMed]
    4. Heart Rate may also be unreliable for reassurance in a Trauma patient
      1. See Delayed Tachycardia
      2. Patient may have lost ability to mount a tachycardic response (e.g. Beta Blocker use)
      3. Athletic fitness
      4. Autonomic Dysfunction may limit compensatory Tachycardia reflex
      5. Abdominal Hemorrhage may cause vagal response (Bezold-Jarisch)
    5. References
      1. Guly (2010) Resuscitation 81(9): 1142-7 +PMID: 20619954 [PubMed]

V. Risk Factors: Massive Hemorrhage (requiring Massive Transfusion)

  1. Assessment of Blood Consumption Score (ABC Hemorrhage Score) >2
  2. Positive Focused Assessment Sonography for Trauma (FAST)
  3. Hypotension with Blood Pressure 90 mmHg or less
  4. Tachycardia with Heart Rate 120 bpm or higher
  5. Penetrating Injury
  6. Elevated serum Lactic Acid
  7. Low End-Tidal CO2
    1. End-Tidal CO2 may also be moderately reduced in Hyperventilation
    2. Very low End-Tidal CO2 (<15) suggests poor perfusion
    3. Stone (2017) Injury 48(1): 51-7 [PubMed]

VI. Causes

  1. Trauma (most common)
    1. Blunt Trauma
    2. Penetrating Trauma
  2. Atraumatic Hemorrhage
    1. Abdominal Aortic Aneurysm rupture
    2. Pulmonary Hemorrhage (e.g. Lung Cancer, Bronchiectasis, Tuberculosis)
    3. Upper Gastrointestinal Bleeding (e.g. Esophageal Varices, Peptic Ulcer Disease)
    4. Lower Gastrointestinal Bleeding (e.g. Diverticular Hemorrhage, Angiodysplasia, Aortoenteric Fistula)
    5. Uterine Bleeding in Pregnancy (e.g. Ectopic Pregnancy, Placental Abruption, Placenta Previa)

VII. Causes: Hemorrhage Compartments (Mnemonic: "Blood on the floor, and 4 more")

  1. External sites and scalp
  2. Occult Traumatic Hemorrhage sites
    1. Chest
    2. Pelvis
    3. Abdomen (and Retroperitoneum)
    4. Thigh and long bones

VIII. History: Bleeding Source

  1. Trauma
    1. Chest Trauma
    2. Abdominal Trauma
    3. Penetrating Trauma (Gunshot Wound, Stab Wound)
    4. Pelvic Fracture
    5. Femur Fracture
    6. Obstetrical Trauma
    7. Motor Vehicle Accident
    8. Scalp Laceration
  2. Non-Traumatic Sources
    1. Epistaxis
    2. Hemoptysis
    3. Hematemesis
    4. Melana, Maroon Stool or Hematochezia
    5. Vaginal Bleeding

IX. Symptoms

  1. Generalized weakness
  2. Syncope
  3. Altered Mental Status or Confusion
  4. Lethargy

X. Exam

  1. See Shock
  2. See Trauma Evaluation
  3. Complete Trauma Evaluation
    1. Sources of bleeding (chest, Abdomen, Pelvis, retroperineum, long bones)
    2. Completely expose the patient (Mnemonic: Armpits, Back and Breasts, Butt cheeks and Sac)
    3. Evaluate for Scalp Lacerations, Epistaxis (including posterior bleeding)
    4. Evaluate for flank Ecchymosis, Scrotal Swelling, pulsatile abdominal mass, unstable Pelvis
  4. Reassess frequently
    1. Young healthy patients may with little warning, precipitously decompensate into cardiovascular collapse
  5. Tachycardia
    1. See Heart Rate for normal ranges for age
    2. Early warning sign of shock in most cases
    3. Cold and tachycardic is shock until proven otherwise
    4. However Heart Rate can be misleadingly normal in cases of Delayed Tachycardia (see above)
  6. Urine Output
    1. Normal Urine Output is >0.5 ml/kg/h in adults (>1 ml/kg/h in children, >2 ml/kg/h in infants)
  7. Arterial Injury Findings
    1. Hard Signs
      1. Pulsatile Bleeding
      2. Absent distal pulses
      3. Expanding Hematoma
      4. Arterial Bruit
      5. Arterial thrill
    2. Soft Signs
      1. Initial pulsatile bleeding at prehospital evaluation
        1. Resolution of pulsatile bleeding does not exclude arterial bleeding
        2. Arterial spasm after injury may obscure hard arterial injury findings
      2. Non-expanding Hematoma
      3. Neurologic deficits
      4. Close proximity of wound to major vessels

