Types of Shock

Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. The most common symptoms include tachycardia, tachypnea, hypotension, altered mentation, and oliguria. Treatment measures vary depending on the suspected cause of shock and may include mechanical ventilation, IV crystalloids, vasopressors, and blood transfusion.

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Definition and Classification

Definition

Shock is a life-threatening condition of organ dysfunction resulting from tissue hypoxia due to decreased oxygen delivery, increased oxygen consumption, and/or defective oxygen utilization.

Classification

  • Distributive: characterized by a reduction in systemic vascular resistance (SVR) and a compensatory increase in cardiac output (CO)
    • Septic shock
    • Pancreatitis
    • Severe burns
    • Anaphylactic shock
    • Neurogenic shock
    • Endocrine shock
    • Adrenal crisis
    • Drug- and toxin-induced shock 
  • Cardiogenic: characterized by reduced CO due to a primary cardiac problem
    • Myocardial infarction
    • Myocarditis
    • Arrhythmic
    • Valvular
      • Severe aortic valve insufficiency
      • Severe mitral valve insufficiency
  • Hypovolemic: characterized by reduced CO due to reduced preload
    • Hemorrhagic
    • Gastrointestinal (GI) losses
    • Burns
    • Polyuria
      • Diabetic ketoacidosis
      • Diabetes insipidus
  • Obstructive: characterized by reduced CO due to an extracardiac obstruction
    • Tension pneumothorax
    • Pulmonary embolism
    • Cardiac tamponade
    • Aortic dissection
    • Restrictive pericarditis
  • Mixed/multifactorial: Often, 1 class does not exist in isolation.
Table: Hemodynamic characteristics of the major types of shock
Type of shockCentral venous pressure (CVP)Pulmonary capillary wedge pressure (PCWP)Cardiac outputSystemic vascular resistance
Distributive
Cardiogenic
Obstructive↓↑
Hypovolemic

Pathophysiology and Stages

Pathophysiology

  • Initial insult (most commonly resulting in circulatory failure) → impaired oxygen delivery (most common mechanism of tissue hypoxia) → tissue hypoxia → anaerobic metabolism (pyruvate to lactate conversion and reduced adenosine triphosphate (ATP) production) → failure of cells to maintain osmotic, ionic, and pH homeostasis → cellular swelling and death → activation of inflammatory cascades and microvascular alterations → organ dysfunction/shock  
  • Determinants of oxygen delivery (DO2) include CO and arterial oxygen content (CaO2):
    DO2 = CO × CaO2
    • CO = heart rate (HR) × stroke volume (SV)
      • SV = (preload × contractility) / systemic vascular resistance (SVR)
    • CaO2 ≈ hemoglobin (Hb) × 1.39 × arterial oxygen saturation (SaO2); therefore, variables that affect DO2 include CO (HR and SV (preload, contractility, and SVR)) and CaO2 (Hb and SaO2)
  • Other mechanisms of tissue hypoxia (less common than impaired oxygen delivery): 
    • Increased oxygen consumption 
    • Impaired oxygen utilization (e.g., cyanide poisoning)

Stages of shock

  1. Preshock or compensated shock
    • Reversible with interventions
    • Perfusion and oxygen delivery are relatively normal despite the insult.
    • No overt signs of organ dysfunction ± mild laboratory signs of organ dysfunction (e.g., mildly elevated creatinine, troponin, or lactate)
  2. Shock or decompensated shock
    • Reversible with interventions
    • Perfusion and oxygen delivery are abnormal.
    • Overt signs of organ dysfunction are present.
  3. Irreversible shock
    • Permanent organ dysfunction
    • Progression to multisystem organ failure

Diagnosis

Always maintain a high clinical suspicion for shock. Suggestive features include tachycardia, hypotension, altered mentation, oliguria, weak peripheral pulses, and cool and clammy skin.

