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Background Routine preoperative medical testing is commonly performed in patients scheduled to undergo cataract surgery, although the value of such testing is uncertain. We performed a study to determine whether routine testing helps reduce the incidence of intraoperative and postoperative medical complications.
Methods We randomly assigned 19,557 elective cataract operations in 18,189 patients at nine centers to be preceded or not preceded by a standard battery of medical tests (electrocardiography, complete blood count, and measurement of serum levels of electrolytes, urea nitrogen, creatinine, and glucose), in addition to a history taking and physical examination. Adverse medical events and interventions on the day of surgery and during the seven days after surgery were recorded.
Results Medical outcomes were assessed in 9408 patients who underwent 9626 cataract operations that were not preceded by routine testing and in 9411 patients who underwent 9624 operations that were preceded by routine testing. The most frequent medical events in both groups were treatment for hypertension and arrhythmia (principally bradycardia). The overall rate of complications (intraoperative and postoperative events combined) was the same in the two groups (31.3 events per 1000 operations). There were also no significant differences between the no-testing group and the testing group in the rates of intraoperative events (19.2 and 19.7, respectively, per 1000 operations) and postoperative events (12.6 and 12.1 per 1000 operations). Analyses stratified according to age, sex, race, physical status (according to the American Society of Anesthesiologists classification), and medical history revealed no benefit of routine testing.
Conclusions Routine medical testing before cataract surgery does not measurably increase the safety of the surgery.
In 1993, the Agency for Health Care Policy and Research published guidelines for the management of cataracts.9 The agency endorsed "appropriate" testing but did not provide specific recommendations based on reported data. We subsequently performed a national survey of ophthalmologists, anesthesiologists, and internists and found that the majority of the respondents routinely ordered complete blood counts, measurements of serum electrolytes, and electrocardiograms preoperatively.4 Other tests, such as chest radiography, blood-clotting studies, and urinalysis, were also ordered often, although less frequently. Many physicians did not think that the tests were necessary but ordered them anyway because of institutional requirements, medicolegal concerns, or a belief that another physician wanted them performed. We have estimated that the direct cost to Medicare of routine medical testing before cataract surgery is $150 million annually.10 Because of variation in the tests ordered and uncertainty about the effectiveness of such testing, we performed a prospective, randomized clinical trial to assess whether routine medical testing before cataract surgery reduces the rate of complications during the perioperative period.
Methods
Patients and Medical Procedures
The study was designed to be a large trial with few exclusion criteria and easily assessable principal outcomes. Nine clinical centers participated. These nine centers represented a mix of private practices operating at free-standing ambulatory-surgery centers, academic medical centers, and community hospitals. The study imposed no changes in the procedures for anesthesia or cataract surgery that were routine for each center and each surgeon. The study protocol was approved by the human-subjects committees of all nine centers.
Patients scheduled to undergo cataract surgery were recruited between June 1, 1995, and June 30, 1997. Patients were excluded from the study if they were less than 50 years old, were to receive general anesthesia, had had a myocardial infarction within the preceding 3 months, had undergone any preoperative medical testing during the 28 days before enrollment, or could not speak English or Spanish. Patients were not excluded for any other reason. All patients provided written informed consent before enrollment.
For the patients who agreed to participate in the study, each scheduled cataract operation in a single eye was randomly assigned either not to be preceded by routine medical testing (the no-testing group) or to be preceded by routine testing (the routine-testing group). Patients were informed of the group assignment of their operation and were given a letter and study brochure to take to the health care provider who was to perform the preoperative medical assessment. If the patient's operation was randomly assigned to the no-testing group, the letter requested that no preoperative testing be performed, unless the patient presented with a new or worsening medical problem that would warrant medical evaluation with testing even if surgery were not planned. For patients whose operations were randomly assigned to the routine-testing group, the letter requested that a 12-lead electrocardiogram, complete blood count, and measurements of serum electrolytes, urea nitrogen, creatinine, and glucose be obtained. The study imposed no other requirements on the preoperative medical evaluation. For patients with diabetes, blood glucose was measured on the day of surgery, regardless of the group assignment, at the centers that routinely performed this measurement during perioperative monitoring.
