📋 Definition & Pathophysiology
Definition
Distributive shock is characterized by severe peripheral vasodilation and maldistribution of blood flow, leading to inadequate tissue perfusion despite normal or increased cardiac output. It represents a state of relative hypovolemia where the vascular space expands beyond the circulating blood volume's capacity to fill it.
Core Pathophysiology
The Distributive Cascade:
- Vasodilatory Trigger: Infection, allergen, or neurologic injury
- Inflammatory Response: Release of inflammatory mediators (cytokines, histamine, bradykinin, nitric oxide)
- Profound Vasodilation: Loss of vascular tone in arterioles and venules
- Relative Hypovolemia: Expanded vascular space > circulating volume
- Maldistribution of Blood Flow: Arteriovenous shunting bypasses capillary beds
- Decreased SVR: Systemic vascular resistance drops dramatically
- Tissue Hypoperfusion: Despite normal/high cardiac output, oxygen delivery to tissues is inadequate
- Cellular Dysfunction: Mitochondrial dysfunction, impaired oxygen extraction, lactic acidosis
- Multi-Organ Dysfunction: Progressive organ failure if untreated
Hemodynamic Profile
| Parameter | Distributive Shock | Hypovolemic Shock | Cardiogenic Shock |
|---|---|---|---|
| Cardiac Output | ↑ or Normal | ↓ | ↓ |
| SVR | ↓↓ (Low) | ↑ (High) | ↑ (High) |
| PCWP/CVP | ↓ or Normal | ↓ | ↑ |
| Skin | Warm (early) or Cool (late) | Cool, clammy | Cool, mottled |
| Blood Pressure | ↓ (Wide pulse pressure) | ↓ (Narrow pulse pressure) | ↓ |
Types of Distributive Shock
🦠 Septic Shock
Most Common (60% of all shock)
- Cause: Overwhelming infection with systemic inflammatory response
- Mortality: 30-50%
- Key Feature: Infection + vasodilation + organ dysfunction
- Mediators: Cytokines (IL-1, IL-6, TNF-α), nitric oxide, endotoxins
⚡ Anaphylactic Shock
IgE-Mediated Type I Hypersensitivity
- Cause: Severe allergic reaction to allergen
- Onset: Minutes to hours after exposure
- Key Feature: Rapid onset, airway compromise, urticaria
- Mediators: Histamine, tryptase, leukotrienes
🧠 Neurogenic Shock
Loss of Sympathetic Tone
- Cause: Spinal cord injury (typically above T6)
- Key Feature: Hypotension + bradycardia (loss of sympathetic outflow)
- Classic Triad: Hypotension, bradycardia, warm/dry skin
- Onset: Immediate after spinal injury
💊 Other Causes
- Adrenal Crisis: Cortisol deficiency → vasodilation
- Drug-Induced: ACE inhibitors, calcium channel blockers, narcotics
- Toxic Shock Syndrome: Staph/Strep exotoxins
- Pancreatitis: Severe inflammatory response
💎 Clinical Pearls
- "Warm shock" vs "Cold shock": Early distributive shock may present with warm extremities due to vasodilation. Late/decompensated shock presents with cool extremities as cardiac output eventually fails
- Wide pulse pressure: Decreased diastolic BP with relatively preserved systolic BP creates wide pulse pressure (>40-50 mmHg)
- Bounding pulses: Initially due to high cardiac output and low SVR
- Flash pulmonary edema: Aggressive fluid resuscitation can precipitate pulmonary edema despite low filling pressures due to capillary leak
