Drexel researchers have developed a non-invasive device for quantitative, real-time monitoring of the depth of anesthesia both during general anesthesia in surgery and sedation in endoscopy and colonoscopy procedures. The device uses functional near-infrared (fNIR) spectroscopy to measure physiological parameters that correlate with the depth of anesthesia. Drexel’s depth of anesthesia monitor was successfully tested in a 50-patient proof of concept study, demonstrating statistically significant separation between different degrees of anesthesia.

Awareness under general anesthesia occurs when surgical patients become conscious, or awake, and can recall events or conversations that happen in the operating room, or feel excruciating pain. While the incidence is relatively low at 0.13%, with 20 million annual surgeries it results in 26,000 cases of awareness under general anesthesia in the United States alone. Such incidents can be a distressing or traumatic experience for the patient, leaving a lifetime of residual emotional and psychological problems ranging from sleep disorders, daytime anxiety to post-traumatic stress disorder, and often leading to litigation against the hospitals and physicians who performed the procedure. Due to the severe effect on the patients, awareness under anesthesia received designation of the sentinel event from the Joint Commission in 2004. As it is impossible to predict which patient might wake up during surgery, anesthesia awareness monitors should be used in every procedure, thus representing a significant market opportunity.

In diagnostic and screening procedures such as endoscopy and colonoscopy, amounting to more than 15 million annual procedures in the US alone, patient awakening is of lesser concern. Rather, it is more important to not administer excessive sedation to avoid adverse events, especially in overweight individuals or those with certain disorders. Avoiding adverse effects and excessive sedation will result in significant savings far outweighing the modest cost of anesthesia monitoring, which is estimated at about $20 per procedure. Aging of the population will increase the number of such procedures, presenting a rapidly growing additional market for the anesthesia monitoring.

There has been significant interest in developing depth of anesthesia monitors that can continuously and reliably monitor the anesthesia state during a surgical procedure. To date, such devices have largely been based on the measurement of electrophysiological signals such as electrocardiographic (ECG) signals, electroencephalographic (EEG) signals, auditory and somatosensory evoked potentials, and craniofacial electromyographic (EMG) signals. All such devices rely on measuring electric currents, which are inadequate for measuring effects of certain common anesthetics such as opioids. As a result, such devices found limited applications. Contrary to these earlier approaches, the fNIR technology measures hemodynamic parameters of the brain, which are directly affected by most of the opioids through neuro-vascular coupling, thus making it particularly suitable for quantitative monitoring of depth of anesthesia. Since Drexel’s anesthesia monitor directly measures brain’s hemodynamic response to the anesthetic, its readings are easily understood by anesthesiologists who prefer measurements reflecting human physiology rather than abstract numbers produced by EEG techniques. In spite of the deficiencies of the existing devices that are not trusted by anesthesiologist, resulting in small market penetration, they generate >$200 million in sales annually. With its physiologically-based performance, the market size for anesthesia monitoring using the fNIR device can be expanded several-fold.