Optical sensors for the in vivo assessment of flap perfusion in plastic surgery

Zaman, Tina (2013). Optical sensors for the in vivo assessment of flap perfusion in plastic surgery. (Unpublished Doctoral thesis, City University London)

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Abstract

Following mastectomy for breast cancer a wide variety of surgical techniques are currently available for post mastectomy breast reconstruction where autologous tissue is used to construct a natural looking breast. One of the most common types of reconstructive surgeries use Deep Inferior Epigastric Perforator (DIEP) free flap where skin and adipose tissue along with their blood supplies are transferred from the lower abdomen to the chest. The success of free flap reconstructive surgery depends strongly on the maintenance of adequate perfusion in the flap. Early diagnosis of ischaemia and surgical exploration to restore blood flow can often salvage the flap and may prevent graft failure. Even though many techniques have been used, there is still a need to develop a non-invasive, easy to use, reproducible and inexpensive monitoring device to assess flap perfusion. In an attempt to overcome the limitations of the current flap perfusion monitoring techniques a prototype reflectance three wavelength photoplethysmographic (PPG) sensor was developed. The PPG sensor consisted of two infrared (940 nm), two green (520 nm) and two red (660 nm) LEDs and a photodiode. A PPG processing system was also constructed in order to drive the optical components on the sensor and to detect and pre-process the PPG signals. A Virtual Instrument (VI) was also implemented in LabVIEW in order to display, analyse and archive the PPG signals with the capability of real-time estimation of arterial oxygen saturation (SpO2) values. The system was evaluated in a pilot study on fifteen patients undergoing breast reconstructive surgery using (DIEP) flaps. Good quality red, infrared and green PPG signals were obtained pre-operatively from the donor site (abdomen), intra-operatively (capturing reperfusion of flap following anastomosis) and post-operatively at regular intervals for up to 12 hours post surgery. SpO2 values were also estimated which were found to be in broad agreement with SpO2 values recorded from the commercial pulse oximeter attached to the patients’ finger. The flap PPGs were compared with PPGs and SpO2s acquired from the finger of a small number of patients using a custom made reflectance finger PPG probe, optically and electrically, identical as the flap probe. The finger PPGs were found to be much larger than the flap PPGs which confirms the hypothesis of inadequate perfusion in the flap during and after the operative period. Furthermore the custom made PPG processing system and flap sensor were used successfully on a series of case studies to evaluate the versatility of the system in monitoring PPG signals and estimating blood oxygen saturation in other flaps. These included monitoring two patients undergoing Latissimus Dorsi (pedicle) flap reconstructive surgery and a head and neck free flap surgery where a Vertical Rectus Abdominis Myocutaneous (VRAM) flap was used following total petrosectomy. Also, two patients undergoing reconstructive surgery of the oesophagus using jejunum free flaps were also recruited into the study. For this study a purpose build oesophageal PPG sensor was developed. These case studies demonstrated the ability to use the developed PPG sensors to acquire PPG signals and estimate SpO2s in a variety of flaps. The results have confirmed that the custom made PPG system and sensor has the potential to be used as an alternative technique for monitoring perfusion in various types of flaps at all operative periods.

Item Type: Thesis (Doctoral)
Subjects: R Medicine
Divisions: City University London PhD theses
School of Engineering & Mathematical Sciences > Engineering
URI: http://openaccess.city.ac.uk/id/eprint/3482

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