Anesthesiologists have a long-standing appreciation for risks associated with airway management. During the past 60 years, a variety of studies have demonstrated that events involving the respiratory system are a prominent cause of adverse outcomes in anesthesia practice.¹^–⁸ A few examples help illustrate this point. The Anesthesia Study Commission, which investigated anesthesia-related fatalities in metropolitan Philadelphia during the period 1935–1944, identified respiratory factors such as airway obstruction, hypoxia, and aspiration as the probable cause of death in approximately 19% of cases.⁷ A large, multicenter study by Beecher and Todd, conducted about a decade later when curare and other muscle relaxants were first entering clinical practice, led to the recognition of excess mortality associated with perioperative respiratory depression.¹ In the 1970s, Utting and colleagues analyzed a 7-year series of anesthesia accidents reported to the Medical Defence Union of the United Kingdom (UK).⁸ Of 227 cases resulting in death or brain damage, 36% involved adverse respiratory events such as esophageal intubation, ventilator misuse, and aspiration.

Critical-incident studies have offered a similar picture. A landmark study in the late 1970s by Cooper and colleagues revealed that 29% of reported incidents were related to respiratory events such as airway mismanagement or failure and misuse of ventilators and breathing circuits.² A decade later, the Australian Incident Monitoring Study provided a detailed analysis of the first 2000 cases voluntarily submitted since the late 1980s.⁶ In their collection of critical incidents, problems with ventilation accounted for 16% of reports from anesthesiologists in Australia and New Zealand.

II the Closed Claims Perspective

Closed medical malpractice claims represent an important resource for the study of professional liability associated with airway management. To better appreciate this resource, it is helpful to describe some basic features of claims data.

A medical malpractice claim is a demand for financial compensation by an individual who has sustained injury in connection with medical care. Resolution of a claim usually occurs by an out-of-court process or by litigation. Once a claim is resolved, its file is closed. A closed claim file typically contains a broad assortment of documents related to the adverse outcome. These documents may include medical records, narrative statements by the involved health care personnel, expert and peer reviews, deposition summaries, outcome and follow-up reports, and the cost of settlement or jury award.

Claims represent only a small fraction of all adverse outcomes arising from medical care. The Harvard Medical Practice Study of patients in New York State in 1984 reported that approximately 4% of patients sustained an iatrogenic injury during hospitalization,⁹ but only 1 of every 8 injured patients filed a malpractice claim. Similar findings were described 10 years earlier by the Medical Insurance Feasibility Study in California.¹⁰ These small fractions make it unlikely that claims can be regarded as representing a cross section of all adverse outcomes.

Although claims may not serve as a representative sample of the entire population of adverse outcomes, these cases have a direct and important implication for the study of professional liability: the cost of claims plays an important role in determining the cost of medical malpractice premiums. By studying a large collection of claims, it may be possible to identify types of adverse events that consistently make a large contribution to insurance costs. This information helps focus research and risk management strategies on areas of clinical practice associated with the greatest losses. Successfully reducing losses may lead to lower premiums, with accompanying savings for physicians, patients, and associated third-party participants. Because many types of adverse outcomes are relatively rare, claims files also represent an enriched environment for collecting information about infrequent but catastrophic events. Examination of a large set of rare or unusual adverse outcomes with a common theme provides an opportunity to generate hypotheses of causation and remedy that may not be evident to anesthesiologists who experience such cases as isolated events.

Since 1985, the Committee on Professional Liability of the American Society of Anesthesiologists (ASA) has engaged in a structured analysis of closed anesthesia claims in the United States, known as the ASA Closed Claims Project. Cases involving adverse anesthetic outcomes are retrieved from the closed claims files of U.S. medical-liability insurance carriers who voluntarily participate in the project. Claims for dental injury are not included in the ASA Closed Claims Project, and the data reported in this chapter also exclude claims associated with chronic pain management. In aggregate, the participating carriers provide coverage for approximately 36% of U.S. anesthesiologists. Because several years often elapse between the occurrence of an adverse event and the closure of its associated claim, the majority of cases span an interval from the 1980s to the early 2000s. The database now contains more than 8000 cases.

A detailed description of data collection procedures for the Closed Claims Project has been reported previously.^11,¹² In brief, each claim file is reviewed by a practicing anesthesiologist, and a standardized form is used to record detailed information on characteristics of patients, surgical procedures, anesthetic agents and techniques, involved personnel, sequence of events, standard of care, critical incidents, clinical manifestations, responsibility, and outcome. Standard of care is rated on the basis of reasonable and prudent practices at the time of the event. Practice patterns that may have evolved at a later date are not retrospectively applied when the standard of care is rated. An adverse outcome is deemed preventable with better monitoring if the reviewer finds that the use—or better use—of any monitor would probably have prevented the outcome, whether or not such a monitor was available at the time of the event. An acceptable level of interrater reliability has been established for reviewer judgments on the standard of care and preventability of adverse outcomes with better monitoring.¹³

A Principal Features of Adverse Respiratory Outcomes and High-Frequency Adverse Respiratory Events

1 Basic Features

Adverse respiratory events constitute the single largest source of injury in the Closed Claims Project (Table 55-1). A detailed analysis of these events was initiated when the database reached a total of 1541 claims.¹⁴ The contrast between adverse respiratory events and other claims was particularly unfavorable. Respiratory event–related claims were (and still are) characterized by a high frequency of devastating outcomes and costly payments (Table 55-2).