- Lactic acidosis despite normal BP: Microcirculatory dysfunction causes tissue hypoxia even with adequate macrocirculation
🔬 Clinical Presentation
Common Features Across All Types
| System | Early Findings | Late Findings |
|---|---|---|
| Cardiovascular | Tachycardia, bounding pulses, warm extremities, wide pulse pressure | Persistent hypotension, weak pulses, cool extremities, arrhythmias |
| Neurological | Anxiety, agitation, confusion | Altered mental status, obtundation, coma |
| Respiratory | Tachypnea, increased work of breathing | Respiratory failure, ARDS |
| Renal | Decreased urine output | Oliguria/anuria, acute kidney injury |
| GI | Nausea, ileus | GI bleeding, liver dysfunction |
| Skin | Warm, flushed (early) | Cool, mottled, cyanotic (late) |
Distinguishing Features by Type
| Feature | Septic | Anaphylactic | Neurogenic |
|---|---|---|---|
| Onset | Hours to days | Minutes to hours | Immediate |
| Heart Rate | Tachycardia | Tachycardia (initially) | Bradycardia (key finding) |
| Temperature | Fever or hypothermia | Normal | Poikilothermia (varies with environment) |
| Skin | Warm/flushed or mottled | Urticaria, angioedema, flushing | Warm, dry below injury level |
| Respiratory | Tachypnea, possible ARDS | Bronchospasm, stridor, airway edema | Variable (depends on injury level) |
| Key Diagnostic | Infection source, positive cultures | Recent allergen exposure, elevated tryptase | Spinal cord injury on imaging |
🦠 Septic Shock - Comprehensive Management
Definitions (Sepsis-3 Criteria, 2016)
| Term | Definition | Clinical Criteria |
|---|---|---|
| Sepsis | Life-threatening organ dysfunction caused by dysregulated host response to infection | Suspected/confirmed infection + SOFA score ≥2 |
| Septic Shock | Subset of sepsis with circulatory/cellular/metabolic dysfunction | Sepsis + Vasopressors needed to maintain MAP ≥65 mmHg + Lactate >2 mmol/L DESPITE adequate fluid resuscitation |
Quick SOFA (qSOFA) - Bedside Tool
≥2 points = High risk for poor outcomes, consider sepsis
- Respiratory rate ≥22/min (1 point)
- Altered mental status (GCS <15) (1 point)
- Systolic BP ≤100 mmHg (1 point)
Surviving Sepsis Campaign Bundle (2021)
Hour-1 Bundle (ALL within 1 hour of recognition)
Measure Lactate Level
• Obtain serum lactate immediately
• Lactate >2 mmol/L = tissue hypoperfusion
• Lactate >4 mmol/L = severe shock, poor prognosis
• Remeasure q2-4h to assess clearance
Obtain Blood Cultures BEFORE Antibiotics
• Draw 2 sets from different sites (aerobic + anaerobic)
• Include at least 1 peripheral and 1 from each vascular access device if present
• Do NOT delay antibiotics >45 minutes for cultures
• Also obtain: urine culture, sputum culture, wound cultures as appropriate
Administer Broad-Spectrum Antibiotics
• Give within 1 hour of septic shock recognition
• Broad coverage: cover Gram-positive, Gram-negative, anaerobes
• Consider MRSA, Pseudomonas coverage based on local patterns
• Adjust based on source (pneumonia, UTI, intra-abdominal, etc.)
