Tissue Oximetry for Monitoring Free DIEP Flap Viability: Factors to Consider towards Optimizing Postoperative OutcomeFunding None.
23 July 2018
16 October 2018
17 December 2018 (eFirst)
With great interest we read the recent article entitled “Postoperative monitoring of free DIEP flap in breast reconstruction with near-infrared spectroscopy: variables affecting the regional oxygen saturation'' by Salgarello et al in the latest issue of the Journal of Reconstructive Microsurgery. The authors reported a positive linear correlation between tissue oximetry values and several free flap characteristics and thereby demonstrated that near-infrared spectroscopy is a reliable tool for free flap monitoring. Through this letter, we would like to suggest additional factors to address for optimization of postoperative outcome following “deep inferior epigastric perforator” flap (DIEP-flap) surgery.
In autologous breast reconstructive surgery, the DIEP-flap method is increasingly popular given a low risk of microvascular thrombosis (3.38%) compared with other free flaps. With respect to postoperative monitoring of DIEP-flaps using tissue oximetry, several practical and technical factors need to be taken into account. First, the surface area of the sensor. Spurious readings from surrounding tissues can be found in the case of a relatively large surface area compared with the surface area of the flap itself. In the latter situation, the regional tissue oxygen saturation (rSO2) does not represent the area of interest. In the discussion, the authors elaborate on the aberrant saturation values found in flaps with skin islands less than 3 cm, indicating that interpretation of these data is challenging, which advocates for the use of smaller sensors for DIEP-flap monitoring.
Next, quality of the vascular supply is one of the biggest concerns for the reconstructive surgeon. To assess vascularization and the subsequent method of surgical resection of DIEP-flaps, several strategies have been described, for example, the “perfusion zones” by Holm et al. To date, consensus is lacking regarding a superior resection method. Salgarello et al did not describe their resection method, which might have had an effect on both clinical outcomes and rSO2 readings. Moreover, they performed the tissue oxygenation measurements in the “early-stained'' area and did not address the perfusion zones as earlier described.  Standardization of tissue oximetry measurements is important to enable comparison across studies and contributes to inclusion of tissue oximetry in standard monitoring protocols.
Another parameter affecting flap viability concerns the duration of the ischemia period. As shown by Lee et al, an ischemia time exceeding 99.5 minutes significantly increases the chance of fat necrosis (odds ratio = 9.449). Although Salgarello et al included several crucial surgical factors in their study, such as the flap weight, flap area, perforator number, and perforator size, ischemia time was excluded, which might lead to underestimation of the role of ischemia time in the development of postoperative complications.
In conclusion, a combination of various patient-related, surgical, and postoperative factors potentially influences the viability of a free flap transplant. Further clinical studies are needed to improve the knowledge on the added value of tissue oximetry following free flap surgery.
- 1 Salgarello M, Pagliara D, Rossi M, Visconti G, Barone-Adesi L. Postoperative monitoring of free DIEP flap in breast reconstruction with near-infrared spectroscopy: variables affecting the regional oxygen saturation. J Reconstr Microsurg 2018; 34 (06) 383-388
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