Monday 1 May, 2006

“Maintenance” IV fluids in euvolaemic adults

Posted in Emergency Dept., Medicine, Michael Tam, Surgery, Wards at 17:37 by Michael Tam

Index: Intravenous fluid therapy :: Printer friendly

Original article by: Michael Tam

Bag of IV fluids

Bag of IV fluids

The easy (autopilot) way:


  1. That the patient is relatively “normal
    • normal size
    • relatively well
    • no kidney failure
    • no heart failure
    • no electrolyte disturbance
    • no particular abnormal losses
  2. patient is “nil-by-mouth” (i.e., they have no other sources of hydration)
  3. patient is euvolaemic – i.e., not dehydrated or fluid overloaded.

If any of the assumptions are false, then you should seriously consider working it out properly. If they are all true, then you can use the following regimens (assuming standard 1L IV fluid bags):

Regimen One

  • Bag 1: 0.9% NaCl (“normal saline”) + 30 mmoL KCl (use premixed if available) then
  • Bag 2: 5% dextrose + 30 mmoL KCl then
  • Bag 3: 5% dextrose then back to Bag 1.

Regimen Two

  • Bag 1: 0.18% NaCl + 4% dextrose (“4% and a fifth”) + 30 mmoL KCl (use premixed if available) then
  • Bag 2: 0.18% NaCl + 4% dextrose + 30 mmoL KCl then
  • Bag 3: 0.18% NaCl + 4% dextrose then back to Bag 1.

Intravenous fluid infusion rate

  • Usual sized person: 125 mL/h (or “q8h”)
  • Smaller or older person: 100 mL/h (or “q10h”)
  • Tiny, old and frail person: 84 mL/h (or “q12h”) – though you shouldn’t be writing fluids on “autopilot” for the tiny, old and fail person.

You are hereby warned that imprudent use of “autopilot” therapy with intravenous fluids can (though rarely) harm your patients.

The proper way

In the usual setting, when you are prescribing intravenous fluids, you need to consider the following components:

  1. Water
  2. Sodium
  3. Potassium

Although you don’t “usually” have to worry about it you also need to be mindful of:

  • Calcium
  • Magnesium
  • Phosphate
  • Chloride

To work out water requirements, the “paediatric formula” is good for adults too and I recommend it:

Water infusion rate:

4 mL/kg/hr for the first 10 kg of body weight

+ 2 mL/kg/hr for the next 10 kg of body weight

+ 1 mL/kg/hr for the remainder of body weight

Then work out our sodium and potassium requirements:

Sodium: 1-2 mmol/kg/day

Potassium: 0.5-1 mmol/kg/day

So, for an otherwise healthy, euvolaemic 70 kg man:


  • (4 mL/kg/hr x 10 kg) + (2 mL/kg/hr x 10 kg) + (1 mL/kg/hr x 50 kg)
  • = 40 mL/hr + 20 mL/h + 50 mL/h
  • = 110 mL/hr (2.6 L per day)


  • 1 to 2 mmol/kg/day
  • = 70 to 140 mmol/day


  • 0.5 to 1 mmol/kg/day
  • = 35 to 70 mmol/day

Now, we need to convert this into the premixed bags of IV fluid:

What is in a bag of fluid?

0.9% NaCl solution (aka, “normal saline”)

  • 1L of water
  • 150 mmol of Na+
  • 150 mmol of Cl-

0.18% NaCl + 4% dextrose solution (aka, “4% and a fifth”)

  • 1L of water
  • 30 mmol of Na+
  • 30 mmol of Cl-
  • 40 grams of glucose

5% dextrose

  • 1L of water
  • 50 grams of glucose

As you can see, if you use the “autopilot” IV fluid regimens, they give pretty close to what we need.

Regimen one gives in 24 hours:

  • 3L of water (target = 2.6 L)
  • 150 mmol of sodium (target = 70-140 mmol)
  • 60 mmol of potassium (target = 35-70 mmol)

Regimen two gives:

  • 3L of water
  • 90 mmol of sodium
  • 60 mmol of potassium

… which is why the “autopilot” regimens work. Most people eventually work this out through trial and error, but knowing what you’re actually doing is probably preferrable.