History

  • Fever and productive cough: distributive shock due to pneumosepsis
  • Hives, dyspnea, and facial edema: distributive shock due to anaphylaxis
  • Exertional chest pain and dyspnea: cardiogenic shock due to myocardial infarction
  • Presyncope or syncope: cardiogenic shock due to arrhythmias
  • Acute-onset dyspnea or chest pain and a history of malignancy, inactivity, or leg swelling: obstructive shock due to pulmonary embolism
  • Severe diarrhea: hypovolemic shock due to gastrointestinal loss

Physical examination

  • Compensated shock:
    • Tachycardia: to compensate for CO
    • Tachypnea: to compensate for metabolic acidosis
    • Hypotension: systolic blood pressure (SBP) < 90 mm Hg, mean arterial pressure (MAP) < 65 mm Hg in normotensive individuals or higher in patients with uncontrolled hypertension
    • Decreased capillary refill 
    • Cold and clammy skin
  •  Decompensated shock: signs of organ failure
    • Confusion/altered mental status: central nervous system (CNS) hypoperfusion
    • Oliguria (< 0.5 mL/kg/hr) in a patient without a history of renal disease: renal hypoperfusion
  • Specific findings:
    • Bilateral rales: pulmonary edema due to left heart failure or acute respiratory distress syndrome 
    • Warm distal extremities, capillary refill in < 2 seconds, and bounding pulses: high CO such as in distributive shock
    • Cool extremities, delayed capillary refill, weak pulses, and a narrow pulse pressure suggest low CO:
      • Elevated jugular venous pressure (JVP) and peripheral edema: cardiogenic shock with right heart failure
      • Elevated JVP and pulsus paradoxus (i.e., > 10 mm Hg drop in systolic blood pressure during inspiration): obstructive shock due to cardiac tamponade 
      • Reduced JVP (< 8 cm): hypovolemic shock
    • Infected skin/mucosal lesions: septic shock
    • Large ecchymosis suggests major internal bleeds: hypovolemic shock
    • Blood on digital rectal examination: hypovolemic shock due to GI bleeding
    • Unilateral absence of breath sounds with tympanic percussion, subcutaneous emphysema, and lateral deviation of trachea: obstructive shock due to tension pneumothorax

Laboratory studies

  • Lactate: 
    • Serial measurements are recommended to evaluate response to therapy. 
    • Elevations correlate with worse outcomes. 
  • Renal function tests: blood urea nitrogen (BUN) and creatinine
  • Liver function tests: Elevation of alkaline phosphatase (ALP) to more than 3 times normal may suggest biliary obstruction as the cause of sepsis and distributive shock. 
  • Cardiac enzymes: Elevations may indicate myocardial infarction, myocarditis, or pulmonary embolism.
  • Complete blood count (with differential): Elevation of leukocytes with a left shift (immature granulocyte count > 3% by automated analyzer or manual band count > 10%), although not diagnostic, may indicate infection.
  • Prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR): Elevations may indicate a coagulopathy related to septic shock.
  • Cultures including blood, urine, and sputum
  • Urinalysis: Pyuria indicates infection.
  • Arterial blood gas: shows degree and type of acid-base disorder and hypoxemia
  • Electrocardiogram (ECG) may suggest etiology of shock:
    • ST-segment elevation: myocardial infarction
    • Tachyarrhythmias or bradyarrhythmias
    • S1Q3T3 pattern: pulmonary embolism
    • Reduced QRS voltage + electrical alternans: pericardial tamponade

Imaging

  • Radiographic evaluation including chest X-ray and thoracoabdominal computed tomography (CT) scan
  • Point-of-care ultrasound: 
    • Heart: left ventricle (LV) and right ventricle (RV) function, valvular function, pericardium, inferior vena cava (IVC) diameter and collapsibility
    • Chest: pneumothorax, hemothorax, empyema, thoracic aortic aneurysm
    • Abdomen: peritoneal cavity for fluid accumulation and bleeding, abdominal aortic aneurysm
    • Proximal lower extremities: deep venous thrombosis

Scores and indices

  • Shock index (SI): heart rate (HR; beats/min) / SBP (mm Hg)
    • SI of 0.5–0.7: Normal
    • SI > 0.9: indicates critical bleeding and transfusion requirement
  • qSOFA (quick Sequential (sepsis-related) Organ Failure Assessments) score: Presence of 2 of the following 3 criteria indicates a worse outcome in a patient suspected of having sepsis and triggers an immediate diagnostic workup and treatment as appropriate.
    • SBP < 100 mm Hg 
    • Respiratory rate > 22/min
    • Altered mental status

Management

Shock is a medical emergency!
Initiate simultaneous treatment and evaluation for etiology, utilizing findings from history, physical examination, hemodynamic monitoring, and laboratory studies. This is best accomplished within a multidisciplinary team in a resource-equipped setting such as the intensive care unit (ICU).

