The practice of anesthesiology has always been associated with technological advancements. Innovations in the 19th century, such as the development of the sphygmomanometer and the esophageal stethoscope, gave the earliest anesthesiologists new abilities to accurately assess blood pressure, respiration, and cardiac rhythm. It is unlikely that these pioneers would recognize the modern OR, with its dizzying array of machines and monitors that give 21st century anesthesiologists capabilities our 19th century counterparts could scarcely imagine. In this article, we will provide a brief overview and consideration of several innovative intraoperative monitoring technologies that may further expand the capabilities of the next generation of anesthesiologists.
Integration of real-time monitoring of brain function during anesthesia is an area of increasing focus. While full montage EEG is considered the gold standard for brain activity monitoring, it requires interpretation of raw data and is too time-intensive for routine OR use. Alternatively, EEG patterns can be summarized using mathematical parameters and presented in the form of processed EEG (pEEG) (J Cardiothorac Vasc Anesth 2019;33 Suppl 1:S3-10). Examples of commercially available pEEG monitors include the Bispectral (BIS™ [Medtronic]), Entropy™ (GE Healthcare), and NeuroSENSE™ (NeuroWave). While there is evidence that the use of pEEG monitors reduces anesthetic consumption, additional studies are needed to evaluate their impact on postoperative outcomes (J Cardiothorac Vasc Anesth 2019;33 Suppl 1:S3-10).
Neuromuscular blockade (NMB) is an essential component of the practice of anesthesiology. Accurate measurement of the depth of NMB and its adequate reversal are integral to patient safety and good clinical outcomes. That inadequate recovery from NMB may occur in more than half of patients and be associated with an increased incidence of postoperative pulmonary complications further indicates the need for innovation to achieve a more accurate monitor (Br J Anaesth 2020;125:466-82). The depth of NMB can be monitored both qualitatively (e.g., subjective evaluation of peripheral nerve stimulation) and quantitatively. Quantitative means are preferred (Br J Anaesth 2020;125:466-82) and include techniques such as mechanomyography, acceleromyography, and electromyography (Anaesthesia 2020;75:187-95; Br J Anaesth 2020;124:712-7). Mechanomyography is often considered the laboratory gold standard for quantitative monitoring, but it is not commercially available and thus unsuitable for routine use (Anaesthesia 2020;75:187-95). Though acceleromyography is the most widely used objective monitoring technique in practice, recent studies suggest that electromyography (e.g., TwitchView [Blink Device Company]) may more closely resemble mechanomyography (Anaesthesia 2020;75:187-95; Br J Anaesth 2020;124:712-7). Thus, the next generation of NMB monitoring will likely come from innovation in electromyography-based devices and enhance providers' ability to evaluate the depth of paralysis.
Intraoperative monitors that measure nociception/antinociception have the potential to accurately guide analgesic administration and improve patient care. Using different measurements of sympathetic and parasympathetic nervous system activity, several commercially available devices can evaluate the interplay between nociception and antinociception (Anesth Analg 2020;130:1261-3; Br J Anaesth 2019;123:e312-21). Depending on the tool, patient data from electroencephalography, electromyography, plethysmography, heart rate variability, skin conductance, and pupillary dilatation are used as inputs (Curr Opin Anaesthesiol 2019;32:727-34). Available monitors include the Surgical Plethysmographic Index (GE Healthcare), Nociception Level index (Medasense Biometrics Ltd.), Analgesia nociception index (PhysioDoloris, MetroDoloris), pupillometry, and pupillary pain index (AlgiScan, IDMed) (Anesth Analg 2020;130:1261-3; Curr Opin Anaesthesiol 2019;32:727-34). Despite their physiologic basis, these monitors have limitations, and their accuracy is impacted by several factors (Br J Anaesth 2019;123:e312-21). Studies evaluating the use of these tools and their impact on clinically significant outcomes have produced conflicting results (J Clin Monit Comput 2020;34:629-41). While the idea of an accurate, automated intraoperative “pain monitor” is exciting, more studies are needed to establish if any of the currently available devices deliver on this promise. Furthermore, it is unknown if the use of this technology will translate to adequate analgesia with reduced opioid administration and, ultimately, improved perioperative outcomes (Anesthesiology 2021;134:645-59).
Intermittent pulmonary artery thermodilution is considered the clinical standard for cardiac output measurement. Because this technique requires placement of a pulmonary artery catheter and is associated with several complications, minimally invasive and non-invasive alternatives for the measurement of cardiac output have increasingly gained popularity. Such methods include arterial catheter-based pulse wave analysis (FloTrac [Edwards Lifesciences] and LiDCOrapid [LiDCO]), esophageal Doppler (CardioQ-ODM [Deltex Medical]), finger cuff pulse wave analysis (ClearSight [Edwards Lifesciences]), and thoracic impedance/electrical cardiometry (ICON [Osypka Cardiotronic]) (Anesthesiology 2020;133:921-8). Like other clinical tools, these devices are associated with limitations, and they may rely on several mathematical assumptions (J Cardiothorac Vasc Anesth 2019;33:1742-52). Thus, in certain clinical settings, noninvasive cardiac output measurements have not been found to be interchangeable with bolus thermodilution in terms of both absolute and changes in values (Anaesth Crit Care Pain Med 2020;39:75-85; Br J Anaesth 2017;118:298-310). Additional studies are needed to determine the clinical utility of this technology, and providers should exercise caution when interpreting their findings.