XI. Labs

  1. See Shock
  2. Complete Blood Count with Platelet Count
    1. First Hemoglobin is unreliable within first 8 hours of Hemorrhage (provides baseline for trending)
  3. Venous Blood Gas
    1. Degree of Metabolic Acidosis may help grade shock severity
  4. Coagulation Pathway Labs (INR, aPTT)
  5. Type and Crossmatch for Blood
  6. Ionized Calcium
    1. Hypocalcemia may decrease hemodynamics and increase Coagulopathy
  7. Pregnancy Test (urine HCG or serum HCG)
  8. Other tests
    1. Thromboelastography (TEG/ROTEM)
      1. Measures viscoelastic blood properties which may help guide transfusions

XII. Diagnostics

  1. Electrocardiogram (EKG)
    1. Cardiac Contusion
    2. Demand Myocardial Ischemia
  2. Other measures
    1. Diagnostic Peritoneal Lavage (DPL)
      1. Largely replaced by Bedside Ultrasound in U.S. (FAST Scan)

XIII. Imaging

  1. Focused Assessment with Sonography for Trauma (eFAST)
    1. Free fluid within Abdomen or Pelvis
    2. Pericardial Effusion or Cardiac Tamponade
    3. Hemothorax
    4. Pneumothorax
  2. Rapid Ultrasound in Shock (RUSH Exam, "Pump, Tank and Pipes")
    1. Pump Evaluation (Cardiac Systolic Function)
    2. Tank Evaluation (Vascular volume status)
      1. See Inferior Vena Cava Ultrasound for Volume Status
    3. Pipes Evaluation (Large vessel integrity)
      1. See Abdominal Aorta Ultrasound
  3. Chest XRay (portable)
    1. Hemopneumothorax
  4. Pelvis XRay (portable)
    1. Pelvic Fracture
  5. Femur or Hip XRay (or other Long Bone XRay)
    1. Obtain as indicated
  6. CT Chest AbdomenPelvis with IV contrast (if stable enough)
    1. Consider with CT Angiography for vascular injury
    2. May identify bleeding source and targets for surgical or endovascular management
  7. CT Spine
    1. Consider if Neurogenic Shock suspected
  8. CT Angiography
    1. Consider in suspected extremity arterial injury

XIV. Differential Diagnosis

  1. Cardiogenic Shock
    1. Tension Pneumothorax
    2. Cardiac Tamponade
  2. Neurogenic Shock secondary to Spinal Cord Injury
    1. Neurogenic Shock does not occur in isolated intracranial injury
  3. Other non-Traumatic shock
    1. See Shock for Undifferentiated Shock approach
    2. Hypovolemic Shock (e.g. Dehydration)
    3. Septic Shock

XV. Evaluation

  1. Hemorrhage Classification (Class I-IV) is unreliable
    1. See Hemorrhage Classification
  2. Shock Index
    1. Shock Index = (Heart Rate) / (Systolic Blood Pressure)
    2. Shock Index >0.9 predicts need for increased transfusion requirements and early mortality risk
  3. Assessment of Blood Consumption Score (ABC Hemorrhage Score)
    1. Four point score (Penetrating Trauma, SBP<90 mmHg, Heart Rate>120, positive FAST Exam)
    2. ABC Hemorrhage Score 3 or 4 predicts Massive Transfusion Protocol
  4. Trauma Associated Severe Hemorrhage (TASH)
    1. Based on SBP, pulse, gender, Hemoglobin, FAST Exam, Base Excess and pelvic/Femur Fracture
    2. Yucel (2006) J Trauma 60(6):1228-36 +PMID:16766965 [PubMed]
  5. McLaughlin Score
    1. Based on pulse >105 bpm, sbP <110 mmHg, pH<7.25, Hematocrit <32%

