Near Infrared Spectroscopy for the detection of oxygenation and perfusion deficits in paediatric anaesthesia and surgery

Abstract

Although near infrared spectroscopy (NIRS) has been available in the clinical environment for nearly twenty years, many questions still exist regarding it's utility and validity. This thesis explores tissue oxygenation monitoring using NIRS in three specific clinical scenarios, each exploring aspects of these issues. The first study focussed on the ability of muscle StO2 (tissue haemoglobin oxygen saturation) monitoring to detect clinically significant vascular compromise in paediatric patients with supracondylar fractures. Significantly lower StO2 values were observed in injured limbs with vascular compromise, which normalized following fracture reduction. The results suggest that muscle StO2 monitoring may be a useful addition to standard clinical means of assessing perfusion following paediatric supracondylar fractures. The second study used a juvenile porcine model of acute hepatic ischaemia to determine the potential utility of transcutaneous hepatic StO2 measurement, for use in the post-transplantation environment. Although a transcutaneous optical signal of ischaemia was detectable, its magnitude was too small for reliable clinical use, and was heavily influenced by animal size. These findings reinforced the concern in the literature regarding the depth of penetration of standard clinical StO2 monitors, and recommended against the use of somatic organ StO2 monitoring in patients of greater than 10kg. The third study was a multinational observational study of cerebral StO2 in infants and neonates undergoing general anaesthesia which found that severe cerebral desaturation during anaesthesia was uncommon. This is the largest observational study to date, and concluded that unrecognized severe desaturation lasting three minutes or longer in infants is too rare an event to explain subsequent development of neurocognitive abnormalities. These studies explore the potential utility of tissue StO2 monitoring in three distinct clinical scenarios. They each address a separate aspect of monitoring utility: agreement with clinical judgement, validity of measurements in new applications, and determination of normal values. Together, they highlight some of the challenges in the clinical use of medical diagnostic and monitoring technology. Tissue oxygenation monitoring utilizing near infrared spectroscopy has substantial potential clinical utility, but requires users to be aware of its basic principles of operation, and its technical limitations.