TABLE 55-1 Most Common Damaging Events in U.S. Closed Anesthesia Claims*

TABLE 55-2 Comparison of Respiratory and Nonrespiratory Events*

Just three mechanisms of injury accounted for almost two thirds of all claims for adverse respiratory events (Table 55-3). These mechanisms were inadequate ventilation (24% of cases), esophageal intubation (12%), and difficult intubation (DI; 24%). In the 1990s, after the adoption of pulse oximetry and end-tidal CO₂ (EtCO₂) as monitoring standards, DI (28%) and inadequate ventilation (18%) remained the most common adverse respiratory events, but esophageal intubation (5%) had decreased greatly compared with earlier decades (see Table 55-3). Evaluation of claims from the early 2000s suggests that this profile of adverse respiratory events is staying the same.

TABLE 55-3 Most Common Adverse Respiratory Events as Proportion of All Respiratory Events in Decade*

Aspiration was the third most common adverse respiratory event in the 1990s and 2000s. The remaining adverse respiratory events were produced by a variety of low-frequency mechanisms including airway obstruction, bronchospasm, premature and unintentional extubation, endobronchial intubation, inadequate inspired oxygen delivery, and equipment failure. Special features of low-frequency events are discussed later in this chapter.

A detailed display of outcome and payment data for the three most common types of adverse respiratory events since 1990 (inadequate ventilation, DI, and aspiration) is shown in Table 55-4. Death and permanent brain damage were more frequent in claims for respiratory events compared with nonrespiratory events (P < 0.05). Claims for inadequate ventilation exhibited the highest proportion of death and brain damage (89%, see Table 55-4). Overall, payment for respiratory-related claims ranged from $1260 to $11 million (in 2008$). Most claims (61%) resulted in payment. Claims for adverse respiratory events typically involved healthy adults undergoing nonemergency surgery with general anesthesia (GA) (Table 55-5).

TABLE 55-4 Outcome, Payment, and Frequency for the Most Common Adverse Respiratory Events Occurring in 1990 or Later*

TABLE 55-5 Basic Clinical Features of Cases Involving Adverse Respiratory Events Occurring in 1990 or Later *

Feature	Respiratory Events (n = 867)	All Others (n = 3681)
Age in years (mean ± SD)	47.2 ± 19.8	45.5 ± 18.7
Pediatric	8%	5%
ASAPS 1-2	42%	53%
Emergency	26%	18%
Gender
Female	51%	59%
Male	49%	41%
Primary anesthetic
General	81%	62%
Regional	4%	27%
Monitored anesthesia care (MAC)	8%	6%
Other^†	7%	6%

ASAPS, American Society of Anesthesiologists Physical Status; SD, standard deviation.

^* P < 0.05 for respiratory compared with nonrespiratory events in all categories (chi square test for proportions, t-test for age). Total anesthesia claims = 8954. Claims for chronic pain management and all claims prior to 1990 are excluded.

^† Includes combined regional and general anesthesia, standby, and unknown.

Data from ASA Closed Claims Database, 2008.

The reviewers judged that better monitoring would have prevented the adverse outcome in 20% of the 867 claims for adverse respiratory events since 1990. In contrast, only 7% of nonrespiratory claims were judged preventable with better monitoring (P < 0.01). Half (54%) of all claims for inadequate ventilation were considered preventable with better monitoring, as opposed to 5% of claims for DI and only 1% of claims for aspiration.

For the claims considered preventable with better monitoring, the reviewers pointed to pulse oximetry, capnometry, or both in most cases. Data on the role of better monitoring in the prevention of adverse outcomes must be interpreted with particular care, because the reviewers were not asked to consider confounding factors such as equipment malfunction, diversion of attention, or the impact of false-positive and false-negative results. Therefore, the reviewers’ judgments should be regarded as a near-maximum (and probably unattainable) estimate of the efficacy of better monitoring. It should also be noted that this analysis is based on claims for events that occurred after the adoption of pulse oximetry and EtCO₂ as ASA standards.

2 Inadequate Ventilation

The largest class of adverse respiratory events was inadequate ventilation. The distinguishing feature in this group of claims was the reviewer’s inability to identify a specific mechanism of injury. In part, the inability to assign a mechanism of injury may reflect uncertainty on the part of the original health care providers. Because most adverse events occurred before the widespread use of pulse oximetry and capnometry, the uncertainty may be due to the limitations of traditional clinical signs, such as chest excursion, reservoir bag motion, and breath sounds. With increasing use of quantitative measures of ventilation, fewer cases have been assigned to the category of inadequate ventilation. These events have declined in occurrence from 37% of all respiratory events in the 1970s to 25% in the 2000s (see Table 55-3). It is also possible that a delayed rather than contemporaneous approach to the investigation of adverse outcomes is not powerful enough to provide an understanding of many events.

