Hyperkalemia

[sonuritu]

This has confused me now...

Shargel has this example on hyperkelemia in Clinical lab values chapter (pg778).

As a rule --- With every 0.1 unit change in pH, the K concentration changes by 0.6 mEq/l

Now initial Ph was 7.4 and final is 7.1, so a net decrease in ph is 0.3
Hence total change in K concentration should be 1.8mEq/L

If the initial concentration was 4.5 mEq/L Final should be 6.3 (4.5+1.8)

Shargel on the other hand says 2.7 (4.5-1.8) ??????

Can someone explain?

[arorarakh]

Hi Sonuritu,

Here is my understanding of this example in shargel about k value in case pH value deviates from 7.4.
In this particular example pH value decreased from 7.4 to 7.1 and for every 0.1 unit change in ph, the k conc changes by 0.6.
Now here is the trick - if pH value decreases you have to subtract the calculated value from the measured K concentration
for example - K conc is 4.5 in this case and correction factor is (7.4-7.1) * 0.6 = 1.8
now since there is decrease in pH value , you will have to subtract 1.8 from 4.5 (4.5 - 1.8) and the k concentration after correction would be 2.7mEq/L

What you did (4.5 + 1.8) would be in the case if pH value had changed from 7.4 to 7.7.

This is what I understood. hope it helps.

Thanks

[sonuritu]

Appreciate your response.
But my understanding is that a decrease in ph pushes the intracellular k out of the cells... Which should eventually increase the serum k concentration,in which case the above equation needs to have k conc increAsed by a factor of 1.8.
What do you say?

[arorarakh]

Hi Sonuritu,

In addition to my previous response there is one more explantion to your question.
K is basically intracellular cation. When we measure its value in Lab it is extracellular K value that ranges between (3.5 - 5.0 mEq/L). In case of acidosis ,that is lowering of blood PH( here it is 7.1 from 7.4) . In acidoses H + increases in blood/plasma. Body tries to compensate for acidosis by pushing H+ inside the cell and intracellular K+ ion outside the cells. This results in slight increase in extracelluar k+ conc. So one has to subtract the correction factor from the lab value to know the correct k conc.

[arorarakh]

The reason for subtracting the correction factor from actual pot conc in case of acidosis is that, once you correct the acidosis for eg diabetic ketosis (in this case we willl assume pH will be corrected to 7.4) then it will result in movement of K= ions into the cell from the blood/Plasma- condition wil be called Hypokalemia. Ideally when we treat Acidosis, we also supplement potassium to the patient. if we do not give K+ , patient can crash with hypokalemia, though initially your lab value showed high potassium and you did not supplement the potassium. In reality you have to know the real K+ value by subtracting correction factor from the lab value.

This correction helps to treat patients. In this case 4.5 value is the false increase in K+level. This isbecause of shift of potassium but not true hyperkalemia. Once patients blood pH normalises, K+ will shift back from extracellular to intracellular and then it will result in hypokalemia if we do make the correction value by subtraction. If Doctor knows the correct value after subtraction then he will definitely supplement potassium also while treating for acidosis.

Hope it helps.

[sonuritu]

The reason for subtracting the correction factor from actual pot conc in case of acidosis is that, once you correct the acidosis for eg diabetic ketosis (in this case we willl assume pH will be corrected to 7.4) then it will result in movement of K= ions into the cell from the blood/Plasma- condition wil be called Hypokalemia. Ideally when we treat Acidosis, we also supplement potassium to the patient. if we do not give K+ , patient can crash with hypokalemia, though initially your lab value showed high potassium and you did not supplement the potassium. In reality you have to know the real K+ value by subtracting correction factor from the lab value.

This correction helps to treat patients. In this case 4.5 value is the false increase in K+level. This isbecause of shift of potassium but not true hyperkalemia. Once patients blood pH normalises, K+ will shift back from extracellular to intracellular and then it will result in hypokalemia if we do make the correction value by subtraction. If Doctor knows the correct value after subtraction then he will definitely supplement potassium also while treating for acidosis.

Hope it helps.

Certainly!!!! Thanks!