DEFINITION
Hypokalemia is defined as a serum potassium level of less than 3.5 mmol/L.
Normal level= 3.5-5.5 mmol/L.
It is encountered in >20% of patients.
Patients are usually asymptomatic but severe arrhythmias and rhabdomyolysis can occur. Non-specific complaints include easy fatiguability and skeletal muscle weakness.
The preferred method of replacement is via the oral route but at times this is not possible. The article below will give you an idea about how to calculate the amount of KCl to be given I.V.
1) Potassium deficit in mmol is calculated as given below:
Kdeficit (mmol) = (Knormal lower limit - Kmeasured) x kg body weight x 0.4
2) Daily potassium requirement is around 1 mmol/Kg body weight.
3) 13.4 mmol of potassium found in 1 g KCl. (molecular weight KCl = 39.1 + 35.5 = 74.6)
Suppose we get an asymptomatic patient of 70 Kg with a serum potassium level of 3.0 mmol/L and he is on nil by mouth but having an adequate diuresis, we proceed this way.
1) Deficit of potassium in mmol = (3.5 - 3.0) x 70 x 0.4 = 14 mmol
2) Daily potassium requirement = 1 x 70 = 70 mmol
3) Total requirement = 14+70 = 84 mmol = (84/13.4) = 6.3 g KCl
Therefore we can give the patient 1.0 g KCl (around 13 mmol of K+) in 500 mL Normal Saline (N/S) solution to run 4 hourly and reassess the serum potassium level after 1 day. So, in around 24 hours, we have given the patient around (24/4 = 6 pints of N/S solution, total KCl administered = 6.0 g i.e. around 80 mmol K+). Now if on the next day, he is still nil by mouth and there is still some degree of hypokalemia, we can repeat the above calculations to find his new total requirement and adjust the dosage accordingly.
But, if we have a symptomatic patient or someone with changes on the EKG, then better give 20 mmol of K+ in 50 mL of N/S via syringe pump over an hour through a central line and then recheck the serum potassium 1-2 hours after completion of the infusion. In extreme cases we can even go for up to 40 mmol of K+ per hour.
1) Never give potassium I.M or rapid I.V push
2) Never give more than 1.5 g KCl or 20 mmol of K+ over 1 hour without any continuous ECG monitor.
3) Do not just add the KCl solution to the hanging I.V fluid bag. Fully invert it around 10 times to ensure proper mixing.
4) 1 tab of Slow K gives around 8 mmol potassium.
5) 10 mL of KCl syrup = 20 mmol of K+.
6) Peripheral veins are damaged by a potassium concentration greater than 30 mmol/L i.e. 1.1 g KCl/ 500 mL I.V infusion solution. For higher concentrations, central lines are preferred.
7) Hypokalemia is associated with hypomagnesemia and the severity of the hypokalemia correlates with a similar degree of hypomagnesemia. Magnesium replacement should usually accompany potassium repletion. Unless the patient receives at least 0.5 g/hr of magnesium sulfate along with potassium replacement, potassium will not move intracellularly and the patient will lose potassium through excretion.
8) Correction of large potassium deficits may require several days. Oral and intravenous replacement can occur simultaneously.
9) Monitoring the plasma potassium level as an index of total body potassium is like evaluating the size of an iceberg by its tip since only 2% of total body potassium is extracellular. Thus repeated measurements of the serum potassium should be done. In an averaged-size adult with a normal serum K+ of 4 mEq/L, a total body K+ deficit of 200–400 mEq is required to produce a decrease in plasma K+ of 1 mEq/L.
10) Please leave a comment stating how useful the calculation turned out to be in your clinical practice (if ever you used it).
Further readings:
Alcoholic liver disease - complete review
Hypokalemia- ecg changes
Last reviewed on : 1 September 2015
great blog...it helps a lots...thank u =)
ReplyDeletethanks a lot, it really helps
ReplyDeleteThank you for the information, really helped
ReplyDeletemake it in meq/l please,usually we dont adv pottasium in grams.
ReplyDelete1 meq k+ = 1mmol
Deleteso in above eg. 84 mmol = 84 meq
ie; nearly 2 amp. of kcl20 in 5% dex or NS @ 0.5cc/hr
to be cont...
Deleteie; nearly 2 amp. of kcl20 in 5% dex or NS @ 0.5cc/hr
ie in 4-6 hrs
2 such therapies to correct 84 meq loss
becoz one can't add >10meq in 100 cc
ie in 5oocc not more than 2 amp of kcl20
hope you understood if yes kindly reply
:)
superb explaination...anyway just wanna know what's ur references??
DeleteThanx...just saved a patient
DeleteVery nice to do it it's very helpful
DeleteThe old calculation was only (.4xwtx deficits ) but with adding the daily requirement it is very much accurate.
