Hemorrhagic shock

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"hemorrhagic shock"[MeSH Terms] AND management

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Hemorrhagic Shock

Hemorrhagic shock is a state of life-threatening circulatory failure caused by rapid, significant loss of intravascular blood volume, leading to inadequate oxygen delivery to tissues, cellular hypoxia, and - if uncorrected - irreversible organ failure and death.

1. Definition and Overview

Hemorrhagic shock results from a rapid reduction in intravascular blood volume from any cause. Rapid hemorrhage first triggers increased cardiac contractility and heart rate (HR), followed by baroreceptor activation and peripheral vasoconstriction. An initial slight increase in diastolic BP with narrowing of pulse pressure progresses to decreased ventricular filling, reduced cardiac output, and then a fall in systolic BP. Critically, HR and BP responses are notoriously variable - no firm conclusion can be made at the bedside about the presence or degree of hemorrhagic shock from vital signs alone.

ROSEN's Emergency Medicine, p. 58

2. Pathophysiology

Macrocirculatory Response

An imbalance develops between systemic O2 delivery and O2 consumption. Blood loss causes hemodynamic instability, coagulopathy, decreased O2 delivery, reduced tissue perfusion, and cellular hypoxia. The initial response is mediated by the neuroendocrine system: reduced arterial pressure triggers vasoconstriction and catecholamine release to preserve flow to the heart, kidney, and brain at the expense of other vascular beds.

Released hormones and mediators include: renin, angiotensin, vasopressin (ADH), growth hormone, glucagon, cortisol, epinephrine, and norepinephrine. As oxygen debt mounts, damage-associated molecular patterns (DAMPs), mitochondrial DNA, and formyl peptides contribute to systemic inflammatory response.

Miller's Anesthesia, 10e, p. 9383

Microcirculatory Response

Individual ischemic cells take up interstitial fluid, further depleting intravascular volume. Cellular edema may restrict blood flow in adjacent capillaries, causing the "no-reflow" phenomenon - preventing reversal of ischemia even after macroperfusion is restored.

Ischemic cells produce lactate and free radicals which accumulate in circulation. They also release inflammatory factors: prostacyclin, thromboxane, prostaglandins, leukotrienes, endothelin, complement, interleukins, TNF, and others. This inflammatory cascade becomes a disease process independent of its origin and lays the foundation for multiple organ failure (MOF).

The shock cascade - showing how ischemia triggers immune amplification leading to multi-organ injury

The "shock cascade" - ischemia triggers a self-amplifying immune response injuring non-ischemic organs. (Miller's Anesthesia, 10e)

The Role of Base Deficit and Lactate

Even before cardiac output declines, blood flow is redirected away from non-critical organs, which begin producing lactic acid. Acidosis often precedes any significant decrease in cardiac output. Bicarbonate ions buffer the blood pH, keeping it near neutral even as lactic acid accumulates. The base deficit (amount of strong base needed to normalize 1 L of blood to pH 7.4) represents an index of how far the bloodstream has depleted this reserve.

Normal base deficit: more positive than -2 mEq/L
A more negative base deficit can appear early in hemorrhage, even while blood pH and BP remain normal
The base deficit therefore distinguishes trivial blood loss from clinically significant hemorrhage
ROSEN's Emergency Medicine, p. 58

3. Progressive vs. Nonprogressive Shock

This is one of the most important physiologic concepts in understanding hemorrhagic shock:

Time course of arterial pressure in dogs after different degrees of acute hemorrhage, showing progressive (fatal, red curves) vs. nonprogressive (survivable, black curves) trajectories

Figure 24.2 from Guyton & Hall - Blood loss above a critical threshold shifts the patient from compensated to progressive (irreversible) shock.

Nonprogressive (Compensated) Shock: If blood loss does not cross a critical threshold, compensatory mechanisms prevail:

Baroreceptor reflexes - powerful sympathetic stimulation (activated within 30 seconds)
CNS ischemic response - even more powerful sympathetic activation (triggered when MAP falls below ~50 mmHg)
Reverse stress-relaxation - blood vessels contract around diminished blood volume
Renin-angiotensin-aldosterone activation - arteriolar constriction + salt/water retention
Vasopressin (ADH) secretion - arteriolar/venous constriction + renal water retention
Catecholamine release - increased HR and vasoconstriction
Fluid shifts - absorption from interstitial spaces and intestinal tract, thirst

Progressive Shock: Beyond the critical threshold, shock causes more shock via positive feedback vicious cycles:

