5.3 Isotonic Fluid Bolus 10–20 mL/kg & Reassessment

The bolus is a treatment and a test

In PALS, an isotonic fluid bolus is both therapy and diagnostic probe. You give a measured volume quickly, then ask whether perfusion improved and whether the lungs and liver are tolerating the volume. Candidates fail megacodes when they either (a) never give volume to a clearly hypovolemic child or (b) pour repeated boluses without reassessing and push a cardiogenic child into frank pulmonary edema.

Standard teaching numbers

Memorize the headline: isotonic crystalloid 10–20 mL/kg, commonly 20 mL/kg for straightforward hypovolemic/distributive shock, with reassessment after each bolus.

Which fluid?

PALS teaching centers on isotonic crystalloids for initial expansion (examples in practice include balanced crystalloids or 0.9% sodium chloride per protocol). Hypotonic fluids are not initial shock boluses. Colloid is not the routine first-line PALS exam answer for the first pediatric hypovolemic bolus. Blood products are the volume of choice when the deficit is blood.

How to deliver the bolus: rapid means rapid

A "20 mL/kg bolus" that trickles in over 45 minutes is not PALS resuscitation technique for decompensated hypovolemia.

Practical delivery points

1. Calculate the volume using measured or estimated weight (length-based tape if unknown): weight (kg) × 10–20 mL.
2. Draw up or bag the bolus so the team can push it quickly.
3. Use push-pull syringe technique, a pressure bag, or a rapid infuser as available and appropriate for the line.
4. Deliver through a working IV or IO. Confirm the line flushes and the limb/IO site is not extravasating.
5. Announce start and completion with closed-loop communication: "20 mL/kg isotonic crystalloid IO in now" → team member confirms when complete.
6. Reassess immediately after the bolus finishes—not after a coffee break.

IO when IV is delayed

If peripheral IV access is not rapidly successful in a critically ill or arresting child:

• Establish intraosseous access without prolonged delay
• IO routes accept crystalloid, blood, and resuscitation medications
• Continue attempts at IV access in parallel once IO is working if needed for additional lines
• Watch the IO site for infiltration and limb compartment issues

Exam items love the provider who keeps searching for a perfect vein while the hypotensive infant remains without volume. Timely IO is correct, not a last resort after ten failed sticks.

Reassessment checklist after every bolus

After each 10–20 mL/kg bolus, systematically re-evaluate. This is the evaluate–identify–intervene loop applied to fluid therapy.

Perfusion response (looking for improvement)

If the child improves but still meets shock criteria, another carefully considered bolus may be appropriate. If the child does not improve, ask:

• Is access actually working?
• Is hemorrhage ongoing (need blood/surgery)?
• Is the shock type wrong (distributive needing vasoactives, cardiogenic, obstructive)?
• Is glucose low?
• Has the child progressed toward arrest?

Fluid overload / cardiogenic warning signs

Stop or slow further empiric large-volume crystalloid and reconsider the diagnosis if you see:

• New or worsening pulmonary rales / crackles
• Increasing respiratory distress or hypoxemia after fluids
• Hepatomegaly (enlarging liver span)
• New gallop or marked jugular venous distention when assessable
• Clinical picture increasingly consistent with cardiogenic or fluid-intolerant physiology

In those cases, smaller subsequent volumes (if any), expert pediatric critical care support, and inotropic/vasoactive strategies (Chapter 6) take priority over "another 20 mL/kg because the protocol said fluids."

Glucose: the forgotten reassessment item

Critically ill infants and children frequently have hypoglycemia or clinically important glucose abnormalities. Check bedside glucose early in shock care and treat hypoglycemia per PALS/local dosing while volume resuscitation continues. Altered mentation should never be attributed solely to hypoperfusion without considering glucose.

Putting numbers into scenarios

Scenario 1 — Straightforward hypovolemic bolus

A 15 kg toddler with gastroenteritis is in compensated hypovolemic shock. Planned bolus: 20 mL/kg × 15 kg = 300 mL isotonic crystalloid rapid IV/IO. After the bolus, heart rate falls from 180 to 150, CRT improves from 4 s to 2 s, and mentation brightens. SBP remains normal. Plan: continue monitoring; consider additional bolus if perfusion still inadequate or losses continue; start cause-specific care and maintenance planning.

Scenario 2 — Hypotensive shock needing repeated titration

A 20 kg child with septic distributive features is hypotensive. Give 20 mL/kg = 400 mL rapid crystalloid, reassess. If still hypotensive with poor perfusion and no overload signs, repeat boluses while arranging vasoactive support and antibiotics (full septic pathway in Chapter 6). Do not walk away between boluses; the reassess step is mandatory.

Scenario 3 — Cardiogenic caution

A child with known cardiomyopathy presents cool, tachycardic, with mild hepatomegaly and crackles. Shock is present, but large undifferentiated 20 mL/kg serial boluses are dangerous. Use smaller (about 10 mL/kg) cautious challenges only if hypovolemia is also suspected, reassess after each, and prioritize expert support and inotropes rather than volume loading.

Scenario 4 — Hemorrhage

A trauma patient receives a limited crystalloid bridge while blood is being prepared, then blood products and hemorrhage control—not five back-to-back 20 mL/kg saline boluses as the complete plan.

Common exam traps

• Trap: "Bolus" as a slow maintenance-rate infusion. → Boluses for shock are rapid.
• Trap: No reassessment language in the answer. → Correct answers usually include reassess after each bolus.
• Trap: Automatic 20 mL/kg × many without considering cardiogenic signs. → Watch for rales and hepatomegaly.
• Trap: Delaying all fluid until a perfect ultrasound and full lab panel return in a crashing hypotensive child. → Access and volume (or blood) while diagnostics run in parallel.
• Trap: Forgetting IO when IV fails. → IO is appropriate and expected when delay is harming the child.
• Trap: Forgetting glucose. → Check and treat.

Chapter 5 synthesis

You now have the foundation of pediatric shock care:

1. Shock is inadequate perfusion, split into compensated vs hypotensive using age-based BP thresholds and full perfusion assessment.
2. Hypovolemia—hemorrhagic or non-hemorrhagic—is the most common pathway; treat losses, use crystalloid or blood appropriately.
3. Deliver isotonic 10–20 mL/kg boluses rapidly via IV/IO, reassess every time, stop or slow for overload/cardiogenic signs, and check glucose.

Chapter 6 builds on this foundation with distributive/septic, cardiogenic, and obstructive shock pathways where vasoactives, careful fluids, and cause-specific relief dominate after the same recognition and reassessment discipline.