logic in selecting IV fluids?

[bulldog]

any good resource on what IV fluids to select?

i.e. seems like u can us NS for most patients who come in looking dehydrated.
-if they're NPO, then I've seen D51/2NS or D5NS used. what's the difference between the two in terms of the Na content?

thanks.

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[mlw03]

you seem to have the basic gist of it. 1/2 normal saline means that the concentration of Na and Cl is half that of normal saline, so the overall solution is hypotonic instead of isotonic. so i think NS has 154 mEq of Na, while 1/2 NS would then have 77.

as to the logic, i'm not sure why you switch to 1/2 NS for maintanence (or 1/4 NS for kids < 10kg), but i know that for dehydration you want something isotonic like NS (or LR) because the goal is to increase INTRAVASCULAR volume quickly, and isotonic solutions are the safest, most economical way to do this.

 

[proman]

There's no one ideal fluid for every situation. For resuscitation, crystalloids allow rapid repletion of volume. 0.9% sodium chloride is slightly hypertonic compared to plasma (308 mOsm/L vs 290). Lactated Ringer's is slightly hypotonic (273 vs 290). Since they are both so close to plasma, they are considered the isotonic fluids. You can get a hyperchloremic metabolic acidosis from large volumes of 0.9% NaCl (typically 5+liters). You can get hyponatremic from large volumes of LR. Either are acceptable for volume resuscitation.

For maintenance, sodium content and tonicity matters. I personally think that maintenance fluids for most patients is overutilized. If you use 0.9% NaCl for an extended amount of time, the plasma sodium content will increase and you may get hypernatremic. To avoid this, solutions like 0.45% or lower are used. If the patient is not eating, and you are concerned about providing calories to prevent protein breakdown, dextrose is added to the fluid. 3 liters of a 5% dextrose solution provides 500 kcal a day enough to be protein sparing. Adding D5 to NS results in a hypertonic solution (560 mOsm/L). If the patient's glucose metabolism is impaired, you could cause cellular dehydration from the hypertonic solution. D5 0.45% NaCl avoid this.

Really consider the consequences of fluids. If they don't need salt or water, chances are they don't need any fluid. NPO isn't an indication (we all sleep at night without IVs going).

Does that answer your question?

 

[elperro]

Thanks Proman, really great post. As an intern, I do a lot of things, live IVF, a certain way because "that's the way it's done." It is nice to understand the "why" sometimes.

 

[jennyboo]

any good resource on what IV fluids to select?

One thing that really helped me to understand what is in each crystalloid is to pick up the bag and look at it. Seriously. Pick up a bag of normal saline and read the ingredients. It tells you exactly how many millequivalents of each ion are in the bag. How many mEq of sodium are in a bag of normal saline? How many mEq chloride? Compare that to your patient's chem7 and you can guesstimate the general direction your patient's chem7 will go in if you give lots of it. Then read a bag of lactated Ringer's. Keep looking back and forth between your chem7 and your IVF bag. This small exercise shown to me as a medical student has stuck with me for life!

General overview: If you want to actually read about volume resuscitation, choice of IV fluids, and crystalloids vs colloids, any old chapter in any book should do. I thought the IVF chapter in THE ICU BOOK was okay.

How to calculate maintenance fluids: The medical student Surgical Recall book. Not kidding. Generally didn't bother to do this if it was just going to be "NPO after midnight for [procedure] in AM."

 

[46&2]

Really consider the consequences of fluids. If they don't need salt or water, chances are they don't need any fluid. NPO isn't an indication (we all sleep at night without IVs going).

It would be very odd to see someone who was NPO without any fluid running. While NPO itself isn't an indication, the reason why the pt is NPO is usually why IVF are given. People may be on bowel rest (pancreatitis, partial small bowel obstruction) or NPO overnight in preparation for a major operation. We may sleep at night without IVF, but we're going to eat and drink in the AM. The patients won't. It's better to be a little ahead than behind on fluids.

I would be really hesitant to have a patient NPO without IVF.