• De-escalate once cultures and sensitivities return
Begin Rapid Fluid Resuscitation
• 30 mL/kg crystalloid bolus for hypotension or lactate ≥4 mmol/L
• Use balanced crystalloids (LR or Plasma-Lyte preferred over NS)
• Administer rapidly over 2-3 hours
• Reassess hemodynamics after each bolus
• Use dynamic measures to guide further fluids (see below)
Start Vasopressors if Hypotensive
• If MAP <65 mmHg DURING or AFTER initial fluid resuscitation
• Norepinephrine first-line (α and β agonist)
• Target MAP ≥65 mmHg
• Central line preferred but peripheral OK initially
• Consider second agent if NE >0.5 mcg/kg/min
Source Control
- Identify and control source within 6-12 hours:
- Drain abscesses
- Debride necrotizing soft tissue infections
- Remove infected devices/foreign bodies
- Cholecystectomy for cholecystitis
- Operative intervention for perforated viscus
- Do NOT delay for marginal improvement in patient status
- Choose least invasive method that achieves adequate source control
Fluid Resuscitation Strategy
| Phase | Goal | Strategy |
|---|---|---|
| Initial (0-6 hrs) | Restore intravascular volume | 30 mL/kg crystalloid bolus. Reassess with dynamic measures. Additional boluses as needed |
| Optimization (6-24 hrs) | Achieve resuscitation endpoints | Guided by lactate clearance, MAP, UOP, ScvO₂. Conservative fluid approach once stabilized |
| De-escalation (24+ hrs) | Mobilize fluid, achieve negative balance | Stop maintenance fluids, consider diuretics if volume overloaded |
Resuscitation Endpoints
| Parameter | Target |
|---|---|
| MAP | ≥65 mmHg (may need higher in chronic HTN) |
| Lactate Clearance | ≥10-20% per 2-4 hours, normalize to <2 mmol/L |
| Urine Output | ≥0.5 mL/kg/hr |
| ScvO₂ | ≥70% |
| Skin Perfusion | Warm extremities, capillary refill <3 sec |
| Mental Status | Normalized (if no other cause) |
Antibiotic Selection by Source
| Source | Likely Pathogens | Empiric Coverage |
|---|---|---|
| Pneumonia (CAP) | S. pneumoniae, H. influenzae, atypicals | Ceftriaxone + Azithromycin OR Levofloxacin |
| Pneumonia (HAP) | MRSA, Pseudomonas, resistant GNRs | Vancomycin + Piperacillin-tazobactam (or Cefepime or Meropenem) |
| Urinary Tract | E. coli, Klebsiella, Proteus, Enterococcus | Ceftriaxone OR Piperacillin-tazobactam (add Vancomycin if risk for Enterococcus) |
| Intra-Abdominal | GNRs, anaerobes (B. fragilis), Enterococcus | Piperacillin-tazobactam OR Meropenem + Vancomycin |
| Skin/Soft Tissue | S. aureus (MRSA), Streptococcus, anaerobes | Vancomycin + Piperacillin-tazobactam (for necrotizing infections) |
| Unknown Source | Broad coverage needed | Vancomycin + Piperacillin-tazobactam (or Meropenem) |
💎 Septic Shock Pearls
- Lactate clearance >10% per 2-4 hours is more important than absolute normalization
- Early goal-directed therapy (EGDT) protocols are less emphasized now; focus on clinical endpoints
- Balanced crystalloids (LR/Plasma-Lyte) preferred over normal saline (less AKI, mortality)
- Albumin has no mortality benefit and is NOT recommended routinely
- Procalcitonin can guide antibiotic duration but should not delay initiation
- Stress-dose steroids (hydrocortisone 200 mg/day) if refractory to fluids and vasopressors
⚡ Anaphylactic Shock - Emergency Management
Definition & Pathophysiology
Anaphylaxis: Severe, life-threatening, systemic hypersensitivity reaction characterized by rapid onset of airway, breathing, and/or circulation problems, usually associated with skin and mucosal changes.
Pathophysiology:
- Allergen Exposure: Re-exposure to allergen in previously sensitized individual
- IgE-Mediated Degranulation: Mast cells and basophils release mediators
- Mediator Release: Histamine, tryptase, leukotrienes, prostaglandins, PAF
- Systemic Effects:
- Vasodilation → hypotension
- Increased vascular permeability → third-spacing, relative hypovolemia
- Bronchospasm → respiratory distress
- Mucous membrane swelling → airway compromise
Clinical Criteria for Diagnosis
| Criterion | Description |
|---|---|
| 1. Acute onset (minutes to hours) with involvement of skin/mucosa PLUS at least one of: |
• Respiratory compromise (dyspnea, wheeze, stridor, hypoxemia) • Reduced BP or symptoms of end-organ dysfunction (syncope, incontinence) |
| 2. Two or more of the following after exposure to likely allergen: |
• Skin/mucosal involvement (urticaria, angioedema, flushing) • Respiratory compromise • Reduced BP or associated symptoms • Persistent GI symptoms (crampy pain, vomiting) |
| 3. Reduced BP after exposure to known allergen: |
• Infants/children: Low SBP for age or >30% decrease from baseline • Adults: SBP <90 mmHg or >30% decrease from baseline |
Common Triggers
🍽️ Foods (Most common in children)
- Peanuts, tree nuts
- Shellfish, fish
- Milk, eggs
- Wheat, soy
💉 Medications
- Antibiotics (penicillins, cephalosporins)
- NSAIDs
- Neuromuscular blocking agents
- Contrast dye
🐝 Venoms
- Bee/wasp stings
- Fire ants
- Snake bites
🧤 Other
- Latex
- Exercise (exercise-induced)
- Idiopathic
Emergency Management Algorithm
Immediate Assessment & Call for Help
• Recognize anaphylaxis immediately
• Call for help / activate emergency response
• Position patient: supine (or sitting if respiratory distress, pregnant = left lateral)
• Assess airway, breathing, circulation
Epinephrine IM - FIRST-LINE TREATMENT
Give IMMEDIATELY - Do NOT delay!
