Fluid charting comes up as a station. Most candidates have never been taught it properly; they learned by copying whatever the registrar wrote.

This is the method. Follow it in order and you can do it every time.

The short version:

• Water: 25 to 30 mL/kg/day, or 20 to 25 if older, frail, renal impairment or cardiac failure
• Sodium, potassium, chloride: 1 mmol/kg/day Glucose: 50 to 100 g/day
• Australian maintenance bag: sodium chloride 0.3% + glucose 3.3% (Na 51, Cl 51, glucose 33 g per litre)
• No premixed 0.3%/3.3% with potassium exists here. Use 18%/4% + 20 or 30 mmol KCl
• Peripheral potassium ceiling: 40 mmol/L, 10 mmol/hour

What do you check before you chart anything?

Never chart from the last prescription. Look at:

1. Can she drink? If she can, she may not need a drip at all. Ask this first, out loud.
2. Her weight. Every calculation depends on it. Ideal body weight if she is obese.
3. Her renal function. Urea, creatinine, and today’s electrolytes.
4. Her urine output. Below 0.5 mL/kg/hour is oliguria.
5. Her fluid balance chart. Yesterday’s totals, and whether she is behind.

Then examine her. Say all of this out loud in a station, it is marked.

Which type of fluid does she need?

Name it before you prescribe. There are three you will use.

Resuscitation — she is shocked or acutely hypovolaemic. Bolus of isotonic crystalloid, then reassess. In haemorrhage, control the bleeding first; do not pour in litres.

Replacement — she is losing fluid now. Vomiting, diarrhoea, stoma, drains, burns. Replace what is going out.

Maintenance — she simply cannot drink. Smallest volume of the three. Most often over-prescribed.

She may need two at once. Say so: “She needs replacement for her losses on top of her maintenance.”

Two more worth naming if asked: redistribution (fluid is in the wrong compartment — sepsis, liver failure, heart failure) and reassessment (unstable patients every 2 to 4 hours, everyone else at least daily).

How do you calculate maintenance fluids?

Four steps.

Step 1. Water.

• Healthy adult: 25 to 30 mL/kg/day
• Older, frail, renal impairment, cardiac failure, malnourished: 20 to 25 mL/kg/day

For a 70 kg healthy adult that is 1750 to 2100 mL. Not three litres. Above 2.5 L/day you start causing hyponatraemia.

Step 2. Electrolytes.

• Sodium, potassium, chloride: 1 mmol/kg/day each
• Glucose: 50 to 100 g/day

Write these numbers down. You will check your prescription against them.

Step 3. Deficit.

If she is behind on the chart, add it. Replace half over the first 8 hours and half over the next 16. If cardiac reserve is poor, slow that to half over 12 hours and half over 24.

One thing to watch. Fluid balance charts record only what can be measured. Insensible losses are often written as zero. They are not zero — an adult loses at least 800 mL a day through skin and breathing, roughly 50 mL an hour, offset by about 400 mL of metabolic water. If the chart totals as though insensible loss were nil, she is more behind than it says. Point that out.

Step 4. Pick your bags and add up what you have given.

What is in each IV fluid bag?

Per litre. Learn this table.

 

Two things to notice.

One litre of 0.9% saline contains 154 mmol of sodium. A 70 kg adult needs 70 mmol for the whole day. That is why saline is a poor maintenance fluid and a good replacement fluid.

The bag Australian guidance names for adult maintenance is 0.3% sodium chloride with 3.3% glucose. UK resources use 0.18%/4%. Both exist here. If you memorised numbers from an overseas guide, they are for a different bag.

 

Australian IV fluid bag compositions, sodium potassium chloride and glucose per litre

The potassium problem: what you can actually order

There is no premixed bag of 0.3%/3.3% with potassium in Australia. So the worked examples you will read describe a bag you cannot order.

What you can order off the shelf:

 

Do not add potassium to a bag yourself. Use a premix. Ward preparation is permitted in some states only when premix and pharmacy compounding are both unavailable, under protocol, with a second check. Concentrated ampoules are not ward stock. Never add potassium to a bag that is already hanging.

So if she needs maintenance fluid with potassium, the practical Australian answer is usually 0.18% sodium chloride with 4% glucose plus 20 or 30 mmol KCl — because that premix exists.

What the actual chart looks like

There is no national IV fluid chart in Australia. The NIMC does not have a fluid section — it has a tick-box that says “Additional charts: ☐ IV fluid”, which is the national chart telling you to go and get a different one. Fluid charts are state forms.

In NSW there are two, and you need both.

