Intravenous Fluid Therapy
NICE CG174-based guidance on IV fluids in adults — indication, fluid choice, rates and monitoring
Intravenous (IV) fluid therapy is one of the most commonly prescribed treatments in hospital medicine, yet it carries significant risks when used inappropriately. NICE Clinical Guideline CG174 (2013, updated 2017) provides a comprehensive framework for the safe prescribing of IV fluids in adults in hospital, covering routine maintenance, replacement of deficits, resuscitation, and redistribution of fluid compartments.
The 5 Rs Framework (NICE CG174)
NICE CG174 organises IV fluid prescribing around five clinical goals — known as the '5 Rs': Resuscitation (restoring circulating volume in shocked or compromised patients), Routine maintenance (providing daily requirements of water, sodium, potassium, and glucose), Replacement (correcting pre-existing deficits or ongoing abnormal losses), Redistribution (managing abnormal fluid distribution, e.g. third-space losses, oedema), and Reassessment (monitoring and adjusting fluid prescriptions regularly). Before prescribing any IV fluid, clinicians should consider which of these five purposes applies, choose the appropriate fluid type and volume, and review the patient's response regularly. Over-prescribing IV fluids is as dangerous as under-prescribing — fluid overload causes pulmonary oedema, heart failure, and AKI.
General Maintenance Fluids (Normal Adults)
For adults who cannot meet their daily requirements orally, NICE CG174 recommends a restrictive, isotonic approach to maintenance. Daily targets: approximately 25–30 mL/kg/day water; 1 mmol/kg/day sodium, potassium, and chloride; 50–100 g/day glucose (to limit starvation ketosis). Preferred regimen: Hartmann's solution (compound sodium lactate) or 0.9% sodium chloride with 20–40 mmol potassium added per litre, running at approximately 1–2 mL/kg/hour. Avoid glucose 5% as a sole maintenance fluid in surgical patients — it provides insufficient sodium and no electrolytes other than glucose. Reassess at least every 24 hours. Caution in elderly, cardiac, renal, or hepatic patients — reduce rates and volumes significantly in these groups.
Hypovolaemia and Fluid Resuscitation
Hypovolaemia occurs when circulating volume is reduced — from haemorrhage, dehydration, vomiting, diarrhoea, or sepsis. Clinical signs include tachycardia, hypotension, reduced skin turgor, oliguria (<0.5 mL/kg/hour), elevated lactate, and confusion. NICE CG174 recommends crystalloid-first resuscitation. Preferred fluid: Hartmann's solution (compound sodium lactate) — the NICE-preferred resuscitation fluid due to its physiological electrolyte composition and lower risk of hyperchloraemic acidosis compared with 0.9% NaCl. 0.9% sodium chloride (normal saline) is acceptable for resuscitation but large volumes cause hyperchloraemic metabolic acidosis. Regimen: 500 mL crystalloid bolus over 15 minutes, then reassess. Repeat bolus if haemodynamic compromise persists. Target: MAP ≥65 mmHg, urine output >0.5 mL/kg/hour, improvement in clinical signs. Colloids (e.g. human albumin solution) have a limited role — do not use synthetic colloids (starches) due to risk of AKI and coagulopathy. Always look for and treat the underlying cause of hypovolaemia.
Sepsis and Septic Shock
Sepsis requires immediate, time-critical fluid resuscitation as part of the Sepsis 6 bundle (NICE NG51, 2016; Surviving Sepsis Campaign). IV fluid is one of the six key actions within the first hour. Fluid choice: 0.9% sodium chloride or Hartmann's solution — Hartmann's preferred for large volumes to reduce hyperchloraemic acidosis risk. Regimen (NICE NG51): 500 mL crystalloid bolus IV over 15 minutes; repeat and reassess. For septic shock (hypotension refractory to initial bolus): escalate to HDU/ITU, consider vasopressors (noradrenaline). Target end-points: MAP ≥65 mmHg, urine output >0.5 mL/kg/hour, serum lactate normalising (<2 mmol/L). Caution: avoid fluid overload — reassess after each 500 mL bolus. In patients with heart failure or AKI, smaller boluses (250 mL) and more frequent reassessment are safer. Adjuncts: IV antibiotics within 1 hour, blood cultures before antibiotics, oxygen, urine output measurement, serum lactate measurement.
