Shock

Overview

Introduction

• Clinical definition
  • decreased oxygen delivery, increased oxygen consumption, or impaired oxygen utilization that results in cellular and tissue hypoxia
    • this occurs in cases of reduced tissue perfusion (e.g., hemorrhage)
    • there are 4 types of shock
      • cardiogenic
      • hypovolemic
      • distributive
• obstructive

Cardiogenic

• Clinical definition
  • shock secondary to intracardiac causes results in a decreased cardiac output
    • self-perpetuating since
      • hypotension will result in decreased perfusion to the coronary vessels thus
        • worsening ischemia
      • decreased stroke volume will in turn increase the amount of blood in the left ventricle (LV) which
        • increases LV size and thus myocardial oxygen demand
• Etiology
  • causes of cardiogenic shock can be divided into three categories
    • cardiomyopic
      • myocardial infarction (e.g., > 40% of the LV mass is infarcted)
      • heart failure exacerbations (e.g., dilated cardiomyopathy)
      • myocarditis
      • stunned myocardium in the setting of prolonged ischemia
      • drug induced (e.g., β-blockers)
    • arrhythmic
      • tachyarrhythmias (e.g., atrial fibrillation)
      • bradyarrhythmias (e.g., Mobitz type II second degree heart block)
    • mechanical
      • valvular pathology (e.g., valvular rupture, insufficiency, and severe stenosis)
      • atrial myxoma
• Clinical findings
  • cold and clammy skin
• Treatment
  • intravenous inotropes (e.g., dobutamine) 
  • intra-aortic balloon pump in certain cases
  • percutaneous left ventricular assist device (LVAD)
• in cases where more extensive and prolonged support is needed to achieve hemodynamic stability

Hypovolemic

• Clinical definition
  • shock secondary to reduced intravascular volume 
    • the reduced preload results in a decreased cardiac output
• Etiology
  • causes of hypovolemic shock can be divided into
    • hemorrhagic (e.g., trauma and gastrointestinal bleeding)
    • non-hemorrhagic
      • decreased intravascular volume not due to loss of blood
        • gastrointestinal losses (e.g., diarrhea)
        • skin loss (e.g., heat stroke and burns)
• Clinical findings 
  • cold and clammy skin
• Treatment
• intravenous fluids

Distributive

• Clinical definition 
  • shock secondary to severe peripheral vasodilation
• Etiology
  • septic shock
    • presents with decreased vasopressin levels 
  • non-septic causes include
    • systemic inflammatory response syndrome (SIRS)
    • neurogenic shock (e.g., traumatic brain and spinal cord injury and neuro-axial anesthesia)
    • anaphylaxis
• Clinical findings
  • warm or dry skin
• Treatment
  • intravenous fluids and vasopressors 
• in patients with septic shock and hypotension refractory to fluids and vasopressors, adrenal insufficiency should be suspected and treated empirically with hydrocortisone 

Obstructive

• Clinical definition
  • shock secondary to extracardiac causes of pump failure (most common)
    • typically is associated with impaired right ventricular output
• Etiology
  • causes of obstructive shock can be divided into
    • pulmonary vascular (e.g., severe pulmonary embolism and pulmonary hypertension)
    • mechanical (e.g., tension pneumothorax, pericardial tamponade, and constrictive pericarditis
• Clinical findings
  • cold and clammy skin
• Treatment
  • manage the obstruction