Blood to interstitial fluid volume ratio in chronic hypokalaemic states.

The distribution of extracellular fluid over the intra- and extravascular spaces was determined in hypokalaemic and normokalaemic patients. In six patients with Bartter's syndrome, four with pseudo-Bartter's syndrome, and twenty with essential hypertension (EH) chronically treated with chlorthalidone, serum potassium (serum K+) and extracellular fluid volume (ECFV) were decreased, while plasma volume (PV) and blood volume (BV) were normal (see Table 1 for means, standard deviations, and levels of significance). Consequently, the ratio of BV to interstitial fluid volume (IFV) was increased. In ten patients with EH on long-term combined enalapril chlorthalidone therapy, eight EH patients on long-term spironolactone treatment, and twenty-three EH patients treated by short-term sodium restriction, PV, BV, and ECFV were decreased, but serum K+ and BV/IFV were normal. In six patients with primary hyperaldosteronism (PHA) serum K+ was decreased, while PV, BV, and BV/IFV were elevated. Significant negative correlations between sK and BV/IFV were found in the Bartter patients (r = -0.88) and the pooled data of all patients (r = -0.50). These findings suggest an association between chronic hypokalaemia and a fluid shift from the extra- into the intravascular space. The hypothesis that this phenomenon is due to a decreased venous resistance as a consequence of chronic hypokalaemia is discussed.