Description

• State characterized by inadequate tissue perfusion leading to hypoxia and organ dysfunction.
• Types of shock:
  • Hypovolemic shock: Low preload due to intravascular volume loss
  • Cardiogenic shock: Consequence of cardiac pump failure characterized by persistent systolic pressure <80–90 mm Hg (at least 30 minutes) or mean arterial pressure 30 mm Hg lower than baseline, with severe reduction in the cardiac index and adequate or elevated filling pressures
  • Septic shock: Severe sepsis + systemic mean BP <60 mm Hg (or <80 mm Hg if the patient has baseline hypertension [HTN]) despite fluid resuscitation. Maintaining the systemic mean BP >60 mm Hg (or >80 mm Hg if the patient has baseline HTN) requires dopamine >5 mcg/kg/min, norepinephrine <0.25 mcg/kg/min, or epinephrine <0.25 mcg/kg/min despite adequate fluid resuscitation.
  • Neurogenic shock: Vasodilation associated with loss of sympathetic tone; venous pooling in periphery

Epidemiology

Accidental injuries are the leading cause of death between 1 and 44 years of age. Cardiogenic shock: 7% in patients with acute myocardial infarction (MI). >750,000 cases/year of sepsis in the US

Incidence
Male > Female. Sepsis is highest among African American males.

Risk Factors

• Hypovolemic shock: Hemorrhage, dehydration, burns
• Cardiogenic shock: Older age, anterior MI, HTN, diabetes mellitus, multivessel coronary artery disease, prior MI or diagnosis of heart failure, STEMI, and left bundle branch block.
• Septic shock: Bacteremia, age >65 years, immunosuppression, critical illness, malnutrition, cancer, pneumonia, genetic factors
• Neurogenic: Spinal anesthesia, spinal cord injury, anaphylactic shock, fainting (vasovagal)

General Prevention

Prompt recognition and early treatment

Etiology

• Hypovolemic shock (hemorrhagic):
  • Blood loss: Trauma (e.g., injuries to liver, spleen, lung; fractures, wounds), GI bleeding (e.g., gastric and duodenal ulcer, colonic polyps, diverticulosis, or tumors), rupture of aortic or ventricular aneurysm, ectopic pregnancy, hemorrhagic ovarian cyst, DUB:
    • Class I: Blood loss up to 750 mL (15% blood volume), pulse <100, BP normal with normal or increased pulse pressure, normal capillary blanch test, respiratory rate 14–20, urine output >30 mL/hr, slightly anxious
    • Class II: Blood loss 750–1,500 mL (15–30% blood volume), pulse >100, BP normal with decreased pulse pressure, positive capillary blanch test, respiratory rate 20–30, urine output 20–30 mL/hr, mildly anxious
    • Class III: Blood loss 1,500–2,000 mL (30–40% blood volume), pulse >120, BP decreased with decreased pulse pressure, positive capillary blanch test, respiratory rate 30–40, urine output 5–15 mL/hr, anxious + confused
    • Class IV: Blood loss >2,000 mL (>40% blood volume), pulse >140, BP decreased with decreased pulse pressure, positive capillary blanch test, relative risk (RR) >35, urine output negligible, confused, lethargic
• Hypovolemic shock (nonhemorrhagic): Dehydration, vomiting, diarrhea, heat stroke, or burns; third-space loss of plasma volume
• Cardiogenic shock:
  • Acute MI (>40% of left ventricular myocardium), right ventricular infarction, β- and calcium channel blocker overdose
  • Dilated cardiomyopathies (e.g., viral, alcohol, Adriamycin)
  • Arrhythmias: Heart block, ventricular tachycardia/fibrillation, atrial fibrillation with rapid ventricular response, bradycardias, and so forth
  • Mechanical difficulties: Valvular dysfunction, papillary muscle rupture, aortic or mitral valve dysfunction; ventricular septal rupture
  • Obstruction:
    • Pericardial tamponade, tension pneumothorax, constrictive pericarditis
    • Aortic dissection or pulmonary embolism
• Septic shock: UTI is the most common source in the elderly:
  • Systemic inflammatory response syndrome: Requires ≥2 criteria. Temperature >38.5°C or <35°C, heart rate >90 beats/min, respiratory rate >20 breaths/min or PaCO₂ <32 mm Hg, WBC >12,000/mm³, <4,000 cells/mm³, or >10% immature forms
  • Sepsis: Requires ≥2 of the following criteria, and documented infection. Temperature >38.5°C or <35°C, heart rate >90 beats/min, respiratory rate >20 breaths/min or PaCO₂ <32 mm Hg, WBC >12,000 cells/mm³, <4,000 cells/mm³, or >10% immature (band) forms. Documented infection requires positive culture or Gram stain of blood, sputum, urine, or normally sterile body fluid positive for pathogenic microorganism; or focus of infection identified by visual inspection.
  • Severe sepsis (sepsis + at least 1 additional criterion): Mottled skin; capillary refill of ≥3 seconds, urinary output of <0.5 mL/kg for at least 1 hour or requiring dialysis; lactate >2 mmol/L; abrupt change in mental status or abnormal EEG findings; platelet count of <100,000 cells/mL or disseminated intravascular coagulation; acute lung injury/acute respiratory distress syndrome (ARDS); or cardiac dysfunction (echocardiography)
• Neurogenic shock: Acute spinal injury, general or spinal anesthesia, vasovagal reaction

Commonly Associated Conditions

Adrenal failure in septic shock, change of mental status, renal failure