Total body and exchangeable potassium in chronic airways obstruction: a controversial area?

Electrolyte disorders in the elderly

Normal human ageing impairs homeostatic mechanisms in such a way as to exaggerate and prolong the effects of stress. Thus, an event--pathological or traumatic--which produces a trivial change in plasma electrolytes of young people may produce major oscillations of plasma levels in the elderly, which take much longer to return to 'normal levels'. This is especially apparent with perturbations in the plasma levels of sodium and potassium, mainly due to changes in renal function and neurohumeral mechanisms which occur with increasing age. Paradoxically this does not mean that the clinician should be over-enthusiastic in attempting to correct electrolyte imbalance because, for the same reasons, the danger of over-treatment producing the opposite and equally dangerous electrolyte imbalance is ever-present. Indeed, in clinical practice most electrolyte disturbances in old age are iatrogenic in origin. Cautious patience and vigilance should be the clinical approach with elderly patients. A high index of suspicion should lead to a careful appraisal of the drug (diuretic, intravenous fluid) and environmental (dehydration) aetiology of most electrolyte disturbances in old age.

Can body potassium of old people be predicted from anthropometric data?

Body potassium was measured by whole body counting in a group of carefully screened healthy individuals, mean age 75 years. The results have been compared with values predicted by eight formulae in the literature derived using similar methods. The mean predicted results ranged from 87% to 102% of the mean observed level in male subjects and from 87% to 137% in female subjects. Individual male results range from 55% to 123% and in female subjects from 72% to 146% of the observed value. It is concluded that there are no published formulae which will adequately predict whole body potassium levels in old people--the very group likely by virtue of age-related disease, to need measurements of body potassium.

Whole body potassium and total exchangeable potassium in elderly patients with cardiac-failure

Body potassium status of patients with cardiac failure may be estimated by a number of methods, but increasing reliance is being placed upon radioisotope dilution with 42K which measures the total exchangeable potassium. Total exchangeable potassium comprises between 86 per cent and 97 per cent of whole body potassium in healthy subjects. We have measured total exchangeable potassium in 22 oedema-free elderly patients with stable cardiac failure and compared the results with simultaneously determined measurements of whole body potassium obtained by whole body counting. The mean whole body potassium was 2360 +/- 640 mmol. The mean value of total exchangeable potassium measured at 24 hours was 1820 +/- 610 mmol (77% of whole body potassium) and increased further to 2000 +/- 600 mmol (84%) when measured after 48 hours. In patients with cardiac failure and, perhaps, also other patients with a history of fluid retention, the mixing of a tracer dose may be significantly delayed, which if not appreciated may lead to an overestimate of potassium depletion.

Potassium depletion and tissue loss in chronic heart-disease

Weight-loss, total body-potassium, and total body-nitrogen were measured in 12 men and 15 women with severe chronic heart-disease. Compared with age-matched healthy controls, the men had lost an average of 13 kg in weight, 915 mmol of potassium, and 354 g of nitrogen, whereas the women had lost 5.6 kg of weight, 327 mmol of potassium, and 66 g of nitrogen. Although the potassium/nitrogen ratio in the lost tissue is not precisely known, the loss of nitrogen indicates that most of the potassium loss in men is due to tissue loss and that there is little fall in the intracellular concentration of potassium in either the men or the women.

Potassium studies in chronic obstructive airways disease

Seventeen male patients with chronic obstructive airways disease in remission were separated into two groups according to arterial carbon dioxide tensions. Hypercapnia was associated significantly with hypoxia and increased red cell volume whereas normocapnia was not. Normocapnic patients were significantly lighter than those with hypercapnia. Total body potassium (TBK) measured by the whole body monitor was significantly low in two of the patients studied (P less than 0.005). The mean value for TBK for the normocapnic group as a whole was significantly low (P less than 0.005), but the mean value for the hypercapnic group was not. Serum potassium and erythrocyte potassium concentrations were normal even when TBK was low, and diuretics had no apparent influence on these potassium values. Of four patients (two in the series and two others) who had TBK measured after a recent episode of cor pulmonale, three had significantly low values. The only previous studies using a whole body monitor to measure TBK in chronic obstructive airways disease found no such low values, though other workers estimating exchangeable potassium by isotope dilution techniques had found evidence of gross potassium depletion. It is concluded that low TBK does indeed occur in patients with chronic obstructive airways disease and that gross depletion is more likely to follow an episode of cor pulmonale.