Intraoperative respiratory monitoring involves assessment of both a mechanical process (ventilation) and a physiologic one (aerobic respiration). Modern ventilators allow anesthesiologists to tightly control some respiration parameters (e.g., rate, tidal volume, pressure, and inspired oxygen concentration) while monitoring mechanical indicators of ventilation (e.g., resistance and compliance) to more clearly elucidate patients' work of breathing. Additionally, pulse oximetry and end-tidal carbon dioxide monitoring allow for assessment of the physiologic parameters of gas exchange. One potential avenue for innovation includes the measurement of esophageal pressure during mechanical ventilation. While mostly utilized in the ICU to personalize lung protective strategies and reduce work of breathing (Intensive Care Med 2016;42:1360-73), this technology could be used for similar purposes in the OR. Similarly, continued advances in flow-volume and pressure-volume curve measurements may allow for improved respiratory compliance monitoring and more-tailored intraoperative ventilation strategies. The Oxygen Reserve Index (ORI) is a recent innovation that provides a non-invasive, real-time assessment of oxygenation status using multiple wavelength pulse oximetry of both arterial and venous blood. It has shown promise in early prediction of desaturation events and potentially allowing for extra seconds for intervention (J Clin Monit Comput 2018;32:379-89). Other potential uses of multiple wavelength pulse oximetry include non-invasive assessment of hemoglobin (Anesth Analg 2016;122:565-72) and prediction of fluid responsiveness (J Clin Monit Comput 2016;30:265-74).
Another exciting research avenue with myriad implications for anesthesiologists is artificial intelligence (AI). AI involves analysis of an existing data set to create algorithms to deduce wider knowledge. The results of our web searches, internet-based advertisements, and media recommended to us by video streaming services are all powered by AI algorithms. Penetrance into the health care marketplace has been slower, but early examples within anesthesiology include closed-loop and remote control-guided anesthesia delivery systems (Int Anesthesiol Clin 2020;58:7-16). One of the more tantalizing prospects involves the prediction of intraoperative morbidity and mortality prior to clinical presentation. A recent study has shown promising results in predicting intraoperative hypotensive or hypoxic events up to 15 minutes in advance (Anesthesiology 2018;129:663-74). Some researchers have developed algorithms that predict difficult intubation based on evaluation of a picture of a patient's face (IEEE Trans Biomed Eng 2016;63:328-39), while others identify vocal cords and tracheal rings on bronchoscopy video images to assist with fiberoptic intubation (J Med Syst 2020;44:44). While none of these innovations are ready for integration into clinical practice, they represents a unique opportunity to give future anesthesiologists the cognitive “boost” needed to improve patient care by proactively intervening based on prediction rather than reactive intervention to clinical deterioration.
The miniaturization of ultrasound technology has allowed its use in more and varied clinical environments. It has revolutionized the practice of regional anesthesia by allowing for precise needle placement, and the bedside, non-invasive diagnostic capabilities of ultrasound that are routinely used in the ICU or emergency department are now becoming widely utilized for intraoperative care. For example, a focused cardiac ultrasound exam is briefer than a formal transthoracic echocardiogram but can be an invaluable tool for the anesthesiologist to quickly assess cardiac anatomy and physiology (Anesth Analg 2017;124:761-5). Kobal et al. demonstrated that medical students, armed with a handheld ultrasound and a little education, were as accurate as the physical examination of board-certified cardiologists in making cardiovascular diagnoses (Am J Cardiol 2005;96:1002-6). As miniaturization continues and technology costs fall, we could envision a future role where ultrasound is as ubiquitous in the OR as the stethoscope. With integration into electronic medical records, the diagnostic capabilities of point-of-care ultrasound, or POCUS, may allow future anesthesiologists the ability for easier documentation of a wide array of quantitative diagnostic procedures to better care for patients.
Other novel techniques for assessing end-organ and physiologic function continue to emerge. For example, intraoperative cerebral monitoring (e.g., jugular bulb saturation, near-infrared spectroscopy, transcranial Doppler) can provide anesthesiologists with information on cerebral hemodynamics and oxygenation (J Neurosurg Anesthesiol 2019;31:378-84). Additionally, real-time hemostasis monitoring using viscoelastic testing (e.g., ROTEM® delta Instrumentation Laboratory) or platelet function evaluation (e.g., platelet function analyzer 100, Siemens Medical Solutions, Inc.) may allow for both more rapid and directed therapy (Int J Obstet Anesth 2006;15:7-12).
Innovation continues to transform the practice of anesthesiology. Time will tell which, if any, of these innovations will become the standard tools of tomorrow's anesthesiologist. While there is much promise for these and other technologies, many questions remain. Will we really be able to measure nociception as accurately as we measure blood pressure? Will hand-held ultrasound machines replace the stethoscope in patient assessment? Will AI algorithms allow us to predict clinical decompensation? The answers to these and other questions remain unclear. What is clear, though, is that anesthesiologists will continue to leverage today's innovations to ensure we can continue to provide superior care for our future patients.
Dr. Joshi is a consultant for Baxter Pharmaceuticals and Pacira Pharmaceuticals.