• Dose: 0.01 mg/kg (max 0.5 mg) of 1:1000 epinephrine IM
• Adults: 0.3-0.5 mg IM (0.3-0.5 mL of 1:1000)
• Children: 0.01 mg/kg IM (max 0.3 mg)
• Site: Anterolateral thigh (vastus lateralis) - fastest absorption
• Repeat q5-15 minutes if no improvement or symptoms recur
• Most patients respond to 1-2 doses
Airway Management
• High-flow oxygen 15L via NRB
• Monitor for stridor, inability to swallow, drooling
• Early intubation if: Stridor, tongue/airway swelling, respiratory distress
• Have difficult airway equipment ready
• Consider awake fiberoptic intubation if airway edema present
• Emergency cricothyrotomy if cannot intubate/ventilate
IV Access & Fluid Resuscitation
• Establish TWO large-bore IVs immediately
• Aggressive fluid resuscitation: 1-2L crystalloid bolus (20 mL/kg in children)
• May require 4-6L in first hour due to massive capillary leak
• Monitor for fluid responsiveness
Second-Line Medications
H1 Antihistamine:
• Diphenhydramine 25-50 mg IV/IM
H2 Antihistamine:
• Ranitidine 50 mg IV OR Famotidine 20 mg IV
Corticosteroids (prevent biphasic reaction):
• Methylprednisolone 125 mg IV OR Hydrocortisone 200 mg IV
Bronchodilators (if bronchospasm):
• Albuterol nebulizer 2.5-5 mg
Refractory Anaphylaxis Management
If hypotension persists despite epinephrine and fluids:
• Epinephrine infusion: 0.1-1 mcg/kg/min IV titrated to effect
• Glucagon (if on beta-blockers): 1-2 mg IV bolus, then infusion
• Vasopressin: Consider as adjunct
• Methylene blue: Last resort for refractory shock (1-2 mg/kg over 20-60 min)
- Delaying epinephrine: Epinephrine is FIRST-LINE. Give IM immediately!
- Wrong route: IM epinephrine (1:1000) in thigh, NOT IV
- Inadequate fluids: May need 4-6L due to massive capillary leak
- Relying on antihistamines alone: They are adjuncts, not primary treatment
- Premature discharge: Observe 4-6 hours minimum (biphasic reactions in 20%)
Biphasic Reactions
- Occur in 20% of anaphylaxis cases
- Second wave of symptoms 4-12 hours after initial resolution (can be up to 72 hours)
- Can be equally or more severe than initial reaction
- Management: Observe all patients 4-6 hours minimum, longer if severe initial reaction or required multiple doses of epinephrine
Discharge Planning
- Prescribe epinephrine auto-injector (EpiPen, Auvi-Q): 2 devices
- Educate on recognition and auto-injector use
- Medical alert bracelet
- Allergy/immunology referral
- Strict avoidance of known trigger
- Prednisone 40-60 mg PO daily × 3-5 days to prevent biphasic reaction
💎 Anaphylaxis Pearls
- Epinephrine has NO absolute contraindications in anaphylaxis - always give it!
