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(Chest. 2004;125:1635-1641.)
© 2004 American College of Chest Physicians

The Effect of a Computerized Reminder System on the Prevention of Postoperative Venous Thromboembolism*

David Mosen, PhD, MPH; C. Gregory Elliott, MD, FCCP; Marlene J. Egger, PhD; Michael Mundorff, MBA; James Hopkins, MD; Robert Patterson, MD, MSc and Reed M. Gardner, PhD

* From the Department of Public Health & Preventive Medicine (Dr. Mosen), Oregon Health & Science University, Portland, OR; the Pulmonary/Critical Care Division (Drs. Elliot and Hopkins), LDS Hospital, Salt Lake City, UT; the Department of Family and Preventive Medicine (Dr. Egger), and Medical Informatics (Drs. Patterson and Gardner), University of Utah School of Medicine, Salt Lake City, UT; and Institute for Health Care Delivery Research (Mr. Mundorff), Intermountain Health Care, Salt Lake City, UT.

Correspondence to: C. Gregory Elliott, MD, FCCP, Pulmonary Division, LDS Hospital, Eighth Ave and C St, Salt Lake City, UT 84143; e-mail: ldgellio{at}ihc.com


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objective: To measure the effect of an altered process of care, directed by a computerized reminder system, on rates of symptomatic postoperative venous thromboembolism.

Design: Comparisons of preintervention and postintervention measurements.

Setting: A university-affiliated community hospital in Utah.

Patients: Two-thousand seventy-seven consecutive patients who underwent major operations in four surgical divisions between January 1, 1997, and October 31, 1997 (preintervention), and 2,093 consecutive patients who underwent the same procedures between January 1, 1998, and October 31,1998 (postintervention).

Intervention: A program to prevent venous thromboembolism developed from American College of Chest Physicians guidelines, and an altered work process directed by a computerized reminder system.

Measurements: Rates of symptomatic, objectively confirmed deep vein thrombosis (DVT), pulmonary embolism (PE), and death attributable to venous thromboembolism occurring within 90 days of the date of surgery.

Results: The preintervention and postintervention cohorts did not differ with respect to age, severity of illness, number of risk factors for venous thromboembolism, or individual risk factors for venous thromboembolism. The overall prophylaxis rate increased from 89.9% before implementation of the computerized reminder system to 95.0% after implementation (p < 0.0001). The combined 90-day rate of symptomatic DVT, PE, and death attributable to PE remained the same (preintervention, 1.0%; postintervention, 1.2%; odds ratio, 1.21; 95% confidence interval, 0.67 to 2.20). Forty of 46 venous thromboembolic complications (87%) occurred despite the delivery of American College of Chest Physicians-recommended measures to prevent venous thromboembolism.

Conclusions: Computerized reminder systems combined with altered care procedures increase the rate of prophylaxis against venous thromboembolism without decreasing the rate of symptomatic venous thromboembolism when the baseline rate of prophylaxis is high. A population of surgical patients exists who are resistant to American College of Chest Physicians-recommended prophylactic measures against venous thromboembolism. New strategies are needed to address prophylaxis-resistant venous thromboembolism.

Key Words: computer reminders • deep vein thrombosis • prevention • prophylaxis • pulmonary embolism


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Deep vein thrombosis is a common complication after elective major surgery.1 Without prophylaxis, approximately 25% of patients who undergo general surgical procedures and approximately 50% of patients who undergo hip replacement acquire deep vein thrombi that are detected by venography.1 Symptomatic deep vein thrombosis (DVT) and pulmonary embolism (PE) occur less frequently, but symptomatic venous thromboembolic disease causes substantial morbidity and may prove rapidly fatal.234

Effective methods exist to prevent venous thromboembolism.1 However, these methods are underused.56789 In 1986, a study5 of 16 Massachusetts hospitals showed that only 32% of surgical patients who were at high risk for DVT received prophylaxis. Continuing medical education with or without a quality improvement component improved the rate to approximately 50%,6 but rates of prophylaxis remain low for high-risk surgical patients despite educational efforts and the publication of consensus statements.78 Furthermore, one study9 found that 17% of venous thromboembolic events were potentially preventable. The omission of thromboprophylaxis was common, particularly in the setting of nonorthopedic surgery.

