FLAP FLOW AND CARDIAC-OUTPUT AS FUNCTIONS OF PULMONARY-ARTERY WEDGE PRESSURE - EXPERIMENTAL-STUDY IN THE PIG

Cardiac output (CO) is redistributed during hypovolemia, but it has no t been clearly documented how this influences flap perfusion. Simultan eous changes in perfusion of a muscle nap and CO as modulated by reduc tions in cardiac filling pressure were compared in a pig model. The hy pothesis was that flap flow (FF) would remain relatively constant as C O was reduced, according to the Frank-Starling curve. Under general an esthesia, five domestic pigs were utilized. Following right carotid ar tery cannulation, measurement of systemic blood pressure and blood gas analysis were carried out. An oximetric Swan-Ganz catheter insertion via the right internal jugular vein was used to measure CO, temperatur e, and pulmonary artery wedge pressure (PAWP). In the lateral decubitu s position, a right latissimus dorsi muscle flap was elevated in the a nimal, using standard technique. The insertion of the muscle was divid ed, and a l-cm section of thoracodorsal artery was mobilized to measur e flap perfusion with a transonic Doppler flowmeter. After baseline me asurements of PAWP, CO, and FF were obtained, blood volume was reduced in 350-cc aliquots at 10-min intervals. After each aliquot was remove d, the hemodynamic parameters were again recorded. This procedure was repeated until the CO was less than 1.0 liter/min; at this point the p ig was sacrificed. The mean baseline PAWP was 15.6 +/- 4.0 mmHg, which was reduced to 2.2 +/-. 1.1 mmHg (p < 0.05) by the end of the experim ent. The mean baseline FF was 5.6 +/- 1.9 cc/sec, and the mean baselin e CO was 4.6 +/- 1.0 l/min; these were reduced to 0.4 +/- 0.4 cc/sec ( p < 0.05) and 1.1 +/- 0.1 l/min (p < 0.05), respectively, by the end o f the experiment. FF and CO were plotted as a function of PAWP and the two regression curves were evaluated by analysis of covariance. The s lope of these curves was not different, p = 0.4. The hypothesis that F F would be preserved in the face of reductions in CO did not prove to be correct in this experiment. Changes in FF paralleled changes in CO as the PAWP was reduced. Inhalation anesthesia and local sympathectomy may influence flap perfusion during hypovolemia. These results unders core the importance of avoiding hypovolemia during flap surgery, in or der to maintain flap perfusion.