In our Hospital Setting we used this kind of formula in dealing with Potassium deficit patients:
ReplyDeletePotassium Deficit= {[(Desired K - Actual K)(Weight in Kg)(350)] / 3 Days} +/- 50
This is a very useful and helpful information. Thank you
DeleteThis is very helpful. Thank you for posting. :)
ReplyDeleteAwesome information
ReplyDeletethnx :-)
ReplyDeleteIt's been of helpful as it is well ellaborated.
ReplyDeleteThis comment has been removed by the author.
ReplyDeletereally?
Deletewonderful,,,
ReplyDeleteGood calculation and information.
ReplyDeleteVery useful piece
ReplyDeletekeep up with the good work.i am grateful
ReplyDeleteGood one
ReplyDeleteglad i found this site. very helpful. thanks.
ReplyDeletewould like to know why we need times 0.4 for the deficit of potassium?
ReplyDelete1 tsf or 5 ml KCl is equivalent to 540 mg KCl. So giving 2 tsf or 10 ml KCl would equal to 1080 mg KCl. Devide it with 74.6 and we get 14.47
ReplyDeleteSo 10 ml KCl syrup= around 14 mmol K+
Anyhow a very handy article. Many thanks.
Thanks very much . Really helpful
ReplyDeleteInformative and helpful article.
ReplyDeleteThank you so much.
Informative and helpful article.
ReplyDeleteThank you so much.
For pt with hepatic failure can I give kcl in dextrose 10%
ReplyDeleteThank you. Informative and applicable
ReplyDeleteThank you.Very helpful
ReplyDeleteVery informative
ReplyDeleteCan someone calculate it for me? Patient: 48 kg, serum K 2.9
ReplyDeleteI'm not sure I got it right. I'm a student.
If the serum k is 2.9, use the following formula
DeleteDeficit=(3.5-serum k)×weight×0.4
This equals 11.52
Now add 48 to it for the daily k requirement= 59.52
So 59.52 know of k is required by this patient.
Very helpful information regarding calculation of the deficit and total dose needed for repletion. However, I've never seen a hospital that will allow you to do a 20mEq bolus in a 50ml syringe on a pump - way too risky! Nor would they make a 40mEq/500ml bag because they most likely have either 1 or 2 strengths of pre-made piggybacks that they purchase for K-repletion protocols. Most hospitals in the US limit the IVPB size to 10mEq/100ml due to safety concerns, unless a patient meets certain criteria such as fluid-restrictions, having a central line, is on cardiac monitoring, and/or in the ICU. If a patient meets some of these criteria, they may allow a 10mEq/50ml or 20mEq/100ml piggyback.
ReplyDeleteRather than following external/3rd-party advice on how to mix/administer the dose, please use these calculations to figure out how much needs to be given, then ask your hospital pharmacist about the facility policy regarding K boluses and how to best go about administering the dose. It's much safer, and will also save you the obligatory phone call from the pharmacist to educate you about their approved processes!
Signed - a hospital pharmacist with 26yrs experience
May I know what book that you used as the references to that formula?
ReplyDeleteneed your answer soon.
thx..
Sir, your fornula for potassium deficit calculn seems to be at fault!! Potassium drficit is not an extracellular but an intracellular phenomenon... So actual deficit is much much more than thaat calculated by formula u have mentioned... This formula is for calculating Sodiun deficit and not potassium
ReplyDeleteFor every o.5 meq/l decrease in s. potassium below normal, there os a 100 meq/l potassium deficit...
Reference -
Delete1. https://safetyandquality.gov.au/wp-content/uploads/2012/01/tools_royalhobart.pdf
Abhshek Savala i think the threshold for clinical illness is very much wide between intra cellular level in comparison with the intra vascular level but the threshold for clinical illness between intra vascular level is that we know not less than 3.5 .
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ReplyDeletewell for post operative patient (eg laprotomy) i havent seen anyone replace npo defecit for 3 to 4 days. only potassium defecit is replaced without replacing the daily requirements. how much are the potassium reserves in the body.
ReplyDeleteAs we all know, K Cl is an intracellular element and barely reflects in serum level correctly. Awareness and daily supplements in IV infusion in surgical patients post operatively is d best way alongwith sodium and other fluid-water balance. Daily requirements should be added in IV infusion without waiting for deficit to develop. By then, it will be late to do so and very difficult. It's defficiency has vital damaging effects.
ReplyDeletecan you please explain how did you get 0.4 from the formula Kdeficit (mmol) = (Knormal lower limit - Kmeasured) x kg body weight x 0.4? and is there any reference for the formula?
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ReplyDeleteWith 1 ampule kcl ,how much milliequivalent of potassium will increase
ReplyDelete1amp is 10ml kcl ie 20 meq, now calculate.For corrections one has to know the deficit and body wt
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