Approach to shock - recognize shock early

Approach to shock

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Respiratory support

  • Indications for endotracheal intubation and mechanical ventilatory support: 
    • Significant hypoxemia (PaO2 < 60 mm Hg or oxygen saturation < 90%)
    • Hypoventilation (rising partial pressure of carbon dioxide (pCO2)) 
    • Significantly altered level of consciousness 
    • Inability to protect airways with risk of aspiration 
    • Persistent metabolic acidosis with pH < 7.20
  • Goal: arterial oxygen saturation of 92%95%

Monitoring

  • Peripheral venous access: for possible fluid and antibiotic therapy
  • Central venous catheter placement: 
    • Consider if resuscitation is inadequate through peripheral access.
    • Applications: aggressive fluid administration, vasopressor therapy, hemodynamic monitoring, means to measure central venous oxygenation and pulmonary capillary wedge pressure through a Swan-Ganz catheter, if indicated 
  • Intraosseous device: for rapid central venous access in critically ill patients
  • Arterial line: 
    • For continuous monitoring of arterial pressure 
    • For continuous monitoring of oxygen tension as peripheral oximetry may be unreliable during hypoperfusion
    • For repeated measurements of acid-base status and lactate
  •  Urinary catheter placement: for hemodynamic monitoring through hourly urinary output

Volume resuscitation

  • Close monitoring of volume status with frequent adjustment of therapy as necessary
  • Intravenous fluids (mainly crystalloids): most patients with undifferentiated shock 
    • All patients with hypovolemic and distributive shock (e.g., 30 mL/kg in septic shock)
    • Some patients with cardiogenic shock (e.g., acute right ventricular infarction)
  • Blood products:
    • Packed RBCs: hypovolemic shock and ongoing hemorrhage 
    • Fresh frozen plasma (FFP) and platelets:
      • Massive transfusions
      • Coagulopathy
  • Non-invasive monitoring methods indicating a volume-responsive state:
    • Passive leg raise: significant change in pulse pressure or CO (not blood pressure!) after administering a fluid bolus and repositioning the patient from a recumbent position with a 45-degree head elevation to Trendelenburg with a 45-degree leg elevation 
    • Significant variation of pulse pressure or SV during the respiratory cycle in an intubated patient
    • Echocardiography: reduced IVC diameter and IVC collapse, serial LV function assessment
  • Invasive methods such as Swan-Ganz catheter for PCWP: no longer recommended for routine monitoring of volume status in shock because hemodynamic assessment can generally be made non-invasively
Dynamic monitoring (CO or SV)

Passive leg raise. CO, cardiac output; SV, stroke volume.

Image by Lecturio.

Pharmacologic treatment

  • Vasopressor and inotropic therapy:
    • If hypotension remains despite restoration of intravascular volume with fluids
    • Distributive shock (most commonly septic): norepinephrine (1st line), vasopressin (2nd line)
    • Cardiogenic shock: dobutamine 
    • Mixed distributive and cardiogenic shock: norepinephrine + dobutamine
  • Antibiotics:
    • Obtain blood cultures.
    • Administer antibiotics within the 1st hour after diagnosis of shock. 
    • Discontinue antibiotics if sepsis is excluded.
  • Specific therapies:
    • Distributive shock due to anaphylaxis: 
      • Removal of allergen
      • Epinephrine
      • IV fluids and vasopressors
    • Distributive shock due to adrenal insufficiency: high-dose steroids
    • Cardiogenic shock due to myocardial infarction: revascularization
    • Cardiogenic shock due to arrhythmias: advanced cardiac life support including cardioversion and placement of temporary pacemakers
    • Hypovolemic shock due to GI bleeding: endoscopic and/or surgical intervention  
    • Obstructive shock due to tension pneumothorax: immediate decompression with placement of a chest tube
    • Obstructive shock due to massive pulmonary embolism: thrombolytic therapy or surgical removal of clot
    • Obstructive shock due to pericardial tamponade: pericardial window

References

  1. Kasper DL, Fausi AS, Hauser SL, Longo DL, Lameson JL, Loscalzo J. Harrison’s Principles of Internal Medicine. New York, NY: McGraw-Hill Education; 2018.
  2. Gaieski DF, Mikkelsen ME. Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock. In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2020.

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