XVI. Management: Hemorrhage Control

  1. Emergent Trauma surgery Consultation
    1. Poor response to Fluid Replacement or blood replacement indicates surgical management (or via angiography)
  2. Stop external bleeding immediately
    1. Apply direct manual pressure to external bleeding sites
      1. Focal, isolated manual pressure is the most important single measure for compressible Hemorrhage
      2. No amount of gauze can replace the directed manual pressure of a finger or hand over a external Hemorrhage site
      3. When controlled, pressure dressing may replace manual pressure (see below)
        1. Observe closely for continued bleeding after manual pressure is replaced with pressure dressing
        2. Reapply direct, focal manual pressure if bleeding recurrs despite pressure dressing
    2. Pressure dressing may replace manual pressure if it adequately controls bleeding
      1. Israeli Bandage is elastic wrap with gauze impregnated with clotting agent
      2. Sanitary napkins or pads may also be used with overlying direct pressure at wound site
      3. Small ball of gauze directly overlying Hemorrhage applied under pressure dressing
      4. Maintain direct pressure over bandage as needed to control bleeding
    3. Rapidly bleeding sites (e.g. Scalp Wounds) may be temporized with staples or Suture
    4. Consider occult Hemorrhage sources (see above)
    5. Bleeding refractory to manual pressure
      1. Notify Trauma surgery of emergent surgical intervention for rapid, uncontrolled bleeding
      2. Tourniquet (Pneumatic Tourniquet or Windlass Tourniquet)
        1. Indicated for rapid extremity bleeding not controlled with direct manual pressure
        2. Temporizing only until surgical intervention within 1-2 hours
        3. Permanent ischemic injury occurs if Tourniquet left in place >4-5 hours
        4. Ineffective in junctional sites (e.g. axilla, groin, adductor canal)
        5. Obviously unusable at neck and trunk
      3. Topical Hemostatic Agent (Chitosan Dressing, Zeolite Mineral Dressing, Kaolin Mineral Dressing)
        1. Indicated for rapid bleeding in sites where Tourniquets cannot be used (see above)
        2. Not widely available outside of military and large Trauma Centers as of 2013
        3. Risk of wound contamination with hemostatic agent
      4. Foley Catheter
        1. Inserted into a bleeding wound site
        2. Balloon inflated with Normal Saline
        3. May be effective at bleeding sites where Tourniquets may not be used
          1. Consider at junctional sites (e.g. groin, neck)
      5. XStat (RevMedX, limited efficacy and safety data)
        1. FDA approved for gun shot wounds in 2014
        2. Syringe filled with small, compressed cellulose sponges
        3. Syringe applicator inserted at exsanguinating gun shot wound
  3. Non-compressible Massive Hemorrhage
    1. Emergency Thoracotomy (in Cardiac Arrest)
      1. Massive chest Hemorrhage with CPR <15 min in Penetrating Trauma, CPR <10 min in blunt Trauma
    2. Resuscitative Endovascular Balloon Occlusion of the Aorta or REBOA (Peri-Arrest with systolic Blood Pressure <70 mmHg)
      1. Massive intraabdominal or pelvic Hemorrhage
    3. Pelvic Binder
      1. Unstable Pelvic Fracture with separation (e.g. open book or vertical sheer Pelvic Fracture)
      2. Apply binder empirically pre-imaging if Pelvic Fracture suspected in the Peri-Arrest, Hemorrhagic Shock patient
  4. Additional stabilization measures while temporizing until definitive surgical management
    1. Tranexamic Acid (Cyklokapron)
      1. Blocks plasmin formation (preventing Fibrinolysis)
      2. TXA 1 g IV load over 10 minutes, then 1 g IV over 8 hours (or a single 2 g bolus)
      3. Indicated in first 3 hours following onset of Hemorrhage
        1. Often given empirically during Ambulance transport or on ED arrival
        2. Also consider when other measures fail or surgical intervention delayed
        3. Associated with small survival benefit
          1. Survival benefit decreases 10% with every 15 minute delay
      4. References
        1. Roberts (2011) Lancet 377(9771):1096-101 [PubMed]
        2. Guyette (2020) JAMA Surg 156(1): 11-20 [PubMed]
    2. Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA)
      1. Percutaneous balloon delivered via groin catheter and inflated in aorta above level of Hemorrhage
      2. Indicated in severe bleeding Pelvic Fractures who have not had Cardiac Arrest
        1. Used as an immediate temporizing measures, pending emergent definitive surgical management

