Shock, Undifferentiated Shock, Targets of Adequate Perfusion In Fluid Replacement, Fluid Responsiveness Markers, Hypovolemic Shock, Hypovolemia, Dehydration, Distributive Shock

  • Definitions
  1. Shock
    1. Impaired tissue oxygenation and perfusion
    2. Imbalance in delivery and consumption of oxygen and metabolic substrates
    3. Numerous causes and mechanisms, but 4 general types: Hypovolemic, Distributive, Cardiogenic, Obstructive
  • Pathophysiology
  • Shock
  1. Circulatory insufficiency resulting in inadequate oxygen supply for given demand
  2. Triggers a cascading metabolic spiral culminating in cell injury and cell death
    1. Intracellular Calcium overload
      1. Free radical oxidative damage
      2. Impaired mitochondrial ATP synthesis
      3. Impaired Muscle relaxation and myocardial contractility
    2. Metabolic Acidosis
      1. Results from anaerobic metabolism, Lactic Acidosis, and Renal Failure
      2. Increases Calcium overload
      3. Decreases myocardial and other Muscle contractility
      4. Decreased Catecholamine response
      5. Increased Interstitial Edema
    3. Pro-inflammatory Cytokines (e.g. Interleukins, Tumor Necrosis Factor)
      1. Limited to specific shock types (e.g. Septic Shock, Anaphylaxis)
      2. Systemic vasodilation secondary to endothelial cell activation and nitric oxide release
  3. Compensatory mechanisms (Blood Pressure may be normal when compensation is adequate)
    1. Cardiac Output increase
      1. Responds to Catecholamine and Cortisol release
    2. Arterial Vasoconstriction
      1. Selective shunting of Blood Flow from the skin, skeletal Muscle, Kidney and Gastrointestinal Tract
    3. Venous constriction
      1. Increases Preload and return of blood to heart and brain
    4. Increased Sodium and water reabsorption
      1. Antidiuretic Hormone
      2. Renin-Angiotensin System
  4. Failed compensation
    1. Metabolic Acidosis
    2. Coagulopathy (including Disseminated Intravascular Coagulation)
    3. Inflammatory mediator release
    4. Multiorgan dysfunction and death
    5. Hypotension
  • Types
  1. Precautions: Undifferentiated Shock
    1. Many shock presentations are combinations of more than one shock type
    2. Septic Shock is primarily Distributive Shock, but also associated with third spacing and Hypovolemic Shock
    3. A massive tension pneumo-Hemothorax may cause both obstructive shock and Hypovolemic Shock
  2. Hypovolemic Shock
    1. Defined as intravascular fluid volume that is insufficient for adequate end-organ perfusion
    2. Hemorrhagic Shock (acute blood loss)
      1. Examples: Trauma (most common), Ruptured Abdominal Aortic Aneurysm, GI Bleed
    3. Dehydration
      1. Examples: Acute Gastroenteritis with Vomiting, Diarrhea, Diabetic Ketoacidosis
    4. Third-Spacing
      1. Examples: Burn Injury, Pancreatitis
  3. Distributive Shock
    1. Defined as systemic vasodilation that renders an otherwise sufficient circulating volume to be inadequate
      1. Hemodynamic parameters are paradoxically opposite other forms of shock
      2. SVR decreases (primary) and Cardiac Output, Pulse Pressure, SvO2 and ScvO2 increases
    2. Adrenal crisis
      1. Fever may be present (as in Septic Shock)
    3. Septic Shock
      1. Systemic inflammatory response with diffuse, peripheral vasodilation and decreased Cardiac Output
    4. Neurogenic Shock (esp. cervical and upper thoracic Spinal Cord Injury above T6)
      1. Loss of sympathetic nervous function
      2. Results in decreased vascular tone, Hypotension with paradoxical Bradycardia
      3. Neurogenic Shock does not cause a narrowed Pulse Pressure (sympathetic reflex)
      4. Contrast with Spinal Shock (below T6 Level), which results in Flaccid Paralysis below the lesion
    5. Anaphylaxis
      1. Mast Cell degranulation
      2. Cytokine-induced vasodilation
  4. Cardiogenic Shock
    1. Defined as cardiac pump failure (decreased Cardiac Index <1.8, increased left heart filling pressures)
    2. Congestive Heart Failure
    3. Cardiomyopathy (e.g. Viral Myocarditis, cardiotoxic agents)
    4. Trauma (e.g. Cardiac Contusion)
