2. Hypovolemic Shock

Quick Recap

Cardiovascular System, Protocol 3/12. Covers both hemorrhagic and non-hemorrhagic hypovolemic shock, with emphasis on damage control resuscitation for massive hemorrhage.

1. Definition

Shock resulting from inadequate intravascular volume (preload) to maintain adequate cardiac output and tissue perfusion. Hemorrhagic (traumatic or non-traumatic bleeding) or non-hemorrhagic (GI losses, burns, third-spacing, severe dehydration, diabetes insipidus, heat-related losses).

2. Pathophysiology

Reduced circulating volume -> reduced venous return/preload -> reduced stroke volume -> compensatory tachycardia and vasoconstriction maintain BP initially (compensated shock) -> as loss continues, compensatory mechanisms fail -> hypotension and end-organ hypoperfusion (decompensated shock). In hemorrhage specifically, the "lethal triad" of acidosis, hypothermia, and coagulopathy develops from ongoing blood/volume loss and is self-perpetuating — acidosis and hypothermia both impair clotting factor function, worsening coagulopathy, which worsens bleeding, which worsens all three. This triad is the central physiologic target of damage control resuscitation.

3. Immediate Stabilization (ABCDE)

Airway/Breathing: secure per standard indications; note that positive pressure ventilation can further reduce preload in an already volume-depleted patient — be prepared for hemodynamic deterioration at induction/intubation.

Circulation — the core of management:

• Hypotension in a trauma patient is assumed due to significant hemorrhage (>30% blood loss) until proven otherwise, once tension pneumothorax is excluded
• Access: at least two large-bore (14-16G or larger) peripheral IVs, or an 8.5F central line; use a mechanical rapid transfusion device and fluid warmer
• Source control is definitive treatment, not fluids — pressure dressing, tourniquet, surgical exploration, or angioembolization depending on source; do not let resuscitation delay source control
• eFAST (extended focused assessment with sonography in trauma) and chest/pelvic radiographs in all trauma patients to localize the "five places blood hides": chest, abdomen, pelvis, long bones, and the floor (external hemorrhage)
• Tranexamic acid (TXA): 1g bolus followed by 1g over 8 hours, within 3 hours of trauma, for all patients with significant hemorrhage
• Blood product resuscitation: for ongoing hemorrhage, transfuse group O blood immediately (O-positive for men/non-childbearing-age women; O-negative for women of childbearing age) pending type-specific blood after the first ~4 units
• Damage control resuscitation principles:
• Minimize crystalloid — large-volume crystalloid causes hemodilution coagulopathy and is associated with worse outcomes (respiratory failure, compartment syndrome)
• Higher ratios of plasma and platelets to RBCs (approaching 1:1:1 PRBC:FFP:platelets) rather than RBC-predominant resuscitation — PROPPR trial informs this ratio-based approach
• Prefer plasma early — has been shown to help repair the damaged endothelial glycocalyx, a mechanistic rationale beyond simple factor replacement
• Avoid colloids in hemorrhagic shock
• Actively rewarm (warmed fluids, blankets, radiant lamps, warmed humidified air) — hypothermia directly worsens coagulopathy and cardiac function
• Correct ionized hypocalcemia/hypomagnesemia — citrate in transfused blood binds calcium and magnesium; give calcium chloride/magnesium chloride as needed, especially during massive transfusion
• Early massive transfusion protocol (MTP) activation: trigger if patient may need >3 units RBC within 1 hour — early activation improves outcomes; use scores like TASH or ABC score to identify likely MTP candidates early rather than reactively
• Permissive hypotension (targeting a lower-than-normal BP, e.g., SBP ~80-90 mmHg or MAP ~50-65, in patients without traumatic brain injury) until definitive hemorrhage control is achieved — supported by systematic review/meta-analysis evidence over conventional full-volume resuscitation targets, though normalization is still the goal once bleeding is controlled
• REBOA (resuscitative endovascular balloon occlusion of the aorta): temporizing measure for exsanguinating torso hemorrhage, selectively occluding the aorta to preferentially perfuse brain/heart until definitive hemostasis achieved
• Reversal of anticoagulation if applicable: prothrombin complex concentrate, FFP, andexanet alfa (factor Xa inhibitors), or idarucizumab (dabigatran)

Disability: altered mentation is both a sign of severity (Class 3-4 hemorrhage) and a marker to trend with resuscitation response.