3 Esophageal Intubation

Prompt detection of esophageal intubation is a key concern in anesthesia practice. At present, anesthesiologists rely primarily on capnometry to confirm endotracheal intubation. The ASA Closed Claims Project database provides an important lesson about the pitfalls of less quantitative methods.

In 1990, we performed an in-depth analysis of 94 closed claims for esophageal intubation.¹⁴ Almost all (92%) of these claims occurred during the period 1975–1985, before routine use of intraoperative capnometry. The single most striking finding was that detection of esophageal intubation required at least 5 minutes in most cases (97%). Our immediate reaction was simply, “What took so long?” We wondered whether such delays in detection were caused by incompetence or negligence (e.g., intubation performed by a legally blind physician, minimal attention to the patient during the procedure), but we found only eight claims (9%) that could be explained in such a way.

A closer look at the esophageal intubation claims suggested that reliance on indirect tests of ventilation may have been an important factor contributing to delay. For example, auscultation is a test that is traditionally used during the first few minutes after intubation. In our set of claims, auscultation of breath sounds was documented in 62 of the 94 claims for esophageal intubation (63%). In 3 (5%) of these cases, breath sound auscultation led to a correct diagnosis of esophageal intubation. In 30 cases (48%), auscultation led to the erroneous conclusion that the endotracheal tube (ETT) was located in the trachea when it was actually in the esophagus. This result was termed a misdiagnosis of endotracheal intubation.

The diagnostic error in such cases was recognized in a variety of ways, including later reexamination with direct laryngoscopy, absence of any object in the trachea at the time of an emergency tracheostomy (despite ongoing “ventilation” through an ETT), resolution of cyanosis after reintubation (often by a second participant), and discovery of esophageal intubation at autopsy. In 29 (47%) of the 62 claims in which auscultation was documented, the records did not contain sufficient information to determine how the auscultatory findings were interpreted. In another 32 cases (34%), there was no information about the use of auscultation.

Using this information, we constructed a best-case scenario by assuming that auscultation led to a correct diagnosis in the 3 cases in which it actually did so, as well as in the 61 cases in which there was no information about its role or the information was unclear. Using this approach of constructing a hypothetical situation to demonstrate the greatest possible benefit, auscultation is still associated with a misdiagnosis rate of 32% (30 of 94 cases). Although the limitations of auscultation are well known,¹⁵ we think these claims emphasize the importance of confirming intubation with the quantitative and ongoing information provided by capnometry.

Another indirect test of ventilation is cyanosis. Almost all of the esophageal intubation claims that we studied took place before pulse oximetry became part of the ASA Standards for Basic Anesthetic Monitoring. The human eye is relatively insensitive to the changes in skin color that occur during arterial desaturation,^16,¹⁷ so it is not surprising that cyanosis preceded the recognition of esophageal intubation in only 34% of cases. One might also expect cardiovascular clues to accompany hypoxemia or hypercarbia and that these clues might alert the anesthesiologist to the possibility of esophageal intubation. Indeed, at least one major hemodynamic derangement was recorded in 79 (84%) of the 94 claims for esophageal intubation, and this knowledge preceded the recognition of esophageal intubation in 60 claims (65%). In order of frequency, the abnormalities included bradycardia, asystole, hypotension, unspecified dysrhythmia, tachycardia, and ventricular fibrillation (Table 55-6). Such changes certainly have the potential to serve as cues, but when they are extremely severe (e.g., ventricular fibrillation, asystole) they draw attention away from the underlying problem and leave very little time for effective remedies. These features point to the importance of confirmatory tests that provide early, direct, and ongoing confirmation of ventilation through the ETT.

TABLE 55-6 Major Hemodynamic Derangements Accompanying Esophageal Intubation Claims *

Hemodynamic Derangement	Percent of Claims (n = 94)
Bradycardia	57
Asystole	55
Hypotension	49
Unspecified dysrhythmia	10
Tachycardia	5
Ventricular fibrillation	1

^* Percentages sum to more than 100 because of multiple derangements. Total anesthesia claims = 1541.

Data from ASA Closed Claims Database, 1990. Table adapted from Caplan RA, Posner KL, Cheney FW, et al: Adverse respiratory events in anesthesia: A closed claims analysis. Anesthesiology 72:828, 1990.

Is injury from undetected esophageal intubation no longer a concern? As shown in Table 55-3, claims for esophageal intubation decreased considerably in the 1990s and later compared with the prior two decades. A few claims for esophageal intubation still enter the database, but they usually involve cases in which capnometry was unavailable or not used or the procedure took place in a remote location.¹⁸

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