LYMPHATIC REMOVAL OF DIALYSATE FROM THE PERITONEAL-CAVITY OF ANESTHETIZED SHEEP

Several investigators have suggested that the lymphatic circulation reduces ultrafiltration in continuous ambulatory peritoneal dialysis (CAPD). The purpose of this study was to assess lymphatic drainage of the peritoneal cavity directly in anesthetized sheep under dialysis conditions. Lymph was collected from the caudal mediastinal lymph node and the thoracic duct, both of which are involved in the lymphatic drainage of the ovine peritoneal cavity, and from the prescapular lymph node, which is not involved in peritoneal lymphatic drainage. Fifty ml/kg volumes of a mildly hypertonic dialysis solution (Dianeal 1.5%) containing 25-mu-Ci I-125-human serum albumin were instilled into the peritoneal cavity, and lymph flows and the appearance of labeled protein in the lymphatic and vascular compartments were monitored for six hours. Following the instillation of dialysis fluid there was a tendency for lymph flow rates from the thoracic duct to increase but these changes were not significant. However, flow rates from the caudal lymphatic demonstrated significant increases, especially in the final three hours of the monitoring period. Only about 8% of the radiolabeled albumin was removed from the peritoneal cavity over six hours (that is, 92% was left in the peritoneal space). Of the albumin removed, approximately 17% of this was drained by abdominal visceral lymphatics into the thoracic duct. About 25% passed through the diaphragm into the caudal mediastinal lymph node and into efferent lymph. Since the efferent lymphatic duct of the caudal mediastinal node empties directly into the thoracic duct, about 42% of all protein removed from the peritoneal cavity of the sheep was ultimately transported to the thoracic duct. Over half (58%) of the protein removed from the peritoneal cavity was transported to the blood by routes not involving the thoracic duct. Expected net ultrafiltration volumes appeared to be reduced by lymphatic drainage. The drainage of peritoneal fluid into the thoracic duct over the six hour period was calculated to be 0.042 +/- 0.013 ml/hr/kg and that into the caudal mediastinal lymphatic 0.157 +/- 0.034 ml/hr/kg. On the basis of the assumption that the labeled protein entering the bloodstream was delivered exclusively by lymphatics, we estimated that the total rate of lymph flow from the ovine peritoneal cavity during dialysis was 12.81 +/- 1.84 ml/hr or 0.454 +/- 0.062 ml/hr/kg.