A potassium deficiency results when a patient is maintained on parenteral feedings with an inadequate replacement of the potassium ion. This deficiency is severer when the patient has a marked loss of gastro-intestinal fluid through suction, fistula, or diarrhea. The deficiency may be increased further by the stress response to surgery, which is known to increase the rate of urinary excretion of potassium. As a compensating factor, the homeostatic mechanisms tend to maintain a normal level of potassium in the extracellular water at the expense of the intracellular potassium; but when the loss has continued for a sufficient length of time, the patient develops metabolic alkalosis.11,22
The methods usually used to measure potassium give an estimate of the quantity in the extracellular space only. This extracellular space represents only 5% of the total body potassium pool.9,11,15,17,18,22,29 Obviously, there is need for an efficient method of measuring intracellular potassium.