Surgical Critical Care: Shock

Shock

Definition

  • Shock: Cellular/Tissue Hypoxia from Reduced Oxygen Delivery, Increased Oxygen Consumption or Inadequate Oxygen Utilization
  • Generally Caused by Circulatory Failure with Hypotension
    • Can Present with Hypertension in Certain Cases

4 Classifications of Shock

  • Distributive Shock – Severe Peripheral Vasodilation (50% – Most Common Cause)
    • Septic Shock
    • Systemic Inflammatory Response Syndrome (SIRS)
    • Neurogenic Shock
    • Anaphylactic Shock
    • Endocrine Shock (Addisonian/Adrenal Crisis)
    • Drug/Toxin-Induced Shock
  • Cardiogenic Shock – Cardiac Etiology Causing Reduced Cardiac Output (14%)
  • Hypovolemic Shock – From Reduced Intravascular Volume (31%)
    • Hemorrhagic Shock
    • Non-Hemorrhagic Hypovolemic Shock
  • Obstructive Shock – Extra-Cardiac Etiology of Cardiac Pump Failure (1%)

Mortality

  • Distributive Shock: 20-50%
    • Septic Shock: 40-50%
    • Neurogenic Shock: 13-23%
    • Endocrine Shock (Addisonian/Adrenal Crisis): 6%
  • Cardiogenic Shock: 50-75% (Highest Risk)
  • Hypovolemic Shock: 20-37%

Hemodynamic Changes & Differentiation

  Preload
(PCWP)		 Contractility
(CO/CI)		 Afterload
(SVR)		 SvO2 VC
Distributive Shock ↓ ↑1 ↓ – –
Septic ↓ ↑ ↓ ↓/↑2 ↑
Neurogenic ↓ ↓ ↓ ↓ –
Cardiogenic Shock ↑↑3 ↓ ↑ ↓ –
Hypovolemic Shock ↓ ↓ ↑ ↓ ↓
Obstructive Shock ↓4 ↓ ↑ ↓ –
    • 1: Distributive Shock Generally Causes Increased CO/CI Except in Neurogenic Shock Where it is Decreased
    • 2: Septic Shock Caused Decreased SvO2 Early Due to Increased Oxygen Consumption & Then Increased SvO2 Later Due to Decreased End-Oxygen Utilization (Not Impaired Perfusion)
    • 3: Cardiogenic Shock Due to Right Ventricular Failure Causes Decreased PCWP
    • 4: Obstructive Shock Due to Pericardial Tamponade Causes Paradoxically Increased PCWP Due to External Compression Despite Decreased Left-Sided Preload

Distributive Shock

Causes of Distributive Shock

  • Septic Shock
  • Neurogenic Shock
  • Anaphylactic Shock
  • Endocrine Shock (Addisonian/Adrenal Crisis)
  • Drug/Toxin-Induced Shock

Septic Shock

Systemic Inflammatory Response Syndrome (SIRS) Induced Shock

Neurogenic Shock

  • Definition: Shock Caused by a Loss of Sympathetic Tone from Severe TBI or Spinal Cord Injury
    • Seen in Spinal Injuries Above the T6 Level
  • Incidence:
    • Cervical Spine Injury: 19.3%
    • Thoracic Spine Injury: 7%
  • Presentation:
    • Hypotension
    • Bradycardia
    • Extremities Remain Warm from Vasodilation
    • Flushed Skin
    • May See Priapism from Vasodilation
  • Treatment: IV Fluids (#1) & Vasopressors
    • Vasopressor Choice:
      • Norepinephrine (Preferred)
      • Phenylephrine – May Cause Reflex Bradycardia
    • Goal MAP > 85 for 5-7 Days – Little Actual Data to Support

Anaphylactic Shock

  • Definition: Shock from a Severe Allergic Reaction
  • Mediated by IgE with a Massive Histamine-Mediated Vasodilation
  • Most Common Cause:
    • Children: Foods
    • Adults: Insect Venom (Wasps & Bees)
  • Treatment: Epinephrine (Most Important) & IV Fluids
    • Epinephrine Dose: IM 0.3-0.5 mg of 1 mg/mL (1:1,000)
      • Repeat Every 5-15 Minutes
    • Possible Adjuncts:
      • Antihistamines (Diphenhydramine)
      • Corticosteroids
      • Albuterol for Bronchospasms

Endocrine Shock (Addisonian/Adrenal Crisis)

Drug/Toxin-Induced Shock

  • Definition: Shock Drugs or Toxins
  • Causes:
    • Drug Overdoses
    • Transfusion Reactions
    • Bites (Snakes, Spiders & Insects)
    • Heavy-Metal Poisoning (Iron & Arsenic)
    • Cyanide

