CHANGES IN LEFT THORACIC-DUCT LYMPH-FLOW DURING PROGRESSIVE ANEMIA INTHE OVINE FETUS

OBJECTIVE: The purpose of this study was to evaluate the extent to whi ch increased lymph flow can return fluid and protein to the circulatio n in the chronically anemic fetus. STUDY DESIGN: Thoracic duct lymph f low rate over a range of outflow pressures was measured in 8 near-term fetal sheep 4 to 5 days after surgery and daily thereafter for 5 days . After each day's study 60 to 150 mi of blood was withdrawn at a rate of 1 mi per minute. Regression analysis was used to establish the lym ph flow function curve. Lymph and plasma protein concentrations and ly mph flow rate were compared by analysis of variance for repeated measu res. RESULTS: As the hematocrit was reduced from 34.6% +/- 1.3% (mean +/- SE) to 14.4% +/- 1.0%, thoracic duct lymph flow increased from 0.1 2 +/- 0.01 to 0.28 +/- 0.02 ml/min/kg. Plasma total protein concentrat ion did not change, lymph protein concentration fell (2.6 +/- 0.1 to 2 .4 +/- 0.1 gm/dl), and the difference between plasma and lymph protein concentrations increased (1.04 +/- 0.05 to 1.34 +/- 0.10 gm/dl). Prot ein returned to the circulation increased from 11.5 +/- 0.3 to 23.7 +/ - 1.5 mg per minute. Central venous pressure did not change and remain ed less than the breakpoint pressure. Although the plateau lymph flow rate increased, neither the breakpoint or stopflow pressures of the ly mph flow function curve were altered. CONCLUSIONS: Fetal lymph flow an d thereby capillary filtration increased progressively as anemia becam e more severe. The increase in lymph flow did not appear to be limited by outflow pressure. By returning protein to the circulation, an incr ease in thoracic duct lymph flow helped to limit expansion of extravas cular fluid volume during chronic fetal anemia.