8.4 Hypovolemic Shock
Key Takeaways
- Hypovolemic shock is hemorrhagic or non-hemorrhagic; the shared physiology is an empty tank, not a failed pump.
- Advanced Trauma Life Support hemorrhage classes are teaching labels, not Board of Certification for Emergency Nursing–owned percentages—treat the exam in front of you.
- Narrow pulse pressure, mottling, a rising lactate, and a falling end-tidal carbon dioxide mark decompensation before a single cuff number looks shocky.
- Stop the bleed with a tourniquet, pelvic binder, or packing and give blood first; a vasopressor is only a temporizing bridge in a bleeder.
- Scene care starts with hemorrhage control you perform; interfacility care starts by finding the occult empty tank you inherited.
Hypovolemic shock is an empty tank. Domain 2.C.2.a of the August 2026 Board of Certification for Emergency Nursing (BCEN) Certified Flight Registered Nurse (CFRN) outline isolates it from obstructive, distributive, and cardiogenic shock (Chapter 9) so you do not treat a bleeder like a septic vasodilator or a failing left ventricle. The cabin hides the diagnosis: a bouncing cuff lies, and packaging covers the pool of blood. Name the subtype, recognize the trend, stop the loss, then fill with the right fluid.
Hemorrhagic versus non-hemorrhagic
Two empty tanks, two bags
Hemorrhagic hypovolemia is blood leaving the vascular space—external on the roadside, or hidden in the chest, abdomen, pelvis, retroperitoneum, or long-bone compartments. Non-hemorrhagic hypovolemia is volume leaving without red cells as the primary loss: gastrointestinal (GI) fluid from vomiting or diarrhea, evaporative and third-space loss from burns, bowel obstruction, pancreatitis, or a large collection. Both are inadequate preload. They do not get the same bag.
| Subtype | Typical flight source | First fluid after hemorrhage control | What not to do |
|---|---|---|---|
| Traumatic hemorrhage | Scene blunt or penetrating trauma | Whole blood or a 1:1:1 component ratio (section 8.2) | Stack crystalloid and squeeze with a pressor |
| GI bleed | Interfacility variceal or lower-GI hemorrhage | Blood products; airway plan if hematemesis | Call it distributive because the skin is pale |
| Burn / evaporative | Scene or burn-center transfer | Isotonic crystalloid by a burn formula | Default to uncrossmatched whole blood for isolated burn shock |
| GI / third-space medical | Vomiting, obstruction, pancreatitis | Balanced crystalloid with reassessment | Assume a normal cuff means the tank is full |
Advanced Trauma Life Support (ATLS) still teaches classes of hemorrhage as a communication tool. Class I is a small loss with minimal vital-sign change. Class II often shows tachycardia and a narrowing pulse pressure. Class III is frank hypotension and marked tachycardia. Class IV is preterminal, with a collapsing pressure. Those class percentages are teaching labels, not BCEN-owned cutoffs. Do not treat 15 percent or 30 percent of blood volume as if it were printed on the exam outline. Use the class language to describe a trend, then look at the patient.
Recognition when the cabin lies
Compensation is vasoconstriction. Skin mottles, capillary refill lengthens, the pulse pressure narrows, and urine output disappears. Lactate, if you have a cartridge, rises when oxygen delivery fails. End-tidal carbon dioxide (ETCO2) falls when pulmonary blood flow falls—low ETCO2 in a ventilated trauma patient who is not being hyperventilated is a perfusion alarm. A single noninvasive blood pressure (NIBP) of 108/88 mm Hg on a vibrating litter can still be class II shock. Feel a pulse, look at the plethysmograph, trend ETCO2, and lift the sheet.
Children stay "normal" until they are not. Older adults on beta blockers never give you the tachycardia you were waiting for. Pregnancy has a larger circulating volume, so she can lose more before the cuff collapses—and the fetus is already under-perfused. The tank is still empty.
Sequence: stop the loss, then fill
Scene versus interfacility
Hemorrhage control comes before a clever drip. Details of tourniquet time, junctional devices, and wound packing live in Chapter 10 (hemostasis). This section owns the shock sequence:
- Tourniquet (TQ) for life-threatening extremity bleeding, high and tight.
- Pelvic binder for the unstable pelvic mechanism; bind over the greater trochanters, not the abdomen.
- Wound packing for junctional and compressible cavities you can reach.
- Then blood first for the hemorrhagic phenotype (section 8.2), not a third liter of cold saline (section 8.1).
A vasopressor is not a substitute for volume in a bleeder. Norepinephrine or push-dose epinephrine may temporize a disappearing mean arterial pressure (MAP) while the unit is handed through the door. That is a bridge. If you leave the pressor running and never give blood, you have clamped an empty pipe. Non-hemorrhagic hypovolemia needs crystalloid (or burn-formula volume); a pressor before the tank is filled recreates the same empty-pipe problem.
A scene start is discovery. You own hemorrhage control, access, the first blood, tranexamic acid (TXA) if indicated, and the decision to lift with a just-enough pressure versus staying for a second unit. The lethal mistake is packaging a half-controlled bleeder so you can "resuscitate in the air," where you cannot pack a pelvis under a vacuum mattress.
An interfacility start is inheritance. The sending note says "stable after 2 units." Find the occult empty tank: a filling drain, a falling ETCO2, a binder that was never placed, a GI bleed still in the stomach, or a burn patient hours behind on calculated volume. Confirm what was given, what is in the cooler, and whether calcium and TXA already happened. Then fly a sequence, not a label.
Reassess after every move. Loading, climb, and a Boyle-driven expansion of a poorly vented drain all change preload. Hypovolemic shock is a trend you either reverse or watch become arrest.
A packaged scene patient has a blood pressure of 108/88 mm Hg, mottled knees, and an end-tidal carbon dioxide that has fallen from 36 to 24 mm Hg on unchanged ventilation. What does this pattern suggest?
A hypotensive patient is bleeding from a pelvic mechanism. Blood is being handed to the door. Which statement is correct?
Which statement correctly separates non-hemorrhagic from hemorrhagic hypovolemic shock?