Interstitial fluid volume, plasma volume and colloid osmotic pressure in patients with nephrotic syndrome

Colloid osmotic pressure in plasma (IIp) and in subcutaneous interstitial fluid (IIi) (wick technique), plasma volume (PV) and interstitial fluid volume (IFV) were measured in nephrotic patients (n = 11) and in healthy controls. Six of the patients were treated with ultrafiltration and the parameters were measured before and after withdrawal of mean 7460 ml (total ultrafiltrate in two sessions). In the nephrotic patients mean IIp was 11.6 mmHg and IIi was 3.9 mmHg compared to 28.6 mmHg and 15.8 mmHg, respectively, in healthy controls. PV was in the normal-to-high range and IFV was increased to 150% of the valued in controls. No statistically significant change in PV, IIp or IIi was found after ultrafiltration, and IFV was reduced by 20%. The results indicate that reduction in IIi is an important oedema-preventing factor and that the reduction in interstitial protein mass is more than proportional compared to the degree of hypoproteinaemia. Ultrafiltration in the rate and magnitude we have used, leads to reduction in IFV, but small changes in PV, IIp or IIi.