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Patterns of Referral for Inferior Vena Caval Filtration: Delays and Their Impact

¹ All authors: Department of Radiology, The University of Chicago Hospitals, 5841 S Maryland Ave, MC 2026, Chicago, IL 60637.

Received August 4, 2003; accepted after revision April 6, 2004.

 
Address correspondence to B. Funaki (bfunaki{at}midway.uchicago.edu).

Abstract

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OBJECTIVE. We sought to study the referral patterns for inferior vena caval filtration and explore the relationship between delays in filter insertion and clinical outcomes.

MATERIALS AND METHODS. We retrospectively reviewed 101 consecutive inferior vena caval filters inserted in 101 patients in a university hospital between the June 2000 and July 2001. A time line was created listing the time of diagnosis of deep venous thrombosis or pulmonary embolism, contraindication or complication of anticoagulation therapy, and time of insertion of inferior vena caval filter.

RESULTS. The average elapsed time between the clinical indication for caval filtration and filter placement in all patients was 1.64 days (range, 0–17 days). Two patients (2%) sustained pulmonary emboli after being diagnosed with deep venous thrombosis before receiving a filter. The lengths of time between filter indication and insertion for these patients were 2 and 8 days.

CONCLUSION. In our hospital, there are wide variations in perceived urgency of vena caval filtration. In two patients, delays longer than 24 hr between indication and insertion of inferior vena caval filters resulted in symptomatic pulmonary emboli.

Introduction

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Since its introduction in 1973, the inferior vena caval (IVC) filter has become the preferred prophylaxis for pulmonary embolism in patients with deep venous thrombosis or with contraindications to anticoagulation therapy [1–4]. Many studies have documented the safety and efficacy of IVC filters [5–12], although the utility of the filters is not universally accepted. Very little data exist regarding referral patterns for caval filtration from primary care physicians, particularly with respect to the timing of IVC filter placement when unambiguous indications exist.

The purpose of this study was twofold. First, we sought to compare the time of filter insertion with respect to the time of filter indication in patients admitted to a university hospital with clear indications for IVC filtration and to explore the clinical impact of delays between indication and insertion in terms of inhospital patient morbidity and mortality.

Materials and Methods

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Our retrospective study was approved by the institutional review board of our hospital. Between the months of June 2000 and July 2001, 101 consecutive IVC filters were placed in 101 patients. A retrospective review of the medical records including discharge summaries, inpatient progress notes, laboratory values, and imaging reports for these patients was performed. Fourteen patients were excluded from the study: 11 patients received filters electively before undergoing high-risk surgery (none of whom had documented pulmonary embolism or deep venous thrombosis), two patients with deep venous thrombosis documented in the medical records had diagnoses made at an outside institution at indeterminate times and dates, and one patient had no documented indication for IVC filtration. None of the patients excluded from the study was diagnosed with deep venous thrombosis or pulmonary embolism at our institution.

Of the remaining 87 patients (30 men and 57 women; age range, 25–91 years, mean, 62.6 years) included in this study, 39 patients (45%) had a previously established contraindication to anticoagulation therapy, and 48 patients (55%) received anticoagulation treatment in-house before failing to respond to or developing a complication of anticoagulation therapy (Table 1). In the latter group, 39 patients developed a complication attributed to anticoagulation, and nine patients developed new deep venous thrombosis or pulmonary embolism while receiving anticoagulation therapy. In this latter group of nine patients, only five patients had adequate levels of anticoagulation achieved.