Computer reminder systems combined with altered care procedures can improve the delivery of preventive care.101112 These techniques have increased preoperative prophylactic antibiotic administration from 40 to 99%,10 and have reduced the rates of postoperative wound infections from 1.8 to 0.9%,13 with attendant reductions in the overall cost of care.10 Computer-generated reminders combined with altered care procedures for prophylaxis against postoperative venous thromboembolism increased the rate of these prophylactic measures at the LDS Hospital from 85.2% in 1996 to 99.3% in 1997.11 However, no study has determined whether computerized reminder systems and altered care procedures can decrease the rates of symptomatic venous thromboembolism. In this study, we examined the effect of computer-generated reminders and altered care procedures on rates of symptomatic venous thromboembolism after major surgery.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Setting
The LDS Hospital is a licensed, 520-bed, community teaching affiliate of the University of Utah School of Medicine in Salt Lake City. More than 30,000 major and minor surgical procedures are performed each year, although pediatric patients do not undergo surgery at LDS Hospital. The present study used the Health Evaluation Through Logical Processing (HELP) hospital information system.1415 The HELP system tracks all aspects of surgical procedures, including date and time, the type of operation performed, and the surgeon.1617

Study Design
The study was designed to test the primary null hypothesis that the 90-day rate of combined postoperative venous thromboembolic complications (ie, DVT, PE, or death attributable to venous thromboembolism) before implementation of a computer-directed decision system for the prevention of postoperative DVT does not differ from the 90-day rate of combined postoperative venous thromboembolic complications after implementation of a computerized decision support system for the prevention of postoperative DVT. Previous reports1118 have described the intervention in detail. In brief, the HELP system makes patient-specific and epidemiologic information available at the point of care. Surgeons at the LDS Hospital developed a consensus that patients who underwent any of 224 procedures should receive prophylaxis against venous thromboembolism, using the recommendations of the American College of Chest Physicians.19 The HELP system searched the integrated clinical database three times daily (at 7:00 AM, 11:00 AM, and 3:00 PM) for pointer to text codes of specific surgical procedures for which DVT prophylaxis was indicated. When a pointer to text code in the clinical database matched that of the expert knowledge database, a reminder consisting of the letters "DVT" appeared in both the online as well as the printed operating schedule adjacent to the patient’s name. Surgical staff changed their work pattern to assure that designated patients received an anticoagulant (all total joint replacement surgery patients) or sequential pneumatic compression devices. Sequential pneumatic compression devices were placed at the time of anesthetic induction and remained on until the patient walked postoperatively. This intervention improved the prophylaxis rate from 85.2% (November 1996 to January 1997) to 99.3% (November 1997 to January 1998).11 The use of prophylaxis against DVT was documented by an electronic search of the Enterprise Data Warehouse (EDW) maintained by Intermountain Health Care using standard query language and billing codes.1118 Manual audits of medical records were performed to confirm that DVT prophylaxis was not provided when the use of prophylactic anticoagulants or pneumatic compression devices was not identified by the electronic search.

Patient Demographics
We obtained patient demographics from electronic medical records contained in the EDW maintained by Intermountain Health Care. The EDW is one of the most comprehensive database in the managed care industry in terms of its ability to track inpatient, outpatient, and laboratory information.20 The system contains data collected from admitting departments, accounts receivable, and medical records, and it summarizes inpatient length of stay, emergency department visits, urgent care visits, or outpatient registrations. Such data are used to measure clinical and financial outcomes.212223 Severity of illness was measured using a standard validated formula.24

Identification of Venous Thromboembolic Disease
We searched electronic databases (ie, the EDW) using International Classification of Diseases, 9th revision, clinical modification codes for venous thromboembolism (ie, codes 415.1, 451.11, 451.18, 451.2, 451.81, 451.9, 453.1, 453.2, 453.8, and 453.9).25 We anticipated that this method would identify hospital readmissions or emergency department evaluations at all Intermountain Health Care facilities within 90 days of the index surgery based on previous observations of such events.26 We performed electronic searches for inpatient deaths of patients within 90 days of the surgical procedures. We also searched these databases to identify patients who underwent additional surgical procedures during the 90-day follow-up after the index surgery.

All events (ie, DVT, PE, and deaths) were adjudicated by three physicians who were blind to the study hypothesis. Medical records and reports of objective tests (eg, compression ultrasonography, ventilation and perfusion lung scans, CT scan, or pulmonary arteriograms) were reviewed. The confirmation of symptomatic venous thromboembolic disease required both symptoms of venous thromboembolism and positive findings on CT scan or conventional pulmonary arteriography, ventilation-perfusion lung scanning, venous compression ultrasonography, or venography.2728

