01Principles and purposeThe professional or clinical skill and the decisions it supports.
Fluid prescribing is a physiological intervention with the same potential for harm as a medicine. The “five Rs” are resuscitation, routine maintenance, replacement, redistribution and reassessment. Begin by naming the indication. Resuscitation treats intravascular hypovolaemia with impaired perfusion; maintenance supplies ordinary daily needs when intake is inadequate; replacement addresses additional losses; redistribution describes abnormal internal shifts such as oedema or ascites. One bag cannot be assumed to meet all four purposes.
Assess volume and perfusion using history, trends and examination rather than a single sign. Consider intake, thirst, vomiting, diarrhoea, drains, urine, bleeding, fever and medicines. Examine pulse, blood pressure including postural change when safe, capillary refill, jugular venous pressure, mucous membranes, oedema and lungs. Track urine output, weight, fluid chart, urea, creatinine and electrolytes. Sepsis, haemorrhage, cardiac failure and endocrine disease can produce mixed pictures in which oedema coexists with reduced effective circulating volume.
For adults covered by NICE CG174 who need resuscitation for an appropriate non-sepsis indication, give 500 mL of a crystalloid with sodium 130–154 mmol/L over less than 15 minutes and reassess. Suspected sepsis is explicitly redirected to its dedicated guideline: for an adult at high risk of severe illness or death, NG253 uses an initial 250 mL isotonic electrolyte crystalloid, preferably balanced, ideally over 10–15 minutes, then reassessment after every bolus. The prescription is a trial with an endpoint: mental state, pulse, blood pressure, capillary refill, urine output and overload. The general CG174 guideline also excludes several complex groups, including pregnancy and severe renal or liver disease.
Routine maintenance begins with a calculation, then adjustment. For a 70 kg adult, 25–30 mL/kg/day gives 1,750–2,100 mL water per day. Approximately 1 mmol/kg/day of sodium, potassium and chloride means about 70 mmol of each per day; 50–100 g glucose limits starvation ketosis but does not provide full nutrition. This is a starting estimate. Existing oral intake, drug infusions, fever, renal clearance, cardiac function, frailty and obesity change the final prescription.
Replacement requires an input-output ledger. Estimate measured stool, stoma, drain, gastric and urine losses; identify what water and electrolytes each loss contains; replace at a clinically appropriate interval while monitoring. A patient may need maintenance plus replacement, but adding them blindly causes overload. Redistribution and electrolyte disorders require diagnosis-specific planning because total-body sodium, plasma sodium and intravascular volume are different variables. Rapid correction can cause neurological injury; use the relevant condition pathway and senior help.
Reassessment closes the prescription. Mark a review time on every order and review cumulative balance, weight, respiratory status, peripheral oedema, urine output and laboratory trends. Charts contain measurement error, so reconcile them with physiology. Stop IV fluid promptly when enteral intake is adequate. Handover must identify the fluid indication, calculation, recent response, limits for escalation and the clinician responsible for the next review.
Key points
- Prescribe IV fluid only when oral or enteral intake cannot meet a defined need, and state whether the purpose is resuscitation, maintenance, replacement or redistribution.
- For non-sepsis adult resuscitation within NICE CG174 scope, use crystalloid containing sodium 130–154 mmol/L as a 500 mL bolus over less than 15 minutes, then reassess immediately.
- For an adult at high risk of severe illness or death from suspected sepsis under NICE NG253, start 250 mL isotonic electrolyte crystalloid, preferably balanced, ideally over 10–15 minutes and reassess after each bolus.
- Initial routine adult maintenance is 25–30 mL/kg/day water with about 1 mmol/kg/day each of sodium, potassium and chloride, plus 50–100 g/day glucose to limit starvation ketosis.
- Consider 20–25 mL/kg/day for older or frail adults and for renal impairment or cardiac failure; obesity, oedema and complex redistribution need expert adjustment.
- Add abnormal ongoing losses and subtract reliable oral, enteral, medication and blood-product inputs; replacement composition should resemble the measured or estimated loss.
