Hemorrhages and Shock

Definition & Core Idea

  • Hemorrhage = escape of blood from blood vessels
    • Occurs whenever blood leaves the closed circulatory loop.
    • Even a finger-cut qualifies.
  • Can be:
    • External – visible bleeding through skin/wounds.
    • Internal – blood accumulates in body cavities/organ spaces
      • Examples: hemothorax (pleural cavity), hemoperitoneum (peritoneal cavity), hemopericardium (pericardial sac).

Forms, Sizes & Terminology

  • Hematoma – blood collects inside tissue ➔ localized swelling.
  • Size-based skin/mucosal hemorrhages
    • Ecchymosis: 1–2  cm1\text{–}2\;\text{cm} bruise-like patch.
    • Purpura: 3–5  mm3\text{–}5\;\text{mm} lesions.
    • Petechiae: 1–2  mm1\text{–}2\;\text{mm} pin-point spots.
  • Diapedesis – microscopic passage of erythrocytes through intact vessel walls into loose tissue.

Acute vs. Chronic Blood Loss

  • Large & sudden ➔ acute hemorrhage.
  • Small, repetitive, prolonged ➔ chronic hemorrhage (risk of iron-deficiency anaemia).

Etiology (Causes) of Hemorrhage

  • Traumatic vessel injury (penetrating wounds of heart, great vessels, etc.).
  • Spontaneous rupture (e.g., cerebral aneurysm), acute severe anaemia, scurvy, septicaemia.
  • Inflammatory vascular lesions – chronic peptic ulcer, polyarteritis nodosa.
  • Neoplastic invasion – e.g., carcinoma of the tongue eroding vessels.
  • Degenerative vascular disease – atherosclerosis.
  • Elevated intravascular pressure – e.g., retinal hemorrhage in systemic hypertension.

Physiological Impact / Dose–Time Relationship

  • Effects depend on volume (V), rate (t), site.
    • Loss  20%  Vb\text{Loss}\;20\%\;V_b → minimal signs (compensated).
    • Loss  33%  Vb\text{Loss}\;33\%\;V_b rapidly → may be fatal (no time to compensate).
    • Loss  50%  Vb\text{Loss}\;50\%\;V_b slow (≈24 h) → survivable with support.
  • Acute major loss → hypovolaemic shock.
  • Chronic loss → iron-deficiency anaemia.

Hypovolemic Shock – Definition & Overview

  • Hypovolemic shock = critical reduction of intravascular fluid volume.
    • hypo=low,  vol=volume,  emic=blood\text{hypo}=\text{low},\;\text{vol}=\text{volume},\;\text{emic}=\text{blood}.
  • Adult blood volume ≈ 5  L5\;L; loss of ≥15%\ge 15\% (≈750  mL750\;mL) triggers shock S/S.
  • Key haemodynamic consequence: ↓ venous return → ↓ preload → ↓ stroke volume → ↓ cardiac output (CO=HR×SV)\big(CO=HR\times SV\big) → ↓ tissue O₂.

Two Etiological Categories

  1. Relative hypovolaemia (internal / concealed shift)
    • Internal bleeding, third-spacing (burns), long-bone fractures, acute pancreatitis (Cullen & Grey-Turner signs), massive vasodilation in sepsis.
  2. Absolute hypovolaemia (external / visible loss)