Evaluation of pedicled skin flap viability by pH, temperature and fluorescein: an experimental study

In order to test methods of predicting skin flap viability, a skin flap model in Sprague-Dawley rats was established. As criteria for studying skin flap survival, we compared measurement of skin pH, temperature, as well as fluorescence photography and computer aided digital morphometry (CADM). Ninety male Sprague-Dawley rats were divided into three groups in which pedicles were clamped for 10, 15, or 20 h. A standardized bipedicled skin flap was prepared, maintained by the epigastric artery, vein and nerve. All flaps were sutured back in place immediately after clamping. We found that postoperative prediction of flap survival based solely upon external appearance was impossible until the 2nd postoperative day. Changes in pH were not statistically significant in the prediction of vital or necrotic flaps. The temperature measurements showed, that in the event of viability the decrease in flap temperature versus the reference temperature (rectal temperature) was significant (P < 0.0094 in Group II, 15 h of ischaemia) or at least a tendency to significance (P < 0.059 in Group III, 10 h of ischaemia) bigger than in the event of partial or total flap necrosis. The photographic documentation using fluorescein showed that all coloured areas survived. Group I (20 h) showed predominantly total flap necrosis. Most flaps in Group III (10 h) exhibited a small necrotic area at the tip. In Group II (15 h) no typical staining pattern could be observed. Furthermore, computer aided digital morphometry demonstrated a decrease of the necrotic area by 7% between the 2nd and 4th postoperative day in Groups II and III. The method which gave the most exact prediction about viability was the fluorescein staining of the flaps via the tail vein.