Volume 10, No. 2 • Summer 1995

IARS Annual Meeting Includes Safety Topics

Douglas Guyton, M.D.

Patient safety related presentations were featured at the International Anesthesia Research Society annual meeting in Honolulu, Hawaii, March 10-14. Highlights are summarized:

In an award-winning scientific exhibit, Drs. Herbert Ferrari and Charles Bowen (St. Louis University) chronicled the evolution and predicted the future direction of the anesthetic record. Dr. Bowen used the oft-quoted analogy between anesthesia providers and fighter pilots to illustrate his predictions: ‘In WWII fighter pilots had only a couple of analog gauges in front of them. As aviation progressed, more and more information became pertinent to the operation of the aircraft, and many pilots flew into the ground as they were attempting to interpret an overwhelming amount of data. Now information is processed so the pilot can make critical decisions quickly, without distracting him from the immediate task of flying the plane.’ Just as aviators have come to rely on information processing, Dr. Bowen is convinced that the future of anesthesia management lies in automated information systems.

Automated record keepers and voice recognition systems are tools that will allow the practitioner more time to devote to direct patient observation. Intelligent alarm systems and ‘heads-up’ displays in visors or eyeglasses which continuously keep vital information in view will rapidly focus attention on important data, allowing the anesthesiologist to intervene earlier during critical events. Although such systems may be perceived initially as distracting toys, the goals of earlier intervention and improved patient safety mandate the development of automated information processing, according to Dr. Bowen.

Regional vs. General

The relative safety of regional vs. general anesthesia was also addressed at the IARS meeting. In his Review Course Lecture, Dr. Michael J. Davies from Melbourne, Australia, outlined perceived distinct advantages of regional anesthesia, particularly for peripheral vascular and carotid artery surgery. Although differences in outcome remain controversial, regional is associated with improved peripheral arterial graft flow rates and decreased risk of arterial thrombosis, he notes. Dr. Davies emphasized the need for further investigation into the role of postoperative epidurals for pain management, which he believes may be associated with improved outcome.

Dr. J. Scharf from the University of South Florida also presented work that suggested spinal anesthesia may be safer than general for patients with cardiac disease. Twenty-nine patients with risk factors for cardiac disease were randomized to either spinal or general anesthesia for procedures of the lower extremity, genito-urinary tract, and lower abdomen. Patients undergoing spinal anesthesia had significantly less myocardial ischemia than patients who received general anesthesia, however no outcome data were reported. [‘And debate goes on, and debate goes on.’]

Residual Paralysis

Two separate reports examined the residual effects of muscle relaxants in PACU patients. Despite using different techniques (neuromuscular stimulation vs. pulse oximetry and physician assessment) both studies found that approximately 15-20% of patients had significantly impaired neuromuscular function on arrival in PACU. Preliminary results from a multi-center study of mivacurium and vecuronium revealed a number of possible risk factors for poor postoperative ventilatory status, including induction with thiopental and pre-existing renal disease. Identification of high-risk patients may help avoid the potentially disastrous consequences of postoperative ventilatory insufficiency.

Two devices designed to confirm endotracheal tube placement were validated for pediatric use. In a series of 248 patients, a self-inflating bulb correctly identified 10 esophageal intubations but failed to confirm tracheal intubation in one morbidly obese patient. A disposable, colorimetric C02 detector was tested in an in vitro experiment by Dr. Eugene Freid at the University of North Carolina. Accuracy ranged from 86 to 100%, falling off with small tidal volumes (5-10 n-d) and rapid rates (60 breaths/min). Dr. Freid was convinced of the device’s utility, saying “Nothing is perfect, but this certainly adds to the clinician’s armamentarium, especially when operating under adverse conditions.’ He noted that emergency personnel had already used the device to correctly confirm endotracheal tube placement in pediatric patients when other techniques were equivocal.

Preop Testing Dangers

In a review course lecture, Dr. Michael F. Roizen (University of Chicago) emphasized the value of the preoperative medical history in anticipating problems and planning therapies accordingly. He also urged using the history to decide which laboratory tests are indicated and relies on a written algorithm to assist him in his own practice. He believes using such a strategy not only lowers costs but may also reduce patient harm from therapies initiated by false positive test results. In support of his beliefs, Dr. Roizen reviewed several studies of patients who underwent laboratory testing without indicated need and showed that fewer patients may have benefited from such screening than were exposed to potential harm by treatment and follow-up of false positive results. A benefit/risk analysis on routine preoperative chest x-rays also showed more harm resulted than good. Dr. Roizen underscored the necessity of a thorough preoperative medical history and the rationale for laboratory testing based on indications and not merely for screening purposes.

Dantrolene Absence Cited as Risk

Dr. R.F. Kaplan (Children’s National Medical Center, Washington, DC) surveyed the availability of dantrolene in hospitals, surgicenters, and oral surgery centers to assess the impact of education and increased awareness since the last survey in 1988. He found that 43% of hospitals, 68% of surgicenters, and 85% of oral surgery centers are not equipped to fully treat a case of malignant hyperthermia. ‘Despite our educational efforts, this represents no change over the past six years in the percentage of institutions using triggering agents that are fully prepared to treat MH. It appears that a more aggressive approach may be necessary to assure all of these institutions are equipped to handle such a life-threatening emergency.’

Citing concerns over reports of increased infection rates in ICU patients receiving continuous propofol infusions for sedation, Dr. P.B. Langevin (University of Florida) re-examined growth rates of staphylococcus aureus in propofol and intralipid. He found that when incubated in a plastic container, such as a disposable syringe, bacterial growth was delayed for approximately eight hours. Bacterial growth is immediate when incubated in glass containers, which contain nitrogen in residues from prior washing. From his studies, Dr. Langevin has concluded that factors other than simple bacterial replication may be responsible for the increased number of staphylococcal infections associated with propofol. ‘One possible explanation could be an interaction between propofol and the bacterial cell membrane, altering the antigenicity of the bacteria and reducing the body’s ability to fight infection.’

Dr. Z. Fang (University of California, San Francisco) examined the production of carbon monoxide (CO) from C02 absorbents acting on volatile agents. [See APSF Newsletter, Fall 1994.1 While CO rarely accumulates in appreciable levels, certain conditions favor its production and may lead to significant exposure to patients. Dryness of absorbent was the most significant factor favoring CO production, with increased temperature, high agent concentrations and type of absorbent (Baralyme > soda lime) also contributory. Dr. Fang suggested that drying of the absorbent from running high gas flows through a circuit over a weekend may cause a risk when halogenated ethers are used during the first case Monday morning.

Gastric emptying times after a fight breakfast of toast, coffee and clear juice were measured by ultrasonography in a joint study from several Norwegian institutions. The investigators found that in healthy patients without gastric motility problems, such a meal cleared in three to four hours, with large interindividual differences. They concluded that a six hour fast should be mandatory after a light meal in order to provide a safety margin for smokers and other patients with unrecognized delayed gastric emptying.

Dr. Guyton is from the Department of Anesthesiology, University of Mississippi Medical Center, Jackson.