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AHRQ releases three new evidence reports

Three new evidence reports were released recently by the Agency for Healthcare Research and Quality. They present the results of systematic reviews of the evidence on anesthesia for cataract surgery, acute exacerbations of chronic obstructive pulmonary disease, and prevention of venous thromboembolism after injury. The reports were prepared by Evidence-based Practice Centers (EPCs) supported by the Agency for Health Care Research and Quality. The reports provide organizations with comprehensive, science-based information on common, costly medical conditions and new health care technologies.

There are 12 AHRQ-supported EPCs; they systematically review the relevant scientific literature on topics assigned to them by AHRQ and conduct additional analyses when appropriate prior to developing their reports and assessments. The goal is to inform health plans, providers, purchasers, and the health care system as a whole by providing essential information to improve health care quality.

Evidence report summaries are now available from AHRQ, both online and in print from the AHRQ Publications Clearinghouse. Copies of the full evidence reports will be available in the near future.

Anesthesia Management During Cataract Surgery

For this report, the EPC examined the risks and benefits of different forms of regional anesthesia and sedation in patients undergoing cataract surgery. The report was prepared by the Johns Hopkins University Evidence-based Practice Center (contract 290-097-0006). Surgery for age-related cataract is the highest volume surgical procedure performed on Medicare beneficiaries, with approximately 1.5 million of these procedures performed in this population in 1996. Because cataract surgery is typically performed on an outpatient basis, it usually involves the application of a local anesthetic in addition to systemic sedation administered by an anesthesiologist or a nurse anesthetist.

Previous research has found substantial national and international variations in anesthesia management strategies for cataract surgery. The variations are due primarily to the preferences of surgeons and anesthesia providers, along with the characteristics of cataract patients. There is uncertainty, however, as to which strategy or strategies provide the best mix of patient comfort, desirable outcomes such as pain control, and freedom from anesthesia-related complications.

The EPC's study concludes that currently employed approaches to anesthesia management provide adequate pain control for successful cataract surgery. However, more data are needed on patient preferences and cost-effectiveness to determine the optimal strategies for anesthesia management during cataract surgery. Among the study's findings are that topical anesthesia does not provide the degree of pain control provided by the various injection techniques, although topical anesthesia is clearly quite effective and avoids the rare complications potentially associated with injection techniques. The literature provides strong evidence that peribulbar and retrobulbar blocks perform similarly. Another common technique, sub-Tenon's block, also appears to be less painful and at least as effective in pain control as the other blocking techniques. Regional blocks using needles have a small but definite risk of major complications, including globe perforation and retrobulbar hemorrhage. There is only weak evidence that intravenous or intramuscular sedation or analgesia improve anxiety control, pain relief, and patient satisfaction with cataract surgery.

The EPC also found that having an anesthesiologist or other anesthesia provider present for every case of cataract surgery is associated with increased costs; however, clinicians do prefer it. Additional data are needed on clinician and patient preferences to determine the cost-effectiveness of this practice. Cataract surgery patients have a high level of satisfaction with anesthesia management regardless of the strategy used. Patients receiving intravenous sedation have a higher rate of postoperative nausea and drowsiness than patients not receiving these agents.

The report also presents background information, describes the methodology used by the EPC, and identifies a number of priorities for future research on anesthesia management during cataract surgery.

Select to access the report summary online. Print copies of the summary (AHRQ Publication No. 00-E014) are available from the AHRQ Publications Clearinghouse. The full evidence report (AHRQ Publication No. 00-E015) is expected to be available by late 2000.

Management of Chronic Hypertension During Pregnancy

The purpose of this report, which was prepared for AHRQ by the University of Texas Health Science Center at San Antonio (contract 290-97-0012), is to help physicians make informed choices about therapeutic interventions for pregnant women with chronic hypertension and to aid organizations in developing guidelines for treatment of this condition. Chronic hypertension, defined as hypertension diagnosed before pregnancy or before 20 weeks gestation, complicates from 1 percent to 5 percent of all pregnancies. This condition is associated with serious maternal and fetal complications, including superimposed pre-eclampsia, fetal growth retardation, premature delivery, placental abruption, and stillbirth.

Addressed in the report are 10 specific questions concerning diagnosis and treatment decisions faced by clinicians who provide care for pregnant women with mild to moderate hypertension. The authors find that the data on treatment of women with hypertension during pregnancy were too scant to prove or disprove clinical improvements of at least 20 percent. Furthermore, although evidence on the adverse effects of antihypertensive agents during pregnancy is limited, there is reason to be cautious in the use of angiotensin-converting enzyme (ACE) inhibitors. The existing studies do not allow determination of an optimum blood pressure for initiating and maintaining treatment in these women. Limited data on low-dose aspirin do not suggest a significant effect on problems related to pregnancy-associated chronic hypertension, according to the report.

Select to access the report summary online. Print copies of the summary (AHRQ Publication No. 00-E010), which includes background and recommendations for future research, are available from the AHRQ Publications Clearinghouse. Copies of the full report (AHRQ Publication No. 00-E011) are expected to be available in late fall 2000.

Prediction of Risk for Patients with Unstable Angina

This report evaluates the published data on techniques for clinicians to divide patients who have sudden-onset angina in groups at high and low risk of life-threatening problems. Unstable angina is a pattern of symptoms that is new in onset, changing in severity or frequency, occurring at rest, and/or lasting longer than 20 minutes. Three key questions were addressed in the report, which was prepared by the University of California, San Francisco/Stanford Evidence-based Practice Center (contract 290-97-0013).

  1. What are the immediate clinical and electrocardiographic characteristics that are independently associated with an increased risk of adverse events in patients with either diagnosed unstable angina or chest pain that suggests cardiac ischemia?
  2. What is the prognostic value of a positive or negative troponin test in such patients?
  3. Are chest pain units and emergency department protocols effective, cost-saving, and safe for triage of patients with suspected unstable angina or myocardial infarction?

In the report, the authors discuss the evidence related to these questions. They found that a positive troponin value was associated with a significant increase in the risk of death in a number of studies. Similarly, the few randomized trials of chest pain units consistently show decreased hospital days and costs when compared with traditional emergency room care. The report presents background information about unstable angina, discusses the methodology used in developing the report, and identifies areas for future research.

Select to access the report summary online. Print copies of the summary (AHRQ Publication No. 00-E030) are available from the AHRQ Publications Clearinghouse. Copies of the full report (AHRQ Publication No. 01-E001) are expected to be available in late fall 2000.

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