Hypotension, shock
Introduction
Shock is a life-threatening condition characterized by circulatory failure resulting in inadequate cellular oxygen utilization. It is a critical topic for the MCCQE1, falling under the Emergency Medicine and Internal Medicine objectives. As a future Canadian physician, mastering the recognition and management of shock is essential for the Medical Expert CanMEDS role.
Definition: Shock is defined as a state of cellular and tissue hypoxia due to reduced oxygen delivery and/or increased oxygen consumption or inadequate oxygen utilization. Hypotension (typically SBP <90 mmHg or MAP <65 mmHg) is a common sign but is not required for the diagnosis of shock.
Pathophysiology and Classification
Understanding the four main categories of shock is vital for the MCCQE1. The underlying mechanism determines the treatment strategy.
Distributive
Distributive Shock (Vasodilatory)
- Mechanism: Severe peripheral vasodilation (reduced Systemic Vascular Resistance - SVR).
- Key Feature: “Warm shock” (warm extremities, bounding pulses initially).
- Etiologies:
- Septic Shock: Most common form of shock in the ICU.
- Anaphylactic Shock: IgE-mediated hypersensitivity.
- Neurogenic Shock: Loss of sympathetic tone (spinal cord injury above T6).
- Adrenal Crisis: Cortisol deficiency.
Hemodynamic Profiles
For MCCQE1, you must be able to differentiate shock types based on hemodynamic parameters (Swan-Ganz catheter data concepts).
| Shock Type | CVP (Preload) | PCWP (Left Heart Preload) | Cardiac Output (CO) | SVR (Afterload) | MvO2 (Mixed Venous O2) |
|---|---|---|---|---|---|
| Hypovolemic | Low | Low | Low | High (Compensatory) | Low |
| Cardiogenic | High | High | Low | High | Low |
| Distributive | Low/Normal | Low/Normal | High (Early) / Low (Late) | Low (Pathologic) | High (Early) |
| Obstructive | High | Low/Normal (unless tamponade*) | Low | High | Low |
*Note: In Cardiac Tamponade, there is equalization of pressures (CVP ≈ PCWP).
Clinical Assessment in the Canadian Context
History (AMPLE)
- Allergies
- Medications (e.g., Beta-blockers masking tachycardia, anticoagulants)
- Past Medical History
- Last Meal (important for intubation/surgery)
- Events leading to presentation
Physical Examination
Look for the “windows of the body” for perfusion:
- Skin: Mottling, capillary refill time (>3 seconds), temperature.
- Kidneys: Urine output (<0.5 mL/kg/hr).
- Brain: Altered mental status (confusion, agitation, obtundation).
The Shock Index (SI)
A useful bedside calculation to identify occult shock in trauma or hemorrhage.
SI = Heart Rate / Systolic Blood PressureNormal: 0.5 - 0.7
Abnormal: >0.9 suggests significant illness/hemorrhage.
Diagnostic Workup
- Labs: CBC, Electrolytes, Creatinine, LFTs, INR/PTT, Lactate (marker of tissue hypoperfusion), Troponin, Blood Cultures (if sepsis suspected).
- ECG: Ischemia, arrhythmia.
- Imaging: CXR, CT Pan-scan (trauma).
POCUS (Point of Care Ultrasound)
Canadian Emergency Medicine heavily emphasizes POCUS. The RUSH Protocol (Rapid Ultrasound for Shock and Hypotension) assesses:
- Pump: LV contractility.
- Tank: IVC size/collapsibility, FAST exam (free fluid), Pleural fluid.
- Pipes: Aorta (AAA), DVT.
Management Guidelines
Management involves simultaneous evaluation and resuscitation.
Step 1: Stabilization (The ABCs)
- Airway: Intubate if GCS <8 or unable to protect airway. Caution: Intubation/sedation can worsen hypotension.
- Breathing: High-flow oxygen to maintain SpO2 >92-94%.
- Circulation: Establish 2 large-bore IVs (14G or 16G).
Step 2: Fluid Resuscitation
- Initial Bolus: 500 mL - 1000 mL crystalloid bolus (balanced crystalloids like Ringer’s Lactate or Plasmalyte are often preferred in Canada over Normal Saline to prevent hyperchloremic acidosis).
- Assess Response: Monitor BP, HR, urine output, and lung sounds (stop if crackles develop).
- Exception: Restrictive fluid strategy in hemorrhagic shock (permissive hypotension) until hemorrhage control, or in cardiogenic shock.
Step 3: Vasoactive Agents
If hypotension persists despite adequate volume loading:
- First-line Vasopressor: Norepinephrine (Levophed) is the agent of choice for Septic, Cardiogenic, and Undifferentiated shock.