Most of us (including patients) have functioning heart and kidneys. Even if we give a patient too much IVF, their urine output can pickup and handle the overload. Most of us don't pay any attention to our own electrolytes. Hence, you see a lot of sameness to IVF. 100mL and 125mL/hr are common rates due to their practicality. It would be tough to run exactly 117 mL/hr for a 1 L bag, and really, what's the difference between 117 and 125 for most stable patients?

Another point is where the patient is losing fluids. Do they have a nasogastric tube or pancreatic drain? Generally, if the patient is losing GI fluids below the stomach, LR is the fluid of choice. This has to do with the composition of the GI fluids being lost. Stomach secretions have more chloride (140), hence we use NS to replace gastric losses.

In acute care, as noted before, for NS vs. LR, there isn't much of a difference. Both of them are acidotic compared to the intravascular compartment, LR less so. LR, in a patient with functioning liver and lungs, theoretically can reduce acidosis as lactate can accept a proton, etc. Some places use NS all the time, only using LR if the patient may have been in shock for a few hours prior to presentation. And don't add D5 to the bag- the patient is likely hyperglycemic due to the initial injury. All that extra dextrose will do is cause some diuresis. Let the patient's insulin do the trick.

Also think to yourself: is the patient on diuretics? Maybe holding these for a day would be better than tweaking the IVF. Maybe their electrolyte abnormalities are iatrogenic.

Books can help but can also confuse. You'll get the rationale behind certain practices (like why we don't bolus with D5 in the bag). But you'll also get too much information. Marino's ICU book may lead you to think colloids are OK. Another book thinks hypertonic saline isn't bad. Both of those thoughts may get you killed depending on what institution you're at. The book may make colloid sound nice, but when you have an attending grilling you over how many randomized controlled trials have showed the superiority of albumin versus crystalloid... well, it's much more convenient to toe the party line (and it likely won't matter to the patient).

There's always special instances. Patients in renal failure on dialysis, who have CHF, DKA, SIADH, diabetes insipidus, etc. Their fluids have to handled more gently. Patients postop- did anesthesia give them adequate fluid replacement, or did they give much too little? And then chronically ill patients who need TPN...

 

[bulldog]

So, can someone summarize the rate as well as conditions u'd use the following fluids?

NS: hypovolemic patient, hypotensive, diarrhea
D51/2NS: NPO for procedure
D5NS: ?
LR:
*I'ved also seen some patients have KCl added to NS. Why's this?


Rate:
500 cc bolus: hypotensive
125 cc/hr: typical value for starting IVF when admitting patient. How long shoulod you keep it at 125 cc vs 75 cc? If they're NPO for extended amount of time?
75 cc/hr: when? maintenance rate? good rate for NPO after midnight?

 

[46&2]

This is a pretty good summary:
http://medicine.ucsf.edu/housestaff/Chiefs_cover_sheets/ivf.pdf.

Sanjiv Shah, M.D.
University of California, San Francisco
Last updated: June 13, 2003

APPROACH TO IV FLUIDS IN THE MEDICAL PATIENT
First let's review the equation for estimating serum osmolality:
Serum osmolality = 2 (Na+) + Glucose/18 + BUN/2.8
See how much more sodium adds to your osmolality then glucose does? That's why D5 &#189;NS is inappropriate for most medical patients who are hypovolemic. They need isotonic fluids (normal saline). Also, remember that dextrose gets almost immediately metabolized to water and CO2 when it enters the circulation so it is not osmotically active for too long.
When considering appropriate IV fluids as you are writing admission order, keep in mind that in general, there are 4 types of medical patients when it comes to administering IV fluids:
1. The hypovolemic patient (most common). Examples include sepsis, pneumonia, intractable nausea/vomiting, etc.
2. The hypervolemic patient (also very common). Examples include CHF, cirrhosis, renal failure, etc.
3. The patient awaiting a procedure (e.g. ERCP).
4. The patient here for an elective reason (expedited work-up of possible malignancy, etc).
Steps to determine appropriate IV fluids for your patient:

Step 1:
Assess the volume status of your patient and figure out why they're being
admitted to the hospital. Will they be NPO?

