Near-Infrared Spectroscopy: Potential Clinical Benefits in Surgery

Abstract

We read with interest the article by Stephen M. Cohn and congratulate the author on a comprehensive overview of the potential clinical roles of near-infrared spectroscopy (NIRS) within surgical practice. The article provides an extremely useful insight into the principles of NIRS technology, and its potential applications for predicting outcomes from hemorrhagic shock, detecting compartment syndrome, assessing peripheral vascular disease (on which topic a systematic review has recently been published), monitoring free flaps, and assisting in diagnosis of necrotizing fasciitis. We share the authors enthusiasm about the future role that NIRS can play in surgery. From our limited experience, we would like to draw attention to two additional surgical applications for NIRS technology, ie, advancing surgical education and as a diagnostic imaging modality. As Cohn describes, NIRS can be used to monitor oxygenation change in the cerebral cortex and has been evaluated in neonates, comatose patients, and those suffering severe brain injury. NIRS has also been used to evaluate variations in cerebral oxygenation during carotid endarterectomy and cardiac surgery. And, providing valuable information on the status of brain oxygenation in response to surgical pathology, NIRS can monitor the hemodynamic response of brain activation in healthy individuals, based on a principle known as “neurovascular coupling” (neuronal activation evokes a temporally offset hemodynamic response). This response comprises a task-induced increase in oxygenated hemoglobin coupled with a decrease in deoxygenated hemoglobin, both of which are detected using NIRS. Our primary research interest in NIRS is aimed at shedding light on cortical excitation patterns in surgical operators themselves, thereby advancing our understanding of technical-skills acquisition at the cortical level. In an analysis of 62 subjects, we observed different prefrontal cortical responses, depending on years of experience and technical skill of the operator. Ongoing work is aimed at understanding how cortical activation patterns change (“neuroplasticity”) in response to learning through deliberate practice. This analysis can assist technical-skills training by helping to track a resident’s progress through the different stages of motor-skills learning. Additionally, brain imaging, together with dexterity analysis, assessment of visual search strategies, and hand-to-eye coordination can provide a more comprehensive understanding of technical surgical skill. The potential of NIRS for monitoring tissue flap oxygenation status, such as in patients undergoing pedicled trans rectus abdominis myocutaneous flap breast reconstruction was briefly discussed by Cohn. The potential of NIRS to image the diseased tumor-bearing breast was not mentioned. NIRS breast-imaging techniques are commonly known as either optical mammography or optical tomography. These techniques use harmless NIR light to provide functional information about breast lesions, such as total hemoglobin content and oxygen saturation, and represent a novel diagnostic arm that could augment traditional imaging modalities. In a recent systematic review of the literature, we found that approximately 85% of breast lesions are detectable using optical mammography. In addition, breast lesions appear to contain at least twice the hemoglobin concentration of background healthy breast tissue. Recent evidence suggests that it might be possible to distinguish cancer from the non cancer-bearing breast, based on hemoglobin concentration and oxygen saturation, although we were unable to find strong evidence to support discrimination between benign and malignant lesions with current NIRS technology. It is likely that combining NIRS with another modality, such as magnetic resonance imaging or ultrasonography, can help to differentiate lesions based on their malignant potential. As Cohn’s comprehensive review demonstrates, there is an increasing list of potential applications for NIRS technology to augment surgical practice. As this technology continues to develop, it is likely that additional promising applications will be found. For promise to be turned into reality, future work must identify which of these applications offers the greatest benefit to patients and which are economically viable options to pursue.