Thoracic duct lymph and PEEP studies in anaesthetized dogs. I. Lymph formation and the effect of a thoracic duct fistula on lymph flow.

The effect of positive end-expiratory pressure ventilation (PEEP, 11-12 mmHg, 60-90 min without, 19 h with circulatory support) on fractional escape rate of plasma proteins (FER), and on thoracic duct lymph flow draining against jugular venous (LFJVP) or atmospheric pressure (LFAP) was studied in anaesthetized dogs. FER was 10.8%/h, 15.3%/h, and 8.5%/h before, during, and after PEEP, respectively, indicating augmented lymph formation probably due to the increase in venous pressure from 4.8 to 10.8 mmHg during PEEP. LFJVP was 39 microliter/min per kg before PEEP, decreased transiently during PEEP but the steady state value (up to 19 h) was not different from control, and increased transiently after PEEP. LFAP was 37, 80, and 38 microliter/min per kg before, during, and after PEEP, respectively. Long-term PEEP increased LFAP fourfold. Changing the drainage mode during PEEP yielded an immediate increase from LFJVP = 34 to LFAP = 79 microliter/min per kg and an instantaneous reduction from LFAP = 95 to LFJVP = 35 microliter/min per kg. Lymph protein concentration and protein lymph/plasma ratio increased concomitantly with LFAP during PEEP suggesting augmented hepatic contribution to LFAP, augmented intestinal contribution was revealed by labelling intestinal lymph using olive oil orally, muscular lymph flow was not increased as shown by i.m. Evans blue. In conclusion, the augmentation of venous pressure by PEEP promotes capillary filtration but obstructs lymph drainage from the thoracic duct into the jugular vein. PEEP imbalances formation and return of lymph and affects the development and removal of oedema.