Postoperative monitoring of microsurgical free-tissue transfers for head and neck reconstruction: A systematic review of current techniques. Part II. Invasive techniques
A systematic review of the literature relating to methods of monitoring viability of microvascular free-tissue transfers in the head and neck region was conducted. The aim of this review is to identify the best method of monitoring that would allow timely salvage of potentially failing free flaps. An analysis and description of the various studied techniques is also given. In this second part, invasive modalities are covered.
Available from: Thomas G Poder
- "Inversely, the microdialysis technique is appropriate for buried flaps and appears to provide comparable results to those of implantable Doppler , but it cannot constitute a first-line solution due to its high acquisition cost and the difficulty of interpretation of the results. The two reviews of the literature conducted by Abdel-Galil and Mitchell  , as well as the review by Luu and Farwell , led to the same conclusions as Smit et al.  with comparable endpoints. "
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The purpose of this paper is to evaluate the efficacy and cost-effectiveness of the implantable Doppler system based on the analysis of the available scientific literature and clinical and cost data available in our hospital. The results of this system are compared to those of conventional free flap monitoring methods.
Materials and methods:
The literature published between 1991 and 2011 was systematically reviewed. All available cost data were collected and several simulations were performed. A retrospective assessment of the efficacy of conventional methods in our hospital was also conducted.
Results and conclusion:
The implantable Doppler system is more effective than the conventional methods used to monitor free flap perfusion. The mean flap salvage rate with the implantable Doppler was 21 percentage points higher (81.4 vs. 60.4). The excess cost compared to conventional methods was about CAD 120 per patient (about EUR 94). However, this excess cost can be compensated or even reversed, depending on the initial flap salvage rate in the health facility and the type of free flap (buried vs. non-buried).
Available from: Timothy Kenneth Mellor
- "The majority of free flaps that fail do so within the first 24 h  and current clinical assessment includes flap colour, temperature and turgidity. Recently, modalities including Doppler flowmetry and microdialysis for measuring metabolism have gained popularity in predicting flap compromise [7, 8]. However, some question whether these techniques are superior to clinical assessment alone . "
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ABSTRACT: We describe an enzyme-based electroanalysis system for real-time analysis of a clinical microdialysis sampling stream during surgery. Free flap tissue transfer is used widely in reconstructive surgery after resection of tumours or in other situations such as following major trauma. However, there is a risk of flap failure, due to thrombosis in the flap pedicle, leading to tissue ischaemia. Conventional clinical assessment is particularly difficult in such ‘buried’ flaps where access to the tissue is limited. Rapid sampling microdialysis (rsMD) is an enzyme-based electrochemical detection method, which is particularly suited to monitoring metabolism. This online flow injection system analyses a dialysate flow stream from an implanted microdialysis probe every 30 s for levels of glucose and lactate. Here, we report its first use in the monitoring of free flap reconstructive surgery, from flap detachment to re-vascularisation and overnight in the intensive care unit. The on-set of ischaemia by both arterial clamping and failure of venous drainage was seen as an increase in lactate and decrease in glucose levels. Glucose levels returned to normal within 10 min of successful arterial anastomosis, whilst lactate took longer to clear. The use of the lactate/glucose ratio provides a clear predictor of ischaemia on-set and subsequent recovery, as it is insensitive to changes in blood flow such as those caused by topical vasodilators, like papaverine. The use of storage tubing to preserve the time course of dialysate, when technical difficulties arise, until offline analysis can occur, is also shown. The potential use of rsMD in free flap surgery and tissue monitoring is highly promising.
Free flap surgery timeline: The flap is raised and MD probe inserted. Glucose and lactate levels were monitored at 1 minute intervals throughout flap removal and the reconstruction of the tongue. Grey lines indicate key events as communicated by the surgeons in real time.
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