Traps for young players

  1. Underhydration
    • wrong rate of fluid for body weight
    • not calculating for other losses
    • not calculating for pre-existing fluid deficit
  2. Overhydration
    • wrong rate of fluid for body weight
    • not taking into account pre-exisiting fluid overload
    • not considering renal (dys)function
  3. Giving too much sodium
    • using endless bags of “normal saline” in the euvolaemic patient
    • not monitoring the serum sodium for someone who has received many bags of IV fluid
  4. No giving enough potassium
    • forgetting to write up potassium (especially post-operatively)
    • not calculating for losses of potassium rich fluid (e.g., diarrhoea and vomitus)

Updated: Michael Tam (19 June 2006)

Please read the disclaimer


  1. Ian Anderson said,

    This is a great explanation of fluid calculation. I think I finally get it! Thanks.

  2. Zakir said,

    Dear Sir,
    I am a 4th year medical student got the article very interesting. I am interested to know what history,physical examination & investigation is important in evaluating true oliguria and success of treatment. What are the alarming sign in the management of postoperative oliguria.

    Kind Regads

  3. Michael Tam said,

    I wrote a brief article on the management of post-operative oliguria here.

    In terms of assessment of oliguria:
    History: thirst, last micturition, history of significant fluid loss, length of operation, ? bowel operation.

    Physical examination: observations (? tachycardia, ? blood pressure, measured urine output), tissue perfusion (capillary return), tissue turgor, mucous membranes, JVP, abdominal examination – specifically palpation for a full bladder.

    Alarming signs are basically if the patient is going into shock: high tachycardia, low blood pressure, poor perfusion, etc.

  4. Barb said,

    I’m not a doctor but a grandmother of a baby that was born with Christmas Tree Anomaly. As a result she has short gut syndrome. She was admitted to hospital for dehydration after a gastro virus made her vomit. They were hydrating her very well but as always before they seem to overdo it and now she is in ICU because her sodium and potassium levels shot up. So when your calculating the IVs, please consider that this is a person’s life you are messing with. This is a 15 month old beautiful baby girl that is spending her 2nd Christmas in the hospital all because her levels were not being watched properly and they did not account for what was already in her body when they smacked another IV drip up there. Doctors, listen to your patients and their parents. They may know more than you think they do and maybe more than you do. After all, this baby is the little girl that will be sneaking up on Christmas morning to peek at presents that someone loves so dearly. And one day it may be your loved one.

  5. Michael Tam said,

    Thank you for your valuable comments Barb. Best wishes for your grand-daughter and I hope that she is able to go home in good health soon.

    I do not necessarily agree with some of your comments and I wrote an article on some of the issues that your comments raise.

  6. Kristie Hack said,

    I have a question.
    Is the actual “bag” the IVF come in permeable?? I mean, are you able to actually write on the bag itself with a permanent marker or should you write on silk tape with the marker and place it on the bag.
    a nurse from KY that does education to staff nurses

  7. Michael Tam said,

    Thanks for your question Kristie.

    I do not know this to be a fact, but my guess is that the plastic the “bag” is made of would almost certainly be impermeable to the common solvents used in a marker pen.

    However, this is perhaps the wrong question.

    If you are asking whether you should write on the bag itself, the answer is “no”. This is simply for the sake of clarity in a clinical situation. Any instructions or additives to the bag of fluid written on the bag itself can be easily missed. In the hospitals I have worked, it is common protocol to write all additives on a separate highly visible fluorescent coloured sticker that is then adhered to the bag of fluid.

    Where this is not available, then writing onto white tape and adhering that onto the bag is not an unreasonable solution. In an emergency situation, I have used tape to directly attach the used ampoules of the additives to the outside of the bag of fluid.

    Best regards.

  8. Kristie Hack said,

    thanks for a quick reply. Just for clarification purposes, we do place adhesive bright orange stickers on the bag of IVF when we have additional additives. The reason we are wanting to write on the bag is to label the bags #1, #2, #3, etc. to keep track of how much total IV fluid the patient receives while in our outpatient services. We do outpatient procedures (colonoscopies, endoscopies, bronchoscopies, etc.) and for JCAHO purposes we have to be able to identify how much IVF the patient receives while in our care. We are going to label the bags so the last nurse (the recovery nurse) that takes care of the patient can easily see how many bags of IVF the patient has had and calculate it like that. With a different nurse using a different form for his/her documentaion purposes, it is too haphazard and time-consuming to flip through each paper in the chart to see when each nurse hangs a bag of IVF. Thanks again………By the way, upon waiting for your reply, I contacted a Baxter sales rep. and was informed that the actual bag is slightly porous and could possibly be permeable and he recommended using the silk tape to apply the info.
    thanks again, Kristie

  9. Sharmishtha Ghangrekar said,

    I was wondering about what I should do with patients with liver failure… I know they and cardiac failure patients are not supposed to receive normal saline as it moves to extravascular space… but could you explain why? And how do I replace their sodium?