    5. Supraventricular Tachycardia or other Arrhythmias
    6. Structural heart defects (e.g. valvular rupture, left to right shunt)
  5. Obstructive Shock
    1. Defined as heart or Great Vessel obstruction to flow with decreased Preload or increased Afterload
    2. Tension Pneumothorax
    3. Pericardial Tamponade
    4. Massive Pulmonary Embolism (increased RV Afterload, RV bowing limits LV filling)
  • Causes (Mnemonic
  1. Septic Shock
  2. Hypovolemic Shock (e.g. Hemorrhagic Shock, severe Dehydration)
  3. Respiratory Compromise (e.g. Tension Pneumothorax, massive Pulmonary Embolism)
  4. Ingestion (toxin, Overdose)
  5. Metabolic (e.g. DKA, Adrenal Insufficiency, Hypothyroidism)
  6. Psychiatric (Water Intoxication)
  7. Cardiogenic Shock (MI, CHF, Cardiac Tamponade)
  8. Anaphylactic shock
  9. Neurogenic Shock (e.g. Spinal Shock)
  10. (2016) CALS Manual
  • History
  1. Medications and toxins
    1. Antiarrhythmics
    2. Anticoagulants
    3. Antihypertensives
    4. Diuretics
    5. Drugs of Abuse
    6. Poisons (Pesticides, Toxic Alcohols, Cyanide exposure)
  2. Hypovolemia sources
    1. Ectopic Pregnancy
    2. Gastrointestinal losses
      1. Severe Diarrhea
      2. Vomiting
      3. Decreased oral intake
    3. Gastrointestinal Bleeding
      1. Melana
      2. Hematochezia
      3. Hematemesis
  3. Distributive causes (especially Septic Shock)
    1. Fever, chills, sweats or myalgias
    2. Infectious sources
      1. Cough or other respiratory symptoms
      2. Headache, neck stiffness or acute neurologic changes
      3. Focal Abdominal Pain (e.g. Acute Cholecystitis, Appendicitis, Diverticulitis)
      4. Urinary symptoms (e.g. Dysuria, urgency, frequency, Flank Pain)
      5. New rashes (e.g. Cellulitis)
    3. Predisposing factors
      1. Indwelling Urinary Catheter
      2. Indwelling lines (e.g. PICC Line)
      3. Retained Foreign Body (e.g. retained tampon)
      4. Recent procedures or surgeries
      5. Immunocompromised state
  4. Cardiogenic causes
    1. Chest Pain
    2. Shortness of Breath on exertion (e.g. decreased walk distance)
    3. Orthopnea or paroxysmal nocturnal Dyspnea
    4. Volume overload (recent increased weight)
  5. Obstructive causes
    1. Venous Thromboembolism Risks
    2. Recent Trauma
  • Signs
  1. Altered Mental Status (lethargy, coma)
  2. Dry mucous membranes
  3. Decreased skin turgur
  4. Pallor
  5. Delayed Capillary Refill
  1. See Primary Survey
  2. See Secondary Survey
  3. General Findings
    1. Diaphoresis
    2. Pallor
    3. Fever
  4. Head and neck findings
    1. Conjunctival pallor (Anemia)
    2. Dry mucous membranes
    3. Flat nondistended Jugular Veins
      1. Exception: Distented jugular neck veins in obstructive shock (e.g. Tension Pneumothorax)
  5. Respiratory findings
    1. Tachypnea
      1. Respiratory compensation for Metabolic Acidosis (e.g. Lactic Acidosis, Ketoacidosis) or
      2. Primary respiratory etiology (e.g. Pneumonia, Pneumothorax, Pulmonary Embolism)
    2. Kussmaul Respirations (deep sighing respirations)
      1. Examples: DKA, Hemorrhage, peritonitis, Uremia
    3. Asymmetric lung sounds
      1. Examples: Pneumothorax, Pneumonia
  6. Cardiovascular findings
    1. New cardiac murmur
    2. Pulsus Paradoxus
    3. Peripheral Edema (unilateral or bilateral)
    4. Decreased Capillary Refill
    5. Peripheral pulses (symmetry)
    6. Cold clammy extremities (peripheral vasconstriction)
      1. Exception: Warm extremities with vasodilation in Distributive Shock
  7. Abdominal findings
    1. Peritoneal signs
    2. Pregnancy
    3. Ascites
    4. Ecchymosis
      1. Seat Belt Sign
      2. Flank or periumbilical Ecchymosis (intra-abdominal Hemorrhage)
  8. Neurologic findings
    1. See Glasgow Coma Scale
    2. Altered Mental Status
    3. From Disorientation to coma
    4. Extremity weakness
  1. See Toxin Induced Vital Sign Changes
  2. Heart Rate
    1. Compensatory Sinus Tachycardia
      1. Expected response to shock but inconsistently present
    2. Paradoxical absolute or Relative Bradycardia
      1. May be seen in severe shock with decreased Cardiac Output
    3. Arrhythmias