Decreased coronary flow → myocardial depression → further decreased cardiac output
Vasomotor center failure (ischemia of medullary centers)
Cardiac depression from acidosis, free radicals, and inflammatory mediators
Breakdown of gut barrier → bacterial translocation → potentiates ARDS
Guyton and Hall Textbook of Medical Physiology, pp. 300-302

4. Organ-Specific Responses

Organ	Response
Brain	Prime trigger of neuroendocrine response; cortical reflexes depressed during hypotension - reversible with mild hypoperfusion, permanent with prolonged ischemia
Heart	Initially protected; maintained or increased coronary flow until late stages; lactate/free radicals act as negative inotropes - terminal event in shock spiral
Kidney	Maintains GFR via selective vasoconstriction; prolonged hypotension → renal cell hibernation → tubular epithelial necrosis → renal failure; high incidence of acute adrenal insufficiency (86% in one observational study)
Lung	Filter for inflammatory by-products; neutrophil/platelet aggregation → increased capillary permeability → ARDS; sentinel organ for MOD
Gut	Earliest organ affected; intense vasoconstriction → "no-reflow" → intestinal cell death → breakdown of gut barrier → bacterial translocation → potentiates ARDS and MOD
Liver	Complex microcirculation susceptible to reperfusion injury; contributes to inflammatory response; failure of synthetic function (coagulopathy)

Miller's Anesthesia, 10e, pp. 9385-9387

5. Classification of Hemorrhagic Shock

The ATLS classification based on volume of blood loss:

	Class I	Class II	Class III	Class IV
Blood loss (mL)	Up to 750	750-1500	1500-2000	>2000
Blood loss (% BV)	Up to 15%	15-30%	30-40%	>40%
Pulse rate	<100	>100	>120	>140
Blood pressure	Normal	Normal	Decreased	Decreased
Pulse pressure	Normal/increased	Decreased	Decreased	Decreased
Respiratory rate	14-20	>20-30	30-40	>35
Urine output (mL/h)	>30	20-30	5-15	Negligible
CNS/mental status	Slightly anxious	Mildly anxious	Anxious + confused	Confused + lethargic

Note: Pregnant patients maintain a larger circulating blood volume and must lose a relatively larger volume before manifesting signs of hypovolemia.

Schwartz's Principles of Surgery, 11e, p. 220

6. Initial Resuscitation Strategy

Patients can be stratified by their response to initial fluid resuscitation:

Responders: Vital signs normalize - unlikely to have significant ongoing hemorrhage; proceed with orderly evaluation
Transient responders: Initially improve, then deteriorate hemodynamically - challenging to triage; likely ongoing hemorrhage
Nonresponders: Persistent hypotension despite aggressive resuscitation - mandate immediate source identification and intervention

Hemorrhage Control

Five potential sources of blood loss: scalp, chest, abdomen, pelvis, extremities. Estimated blood loss by fracture site:

Each rib fracture: 100-200 mL
Tibial fracture: 300-500 mL
Femoral fracture: up to 1500 mL
Pelvic fracture: massive, potentially exsanguinating
Schwartz's Principles of Surgery, 11e, pp. 220-221

7. Resuscitation: Blood Products and Damage Control

In hemorrhagic shock, blood products are the resuscitative fluid of choice. Crystalloid administration leads to anemia and coagulopathy.

Component Therapy

Massive transfusion protocol (MTP): 1:1:1 ratio of FFP : pRBCs : platelets
Early empiric use of type O RBCs (O-negative for women of childbearing age) and thawed AB plasma at a 2:1 ratio pending type-specific blood

Whole Blood

Recent data suggest that whole blood may be superior to component therapy when available in hemorrhagic shock.

Viscoelastic Testing (TEG/ROTEM)

TEG and ROTEM provide dynamic, real-time assessment of clotting ability and strength
Guide targeted use of FFP, cryoprecipitate, platelets, or tranexamic acid (TXA)
Mortality benefit demonstrated vs. empiric MTP in penetrating trauma patients receiving >10 units pRBCs (33.3% vs. 54.1% in one 2013 study)
Endorsed by the Eastern Association for the Surgery of Trauma (EAST) guidelines

Tranexamic Acid (TXA)

TXA is an important adjunct in hemorrhagic shock. Prompt recognition of fibrinolysis via viscoelastic assays enables timely TXA administration.

