Mechanism of development (pathogenesis)
Regardless of the etiology (blood loss, organ damage, gas exchange disorders), the pathogenesis is fundamentally driven by hypovolemia. It can be:
- Absolute — actual loss of blood externally or into body cavities. For example, a closed femoral fracture can result in up to 1.2 L of blood pouring into the tissues.
- Relative — blood volume remains unchanged, but blood is pooled within dilated peripheral vessels.
Blood volume deficiency leads to a reduction in venous return and low cardiac output syndrome (the heart pumps less blood). To survive, the body initiates an adaptive response — centralization of circulation. Peripheral vessels constrict sharply to maintain blood flow to the brain and myocardium.
However, prolonged peripheral vasospasm causes tissue hypoxia. Under-oxidized products accumulate in the capillaries, metabolic acidosis develops, and erythrocytes clump together (sludge syndrome). Over time, compensatory mechanisms fail, leading to multiple organ dysfunction syndrome.
Criteria for severity assessment
Relying solely on blood pressure figures is a common clinical error. During shock, blood pressure may be artificially maintained through vasoconstriction. To obtain an objective clinical picture, a set of parameters is evaluated:
- Allgöwer index (pulse / systolic blood pressure). An increase in this value to 1.5 and above indicates the development of irreversible changes.
- Capillary refill test (skin turgor / blanching sign). Normally, after pressing on the nail bed, color returns in no more than 2 seconds. A delay indicates capillary paresis.
- Rectal-skin gradient. The temperature difference between the rectum and the skin of the foot. Normally 3–5 °C. This is a highly sensitive criterion for peripheral microcirculation that remains reliable regardless of blood pressure.
- Central venous pressure (CVP). Reflects the volume of venous return (normal range is 60–140 mm H₂O).
- Hourly diuresis. A urinary catheter is placed in all patients with severe trauma. A urine output drop below 30 mL/h is a sign of impaired renal blood supply.
Modern stages of shock progression
The outdated division of shock into erethistic and torpid phases is no longer used today because it poorly reflects prognosis. Modern classification identifies three stages:
- Compensated shock. Volumetric blood flow drops, peripheral perfusion decreases (pallor, delayed capillary refill). Meanwhile, blood pressure may remain normal due to the centralization of circulation.
- Decompensated reversible shock. Venomotor tone reserves are exhausted, and arterial and central venous pressures drop.
- Decompensated irreversible shock. Deep hypoxia and multiple organ failure. The objective criterion for irreversibility is the lack of a blood pressure response to intravenous norepinephrine administration and fluid/blood transfusion.
Shock prevention: immobilization and nerve blocks
The most critical pre-hospital objective is to prevent the worsening of shock. This is achieved through transport immobilization using standard or improvised splints. It prevents secondary tissue injury from bone fragments and reduces pain signaling. The rule of immobilization is mandatory fixation of the injured segment and at least two adjacent joints (three for the femur and humerus). Splints are applied over clothing after being pre-molded to the patient's anatomy.
In a hospital setting, novocaine (procaine) blocks are used for analgesia:
- Shkolnikov block — indicated for pelvic fractures (the anesthetic is injected into the fascial space of the iliac fossa).
- Vishnevsky vagosympathetic block — indicated for chest injuries to prevent pleuropulmonary shock.
Out-of-hospital nerve blocks are performed extremely rarely due to the high risk of introducing infection into the hematoma.
Briefly: answers to topical questions
What is the volume of occult blood loss in closed fractures of various skeletal bones?
In closed bone fractures, occult blood loss can reach 1.5–2.0 L. Estimated values depend on the site of injury:
- Pelvis (both semi-rings) — 1500–2000 mL
- Femur — 800–1200 mL
- Tibia — 350–650 mL
- Humerus — 200–500 mL
- Ribs (single rib) — 100–150 mL
What are the severity grades of traumatic shock categorized by specific Allgöwer index values?
Depending on the Allgöwer index values, three main severity grades of traumatic shock are distinguished, as well as a terminal state.
| Shock severity grade | Allgöwer index |
|---|---|
| I | 0,7 — 0,8 |
| II | 0,9 — 1,2 |
| III | > 1,2 |
| IV (terminal state) | - |
Normally, this index is 0.5–0.6. An increase in the index to 1.5 or higher indicates the development of irreversible shock.
Which drug groups and solutions are used for initial infusion therapy in decompensated traumatic shock?
For infusion and transfusion therapy in decompensated hypovolemic shock, three media groups are used:
- Blood and blood products — 1000 mL for blood loss of 500–1500 mL; 2000 mL for blood loss ≥ 2000 mL.
- Colloid solutions — 500 mL for blood loss of 500–1500 mL; 1500 mL for blood loss ≥ 2000 mL.
- Crystalloid solutions — 1000 mL for blood loss of 500–1500 mL; 2000 mL for blood loss ≥ 2000 mL.
The total volume of administered fluid is 1500–2500 mL for a blood loss of 500–1500 mL, and 2500–5500 mL for a blood loss ≥ 2000 mL. The infusion rate during the first 3 hours is 350 mL/h or 600 mL/h, respectively; the average rate is 350 mL/h or 300 mL/h.
What are the classic clinical symptoms of the erethistic phase of traumatic shock?
The classic clinical symptoms of the erethistic phase of traumatic shock are caused by the activation of the sympathoadrenal system. The main manifestations include:
- Agitation — the patient is in an excited state.
- Pallor — the skin and mucous membranes become pale.
- Tachycardia — rapid pulse is observed.
- Arterial hypertension — blood pressure is elevated.
This phase is very brief and occurs immediately after injury, subsequently giving way to the torpid phase characterized by general lethargy and stupor.
Class and exam questions
What is the potential volume of occult blood loss in a closed femur fracture?
Between 800 and 1200 mL of blood can pour into the surrounding soft tissues, causing pronounced absolute hypovolemia even without external bleeding.
How to quickly assess microcirculation without complex equipment?
It is enough to check the capillary refill sign — press on the nail bed and release. If the color takes longer than 2 seconds to return, peripheral blood flow is impaired.
What else to study on this topic
- Trauma severity assessment using the Trauma Score (TS) and Glasgow Coma Scale (GCS)
- Technique for performing local novocaine blocks (Shkolnikov block, vagosympathetic block, intercostal block)
- Hemodynamic differences between cardiogenic, obstructive, and hypovolemic shock
- Rules and common pitfalls of transport immobilization
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