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Preference and Compliance in Postoperative Thromboembolism Prophylaxis Among Gynecologic Oncology Patients

From the Division of Gynecologic Oncology, Duke University Medical Center, Durham, North Carolina; and the Kerr L. White Institute for Health Science Research, Atlanta, Georgia.

Address reprint requests to: Daniel L. Clarke-Pearson, MD, Duke University Medical Center, Division of Gynecologic Oncology, Box 3079, Durham NC 27710; E-mail: clark001{at}mc.duke.edu.

	ABSTRACT

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OBJECTIVE: To compare low molecular weight heparin and external pneumatic compression in terms of patient preference and compliance to determine if either of these two methods is superior in postoperative thromboembolism prophylaxis of gynecologic oncology patients.

METHODS: A total of 211 patients undergoing major surgery for a suspected gynecologic malignancy were randomized to receive thromboembolism prophylaxis with either external pneumatic compression or low molecular weight heparin. Surveys regarding thromboembolism prophylaxis were completed by patients before surgery and approximately 7 days postoperatively. Patient preferences as well as reasons for patient dissatisfaction with prophylactic methods were elicited in the questionnaires. In addition, patient compliance with prophylaxis was recorded twice a day during hospitalization. Patients were not considered to be compliant with prophylaxis if the external pneumatic compression device was not functioning properly or if the administration of low molecular weight heparin was not given in a timely manner.

RESULTS: The majority of patients were satisfied with the prophylactic method that they received to the extent that they would prefer the treatment they received to one they had not necessarily experienced. The postoperative preferences of 78% of patients receiving low molecular weight heparin and 74% of those wearing external pneumatic compression corresponded to what the patients actually received as a method of thromboembolism prevention. Patient compliance with prophylaxis was noted to be inadequate in ten of 104 (9.6%) patients receiving external pneumatic compression and seven of 103 (6.8%) patients receiving low molecular weight heparin.

CONCLUSION: Pneumatic compression and low molecular weight heparin are similar both in terms of patient preference and compliance among gynecologic oncology patients receiving postoperative thromboembolism prophylaxis.

Thromboembolic complications are a frequent source of morbidity and comprise a significant portion of the mortality associated with gynecologic oncology surgery. Because most cases of fatal pulmonary embolism result in rapid death despite therapy, methods of prophylaxis have been used to minimize postoperative morbidity and mortality related to thromboembolism. We previously have shown that although unfractionated heparin and external pneumatic compression are similar in prophylactic efficacy, unfractionated heparin is associated with an increase in perioperative transfusion requirements.¹ Meta-analysis has suggested that low molecular weight heparin is associated with less risk of perioperative bleeding when compared with unfractionated heparin.² A recent comparison of low molecular weight heparin and external pneumatic compression by our group did not reveal an increased rate of bleeding. If the complication rate is similar between these two prophylactic modalities, differences in patient preference or compliance may assist in determining which of the two methods is superior. The purpose of this randomized prospective trial was to compare patient preference and compliance among patients receiving external pneumatic compression versus low molecular weight heparin.

	MATERIALS AND METHODS

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A prospective randomized trial approved by the Duke Institutional Review Board was conducted by our group to compare external pneumatic compression and low molecular weight heparin in terms of complications, patient preferences, and compliance. A comparison of complications and thromboembolic outcomes related to prophylaxis has been previously reported separately.³ In this investigation, 211 women 40 years or older with a suspected gynecologic malignancy meeting eligibility criteria were randomized to either external pneumatic compression or low molecular weight heparin, dalteparin (5000 U daily) postoperatively. Computer-generated randomization was performed by the clinical research office of the Duke Comprehensive Cancer Center. Patients were continued on prophylaxis until ambulatory or until day of discharge. Preoperative and postoperative patient surveys were completed by all patients and compared.

A preoperative patient survey was developed that assessed patients’ prior experiences with thromboembolism prophylaxis and preference before receiving external pneumatic compression or low molecular weight heparin. The preoperative survey assessed patients’ attitudes toward injections with five questions: 1. Does getting a injection make you anxious?; 2. Do you try to avoid getting injections?; 3. Are you fearful or afraid when you receive an injection?; 4. Are injections painful experiences for you?; and 5. Are injections unpleasant experiences for you?. Respondents responded on a 6-point scale ranging from "all of the time" to "none of the time." Each of the five questions was scored from 1 to 6 with higher scores corresponding to a more positive attitude about shots. A mean of the question scores was calculated for each patient as a measure of attitude toward injections. The Cronbach calculated for these items in a pilot study of the first ten patients and the complete series of 207 patients was more than 0.90, indicating the scale had excellent internal consistency. As part of the preoperative survey, patients were asked about 1) previous experiences with medical monitoring equipment, and 2) previous experiences with low molecular weight heparin and/or external pneumatic compression for the prevention of deep vein thrombosis. Finally, the survey asked patients to indicate whether they would prefer low molecular weight heparin or external pneumatic compression if they were given the opportunity to choose the method of prophylaxis.

