Can a 500ml Dextrose Normal Saline (DNS) IV bolus with ondansetron be given to a 15-year-old boy with vomiting?

Can a 500ml DNS IV Bolus with Ondansetron Be Given to a 15-Year-Old Boy with Vomiting?

Yes, you can give a 500ml DNS (Dextrose Normal Saline) IV bolus with ondansetron to a 15-year-old boy with vomiting, but only if he has severe dehydration, shock, altered mental status, or has failed oral rehydration therapy. 1

Assessment of Hydration Status First

Before administering IV fluids, you must determine the severity of dehydration:

• Mild to moderate dehydration: Oral rehydration solution (ORS) is first-line therapy 1
• Severe dehydration: Isotonic IV fluids (lactated Ringer's or normal saline) are indicated when there is severe dehydration, shock, altered mental status, or failure of ORS therapy 1

The physical examination is the best way to evaluate hydration status—look specifically for abnormal pulse, poor perfusion, altered mental status, and signs of shock 1, 2

IV Fluid Administration Guidelines

For severe dehydration requiring IV therapy:

• Administer isotonic crystalloid boluses (normal saline or lactated Ringer's preferred over DNS) until pulse, perfusion, and mental status normalize 1
• Continue IV rehydration until the patient awakens, has no aspiration risk, and has no ileus 1
• Once stabilized, switch to ORS for remaining deficit replacement 1

Important caveat: The guidelines specifically recommend isotonic fluids like normal saline or lactated Ringer's rather than DNS for severe dehydration 1. DNS contains dextrose which is not necessary for initial resuscitation unless there is ketonemia or concern for hypoglycemia 1

Ondansetron Use in This Patient

Ondansetron is appropriate for this 15-year-old:

• Ondansetron may be given to facilitate tolerance of oral rehydration in children >4 years of age and adolescents with acute gastroenteritis associated with vomiting 1
• The recommendation is weak, moderate quality evidence 1
• Ondansetron should only be used once the patient is adequately hydrated—it is not a substitute for fluid and electrolyte therapy 1

Dosing for ondansetron:

• 0.15 mg/kg IV (maximum 4 mg per dose) 3, 4
• For postoperative nausea/vomiting in patients >40 kg: 4 mg IV 3

Clinical Algorithm

Step 1: Assess hydration status and look for red flags (bilious/bloody vomiting, altered sensorium, toxic appearance, severe dehydration, bent-over posture) 4

Step 2: Determine fluid therapy approach:

• Mild-moderate dehydration without red flags: Start with ORS; consider ondansetron to facilitate oral intake 1, 2
• Severe dehydration, shock, altered mental status, or ORS failure: Use isotonic IV fluids (normal saline or lactated Ringer's preferred) 1

Step 3: If using IV fluids:

• Give isotonic crystalloid boluses until hemodynamically stable 1
• Monitor pulse, perfusion, mental status, and fluid input/output 1
• Once stable, transition to ORS for remaining deficit 1

Step 4: Add ondansetron only after adequate hydration is achieved to prevent further vomiting and facilitate oral intake 1

Key Pitfalls to Avoid

• Do not use DNS as first-line for severe dehydration—isotonic fluids without dextrose (normal saline or lactated Ringer's) are preferred unless there is ketonemia or hypoglycemia 1
• Do not give ondansetron as a substitute for proper fluid resuscitation—it is ancillary therapy only 1
• Do not skip oral rehydration attempts in mild-moderate dehydration—ORS is as effective as IV fluids and should be tried first 1, 2
• Monitor for fluid overload during rapid resuscitation, especially in patients with cardiac or renal compromise 1
• Ondansetron is compatible with normal saline and 5% dextrose solutions for dilution 3