Shock

Basics

Description

  • Inadequate supply of blood and oxygen to meet the metabolic demands of the tissues
  • Toxic metabolites are not removed
  • If untreated, inevitable progression from inadequate perfusion to organ dysfunction and ultimately to death
  • Major categories of shock:
    • Hypovolemic shock:
      • Decreased circulating blood volume
      • Suspect hemorrhage if acute onset
      • Severe dehydration if progressive onset and elevated hematocrit, BUN, and/or creatinine
    • Obstructive (cardiogenic) shock:
      • Decreased cardiac output and myocardial dysfunction leading to tissue hypoxia in the setting of adequate intravascular volume
      • Venous congestion with increase in central venous pressure
      • Compensatory increase in SVR
      • May be caused by cardiac dysfunction or obstruction of inflow/outflow of blood to/from the heart
    • Septic shock:
      • An initial infectious insult overwhelms the immune system
      • Biochemical messengers (cytokines, leukotrienes, histamines, prostaglandins) cause vessel dilatation
      • Capillary endothelium become disrupted causing vascular leak
      • Drop in SVR leads to inadequate tissue perfusion
      • Secondarily, decreased cardiac output from “cardiac stun” results in cold septic shock
    • Neurogenic shock:
      • Spinal cord insults disrupt sympathetic stimulation to vessels
      • Loss of sympathetic tone causes arteriodilating and vasodilatation
      • Lesions proximal to T4 disrupt sympathetic, spares vagal innervation causing bradycardia
    • Anaphylactic shock:
      • An antigen stimulates the allergic reaction
      • Mast cells degranulate
      • Histamine releases, along with autocoids, stimulate an anaphylaxis cascade
      • Vascular smooth muscle relaxes
      • Capillary endothelium leaks
      • Drop in SVR leads to inadequate tissue perfusion
    • Pharmacologic agents may cause shock through smooth muscle dilation or myocardial depression

Etiology

  • Hypovolemic shock:
    • Abdominal trauma, blunt or penetrating
    • Abortion – complete, partial, or inevitable
    • Anemia – chronic or acute
    • Aneurysms – abdominal, thoracic, dissecting
    • Aortogastric fistula
    • Arteriovenous malformations
    • Blunt trauma
    • Burns
    • Diabetes
    • Diarrhea
    • Diuretics
    • Ruptured ectopic pregnancy
    • Epistaxis
    • Fractures (especially long bones)
    • Hemoptysis
    • GI bleed
    • Mallory–Weiss tear
    • Penetrating trauma
    • Placenta previa
    • Postpartum hemorrhage
    • Retroperitoneal bleed
    • Severe ascites
    • Splenic rupture
  • Toxic epidermal necrolysis:
    • Vascular injuries
    • Vomiting
  • Cardiogenic shock:
    • Cardiomyopathy
    • Conduction abnormalities and arrhythmias
    • MI
    • Myocardial contusion
    • Myocarditis
    • Pericardial tamponade
    • Pulmonary embolus
    • Tension pneumothorax
    • Valvular insufficiency
    • Ventricular septal defect
  • Septic shock:
    • Acute respiratory distress syndrome
    • Bacterial infection
    • Bowel perforation
    • Cellulitis
    • Cholangitis
    • Cholecystitis
    • Endocarditis
    • Endometritis
    • Fungemia
    • Infected indwelling prosthetic device
    • Intra-abdominal infection or abscess
    • Mediastinitis
    • Meningitis
    • Myometritis
    • Pelvic inflammatory disease
    • Peritonitis
    • Pyelonephritis
    • Pharyngitis
    • Pneumonia
    • Septic arthritis
    • Thrombophlebitis
    • Tubo-ovarian abscess
    • Urosepsis
  • Anaphylactic:
    • Drug reaction (most commonly to aspirin, β-lactam antibiotics)
    • Exercise (rare)
    • Food allergy (peanuts, tree nuts, shellfish, fish, milk, eggs, soy, and wheat account for 90% of food-related anaphylaxis)
    • Insect sting
    • Latex
    • Radiographic contrast materials
    • Synthetic products
  • Pharmacologic:
    • Antihypertensives
    • Antidepressants
    • Benzodiazepines
    • Cholinergics
    • Digoxin
    • Narcotics
    • Nitrates
  • Neurogenic:
    • Spinal cord injury

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