- Potassium is prescribed only after checking renal function, current concentration, ECG risk and local product limits; never add potassium manually to an IV fluid bag or improvise concentration or administration rate.
- Every prescription requires a time, endpoint and review of observations, examination, fluid balance, weight and appropriate laboratory trends.
02Situations and prioritiesThe context, relevant information and actions that matter most.
Hypotension, tachycardia, prolonged capillary refill, altered mentation, cool peripheries, oliguria or lactate elevation can indicate impaired perfusion but require causal assessment.
Reduced intake, thirst, dry mucosa, postural symptoms, concentrated urine and weight loss suggest water deficit without necessarily requiring rapid bolus therapy.
Rising weight, peripheral or sacral oedema, pulmonary crackles, increasing oxygen need and elevated venous pressure indicate excessive or redistributed fluid.
Vomiting, diarrhoea, stoma output, drains, fever, burns and polyuria can exceed routine needs and alter electrolyte composition.
Cardiac, renal or hepatic failure, pregnancy, burns, severe malnutrition and major electrolyte disturbance sit outside simple maintenance arithmetic.
Antibiotic infusions, drug diluents, enteral feed, flushes, blood products and oral drinks all contribute to water and solute balance.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
ABCDE and perfusion assessment - Why
- Identify immediate circulatory compromise and its cause before choosing fluid.
- Interpretation and limitations
- If shocked, treat the cause and use a time-limited resuscitation trial; if not shocked, distinguish deficit, maintenance need and redistribution.
- 02
Fluid balance and weight - Why
- Reconcile documented input and output with daily weight and physical findings.
- Interpretation and limitations
- A one-litre retained water change approximates one kilogram, but scales, timing and unmeasured losses introduce error.
- 03
Urea, creatinine and electrolytes - Why
- Assess renal handling and deficits before and during IV therapy.
- Interpretation and limitations
- Trends guide adjustment; plasma sodium reflects water balance relative to solute and is not a direct measure of total-body sodium.
- 04
Urine output trend - Why
- Measure output accurately when clinically indicated and relate it to perfusion, obstruction and renal injury.
- Interpretation and limitations
- Oliguria can reflect hypovolaemia, intrinsic renal injury or obstruction; repeated blind fluid boluses can worsen overload.
- 05
Loss measurement - Why
- Measure drains, stoma and urine where possible and estimate other losses transparently.
- Interpretation and limitations
- Replacement is added to maintenance only after accounting for all other inputs and should be reviewed as the loss changes.
- 06
Post-prescription reassessment - Why
- Repeat observations, perfusion and overload examination at the stated endpoint.
- Interpretation and limitations
- Improvement supports the intervention; absent response or harm requires stopping, reclassification and senior escalation.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked exampleMaintenance calculation with verificationA 70 kg adult cannot drink for 24 hours, is haemodynamically stable, has no abnormal losses and has normal renal and cardiac function.+
- 1Classify the indication as routine maintenance after confirming there is no resuscitation need, deficit requiring separate correction, abnormal loss or redistribution problem.
- 2Calculate water at 25–30 mL/kg/day: 70 × 25 = 1,750 mL and 70 × 30 = 2,100 mL over 24 hours; document the range and select within it using clinical context.
- 3Calculate approximate daily electrolytes at 1 mmol/kg each: about 70 mmol sodium, 70 mmol potassium and 70 mmol chloride, and account for 50–100 g glucose plus every non-IV-fluid input.
- 4Prescribe available fluids through the local safe system, then verify cumulative balance, weight, examination, urine output, renal function and electrolytes at the planned review; stop when enteral intake resumes.
02Emergency approachAdult fluid resuscitation trialAn adult with suspected infection has cool peripheries, prolonged capillary refill and hypotension without pulmonary congestion.+
- 1Call for senior help, perform ABCDE assessment and treat the cause while confirming that a fluid resuscitation trial is appropriate.
- 2Because this is suspected sepsis with high-risk circulatory features, give 250 mL isotonic electrolyte crystalloid, preferably balanced, ideally over 10–15 minutes under NICE NG253 rather than applying the general CG174 500 mL regimen.
