The use of IV sedation by nonanesthesia providers has increased tremendously, largely due to the growth in out-of-operating room invasive diagnostic and therapeutic procedures. Numerous articles deal with the use of propofol by clinicians lacking anesthesia training, a phenomenon that began outside the United States and surprised many in the U.S. anesthesia community. In 2002, 2 years before the American Society of Anesthesiologists and American Association of Nurse Anesthetists published their joint statement regarding propofol administration, an Australian publication described propofol-based sedation in 28,472 colonoscopies and gastroscopies done between 1996 and 2000.1 Over 80% of these cases were performed by “general practitioner sedationists,” and their rate of respiratory and cardiovascular adverse events was not significantly worse than those reported by trained anesthesiologists. In the same year as that Australian publication, the Centers for Disease Control estimated that 14.2 million colonoscopies were done each year in the United States,2 and survey data suggested that 98% of these were performed with sedation.3 Since that time, an increasing amount of sedation has been done by gastroenterologists using propofol, despite cautionary statements by anesthesiologists. In 2009, the American Society of Anesthesiologists amended its 2004 statement, saying that “...patients receiving propofol should receive care consistent with that required for deep sedation,” and the American Society of Anesthesiologists reiterated its position that propofol used this way “...should be administered only by persons trained in the administration of general anesthesia...”a. That same year, Rex et al.4 published a collection of safety data describing endoscopist-directed administration of propofol for 646,080 cases (223,656 published and 422,424 unpublished). Many of the articles describe careful protocols for nurse and physician training and patient monitoring, and some of these protocols were developed with assistance from anesthesiologists. While it is true that many of these data are anecdotal, there are only 4 reported deaths, and the safety record overall is a very good one.
We have now reached a point where most clinical articles on sedation are appearing in nonanesthesia journals. It is only natural that anesthesiologists take a special interest in this topic and feel that we are still in the best position to make recommendations for safe practices. Many of us remember the deaths that followed the introduction of midazolam into practice, many occurring in radiology and gastrointestinal endoscopy suites.5 But that was in the 1980s, and sedation practice has been completely transformed in the interim. In order for our specialty to be a part of this discussion and to publish recommendations that are credible and relevant, it is imperative that we study and discuss sedation as it is actually being practiced. In this issue of Anesthesia & Analgesia, there are 2 moderately sized evaluations of monitoring during nurse-administered sedation. In both studies, the results appear valid, but the safety outcomes had less to do with monitors than the specific ways that sedation was managed. In this respect, the 2 protocols could not have been more different.
Yang et al.6 investigated the influence of Bispectral Index (BIS) monitoring on the incidence of cardiovascular and respiratory adverse events during moderate sedation (Ramsey Sedation Scale target score of 2–3). Midazolam–opioid sedation was used, since propofol sedation was not allowed to be administered by nurses at Duke during the time of the study. The cases included gastrointestinal endoscopies, bronchoscopies, examinations under sedation, and central line placements, and no supplemental oxygen was administered. The authors stated they undertook this study due to the “...paucity of prospective data on sedation practice...” and hoped to show that BIS decreases the incidence of adverse events. The results were not surprising. These were short cases, with well-trained nurses targeting moderate sedation, and there were insufficient adverse events to demonstrate any important advantages for this monitor. The only signal from the opioid–midazolam combination was hypoxemia in 45 of the 999 patients; however, only 3 of these patients became apneic. These data support the concept that avoiding supplemental oxygen permits the oximeter (rather than BIS) to act as an early warning of excess sedation and ventilatory depression. Is this protocol the current reality of sedation practice? If so, it would be difficult to show a reduction in adverse events in any study of reasonable size.
The trial by van Loon et al.7 was quite different. The investigators hypothesized that monitoring with capnography would decrease the incidence of hypoxemia. They included 415 women having gynecologic procedures, but these patients were given deep propofol sedation (a Ramsey Sedation Scale target of 5—sluggish response to a loud verbal stimulus). Like the Yang et al.6 study, no supplemental oxygen was used “according to the institutional sedation protocol.” Propofol was administered by intermittent bolus, with an initial dose of 100 mg, and subsequent doses of 20 to 30 mg (doses that suggest a brief period of general anesthesia probably occurred in many patients). Both the gynecologists and the sedation nurses underwent sedation training as well as prospective testing of their knowledge. The nurses were allowed to use chin-lift or jaw thrust but not positive pressure ventilation or intubation. Subjects were randomized to be monitored by visual observation of breathing versus sensitive microstream capnography. The incidence of hypoxemia (SpO2 <91%) was quite high and not significantly different between the groups (25.7% vs 24.9%, capnography vs standard). More troubling findings were the lack of significant difference in the incidence of profound hypoxemia (SpO2 <81%; 3.4% vs 2.9%) and in the number of patients with hypoxemia lasting 60 seconds or more (3.9% vs 1.4%). The severity and frequency of hypoxemia were due not only to the dose of propofol and the avoidance of supplemental oxygen but probably also the use of bolus administration. The authors speculate about the lack of “effectiveness” for capnography, but a much more important conclusion is the risk of using deep propofol sedation, unless one is prepared to treat hypoxemia more aggressively.
The safety of sedation is a function of many variables, and most of these are second nature to anesthesiologists. These include not only the training of the providers but also the availability of backup, the type of patient and surgical procedure, the level of sedation targeted, the drugs and the way they are administered, and also the type of monitoring. I do not disagree with the conclusions about monitoring from these 2 studies, but in both cases, it was the sedation protocol rather than the monitor that had the real effect on the potential for harm. The Yang et al.6 study avoided harm almost entirely, while the van Loon et al.7 study used a technique that produced much more significant effects on respiration.
In the hands of nonanesthesiologists, deep sedation and moderate sedation present entirely different levels of risk, yet many of us have seen deep propofol sedation (often general anesthesia) used without hesitation during colonoscopies. Do we know the actual numbers? Should we look the other way? If our decision is “no,” then perhaps the real value for BIS and other processed electroencephalography monitors may be to document the fact that deep sedation or anesthesia was not used. If we do feel that deep propofol sedation is permissible, should we accept a hospital “standard” that does not allow the use of supplemental oxygen, a practice that can produce so much hypoxemia? If the answer is “no,” then perhaps capnometry adds value by allowing the administration of oxygen while still monitoring for inadequate ventilation. If nonanesthesiologists continue to use deep sedation with propofol, these are questions about monitoring that will have real relevance for patient safety. I hope it will be anesthesiologists who ask these questions and publish the answers.
Name: Carl Rosow, MD, PhD.
Contribution: This author wrote the manuscript.
Attestation: Carl Rosow approved the final manuscript.
This manuscript was handled by: Peter S. A. Glass, MB, ChB.
a Statement on Safe Use of Propofol. Approved by the American Society of Anesthesiologists House of Delegates on October 27, 2004, and amended on October 21, 2009. www.asahq.org. Accessed November 15, 2013. Cited Here...
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