The research nurse administered the preoperative survey to the majority of patients at the clinic visit before their surgery. Although in most cases the research nurse obtained informed consent for participation in the randomized trial at this time, the nurse and patients had no knowledge of their assignment to either low molecular weight heparin or external pneumatic compression at the time of survey administration.

Postoperative compliance with prophylaxis was measured twice a day. In patients with external pneumatic compression, the correct application of compression sleeves, connection of tubing, and functioning of the compressor were assessed by physicians during morning and evening rounds. The patient was not considered to be compliant if the machine were not evaluable at that time. For patients who were ambulating or bathing at the time of evaluation, the device was not checked. Patients receiving low molecular weight heparin were similarly assessed for timely administration of daily injections as an indirect measure of compliance. The patient receiving low molecular weight heparin was not compliant with prophylaxis if injections were administered later than 60 minutes of the scheduled time.

A postoperative patient preference survey was developed to assess patients’ experience with the preventative method to which they were randomized (ie, low molecular weight heparin or external pneumatic compression) and their postoperative preference for either modality. The postoperative survey, in addition to reevaluating patient preference, also addressed specific reasons for patient dissatisfaction. The research nurse administered the postoperative survey to patients within 7–10 days of surgery. Most of these surveys were completed by telephone because the majority of patients were discharged from the hospital by this point in their recovery.

Study participants were asked to indicate their preference for one of two prophylactic methods: external pneumatic compression and low molecular weight heparin. We assumed that the probability was 0.5 that patients would prefer low molecular weight heparin and 0.5 that patients would prefer external pneumatic compression. However, we hypothesized that a significantly greater proportion of patients than 0.5 would prefer low molecular weight heparin to external pneumatic compression because of the convenience of low molecular weight heparin. Therefore, the primary hypothesis tested was the following:

where p_LMWH is the proportion of women who indicate a preference for low molecular weight heparin at pre- or postsurgery. We tested this hypothesis using a one-sample z test. Assuming 200 patients, a one-tailed test, and an level of 0.05, we estimated 89% power to detect a true proportion of 0.6. We assumed that randomization was effective in eliminating any potential confounding variables. However, to gain confidence in this assumption before testing the primary hypothesis, we used the t test for differences in means of independent observations to test the hypothesis that there were no differences between the study groups in their attitudes toward shots.

We used the ² test of association to test the hypotheses that there were no differences between the study groups in the proportion of patients who had previous experience with medical monitoring devices, external pneumatic compression for prevention of blood clots, and/or low molecular weight heparin for the prevention of blood clots. Because interim analysis compliance had been measured during the study, the level for all statistical tests of compliance was set at P < .01.

	RESULTS

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Complete preoperative and postoperative preference data were available for 207 of the 211 patients participating in the trial. The four patients excluded from the preference analysis consisted of one patient lost to follow-up and three patients who were discharged to a nursing care facility in a confused state preventing an accurate completion of the postoperative survey. Of the remaining 207 patients, 103 randomized to the low molecular weight heparin group, and 104 were assigned to the external pneumatic compression group. Pretreatment characteristics were similar between the two groups, as illustrated in Table 1. The median age of the study population was 61 years. One patient who was 35 was mistakenly entered into the investigation, and this error was acknowledged after collection of data. The patient was not excluded because of intent-to-treat principles. The patients were mostly white with a median weight of 72 kg.

The majority of patients in the low molecular weight heparin group (92%) received prophylaxis for 3 days or more. A total of 4% of patients reported either swelling, pain, or anxiety related to low molecular weight heparin prophylaxis. Approximately 93% of patients assigned to the external pneumatic compression group continued prophylaxis for 3 days or more. A small proportion of patients (11%) indicated that they removed the compression sleeves when the nurse was not in the room. Patients also reported problems associated with the device 14% of the time. The pump was not turned on in the majority of these cases. The most common side effect reported by patients given external pneumatic compression was excessive perspiration. A total of 26% of patients experienced discomfort, inconvenience, problems and/or side effects related to the external pneumatic compression (Table 2).

	DISCUSSION

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Our results failed to show that patients preferred low molecular weight heparin to external pneumatic compression preoperatively or postoperatively. Previous experiences with medical monitoring equipment or with either external pneumatic compression or injections did not contribute to patient preference. The level of anxiety related to injections did not differ between the two groups, eliminating this experience as a bias in our conclusions. The majority of patients (76%) preferred the method of prevention that they received. Of these patients, 32% (49% of the total patients) apparently were satisfied with the method of prevention that they received to such an extent that they reversed their preoperative preference postoperatively. The postoperative survey did not ask patients to explain the reason for their preference, and no consistent pattern emerged to explain why 24% of patients did not prefer the method of prevention that they received. Most of these patients retained their preoperative preference. Patient satisfaction with a particular prophylactic modality did not appear to be related to the type of surgical procedure performed.

