5.2 Hypovolemic Shock

Hypovolemic shock: not enough volume in the tank

Hypovolemic shock occurs when intravascular volume is too low to support adequate preload and stroke volume. Cardiac pump function may be intrinsically normal, but the heart has less venous return to eject. Cardiac output falls, compensatory tachycardia and vasoconstriction appear, and tissue perfusion fails. In pediatrics, hypovolemia is the most common form of shock, so PALS expects you to recognize it quickly and restore volume while treating the cause.

Hypovolemia sits inside the evaluate–identify–intervene framework:

1. Evaluate: PAT may show abnormal appearance and/or circulation to skin; primary assessment shows tachycardia, poor pulses, delayed CRT (often), dry mucosa, and later hypotension.
2. Identify: Circulatory problem → hypovolemic subtype (hemorrhagic vs non-hemorrhagic).
3. Intervene: Oxygen as needed, stop losses when possible, rapid IV/IO access, isotonic crystalloid and/or blood products, reassess after every bolus, check glucose.

Why children decompensate from volume loss

Infants and young children have smaller absolute blood volumes. A volume loss that looks "modest" in milliliters can be a large fraction of circulating volume. Ongoing diarrhea, poor intake, and fever accelerate losses. Trauma and surgical bleeding can empty the tank even faster. Because compensation is strong, the child may look only "a little dehydrated" to an inexperienced provider until SBP crashes—so use perfusion signs, not parental reassurance alone.

Hemorrhagic vs non-hemorrhagic hypovolemia

Split hypovolemic shock by what left the vascular space:

Hemorrhagic hypovolemic shock

Blood is leaving the vascular compartment—externally or internally.

Management theme: Control the bleeding and restore oxygen-carrying capacity. Endless clear fluid without blood in significant hemorrhage dilutes clotting factors and hemoglobin and does not replace what was lost.

Non-hemorrhagic hypovolemic shock

Volume is lost as fluid other than whole blood, or fluid is sequestered out of the vascular space.

Non-hemorrhagic hypovolemia is usually treated first with isotonic crystalloid boluses and cause-specific care (antiemetics/OR rehydration when mild and appropriate; IV/IO fluids when shock is present; insulin pathway in DKA with careful fluid strategy per protocol—exam-level awareness that DKA is not "pour unrestricted fluid without a plan"). For PALS shock recognition, the unifying idea is low effective intravascular volume.

Clinical picture you must recognize

Hypovolemic shock produces a cold shock pattern more often than warm distributive shock, especially in dehydration and hemorrhage:

Volume-loss and dehydration signs

• Dry mucous membranes
• Sunken eyes
• Sunken fontanelle in infants
• Decreased tears, poor skin turgor (supporting clues; not sole criteria)
• History of vomiting, diarrhea, poor intake, polyuria, burns, or bleeding

Cardiovascular and perfusion signs

• Tachycardia (early and reliable)
• Cool extremities; pallor or mottling
• Weak or thready peripheral pulses; central pulses may remain stronger until late
• Delayed capillary refill (interpret with caveats from Section 5.1)
• Narrowed pulse pressure as stroke volume falls
• Oliguria
• Progressive lethargy or irritability
• Late: hypotension for age → hypotensive hypovolemic shock

What may still look "OK" early

• Blood pressure may be normal (compensated phase)
• SpO2 may be normal if lungs are clear and the child is still breathing effectively
• A brief crying episode can make an inexperienced provider think the child is fine—recheck when calm and look at mucosa, fontanelle, CRT, and trend in heart rate

Differentiating from other shock types (preview)

You do not need a perfect label in the first 30 seconds, but you should lean toward hypovolemia when losses are obvious and cardiac failure signs are absent. If the child deteriorates after fluids with rales and hepatomegaly, re-identify (Chapter 6 cardiogenic pathway).

Management priorities for hypovolemic shock

1. Support ABCs while you resuscitate volume

• Provide oxygen for hypoxia or significant shock as clinically indicated
• Support ventilation if respiratory failure or cardiopulmonary failure is present
• Place the child on a monitor; obtain frequent blood pressures
• Check point-of-care glucose early—hypoglycemia commonly accompanies pediatric critical illness and alters mentation

2. Control hemorrhage when bleeding is the cause

• Direct pressure, packing, tourniquet when indicated for life-threatening extremity bleeding (per trauma protocols/training)
• Rapid transport / surgical or interventional control for internal bleeding
• Avoid delays for nonessential procedures while bleeding continues unchecked

3. Obtain vascular access rapidly

• Attempt peripheral IV, but do not spend prolonged time on repeated failed sticks in a crashing child
• Intraosseous (IO) access is appropriate when IV access is delayed—fluids, blood, and medications can run IO
• Use a length-based tape or known weight for dosing and bolus calculations

4. Restore circulating volume

Non-hemorrhagic hypovolemia (typical PALS teaching):

• Give isotonic crystalloid (e.g., balanced crystalloid or normal saline per local protocol) in boluses of about 20 mL/kg, recognizing the broader 10–20 mL/kg teaching range when caution is needed
• Push/pull or pressure-bag techniques so the bolus is rapid, not a slow drip over an hour
• Reassess after every bolus (next section)
• Repeat boluses as needed for ongoing hypovolemic shock while watching for fluid overload signs

Hemorrhagic hypovolemia:

• Prioritize blood products when significant blood loss is the problem—packed red cells and balanced blood-product strategies per trauma/PALS-aligned institutional protocols
• Use crystalloid judiciously to buy time, but do not substitute endless crystalloid for blood when the child is bleeding out
• Think damage-control resuscitation: stop bleeding, replace blood, avoid dilutional coagulopathy from massive clear fluid alone, prevent hypothermia

5. Treat the underlying cause in parallel

• Antiemetics and later oral challenge only after shock is resolving and the child can protect the airway
• Antibiotics if septic third-spacing/sepsis is the true driver (may overlap distributive—Chapter 6)
• Burn fluid pathways after initial stabilization
• Surgical consultation for acute abdomen or trauma

Clinical scenario (synthesis)

Case A — Non-hemorrhagic: A 9-month-old with 48 hours of vomiting and diarrhea is tachycardic, has a sunken fontanelle, dry lips, cool feet, CRT 4 seconds, and SBP still above the infant hypotensive threshold. Identify: compensated hypovolemic shock from dehydration. Intervene: oxygen as needed, IO if IV fails quickly, rapid 20 mL/kg isotonic crystalloid, reassess, repeat as indicated, check glucose, plan ongoing replacement of continuing losses.

Case B — Hemorrhagic: A 7-year-old pedestrian struck by a vehicle has a rigid, distending abdomen, tachycardia at 160/min, weak pulses, mottling, and falling SBP. Identify: hypotensive hemorrhagic hypovolemic shock likely from intra-abdominal bleeding. Intervene: airway/oxygen support, hemorrhage-control mindset, rapid access, blood products and surgical pathway—not serial unlimited crystalloid-only boluses that delay definitive care and dilute clotting capacity.

If you can sort hemorrhagic from non-hemorrhagic, paint the classic dry-and-tachycardic picture, and choose blood-first thinking for major hemorrhage versus crystalloid boluses for dehydration, you have the hypovolemia core of the PALS Shock domain. Section 5.3 details bolus size, push technique, and the reassessment checklist that prevents both under-resuscitation and fluid overload.