Diagnoses of pulmonary embolism and deep venous thrombosis were made using CT, ventilation–perfusion scanning, and duplex sonography. Using a Lightspeed QX/i helical CT scanner (GE Healthcare), we evaluated pulmonary arteries up to and including the segmental vessels from the bases to the apices of the lungs. The patients were examined during suspended inspiration when possible. A total volume of 125 mL of nonionic contrast material was injected at a rate of 4 mL/sec. Imaging began 15–25 sec after initiation of the contrast material injection with parameters of 1.25-mm collimation, 120 kV, 200 mA, and a 2.0-mm pitch. The images were reconstructed at 1.25-mm intervals. On examination at soft-copy workstations, we defined a clot as being present if contrast material outlined a central intraluminal defect or if a vessel was totally occluded by low-attenuation material. The veins between the pelvis and the popliteal fossa were then examined for deep venous thrombosis. On a ventilation–perfusion scan, pulmonary embolism was diagnosed when the scan was deemed to indicate a high probability of embolism using the revised Prospective Investigation of Pulmonary Embolism Diagnosis criteria [13]—two or more large mismatched segmental defects without a radiographic abnormality or any equivalent combination of mismatched defects. If the scan indicated a low or intermediate probability of embolism, then duplex sonography was performed. This procedure consisted of real-time examination of the common femoral, superficial femoral, and popliteal veins, and deep venous thrombosis was diagnosed by failure to compress veins on gray-scale imaging or by visualization of thrombus or absence of flow on color Doppler sonography [14].

Thirteen patients (15%) were diagnosed with deep venous thrombosis and pulmonary embolism. Both diagnoses were made on the basis of CT findings in five patients, and deep venous thrombosis and pulmonary embolism were diagnosed using sonography and CT, respectively, in five patients. We are unaware of the diagnostic tests used to diagnose deep venous thrombosis or pulmonary embolism in three patients. An additional 13 patients (15%) were diagnosed with pulmonary embolism alone; nine were diagnosed with CT and four were diagnosed with ventilation–perfusion scanning. Another 61 patients (70%) were diagnosed with deep venous thrombosis alone; the diagnosis was made with sonography in 50 patients, CT in nine patients, and history and physical examination in one patient. We were unable to determine the diagnostic test used in one patient.

The character of deep venous thrombosis and pulmonary embolism in this series is largely unknown. The extent of deep venous thrombosis was not recorded except for the extension of femoral deep venous thrombosis into the pelvis. The length of time that the deep venous thrombosis had been present was also not recorded. No attempt was made to quantify chronicity of deep venous thrombosis or pulmonary embolism in our series. When deep venous thrombosis or pulmonary embolism was diagnosed, the age of the clots was not determined because CT and sonography cannot be used to accurately determine the chronicity of clot with appreciable specificity. Additionally, 13 patients were admitted to our hospital while taking anticoagulants; therefore, the duration of anticoagulant therapy is not known or obtainable.

A time line was created including the following data points: the time of diagnosis of deep venous thrombosis or pulmonary embolism, time of contraindication or complication of anticoagulation therapy, and insertion of IVC filter. In patients who initially received anticoagulation medication, the time that coagulation parameters (i.e., international normalized ratio, prothrombin time, and activated partial thromboplastin time) normalized was used to determine the time that the need for the IVC filter was indicated. In patients with known contraindications to anticoagulation medications, the time of filter indication was the same time as the diagnosis of deep venous thrombosis or pulmonary embolism. The primary outcome measure was the presence or absence of new pulmonary embolism between the times of filter indication and insertion. This information was determined by noting clinical signs and symptoms and subsequent diagnostic studies. We used the two-sample Student's t test to compare the mean elapsed times between two groups and the z test to compare proportions.

Results

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All IVC filters were inserted in the interventional radiology section of our hospital within 3 hr of request, regardless of the time of day. Delays longer than 3 hr were attributed to clinical decision making in all cases, and reasons for delays in filter insertion were not documented in medical records. Deep venous thrombosis and pulmonary embolism were untreated during the delays. The average elapsed time between the clinical indication for IVC filter and insertion in all patients was 1.64 days (range, 0–17.10 days; Fig. 1). Forty-nine patients (56%) had filters placed within 12 hr of indication. When the two patient groups were viewed separately, the average delay for the group with contraindications to anticoagulation therapy was 2.21 days versus 1.18 days (p = 0.14) in the group that failed to respond to anticoagulation therapy. There was no significant difference in delays between patients with pulmonary embolism (1.61 days) and patients with deep venous thrombosis (1.66 days, p = 0.94). The average elapsed time between filter indication and insertion for patients younger than 60 years and older than 60 years was 2.49 days and 0.98 days (p = 0.042), respectively.

View larger version (9K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —Bar graph depicts elapsed time between indication for inferior vena caval filter and filter placement in 87 patients. = patients whose indication for filter insertion was failure to respond to anticoagulation therapy, = patients whose indication for filter insertion was contraindication to use of anticoagulants.