Step 2:
Based on the type of patient they are, write for IV fluids as follows:
Hypovolemic patient: fluid of choice is normal saline. Your goal here is to
volume resuscitate that patient and normal saline is the best choice. Pearl: if you are planning to give more than 3-4 liters of normal saline, switch to plasmalyte or lactated ringer's (LR) because of the risk of "expansion acidosis". These fluids are isotonic, just like normal saline.

Hypervolemic patient: avoid fluids at all costs.

Pre-procedure or NPO patient: treat this patient like a surgical patient if the
patient is going to be NPO for longer than 6-12 hours. Administer D5
&#189; NS at 75-100 cc/hour (don't have to be too accurate). Don't give fluids blindly (if the patient is pre-procedure but is old (predisposed to fluid overload because of stiff LV) or has history of CHF, don't give fluids! Pearl: the reason for giving dextrose (D5) is to prevent catabolism.

Patient healthy, here for elective reason: no need for fluids if they are taking
PO's.

Step 3:
Write for a rate for IV fluids:
In medical patients, the rate is somewhat arbitrary and you have to use your
judgement. If you are trying to fluid resuscitate that patient, you might be giving fluids "wide open" or 500 cc/hr. If you are just giving fluids to the NPO patient, give fluids at 75-100 cc/hr.

 

[drj357]

A good simple guide would work like so:

For dehydration:

Bolous 1/2 liter of NS and If you need do it again.
Then you can do a maintenance dose after that. About one liter over 24 hrs.

this is for adult patients who are not hypo or hypernautrimic.

If they are hypo or hyper Na then it get complicated and I suggest you read the washington manual on this. There is a very good segment on it.

But if you are asking this question on this site, it mean that you should read about it or sit down with your attending to show you how to go about it.
READ FIRST THEN SIT WITH THE ATTENDING.

 

[proman]

This is a pretty good summary:
http://medicine.ucsf.edu/housestaff/Chiefs_cover_sheets/ivf.pdf.


Pre-procedure or NPO patient: treat this patient like a surgical patient if the
patient is going to be NPO for longer than 6-12 hours. Administer D5
½ NS at 75-100 cc/hour (don’t have to be too accurate). Don’t give fluids blindly (if the patient is pre-procedure but is old (predisposed to fluid overload because of stiff LV) or has history of CHF, don’t give fluids! Pearl: the reason for giving dextrose (D5) is to prevent catabolism.

Patient healthy, here for elective reason: no need for fluids if they are taking
PO’s.

46&2: you posted a list of patients who needed fluids, not because they were NPO but because they had an underlying medical condition/therapy that dictated fluid. I'm not arguing that. I want to know, in the patient who is NPO for a procedure the following day, what you hope to treat or prevent by giving crystalloid during the NPO period? And, I want to know how you expect the 200 ml of intravascular volume expansion from your IVF is going to help that?

 

[proman]

So, can someone summarize the rate as well as conditions u'd use the following fluids?

NS: hypovolemic patient, hypotensive, diarrhea
D51/2NS: NPO for procedure
D5NS: ?
LR:
*I'ved also seen some patients have KCl added to NS. Why's this?

You have obligate K losses through GI and mostly renal sources. I don't think there's any need to replete these losses since whatever you give in maintenance fluids is a tiny portion of total body potassium stores. If the patient becomes hypokalemic the next day, it's not because your maintenance fluid lacked K. One more thing, if you need to bolus your patient, never use fluid that is 1) hypotonic or 2) containing K.

 

[Faebinder]

This is a pretty good summary:
http://medicine.ucsf.edu/housestaff/Chiefs_cover_sheets/ivf.pdf.

