Comparison of flap ischemia induced by arterial or venous occlusion in pigs with the aid of microdialysis

The objective of the present investigation was to study the early metabolic consequences of either arterial (AI) or venous (VI) ischemia in experiment ally constructed skin flaps. It was of specific interest to evaluate whethe r a microdialysis monitor could discriminate between conditions where eithe r a vein or an artery was clamped. For that purpose, bilateral buttock skin flaps were elevated on 13 pigs. One side of the pig served as AI model, an d the opposite side as VI model. The ischemic period lasted 2 h. Microdialy sis catheters were introduced into the flap tissue of both sides and also i nto an unoperated control area. This made it possible to measure and compar e glucose, lactate, and glycerol concentrations in flap and control tissue. Metabolic consequences of ischemia could be evaluated by determining chang es in the interstitial concentrations of these substances before, during, a nd after AT and VI. To verify cessation and reinstitution of blood flow dur ing vascular occlusion and reperfusion, laser Doppler monitoring (LDF) and clinical assessment were used in parallell with microdialysis. The glucose level fell significantly in response to both AI and VI (P<0.01 and P<0.01, respectively), whereas the corresponding lactate and glycerol levels increa sed significantly (P<0.01 and P<0.05, respectively). The glucose response t o Al did not differ significantly from that obtained in response to VI. Sig nificantly higher concentrations of lactate and glycerol were, however, obs erved during AI as compared with VI (P<0.05 and P<0.05, respectively). In c onclusion, this study shows that microdialysis rapidly detects metabolic ch anges inside a newly raised pig buttock flap. The study also shows that the microdialysis technique is capable of discriminating between arterial and venous occlusion. Significantly higher lactate and glycerol levels during A I than during VI indicate that the clinically observed more deleterious eff ects of VI are not reflected metabolically in this study. Whether this is a consequence of the relatively short occlusive period or due to other facto rs, such as capillary damage during VI, needs further elucidation.