  10. Michael Tam said,

    I would recommend reading a good physiology and pathology textbook, but from memory, in chronic hepatic dysfunction there is relatively excess of steroid based hormones as they are normally metabolised in the liver. For example, excess oestrogen results in gynaecomastia.

    As such, there is mineralocorticoid (e.g., aldosterone) excess resulting in the retention of sodium in the distal tube of the nephron. Water follows the sodium ion, so patients with chronic hepatic dysfunction retain both water and sodium. Reduced synthesis of albumin leads to a reduction in oncotic pressure, subsequently leading to fluid being lost to the extravascular space, particularly, the interstium (i.e., oedema and ascities).

    This is why diuretics like spironolactone (an aldosterone receptor antagonist) is particularly helpful in liver failure.

    A patient with chronic hepatic failure would therefore likely have an excess of total body sodium, even if it isn’t necessarily reflected in their serum levels and giving saline rich fluids will worsen their fluid retention.

    • rose said,

      what iv fluid is vest recomended with liver failure?that will help the patiet…

  11. i wuld like to find out why we give iv fluids normal saline to patients straight away after admission. please can you help on this one because i have an assignment on thursday about why you administer normal saline

    thank you

  12. thank you for yor considerations

  13. Michael Tam said,

    There isn’t really enough information in your question for me to answer that. Intravenous fluids are only required if the patient is unable to take fluids orally and there can be many reasons why that may be the case (e.g., vomiting or awaiting surgery).

  14. Hildy said,

    do you subscribe to the Stewart SID theory that NS is an acidotic fluid due to the chloride content?

  15. Michael Tam said,

    Given that I have seen hyperchloraemic acidosis in ICU that was probably in part due to large quantities of NS the answer would be yes.

    However, I also don’t think that it makes much (or any) difference in the typical usage of NS. I personally prefer NS to Hartmann’s solution as it is always available, its easier to calculate electrolyte content, and there is no problem with using blood products in the same line.


  16. Jared said,

    I am in the hospital now. I have been here for about 48 hours. They put on a saline drip when I came in and I went through at least 8 bags up through tonight. I developed a bad headache tonight and was urinating a ton about every ten minutes. I asked them to take the IV out and they did and now three hours later I feel much better. Could I have been over-saturated? I have also been driking water the whole time as well. In backround, I came in after having a episode of shaking and getting really cold with a bunch of other symptoms. They thought I had endocarditis but the cultures have not grown anything and the echo results looked ok. Should I ask them to check potassium and electrolytes? Could I have just gotten overhydrated tonight?

    P.S. — you have to love hospitals with wireless internet

  17. Michael Tam said,

    Dear Jared,

    In the absence of any further information, I cannot confidentally tell you one way or another, but your history and symptoms do sound consistent with overhydration.

    With regards to checking your serum electrolytes, it is probably not necessary. As long as you are eating and drinking and there is no reason to suspect that you have kidney dysfunction, your kidneys will return your water and electrolyte balance back to homeostasis.

    In any case, if you have any questions about your management, don’t hesistate to discuss it with your treating physician.

    Best regards and I hope everything turns out well for you.

  18. zeinab said,

    i just want to know why there is some nurses donnot make fluid calculation before given and she give abottle of any fluid may be in less than 1 hour so i hope all nursing staff when giveing i v fluid she must know the importance of make fluid calculation

  19. Whitey said,

    G’day Michael,

    Great article. I went to a tutorial that covered most of what you’ve written when I was in fifth year medical school (a little while ago) and I still have the notes carefully preserved. Apart from that one lecture which many students didn’t get, I would have graduated with absolutely no idea about the practical aspects of prescribing IV fluids.

    Interestingly, med students still don’t seem to get taught this properly…they get taught it, but not in any practical sense. If you explain how to calculate water volumes, sodium requirements and potassium requirements – and then give them a ‘standard’ regimen – suddenly everything makes sense. Lightbulbs switch on in their brains, and suddenly all is well in the world.

