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IV fluid help

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Calculation #1:

Weight Conversion: If weight isn't in kg, convert it.


Weight In Pounds / 2.2 = Weight In Kilograms







Calculation #2:

Calculate Maintenance Fluids: Dependent on weight, not a linear relationship at low weights.


Weight 0-10kg:

Maintenance Fluids (cc) = 100cc/kg × Weight(kg)


Weight 11-20kg:

Maintenance Fluids (cc) = 1000cc + (( Weight(kg) - 10kg ) × 50cc/kg )


Weight >20kg:

Maintenance Fluids (cc) = 1500cc + (( Weight(kg) - 20kg ) × 20cc/kg )





Calculation #3:

Calculate Maintenance Sodium and Potassium: This assumes that the daily requirements of Sodium (Na) and Potassium (K) are: 3mEq Na/100Kcal or 3mEq Na/100cc and 2mEq K/100Kcal or 2mEq K/100cc.


Maintenance Sodium (mEq/24hour) = Maintenance Fluids(cc) × 3mEq Na /100cc/24hour

Maintenance Potassium (mEq/24hour) = Maintenance Fluids(cc) × 2mEq K /100cc/24hour





Calculation #4:

Calculate Fluid Deficit: Assumes that 1% dehydration = 10cc/kg


Fluid Deficit (cc) = Weight(kg) × Percent Dehydration (%) × 10cc/kg


Type Percent Dehydration Physical Exam Findings

Mild Adult:2-4%

Peds:5% Thirsty

Dry Membranes

No Tears

Moderate Adult:5-7%

Peds:10% Soft Eyes

Soft Fontanelle

Severe Adult:8-10%

Peds:15% Elevated Heart Rate

Skin Tenting





Calculation #5:

Calculate Sodium and Potassium Deficit:


Must first determine how quickly and from where the deficit was lost.


Type Duration of Loss From Where

Normal Losses 3-5 days 60% Extracellular /40% Intracellular

Rapid Losses < 24 hours 80% Extracellular /20% Intracellular

Chronic Losses > 5 days 50% Extracellular /50% Intracellular


Sodium Deficit (mEq) = Fluid Deficit (cc) × Percent Extracellular*(%) × 3mEq Na /100cc

Potassium Deficit (mEq) = Fluid Deficit (cc) × Percent Intracellular*(%) × 2mEq Na /100cc


*Recall that the major extracellular cation is Sodium and the major intracellular cation is Potassium.


If the patient is hypertonic (i.e. Serum Sodium > 155mg/dl) then calculate the free water deficit.


Free Water Deficit (cc) = [Observed Sodium - Ideal Sodium] × 4ml/kg × Weight (kg)


Then, calculate the Sodium and Potassium Deficit based on the true fluid deficit.


Sodium Deficit (mEq) = [ Fluid Deficit (cc) - Free Water Deficit (cc)] × Percent Extracellular*(%) × 3mEq Na /100cc


Potassium Deficit (mEq) = [ Fluid Deficit (cc) - Free Water Deficit (cc)] × Percent Intracellular*(%) × 2mEq K /100cc


If the patient is hypotonic (i.e. Serum Sodium < 130mg/dl) then calculate the extra sodium needed to raise the serum sodium to 135mg/dl.


Extra Sodium (mEq) = [135mg/dl - Serum Sodium (mg/dl)] × Weight (kg) × 0.6





Calculation #6:

If a bolus is given, calculate the effect on fluid deficit and sodium deficit.


New Fluid Deficit = Calculated Fluid Deficit (cc)(from Calculation #4) - Amount of Fluid Bolus (cc)


New Sodium Deficit = Calculated Sodium Deficit (mEq)(from Calculation #5) - Amount of Sodium In Bolus (mEq)


Amount of Sodium in Bolus = Concentration of Sodium in Bolus† (mEq/L) × Amount of Fluid Bolus (L)


† In a bag of Normal Saline there are 155mEq/L

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This are the calculations we use for patients who are NPO and coming to surgery:


1st 10 kg = 20cc/kg/hr


next 10 kg = 10cc/kg/hr


So far, you have 60cc/kg/hr for weights up to 20kg.


