Lowered Tissue-Fluid Oncotic Pressure Protects the Blood Volume in the Nephrotic Syndrome

Abstract

We have studied the role of adjustments of tissue-fluid colloid osmotic pressure (COP) in the maintenance of the blood volume in 10 patients with the nephrotic sydrome before and after diuretic treatment until dry weight. A mean weight reduction of 13.5 ± 6.4 kg was attended by a fall in blood volume in 3 patients and no change in 6, but the final blood volume was within the normal range: 84.3 ± 3.7 ml/kg (normal value: 87.6 ± 8.8 ml/kg). Albumin content and COP of tissue-fluid, obtained with subcutaneous wicks, were low before edema removal and rose slightly after it, parallel to changes in the plasma. Thus, the transcapillary gradient in COP did not change: 6.5 ± 1.5 mm Hg before and 6.2 ± 1.7 mm Hg after diuretic treatment. Considering the low plasma COP, 8.6 ± 1.6 mm Hg in edematous and 11.7 ± 3.7 mm Hg in dry conditions, this gradient was only slightly below the value of about 10 mm Hg normally found with this technique. We conclude that a lowered tissue-fluid COP is important for the preservation of blood volume in dry patients with the nephrotic syndrome. In addition, this adaptation can explain why the blood volume is often normal and not expanded despite the sometimes huge overhydration in these patients.

Transcapillary Oncotic Pressure in the Edema of Congestive Heart Failure

“…Mean serum albumin was 3.57 ±(SD) 0.312 g/100 mg total serum proteins 6.19 ±(SD ) 1 [9,10]. Normal transcapillary gradient at the ankle is approximately 10 mm Hg.…”

“…It was initially surprising to find that the expression np -Jtj or An, the oncotic pressure difference across the capillary wall, was greater than normal in peripheral edema due to cardiac failure. In normal persons, jtp is approximately 25 mm Hg, rt| 10-14 mm Hg as measured using wicks at ankle or thorax [I, 9,10]. This results in an oncotic pressure gradient of 10-14 mm Hg across the normal capillary.…”

“…The method of measuring normal tissue fluid oncotic pressure has been reviewed by Auckland and Nicholaysen [1,11], as well as by Dorhout-Mees' group [4,9,10], using wicks introduced through the skin. The method we have used that of measuring edema fluid collected in a needle, -is essentially similar to the use of Southey's tubes, and the average oncotic pressure of tissue fluid found in cardiac edema is approximately I mm Hg, or about one-tenth of the tissue oncotic pressure measured using wicks in the normal subject at the ankle.…”

Ratio of Urinary Potassium to Urinary Sodium and the Potassium and Edema Status in Nephrotic Syndrome

“…The 2 groups showed the same levels of serum albumin. There are compensatory mechanisms for preventing interstitial edema or intravascular volume depletion when severe hypoalbuminemia develops, i. e. interstitial albumin is completely transferred to the blood, resulting in a new equilibrium between plasma and interstitial fluid albumin accumulation, before the impending hypovolemia (10,11). However, this process takes time (10).…”

Isolation of interstitial fluid from skeletal muscle and subcutis in mice using a wick method

“…Their absolute mean value for COP i in subcutis was slightly but not significantly lower than our value of 9.1 mmHg for the same tissue. Because COP i varies as a function of COP p (4,11,17), a comparison of the COP i /COP p ratio is more relevant. If related to COP p , their COP i /COP p ratio of 0.42 is significantly lower than our corresponding ratio of 0.49.…”