Development of Future Systems

Anesthetizing patients is a complex business. The number of tasks to perform on a daily basis has increased dramatically, and the number of locations in which they are performed also has risen. Effectively monitoring a patient, charting the patient’s progress, anticipating changes in the surgical field, and adapting the anesthesia care requires a substantial amount of multitasking. Further, delivery of anesthesia care outside the operating room is complicated by variability of locations, workspaces, monitoring equipment, and other medical devices, in addition to the myriad cables and connectors required to keep things running. This often results in suboptimal physical arrangements in the non–operating room anesthesia (NORA) suite.

The introduction of the electronic medical record (EMR) and anesthesia record-keeping systems would, on the surface, seem to help alleviate some of the complexity and multitasking involved in the care of the patient during a procedure. However, that industry remains immature. A lack of standards for device integration further complicates the adoption of these systems with truly automatic functioning. Additionally, because a true wireless monitoring system is not available to the anesthesiologist, this integration comes at the cost of additional cables in the work space, making things even more difficult for a practitioner to function effectively.

Coupled with the difficulties described is the increasing need for anesthesiologists in non–operating room settings. The use of diagnostic endoscopy for the evaluation of upper and lower gastrointestinal disorders has dramatically increased in the last decade. This rise in performed procedures comes with a concomitant increase in the use of trained anesthesia providers to administer sedation for these patients. Further, the proportion of low-risk patients (American Society of Anesthesiologists [ASA] class 1 or 2) receiving sedation services from an anesthesiologist or certified registered nurse anesthetist has grown out of proportion to the overall number of procedures performed in the gastrointestinal suite. In this same period, the cost of anesthesia services has increased. One study estimates that the cost of anesthesia services for these procedures in the United States amounted to $1.1 billion in 2009. Another study shows that participation by anesthesia personnel in these procedures is expected to increase to greater than 50% by 2015.

The escalating costs and use of an already limited resource naturally leads to the discussion of exactly which services are being offered and whether a safer, more economical way exists to provide these services. This discussion is complicated by the fact that it is increasingly commonplace for North American patients to request general anesthesia or at least deeper levels of sedation than are typically provided for procedures of this type, although at the same time proceduralists would prefer to use medications such as propofol but are afraid to do so because of the risks involved. A review of the literature through 2009 shows at least 460,000 cases of nonanesthesiologist-administered propofol sedation for endoscopy. The majority of those cases involved administration of propofol sedation by nurses. Three deaths were recorded in this group, occurring during or after esophagogastroduodenoscopy (EGD).

The provision of anesthesia consists of several components: unconsciousness or anesthetic depth, analgesia, and neuromuscular blockade. Each of these associated components requires careful monitoring. New monitors are available to assist in the anesthetic management of the patient. These recently introduced monitors provide improvements in patient safety by using new physiological monitoring systems purported to aid in assessment of anesthesia depth. Automatic delivery systems, most commonly in the form of target-controlled infusion (TCI, or open-loop systems) pumps also have made an appearance in some markets.

A TCI is an infusion controlled to enable a user-defined drug concentration in a tissue of interest. Kruger-Thiemer first suggested this concept in 1968, but it was not until the 1980s that pharmacokinetic models and equations were incorporated into computer-controlled devices. The first TCI pump introduced to clinical practice was the Diprifusor in 1996 ( Figure 23-1 ). Pumps and pharmacokinetic models have continued to evolve since that time.

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Diprifusor pump.

(Courtesy of Carefusion, San Diego, CA.)

These advances, when taken together, have opened the door for the creation of fully closed-loop systems. These closed-loop systems are designed to not just deliver a drug in a controlled fashion but to also monitor the patient for a parameter appropriate to the particular medication in use—for example, monitoring respiratory rate and end-tidal carbon dioxide (ETCO ₂ ) as a feedback mechanism while infusing remifentanil. The introduction of decision support systems has paralleled these developments (more commonly in the military and critical care setting) to further help personnel make appropriate decisions.

The medical device industry has worked to develop automated systems for delivery of anesthesia care as it applies to the healthiest patients having the least complicated procedures. The focus of this chapter is the current state of automated or computer-assisted systems and those known to be in development. Although these devices are not yet routinely available in the United States, the SEDASYS System (Ethicon Endo-Surgery, Cincinnati, Ohio) was recently approved by the U.S. Food and Drug Administration (FDA) (on May 3, 2013). Canada and several European countries allow use of the SEDASYS System.