- IM route is superior to SC: Faster absorption, higher peak levels
- Thigh > arm: Anterolateral thigh achieves therapeutic levels faster
- Patients on beta-blockers: May be refractory to epinephrine. Consider glucagon 1-2 mg IV
- Tryptase level: Draw within 3 hours of symptom onset (peaks at 1 hour). Confirms mast cell degranulation
- Cardiac arrest in anaphylaxis: Prolonged CPR often successful due to reversible cause
🧠 Neurogenic Shock
Definition & Pathophysiology
Neurogenic shock results from loss of sympathetic tone following spinal cord injury (typically above T6), leading to unopposed parasympathetic activity. This causes profound vasodilation and bradycardia.
Classic Triad
- Hypotension: Due to loss of sympathetic vascular tone (vasodilation)
- Bradycardia: Loss of cardiac sympathetic innervation (T1-T4)
- Warm, dry skin: Peripheral vasodilation below level of injury
Spinal Shock vs Neurogenic Shock
| Feature | Spinal Shock | Neurogenic Shock |
|---|---|---|
| Definition | Temporary loss of spinal reflex activity below injury | Hemodynamic instability from loss of sympathetic tone |
| Clinical | Flaccid paralysis, areflexia, loss of sensation | Hypotension, bradycardia, warm skin |
| Duration | Days to weeks | Days to weeks (hemodynamic instability) |
| Resolution | Return of reflexes (often hyperreflexia) | Gradual recovery of sympathetic tone |
Management
Spinal Cord Injury Management
• Immobilize spine immediately
• Maintain spinal precautions
• Early neurosurgical consultation
• MRI to assess injury extent
• High-dose methylprednisolone is NO longer recommended
Hemodynamic Management
MAP Goal: 85-90 mmHg for 5-7 days (optimize spinal cord perfusion)
Initial: Fluid resuscitation 1-2L crystalloid
Caution: Risk of pulmonary edema (excessive fluids worsen outcomes)
If hypotension persists:
• Vasopressors: Norepinephrine or phenylephrine
• For bradycardia: Atropine 0.5-1 mg IV (may need repeat doses or pacing)
Supportive Care
• DVT prophylaxis (high risk)
• Stress ulcer prophylaxis
• Bladder catheterization
• Temperature regulation (poikilothermia)
• Respiratory support as needed
💎 Neurogenic Shock Pearls
- Bradycardia + hypotension = think neurogenic shock in trauma setting
- Higher MAP targets: 85-90 mmHg (vs 65 in other shock) to optimize spinal cord perfusion
- Beware fluid overload: Use vasopressors early, conservative fluids
- Injury level matters: Above T6 → neurogenic shock. T1-T4 → bradycardia more prominent
🔍 Diagnostic Approach
Initial Assessment
- History: Recent infection, allergen exposure, trauma, medications
- Physical Exam: Vital signs, skin (warm vs cool), cardiac exam, lung sounds
- Identify shock type: Clinical presentation + hemodynamics
Essential Labs
| Test | Purpose | Findings |
|---|---|---|
| Lactate | Tissue perfusion marker | >2 mmol/L indicates hypoperfusion |
| Blood Cultures | Identify organism in sepsis | Draw before antibiotics |
| CBC | Infection, anemia | Leukocytosis or leukopenia in sepsis |
| CMP | Organ function, electrolytes | AKI common |
| Procalcitonin | Bacterial infection marker | >0.5 ng/mL suggests bacterial sepsis |
| Tryptase | Mast cell degranulation | Elevated in anaphylaxis (draw within 3 hrs) |
| Cortisol | Adrenal insufficiency | Random <18 mcg/dL suggests insufficiency |
Imaging
- Chest X-ray: Pneumonia, ARDS
- CT imaging: Identify infection source (abdomen/pelvis for intra-abdominal sepsis)
- Echocardiography: Assess cardiac function, rule out other shock types
- Spinal imaging (MRI): If neurogenic shock suspected
