Read the hemodynamics, not the history
The shock matrix
| THE TANK IS EMPTY Hypovolemic | THE PUMP OR PATH IS BLOCKED Cardiogenic and obstructive | THE PIPES ARE OPEN Distributive | |
|---|---|---|---|
| Preload · neck veins | ↓ Flat | ↑ Distended | ↓ relative, flat |
| Afterload · systemic vascular resistance | ↑ | ↑ | ↓ |
| Cardiac output | ↓ | ↓ | ↔ or ↑ early, ↓ late |
| Heart rate | ↑ | ↑ | ↑ (↓ in neurogenic) |
| Skin | Cool, pale, clammy | Cool, mottled | Warm, dry or flushed early |
| Pulse pressure | Narrow | Narrow | Wide |
| What is actually wrong | Volume has left the circuit: hemorrhage, burns, vomiting, diarrhea, third spacing | Cardiogenic is the muscle failing. Obstructive is tension pneumothorax, cardiac tamponade, or massive pulmonary embolism | Vasodilation and capillary leak: septic, anaphylactic, neurogenic |
| First move | Replace volume and control the loss | Relieve the obstruction, or support the pump | Fluid plus a vasoconstrictor, and source control |
| What makes it worse | crit Vasoconstrictors given instead of fluid | crit Aggressive fluid poured into a heart or a path that cannot move it | crit Fluid alone when the vessels are the problem |
The three flavors of distributive shock
- Septic. An infection source plus vasodilation, capillary leak, and a rising lactate. Skin warm and flushed early, cool and mottled once it has gone on too long. First move is fluid, cultures, antibiotics, and a vasopressor if the pressure will not hold.
- Anaphylactic. Everything above plus stridor, hoarseness, urticaria, angioedema, and bronchospasm within minutes of an exposure. First move is intramuscular epinephrine into the anterolateral thigh, before oxygen, before access, before anything else. Then airway, oxygen, supine with legs elevated, fluid, and repeat dosing if there is no response.
- Neurogenic. The exception that breaks the tachycardia rule. Loss of sympathetic outflow after a cervical or high thoracic injury gives hypotension with bradycardia and warm, dry skin below the level of injury. Fluid is given cautiously, a vasoconstrictor is usually required, and spinal precautions are maintained throughout. Injury classification is → BOOK 10 · P5.
The three-question read
Neck veins flat or full. Skin cool or warm. Rate fast or slow. Three answers name the family before a single word of history is taken.
Memory hook: FLAT · COOL · FAST is the hypovolemic signature. Change one variable and you change columns. Full neck veins move you to column 2. Warm skin moves you to column 3. Slow rate with warm skin moves you to neurogenic.
Margin notewarm and hypotensive is not reassuring.
Watch outA patient can be hypotensive and warm to the touch and still be dying faster than the cold one. Skin temperature is a clue to the mechanism, never a measure of how sick.
Cardiogenic shock is placed here by signature only. The failing heart, its rhythms, and its drugs are → BOOK 08 · P3. Vasopressor pharmacology and titration are named, never taught: → BOOK 05 · P6 and → BOOK 06 · P7. The definitional four-shock map is → BOOK 01 · P44.
TakeawayNeck veins and skin temperature sort every shock into one of three families before you know a single diagnosis.