Despite our inability to demonstrate patient preference for either prophylactic modality, the results indicated that approximately 25% of patients experience some discomfort, inconvenience, or problems with the external pneumatic compression as opposed to only 4% of patients receiving low molecular weight heparin. Although this difference is not statistically significant, the trend suggests that low molecular weight heparin may be less problematic for some patients. Despite the difference in patient perception of problems, postoperative preference did not appear to be affected.

If efficacy, complications, and patient preference are similar between external pneumatic compression and low molecular weight heparin in the postoperative prophylaxis of gynecologic oncology patients, then compliance may be an important determinant of which is the optimal method of prophylaxis. In this investigation, compliance was found to be optimal in 93% of patients receiving external pneumatic compression and 95% of patients receiving low molecular weight heparin (P > .05). Prior descriptive reports of external pneumatic compression compliance in general surgery patients have noted improper functioning of the device has been observed in 52% of patients on routine nursing units and 22% of patients in the intensive care setting.⁴ When compliance with external pneumatic compression was evaluated in this study using the total number of patient examinations, the level of optimal prophylaxis was 97%. Our nursing and physician staff are aware of the need to maintain the optimal functional status of the external pneumatic compression device and have made a commitment to successfully achieve this objective. Not all health care settings can be expected to have as good a compliance rate with external pneumatic compression, and low molecular weight heparin may be better suited towards thromboembolism prophylaxis in these situations. Eleven percent of patients in our study reported removing the external pneumatic compression when the nurse was out of the room, indicating a potential source for inappropriate use of the external pneumatic compression that might diminish its effectiveness. Although this potentially harmful effect may not have affected patient preference, it may have important implications for physician preference in selection of postoperative thromboembolism prophylaxis. On the other hand, we must acknowledge that the effect of compliance with external pneumatic compression and overall outcome is unknown. It may be that using external pneumatic compression for 50% of the time is effective. Future studies are needed to clarify this issue.

In health care settings where compliance is high, cost-effectiveness should be considered in selecting the most appropriate method of prophylaxis. A previous cost analysis by our group was performed comparing external pneumatic compression, unfractionated heparin, and low molecular weight heparin.⁵ Although both low molecular weight heparin and unfractionated heparin were cost-effective compared with no prophylaxis, each was less effective than external pneumatic compression in the base case. The results of the analysis were sensitive to assumptions about the relative risk of deep vein thrombosis, the life expectancy of the patient, the costs of future treatment, and the relative effectiveness of the different strategies: if unfractionated heparin or low molecular weight heparin is even at least 2–3% more effective than external pneumatic compression, then the incremental cost per life-year of either would be less than $50,000 compared with external pneumatic compression.⁵

The majority of patients are satisfied with the method of thromboembolism prophylaxis that they receive. In health care settings where compliance with external pneumatic compression is suboptimal, low molecular weight heparin may provide an alternative method of prophylaxis. In clinical environments where external pneumatic compression can be provided with acceptable compliance, the lower cost associated with this prophylaxis would indicate that external pneumatic compression is the optimal method of prevention.

	Footnotes

 
This study was supported in part by an unrestricted educational grant from Upjohn-Pharmacia and Venodyne.

PII S0029-7844(02)02162-2

Received November 27, 2001. Received in revised form March 7, 2002. Accepted March 21, 2002.

	REFERENCES

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1. Clarke-Pearson DL, Synan IS, Dodge R, Soper JT, Berchuck A, Coleman RE. A randomized trial of low-dose heparin and intermittent pneumatic calf compression for the prevention of deep venous thrombosis following gynecologic oncology surgery. Am J Obstet Gynecol 1993;168: 1146–53.[Medline]

2. Lensing AWA, Prins MH, Davidson BL, Hirsh J. Treatment of deep venous thrombosis with low-molecular-weight heparins. Arch Intern Med 1995;155:601–7.[Abstract]

3. Maxwell GL, Synan I, Carney M, Carol B, Dodge R, Clarke-Pearson DL. A prospective randomized trial comparing external pneumatic calf compression stockings to low molecular weight heparin in the prevention of venous thromboembolic events among gynecological oncology patients. Obstet Gynecol 2001;98:989–95.[Abstract/Free Full Text]

4. Comerota AJ, Katz ML, White JV. Why does prophylaxis with external pneumatic compression for deep vein thrombosis fail? Am J Surg 1992;164:265–8.[Medline]

5. Maxwell GL, Myers E, Clarke-Pearson DL. Cost effectiveness of deep venous thrombosis prophylaxis using pneumatic compression, low-dose heparin or low molecular weight heparin in gynecologic surgery. Obstet Gynecol 2000;95:206–14.[Abstract/Free Full Text]

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