      1. Primary Tachycardia or profound Bradycardia with secondary Cardiogenic Shock
  3. Blood Pressure
    1. Hypotension is a late response to shock
      1. In young children, Hypotension is even more ominous, with little warning to cardiovascular collapse
      2. Not uniformly present (do not rely on Blood Pressure alone to diagnose shock)
  4. Pulse Oximetry (Oxygen Saturation)
    1. Hypoxemia
    2. Hypoventilation
  5. Temperature
    1. Hypothermia or Hyperthermia
    2. Abnormal Temperature (high or low) may suggest SIRS Response
    3. Heat Illness or Accidental Hypothermia may also cause Hypotension or shock state
  6. Fingerstick Glucose (bedside Glucose)
    1. Severe Hyperglycemia
      1. Diabetic Ketoacidosis
      2. Hyperosmolar Hyperglycemic State
    2. Hypoglycemia
      1. May suggest overwhelming infection or Adrenal Insufficiency
  7. Other bedside evaluation of shock
    1. Passive Leg Raise Maneuver (predicts response to 300 ml fluid bolus)
      1. Indicative of fluid-responsiveness if Blood Pressure increases or Heart Rate decreases with leg raise
    2. Shock Index
      1. Shock Index = (Heart Rate) / (Systolic Blood Pressure)
      2. Mild Shock: 0.6 to 1
      3. Moderate Shock: 1 to 1.4
      4. Severe Shock: >1.4
  • Labs (as indicated, as markers of hypoperfusion and differential diagnosis)
  1. Bedside
    1. Fingerstick Glucose (bedside Glucose)
  2. Miscellaneous initial labs
    1. Complete Blood Count
    2. Comprehensive metabolic panel
    3. Coagulation tests (INR, PTT)
    4. Venous Blood Gas
    5. Blood Type and Cross Match
  3. Urine tests
    1. Urinalysis and Urine Culture
    2. Urine Pregnancy Test
    3. Urine toxicology
  4. Cardiac Markers
    1. Serum Troponin
    2. Brain Natriuretic Peptide (BNP)
  5. Infection suspected
    1. Serum Lactic Acid (associated with Metabolic Acidosis with Anion Gap)
    2. Blood Cultures
  6. Endocrine labs
    1. Thyroid Stimulating Hormone (TSH)
    2. Serum Cortisol
  • Diagnostics
  1. Electrocardiogram
    1. See EKG in Myocardial Ischemia
    2. See EKG in Pulmonary Embolism
    3. See EKG monitoring in Trauma
    4. See QRS Widening
    5. See Prolonged QT
  2. Noninvasive monitoring (optional, but no proven protocols as of 2015)
    1. End-Tidal CO2 Monitoring
    2. Infrared spectroscopy
  3. Invasive monitoring (central catheter)
    1. Central oxygen
      1. Has been part of surviving Sepsis guidelines
        1. However as of 2015, Lactic Acid may be equivalent and without invasive monitoring
      2. Greater tissue Oxygen Consumption indicated with SvO2 < 65% or ScvO2 <68%
        1. Normal SvO2 or ScvO2 does not exclude hypoperfusion
        2. Mixed venous Oxygen Saturation (SvO2) goal >65%
        3. Central Venous Oxygen Saturation (ScvO2) goal >68%
    2. Central Venous Pressure
      1. Falling out of favor as of 2012
      2. Serial Inferior Vena Cava Ultrasound for Volume Status may be as effective without invasive testing
  • Precautions
  1. Initial shock findings may be subtle (e.g. mild confusion and Sinus Tachycardia)
    1. Initial systolic Blood Pressure may be normal (in compensated shock)
  • Management
  • Approach
  1. See ABC Management
  2. Treatment per specific causes as above
    1. See Trauma Evaluation
    2. See Hemorrhagic Shock
    3. See Septic Shock
    4. See Cardiogenic Shock
  3. Two large bore IVs (18 gauge or larger)
    1. Intraosseous Access if IV Access is unavailable
  4. Fluid Replacement
    1. Crystalloid (LR or NS)
    2. Packed Red Blood Cell Transfusion as indicated (replace blood loss with blood)
  5. Fluid Responsiveness Markers
    1. See targets of adequate perfusion as listed below
    2. Assess Stroke Volume, cardiac ouput or surrogates before and after fluid challenge
      1. Administer 250-500 cc IV crystalloid challenge (over 10 minutes)
      2. Expect increased Stroke Volume >10-15% after fluid challenge
        1. See Stroke Volume Estimation by Bedside Ultrasound (Velocity-Time Integral)
      3. Consider Vasopressors if poor response after the first liter (2L in Septic Shock)
    3. IVC Ultrasound for Volume Status