Exposure: actively search for all five bleeding locations (Section above); look for external sources amenable to direct pressure/tourniquet.

Checklist:

4. Focused History

Mechanism/timing of bleeding or fluid loss, anticoagulant/antiplatelet use, known bleeding diathesis, GI bleed history, burn extent/timing, diarrhea/vomiting duration and volume, heat exposure, diabetes insipidus history, comorbidities affecting transfusion threshold tolerance (cardiovascular disease).

5. Examination + POCUS

Class of hemorrhagic shock by vital signs/mental status (see Severity table below); signs of external bleeding, abdominal distension/tenderness, pelvic instability, long bone deformity.

POCUS/eFAST: free fluid in abdomen/pelvis (Morison's pouch, splenorenal, pelvis), pericardial effusion (exclude tamponade), pneumothorax/hemothorax views, IVC assessment for volume status and fluid responsiveness trend.

6. Syndrome Identification

Confirm hypovolemic (low preload, compensatory tachycardia/vasoconstriction) rather than cardiogenic, obstructive, or distributive shock via POCUS — critical since fluid/blood is the correct first-line therapy here but would be inappropriate or harmful as the primary strategy in pure cardiogenic shock.

7. Differential Diagnosis

8. Severity Assessment (Class of Hemorrhagic Shock)

Caveats: patients on beta-blockers may not mount tachycardia despite significant blood loss; elderly patients have less physiologic reserve and may decompensate abruptly, while children/young healthy patients may maintain normal vitals until severe volume depletion (compensate well, then collapse suddenly). TASH score and ABC score help identify massive transfusion protocol candidates early, before class 3-4 shock is fully established.

9. Investigations

• Bedside: eFAST, serial vital signs/mental status, point-of-care hemoglobin
• Labs: CBC, coagulation panel (PT/PTT/INR), fibrinogen, type and crossmatch, lactate, base deficit (both track shock severity and resuscitation response)
• Point-of-care viscoelastic testing (TEG/ROTEM): rapidly assesses clot kinetics to guide goal-directed correction of coagulopathy, particularly once MTP is discontinued and standard coagulation panels/TEG-ROTEM take over from empiric ratio-based transfusion
• Imaging: chest/pelvic X-ray and eFAST in all trauma patients; CT with IV contrast once hemodynamically stable enough to allow it; diagnostic peritoneal lavage in select patients only (avoid in morbid obesity, prior abdominal surgery, coagulopathy, advanced cirrhosis)

10. Evidence-Based Management (Timeline)

Immediate: control external hemorrhage (direct pressure/tourniquet), large-bore access, eFAST, TXA if indicated, activate MTP if triggered.

First hour: permissive hypotension strategy (non-TBI patients) until source control achieved; balanced blood product ratio; minimize crystalloid; active rewarming; source control via surgery/IR as soon as feasible — this is the true "resuscitation," not additional fluid.

Ongoing (once MTP discontinued): goal-directed correction of residual coagulopathy using TEG/ROTEM and standard coagulation panels rather than continued empiric ratio transfusion; transfusion goal for ongoing/recent hemorrhage: Hb 7-9 g/dL (adjusted upward for cardiovascular disease/ongoing end-organ hypoperfusion signs); platelet count target >50,000/mm3 with ongoing bleeding; correct PT/PTT.

Adjunctive therapies (Table format):

11. Organ Support

Blood product resuscitation as above; mechanical ventilation with attention to preload effects; ECMO for transfusion-related ARDS/refractory hypoxemia; REBOA as a bridge to definitive hemostasis; standard supportive ICU care once stabilized.

12. Consultation Matrix

13. Monitoring Framework

Continuous hemodynamic monitoring, serial Hb/coagulation panel/TEG-ROTEM, serial lactate/base deficit trend as resuscitation adequacy markers, temperature monitoring (active rewarming target), ionized calcium trend during massive transfusion, watch for transfusion reactions/TRALI.