Cardiogenic Shock

Causes of Cardiogenic Shock

  • Cardiomyopathy
    • Myocardial Infarction (Most Common Cause)
    • Severe CHF Exacerbation
    • Myocardial Confusion
    • Myocarditis
    • Advanced Septic Shock
    • Drug-Induced
  • Arrhythmia
  • Mechanical
    • Valve Pathology (Insufficiency, Rupture or Stenosis)
    • Atrial Myxoma

Treatment

  • Primary Treatment: Vasopressors
    • Vasopressor Choice:
      • Norepinephrine (Preferred)
      • Dobutamine (*Historically the Agent of Choice but Newer Evidence Shows Increased Risk of Arrhythmia & Trend to Increased Mortality)
  • Avoid Aggressive IV Fluid Resuscitation – Can Cause Pulmonary Edema
    • May Require an Initial IV Fluid Bolus to Maintain Preload
  • Myocardial Infarction Specifics:
    • Emergent Percutaneous Coronary Intervention (PCI) or Coronary Artery Bypass Graft (CABG)
    • Fibrinolytic Therapy if Unable to Undergo PCI/CABG
  • Mechanical Circulatory Support:

Hypovolemic Shock

Causes of Hypovolemic Shock

  • Hemorrhagic Shock
    • Trauma
    • GI Bleeding
    • Vascular Rupture (AAA)
    • Obstetric Hemorrhage
  • Non-Hemorrhagic Hypovolemic Shock
    • Dehydration
    • GI Loss (Vomiting, Diarrhea or External Drainage)
    • Skin Loss (Burns or Heat Stroke)
    • Renal Loss (Excessive Diuresis or Salt-Wasting Nephropathy)
    • Third-Space Losses (Bowel Obstruction, Operations, Crush Injury, Cirrhosis, etc.)

Hormones in Hypovolemia

  • Early Hormones:
    • Epinephrine & Norepinephrine (Adrenergic) – Vasoconstriction, Increased Contractility & Increased Heart Rate
  • Late Hormones:
    • Renin (Kidney) – RAAS Vasoconstriction & Water Resorption
    • ACTH (Pituitary) – Increases Cortisol
    • ADH (Pituitary) – Water Resorption

Fluid Responsiveness

  • Definition: Assessment if Blood Pressure Will Respond to an IV Fluid Bolus
  • Assessment:
    • Fluid Challenge
      • Test: Patient Given a 500 cc Bolus of Fluid as Fast as Possible (Around 10 Minutes)
    • Passive Leg Raise
      • The Most Well Validated Test of Fluid Responsiveness
      • Test: Patient Placed Supine & Legs Passively Raised to 45 Degrees
        • Quickly Returns a Reservoir of Venous Blood into Central Circulation in 30-90 Seconds
    • Positive Results: 10% Increase in Cardiac Output or Stroke Volume
      • Surrogate Measure without a Pulmonary Artery Catheter: 10% Increase in Pulse Pressure on Arterial-Line
  • Stroke Volume Variation (SVV)
    • SVV (%) = (Maximum SV – Minimum SV) / Average SV
    • Measured Using a FloTrac/Vigileo System
    • Normal Values: 10-13%
      • < 10% Unlikely to Be Volume Responsive
      • > 13-15% Likely to Be Volume Responsive
    • Accurately Measured Only if on Controlled Mechanical Ventilation & In Normal Sinus Rhythm
      • Use Contraindicated if Having Arrhythmias or Spontaneous Ventilation (Irregular Nature of Spontaneous Breaths Causes Variation)
  • Poor Discriminators Not to be Used:
    • Central Venous Pressure (CVP) Measurement
    • Mean Arterial Pressure (MAP) Alone
    • Chest X-Ray
    • IVC Diameter

Hemorrhagic Shock

Non-Hemorrhagic Hypovolemic Shock

  • First Vital Sign Changes:
    • Increased Diastolic Blood Pressure
    • Narrowed Pulse Pressure
  • Physical Exam Findings:
    • Dry Mucous Membranes
    • Decreased Skin Turgor
    • Low Jugular Venous Pressure
  • Treatment: IV Fluids
    • Crystalloids Preferred Over Colloids if Not Due to Hemorrhage
    • Most Accurate Sign of Adequate Fluid Resuscitation: Urine Output

Obstructive Shock

Causes of Obstructive Shock

  • Pulmonary Vascular Obstruction – Right Heart Fails to Create Enough Pressure to Overcome Elevated Pulmonary Vascular Resistance
    • Pulmonary Embolism
    • Pulmonary Hypertension
    • Venous Air Embolism
    • High-PEEP Ventilation
  • Mechanical Obstruction – Decreased Venous Return to Right Heart or Right Ventricular Filling
    • Tension Pneumothorax
    • Tension Hemothorax
    • Pericardial Tamponade
    • Abdominal Compartment Syndrome

Treatment

  • Primary Treatment: Correction of Underlying Cause