Vigilance, Alarms, and Integrated Monitoring Systems

Overview

This chapter discusses several areas in which the interface between human and machine—or more accurately, between the anesthesia caregiver and the anesthesia equipment—plays a crucial role in patient outcomes. At first glance, the topics may seem unrelated. However, vigilance, alarms, and integrated monitoring systems are, in fact, closely interrelated.

The administration of anesthesia is a complex monitoring task and, as such, requires sustained vigilance. Unfortunately, humans are not very good at monitoring because we are error-prone, and our vigilance is susceptible to degradation by a variety of human, environmental, and equipment factors. Designers of anesthesia equipment therefore have attempted to aid the anesthesia caregiver by incorporating devices and systems that augment vigilance and clinical performance. Alarms intended to notify the anesthesia provider of potentially critical situations are effective only if properly designed and implemented. Although many modern anesthesia delivery devices are physically integrated and generally contain systems for gas delivery, monitoring, alarms, and sometimes record keeping, many of the promised benefits of full-scale integration (e.g., “smart” alarms, decision aids) are as of yet not quite fulfilled. The successful implementation of comprehensive integrated anesthesia workstations will require further technologic advances as well as a more complete understanding of the task of administering anesthesia and the factors that affect performance of the anesthesia caregiver in this complex human/machine environment. Research to elucidate these “performance-shaping factors” in anesthesia has been under way for a number of years and is beginning to produce results. Chapter 18 discusses the role that the field of human factors should play in modern anesthesia practice.

Anesthesia Mishaps

In 1985, as many as 3000 preventable incidences of anesthesia-related death or brain damage were estimated to occur in the United States each year. In 2015, Nunnally et al. cite an incidence of perioperative cardiac arrest at 5.6 per 10,000 anesthetics. Although some believe that anesthesia has become safer, many more surgical procedures are now being performed; thus the absolute number of adverse events is certainly not decreasing. In addition, patients undergoing surgery today may be older and sicker than they were in 1985, a consequence of population demographics and economically-driven changes in the U.S. health care delivery system—a fact that might delay, but will not prevent, the use of surgical therapy. A group found a 10-fold reduction in anesthesia-related deaths between 1979 and 1999 in France. In 2009, Li et al. found an incidence of anesthesia-related death at approximately 1 per million population in the United States and approximately 8 per million surgical discharges. Finally, studies suggest that “potentially serious” clinical events are actually quite common in anesthetized patients, but relatively few evolve into adverse patient outcomes. A number of investigators have suggested that human error is a major contributor to the occurrence of anesthetic mishaps. ^, For example, clinician errors, such as making an accidental gas flow change or a “syringe swap,” accounted for up to 70% of anesthetic mishaps in two early studies. ^, In an early, but highly publicized study by Keenan and Boyan, 75% of intraoperative cardiac arrests were attributed to preventable anesthetic errors; an analysis of incidents under monitored anesthesia care concluded that nearly half of the claims could have been prevented by better monitoring.

In the intensive care unit (ICU), clinical errors often may be associated with failed communication among care providers. On the other hand, as is discussed in detail later in this chapter, the majority of adverse anesthesia incidents are likely the result of systemic factors over which the anesthesia provider has little or no control, such as device designs that predispose to human error.

Even under ideal conditions, performance on complicated tasks is rarely perfect. In complex systems involving both humans and machines, human error is almost always a factor in degraded or faulty performance. ^, In aviation, for example, the percent of accidents that resulted from air crew error was reported to be greater than 50%. Accidents usually are caused by the cumulative effect of a number of events rather than one isolated incident. ^, Why do highly trained and experienced individuals make errors? What factors influence the occurrence of these errors? What can be done to decrease their incidence or to mitigate their negative outcome? Research has only begun to provide adequate answers to these important questions.