Hemodynamic Monitoring
Typical Distributive Shock Profile:
- Cardiac output: ↑ or normal
- SVR: ↓↓ (markedly decreased)
- CVP/PCWP: ↓ or normal
- ScvO₂: Often >70% (impaired oxygen extraction)
💊 Vasopressors & Medications
First-Line Vasopressors
Norepinephrine (Levophed) - FIRST-LINE
Titrate to MAP ≥65 mmHg
Usual range: 0.1-0.5 mcg/kg/min
Maximum: 3 mcg/kg/min (consider second agent if >0.5)
Vasopressin (Pitressin)
DO NOT titrate (all-or-none effect)
Use WITH norepinephrine, not as monotherapy
• Works in acidosis (when catecholamines less effective)
• May reduce arrhythmias
Epinephrine
• Refractory shock (IV infusion) when other agents fail
IV infusion: 0.05-0.5 mcg/kg/min, titrate to effect
Phenylephrine (Neo-Synephrine)
Range: 0.5-3 mcg/kg/min
Adjunctive Therapies
Hydrocortisone (Stress-Dose Steroids)
Duration: Until vasopressors no longer needed, then taper
Vitamin C (Ascorbic Acid)
Often given with hydrocortisone and thiamine ("HAT therapy")
💎 Vasopressor Pearls
- Norepinephrine is first-line for septic shock (superior to dopamine)
- Add vasopressin when NE >0.25-0.5 mcg/kg/min (catecholamine-sparing)
- Epinephrine for refractory shock or anaphylaxis
- Goal MAP ≥65 mmHg (higher if chronic HTN, neurogenic shock)
- Wean vasopressors based on lactate clearance and clinical improvement
⚠️ Complications
Organ-Specific Complications
| System | Complication | Prevention/Management |
|---|---|---|
| Pulmonary | ARDS, ventilator-associated pneumonia | Lung-protective ventilation (Vt 6 mL/kg, PEEP), VAP bundle, early mobilization |
| Cardiovascular | Myocardial dysfunction, arrhythmias | Optimize hemodynamics, correct electrolytes, avoid excessive catecholamines |
| Renal | AKI, acute tubular necrosis | Maintain MAP ≥65, avoid nephrotoxins, may require RRT |
| Hepatic | Cholestatic jaundice, hepatic dysfunction | Supportive care, optimize perfusion |
| Hematologic | DIC, thrombocytopenia | Treat underlying infection, transfuse as needed |
| GI | Ileus, stress ulceration, C. diff | Early enteral nutrition, PPI prophylaxis, antibiotic stewardship |
| Neurological | Delirium, ICU-acquired weakness | Minimize sedation, early mobilization, delirium prevention protocols |
Sepsis-Specific Complications
- Septic cardiomyopathy: Reversible myocardial dysfunction (50-60% of cases)
- Septic encephalopathy: Altered mental status without CNS infection
- Adrenal insufficiency: Relative AI common in septic shock
- Hyperglycemia: Stress response, managed with insulin (target 140-180 mg/dL)
- Immunosuppression: Increased risk of secondary infections
Prognostic Indicators
| Factor | Poor Prognosis |
|---|---|
| Lactate | >4 mmol/L, failure to clear |
| SOFA Score | ≥2 point increase = 10% mortality increase |
| Age | >65 years |
| Multiple Organ Failure | ≥3 organs |
| Persistent Hypotension | Despite fluids + high-dose vasopressors |
- Early recognition and treatment initiation
- Appropriate antibiotic therapy within 1 hour (sepsis)
- Adequate source control
- Balanced resuscitation (fluids + vasopressors)
- Lactate clearance >10% per 2-4 hours
- Prevention of secondary complications
💎 Final Pearls
- Time is tissue: Every hour delay increases mortality
- Bundle compliance improves outcomes: Sepsis Hour-1 Bundle saves lives
- Source control is critical: Antibiotics alone insufficient if undrained abscess
- Balance resuscitation: Neither under- nor over-resuscitate with fluids
- De-escalate early: Narrow antibiotics, wean vasopressors, mobilize fluid