Vasopressors

While evidence for early vasopressors in hemorrhagic shock is limited, they may be a necessary temporizing adjunct. A specific vasopressin-deficient state may occur in prolonged shock where vasopressin administration is helpful.

Sabiston Textbook of Surgery, pp. 2892-2903

8. Anesthetic Considerations

Any IV anesthetic given to a trauma patient in hemorrhagic shock may potentiate profound hypotension and even cardiac arrest by inhibiting circulating catecholamines.

Etomidate is preferred for induction - maintains hemodynamics better than alternatives in hemorrhagic shock
Opioids should be given in reduced doses to minimize hemodynamic consequences and prevent prolonged effect
Propofol is particularly hazardous - avoid or use with extreme caution
Miller's Anesthesia, 10e, pp. 4687-4696

9. Complications

Complication	Mechanism
ARDS	Pulmonary neutrophil/platelet aggregation; gut bacterial translocation; inflammatory mediators
AKI	Renal hypoperfusion → tubular necrosis; relative adrenal insufficiency compounds this
Coagulopathy / "Lethal Triad"	Dilution (crystalloid), acidosis, hypothermia - each impairs clotting; the triad is self-reinforcing
Multiple organ failure (MOF)	Progressive inflammatory cascade; lung is the sentinel organ
"No-reflow" phenomenon	Cellular edema in capillary beds prevents reversal of ischemia even after macroperfusion is restored

Key References:

Guyton and Hall Textbook of Medical Physiology - Chapter 24: Circulatory Shock
Schwartz's Principles of Surgery, 11e - Chapter 7: Trauma
Miller's Anesthesia, 10e - Chapter 62: Pathophysiology and Resuscitation from Hemorrhagic Shock
Sabiston Textbook of Surgery - Hemorrhagic Shock management
ROSEN's Emergency Medicine - Hemorrhagic Shock

Causes

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Causes of Hemorrhagic Shock

Hemorrhagic shock arises whenever blood loss - from any site, internal or external - exceeds the body's compensatory capacity. The causes are best organized by anatomical category and clinical setting.

1. Traumatic Causes

Trauma is the most common cause overall, especially in young adults. ATLS identifies five anatomical compartments where life-threatening blood can accumulate:

External / Compressible Hemorrhage

Scalp lacerations (highly vascular; easily underestimated)
Extremity wounds - lacerations, amputations, penetrating injuries
Open fractures with soft-tissue disruption

Thoracic (Chest)

Hemothorax - blunt or penetrating trauma to lung parenchyma, intercostal vessels, or great vessels
Massive hemothorax: initial chest tube output >1 L is an indication for immediate thoracotomy
Aortic injury (blunt deceleration or penetrating)
Cardiac laceration

Abdominal / Peritoneal

Solid organ injury: spleen (most common in blunt abdominal trauma), liver, kidneys
Mesenteric vascular injury
Penetrating injuries: gunshot/stab wounds to abdominal viscera and vasculature
Extensive hemoperitoneum detected on eFAST

Pelvic

Pelvic fractures - venous plexus and internal iliac artery disruption; potentially exsanguinating
Pelvic fractures are notorious for massive occult blood loss - pelvis can accommodate several liters
Wrapping with a pelvic binder is an immediate temporizing measure

Extremity Fractures (Long Bone)

Each rib fracture: 100-200 mL
Tibial fracture: 300-500 mL
Femoral fracture: up to 1,500 mL
When fractures are additive, cumulative blood loss can be hemodynamically significant
Schwartz's Principles of Surgery, 11e, pp. 220-221

2. Gastrointestinal Hemorrhage

GI bleeding is among the most common non-traumatic causes of hemorrhagic shock.

Upper GI Bleeding (proximal to ligament of Treitz)

Cause	Notes
Peptic ulcer disease (PUD)	Most common cause (~40% of upper GI hemorrhage); includes gastric and duodenal ulcers
Esophageal/gastric varices	Cause of upper GI bleeding in cirrhotic patients ~59% of the time; high mortality
Erosive esophagitis / gastritis	Including stress ulcers in critically ill patients
Mallory-Weiss tears	Mucosal lacerations at gastroesophageal junction from retching
Dieulafoy's lesion	Aberrant submucosal artery; can cause massive occult bleeding
Aortoenteric fistula	Rare but immediately life-threatening; especially after prior aortic graft surgery

Lower GI Bleeding (distal to ligament of Treitz)