Statistical Analysis
We compared the preintervention patients to the postintervention patients with respect to the 90-day postoperative rates of the combined end point of symptomatic DVT, PE, or death attributable to venous thromboembolism using a {chi}2 analysis. We used logistic regression to adjust for differences in the proportions of surgical procedures and other confounding variables. We chose a one-sided {alpha} level of 0.05, since only a decrease in the combined rate of DVT, PE, and death attributable to venous thromboembolism would provide evidence of the effectiveness of the intervention. Comparisons of demographic characteristics before vs after intervention were made to identify possible confounders for the primary analysis. The 5% significance level was used to conservatively identify potential confounders for subsequent adjustment. Preintervention vs postintervention tests of prophylaxis rates for each of four surgical divisions were analyzed by {chi}2 test with Bonferroni correction to a 5%/4 = 1.25% significance level. A priori we estimated a 2% combined 90-day postoperative rate of symptomatic venous thromboembolism,329 and we estimated that we required at least 2,067 patients in the preintervention cohort and at least 2,067 patients in the postintervention cohort to have 80% power to detect a 50% reduction (absolute reduction, > 1%) in the combined 90-day postoperative rate of symptomatic venous thromboembolism.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Patient Populations
During the 20-month study period, 4,170 patients underwent designated surgical procedures at the LDS Hospital. Two thousand seventy-seven patients underwent designated surgical procedures for which DVT prophylaxis was indicated from January 1, 1997, to October 31, 1997 (preintervention), and 2,093 patients underwent designated surgical procedures for which DVT prophylaxis was indicated from January 1, 1998, to October 31, 1998 (postintervention). The preintervention and postintervention cohorts did not differ with respect to age, severity of illness, number of risk factors for venous thromboembolism, or individual risk factors for venous thromboembolism (Table 1 ). Fewer patients in the postintervention population underwent urology procedures (preintervention, 6.1%; postintervention, 4.3%; p < 0.05), and a higher proportion of postintervention patients were women (preintervention, 66.6%; postintervention, 70.5%; p < 0.05). Logistic regression analysis adjusted for these differences in the primary analysis. Seventy-six patients (1.8%) underwent an additional surgical procedure during the 90-day follow-up period. These procedures were distributed equally among the preintervention and postintervention cohorts (Table 1), and 75 of the 76 patients received prophylaxis against venous thromboembolism for the additional procedure.


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  		Table 1. Descriptive Statistics*

 
Prophylaxis Against Venous Thrombosis
The overall rate of prophylaxis increased from 89.9% before implementation of the computerized reminder system to 95.0% (p < 0.0001) after implementation of the computerized reminder system (Table 2 ). The rates of prophylaxis increased significantly for general surgical procedures (preintervention, 94.0%; postintervention, 98.7%; p < 0.0001) and for gynecologic procedures (preintervention, 85.1%; postintervention, 99.5%; p < 0.0001). The increased rates of prophylaxis reflected the increased use of sequential pneumatic compression devices for patients undergoing laparoscopic cholecystectomy, laparoscopic appendectomy, and all three high-volume gynecologic surgery procedures (ie, total abdominal hysterectomy, vaginal hysterectomy, and laparoscopic-assisted vaginal hysterectomy).


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  		Table 2. Use of DVT Prophylaxis*

 
Symptomatic Venous Thromboembolism
Twenty patients (1.0%) in the preintervention cohort and 26 patients (1.2%) in the postintervention cohort acquired symptomatic venous thromboembolism within 90 days of undergoing the surgery. After adjustment by logistic regression for differences in gender, surgery type, severity of illness, and total DVT/PE risk factors, we found no significant impact of the computer reminder system (odds ratio, 1.21; 95% confidence interval, 0.67 to 2.20). The majority of patients (40 of 46) with symptomatic venous thromboembolism had received American College of Chest Physicians-recommended prophylaxis against venous thromboembolism, and only 2 of 46 venous thromboembolism patients did not receive some form of venous thromboembolism prophylaxis. Age, gender, severity of illness, risk factors for thromboembolism, and operative procedures did not differ for patients who developed venous thromboembolism before or after implementation of the computerized reminder system, although there was a trend toward a reduced rate of venous thromboembolism after laparoscopic cholecystectomy (Table 3 ). Cases of DVT and PE were more likely to occur in older patients who had severity of illness scores indicative of more severe illnesses and more risk factors for venous thromboembolism (Table 4 ). The 46 patients who acquired venous thromboembolism were more likely to have received anticoagulant therapy and more than one method of venous thromboembolism prevention, underscoring their high risk for venous thromboembolic disease. None of the 76 patients who underwent a second operation during the 90 days following the index surgery acquired symptomatic venous thromboembolism.