- 3Reassess after that bolus using pulse, blood pressure, capillary refill, mental state, urine output, respiratory status and signs of pulmonary overload; if improvement is insufficient and there is no overload, consider a further 250 mL and reassess again.
- 4Count all pre-arrival and in-hospital boluses toward the NG253 maximum of 1,000 mL. If improvement is inadequate by that point, stop automatic fluid escalation, obtain senior advice and reassess shock mechanism and critical-care needs.
03Applied approachReplacing high stoma lossesA stable patient receives maintenance fluid but develops increasing measured stoma output and falling weight.+
- 1Quantify output by interval and check oral intake, urine, weight, observations and electrolyte trends.
- 2Separate baseline maintenance from additional replacement and estimate the water and solute composition of the measured loss.
- 3Use the local specialist plan to replace losses and correct deficits safely, with surgical, nutrition or renal input when needed.
- 4Review frequently and reduce replacement as output falls, avoiding continuation of yesterday’s rate after physiology changes.
05Relevant medicines and safetySpecific regimens and precautions when the skill involves prescribing.
Adult resuscitation crystalloid
Give 500 mL of crystalloid containing sodium 130 to 154 mmol/L over less than 15 minutes, then reassess.Applies only to adults within NICE CG174 scope and not suspected sepsis or another condition with a dedicated regimen. Reassess after every bolus; use the current condition-specific pathway for excluded groups, overload risk or complex shock.
Initial adult routine maintenance fluid
Supply 25 to 30 mL/kg/day water, approximately 1 mmol/kg/day each sodium, potassium and chloride, and 50 to 100 g/day glucose.Adjust for every other input, loss and comorbidity; consider 20 to 25 mL/kg/day in older, frail, renal-impaired or cardiac-failure patients and follow local potassium safeguards.
06Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- For resuscitation, reassess after each bolus; repeated unreviewed boluses are a prescribing error.
- For ongoing IV therapy, review at least daily and more often when unstable, with clinical examination, balance, weight and laboratory data.
- Measure or estimate abnormal losses by interval and revise replacement as the rate and composition change.
- Monitor potassium and renal function before and during supplementation, following local concentration and administration safeguards.
- Document oral and enteral recovery and discontinue IV fluid as soon as it no longer has a defined indication.
- At every transition, hand over indication, cumulative balance, last response, next review time and escalation limits.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Sodium concentration is not volume status
Hyponatraemia and hypernatraemia describe water relative to solute; either can coexist with low, normal or high extracellular volume.
Maintenance glucose is limited
The recommended glucose amount reduces starvation ketosis but does not meet nutritional energy requirements or treat established malnutrition.
A bolus is a diagnostic intervention
The response and adverse effects supply information; writing several sequential boluses without reassessment discards that information.
Charts need reconciliation
Missing oral intake, unmeasured losses and inaccurate urine collection can make arithmetic precise but wrong; compare with weight and examination.
Scope changes the regimen
Children, pregnancy, burns and severe renal or liver disease require their own guidance or expert plan, not extrapolation from adult CG174.
Exam calculation discipline
State indication, formula, arithmetic, units, adjustments and review endpoint so an examiner can see both numerical and clinical reasoning.
Replacement is dynamic
A measured loss should be replaced over a defined interval and recalculated; a fixed rate becomes wrong when the loss changes.
Prescriptions need totals
Write the intended 24-hour water and electrolyte totals, not only individual bags, so cumulative excess is visible.
08Common pitfallsFrequent interpretation and management errors.
- 01
Using maintenance fluid to resuscitate shock or repeating resuscitation fluid as routine maintenance.
- 02
Prescribing by bag habit without weight, indication, other inputs or abnormal losses.
- 03
Adding potassium without current renal function, electrolyte results and local administration safeguards.
- 04
Responding to oliguria with repeated fluid before considering obstruction, intrinsic renal injury or overload.
- 05
Treating oedema as proof of adequate circulating volume or treating low sodium as proof of sodium depletion.
- 06
Failing to mark a review time, stop IV therapy or transfer ownership at handover.