To the Editor:—

In “Anesthesiologist Direction and Patient Outcomes,” Silber et al.  1described a reduction in risk-adjusted mortality associated with larger hospitals, higher nurse-to-bed ratios, and direction of anesthesia care by an anesthesiologist. Focusing on the effects of “directed” care, they observed that after adjustment for a variety of patient and institutional characteristics, patients for whom anesthesiologists submitted bills for performing or directing anesthesia care (the “directed” group) had fewer deaths than patients receiving “undirected” care, 61 percent of whom were not billed for anesthesia. This study has attracted considerable attention among physician and nurse anesthetists, public officials, and the public. However, this study neither compares the safety of physician and nurse anesthetists nor provides data that distinguish anesthesia safety from surgical outcomes.

The published study reported 7,665 deaths (3.5%) within 30 days after 217,440 operations in Medicare beneficiaries. This rate is nearly 9,000 times the often-cited anesthesia-related mortality rate of 1:250,000. 2The study also reported 91,024 complications (41.9%), including psychosis, internal organ damage, gastrointestinal or internal bleeding, sepsis, deep wound infection, gangrene, gastrointestinal obstruction, and return to surgery. Clearly, these extraordinarily high mortality and complication rates are functions of a “wide net” cast, which includes perioperative events, many of which temporally and clinically are unrelated to anesthesia care.

The 58 excess deaths observed in the “undirected” group have several plausible etiologies, many of which were acknowledged by the authors. Among them are the following: (1) misassignment of unbilled “directed” cases to the “undirected” group on the assumption that financial incentives always result in anesthesiologists’ billing for direction; (2) the decision to categorize a case as “undirected” if any “undirected” anesthesia was administered during the hospital stay, even if “directed” anesthesia was administered during the primary operation that resulted in complications and subsequent death; (3) high mortality in cases performed by undirected residents; (4) coding and billing errors; (5) clinical information insufficient for complete risk adjustment; (6) unrecognized differences in institutional support; (7) the effect of patient care unrelated to anesthesia administration; and (8) multicollinearity within the logistic models. 3Cognizant of the limits of this study, the authors themselves observed the need for an “in-depth, large-scale medical chart review of surgical cases” to “assist in determining the etiology of differences in outcomes.”

The study published in Anesthesiology contains some interesting speculation about data and analyses that ultimately may prove fatally flawed or that may lead to future productive investigation. However, it remains a work hampered by the amorphous nature of the “undirected” group, the methodologic issues noted, and the enumeration of surgical outcomes unrelated to anesthesia administration.

Silber JH, Kennedy SK, Even-Shoshan O, Chen W, Koziol LFL, Showan AM, Longnecker DE: Anesthesiologist direction and patient outcomes. A nesthesiology 2000; 93: 152–63
MacKenzie RA: Congressional testimony before the Antitrust Subcommittee, Senate Judiciary Committee, June 7, 2000
Kleinbaum DG: Logistic Regression. New York, Springer, 1994