    Echoing Barb’s comments above, I think this is important to get right. I had my daughter in the ED a few months back in a major tertiary teaching hospital. It was 3am in the morning, she was 5%+ dehydrated and not passing urine. The ED resident wrote her up for IV fluids and because the potassium looked like way too much (particularly in an oliguric patient) I started doing some rough calculations. When queried on what method of calculating potassium he’d used, the resident bluffed a bit, and then stated ‘The registrar told me to put in ‘shitloads’ of potassium, so that’s what I did!’.

    On further discussion he explained to me that they don’t really worry too much about this kind of thing as ‘the kidneys will normally sort it out.’

    On a good day, yes…

    So good work Michael. This is the best, most understandable article on the subject that I’ve seen.

    Senior Lecturer in Rural and Remote Medicine

  20. Michael Tam said,

    Thanks for your kind comments Rob!


  21. Samantha said,

    Hiya, I’m a 3rd year medical student and I’m about to do my 3rd year clinical osces in a couple of days and I know fluid balance will def come up but we hadn’t really been taught it so I’m so glad I found this!
    Thank u!

  22. Duy said,

    How many days of IVT before Ca, PO4 and Mg supplements should be considered? Thanks.

  23. Duy said,

    And what are the daily requirements + example regimens?

    It’s difficult to find practical info on this topic. Much appreciated.

  24. Michael Tam said,

    There is set answer to this question. It would depend very much on losses and serum levels electrolytes.

  25. sarah said,

    I am so glad i stumbled this website. I couldnt add it to my desktop shortcut quick enough .

    I am a first year nursing student and find the information you provide valuable in an easy to understand way.

    thankyou and congratulations on a the great work you do

  26. Mitu said,

    I have a question.Can you pls tell me from when(age)we can change the maintenance fluid from 0.45%NaCl to 0.2% NaCl ?

  27. Dan said,

    Michael, it seems that most of my patients are obese, with weights well into the 100s. Is maintenance fluid based on actual, or ideal body mass? Should I really be charting my 140kg patient with 5L of fluid for maintenance?

  28. Michael Tam said,

    Ideal body mass.

  29. Wong Vui Jye said,

    Hi! My hospital nursing comunity claim that we cant use permanent marker on our iv drip because some component may be absorb into the drip. Is there such a thing because I couldnt find anything to support or disproved what they have said. Please help

  30. Michael Tam said,

    I have seen this mentioned before. Presumably, some of the solvents in a permanent marker could conceivably be absorbed into the plastic of a bag of fluids.

    In any case, it is good practice that information is on a bag of fluids be prominently displayed and this would be best done by writing an a fluorescent adhesive sticker.

  31. Rita said,

    Hi… I’m a Final year medical student… This articel was waaaay easier to understand than all those complicated notes we use in med school. Could you PLEASE show us hot to calculate perioperative/post operative fluid losses with on going losses?… thanks ..

  32. Kasim M. Ali said,

    Thank you doctor for your valuable and interesting lectures about IV fluid therapy

  33. Lori Batchler said,

    Could IV fluid overload given with a severed ureter and a crimped ureter for 30 hours cause diastolic dysfunction with secondary mild pulmonary hypertension?

    • Michael Tam said,

      Conceivably yes.

      • Lori Batchler said,

        Could you explain? My pulmonary dr. is saying that it is not possible. He has diagnosed me with exersize induced pulmonary hypertension secondary to diastolic dysfunction. Four years ago, I had a hysterectomy with complications (bilateral ureteral obstruction) and I was given 5 liters of fluid from 9pm until 12pm the next day. I was tranferred to another hospital for repair surgery and did not pass any urine into the catheter bag until after that surgery at around 10 pm the following night. I had to have stents put in both ureters, removal of those stents, with another stent surgery and removal of the ureter that had been crimped. I thought I was ok, until three mos after my original surgery, I began to swell in my face and hands and had shortness of breath. The urologist said it was my age (43) and 100 degree weather. I later developed pitting edema. three years after the fact, I am in this condition controlled with meds. I just don’t understand why my dr says the two are not related? Please help me understand the whys or why nots. Sincerely, Lori

  34. Lori Batchler said,

    Sorry, I didn’t have a ureter removed, I had stent removal of that ureter.