XVII. Management: Volume Replacement

  1. Two large bore IVs (14 or 16 gauge if able, otherwise 18 gauge)
    1. Shorter tubing and larger bore provides faster IV rate
    2. Intraosseous Access if peripheral IV not immediately attainable
    3. Obtain Central Venous Line as available
      1. Large catheter introducer (8F or 9F) is preferred over multilumen
  2. Intravenous Fluids and Packed Red Blood Cells
    1. See Fluid Resucitation in Trauma
    2. Judicious use of crystalloid in Class II Hemorrhage or higher
      1. React to early signs and symptoms of acute blood loss with Hemorrhage Control and blood replacement
      2. ATLS and textbooks still describe the use of NS or LR for 1-2 Liter bolus
      3. However, new practices suggest limiting crystalloid in favor of Blood Products (permissive Hypotension)
        1. Goal systolic Blood Pressure 80-100 mmHg
        2. IV fluids may artificially increase local pressure at non-compressible clot sites causing rebleeding
        3. IV fluids may dilute Coagulation Factors and Platelets (worsening Coagulopathy and increasing bleeding)
        4. Bickwell (1994) N Engl J Med 331(17): 1105-9 +PMID:7935634 [PubMed]
      4. Restrictive Resuscitation (permissive Hypotension) contraindications
        1. Prolonged transport time
        2. Transfer to Trauma Center
        3. Traumatic Brain Injury
        4. Hypotension, negative FAST Exam and normal Hemoglobin
      5. References
        1. Spanger and Inaba in Herbert (2015) EM:RAP 15(3):6-8
    3. Hemorrhage should be replaced with Blood Products
      1. Indications
        1. Mean arterial pressure 65 (or systolic Blood Pressure 70-90 mmHg)
          1. May need to target higher MAP (e.g. 80 mmHg) in Head Injury
        2. Poor response to IV fluids
          1. Persistent Tachycardia, Hypotension or Tachypnea
          2. Urine Output <50 ml/hour (<1ml/kg/hour)
      2. Start with 2-4 units (prepare at least 4 units pRBC for more severe Hemorrhage)
        1. Type specific blood can be ready within 30-40 minutes
        2. In the crashing patient give unmatched type-specific blood, Low titer O or O negative blood
          1. Men may be given O+ Blood
          2. Give RhoGAM prior to discharge if found to be Rh Negative (prevents future reactions)
        3. After 2 units of blood (e.g. uncross-matched), reassess
          1. If stabilized, then no need at that time to activate Massive Transfusion Protocol
          2. If not stabilized, and 3 or more units needed at start, activate Massive Hemorrhage Protocol
            1. See Massive Transfusion Protocol
            2. Balance pRBC transfusion with Platelets and plasma (1:1:1 or 2:1:1)
      3. Massive Hemorrhage with administration of more than 4 units requires matching Blood Products
      4. Consider Autotransfusion (e.g. Hemovac or Cell Saver)
        1. Indicated for massive bleeding if blood can be drained and not contaminated)
      5. Use blood warmer when available
        1. Prevents Hypothermia with transfusion

