Dual X-ray absorptiometry (DXA) performs noninvasive assessment of bone and soft tissue with high precision. However, soft tissue algorithms assume that 73.2% of the lean body mass is water, a potential source of error in fluid retention. We evaluated DXA (model QDR-2000; Hologic Inc, Waltham, MA), bioelectrical impedance analysis (BIA), and simple anthropometry in 19 patients (9 women and 10 men, mean age 46 y) before and after hemodialysis, removing 0.9-4.3 L (x: 2.8L) of ultrafiltrate. The reduction in fat-free mass (FFM) measured by DXA was highly correlated with the ultrafiltrate, as determined by the reduction in gravimetric weight (r = 0.975, P < 0.0001; SEE: 233 g), whereas BIA was considerably less accurate in assessing FFM reductions (r = 0.66, P < 0.01; SEE: 757 g). Lumbar bone mineral density (BMD) was unaffected by dialysis, as were whole-body fat and BMD. Whole-body bone mineral content, however, was estimated to be 0.6% lower after dialysis. None of the simple anthropometric measurements correlated significantly with the reduction in FFM. In an unmodified clinical setting, DXA appears to be superior to other simple noninvasive methods for determining body composition, particularly when the emphasis is on repeated measurements.

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The acid-base characteristics of two peritoneal dialysis solutions containing either lactate or acetate are compared and the time course of changes in intraperitoneal pH following instillation into the abdominal cavity is measured. The concentration of titratable acid (cTA) is 5.58 mmol/l or 7 times as high in solutions containing acetate as in those containing lactate (0.79 mmol/l). The buffer capacity, -dcTA/dpH, is 11.43 and 1.82 mmol/l, respectively. Following intraperitoneal instillation of 1.5 liter of the solutions, the time course is 2–3 times as long before intraperitoneal pH reaches 7 using acetate (18 min) as when using lactate (7 min). The above mentioned difference in acid-base characteristics as well as an individual acetate intolerance is supposed to be the cause for the development of abdominal pains and peritoneal irritation observed in some patients using acetate-containing solutions.123 mmol/l of sodium bicarbonate is to be added to the acetate solution to raise the pH value from 5.6 to 7.4. Neutralization using sodium bicarbonate will thus result in sodium intoxication of the patient. The use of lactate instead of acetate for peritoneal solutions is advocated.

Previous in vitrobiocompatibility studies have shown bicarbonate-based continuous ambulatory peritoneal dialysis (CAPD) fluids to be superior to those based upon lactate/acetate. To evaluate these findings in vivo, 41 rabbits were subjected to CAPD for four weeks in a randomized prospective study using either Dianeal, a commercially available dialysis fluid containing lactate, or 87b, a bicarbonate-based CAPD fluid. Ten rabbits with CAPD catheters, which were flushed with a heparin solution every 36 hours, served as controls. None of the control rabbits showed clinical or histopathological signs of peritonitis, while 8 of 20 in the Dianeal group and 6 of 21 in the 87b group contracted peritonitis. Four rabbits in the Dianeal group had to be sacrificed early due to severe peritonitis. Post mortem examinations, including scanning and light microscopy, did not reveal any macroscopic or microscopic differences among the three groups of noninfected animals. No significant distinctions between the groups could be made for body temperature, weight gain, dialysate volume, dialysate differential leukocyte count, dialysate protein content, and food intake during the course of the study. In conclusion, the present animal model did not reveal any major difference in the biocompatibility between the lactate and the bicarbonate-based CAPD fluids.

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