    • Michael Tam said,

      I interpreted your initial query as whether the IV fluid overload could cause acute heart failure. It is unlikely those events would lead to any continuing cardiac dysfunction.

  35. Dr Sandeep goel said,

    Thanks very much doc, for such a valuable article, please keep writing and give us these priceless informations. God bless u

  36. Englishman said,

    Man… I’m just checking this at fly…gonna go to bed now. But this is GREAT, I’v been looking for this in papers, books, but I cannot find it. Now I will finaly understand this topic.


  37. Sriram said,

    Thank u sir.

  38. nancy said,

    Thank you very much!!!!!!!!!!!!!!!

  39. Gareth said,

    hey, nice site, I have to say though I prefer Hartmann;s/CSL to N Saline because of the excess sodium load that Saline results in, particularly in patients who have significant activation of their Renin-Angiotensin-Aldosterone System who tend to retain Sodium. Also, the GIFTASUP guidelines suggest replacing N Saline with CSL for most purposes.

  40. obadah said,

    thank you

  41. Fatimah said,

    Hi I am a com service doctor and these explanations were terrific..I would also like an explanation about how to calculate the rate of potassium in the iv solution.thank you..x

  42. priya said,

    hi micheal

    that was a very succint explanation! thanks

    i dont understand how a fluid like normal saline which has a neutral pH could cause hyperchloremic acidosis if transfused in large quantities. could u please tell me why?

  43. Mos said,

    Hi Michael, great info btw!

    I have a quick question for you:

    What is the maximum infusion rate for maintenance fluids in adults?
    (The RCH guideliness suggest 100ml/hr for kids)


  44. shahirae said,

    I’m 30 min into my exams, and I finally getting. :)

  45. Vinicius Nascimento said,

    Dear Dr Tam;

    Considering the UK guidelines 2011, would you change the choice of fluids (let’s say 0.9 NS to Hartmann’s) when infusing maintenance levels in a “normal” person 70 kg?

    My other question: Would you change 0.9 NS to Hartmann’s or Ringer Lactate when RESUSCITATING a patient?

    Thanks a lot for the attention.

    Best Regards.

  46. dr.basavaraj said,

    thanks lot. its v.easy and clear.

  47. francis said,


  48. Bernie said,

    Just writing up a text for nurses on fluid and electrolytes. Great explanatory article! :-)

  49. Aufar Bahri said,

    Hello Dr Tam,

    Great article, thanks! I’m a house officer from NZ and this helped me understand fluid therapy. I just wanted to clarify something. I came across this article:

    Moritz ML, Ayus JC. Prevention of Hospital-Acquired Hyponatremia: A Case for Using Isotonic Saline. Pediatrics Vol. 111 No. 2 February 1, 2003 pp. 227 -230 (doi: 10.1542/peds.111.2.227)
    accessible at:

    Which argued that as hospital patients are prone to ADH excessive states due to their illness, and therefore sometimes unable to excrete free water, we should be giving isotonic saline as prophylaxis against acute hyponatraemia (ie. more NS?). Granted, the article was addressed for a paediatric setting. But their logic seems applicable to adults too. I’m tending to prescribe more NS because of this (of course checking for electrolytes) Any thoughts on this? Thanks

    Aufar Bahri

    • Michael Tam said,

      Dear Dr Bahri,

      The use of saline rich intravenous solutions in the paediatric population is now uncontroversial and is definitely best practice. It is important to recognise, however, that it is uncommon for children who are well and euvolaemic to require IV fluids in the first place. This is not the case in adults (e.g., those waiting for elective surgery). We do need to be careful in giving inappropriately high amounts of sodium and water – iatrogenic pulmonary oedema is not uncommonly seen in hospitals!

      Yours sincerely,

  50. erick said,

    so helpfull

  51. Karen Wotton said,

    Calculation of daily maintenance fluids
    Have been using the 4:2:1 rule for some time but wondering whether there are any formulas for calculating more specific daily maintenance fluid requirements which take into account: age, weight and gender – particularly when we know percentage water in the human for adult is 70% whereas water percentage for the frail elderly is 50%?

    Calculation hrly urine output
    Also note that you recommend 40mL/hr whereas 50 kg female 20mL/hr.

  52. […] Great WordPress article from “The Medicine Box” […]

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