Randomization
Each planned cataract operation in a single eye was randomly assigned to the routine-testing or no-testing group. If a patient was enrolled for surgery in one eye and was subsequently enrolled for surgery in the other eye, the second operation was randomly assigned to a study group independently of the first. Patients undergoing surgery in the second eye were not eligible for the study if the operation was scheduled to be performed within 28 days after the operation in the first eye. Randomization was stratified according to clinical center, age (in decades), and health status as reported by the patients (fair, good, very good, or excellent vs. poor) and was performed in blocks of four. The scheduled operations for patients within a given age and health-status category were randomly assigned to one of the two study groups until two operations had been assigned to each of the two groups, completing the block of four. Randomization was performed by computer at the time of enrollment at each center.
Representativeness and Crossovers
The representativeness of the enrolled patients was assessed by comparison of their risk of perioperative complications (according to the American Society of Anesthesiologists [ASA]11 classification) with the risk among patients who were potentially eligible but not invited to participate in the study (because of the large number of cataract operations, which prohibited enrollment of all eligible patients) during a one-month period in each of the two years of enrollment. The ASA classification of risk is based on a rating of the patient's physical status, from I (healthy) to V (moribund). Crossover status was determined according to the information about preoperative tests that was recorded in the surgical chart on the day of surgery. Crossover was considered complete if a patient whose operation had been randomly assigned to the routine-testing group did not undergo any tests or, conversely, if a patient whose operation had been assigned to the no-testing group underwent all three standard preoperative tests. Crossover was considered partial if a patient whose operation had been assigned to either group underwent one or two of the three standard tests.
Data Collection and Outcomes
Base-line and preoperative data were collected with use of a standardized medical-history questionnaire, completed by the patient at the time of enrollment, and a brief medical-history form (for documentation of coexisting illnesses and medications), completed by the health care provider at the time of the preoperative medical examination. Intraoperative medical events and treatments were recorded on a standardized form by the anesthesiologist or nurse anesthetist. Additional data from the day of surgery included the time of discharge (and the reason for a delay, if any), recorded by a member of the nursing staff. Postoperative information (including subsequent hospitalizations, unscheduled visits to a physician, or death) was collected by standardized telephone interview of the patient (or a family member, in the case of death) conducted by the study coordinator one week after the operation.
Table 1 lists the definitions of adverse events used in the study. Whenever a response on a data-collection form indicated that an event had occurred, the relevant medical records were reviewed by two investigators (an internist and an anesthesiologist) to determine whether it met one of the study's definitions of an adverse event. The reviewers of events were not informed of the study-group assignment of the patients, but it was not feasible to remove all references to preoperative test results from the medical records. However, the event reviewers dictated a summary of each medical event without mentioning the presence or absence of preoperative medical and laboratory test results. This summary was subsequently reviewed in a masked fashion by one of two investigators (both of whom were internists and neither of whom was an event reviewer), who made a clinical judgment about whether a preoperative test was likely to have affected (and by what mechanism) the probability of the event's occurrence or its severity and whether, for postoperative events, there was a plausible relation between the event and the cataract surgery. Medical events that occurred on the day of surgery before discharge were considered to be related to the performance of the surgery.
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The primary analysis of events was performed on an intention-to-treat basis. For the overall event rate, events were counted on a per-operation basis (i.e., patients who had events both intraoperatively and postoperatively contributed one event to the overall rate). A secondary analysis was performed according to the treatment actually received (routine testing vs. no testing). Stratified analyses were performed to determine whether preoperative testing might have had effects that differed among various subgroups of patients.
Before enrollment began, the data safety and monitoring committee discussed criteria for stopping the study early and decided not to apply a specific statistical rule for stopping it. Interim data supplied to the committee did not support early termination of the study.