Diabetic Ketoacidosis (DKA)
DKA requires aggressive IV fluid resuscitation to restore intravascular volume and correct electrolyte abnormalities. JBDS/NICE joint guidance provides the DKA management protocol. Fluid choice: 0.9% sodium chloride (normal saline) — primary resuscitation fluid in DKA. Standard regimen (JBDS Protocol): 1 litre 0.9% NaCl over first hour; then 1 litre over next 2 hours; then 1 litre over next 2 hours; then 1 litre over 4 hours; then 1 litre over 4 hours; then 1 litre over 6 hours — adjust based on clinical response and urine output. Potassium replacement: add 40 mmol KCl per litre if K+ 3.5–5.5 mmol/L; do not add if K+ >5.5 mmol/L; hold insulin and get cardiac monitoring if K+ <3.5 mmol/L. Switch to 10% glucose 125 mL/hour when blood glucose falls below 14 mmol/L (continue 0.9% NaCl alongside). Resolution criteria: pH >7.3, bicarbonate >15 mmol/L, blood glucose <14 mmol/L, ketones <0.6 mmol/L. Monitoring: hourly CBG, ketones, urine output; 2-hourly ABG/VBG; ECG if K+ abnormal; minimum 4-hourly U&E.
Hyperkalaemia
IV fluids play a supporting role in the acute management of hyperkalaemia. The primary treatment approach focuses on membrane stabilisation, intracellular shift, and removal of potassium — IV fluids help by promoting urinary potassium excretion and avoiding potassium-containing fluids. Avoid potassium-containing fluids: do NOT use Hartmann's solution, Plasmalyte, or KCl-containing bags if K+ is elevated. Use 0.9% sodium chloride for IV access and fluid replacement in hyperkalaemia. For the intracellular shift component: 10 units Actrapid insulin in 50 mL 50% glucose given IV over 15–30 minutes (with 10% dextrose infusion to prevent hypoglycaemia). IV sodium bicarbonate 8.4% may be considered in severe acidosis to help shift potassium intracellularly, though evidence is limited. Fluid replacement with 0.9% NaCl supports renal excretion of potassium in patients with adequate renal function. Calcium gluconate 10 mL of 10% solution IV over 5–10 minutes (for cardiac protection) — does not lower serum K+ but protects the heart while other measures take effect. Monitor ECG continuously in severe hyperkalaemia (K+ >6.5 mmol/L or ECG changes).
Hyponatraemia
Hyponatraemia (Na+ <135 mmol/L) requires careful fluid management — the choice of fluid and rate of correction depends on the cause, severity, and acuity. Acute severe symptomatic hyponatraemia (Na+ <125 mmol/L with seizures, altered consciousness): 150 mL 3% hypertonic saline IV over 20 minutes; repeat if symptoms persist; aim for 5 mmol/L rise in Na+ over first hour. Chronic hyponatraemia (>48 hours): correct slowly — maximum 10–12 mmol/L per 24 hours; maximum 8 mmol/L per 24 hours in high-risk groups (alcoholism, malnutrition, liver disease). Rapid correction risks osmotic demyelination syndrome (central pontine myelinolysis) — potentially irreversible neurological injury. For hypovolaemic hyponatraemia (e.g. from diuretics, vomiting, diarrhoea): 0.9% NaCl IV to restore volume. For euvolaemic hyponatraemia (SIADH): fluid restriction (500–1000 mL/day); remove precipitating cause (drugs: SSRIs, carbamazepine, cyclophosphamide, NSAIDs, PPIs). For hypervolaemic hyponatraemia (heart failure, liver cirrhosis): fluid restriction and diuretics; avoid 0.9% NaCl. Monitor sodium levels every 4–6 hours during active correction.
