There are certain situations where you need to prescribe IV fluids which vary from fluid resuscitation to maintenance fluids if a patient is nil-by-mouth (NBM) (e.g. pre-operatively, 'drip & suck' for bowel obstruction, acute pancreatitis, recent stroke with unsafe swallow).

The Nice Guidance CG174 Intravenous fluid therapy in adults in hospital contains an excellent PDF
document about this.

You will often be bleeped "doctor, can you prescribe fluids for my patient". Before prescribing IV fluids for any patient…
  • Request an SBAR handover that focuses on whether this is fluid resuscitation or maintenance by requesting a NEWS score, reviewing indications (as above) & when they last had fluids (orally or IV)
  • Take an ABCDE approach that includes a fluid assessment. Remember a patient can have a "normal" blood pressure and still be substantially fluid deplete if they are usually hypertensive or are compensating well. Fluid resuscitation may be required if there are signs of shock - unstable observations (e.g. SBP <100, HR >90) or signs such as cold peripheries, CRT >2s
  • If the indications are as they are NBM then they require maintenance fluids
  • Use their latest blood tests for AKI & electrolytes to help guide what kind and how much fluid to prescribe and which electrolytes are needed.
Fluid resuscitation:
  • If the patient is shocked, review the cause e.g. septic/hypovolaemic/anaphylactic/cardiogenic
    • IV Fluids may worsen the situation (e.g. in cardiogenic shock with overloading)
    • Ensure the cause is being addressed: e.g. antibiotics in sepsis
  • Give a 500ml fluid bolus of a crystalloid such as PlasmaLyte, Hartmann's or 0.9% sodium chloride over <15mins. 
  • If the patient is unstable or you are worried, consider seeking senior help straight away with a low threshold for a medical emergency call 
  • A patient with known heart failure may still be dehydrated on clinical examination. In that case you can give a smaller volume of fluid over a longer time period e.g. 250ml over 30mins.
    • Similarly, the very elderly/frail (particularly if they are small) can be prone to overload so consider small boluses in these patients
    • If unsure if fluid deplete, raising their legs can artificially fluid resuscitate a patient. This may improve their observations & clinical exam findings suggesting fluid bolus will be helpful
  • Remember fluid resuscitation is an emergency therefore you should not bolus and leave. Reassess using ABCDE approach
  • Observations should be carried out at 15 minute intervals for rebound hypotension as the fluid re-distributes
  • If a patient requires further resuscitation, then you can give another 250-500ml bolus. If more than 2 bolus are required or you are worried at any stage, seek senior help
  • Seek senior help early if you're worried about fluid overload. It is easier to fix a situation early than late
  • Fluid resuscitation only corrects depletion. Remember they may still need continued IVF for maintenance
Routine maintenance:

Ensure you first review indications. Firstly, we do not routinely drink in the middle of the night therefore patients don't routinely need IV fluids overnight either. Usual indications include insufficient or no oral intake otherwise for therapeutic purposes for electrolytes.

Oral or other enteral fluids are best, it gives the chance for the gut to process & filter what it wants.

Normal daily fluid intake and electrolyte requirements:
  • 25-30ml/kg/day of fluid
  • 1 mmol/kg/day Na+, K+, Clo 
  • 50-100g/day glucose (5% glucose contains 5g/100ml) - NB not by weight
Note these are the minimum requirements to maintain a patient. If they are deplete or have losses (such as diarrhoea, vomiting, high output stoma, drains), these need to be added on top. If they are hypokalaemic for example, then they will need MORE than 1 mmol/kg/day

PlasmaLyte, Hartmann's & 0.9% sodium chloride contain between 130-160 mmol/L of sodium.
To understand this, a bag of ready salted crisp contains about 8 mmol of sodium therefore the average 1L of crystalloid fluid contains the sodium of 15-20 packs of salted crisp.

PlasmaLyte & Hartmann's contains 5 mmol/L of potassium. A banana contains about 15 mmol of potassium so it is about a third of a banana.

As you can imagine, we usually end up giving a lot of sodium to our patients and not enough potassium and usually no glucose. This is usually okay, because the kidneys are able to filter much of the excess sodium out & our potassium stores balance the potassium and we usually have enough glycogen stores to manage being NBM for <24 hours. We run into trouble if we are doing this for more than day as patients will quickly "run out" of potassium stores and become hypokalaemic which is why it is important to give the right amount.

Also note that we are giving 50-100g of glucose per day. That's about 1 bottle of lucozade which is hardly much and contains no protein or fat. If you are giving maintenance only fluids for more than a few days, talk to the dietitian to consider giving proper nutrition.

Worked example of an 80kg male for a 24 hour period
  • 25-30 x 80 kg = 2-2.5L fluid
  • 80 mmol each of Na/K/Cl
  • 50-100g glucose i.e. 1-2L of 5% dextrose/glucose
It is easier to prescribe 1L bags rather than be exact and correct daily based on fluid review. Thus, of the approximately 3L needed we can give 2x 1 litre of 5% glucose and then one litre of any salt solution (0.9% sodium chloride, Hartmann's or PlasmaLyte). This can run 8 hourly or 6 hourly to give the patient a break. This overshoots the sodium requirement, but that will practically always occur and will be filtered out. 

As for potassium, it comes pre-made in fixed amounts of 20 mmol or 40 mmol in ONLY bags that do NOT already contain potassium i.e. dextrose or 0.9% saline. Thus the 80 mmol can either be 2x 40 mmol in the bags of dextrose 5% or 20/20/40 if using 0.9% sodium chloride. 

If the patient has vomited 1 litre during the preceding 24 hours, then another 1 litre will be required. 

IV potassium should not be given at a rate higher than 10mmol/hr e.g. a 1L bag with 40mmol of potassium should be over a minimum of 4 hours

Further tips:
  • Do not prescribe blindly, especially for heart failure patients. Always assess clinically.
  • IV fluids are DRUGS and should not be prescribed unnecessarily. Always find out why they are needed
  • If a patient is able to eat or drink, then there's usually no need to prescribe IV fluids
  • A 80 kg male will require 80 mmol of K+ to keep his potassium static. If he is hypokalaemic, he will require more potassium
  • Always check the magnesium as hypokalaemia will not correct unless magnesium is corrected first
  • For obese patients you will need to use the ideal body weight.
  • Patient’s rarely need more than 3L of fluid per day.
  • Consider reducing fluids in elderly/frail, renal impairment or cardiac failure
By Dr Saman Jalilzadeh Afshari FY2
Edited by Dr Akash Doshi CT1