Cause	Notes
Diverticular bleeding	Most common cause of massive lower GI hemorrhage in adults
Angiodysplasia (arteriovenous malformations)	Common in elderly
Colorectal malignancy	Usually slower bleeding but can be acute
Ischemic colitis	Especially in elderly or post-aortic surgery
Inflammatory bowel disease	Ulcerative colitis > Crohn's disease
Meckel's diverticulum	Classic cause in children and young adults

Goldman-Cecil Medicine; Tintinalli's Emergency Medicine

3. Obstetric and Gynecological Causes

A major cause of hemorrhagic shock in women of reproductive age. "Bleeding during the third trimester should always be considered an emergency because shock may occur within minutes." (Roberts and Hedges' Clinical Procedures in Emergency Medicine)

Cause	Notes
Postpartum hemorrhage (PPH)	Most common obstetric cause; defined as >500 mL (vaginal) or >1000 mL (C-section) blood loss; causes include uterine atony, retained placenta, lacerations
Placenta previa	Painless antepartum hemorrhage; placenta overlies cervical os
Placental abruption (abruptio placentae)	Painful antepartum hemorrhage; premature separation of placenta
Uterine rupture	Risk in scarred uterus (prior C-section); catastrophic hemorrhage
Ruptured ectopic pregnancy	Classic presentation: amenorrhea + abdominal pain + hemodynamic instability + positive pregnancy test; a true emergency
Ruptured ovarian cyst / hemorrhagic corpus luteum	Can cause significant intraperitoneal bleeding

Roberts and Hedges' Clinical Procedures in Emergency Medicine; Miller's Anesthesia, 10e

4. Vascular Causes

Cause	Notes
Ruptured abdominal aortic aneurysm (AAA)	Classically presents as hypotension + back/flank pain + pulsatile mass; immediately life-threatening
Ruptured thoracic aortic aneurysm	Associated with hypertension and connective tissue disorders (Marfan, Ehlers-Danlos)
Aortoenteric fistula	Often secondary to prior aortic graft; "herald bleed" followed by exsanguination
Splenic artery aneurysm rupture	Rare; risk increased in pregnancy; hemoperitoneum
Mesenteric artery or vein rupture	Post-traumatic or spontaneous
Arteriovenous malformations	In any organ system

Current Surgical Therapy, 14e, p. 2377

5. Iatrogenic / Procedural Causes

Post-surgical hemorrhage (abdominal, pelvic, thoracic, vascular surgery)
Post-procedural bleeding (endoscopy, biopsy, arterial line placement, cardiac catheterization)
Anticoagulant-related hemorrhage (warfarin, heparin, DOACs) - particularly in elderly patients
Thrombolytic therapy complications

6. Spontaneous / Medical Causes

Cause	Notes
Hemophilia A/B and other coagulation factor deficiencies	Spontaneous or post-minor trauma hemorrhage
Severe thrombocytopenia	ITP, TTP, HIT, bone marrow failure
Anticoagulant overdose	Warfarin, heparin, DOACs
Disseminated intravascular coagulation (DIC)	Consumption of clotting factors; paradoxically both thrombotic and hemorrhagic
Hepatic failure	Impaired synthesis of coagulation factors (I, II, V, VII, IX, X) + portal hypertension
Spontaneous retroperitoneal hemorrhage	Can be massive; often anticoagulant-related or from adrenal hemorrhage
Intracranial hemorrhage	Subarachnoid or intracerebral hemorrhage does not directly cause hemorrhagic shock (skull is a closed box) but can cause neurogenic shock and coagulopathy

7. Summary Mnemonic: "TRAUMA + GI + OB + VASC"

Category	Key Examples
Trauma	Chest, abdomen, pelvis, long bones, external wounds
GI bleeding	PUD, varices, diverticular disease, Mallory-Weiss
Obstetric/gynecologic	PPH, placenta previa, abruption, ruptured ectopic
Vascular	Ruptured AAA, aortoenteric fistula, splenic aneurysm
Iatrogenic	Post-surgical, anticoagulation
Coagulopathy	Hemophilia, DIC, liver failure

The most common causes encountered in emergency settings are trauma (all age groups), GI bleeding (especially in older adults), and obstetric hemorrhage (in women of childbearing age). Tintinalli's notes that massive transfusion protocols originally developed for trauma are now routinely applied to postpartum hemorrhage and massive GI bleeding as well, reflecting the shared final common pathway of hemorrhagic shock regardless of cause.

Tintinalli's Emergency Medicine, p. 1538; Washington Manual of Medical Therapeutics

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