XVIII. Management: Traumatic Coagulopathy Correction

  1. Mechanism
    1. Acute Traumatic Coagulopathy is a major cause of Hemorrhage related deaths
    2. Hemostasis requires Platelet adherence to damaged vessel endothelium, then stabilized clot with Fibrin
    3. Traumatic Coagulopathy results from multiple factors
      1. Tissue injury, inflammation and hypoperfusion (shock) are key initial factors in Coagulopathy
      2. Progressive shock and hemodilution with Intravenous Fluid worsens Coagulopathy
      3. Hypothermia (<34 C) and acidosis also worsen Coagulopathy
  2. Coagulopathy correction for Massive Blood Transfusion (>10 pRBC units within 24 hours)
    1. See Massive Blood Transfusion for protocol
    2. Massive Blood Transfusion is typically accompanied by Platelet and Plasma Transfusion
    3. Replace 1 unit of plasma for every 1-2 units of Packed Red Blood Cells
    4. Replace 1 unit of apheresis Platelets (6 pack equivalent) for every 8 units of Packed Red Blood Cells
    5. Consider Fibrinogen replacement to 1.5 to 2.0 g/L
    6. Prothrombin Complex Concentrate (PCC) 1-2 doses
      1. Do not use beyond 6-7 hours from bleeding onset (due to increased clotting risk)
    7. Holcomb (2012) Arch Surg 15:1-10 [PubMed]
  3. Monitoring of Traumatic Coagulopathy
    1. Viscoelastic hemostatic assays (e.g. TEG) have largely replaced INR and PTT for monitoring
    2. See Thromboelastography (TEG)
  4. Coagulopathy correction for underlying disorder or medication
    1. Reverse Anticoagulants
      1. See Emergent Reversal of Anticoagulation
      2. Platelet Transfusion for antiplatelet agents (e.g. Aspirin, Clopidogrel)
      3. Protamine for Heparin
      4. Vitamin K, FFP and PCC4 for Warfarin
    2. Specific management for Congenital Blood Coagulation Disorders
      1. Von Willebrand Disease
      2. Hemophilia A
      3. Hemophilia B (Factor IX Deficiency)
    3. Specific management for Acquired Blood Coagulation Disorders
      1. Cirrhosis
        1. Consider Vitamin K supplementation
        2. Decreased Anticoagulant and coagulant factors
          1. Therefore, not typically coagulopathic despite abnormal PT/INR and PTT
      2. Disseminated Intravascular Coagulation (DIC)
        1. Platelet Transfusion to Platelet Count >50,000/mm3
        2. FFP transfusion until PTT and PT/INR are each <1.5x normal
        3. Do not administer Tranexamic Acid (or other antifibrinolytic)
      3. Thrombotic ThrombocytopeniaPurpura
        1. Plasmaphoresis
      4. Drug induced Thrombocytopenia
        1. Withdraw offending medication
      5. End-stage renal disease
        1. Results in Anemia and Thrombocytopenia
        2. Hemodialysis
        3. Erythropoietin
        4. Cryoprecipitate
        5. Conjugated Estrogen
        6. Desmopressin
        7. Tranexamic Acid

