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Article Excerpt
The impact of anesthesia provider credentials on patient outcomes has been a research topic and the subject of policy debates for more than 40 years (Kane and Smith 2004). Although some studies have indicated that credentials (anesthesiologist versus CRNA [certified registered nurse anesthetist]) make a difference to some outcomes, others have not (Abenstein and Warner 1996; Silber et al. 2000; Fleisher and Anderson 2002; Pine, Holt, and Lou 2003; Simonson, Ahem, and Hendryx 2007). After an extensive literature review, Smith, Kane, and Milne (2004) concluded it is not possible to draw a conclusion regarding outcome differences as a function of anesthesiologist versus CKNA provider type. Among the limitations of the current studies they cite are difficulty in risk adjustment, failure to define precisely how hospital anesthesia providers are utilized, and lack of consideration of resources and processes beyond the anesthesia provider model that may also affect outcomes.
Previous studies, relying on administrative data, have characterized anesthesia as being provided by anesthesiologists, CRNAs under anesthesiologist supervision, or unsupervised CRNAs. This characterization ignores potentially large variations across hospitals in the scope of CRNA practice when both anesthesiologists and CRNAs are present. In a recent survey by the authors of obstetrical anesthesia services, we found there are at least five anesthesia provider models based on providers' procedure initiation privileges (e.g., the initiation of spinal, epidural, and general anesthesia) (Minnick and Needleman 2008). The survey also found systematic variations in anesthesia, nursing, and obstetrical medicine resources across obstetrical anesthesia provider models that raise the possibility that provider model may be a proxy for other clinical resource variables usually left unmeasured in typically used databases.
In this paper, we examine the ability of anesthesia provider model and other hospital resources to explain variations in maternal outcomes using a privilege-based characterization of the anesthesia provider model and accounting for relevant nursing, medical, and anesthesia resources.
We focus on obstetrical care and obstetrical anesthesia. Because the labor, delivery, and postpartum service experience is discrete, maternal outcomes are often directly attributable to perinatal care, and almost all care before, during, and after a delivery is within the domains of three departments (nursing, medicine, and anesthesiology), it is more feasible to draw inferences from a retrospective study in this area of health care than in others. Beyond these design advantages, maternal outcomes deserve examination because, although maternal deaths and long-term disability are relatively rare in the United States, the overall morbidity burden (31 percent) is high (Danel et al. 2003; Poole and Long 2004). Given that almost 4 million U.S. women give birth annually, determining improvement strategies is important (National Center for Health Statistics 2005).
METHODS
Sample
The study sample included 1,141,641 obstetrical patients from 369 hospitals (995 hospital years) in six states (California, Florida, Kentucky, New York, Texas, Washington, and Wisconsin) that met the following conditions: reported at least one live birth in the 2002 American Hospital Association Annual Survey; provided at least 1 year of discharge data to their state government; and responded to an author-developed 2004 survey on the organization and resources of nursing, anesthesia, and medical obstetrical services. Hospital discharge data for California, Florida, New York, Washington, and Wisconsin for 1999-2001, and Kentucky and Texas for 2000-2001 were obtained and matched to the surveyed hospitals, as was American Hospital Association Annual Survey data for each year. The sample thus included 995 hospital-years of data with 28 percent from 1999, 36 percent from 2000, and 36 percent from 2001.
The survey variables pertaining to resource and anesthesia provider model utilized in this analysis were chosen based on item response rates and variation across models. Details regarding the survey and variables formation may be found in an earlier paper (Minnick and Needleman 2008).
Measures
Outcomes. Four outcomes were coded from the discharge data. Deaths were coded based on patient discharge status. Following Panchal, Arria, and Labhsetwar (2001), we coded anesthesia and other complications based on secondary diagnoses as reported in the abstract based on The International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM). Anesthesia complications were classified as pulmonary, cardiac, central nervous system, and other (ICD-9-CM codes 668.0-668.2, 668.8, and 668.9). Other complications included cardiac complications (ICD-9-CM codes 674.8x); obstetrical shock (ICD-9-CM codes 669.1x); cardiac arrest and cerebral anoxia (ICD-9-CM codes 669.4x); other cardiovascular events (ICD9-CM codes 674.0x, 430.x-432.x, and 436.x); and pulmonary complications including aspiration pneumonia, pulmonary edema, acute respiratory failure, and acute respiratory distress syndrome (ICD-9-CM codes 507.0, 518.4, 518.5, and 518.8x). The three AHRQ (Agency for Healthcare Research and Quality) Patient Safety Indicators related to obstetrical trauma, were coded into a single indicator variable indicating presence or absence (Agency for Healthcare Research and Quality 2003).
Anesthesia Models. Based upon the survey, hospitals were classified into one of five anesthesia models: anesthesiologist only (ANES-only); CRNA-only; both anesthesiologists and CRNAs practicing at the hospital, with an anesthesiologist required to be present at the initiation of all planned cesarean sections (ANES-CRNA I); both anesthesiologists and CRNAs practicing at the hospital, with an anesthesiologist not required to be present at the initiation of all planned cesarean sections (ANES-CRNA II); and a small group of hospitals in which the anesthesia model differed between labor and delivery and general operating areas (Mixed). Previous work established that this assignment of anesthesia models captured the degree of CRNA supervision more precisely than using a single model designation in institutions where both CRNAs and anesthesiologists practice (Minnick and Needleman 2008).
Other Characteristics of the Obstetrical or Anesthesia Services. Using survey data, we constructed indicator variables that describe the organization of obstetrical services and obstetrical anesthesia. The variables were identified as potentially associated with maternal outcomes as a result of a literature review and deliberations of a panel of experts (Minnick and Needleman 2008). These included the presence of an obstetric anesthesia provider 24 hours per day, facilities to perform a nonemergency cesarean delivery in the labor and delivery area, the proportion of patients reported to labor and deliver in the same room, the number of health care personnel present at a cesarean procedure, minutes to transport a patient for an emergency cesarean delivery from site of labor, and volume (defined as the number of births at the hospital in the year studied divided by 1,000 to make interpretation of the results easier)....
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