Nutritional Assessment and Skeletal Muscle Function in Patients on Continuous Ambulatory Peritoneal Dialysis

Abstract

Nutritional status and skeletal muscle function were studied in 20 CAPD patients (12 men and eight women) who were randomly selected among a total population of 95 CAPD patients. Their ages ranged from 29 to 74 years -mean 59 -and they underwent CAPD for a period of one to 180 (mean 62.2 ± 53.3) weeks. Nutritional assessment included measurement of body anthropometry, serum albumin, transferrin, C3 and C4, lymphocyte counts, total body nitrogen -nitrogen index (NI) and total body potassium (TBK). Function of the adductor pollicis muscle was assessed by electrical stimulation of the ulnar nerve, obtaining the force of contraction at 10 Hz expressed as a per cent of the force at 100 Hz (F 10/F 100) and the maximal relaxation rate (MRR) expressed as % force loss/10 ms. Seven of the 20 patients showed low nitrogen index (NI < 0.80), two had low transferrin levels «1.70 mg/dl) and one had very low albumin levels (26 g/l). There was no statistically significant difference between the NI of men (0.84 ± 0.11) and women (0.90 ± 0.14). TBK varied among the patients with a mean value of 89.9 ± 11.8 g for women and 123.8 ± 25.3 g for men. In all patients, the relative force of contraction of adductor pollicis muscle at low frequencies (F 10/F 100) was within normallimits as was the MRR, which showed a small decrease only in three patients. The results indicate that, although when assessed by conventional nutritional parameters some CAPD patients showed subtle indices of malnutrition and a significant proportion (7/20) have a low nitrogen index, most have well-preserved skeletal muscle function. When nutritional status is assessed by standard biochemical nutritional parameters, anthropometry or total body nitrogen (1-3), patients receiving maintenance hemodialysis or CAPD frequently show protein malnutrition. However the standard biochemical parameters may be altered in the presence of renal failure, independent of nutritional status. Thus depressed concentrations of several serum proteins and variations in anthropometric measurements may reflect changes in fluid status rather than gains or losses in body mass (4). In addition certain anthropometric and biochemical measurements of nutritional status are abnormal in chronically uremic patients, who appear to be particularly robust (5). Moreover, although TBK and TBN have been used as more accurate indices of the lean body mass and the protein content respectively, it is not always easy to interpret these measurements (6). Hence at present it is uncertain how well we can translate indices of standard nutritional assessment into the global concept of the general well being. Recently, several workers have shown that changes in skeletal muscle function provide more sensitive indices of nutritional deprivation, than conventional nutritional parameters (7,8,9). Since previous work showed that uremia does not seem to influence skeletal muscle function (10), we decided to study the relationship between conventional nutritional parameters and skeletal muscle function in 20 randomly selected CAPD patients.