XIX. Management: Other measures and disposition

  1. Immediately stabilize and transfer to Trauma Center or to proper hospital service (e.g. Trauma service)
    1. Limit unnecessary studies that delay transfer
    2. Goal for disposition and transfer is 20 minutes
    3. Involve surgical consultants, intervention radiologists early
  2. Monitoring
    1. Vital Signs (Heart Rate, Blood Pressure, Pulse Pressure)
    2. Mental status
    3. Urine Output via urine catheter (unless suspected Urethral Trauma)
    4. Lactic Acid and Base Excess
    5. Continually reevaluate for concurrent injuries (e.g. Tension Pneumothorax, Cardiac Tamponade)
  3. General measures
    1. ABC Management
    2. Prevent Hypothermia
      1. Remove wet clothing and keep patient covered
      2. Small decreases in Body Temperature below 34 C (93.2 F) increase transfusion needs
      3. Warm Blood Products during transfusion
      4. Consider use of forced air warmer (e.g. Bair Hugger)
    3. Continue to limit further bleeding
    4. Pelvic Binder (or bound bedsheet) for suspected unstable Pelvic Fracture
    5. Pregnant patients in left lateral decubitus position (see Trauma in Pregnancy)
    6. Replace Blood Products and prevent Coagulopathy (see above)
    7. Reverse hypoperfusion in refractory Hypotension
      1. May consider Vasopressors in refractory Hypotension despite continued Massive Transfusion
        1. Limit Vasopressors to adjunctive role to Hemorrhage Control, surgery, transfusion
        2. Vasopressor use is controversial in the U.S. for Hemorrhagic Shock
      2. Vasopressors may be useful with warm, dry extremities (without significant Vasoconstriction)
        1. Vasopressin may reduce amount of Blood Products needed
        2. Norepinephrine may also be considered
      3. References
        1. Swaminathan and Weingart (2024) Pressors in Hemorrhagic Shock, EM:Rap, 10/14/2024, accessed 10/31/2024

XX. Management: Damage Control Surgery Protocol

  1. Stage 0: Ground Zero (pre-hospital and emergency department)
    1. Rapid transfer to Trauma Center and operating room
    2. Stopping Hemorrhage is the primary priority
    3. Prevent Hypothermia
    4. Venous Blood Gas
  2. Stage 1: Initial Operation to control life threatening injuries and bleeding
    1. Control Hemorrhage
    2. Control contamination
    3. Judicious abdominal packing
    4. Rapid temporary abdominal closure
    5. Prevent Hypothermia
  3. Stage 2: ICU Resuscitation
    1. Resuscitation and monitor perfusion
    2. Correct acidosis and Coagulopathy
    3. Rewarm the patient
    4. Optimize oxygenation and ventilation
    5. Measure intraabdominal pressure
  4. Stage 3: Return for Definitive Repair in Operating Room in 12-24 hours
    1. Early reoperation for rebleeding
    2. Definitive surgical repair when patient physiologically stable
    3. Abdominal closure or staged closure
  5. References
    1. Rotondo (1993) J Trauma 35(3): 375-82 [PubMed]
    2. Johnson (2001) J Trauma 51(2): 261-71 [PubMed]

XXI. Complications: Uncontrolled Hemorrhage

  1. Mortality
    1. Leading cause of death in both military and civilian Trauma
  2. Immediate Complications: Lethal Triad
    1. Hypothermia
    2. Metabolic Acidosis
    3. Coagulopathy
  3. Secondary Complications
    1. Sepsis
    2. Multi-system organ failure

XXII. Complications: Massive Blood Transfusion

  1. Hypothermia
  2. Coagulopathy
  3. Metabolic Acidosis
  4. Electrolyte abnormalities
    1. Hypocalcemia
    2. Hyperkalemia

XXIII. References

  1. (2012) ATLS Manual, 9th ed, American College of Surgeons
  2. Freeman and Bourland (2021) Crit Dec Emerg Med 35(12): 3-11
  3. Kim, Tran, Lopez (2018) Crit Dec Emerg Med 32(12): 19-25
  4. Herbert and Alson in Herbert (2016) EM:Rap 16(2): 18
  5. Herbert (2012) EM:RAPC3 2(1): 1-2
  6. Petrosoniak and Swaminathan (2022) EM:Rap 22(11): 5-7
  7. Ringhauser (2019) Crit Dec Emerg Med 33(6): 19-25
  8. Shinkle and Ponce (2016) Crit Dec Emerg Med 30(8): 13
  9. Swaminathan and Shoenberger (2021) EM:Rap 21(8): 1
  10. Swaminathan and van de Leuv (2013) Crit Dec in Emerg Med 27(8): 11-17
  11. Swadron and Inaba in Herbert (2014) EM:Rap 14(12): 5
  12. Weingart and Swaminathan in Herbert (2021) EM:Rap 21(3): 5-8

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