The Adult Fluid Order (SMR120003) — this is where you prescribe. The columns you fill in, left to right:

 

Note what the top of the form asks for before any of that: Facility, Allergies/ADR, and Instructions. The allergy box comes before the prescription, same as on the NIMC.

Note also the two right-hand columns. Every fluid order is independently checked by a second nurse. If your handwriting is ambiguous or you have written “over 8 hours” where the chart wants a rate, you have created work at the bedside and a chance to get it wrong.

 

Blank adult IV fluid order chart showing the columns a prescriber completes: date, fluid type, volume, additive, rate, route, prescriber, and the nursing administration columns

The Daily Fluid Balance (SMR120001) — this is where you find out whether you were right. It runs by time down the left, and it asks for Weight in kg at the top of the page, which tells you how seriously to take daily weights.

• Intravenous input: three lines, A, B and C, each with Site, Solution and Volume, then a progressive total (P)
• Oral input: oral mL, enteral mL, progressive total (OE)
• Progressive total in: P + OE = X
• Output: urine, vomitus/gastric/aspirate, drain 1, drain 2, other/faecal, progressive total (Y)
• Progressive balance: X – Y

Look at the output columns. Urine, vomit, drains, faeces. There is no column for insensible losses, because they cannot be measured — which is exactly why the balance at the bottom of that page is not the patient’s true balance, and why you add roughly 800 mL a day back in your head.

Two practical notes. Your patient may have three infusions running, which is why there are three line columns and why the site is recorded next to each one. And the order chart and the balance chart are separate pieces of paper — writing on one does not populate the other.

 

Blank daily fluid balance chart showing intravenous input for three lines, oral and enteral input, progressive totals, output columns and running balance

In digitised NSW districts you will meet the eMR fluid module instead of these forms. The fields are the same.

Worked example 1: a well 80 kg adult

Mr Dilan Fernando, 34, day 1 after appendicectomy. Nil by mouth. Well. 80 kg. Chart shows even measured balance, insensible recorded as zero.

Water: 80 × 25 to 30 = 2000 to 2400 mL

Electrolytes: 80 mmol each. Glucose 50 to 100 g.

Deficit: chart says even, but insensible is recorded as zero, so he is a few hundred mL behind. Stay at the upper end rather than add a separate deficit.

 

83 mL/hour. One litre 12-hourly.

Check it. Volume 2000 against 2000 to 2400 — good. Glucose 80 g — good. Sodium 62 against 80, potassium 60 against 80 — both slightly under.

That is fine, and say why: “This under-delivers his sodium and potassium slightly, which I am comfortable with overnight in a well 34-year-old with normal kidneys. Adding a third bag would take him to 3000 mL, which is nearly 38 mL/kg and too much. I will check his electrolytes in the morning and stop the drip once he is drinking.”

 

Worked example fluid order chart for an 80 kg adult: two bags of sodium chloride 0.18 per cent with glucose 4 per cent and 30 mmol potassium chloride at 83 mL per hour

 

Worked example daily fluid balance chart over twelve hours showing progressive totals and a balance of plus 131 mL, with insensible losses not recorded

Worked example 2: a frail 82-year-old

Mrs Beatrice Ashgrove, 82, day 2 after fractured neck of femur repair. Drowsy on analgesia, barely drinking. 52 kg. Frail. Creatinine up on baseline.

Same method. Different numbers.

Water: 52 × 20 to 25 = 1040 to 1300 mL

Note what just happened. The healthy-adult figure would have given up to 1560 mL. The frailty rule took 250 to 500 mL a day off her prescription. That is the whole point.

Electrolytes: 52 mmol each.

 

50 mL/hour, and review before the bag finishes rather than writing up a second one now.

Check it. This under-delivers against the formula deliberately: “She is 82, frail, with a rising creatinine. The risk of overload and hyponatraemia is greater than the risk of a day of slightly low sodium. I will weigh her daily and check her electrolytes in the morning. My first priority is getting her drinking — I would review her analgesia, because the reason she is not drinking is that she is drowsy.”

That last line matters. The best fluid decision here is to fix the opioid, not to hang another bag.

 

Worked example fluid order chart for a frail 82 year old: one bag at 50 mL per hour with review before the bag finishes

The numbers to know

Potassium. Peripheral maximum: 40 mmol/L concentration, 10 mmol/hour rate, via pump. Beyond either, you need cardiac monitoring, frequent bloods and a large vein. Higher concentrations need central access.

Hyponatraemia. Assess volume status first. Hypovolaemic gets sodium chloride; euvolaemic or hypervolaemic gets fluid restriction and a search for the cause. Correct by no more than 8 mmol/L in 24 hours. Overcorrection causes osmotic demyelination syndrome.