14. ICU Bundle Checklist (Daily, once past acute massive transfusion phase)

15. Complications

Ongoing/recurrent hemorrhage, transfusion-related complications (TRALI, transfusion reactions, citrate toxicity/hypocalcemia), ARDS from massive transfusion, abdominal/extremity compartment syndrome from large-volume crystalloid, coagulopathy from dilution or ongoing consumption, multi-organ failure from prolonged hypoperfusion, hypothermia-related arrhythmia. Prevention: damage control resuscitation principles (minimize crystalloid, balanced ratios, active rewarming), early source control, early MTP activation. Rescue: ECMO for transfusion-related ARDS, REBOA for exsanguinating hemorrhage, repeat surgical/IR intervention for rebleeding.

16. Escalation & De-escalation

Escalate: ongoing hemorrhage despite initial measures -> escalate to surgery/IR, activate/continue MTP, consider REBOA for exsanguinating torso hemorrhage.

De-escalate: source controlled, hemodynamically stable, coagulopathy corrected -> discontinue MTP, transition to goal-directed (TEG/ROTEM-guided) transfusion, liberalize BP target from permissive hypotension to normalization.

17. ICU Discharge Criteria

Hemodynamically stable off blood products/vasopressors, source of hemorrhage definitively controlled, coagulopathy corrected, Hb stable without ongoing transfusion requirement, temperature normalized, no evidence of compartment syndrome or transfusion-related organ injury.

18. Documentation & Medicolegal Checklist

19. Key Guidelines

European/ATLS trauma hemorrhage management principles; Cannon J. Hemorrhagic shock. N Engl J Med. 2023 (comprehensive contemporary review); Cap A et al. Damage control resuscitation. Mil Med. 2018 (military-derived DCR principles now widely adopted in civilian trauma).

20. Landmark Trials

• PROPPR trial: 1:1:1 vs 1:1:2 plasma:platelet:RBC ratio in severe trauma — informed the shift toward balanced ratio-based massive transfusion.
• TRISS trial (Herbert et al., 1999): restrictive (Hb <7) vs liberal (Hb <10) transfusion threshold in general ICU patients — restrictive strategy non-inferior/potentially superior, foundational for restrictive transfusion practice broadly (though hemorrhagic shock resuscitation targets differ acutely from steady-state ICU anemia management).
• Tran A et al. systematic review/meta-analysis: permissive hypotension vs conventional resuscitation in trauma hemorrhagic shock — supports permissive hypotension as a reasonable strategy pending definitive hemostasis.

21. Controversies

Optimal permissive hypotension target (specific SBP/MAP number) is not rigidly standardized across guidelines and must be individualized, especially with concurrent traumatic brain injury (where adequate cerebral perfusion pressure takes priority over permissive hypotension). Optimal blood product ratio (1:1:1 vs alternative ratios) beyond PROPPR's findings continues to be refined. Role and timing of REBOA remains institution- and expertise-dependent, without universal deployment criteria. Whole blood vs component therapy resuscitation is an area of renewed interest/research without settled consensus in civilian trauma centers.

22. References

1. Hypovolemic Shock chapter. Washington Manual of Critical Care, 4th ed, 2025 (Ch. 2).
2. Cannon J. Hemorrhagic shock. N Engl J Med. 2023;378(4):370-379.
3. Cap A, Pidcoke H, Spinella P, et al. Damage control resuscitation. Mil Med. 2018;183:36-43.
4. Holcomb JB, Tilley BC, Baraniuk S, et al. Transfusion of plasma, platelets, and red blood cells in a 1:1:1 vs 1:1:2 ratio and mortality in patients with severe trauma (PROPPR). JAMA. 2015;313(5):471-482.
5. Herbert PC, Wells G, Blajchman MA, et al. A multicenter, randomized, controlled clinical trial of transfusion requirement in critical care (TRICC). N Engl J Med. 1999;340(6):409-417.
6. Tran A, Yates J, Lau A, et al. Permissive hypotension versus conventional resuscitation strategies in adult trauma patients with hemorrhagic shock: systematic review and meta-analysis. J Trauma Acute Care Surg. 2018;84(5):802-808.
7. Gonzalez E, Moore E, Moore H. Management of trauma-induced coagulopathy with thrombelastography. Crit Care Clin. 2017;33(1):119-134.
8. General Management of Trauma. ICU Protocols: A Step-wise Approach, 2nd ed. Springer; 2020 (Ch. 10).