Fluids and electrolytes

IV fluids: choice, dose and stewardship

Reviewed Nov 2026·3 references
New· views rounded down, updated weekly

Treat fluids as drugs with four phases: resuscitation, optimisation, stabilisation, de-escalation. Balanced crystalloids are reasonable default resuscitation fluids; saline for TBI and hypochloraemia; albumin selectively; never starches.

Definition
Four indications: resuscitation, replacement of ongoing losses, maintenance (often unnecessary when enteral feed and drug diluents already cover water needs), and nutrition.

At the bedside

Timed steps
  1. 1

    Bolus and reassess

    Resuscitation

    250-500 mL balanced crystalloid over 15-30 min; reassess perfusion and fluid responsiveness (PLR, POCUS) before each further bolus.

  2. 2

    Balanced vs saline

    Choose

    SMART (n = 15,802) showed fewer major adverse kidney events with balanced fluids; PLUS and BaSICS showed no mortality difference. Balanced fluids are a reasonable default.

  3. 3

    Use 0.9% saline

    Exceptions

    Severe TBI / raised ICP (BaSICS signal of harm with balanced fluid in TBI), hypochloraemic metabolic alkalosis, hyponatraemia.

  4. 4

    Adult needs

    Maintenance

    Water 25-30 mL/kg/day, Na+ 1 mmol/kg, K+ 1 mmol/kg, glucose 50-100 g/day; count all drug infusions and feeds (fluid creep).

  5. 5

    Once stable

    De-escalate

    Stop maintenance fluid, concentrate infusions, target even or negative balance; diuretics or RRT for overload.

Composition of common IV fluids (mmol/L)

FluidNa+Cl-K+BufferOsmolarity
0.9% NaCl1541540None308
Ringer's lactate (Hartmann's)130-131109-1114-5Lactate 28-29273-278
Plasma-Lyte 148 / A140985Acetate 27, gluconate 23294
5% dextrose000None278 (free water once glucose metabolised)
DNS (5% dextrose in 0.9% NaCl)1541540None586
Human albumin 4-5% / 20%~130-160variable< 2None~300

Values vary slightly by manufacturer; check the bag. Hydroxyethyl starch is associated with AKI and death in sepsis and should not be used.

Red flag · call your senior now
Lung crackles, rising oxygen need, B-lines or a plethoric non-collapsing IVC after boluses: stop fluid.
Pitfall
Running 'maintenance' DNS at 100 mL/h by default in a patient already on enteral feeds and multiple drug infusions.
Pitfall
Hypotonic fluids (dextrose-saline, 5% dextrose) as maintenance in sick patients → hospital-acquired hyponatraemia.
Pearl
Write the fluid order as a drug: type, volume, rate, indication, review time.

Calculators for this topic

Maintenance fluid rate (4-2-1 rule)

Holliday-Segar hourly maintenance: 4 mL/kg/h for the first 10 kg, 2 mL/kg/h for the next 10 kg, 1 mL/kg/h for each kg above 20.

Burns fluid in first 24 h

mL/kg/%TBSA × weight × %TBSA (partial + full thickness). Half in the first 8 h from the time of burn.

References

  1. 1

    Semler MW, Self WH, Wanderer JP, et al. Balanced crystalloids versus saline in critically ill adults (SMART). N Engl J Med. 2018;378(9):829-839

  2. 2

    Finfer S, Micallef S, Hammond N, et al. Balanced multielectrolyte solution versus saline in critically ill adults (PLUS). N Engl J Med. 2022;386(9):815-826

  3. 3

    Zampieri FG, Machado FR, Biondi RS, et al. Effect of intravenous fluid treatment with a balanced solution vs 0.9% saline solution on mortality in critically ill patients (BaSICS). JAMA. 2021;326(9):818-829

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Hyponatraemia

Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.