Shock & Perfusion
Shock kills quietly. By the time the blood pressure drops, the body has already burned through its reserves — and your window is closing. This guide teaches you what perfusion really means, how each type of shock fails, and how to catch the patient who is compensating while there's still time to act.
1What shock actually is
Perfusion is the delivery of adequate oxygenated blood to the body's tissues — and the removal of waste products. When perfusion is adequate, cells get oxygen, make energy, and function. Shock is hypoperfusion: the tissues are not getting the oxygenated blood they need, and cells begin to fail at the cellular level. It's a whole-body process, not a single vital sign.
The circulatory system needs three things working at once — the perfusion triangle:
Every type of shock is a failure of one of those three sides. Figure out which side failed and you've usually figured out the cause — and what the patient will look like.
2Types of shock
Learn each type by which side of the triangle fails. The NREMT loves to hand you a mechanism and a set of findings and ask you to name the type — this table is the answer key.
| Type | Mechanism | Classic causes | Key findings |
|---|---|---|---|
| Hypovolemic | Not enough fluid — blood or plasma volume is lost | Hemorrhage (internal or external), burns, severe dehydration/vomiting/diarrhea | Tachycardia, pale cool clammy skin, delayed cap refill, thirst; BP falls late |
| Cardiogenic | Pump failure — the heart can't move blood forward | Myocardial infarction, congestive heart failure | May have JVD, pulmonary edema (crackles), respiratory distress. Do not lay flat if breathing worsens — sit them up |
| Obstructive | Blood flow is physically blocked | Tension pneumothorax, cardiac tamponade, massive pulmonary embolism | Signs of shock with the mechanism's own signature (absent breath sounds, muffled heart tones, sudden dyspnea) |
| Distributive — Septic | Pipes fail — infection triggers widespread vasodilation and leaky vessels | Severe infection (pneumonia, UTI, wounds) | Fever, warm flushed skin early → cold and mottled late; tachycardia, altered mental status |
| Distributive — Neurogenic | Pipes fail — spinal cord injury cuts the nerve signals that keep vessels tight | Spinal cord injury | Hypotension without tachycardia; warm, dry skin below the injury level |
| Distributive — Anaphylactic | Pipes fail — allergen triggers massive vasodilation plus airway swelling | Foods, stings, medications, latex | Hives, itching, facial/airway swelling, wheezing or stridor, hypotension → epinephrine |
Psychogenic shock — the simple faint — is a sudden, temporary vasodilation triggered by fear, pain, or bad news. The patient drops, blood returns to the brain, and they typically recover within moments. It's transient, but assess for injuries from the fall and for anything more serious hiding underneath.
3Compensated → decompensated → irreversible
Shock is a progression, and the whole game at the EMT level is recognizing it in the first stage — while the body is still winning the fight.
Compensated shock
The body senses falling perfusion and fights back: vessels constrict, the heart speeds up, breathing quickens. The blood pressure holds — for now. Look for:
- Anxiety, restlessness, or a feeling of impending doom — the brain is often the first organ to feel hypoperfusion
- Tachycardia — an unexplained fast pulse is shock until proven otherwise
- Tachypnea — rapid, often shallow breathing
- Pale, cool, clammy skin — blood shunted away from the surface to the core
- Delayed capillary refill
- Thirst
- Normal blood pressure — that's what "compensated" means
Decompensated shock
Compensation fails. The tank is too empty, the pump too weak, or the pipes too wide, and the body can no longer hold the line:
- Falling blood pressure — hypotension finally appears
- Altered or decreasing mental status
- Weak or absent peripheral (radial) pulses
- Mottled, ashen, or cyanotic skin
Irreversible shock
Cellular damage has passed the point of no return. Even if perfusion is restored, organ systems fail. You can't diagnose this stage in the field — which is exactly why you treat aggressively in the first two.
4Reading the trend: serial vitals
A single set of vitals is a snapshot; shock is a movie. Take serial vital signs and watch which direction each number is moving — the trend tells you what one reading can't:
- Pulse rising across sets — the heart is working harder to move less blood
- Respiratory rate rising — the body chasing oxygen debt
- Pulse pressure narrowing — the gap between systolic and diastolic shrinks as vessels clamp down and stroke volume falls
- Blood pressure falling — the late confirmation, not the early warning
Between vital sets, the skin is your perfusion window. It's the first organ the body sacrifices, so color, temperature, and moisture change early: pink-warm-dry says perfused; pale-cool-clammy says the body is shunting blood to the core and you should be moving. Check capillary refill — it's most reliable in kids, but a sluggish refill in any patient is a data point.
Where does this fit in your workflow? Perfusion checks live in the primary assessment and vitals trend through your reassessments — review Patient Assessment for the sequence and Vital Signs & Normal Values for the numbers you're trending against.
5EMT treatment
You can't replace blood volume or fix a failing pump in the field — but the interventions you do have change survival. Run them in order, fast:
6The lethal triad
In serious trauma, three problems feed each other in a death spiral: hypothermia, acidosis, and coagulopathy. Poor perfusion makes cells run anaerobically, producing acid. A cold patient's clotting factors stop working, so bleeding worsens — which deepens the hypoperfusion, which worsens the acidosis, and around it goes.
You can't fix acidosis or clotting in the field, but you sit squarely on the third corner: heat. Trauma patients get cold fast — blood loss, exposed skin, a wet backboard, a 68° ambulance. Strip wet clothing, pile on blankets, crank the heat even if you're sweating. Keeping a trauma patient warm is a treatment, not a comfort measure — every degree you save protects their ability to clot.
7Self-check
Answer before you expand. If you miss one, re-read that section — then go drill it for real.
Q1A 24-year-old with a deep thigh laceration is anxious and restless, pulse 118, respirations 24, skin pale and clammy — BP 118/78. What's going on?
Q2After a fall from height, a patient is hypotensive with warm, dry skin below the waist and a pulse of 72. Hypovolemic or neurogenic — and how do you know?
Q3Why is hypotension an especially late — and dangerous — sign of shock in children?
Q4Your patient has bright red blood soaking through their pant leg. What's your first action — and your next move if it doesn't stop?
Q5A patient stung by a bee has hives, facial swelling, and audible wheezing. What drug do they need, and how is it given?
