◊ BACKGROUND:
Preoperative testing has been criticized as having little impact on perioperative outcomes. We conducted a randomized, single-blind, prospective, controlled pilot study to determine whether indicated preoperative testing can be eliminated without increasing the perioperative incidence of adverse events in selected patients undergoing ambulatory surgery.
◊ METHODS:
One thousand sixty-one eligible patients were randomized either to have indicated preoperative testing or no preoperative testing. In the indicated testing group, patients received indicated preoperative testing: a complete blood count, electrolytes, blood glucose, creatinine, electrocardiogram, and chest radiograph according to the Ontario Preoperative Testing Grid as per current practice, whereas in the no testing group, no testing was ordered. The investigators, data collectors, and patient outcome reviewers were blinded to the group assignment. The primary outcome measures were the rate of perioperative adverse events and the rates of adverse events within 7 and 30 days after surgery.
◊ RESULTS:
Patients' age, gender, American Society of Anesthesiologists status, type of surgery, and anesthesia were similar between the two groups. There were no significant differences in the rates of perioperative adverse events and the rates of adverse events within 30 days after surgery between the no testing group and the indicated testing group. Hospital revisits <or=7 days were higher in the indicated testing group (P < 0.05). None of the adverse events were related to the indicated testing or no testing.
◊ CONCLUSIONS:
This pilot study showed that there was no increase in the perioperative adverse events as a result of no preoperative testing in our study population. A larger study is needed to demonstrate that indicated testing may be safely eliminated in selected patients undergoing ambulatory surgery without increasing perioperative complications.
◊ Reviewed by M. F. Mulroy, MD
Faculty Anesthesiologist,Virginia Mason Medical Center, Virginia Mason Hospital, Seattle, USA
The question of which laboratory tests to perform in anticipation of ambulatory surgery has been a complex one since the rise of the subspecialty in the 1980’s. It was the subject of many panels at the Society of Ambulatory Anesthesia early meetings, and prompted the reinvestigation of the utility of “routine” laboratory testing on otherwise healthy patients. Roizen was one of the first to identify the lack of utility of routine testing and even, as these authors point out, the potential of adverse events when false positive results are pursued. There is compelling statistical data that the discovery of false positives with routine screening tests in otherwise healthy populations are both expensive and potentially harmful. Thus, it is delightful that Dr. Chung and her group have provided us with one more step in the direction of reducing unnecessary “routine” screening. This recent report evaluated the relative safety of eliminating “indicated” tests on a group of 499 patients scheduled for elective outpatient surgery, compared to a group of 527 who proceeded to have the laboratory testing indicated by the Ontario Preoperative Testing Grid. The results are not surprising. It is useful to see that there was no difference in the frequency of adverse events between the groups in the intraoperative or immediate 7-day/30-day postoperative period. It was also noteworthy that none of the adverse events that did occur in either group were related to or could have been prevented or detected by the use of preoperative laboratory testing. It would appear from these results that the authors have moved us closer to the point of eliminating routine testing altogether for the outpatient surgical candidate.
By the authors’ admission, however, there are limitations to their study. First of all, their own power analysis suggested the need for 20,000 patients in order to provide a significant 1% reduction in the rate of adverse outcomes of these procedure in generally healthy outpatients. Thus, their group of 1,061 patients does not provide sufficient power to draw a valid conclusion. The authors’ response is to suggest the role of a much larger multicenter study to confirm their findings. That may be a reasonable next step. However, a more critical issue is whether they have actually tested the question involved.
The assumption from their general comments and the title of their paper might suggest that all preoperative testing can be eliminated. Another potential interpretation of their study is that the guidelines currently used in the Ontario Preoperative Testing Grid are perhaps too broad. A close analysis of their study suggests that there is still a need for specific designated tests based upon the patient’s history, physical examination, and proposed surgery. The methodology involved in this study partially masks this phenomenon. By using exclusion criteria for their investigation, the authors eliminated 22% of the 2,297 eligible patients based on the presence of significant medical conditions (active coronary disease, bleeding disorders, renal disease, symptomatic pulmonary disease, arrhythmias, etc) that would prompt a prudent physician to obtain baseline laboratory evaluations, such as an electrocardiogram, a prothrombin time or a PTT, or a serum potassium. It is presumed that these tests were ordered on those patients who were excluded, and thus the conclusion of this study becomes less clear. One could interpret the data as saying that the authors used a more rigid set of criteria for patient-based laboratory testing than the Ontario Preoperative Testing Grid, and found that the latter screening tool did require unnecessary and unproductive testing. The question that is not answered by this study is what tests were ordered on those 22% of other patients who were screened and excluded, and whether these tests subsequently provided changes in their anesthetic management or in the frequency of adverse events. The identification of these “indicated” tests is really the elusive target that still challenges us all, as was stated in the previous large-scale effort at definition, the ASA Practice Guideline of 2002 which the authors reference.
Meanwhile, the authors’ overall conclusion (most “standard” preoperative testing is unnecessary) is probably valid. A more rigorous follow-up study would have to include a specific evaluation of the validity of each test based on the patient’s preexisting diseases and health status. The current report is insufficient to justify the elimination of electrocardiograms on patients with active cardiac disease, or coagulation studies on patients on chronic anticoagulants, or potassium levels on patients undergoing dialysis. We are still left with the need to perform a preoperative assessment on each patient, and determine the indicated tests to allow surgery to proceed safely. Nevertheless, this report is a step forward to raising the question of where to set the bar for “indicated” preoperative laboratory testing. The authors are to be congratulated for helping us focus again on an issue which can not only improve the efficiency of our preoperative screening, but also reduce false positive laboratory results and the overall cost of health care. |