For weights >20kg, add 1.5cc/kg/hr for the amount of weight over 20kg.


So for a 70kg patient


60cc/hr + ((70kg-20kg) x 1.5cc/kg/hr)

60cc/hr + (50kg x 1.5cc/kg/hr)

60cc/hr + 75cc/hr

135 cc/hr for maintenance IV fluids.


Then simply take the hours of NPO time and multiply by the maintenance rate.


Replace 1/2 the deficit the first hour, then 1/4 of the deficit each of the next two hours, then the maintenance rate after that.


In addition to that, we would add in the 3rd space loss (as much as 10cc/kg/hr or more on an open abdominal case), as well as replace estimated blood loss at a rate 3cc of IV fluid per cc of blood loss, unless significant blood loss is anticipated, in which case we would replace blood loss with colloid (such as Hespan) or PRBC's.


We follow urine output constantly, and adjust our fluid replacement to maintain a urine output of at least 1cc/kg/hr.


Obviously these calculations don't take electrolytes into consideration. We run our fluids in too quickly to use potassium. If we're concerned, we'll run KCl as a background infusion.


Again, these are the calculations we would commonly use in the OR, and are different than what you might use on a general medicine floor.

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Guest PA_in_Jax

Hey Debi,


I know how ya feel. I just finished my first week working in Urology at a major teaching hospital. The majority of my experience has been in Emergency Medicine. I just relocated to Florida and got this Urology position. It's really interesting but mannnnnn... am I learning how little I know. Because of my experience as a PA, I kind of got thrown into the fire.... scorched a little but I THINK all my patients survived. Spent the weekend doing consults and rounding..... I coulda used your Hospitalist expertise a NUMBER of times :eek: !! It's an adventure and as exhausted as I am... I'm enjoying the hell out of it.. Hope you're in the same boat :D !


Good luck and have fun ;)


Ed (aka PA in Jax)

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Easy way to convert weights if you can subtract and divide in your head. Take any three digit weight in lbs., subtract the first two digits of the weight from the total then divide by two (ex. 128-12/2). You will be within a half kilogram each time. For a two digit weight subtract the first digit from the total and divide by two (ex. 91-9/2). Try it.

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  • 1 year later...

Just some tips I'ev picked up when trying to decide which IVF to use for resussitation- post op

If you think they need more resuscitation, or significant on going losses- crystalloid is usually the choice.

Normal saline is usually good resuscitation – especially in situations where k, mg is high, or if they have borderline K,MG and may be going into renal failure/insufficiency – (because it has no additional lytes besides NA,CL)


However it may be a bad choice if they are going to require large amounts of fluid or are acidotic because it may lead to hyperchloremic acidosis.


LR or plasmalyte are more physiologic fluids, both offering some K, (and other lytes remember if using plasmalyte there are different formulations so check the bag for its contents) and a bicarbonate precursor. So they are if the patient is slightly acidotic or has normal pH these are good. But if they have rising K or declining renal function you may change to another IVF to avoid hyperkalemia.


Differences between the 2 (LR plasmalyte)

LR has lactate as bicarb precursor and needs the liver to convert it to bicarb- so if patient has liver failure may choose another


Plasmalyte uses acetate and gluconate, which are metabolized by skeletal muscle to bicarb so can use this independent of liver func.

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If you think they need more resuscitation, or significant on going losses- crystalloid is usually the choice.


On going losses- if blood is the loss, give blood. Don't rely on a hematocrit in pt with significant bleeding- if they act dry or shocky in the face of blood loss, transfuse. Elderly pts with unknown CAD, renal insufficiency, or cerebrovascular disease may not tolerate the lack of perfusion.



Trauma reasearch supports the use of Albumin for volume resuscitation. It may maintain higher oncotic pressure (except in the case of SIRS/capillary leak), and may prevent flooding a an 80 yr old with COPD and an EF 20%.

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