Intravenous Fluids: Choosing Them and the Errors That Cause Harm

Intravenous fluids are prescribed by interns more often than any other treatment and are frequently written without the deliberation given to a tablet. They cause real harm in both directions, and most of that harm comes from prescribing without first stating what the fluid is actually for.

At a glance

Three different tasks

Resuscitation restores circulating volume in a patient who is hypoperfused. It is given as a defined volume over a short period with immediate reassessment afterwards — this is the setting where you give, look, and give again if needed.

Replacement matches ongoing abnormal losses: vomiting, diarrhoea, drain or stoma output, fever, or third-space losses. The composition matters here, because different losses take different electrolytes with them, and replacing the volume without the content creates a new problem.

Maintenance covers the needs of a patient who cannot drink. It is the smallest and most easily overdone of the three. Maintenance regimens continued unchanged for days are a common cause of iatrogenic overload and of electrolyte disturbance.

Writing “IV fluids” without specifying which task you are performing is how a resuscitation volume ends up running as maintenance, or a maintenance regimen gets used to treat hypotension.

Before prescribing

1. Assess the patient’s fluid status clinically — perfusion, pulse, blood pressure and postural change, mucous membranes, skin turgor, jugular venous pressure, urine output, and weight if available.
2. Look for evidence of overload as carefully as for depletion: peripheral oedema, raised jugular venous pressure, crackles, breathlessness.
3. Check current electrolytes and renal function.
4. Look at what has already been given and what has come out. A fluid balance chart is the single most useful document here and is frequently incomplete — completing it is a legitimate first action.
5. Ask whether the patient can drink. Oral intake is safer, cheaper, and often forgotten in a patient with a cannula already in place.
6. Consider comorbidity. Heart failure, kidney disease, liver disease, malnutrition and the elderly all change the margin for error substantially.

Composition, in principle

Fluids differ in their electrolyte content and in how they distribute between compartments. That is what makes them different treatments rather than interchangeable bags. Choosing between them depends on the task, the patient’s electrolytes, their renal function and their comorbidity — and the specific choice for a specific situation belongs to your local guideline, which is what you should be reading at the point of prescribing.

What is worth carrying in your head is the principle: fluid given to restore circulating volume, fluid given to replace a specific loss, and fluid given to meet baseline needs are not the same, and using one where another is indicated is the commonest composition error.

Reassessment is part of the prescription

Fluid prescribing is a loop, not an instruction. After giving, reassess: has perfusion improved, has urine output responded, is there any sign of overload developing, what do the repeat electrolytes show? A standing order that runs for days without review is the mechanism by which most fluid harm happens.

Set a review point when you prescribe, and hand over that the review is due.

Common errors

Last-minute checklist

• State the purpose: resuscitation, replacement, or maintenance
• Assess for depletion and for overload, both deliberately
• Read the fluid balance chart; complete it if it is not
• Check electrolytes and renal function first
• Ask whether they can drink instead
• Adjust for heart, kidney and liver disease and for age
• Set a review point and hand it over
• Reassess after giving — the patient is the feedback

References

• Your national and hospital intravenous fluid therapy guidelines
• Your current national formulary