Free flap pulse oximetry utilizing reflectance photoplethysmography

Optical Fibre Sensor for Simultaneous Measurement of Capillary Refill Time and Contact Pressure

The widely applied capillary refill time (CRT) measurement is currently performed by manually applying pressure and using a stopwatch to record the time taken for the skin to recover its normal colour after a blanching pressure is applied. This method is highly subjective and observer-dependent. This paper presents a new, integrated optical sensor probe, combining monitoring of the capillary refilling process with the blanching pressure applied. The sensor consists of an optical fibre-based reflectance photoplethysmography (PPG) sensor to measure the reflected light signal, as well as a fibre Bragg grating (FBG) to measure the applied blanching pressure and to indicate the time when pressure is released. This sensor was applied to calculate the CRT (1.38 ± 0.66 s) of 10 healthy adult volunteers with (55.2 ± 21.8 kPa) blanching pressures. The form of the capillary refilling data was investigated by fitting using an exponential regression model (R² > 0.96). The integrated probe has the potential to improve the reliability of CRT measurements by standardising the optimum duration and magnitude of the pressure.

Postoperative monitoring of the free jejunal flap: use of colour duplex and systematic review of available techniques

Introduction The free jejunal flap represents the gold standard for circumferential defects in upper digestive tract reconstruction. It is a technically demanding procedure with significant failure rates. Unrecognised failure leads to flap necrosis and potentially fatal sequelae, including sepsis and carotid artery bleed. Despite these catastrophic consequences, however, there remains no consensus on an optimum method for postoperative flap monitoring. Our unit has pioneered the use of external colour duplex ultrasound to monitor flap vascularity. We describe this technique and systematically review other published monitoring systems. Materials and methods A patient underwent oesophageal reconstruction using a jejunal free flap. Monitoring commenced immediately via external application of a colour duplex probe over the flap's vascular pedicle to facilitate flow volume assessment. Further bi-daily assessments were successfully used to monitor the postoperative viability of the flap. The systematic review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Results Six alternative monitoring techniques were identified: exteriorised jejunal segment, implantable Doppler probe, watch window, microdialysis, microendoscopy and reflectance photoplethysmography. Discussion Exteriorised jejunal segment and implantable Doppler probe are most commonly described, yet both are associated with high false positive rates, which is particularly significant in a patient demographic facing increased general anaesthetic risk. Most other techniques remain experimental. External colour Doppler ultrasound provides the surgeon with immediate reassurance following the reconstruction, requires minimal training to use, and eliminates the need for revisional procedures. Conclusion Our initial experience suggests that external colour Doppler ultrasound has exciting potential as an efficient and noninvasive technique for monitoring the free jejunal flap.