Effect of Dobutamine on Lung Microvascular Fluid Flux in Sheep with “Sepsis Syndrome”: Materials and Methods
Ten mature Suffolk sheep, weighing 30 to 40 kg (0.9 to 1.2 m2 of body surface area), were prepared with chronic lymph fistulae using a modification of the technique described by Staub et al. Before study the sheep were premedicated with atropine sulfate and were then anesthetized and intubated. We cannulated the aorta with a nonheparinized Silastic catheter (medical grade tubing; 0.125 outer diameter; Dow Corning) and the pulmonary artery with a No. 8 French, right-heart flow-directed thermodilution catheter (Edwards model 93A-131). The right-heart catheter position was confirmed by the presence of typical pressure recordings. With the balloon inflated, a pulmonary arterial wedge tracing was documented. The balloon was then deflated, and the catheter was flushed for the duration of the experiment with a continuous infusion of 5 percent dextrose in water, to which 1,000 units of heparin had been added (1.0 ml/hr).
Using a right posterolateral thoracotomy through the sixth interspace, the efferent duct of the caudal mediastinal lymph node was then cannulated with a nonheparinized Silastic catheter (medical grade tubing with 0.025 inner diameter and 0.047 outer diameter; Dow Corning). The catheter was secured and externalized through the chest wall. The tail of the caudal mediastinal lymph node was identified, ligated, and divided below the level of the inferior pulmonary ligament. To further reduce potential for contamination by nonpulmonary lymph, all identifiable diaphragmatic and chest wall afferent lymphatic vessels were cauterized in a manner similar to that described by others. Following a left thoracotomy through the fourth intercostal space, the left atrium was then catheterized with a No. 16 French Foley catheter.
This protocol was approved by the University of Western Ontario’s committee governing the experimental care of animals. To ensure that the animals did not suffer discomfort when studied while awake, we administered 50 mg of meperidine intravenously every six to eight hours; in the immediate postoperative period, this was supplemented with acepromazine (25 mg) intravenously to minimize the pain of the thoracotomies and a subsequent laparotomy.