|Microsurgery: Transplantation and Replantation by Harry J. Buncke, MD, et al.|
| Like pulse oximetry, reflection photometry detects the reflected spectra of oxygenated and deoxygenated hemoglobin in the microcirculation of the skin.27 Reflection photometry does not, however, record pulsatile changes. The skin is illuminated by the photometer's fiberoptic light and the reflected light is analysed by a photodiode. Oxygenated hemoglobin has two peaks in its extinction spectra. With deoxygenation, the peaks decrease in amplitude and begin to merge. A microprocessor calculates oxygen saturation based on the difference in the distance between the peaks.
Cutaneous temperature monitoring measures skin temperature as an indicator of perfusion of the monitored tissue and has been used in many experimental and clinical settings.5,24,28-30 With adequate perfusion, the monitored tissue surface temperature should be constant and within a few degrees of a well perfused control area. Changes in core temperature and in ambient temperature and heat retention by dressings may cause spurious readings.
Dermal injection of xenon radioisotope into replanted or transplanted tissue is followed by consecutive radioactivity counts.31-33 Computer calculation of the rate of decrease in measured radioactivity provides a determination of blood flow. The test requires the use of radioactive material and sophisticated counting and computing equipment and cannot be performed at the patient's bedside.
These monitoring strategies measure aspects of tissue metabolism that are associated with viable tissue or that indicate tissue ischemia.
Ischemic tissue becomes progressively acidotic. Implanted pH electrodes provide a means of detecting tissue acidosis that may indicate ichemia.34 Technical complexities have limited this technique to experimental uses.
Radioisotope scanning assesses the viability of vascularized bone flaps, which, if viable, will metabolically incorporate radioactive technetium. These studies, however, are not practical for frequent or critical observations and may be difficult to interpret if significant inflammatory reaction surrounds the bone flap. Their main use has been to document the vascularity of bone flaps following microsurgical transfer.35
TRANSCUTANEOUS OXYGEN MONITORING
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