Ward · prescribing

IV Fluid Prescribing

Step 1

Why

Red flags

The shocked patient written up for maintenance → resuscitate, do not maintain
Fluid overload / pulmonary oedema → stop, do not keep prescribing
Severe or symptomatic hyponatraemia, often from hypotonic maintenance fluids
Ringer’s lactate (K⁺-containing) with AKI or hyperkalaemia: caution

The 5 Rs: resuscitation, routine maintenance, replacement, redistribution, reassessment
Most prescribing errors come from answering the wrong one

Step 2

Resuscitation

The shocked or hypovolaemic patient

500 mL balanced crystalloid (Ringer’s lactate / Plasma-Lyte) or 0.9% saline as a stat bolus < 15 min
250 mL if frail, elderly, or known cardiac / renal disease
Reassess after every bolus: HR, BP, cap refill, urine output, lactate
After ~2000 mL with ongoing instability → call for help + find the cause (bleeding, sepsis, cardiac); still shocked after ~2 L → vasopressors (e.g. noradrenaline) via central access

Step 3

Maintenance

Euvolaemic, nil by mouth

need	amount
water	25–30 mL/kg/day
Na⁺ / K⁺ / Cl⁻	~1 mmol/kg/day each
glucose	50–100 g/day (limits starvation ketosis: not for nutrition)

A typical 70 kg adult ≈ 2–2.5 L/day with ~1 mmol/kg Na and K
Go lower in the elderly, heart failure, and renal impairment: overload is the common harm
KCl additives: add 20–40 mmol KCl per litre of maintenance fluid. Peripheral max ~10 mmol/hr; higher rates or concentrations need cardiac monitoring and central access

Worked examples (70 kg, nil by mouth)

Maintenance ≈ 2–2.5 L/day: e.g. 1 L 0.9% saline + 20 mmol KCl, then 2 × 1 L 5% dextrose + 20 mmol KCl, each over 8 h
Resuscitation: 500 mL Ringer’s lactate (or 0.9% saline) stat over <15 min → reassess → repeat; 250 mL if frail / cardiac / renal

Step 4

Replacement

Add ongoing losses (vomiting, NG, diarrhoea, drains, high stoma) to maintenance, matched to the loss
- Diarrhoea / high stoma → balanced crystalloid (RL)
- Vomiting or NG loss → 0.9% saline + KCl (replaces lost Cl and K)
- Biliary or pancreatic loss → balanced crystalloid
Account for third-spacing in sepsis, pancreatitis, post-op

Step 5

Which bag

What’s in it (mmol/L)

fluid	Na	K	Cl	glucose	buffer
Ringer’s lactate (RL)	131	5	111	–	lactate 29
Plasma-Lyte	140	5	98	–	acetate 27
0.9% saline	154	–	154	–	–
5% dextrose	–	–	–	50 g/L	–
0.45% saline / 5% dex	77	–	77	50 g/L	–

Which bag

Balanced (Ringer’s lactate / Plasma-Lyte): resuscitation + replacement; caution if hyperkalaemic
0.9% saline: resuscitation + replacement; large volumes → hyperchloraemic acidosis
5% dextrose: free water / maintenance water; not a resuscitation fluid
Cl: saline 154, Ringer’s lactate 111 · add KCl 20 to 40 mmol/L for maintenance

Step 6

Bicarbonate

Bicarbonate does two different jobs: a fluid you hang, or a drug you push. Decide which before you draw it up

1 · Buffering a sick patient (dilute, hung as a fluid)

Make it: 3 × 50 mL amps of 8.4% sodium bicarbonate into 850 mL of 5% dextrose or sterile water, giving 1 L at Na⁺ 150, HCO₃⁻ 150 mmol/L (roughly isotonic)
Severe metabolic acidosis: benefit clearest with coexisting AKI (where BICAR-ICU found a mortality signal); without AKI it buys time, it does not fix the cause
To alkalinise urine: salicylate poisoning, tumour lysis, some chemotherapy, occasionally contrast
Recheck a gas and the HCO₃⁻ about every 2 h and retitrate. This is not a set-and-forget bag

2 · Treating a poisoning (concentrated, pushed like a drug)

Neat 8.4%: one 50 mL amp = 50 mmol
Sodium-channel-blocker and TCA toxicity: your trigger is a widening QRS, not the pH on the gas. Dose to the QRS narrowing
Also in severe acidosis during arrest or hyperglycaemic crisis
Strongly hypertonic: use the biggest vein you have, central where time allows. Extravasation causes tissue necrosis

Whichever job you are doing

Never run bicarbonate through a line carrying calcium, Ringer’s lactate included: it precipitates
Bicarbonate drives K⁺ into cells → recheck the potassium and replace it
Watch the overshoot: metabolic alkalosis, hypernatraemia, hyperglycaemia

Free water: D5 + 0.45% saline

Hypotonic, Na⁺ 77 mmol/L: free water with a little sodium in it
The usual vehicle for correcting a free-water deficit in hypernatraemia, and a maintenance option; add KCl as needed
Never a resuscitation fluid

Step 7

Reassess

Daily RFT, fluid balance chart, weight
Examine for overload: crackles, oedema, raised JVP
Stop or reduce IV fluids once the patient is eating and drinking

Last updated · October 2026

Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.