Hypernatraemia. No more than 0.5 mmol/L per hour, 10 mmol/L per day.

Oliguria. Below 0.5 mL/kg/hour.

Hyperkalaemia. ECG first. Calcium is indicated by ECG change, not by the number. Insulin with glucose shifts it — the glucose is there to prevent hypoglycaemia, not to treat. Then remove potassium from the body and review the medications that caused it.

Three things that have changed since you learned this

Balanced versus saline. The Australian and New Zealand PLUS trial found no difference in mortality or kidney injury. Prefer a balanced solution for large volumes or prolonged use because of hyperchloraemic acidosis — but they contain potassium, so think again in renal impairment. Explain your choice; do not pick a side.

Colloids are out. Hydroxyethyl starch has a TGA boxed warning and is contraindicated in critically ill and septic patients. Gelatins are available but not recommended for resuscitation. Use crystalloid.

Glucose 5% is not a resuscitation fluid. It behaves as free water once metabolised and drops the sodium.

Five common mistakes

1. Charting the next bag without seeing the patient.
2. Giving a number, not a prescription. “A litre of saline” is not an answer. Fluid, volume, rate, reason, duration.
3. Not asking whether she can drink.
4. Using the healthy-adult figure in a frail patient. The most common arithmetic error, and the one that causes harm.
5. Ignoring the medication chart. A vomiting patient on an SGLT2 inhibitor needs ketones checked even if her glucose is normal — euglycaemic ketoacidosis. Withhold the SADMANS drugs in acute illness. Watch the triple whammy: ACE inhibitor or ARB plus diuretic plus NSAID.

Frequently asked questions

How do I calculate maintenance fluids for an adult?

Water at 25 to 30 mL/kg/day on ideal body weight, or 20 to 25 mL/kg/day if the patient is older, frail, malnourished, or has renal impairment or cardiac failure. Then 1 mmol/kg/day each of sodium, potassium and chloride, and 50 to 100 g/day of glucose. For a 70 kg healthy adult that is 1750 to 2100 mL and about 70 mmol of each electrolyte.

Which bag is the Australian maintenance fluid?

Sodium chloride 0.3% with glucose 3.3% — 51 mmol/L sodium and chloride, 33 g/L glucose. The 0.18%/4% bag used in UK resources is also available here and is usually what you reach for when you need potassium, because it comes premixed with 20 or 30 mmol KCl and the 0.3%/3.3% bag does not.

Can I add potassium to a fluid bag myself?

Use a premix. Ward preparation is permitted in some states only when premix and pharmacy compounding are both unavailable, under an endorsed protocol with a second-person check, and is more tightly restricted in others. Concentrated ampoules are not ward stock and potassium is never added to a hanging bag.

Why does the fluid balance chart show zero insensible losses?

Because it records only measured losses. Look at the output columns on the NSW Daily Fluid Balance (SMR120001) – urine, vomitus/gastric, two drains, other/faecal. There is no insensible column, because insensible loss cannot be measured. An adult loses at least 800 mL a day through skin and breathing, roughly 50 mL an hour, offset by about 400 mL of metabolic water. A chart totalled as though insensible losses were zero understates the deficit.

How much potassium can run through a peripheral line?

40 mmol per litre and 10 mmol per hour, via pump. Beyond either you need cardiac monitoring, frequent bloods and a large vein. The isotonic 10 mmol in 100 mL premix is designed for peripheral use.

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If you want an honest read on where you are, or a full-dress rehearsal before exam day, you can try a session free or book a mock exam.

Dr Vinu Verghis is the Academic Lead of Oyamed AMC OSCE Coaching, a CPD Home Accredited Provider based in Brisbane. She holds an MBBS, MSc, MPH, FHEA and Cert Clin Ed, examines OSCEs at university level, and has personally walked the AMC pathway. Visit oyamed.com.

Sources: Australian Commission on Safety and Quality in Health Care, Intravenous fluid therapy: Principles for safe, appropriate and sustainable use (2026); Queensland Health, Guidelines for Prescribing Intravenous Fluids for Adults, and Prescribing Guidelines for HYPO- and HYPER-Electrolyte Disturbances in Adults (updated May 2026); NICE CG174, adopted in Australian practice; NSW Clinical Excellence Commission Safety Information 001/24 (2024) and High-Risk Medicine Standard: Potassium (Intravenous) (2025); WA Health Intravenous Potassium Standard (2025); Baxter Healthcare Australian Product Information; Finfer et al., PLUS trial, New England Journal of Medicine (2022); TGA safety advisory on hydroxyethyl starch; ADS/ADEA/ANZCA/NZSSD alert on ketoacidosis with SGLT2 inhibitors (2022).

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