Sanjiv Shah, M.D.
University of California, San Francisco
Last updated: June 13, 2003

APPROACH TO IV FLUIDS IN THE MEDICAL PATIENT
First let’s review the equation for estimating serum osmolality:
Serum osmolality = 2 (Na+) + Glucose/18 + BUN/2.8
See how much more sodium adds to your osmolality then glucose does? That’s why D5 ½NS is inappropriate for most medical patients who are hypovolemic. They need isotonic fluids (normal saline). Also, remember that dextrose gets almost immediately metabolized to water and CO2 when it enters the circulation so it is not osmotically active for too long.
When considering appropriate IV fluids as you are writing admission order, keep in mind that in general, there are 4 types of medical patients when it comes to administering IV fluids:
1. The hypovolemic patient (most common). Examples include sepsis, pneumonia, intractable nausea/vomiting, etc.
2. The hypervolemic patient (also very common). Examples include CHF, cirrhosis, renal failure, etc.
3. The patient awaiting a procedure (e.g. ERCP).
4. The patient here for an elective reason (expedited work-up of possible malignancy, etc).
Steps to determine appropriate IV fluids for your patient:

Step 1:
Assess the volume status of your patient and figure out why they’re being
admitted to the hospital. Will they be NPO?

Step 2:
Based on the type of patient they are, write for IV fluids as follows:
Hypovolemic patient: fluid of choice is normal saline. Your goal here is to
volume resuscitate that patient and normal saline is the best choice. Pearl: if you are planning to give more than 3-4 liters of normal saline, switch to plasmalyte or lactated ringer’s (LR) because of the risk of “expansion acidosis”. These fluids are isotonic, just like normal saline.

Hypervolemic patient: avoid fluids at all costs.

Pre-procedure or NPO patient: treat this patient like a surgical patient if the
patient is going to be NPO for longer than 6-12 hours. Administer D5
½ NS at 75-100 cc/hour (don’t have to be too accurate). Don’t give fluids blindly (if the patient is pre-procedure but is old (predisposed to fluid overload because of stiff LV) or has history of CHF, don’t give fluids! Pearl: the reason for giving dextrose (D5) is to prevent catabolism.

Patient healthy, here for elective reason: no need for fluids if they are taking
PO’s.

Step 3:
Write for a rate for IV fluids:
In medical patients, the rate is somewhat arbitrary and you have to use your
judgement. If you are trying to fluid resuscitate that patient, you might be giving fluids “wide open” or 500 cc/hr. If you are just giving fluids to the NPO patient, give fluids at 75-100 cc/hr.

 

[Mman]

You have obligate K losses through GI and mostly renal sources. I don't think there's any need to replete these losses since whatever you give in maintenance fluids is a tiny portion of total body potassium stores. If the patient becomes hypokalemic the next day, it's not because your maintenance fluid lacked K. One more thing, if you need to bolus your patient, never use fluid that is 1) hypotonic or 2) containing K.

Lactated Ringer's contains 4 meq of potassium per liter and is perfectly acceptable for bolus administration (heck, it's also slightly hypotonic). I agree you don't want to bolus from the bag of potassium hanging for supplementation, but LR is fine.


As to the prior post about rates being 125 or 75 or whatever, it's all mumbo jumbo. For anybody over 20 kg, their maintainance fluid rate is roughly their (wt in kg + 40) per hour. If they weigh 70 kg, maintainance is 110 ml/hr. If they weigh 100 kg, it's 140 ml/hr.

And if a nurse ever asks how fast you want to give a bolus of fluid, just let it run wide open. If somebody needs a fluid bolus, you aren't going to hurt them by giving it faster. An 18 g IV will accomodate roughly 110 ml of fluid per minute, a 16 g roughly 220 ml of fluid per minute. I've seen people order a 500 ml bolus given over 2 hours. At that rate, what's the point?

 

[Tired]

Lactated Ringer's contains 4 meq of potassium per liter and is perfectly acceptable for bolus administration (heck, it's also slightly hypotonic). I agree you don't want to bolus from the bag of potassium hanging for supplementation, but LR is fine.

LR boluses have been linked to abdominal compartment syndrome in trauma resuscitation. Be wary.

 

[proman]

Lactated Ringer's contains 4 meq of potassium per liter and is perfectly acceptable for bolus administration (heck, it's also slightly hypotonic). I agree you don't want to bolus from the bag of potassium hanging for supplementation, but LR is fine.

I should have been more clear. Fully agree that LR is fine for bolusing and resuscitation. I meant to say the fluids that has K added (like 10-40mEq) should never be bolused. Agree?