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.
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.
Evolution of Automated or Computer-Assisted Systems
Traditionally, automated anesthesia delivery systems have been broken down into closed- or open-loop systems; however, that nomenclature does not accurately reflect the reality of the systems currently under development because these systems often share characteristics of both. No matter how these devices are classified in the future, it is important to understand how the current open-loop, or TCI-based, devices function for comparison.
TCI devices were originally presented for clinical use in 1990 and are designed for the delivery of hypnotic or analgesic agents using a pharmacokinetic algorithm. The algorithms are based on commonly used three-compartment models of distribution and elimination. These models are based on population studies correlating drug blood concentrations with target site concentrations. They do not measure any actual effect of the drug and are thus considered open-loop devices. These devices have become relatively popular in Europe, with a prevalence of use in 10% to 25% of all total intravenous anesthesia cases ; however, only one device is currently available in North America.
A review of current TCI systems demonstrated that the main advantage of these systems over manual infusion is a reduction in the number of manual interventions needed to maintain anesthesia at a particular clinical end point. The same review showed a small increase in total propofol consumption but no advantage in terms of induction speed, recovery time, or intraoperative movement. A different study revealed superior hemodynamics and more efficient dosing of remifentanil by TCI than by manual administration.
Although TCI systems were initially built to infuse opioids or propofol, the idea of using TCI methods for volatile anesthetics has more recently emerged with both the Zeus (Dräger, Lübeck, Germany) and Felix (Taema, Antony, France) anesthesia workstations. These systems take advantage of closed-circuit ventilation and use feedback to control direct injection of anesthetic vapor into the breathing circle.
The successful creation of these devices has spurred the development of closed-loop systems, which represent the next step in the evolution of automated anesthesia systems. These newer systems are designed to automatically administer anesthesia by monitoring the effects of the medications in use and using patient response as a feedback mechanism for the system. The currently available closed-loop systems comprise three parts: a computerized operating system programmed with delivery algorithms, a drug delivery system, and an effect monitor. To be effective, these new systems must have a suitable effect that can be precisely measured for the feedback loop of each component of anesthesia being delivered.
A complete anesthesia delivery system has three effects that must be reliably monitored: depth of anesthesia, neuromuscular blockade, and pain control. Neuromuscular blockade is the easiest of the three effects to monitor in clinical practice. Multiple devices on the market take advantage of several mechanisms for measuring neuromuscular blockade. The major problems with many of the current devices are the relative lack of user-friendliness and difficulty in setting up for routine use. By contrast, twitch monitors are simple to use, easy to configure, and provide reliable information when set up appropriately.
Monitoring depth of anesthesia—or level of sedation—has grown in popularity over the last 10 to 15 years. The current devices use proprietary techniques for monitoring spontaneous electroencephalograph activity while displaying a synthesized number that purportedly reflects the patient’s relative depth of sedation (typically on a scale of 1-100). Although controversy exists on the precise utility of these systems and the actual meaning of the numbers displayed, some studies have demonstrated the successful use of these systems as closed-loop systems, not just in efficacy but also in outperforming the manual administration of sedative-hypnotic medications. As additional safeguards, these systems may also measure pulse oximetry and respiratory rate, especially when used for nonsurgical sedation.
Pain control, the third effect monitored, is more difficult to assess because the patient may be heavily sedated, under general anesthesia, or otherwise unable to communicate directly to personnel in the non–operating room location. Several studies have shown that hemodynamic parameters can be useful in the dosing of opioids. Hemmerling et al successfully demonstrated the utility of a scoring system in providing successful feedback control in a closed-loop system, although this was a very small study. Further work is necessary to validate these results.
McSleepy
Researchers at McGill University in Montreal, Canada, developed the world’s first completely automatic anesthesia delivery system, named McSleepy. As a complete anesthesia delivery system, McSleepy monitors the patient’s depth of consciousness, muscle movements, and level of pain and stimulation during surgery. This information is fed back into the system’s brain to adjust administration of the appropriate medication.
McSleepy is relatively simple to use. After an intravenous cannula is placed, sensors are applied to measure the patient’s muscle movement. Height, weight, age, and gender information, as well as the type of surgery being performed, are entered into the main console. McSleepy then allows the anesthesiologist to specify preferences regarding the drug dosages to be used before medication administration and monitoring of the patient. The system monitors data and adjusts dosing every minute while displaying all relevant data on a screen.