- Second-line: Vasopressin or Epinephrine.
- Inotropes: Dobutamine (if myocardial dysfunction is present).
Step 4: Etiology-Specific Management
- Sepsis: Broad-spectrum antibiotics within 1 hour. Source control.
- Anaphylaxis: IM Epinephrine (1:1000) immediately.
- Hemorrhage: Blood products (1:1:1 ratio of PRBCs:Platelets:FFP). TXA (Tranexamic Acid) if within 3 hours of injury.
- Cardiogenic: Revascularization (PCI), mechanical support (IABP, ECMO).
- Obstructive: Needle decompression (tension pneumo), pericardiocentesis (tamponade), thrombolysis (massive PE).
Canadian Guidelines & Clinical Pearls
Surviving Sepsis Campaign (Canadian Standard)
- Measure lactate level. Remeasure if initial lactate >2 mmol/L.
- Obtain blood cultures before antibiotics.
- Administer broad-spectrum antibiotics.
- Administer 30 mL/kg crystalloid for hypotension or lactate ≥4 mmol/L.
- Apply vasopressors if hypotensive during or after fluid resuscitation to maintain MAP ≥65 mmHg.
Choosing Wisely Canada
- Don’t use HES (Hydroxyethyl Starch) for fluid resuscitation in septic shock; use crystalloids.
- Don’t delay palliative care discussions in patients with refractory shock and poor prognosis.
Key Points to Remember for MCCQE1
- Hypotension is a late sign of shock, especially in young, healthy patients who can compensate well.
- Tachycardia is the earliest sign of shock.
- Norepinephrine is the default vasopressor for almost all shock states (except Anaphylaxis -> Epinephrine).
- In Neurogenic shock, the patient will be hypotensive and bradycardic (unlike other forms where tachycardia is present).
- Corticosteroids (Hydrocortisone) are indicated in septic shock refractory to fluids and vasopressors.
Sample Question
Scenario: A 72-year-old male presents to the Emergency Department with a 2-day history of productive cough and fever. On examination, he is confused. Vital signs are: Temperature 39.2°C, Heart Rate 115 bpm, Blood Pressure 75/40 mmHg, Respiratory Rate 28/min, and O2 saturation 88% on room air. He has warm extremities and bounding pulses. The chest X-ray shows a right lower lobe consolidation. Two large-bore IVs are established, and 3 liters of Ringer’s Lactate have been administered rapidly. Repeat blood pressure is 78/45 mmHg.
Which one of the following is the most appropriate next step in management?
Detailed Analysis: This patient is presenting with Septic Shock (infection + persistent hypotension requiring vasopressors to maintain MAP ≥65 mmHg and serum lactate level >2 mmol/L despite adequate volume resuscitation).
- Diagnosis: The clinical picture of fever, cough, consolidation, and “warm shock” (warm extremities, bounding pulses) strongly suggests distributive shock secondary to sepsis.
- Management Logic: The patient has already received 30 mL/kg (approx. 2-3L) of crystalloid fluid, yet remains hypotensive. According to Canadian and international guidelines (Surviving Sepsis Campaign), the next step for fluid-refractory hypotension is the initiation of vasopressors.
- Choice A: Albumin may be considered in patients requiring substantial amounts of crystalloids, but initiating a vasopressor is the priority to restore perfusion pressure immediately.
- Choice B: Dopamine is no longer the first-line agent due to a higher risk of arrhythmias compared to norepinephrine. It is reserved for highly specific situations (e.g., low risk of tachyarrhythmias and absolute bradycardia).
- Choice C: Norepinephrine is the first-line vasopressor of choice for septic shock. It increases MAP primarily via vasoconstriction with little change in heart rate or stroke volume.
- Choice D: IV Hydrocortisone is indicated only if the patient remains hemodynamically unstable despite adequate fluid resuscitation and vasopressor therapy. It is not the immediate next step before vasopressors.
- Choice E: Needle decompression is for tension pneumothorax. While possible, the clinical picture (fever, consolidation, warm shock) fits sepsis much better than obstructive shock, and there is no mention of tracheal deviation or absent breath sounds.
References
- Medical Council of Canada. (n.d.). MCCQE Part I Clinical Decision-Making and Multiple-Choice Question Objectives.
- Evans, L., et al. (2021). Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Critical Care Medicine.
- Rosen’s Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier.
- Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 9th ed. New York, NY: McGraw-Hill Education.
- Choosing Wisely Canada. (n.d.). Critical Care Medicine Recommendations. Retrieved from choosingwiselycanada.org.
- Canadian Trauma Guidelines. Advanced Trauma Life Support (ATLS) principles as applied in Canadian centers.