Vigilance and Monitoring Performance

Vigilance has been equated with “sustained attention.” Attention requires alertness, selection of information, and conscious effort; alertness indicates the receptivity of the individual to external information ( Table 17.3 ). Mackworth, the father of vigilance research, defined vigilance as “a state of readiness to detect and respond to certain specified small changes occurring at random intervals in the environment.” Early research was stimulated by the errors of radar operators who performed the task of detecting barely perceivable events at infrequent and aperiodic intervals for extended periods of time.

The presence of “vigilance” in the official seal of the American Society of Anesthesiologists (ASA) underscores the perceived importance of careful attention to details and detection of subtle signs out of the ordinary. Thus, in a broader sense, anesthetic vigilance might be viewed as a state of clinical awareness in which dangerous conditions are anticipated or recognized. Monitoring , by definition, is a vigilance task; thus, the administration of anesthesia is a complex monitoring task. The anesthesia caregiver must continuously evaluate the patient’s clinical status while assessing the effects of anesthetic and surgical interventions. Memory tasks, decision-making, and vigilance are the most vulnerable to compromise under the stressful work conditions often experienced in the operating room (OR). Although monitoring during quiescent periods of the maintenance phase of anesthesia appears to closely resemble the classic vigilance tasks studied in the laboratory, anesthesia practice commonly involves more complex situations that require divided attention, prioritization, and “situation awareness,” ^, skills that fall outside the classical definition of vigilance.

A large number of laboratory studies have demonstrated a decline in monitoring performance over time, called the vigilance decrement . This performance decline typically is complete within the first 30 minutes of a monitoring session. The vigilance decrement seems to arise primarily as a function of the necessity of attending to a relatively infrequent signal for a prolonged period of time.

Psychologists and engineers have studied vigilance for many years. Investigators in fields outside medicine, most notably aviation, have applied this information to understanding performance on complex monitoring tasks. Studies have identified environmentally induced factors and human/machine interface variables that can impair vigilance and performance in air traffic control, train driving, ^, automobile driving, and nuclear power plant control. The armed forces consider the potential impact of such factors at the earliest stages of the design of new weapons systems.

In most complex monitoring tasks, increased task complexity or task duration generally results in impaired performance ( Fig. 17.1 ). ^, A major factor in the effect of additional tasks on performance appears to be what personal resources, perceptual or cognitive, are required for each new task, and whether those resources are already taxed. Other factors known to impair vigilance include noise, environmental pollution, fatigue, sleep deprivation, and boredom. Performance also may be impaired if the individual is under stress, is in poor health, or uses medication that may impair clinical judgement. Personality factors, training, and experience also affect performance. Performance on complex monitoring tasks can be strongly affected by environmental or task variables. ^,

Research On Vigilance In Anesthesia

In one of the first ergonomic studies of anesthesia, Drui and colleagues used time-motion analysis to examine how anesthesiologists spent their time in the OR. The practice of anesthesia was divided into a number of discrete activities, and the frequency and sequence of each activity were measured. One principal finding was that anesthesiologists directed their attention away from the patient 42% of the time. Additional time-and-motion studies have corroborated and expanded these early results. ^,

Subsequent studies have examined the effects of the level of provider experience and of new technologies, such as electronic anesthesia record-keeping, ^, on the workload and vigilance of providers administering anesthesia. Others have investigated anesthesiologists’ vigilance to auditory and visual ^{, ,} alarm cues and to changes in clinical variables in both the laboratory and during actual procedures. For example, Weinger and colleagues demonstrated that novice anesthesia residents were slower to detect the illumination of an alarm light placed within their monitoring array ( Fig. 17.2 ). The response rate was further impaired during periods of high workload, such as during the anesthetic induction.

Well-controlled studies are essential to understand the nature of anesthesia vigilance and monitoring performance. Studies should be designed to use techniques and procedures that have been repeatedly validated by investigators in other fields. Chapter 18 describes in more detail current research in anesthesia related to clinical performance.