Two patients (2%) received an IVC filter rather than anticoagulation therapy because of free-floating femoral thrombi. Nine (10%) of the filters were inserted during after-hours filter placement (defined as placements performed between 5:00 pm and 7:30 am Monday through Friday and all day Saturday and Sunday). Seven were inserted the same day as was clinically indicated, one was inserted during the night of the subsequent day, and one was inserted 1 week later. No significant difference was found between groups who had filters placed during the day or night with respect to age, sex, or delay.

Two patients (2%) sustained a pulmonary embolism after being diagnosed with deep venous thrombosis and before receiving an IVC filter. Neither had symptoms or a history of pulmonary embolism before hospitalization, and both survived. The first patient, an 81-year-old woman, was diagnosed with deep venous thrombosis at 12:00 pm on a Saturday, and the filter was placed at 3:30 pm on the following Monday (elapsed time, 2.15 days). This patient became symptomatic immediately before filter placement, with a decrease in blood pressure and an increase in respiratory distress. A CT examination confirmed the presence of a saddle embolus. This patient's admission diagnosis was bilateral deep venous thrombosis, and the contraindication for anticoagulation therapy was gastrointestinal bleeding from diverticulosis.

The second patient, a 25-year-old woman, experienced a pulmonary embolism 8 days after being diagnosed with upper and lower extremity deep venous thrombosis. Anticoagulation therapy was contraindicated because of bleeding from a Mallory-Weiss tear. No explanation for the delay in filter placement was recorded in the patient's records, although she was bacteremic from vancomycin-resistant enterococcus, a relative contraindication to filter insertion. After the patient developed acute shortness of breath and hypoxia, a CT examination was performed and confirmed the diagnosis of pulmonary embolism.

Discussion

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Pulmonary embolism is a major cause of morbidity and mortality [1, 15–17]. It is the most common preventable cause of death among hospital patients in the United States [18], with as many as 50,000–200,000 fatalities yearly and at least twice as many nonfatal cases [17]. Approximately 90% of all cases of pulmonary embolism originate from deep venous thrombosis of the lower limbs [19]. Anticoagulation therapy is considered the preferred therapy for deep venous thrombosis [4, 6, 17, 20]; however, as many as 30% of these patients experience recurrent pulmonary embolism despite receiving adequate anticoagulation therapy [21, 22].

The indications for emergency IVC filter insertion have never been defined, and practice patterns for filter insertion vary significantly between teaching hospitals and nonteaching hospitals [1]. The interventional radiology section in our hospital adheres to the policy that IVC filters should be placed when the diagnosis of pulmonary embolism or deep venous thrombosis is made for patients who have absolute contraindications to anticoagulation therapy or who experience new or recurrent pulmonary embolism while receiving adequate anticoagulation therapy, regardless of the time of day. Thus, it is not rare for filters to be inserted after-hours and on weekends. In this series, 10% of filters were inserted on an on-call emergency basis, and all filters were placed within 3 hr of request. The rationale for this policy is summarized by Kaufman [23]: "There is no way to predict which patients with deep vein thrombosis will have pulmonary embolism or when pulmonary embolism will occur." Nonetheless, no studies have found compelling evidence that supports the practice of urgent filter placement, and to our knowledge, there are no accepted guidelines regarding this issue. Aside from our series, there are no data whatsoever concerning the timing of filter placement and possible implications on patient morbidity or mortality, to the best of our knowledge. In the age of evidence-based medicine, data supporting these types of policies must be justified.

Other studies have noted variations in requests for procedures related to the diagnosis and prevention of pulmonary embolism. One investigator found that requests for pulmonary angiography were more frequent on Fridays than any other day [6]. He reported that Friday was also the most common day of the week for IVC filter placement (18.9%) [6]. Only 8.7% and 6.0% of procedures were performed on Saturdays and Sundays, respectively [6].

Because deep venous thrombosis develops over the course of weeks or months, some may argue that urgent placement of an IVC filter is unnecessary. In our study, delays of less than 24 hr had no apparent effect on in-hospital morbidity and mortality, but delays of longer than 1 day were associated with symptomatic pulmonary embolism in two patients. Any delay longer than 3 hr between IVC filter indication and insertion in this series was attributable to clinical decision making rather than to responsiveness of interventional radiologists. In general, our data support the practice of expeditious filter placement but the necessity of after-hours filter placement in newly diagnosed deep venous thrombosis or pulmonary embolism remains debatable.