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  		Table 3. Descriptive Statistics of Venous Thromboembolism Cases (n = 46)*

 

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  		Table 4. Descriptive Statistics for Patients With Venous Thromboembolism Compared With Patients Who Did Not Acquire Symptomatic Venous Thromboembolism*

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The results of this study again provide proof that computerized reminders linked to altered care procedures increase the delivery of preventive care, but the increased delivery of preventive care against venous thromboembolism did not lower the rate of symptomatic venous thromboembolism. A computer reminder system and altered care increased prophylaxis rates significantly, even when the preintervention rates were substantially higher that those reported for most hospitals in the United States.578 The computer reminder system increased prophylaxis rates most dramatically for patients undergoing gynecologic and general surgery procedures, and produced no change for those patients undergoing orthopedic procedures, perhaps reflecting the widespread acceptance of venous thromboembolism prophylaxis by orthopedic surgeons in the United States.6826

The failure of increased rates of prophylaxis to lower the rate of symptomatic venous thromboembolism is important and deserves careful consideration. This finding underscores the point that small (but statistically significant) increases in the rate of prophylaxis may not be linked to an effect on the outcome of interest. A number of studies have demonstrated that computer reminder systems increase the use of measures aimed at the prevention of pneumonia12 postoperative wound infections,1013 and new coronary events,12 but few studies have actually linked computer reminder practices to important patient outcomes. Larsen et al13 showed that the use of computer reminders for preoperative prophylactic antibiotic administration decreased the rate of postoperative wound infections from 1.8 to 0.9%, and Evans et al30 showed that a computerized decision support program improved outcomes and lowered costs related to antibiotic treatment of critically ill patients. Based on this evidence, we believe that computer reminders and altered care procedures may prove highly effective in other surgical settings where prophylaxis rates against venous thromboembolism remain low for high-risk procedures. It is also possible that our study would have shown a benefit if we had identified asymptomatic venous thrombi by mandatory venography.

The occurrence of symptomatic DVT and PE after prophylaxis against venous thromboembolism is another key observation of the present study. Eighty-seven percent of the 46 symptomatic venous thromboembolic complications occurred despite performance of the recommended prophylactic measures. The prophylactic measures were appropriate based on past and current consensus guidelines119 for prophylaxis against venous thromboembolism. The observation of lack of response to venous thromboembolism prophylaxis reinforces one description of this phenomenon4 among hospitalized patients at the Brigham and Women’s Hospital. In contrast to the report of Goldhaber et al4 in medical patients, our observations demonstrate that prophylaxis-resistant thromboembolism also occurs in surgical patients. Furthermore, heparin-induced thrombocytopenia with thrombosis clearly was not the mechanism for lack of response to prophylaxis for at least half of the 46 cases, because we documented that 23 of 46 patients who developed venous thromboembolism had never received unfractionated or low-molecular-weight heparin. Heparin-induced thrombocytopenia with thrombosis may have played a role in the prophylaxis failures reported by Goldhaber et al,4 since at least 35% of the patients received heparin or low-molecular-weight heparin, and 12 of 13 patients for whom PE contributed to death had received either unfractionated or low-molecular-weight heparin. In other studies,3132 heparin-induced thrombocytopenia with thrombosis syndrome has been associated with severe delayed venous thromboembolism after the prophylactic administration of heparin or low-molecular-weight heparin.

There are several potential limitations to the present study. First, we studied two populations sequentially (ie, we employed a historical control group). Thus, it is possible that some unrecognized secular trend biased our results, even though we corrected for observed differences (eg, the proportion of urology procedures in the two populations). Second, we depended on electronic data systems to identify diagnoses of venous thromboembolism within 90 days of the index surgery. This method may lead to an underestimation of the event rate because some patients had their DVT or PE diagnosed outside of the system of electronic surveillance. However, the event rates that we observed are very similar to the rates of symptomatic venous thromboembolism observed following high-risk surgical procedures.3 Furthermore, any underestimate of the event rate should be the same for the preintervention and postintervention time intervals. Although outpatient use of low-molecular-weight heparin might avoid rehospitalization for DVT, the diagnosis was not missed by our method because the use of compression ultrasonography, lung scanning, and pulmonary angiography was detected by the electronic data review.

In the present study, the majority of DVT/PE prophylaxis failures occurred among elderly patients with multiple risk factors for venous thromboembolism who underwent surgical procedures with high risk for venous thromboembolism. This observation provides a direction for future research aimed at testing new strategies for the prevention of symptomatic venous thromboembolism in postoperative patients.


   Footnotes
 
Abbreviations: DVT = deep vein thrombosis; EDW = Enterprise Data Warehouse; HELP = Health Evaluation Through Logical Processing; PE = pulmonary embolism

This research was supported by Pharmacia Research.

Presented in part at the 24th Annual Meeting of the Society of Medical Decision Making, October 23, 2002, Baltimore, MD.

Received for publication September 22, 2003. Accepted for publication December 2, 2003.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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