Skip to main content

Hypokalemia - Potassium replacement calculation


 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

Comments

  1. great blog...it helps a lots...thank u =)

    ReplyDelete
  2. thanks a lot, it really helps

    ReplyDelete
  3. Thank you for the information, really helped

    ReplyDelete
  4. make it in meq/l please,usually we dont adv pottasium in grams.

    ReplyDelete
    Replies
    1. 1 meq k+ = 1mmol
      so in above eg. 84 mmol = 84 meq
      ie; nearly 2 amp. of kcl20 in 5% dex or NS @ 0.5cc/hr

      Delete
    2. to be cont...

      ie; 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

      :)

      Delete
    3. superb explaination...anyway just wanna know what's ur references??

      Delete
    4. Thanx...just saved a patient

      Delete
    5. Very nice to do it it's very helpful
      The old calculation was only (.4xwtx deficits ) but with adding the daily requirement it is very much accurate.

      Delete
  5. In our Hospital Setting we used this kind of formula in dealing with Potassium deficit patients:

    Potassium Deficit= {[(Desired K - Actual K)(Weight in Kg)(350)] / 3 Days} +/- 50

    ReplyDelete
    Replies
    1. This is a very useful and helpful information. Thank you

      Delete
  6. This is very helpful. Thank you for posting. :)

    ReplyDelete
  7. It's been of helpful as it is well ellaborated.

    ReplyDelete
  8. This comment has been removed by the author.

    ReplyDelete
  9. keep up with the good work.i am grateful

    ReplyDelete
  10. glad i found this site. very helpful. thanks.

    ReplyDelete
  11. would like to know why we need times 0.4 for the deficit of potassium?

    ReplyDelete
  12. 1 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

    So 10 ml KCl syrup= around 14 mmol K+

    Anyhow a very handy article. Many thanks.

    ReplyDelete
  13. Informative and helpful article.
    Thank you so much.

    ReplyDelete
  14. Informative and helpful article.
    Thank you so much.

    ReplyDelete
  15. For pt with hepatic failure can I give kcl in dextrose 10%

    ReplyDelete
  16. Thank you. Informative and applicable

    ReplyDelete
  17. Can someone calculate it for me? Patient: 48 kg, serum K 2.9

    I'm not sure I got it right. I'm a student.

    ReplyDelete
    Replies
    1. If the serum k is 2.9, use the following formula
      Deficit=(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.

      Delete
  18. 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.

    Rather 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

    ReplyDelete
  19. May I know what book that you used as the references to that formula?
    need your answer soon.
    thx..

    ReplyDelete
  20. 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


    For every o.5 meq/l decrease in s. potassium below normal, there os a 100 meq/l potassium deficit...

    ReplyDelete
    Replies
    1. Reference -

      1. https://safetyandquality.gov.au/wp-content/uploads/2012/01/tools_royalhobart.pdf

      Delete
  21. 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 .

    ReplyDelete
  22. yet the goal behind this specific article is to demonstrate to you the best approach to safeguard your Facebook account from hackers paying little mind to whether you have a little or substantial page. how to crack someones facebook password

    ReplyDelete
  23. well 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.

    ReplyDelete
  24. As 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.

    ReplyDelete
  25. can 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?

    ReplyDelete
  26. This comment has been removed by the author.

    ReplyDelete
  27. Detractors on alternative medicine claim that it is not worth as being accepted by the medical circles since it lacks components that may be used to support its efficiency. Yet many assert that once alternative medicine is fully tested, then there would be great rooms for wide acceptance.Medizinische Übersetzung

    ReplyDelete
  28. With 1 ampule kcl ,how much milliequivalent of potassium will increase

    ReplyDelete
    Replies
    1. 1amp is 10ml kcl ie 20 meq, now calculate.For corrections one has to know the deficit and body wt

      Delete
  29. This comment has been removed by the author.

    ReplyDelete
  30. This invention is a great source for the internet users. There are a couple of ways you can use the Password Generator template.

    ReplyDelete
  31. I drink 2 litres of flavoured milk every day and 2 protein shakes each with 40g protein. war machines hack

    ReplyDelete

Post a Comment

Popular posts from this blog

The plantar reflex - Babinski's sign

The plantar response is an important test to identify an upper motor neuron lesion.  PROCEDURE  To elicit it, the muscles of the lower limbs must be relaxed. The outer edge of the sole of the foot is stimulated by firmly scratching a blunt object like a key or a stick along it from the heel towards the little toe. This is what  Joseph Babinski did in the year 1896. He described the 'great toe sign' that year and then in 1903 the 'toe abduction or fan sign'. Nowadays, a final medial movement across the sole of the metatarsus is also done. i.e. we start at the heel to the little toe and finally arcing to the big toe. The final arcing movement is absent in the original Babinski plantar response test. Babinski sign refers to a combination of 'the great toe sign' and the 'fan sign'.  SIGNIFICANCE  The normal response is plantar flexion of the toes (down going) and they are drawn together. More precisely, there is flexion of the big toe and addu

Apgar scoring - table, mnemonic

 INTRODUCTION  The  Apgar score  was devised in 1952 by Dr Virginia Apgar (anesthesiologist) as a simple and repeatable method to quickly and summarily assess the health of newborn children immediately after birth.  This helps to identify those requiring resuscitation and can also be used to predict survival in the neonatal period.   MNEMONIC  A mnemonic for learning purposes includes: A - Appearance (skin colour) P - Pulse (heart rate) G - Grimace (reflex irritability) A - Activity (muscle tone) R - Respiration  Another mnemonic is also useful:  How -   Heart rate Ready - Respiration Is -        Irritability This -    Tone Child -   Colour Apgar scoring is divided into 1 and 5-min scores.  1-MIN SCORE    Sixty seconds after complete birth, the five parameters specified in the table above must be evaluated and scored. A total score of 10 indicates that the baby is in the best possible condition. A score between 0-3 me

Differences between hyperemia and congestion

Hyperemia and congestion both indicate a local increased volume of blood in a particular tissue. Hyperemia is an active process that result from augmented blood flow due to arteriolar dilation (e.g. at sites of inflammation or in skeletal muscle during exercise). The affected tissue is redder than normal because of engorgement with oxygenated blood. Congestion, on the other hand, is a passive process resulting from impaired venous return out of a tissue. It may occur due to systemic causes like cardiac failure or a local cause like isolated venous obstruction. The tissue is cyanosed because the worsening congestion leads to accumulation of deoxygenated hemoglobin in the affected tissues. 

Edema - Definition, pathophysiology, causes, clinical features

 DEFINITION  Edema is an abnormal presence of excessive fluid in the interstitial space.  PATHOPHYSIOLOGY  The movement of water and low molecular weight solutes such as salts between the intravascular and interstitial spaces is controlled primarily by the opposing effect of vascular hydrostatic pressure and plasma colloid osmotic pressure. Normally the outflow of fluid from the arteriolar end of the microcirculation into the interstitium is nearly balanced by inflow at the venular end. A small residual amount of fluid may be left in the interstitium and is drained by the lymphatic vessels, ultimately returning to the bloodstream via the thoracic duct. Either increased capillary pressure, diminished colloid osmotic pressure or inadequate lymphatic drainage can result in an abnormally increased interstitial fluid i.e. edema. An abnormal increase in interstitial fluid within tissues is called edema, while fluid collections in the different body cavities are variously