The causes of delays in clinical decision making regarding IVC filter insertion are unknown. In no instance was the reason for delay between indication and insertion directly addressed in the patient's medical records. This oversight is interesting because delays between indication and insertion have the potential to result in patient morbidity or death. We suspect the lack of urgency shown by some clinicians reflects the lack of a consensus in the literature regarding the effectiveness of caval filtration and the absence of established guidelines as to the timing of filter insertion. Most patients had filters inserted on the same day as indicated, and in 10% of cases, the interventional radiology team was called into the hospital after hours for filter insertion, suggesting that some clinicians regard caval filtration as an emergency procedure. In contrast, other patients waited several days and, in several instances, more than 2 weeks for filter insertion.

Practice patterns regarding IVC filters vary substantially [1]. Most of the literature on this subject is either retrospective studies or case reports, leading some to argue that many indications for vena caval interruption are a matter of opinion [2, 3, 20]. In a review in the New England Journal of Medicine on the management of venous thromboembolism, Ginsberg [24] cites indications of IVC filters but notes that "there is no definite evidence of their efficacy." The first prospective, controlled clinical trial evaluating the efficacy of IVC filters found that filters were useful in preventing pulmonary embolism when used in conjunction with anticoagulants; however, there was no improvement in the overall mortality in these patients compared with the mortality of those on anticoagulants alone [25]. Furthermore, patients who received IVC filters in addition to anticoagulants experienced a twofold increase in recurrent deep venous thrombosis within 2 years compared with patients who received only anticoagulants [25]. These types of conflicting reports cast doubt on the effectiveness of caval filtration and may lead clinicians to debate filter insertion. We speculate that these debates may prolong decision making and could lead to the delays seen in this series. Although effectiveness of caval filtration may be debatable, long delays found in this series are difficult to justify because there is no advantage in delaying IVC filtration.

In our series, filters were placed more expeditiously in older patients than in younger patients. We believe that this fact may reflect a reluctance of clinicians to place filters in younger patients because of the morbidity associated with a long-term indwelling filter. In a compilation of vena caval filter data for five different filters available in the United States, Streiff [26] found the rates of inferior vena cava thrombosis ranged from 3.6% (stainless steel Greenfield filter) to 11.2% (Simon Nitinol filter) of patients. This complication predisposes patients to recurrent deep venous thrombosis and postphlebitic syndrome [22, 27, 28]. In contrast, these issues become less relevant in the older, sicker patient population.

Ours study has several weaknesses. First, it is a retrospective study with a relatively small number of patients. Additionally, a chart review study lends itself to interpretive biases concerning the patients' care. Also, the patients included in this series were only those patients who actually received filters. There may have been additional patients with clear indications for filter placement who never received a filter. The outcomes of such patients are unknown. Another weakness is our inability to document asymptomatic pulmonary embolism because no diagnostic imaging was routinely performed between indication and insertion of IVC filters. We believe that asymptomatic pulmonary emboli that occurred during the delays were probably not significant, although this view is debatable.

In summary, we found a large range in the lengths of the delays between IVC filter indication and insertion, reflecting a wide variability in perceived urgency of caval filtration among university hospital primary care physicians. In most patients, delays had no apparent effect on hospital-based morbidity or mortality. However, in two patients, symptomatic pulmonary embolism occurred after the diagnosis of deep venous thrombosis and before IVC filter insertion. Both patients had delays longer than 24 hr between the diagnosis of deep venous thrombosis and filter insertion. Presumably, timely insertion of IVC filters could have prevented pulmonary embolism in these two patients. Thus, our overall experience supports the practice of expeditious filter insertion; however, the need for after-hours filter placement remains debatable because both patients who sustained clinically proven and relevant pulmonary embolism experienced delays of greater than 24 hr between indication and insertion.

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This Article Abstract Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Henkle, G. Articles by Funaki, B. Search for Related Content PubMed PubMed Citation Articles by Henkle, G. Articles by Funaki, B. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?