Results
Characteristics of the Patients
We invited 19,354 patients scheduled to undergo 20,775 cataract operations at the nine participating centers between June 1, 1995, and June 30, 1997, to participate in the study (Figure 1). We enrolled 18,189 patients scheduled to undergo 19,557 operations (participation rate, 94 percent). The two study groups had similar proportions of operations that were canceled and not rescheduled before the conclusion of the study (1.5 percent in the routine-testing group and 1.6 percent in the no-testing group). Among the enrolled patients who did have surgery, data were available from the day of surgery for 100 percent and from one week after surgery for 99.8 percent.
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According to the intention-to-treat analysis, the cumulative rate of medical events was the same in the two groups (31.3 events per 1000 operations) (Table 3). The rate of medical events on the day of surgery was similar in the two groups, as was the rate of events during the postoperative period. Only one patient had a medical event during each of two operations (both of which had been assigned to the routine-testing group).
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The overall rate of complete crossovers was 5.9 percent, with significant variation according to the participating center. The majority (71 percent) of complete crossovers were from the routine-testing to the no-testing group. For older patients, those with worse health according to their own report, and those with a higher ASA risk class, the rate of crossover from routine testing to no testing exceeded the rate of crossover from no testing to routine testing. Among patients whose operations were randomly assigned to the no-testing group, those who did not undergo any tests had a lower rate of medical events (29.1 events per 1000 operations) than those who underwent some of the tests (52.6 events per 1000) or all the tests (36.7 events per 1000). The group that crossed over from no testing to some testing had significantly more coexisting illnesses and worse self-reported health status than those who did not undergo any preoperative testing.
Subgroup Analyses
We found no benefit of routine preoperative medical testing when the analysis was stratified according to the participating center or the age, sex, or race of the patient. Similarly, there were no significant differences in event rates when the data were stratified according to coexisting illness, ASA risk class, or self-reported health status (Table 5). Finally, we explored the hypothesis that routine preoperative testing might have resulted in the cancellation or postponement of surgery for patients found to be at risk for adverse medical events. No support for this hypothesis was found, since the frequency of cancellation or postponement for medical reasons was similar in the two groups (2.5 percent in the no-testing group and 2.3 percent in the routine-testing group).
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Preoperative medical testing for all types of surgery accounts for about $30 billion in health care costs annually.12 Over the past 15 years, a substantial body of research has raised questions about the value of routine medical testing before elective surgery.12,13,14,15,16,17,18 Most abnormalities in laboratory values can be predicted from the patient's history and findings on physical examination; moreover, laboratory abnormalities, when discovered, rarely lead to changes in perioperative treatment. In an attempt to limit preoperative medical testing to patients with specific indications, a variety of guidelines have been developed.13,16,18 In general, however, these guidelines favor the routine preoperative ordering of a complete blood count, serum electrolyte measurements, and an electrocardiogram for patients 65 years old or older, regardless of their health. For patients with specific medical conditions, routine preoperative ordering of these and, in many cases, additional tests has been recommended.
Most patients who undergo cataract surgery are Medicare beneficiaries, who are 65 years old or older. As would be anticipated, the prevalence of coexisting illnesses and associated laboratory abnormalities in this age group is high.3,5,6,7 Presumably, this characteristic might justify the routine preoperative laboratory testing that has historically been performed. Data on preoperative medical testing for cataract surgery are limited to two small studies,3,19 each involving approximately 100 operations. These studies indicated that the results of laboratory tests were frequently not reviewed and that even when they were, patients with abnormal results still received routine intraoperative treatment.