      1. Serial measurements may serve as guide to adequate fluid Resuscitation
    4. Other Bedside Ultrasound Markers
      1. Hyperdynamic left heart and empty left ventricle also indicates additional fluids
      2. Continually reassess for excessive fluid Resuscitation (B Line Artifacts, engorged IVC)
    5. Passive Leg Raise Maneuver
      1. Elevation of both legs above the heart
      2. Provides a transient autologous fluid bolus of 300-400 cc
  6. Vasopressors (refractory severe Hypotension)
    1. Step 1: Norepinephrine
    2. Step 2: Vasopressin
    3. Step 3: Consider Epinephrine for inotropic or chronotropic support
    4. Step 4: Consider Angiotensin II
      1. Weingart (2018) EM:Rap 18(6): 3
      2. Khanna (2017) N Engl J Med 377(5):419-30 [PubMed]
  7. Respiratory support as needed
    1. See Noninvasive Ventilation
    2. See Advanced Airway
    3. See Rapid Sequence Intubation
      1. Ketamine may be a preferred induction agent in Hypotension
    4. Time intubation based on expectation of improvement with initial Resuscitation
      1. May resuscitate first and reassess if expect initial improvement in first 15 minutes
      2. Intubate if response to Resuscitation is expected to be delayed
    5. Choose short-acting post-intubation Sedatives and Analgesics
      1. Avoid Benzodiazepines
      2. Preferred Sedative: Dexmetetomidine
      3. Preferred Analgesic: Fentanyl
  8. Empiric Therapy
    1. See Septic Shock
      1. Empiric antibiotic selection based on suspected source
    2. Treat Hemorrhagic Shock
      1. Blood Products and emergent surgical intervention
      2. Even a 2 gram decrease in Hemoglobin From 9 to 7, decreases Oxygen Delivery by 30%
        1. Contrast with the minimal effect of oxygenation above PaO2 60-70 mmHg
    3. Consider empiric Adrenal Insufficiency management
      1. See Stress Dose Steroid
      2. See Adrenal Insufficiency
      3. Hydrocortisone or Dexamethasone
    4. Consider cardiopulmonary causes with emergent interventions as indicated
      1. Acute Coronary Syndrome
      2. Massive Pulmonary Embolism
      3. Aortic Dissection (or other vascular catastrophe)
      4. Cardiac Tamponade
      5. Cardiogenic Shock
  • Management
  • Targets of Adequate Perfusion
  1. Exam markers
    1. Improved mentation
    2. Improved Capillary Refill (and decreased skin mottling)
    3. No findings of Fluid Overload (increased JVD, lung rales, Hypoxia)
  2. Lab, diagnostics and Vital Sign markers
    1. Mean arterial pressure (MAP): >65 mmHg (>50 mmHg may be preferred in Trauma)
    2. Urine Output: >0.5 ml/kg/h (>1 ml/kg/h in children, >2 ml/kg/h in infants)
      1. Unreliable in Acute Kidney Injury
      2. Delayed response from time of fluid delivery to Urine Output response (risk of Fluid Overload)
      3. Consider monitoring with indwelling Urinary Catheter
    3. Serum Lactate Clearance (10% serum lactate reduction over 2 hours)
      1. Correlates with Central Venous Oxygen Saturation (ScvO2)
    4. IVC Ultrasound for Volume Status
      1. IVC collapses >50% on inspiration and is 1.5 to 2.5 cm in diameter
  3. Invasive markers
    1. Central Venous Pressure (CVP): 8-12 mmHg
      1. Falling out of favor, although still a part of 2012 surviving Sepsis guideline
      2. High CVP target is associated with Fluid Overload risk
    2. Central Venous Oxygen Saturation (ScvO2)
      1. Falling out of favor, although still a part of 2012 surviving Sepsis guideline
      2. No survival benefit in ProCESS, ARISE and ProMISE trials as target in Sepsis
  1. Avoid over-compensating in Fluid Replacement (Positive Fluid Balance, hypervolemia, Fluid Overload)
  2. Adverse effects of Positive Fluid Balance
    1. Delirium
    2. Diastolic Dysfunction
    3. Cardiac conduction abnormalities
    4. Increased respiratory effort
    5. Decreased GFR
    6. Sodium retention
    7. Malabsorption
    8. Ileus
    9. Decreased Wound Healing
    10. Pressure Ulcers
  3. References
    1. Avila (2014) J Brasil Nefrol 36(3): 379-88 [PubMed]
  • References
  1. DeBlieux in Herbert (2016) EM:Rap 16(5):8-9
  2. Loflin (2015) Crit Dec Emerg Med 29(9): 11-18
  3. Goldberg (2015) Crit Dec Emerg Med 29(3): 9-19