Thoracic duct lymph and PEEP studies in anaesthetized dogs

PEEP impedes thoracic duct drainage (LF). This can be counteracted by a thoracic duct fistula. Consequently, lung oedema (LOE) should develop during PEEP more slowly with LF at atmospheric pressure (LF_AP) than with LF against jugular venous pressure (LF_JVP). In 12 anaesthetized dogs LOE was produced by Ringer's solution i.v. (2.5 ml/min per kg) for 6 h during PEEP (10 mmHg) with either LF_AP or LF_JVP. Ringer's+PEEP greatly increased aortic, pulmonary artery and wedge pressures, JVP, and cardiac output. Colloid osmotic pressures in plasma and lymph were drastically reduced, pulmonary effective filtration pressure (EFP) rose by about 20 mmHg. LF_JVP increased 7-fold, LF_AP about 19-fold, the respective loss of plasma proteins was 1.83 and 1.06 g/kg during 6 h. Thermal-dye extravascular lung water showed an increment of 68 with LF_JVP versus 43 l/h/g per mmHg with LF_AP. Final lung water content was at any EFP (12.8–31.9 mmHg) lower with LF_AP than with LF_JVP amounting 512 with LF_JVP versus 377 l/g/per mmHg with LF_AP. LF_AP decreased the development of LOE during PEEP by bypassing the PEEP-induced high JVP and thus facilitating the removal of interstitial fluid. It is hypothesized that a thoracic duct fistula might aid the treatment of patients with LOE due to ARDS and therefore requiring high levels of PEEP.