Our study demonstrates that perioperative morbidity and mortality are not reduced by routine use of commonly ordered preoperative medical tests. The rate of perioperative medical events, including hospitalization and death, was the same in patients who underwent a standard battery of laboratory tests as it was in patients who did not undergo the tests, and there were no significant differences when the data were stratified according to specific coexisting conditions or the severity of a condition. Perioperative death or hospitalization was very rare; in fact, most of the medical events occurred during surgery and were not serious, and it was rarely judged that medical tests would have helped to reduce the risk or severity of an event. Investigators who were unaware of the group assignment of each operation determined that some of the intraoperative events (4.2 percent) and postoperative events (16.4 percent) in the group assigned to routine preoperative testing might have been prevented or the severity of the events ameliorated by such testing. Possible interpretations of this finding are that the treating physicians did not review the test results, that the test results might have prompted a change in patient care without actually improving the outcome, or that there was variation in the criterion for intervention according to specific test results. Although crossover to preoperative testing occurred more frequently among sicker patients whose operations were randomly assigned to the no-testing group than among healthier patients, it is not apparent that testing reduced the risk of adverse perioperative events among those who crossed over. Finally, we did not find evidence that preoperative medical testing resulted in the postponement or cancellation of surgery for patients found to be at risk for medical events.
The principal strengths of this study include its large size, its randomized design, the minimal exclusion of patients, and the virtually complete ascertainment of medical events during the study period. In the light of these strengths, we believe that the results of the study support a change from the common practice of ordering medical tests routinely for patients scheduled for cataract surgery. Of course, this does not mean that medical testing is unhelpful or not indicated for all patients. In our study, the guideline for patients whose operations were randomly assigned to the no-testing group was that tests should be ordered only when the history or a finding on physical examination would have indicated the need for a test even if surgery had not been planned (e.g., electrocardiography for new or worsening angina). We recommend that this approach be adopted as a guideline for the preoperative assessment of patients for cataract surgery.
We have previously estimated that the cost of routine medical testing before cataract surgery exceeds $150 million annually.10 Given the results of this study, it is likely that most of these costs could be saved without any negative effect on patients' health or clinical outcomes. Furthermore, it is reasonable to consider applying our findings to similar populations of patients scheduled to undergo other procedures that are associated with similar surgical risk and in which local anesthesia and intravenous sedation are used.
Supported by a grant (RO1-HSO-8331) from the Agency for Health Care Policy and Research.
Source Information
From the Dana Center for Preventive Ophthalmology, Wilmer Eye Institute (O.D.S., J.K., J.M.T., L.H.L.), the Division of General Internal Medicine, Department of Medicine (E.B.B., B.G.P., E.P.S.), the Department of Anesthesiology (M.A.F.), the Division of Clinical Pharmacology, Department of Medicine (B.G.P.), and the School of Hygiene and Public Health (J.K., J.M.T.), Johns Hopkins University, Baltimore; and Covance Health Economics and Outcomes Services, Washington, D.C. (E.P.S.).
Address reprint requests to Dr. Schein at 116 Wilmer Bldg., Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD 21287-9019, or at oschein{at}jhmi.edu.
References
Other investigators participating in the Study of Medical Testing for Cataract Surgery and study coordinators were as follows: A.B. Aker (investigator) and K. Taylor, Boca Raton, Fla.; R.K. Forster (investigator) and B. Rodriguez, Miami; H.D. Balyeat (investigator) and M. Cunningham, Oklahoma City; D.C. Brown (investigator) and J. Morschhauser, Fort Myers, Fla.; S.F. Brint (investigator), A. Brown, and S. Mayeux, New Orleans; H.V. Gimbel (investigator), R. Hamilton (investigator), and M. Ferensowitz, Calgary, Alta., Canada; B.J. Shingleton (investigator), C.M. Coley (investigator), N. Henry, N. Leahy, and D. McKenna, Boston; B.J. MacInnis (investigator), C. Hill (investigator), and C. Newell, Ottawa, Ont., Canada; E. Lowery and S. Seabrook, Baltimore; Coordinating Center, Dana Center for Preventive Ophthalmology — P. Roman, J. Gregory, D. Gilbert, and M. Robinson; Data Safety and Monitoring Committee — M. Maguire, C. Beattie, K. Dickersin, S. Obstbaum, and D. Sulmasy.
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