Sadasys System
Although McSleepy was the first closed-loop system introduced, the first computer-assisted system to aggressively pursue regulatory approval was designed for gastroenterologists. The SEDASYS System is a sedation delivery system designed to enable nonanesthesiologists to administer propofol in the endoscopy laboratory. Reasons for the focus on endoscopy for the SEDASYS System include the increasing number of procedures in the endoscopy suite, especially to help accommodate the demand for early colon cancer screening, and noted advantages to sedation with propofol over benzodiazepine and opioid combinations in terms of turnover time and patient satisfaction.
Originally endorsed by the FDA’s Anesthesiology and Respiratory Therapy Devices Advisory Committee in 2009, the SEDASYS System was rejected by the FDA in 2010, an unusual occurrence because the FDA typically follows the advice of its advisory committees. Ethicon Endo-Surgery (a division of Johnson & Johnson) appealed the decision, and FDA Commissioner Margaret Hamburg, MD, granted a hearing scheduled for December 2011. However, in November 2011, Ethicon Endo-Surgery announced that it had withdrawn its request for appeal because it had reached a settlement with the FDA’s Center for Devices and Radiologic Health “to settle the company’s appeal” of its previous denial.
The FDA accordingly agreed to reopen the premarket approval application and “review it expeditiously.” The SEDASYS System was approved by the FDA in May of 2013 for the delivery of propofol for minimal-to-moderate sedation during colonoscopy and EGD procedures. The device is also currently approved for sale in Canada for sedation of patients undergoing colonoscopy and in Australia for patients undergoing colonoscopy and EGD. It was granted the mark of approval in the European Union for use during routine colonoscopy and EGD in May of 2010. In the United States, the device carries the following caveats: The device is restricted for use by health care professionals that have the types of training defined in the labeling, and to settings where an anesthesia professional is immediately available for assistance or consultation. Also, the SEDASYS System should not be used in:
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Patients with known hypersensitivity to 1% propofol injectable emulsion or its components
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Patients with allergies to eggs, egg products, soybeans, or soy products
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Patients with a known hypersensitivity to fentanyl
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Pregnant or lactating women
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Delivery of any drug other than 1% propofol injectable emulsion
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Patients with a full stomach
The SEDASYS System initiates sedation with a loading dose based on the patient’s weight and the maintenance infusion rate selected by the physician, delivered over 3 minutes. The maximum initial maintenance rate the physician can select is 75 mcg/kg/min, which yields a 0.5 mg/kg loading dose. After the loading dose is delivered, the SEDASYS System delivers the infusion rate selected by the physician. Detection of oversedation is determined by several mechanisms, including falling oxygen saturation, depressed respiratory rate, and failure of detection of the ETCO 2 curve. If any of these signals occur, the propofol infusion is automatically stopped. Further, the machine adds an additional layer of monitoring by talking to the patient at varied intervals and asking the patient to squeeze a handset. If the patient fails to comply, the propofol infusion is automatically reduced.
Unlike McSleepy, the SEDASYS System is designed to deliver only propofol. The computer-assisted delivery mechanism is integrated with the patient monitoring as part of a feedback loop. The SEDASYS System is equipped with standard ASA monitors, including ETCO 2 . The device is physically made of two primary subunits, a bedside monitoring unit and a procedure room unit ( Figure 23-2 ). The mobile bedside monitoring unit is attached to the patient and moves with the patient throughout the perioperative environment. It has a port for attachment of an oronasal cannula for oxygen delivery, and it monitors and displays oxygen saturation, noninvasive blood pressure, and electrocardiogram. This unit also houses the automated responsiveness monitor, designed to assess patient responsiveness.
Related posts:
Critical Monitoring Issues for Non–Operating Room Anesthesia
Intravenous Anesthesia and Sedation Outside the Operating Room
High-Frequency Ventilation for Respiratory Immobilization
Anesthesia for Colonoscopy
Novel Staffing Coverage for Anesthesia Outside the Operating Room
Anesthesia Concerns in the Magnetic Resonance Imaging Environment
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