Post-operative Fluid Management
Post-operative fluid management requires a careful balance between maintaining euvolaemia and avoiding fluid overload. NICE CG174 recommends a restrictive approach. Early oral intake should be encouraged wherever possible — IV fluids should be stepped down as soon as oral intake is re-established. Routine post-operative maintenance: Hartmann's solution (preferred) or 0.9% NaCl with added KCl 20–40 mmol/L at 1–1.5 mL/kg/hour. Avoid excessive 0.9% NaCl — large volumes cause hyperchloraemic acidosis and are associated with worse post-operative outcomes (NICE CG174). Assess for and replace ongoing losses: surgical drains, nasogastric aspirate, stomal output — replace like for like using the appropriate fluid (e.g. 0.9% NaCl + KCl for gastric losses). Daily reassessment: weigh patient, review fluid balance chart, check U&E and serum albumin. Stop IV fluids as soon as safe oral intake is established. Goal-directed fluid therapy (GDFT) guided by stroke volume or cardiac output monitoring (e.g. LiDCO, oesophageal Doppler) should be considered in high-risk surgical patients.
Heart Failure — Cautious Fluid Management
Patients with heart failure have severely limited tolerance for IV fluids — fluid overload rapidly precipitates acute decompensation and pulmonary oedema. IV fluids should be used with extreme caution and only when specifically indicated (e.g. true hypovolaemia from haemorrhage or dehydration). Avoid IV fluids in fluid-overloaded heart failure patients — diuretics (IV furosemide) are the treatment, not more fluids. If IV fluids are genuinely required (e.g. pre-operative fasting, DKA in a patient with HF): use minimum volumes (250 mL boluses, not 500 mL); prefer Hartmann's or 0.9% NaCl; reassess after every 250 mL; continuous clinical monitoring. Avoid glucose-saline preparations which add unnecessary sodium load. Restrict maintenance fluids to 1–1.5 L/day maximum. Monitor for signs of fluid overload: rising JVP, basal crackles, peripheral oedema, weight gain, worsening breathlessness. Always involve the cardiology team in management decisions. NICE NG106 (Heart Failure): fluid restriction of 1.5–2 L/day is recommended in severe heart failure with hyponatraemia.
Acute Kidney Injury (AKI)
IV fluid management in AKI requires careful individualisation — under-resuscitation worsens pre-renal AKI, while fluid overload causes further renal injury and pulmonary oedema. Pre-renal AKI (hypovolaemia): 500 mL crystalloid bolus (Hartmann's preferred) over 15 minutes; repeat and reassess; target urine output >0.5 mL/kg/hour. NICE NG148 recommends Hartmann's over 0.9% NaCl for large-volume resuscitation (reduces hyperchloraemic acidosis). Intrinsic or oliguric AKI: cautious fluid replacement — do not fluid-load oliguric patients without evidence of hypovolaemia; avoid fluid overload. Avoid potassium-containing fluids (Hartmann's, Plasmalyte) if serum K+ is elevated (>5.5 mmol/L) — use 0.9% NaCl. Stop nephrotoxins: NSAIDs, ACEi/ARBs, aminoglycosides, IV contrast. Fluid balance monitoring: accurate fluid chart, daily weight, urinary catheter for hourly urine output measurement in AKI Stage 2+. Loop diuretics (furosemide) are NOT used to treat AKI — only use if fluid overloaded. Indications for dialysis (NICE NG148): refractory hyperkalaemia, severe metabolic acidosis, symptomatic uraemia, fluid overload unresponsive to diuretics. This article has been prepared following careful evaluation of NICE CG174, NICE NG148, NICE NG51, JBDS DKA Protocol, BNF Fluids and Electrolytes chapter.