Shock: Types and Management

Classification of Shock

Shock is defined as a state of inadequate oxygen delivery relative to tissue demand, resulting in cellular hypoxia. There are four major categories (Harrison's, p. 8234):

Type	Mechanism	Classic Example
Distributive	Maldistribution of blood flow; vasodilation	Septic, anaphylactic, neurogenic
Cardiogenic	Pump failure → decreased CO	MI, severe HF, myocarditis
Hypovolemic	Reduced circulating volume	Hemorrhage, burns, dehydration
Obstructive	Mechanical obstruction to flow	PE, cardiac tamponade, tension pneumothorax

Hemodynamic Profiles

Parameter	Distributive	Cardiogenic	Hypovolemic	Obstructive
CO/CI	↑ (early)	↓	↓	↓
SVR	↓↓	↑	↑	↑
CVP/Preload	↓/normal	↑	↓↓	↑ (tamponade/PE)
PCWP	↓/normal	↑↑	↓	Variable
ScvO₂	↑ (shunting)	↓	↓	↓
Skin	Warm, flushed	Cool, clammy	Cool, clammy	Cool, clammy

1. Distributive Shock

Septic Shock

The most common cause of distributive shock.

Diagnosis: Sepsis + vasopressors needed to maintain MAP ≥65 mmHg + lactate >2 mmol/L despite adequate fluids.

Management (Harrison's, p. 8273 / Surviving Sepsis Campaign):

Fluids: IV crystalloid 30 mL/kg within first 3 hours (saline or balanced crystalloids)
Vasopressors (target MAP ≥65 mmHg):
- Norepinephrine — first-line vasopressor
- Vasopressin — add to reduce norepinephrine dose
- Dopamine — avoid except in bradycardia or tachyarrhythmia risk
Source control: Antibiotics within 1 hour, drain/debride source
Steroids: Hydrocortisone 200 mg/day if refractory to fluids + vasopressors
Lactate-guided resuscitation — normalize elevated lactate levels

Anaphylactic Shock

Epinephrine IM (0.3–0.5 mg, 1:1000) — immediate, first-line
Antihistamines (diphenhydramine, ranitidine) — adjunct only
Corticosteroids — prevent biphasic reaction
IV fluids for hypotension
Airway management if angioedema

Neurogenic Shock

IV fluids first
Vasopressors (norepinephrine or phenylephrine) for refractory hypotension
Bradycardia: atropine or transcutaneous pacing

2. Cardiogenic Shock

Definition: Sustained hypotension (SBP <90 mmHg) + signs of hypoperfusion due to cardiac dysfunction.

Management:

Treat the underlying cause:
- STEMI → emergent PCI (door-to-balloon <90 min)
- Arrhythmia → cardioversion/pacing
Hemodynamic support:
- Vasopressors: Norepinephrine (preferred over dopamine — less arrhythmia)
- Inotropes: Dobutamine for low CO with adequate BP
Mechanical support:
- Intra-aortic balloon pump (IABP)
- Impella, VA-ECMO for refractory cases
Diuretics if pulmonary edema present (cautiously)
Avoid aggressive fluid resuscitation (worsens pulmonary edema)

3. Hypovolemic Shock

Classification by blood loss (Hemorrhagic Shock — ATLS):

Class	Blood Loss	HR	BP	RR	Mental Status
I	<750 mL (<15%)	<100	Normal	14–20	Normal
II	750–1500 mL (15–30%)	100–120	Normal	20–30	Anxious
III	1500–2000 mL (30–40%)	120–140	↓	30–40	Confused
IV	>2000 mL (>40%)	>140	↓↓	>35	Lethargic/unconscious

Management:

Hemorrhagic: Damage control resuscitation
- 1:1:1 ratio — packed RBCs : FFP : platelets
- Tranexamic acid (TXA) within 3 hours of injury
- Permissive hypotension (target SBP 80–90 mmHg) until surgical control
- Surgical/interventional source control
Non-hemorrhagic (dehydration, GI losses):
- IV isotonic crystalloids (normal saline or lactated Ringer's)
- Replace ongoing losses

4. Obstructive Shock

Cardiac Tamponade

Emergency pericardiocentesis (needle or surgical)
Avoid vasodilators; maintain preload

Massive Pulmonary Embolism

Systemic thrombolysis (alteplase 100 mg over 2 h) — if hemodynamically unstable
Surgical embolectomy or catheter-directed therapy — if thrombolysis contraindicated
Anticoagulation (heparin) immediately
Vasopressors (norepinephrine) for hypotension; avoid aggressive fluids (RV strain)

Tension Pneumothorax

Needle decompression (2nd intercostal space, midclavicular line) — immediate
Followed by chest tube insertion

General Shock Management Principles

Step	Action
Airway	Secure airway; intubate if necessary
Access	Large-bore IV x2 or central line; arterial line for monitoring
Fluids	Cautious resuscitation guided by hemodynamics (avoid over-resuscitation)
Vasopressors	Norepinephrine is the default first-line agent for most shock types
Monitor	MAP ≥65 mmHg, UO ≥0.5 mL/kg/hr, lactate clearance, ScvO₂ ≥70%
Cause	Identify and treat the underlying etiology immediately

Key Differentiating Clues at Bedside

Warm extremities + hypotension → Distributive
JVD + muffled heart sounds + hypotension (Beck's triad) → Tamponade
Absent breath sounds + tracheal deviation → Tension pneumothorax
S3 gallop + pulmonary crackles → Cardiogenic
Trauma/active bleeding → Hypovolemic (hemorrhagic)

Sources: Harrison's Principles of Internal Medicine, 21st Edition (pp. 8234, 8273); Surviving Sepsis Campaign Guidelines; ATLS Guidelines.

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