Before May 15, 2001, when VQ scan was the modality of choice, emboli were evenly diagnosed in the lobar (three of six) and segmental (three of six) pulmonary arteries. When spiral CT was used (May 15, 2001, through October 31, 2003), 63.6% of the emboli were diagnosed in the main (11 of 44) and lobar (17 of 44) arteries and 36.4% in the segmental (14 of 44) and subsegmental (two of 44) pulmonary arteries. After October 31, 2003, there was an increase (p < 0.0001) in the number (64) and percentage (75.8%) of PEs being diagnosed in the segmental (54 of 85) or subsegmental (10 of 85) vasculature by MDCT, attesting to the ability of the latter imaging modality to detect smaller emboli (Fig 2).
There were wide variations in the incidence based on the year of surgery and the type of arthroplasty performed. There was an increase (p < 0.0001) in the incidence of diagnosed PE with time from 0.21% (four of 1946) in 2000 to 1.50% (36 of 2400) in 2005 (Fig 1). However, the number of CT studies increased almost 400% from 21 in 2001 to 81 in 2005, and the percent of positive tests increased during the same time from 38.1% to 44.4% (Fig 3).
Patients who had PE develop generally were older (p < 0.0001) (mean, 69.6 years; range, 36.2-90.0 years) compared with the overall population (mean, 64.1 years; range, 12-103 years). The body mass index of patients who had PE was higher (p = 0.001) (mean, 31.98 kg/m2; range, 15.8-54.0 kg/m2) compared with the body mass index of the overall population (mean, 29.95 kg/m2; range, 16.0-68.9 kg/m2).
The incidence of diagnosed PE also varied based on the type of surgical procedure the patient underwent. The incidence of PE after primary knee arthroplasty (1.90%) was higher than the incidence of PE after primary hip arthroplasty (0.58%) (p < 0.001) (Fig 4A). The incidence of PE after all knee arthroplasties combined at 1.81% was higher (p < 0.0001) than all hip arthroplasties combined at 0.56% (Fig 4A). We observed a similar incidence of diagnosed PE after primary (1.18%) and revision (0.73%) procedures. The incidence of diagnosed PE after bilateral procedures (2.11%) performed under the same anesthesia was also higher (p < 0.0001) than unilateral procedures (0.95%) for hip and knee arthroplasties (Fig 4B).
We identified three deaths related to PE accounting for an overall incidence of 0.023% for fatal PE. All deaths occurred in the hospital. Pulmonary embolism was diagnosed by CT scan in two of the patients and by VQ scan in the third. Autopsy was not performed on any of these patients because of family wishes. Despite an increase in the incidence of PE with time, there was no change in the incidence of 90-day mortality during our study.
During the last few years, despite making no alteration in surgical, anesthesia, or perioperative protocols, the incidence of diagnosed PE has increased markedly at our institution. The number of diagnosed PE has increased ninefold during a 5-year period raising serious concerns. The patient safety committee in our hospital tracking this trend called for reexamination of the current anticoagulation regimen and possible implementation of changes in line with recent published recommendations.13 Before departing from our established anticoagulation protocols with more than 20 years of proven safety and efficacy, we decided to investigate this matter further.
This study has several limitations. The study design, as a retrospective analysis of prospectively collected data, may reduce but not avoid possible recall and selection bias. Data collection and analysis of the study population did not include all the factors that may play a role in our study question. We did not include predisposing factors for PE such as previous deep vein thrombosis or PE, comorbidities, level of anticoagulation, and blood transfusions. However, we believe this would not affect our conclusions because there were no changes in our patient population or in patient care during the study period. Differentiating fat, cement, and thrombotic embolism was not possible. Therefore, we assumed patients with a diagnosis of PE had a thrombotic event, although this may overestimate the number. Nonetheless, although we believe we have identified the majority of embolic events, it is impossible to estimate the incidence of nonfatal silent or missed diagnosed PE.
We found the number of imaging investigations ordered for diagnosis of potential PE increased during the 5-year study period. The reason for the latter appeared multifactorial. With the improvements in nursing care and administration of long-acting intrathecal opioids, recording of pulse oximetry after total joint arthroplasty has become a common practice. Therefore, any drop in oxygen saturation triggered medical consultations and possible investigations for PE. The other reason for the increase in the number of investigations performed related to logistics of ordering and performing such tests. Whereas performing VQ scans required preparation, precluding its administration during the weekend or off hours at our institution, CT could be performed with relative ease and at any time.
We also observed the increase in diagnosed PE corresponded with the type of investigative imaging. The introduction of a more sophisticated imaging modality had resulted in a higher incidence of detected PE. CT scanners have been proposed as a first-line test for the diagnosis of PE.44 They have become more sensitive with the evolution from helical (spiral) CT to the more sophisticated MDCT in detecting small emboli.14,31,34,35,41 Other studies have confirmed more segmental and subsegmental emboli are detected by MDCT than spiral CT and VQ scan.4,35,41 However, regardless of the size and location of the PE, patients had prolonged anticoagulation treatment and/or inferior vena cava filter insertion.
Our data are consistent with the notion that the apparent increase in the incidence of diagnosed PE relates to the increase in the number of investigations and the improvement in the sensitivity of imaging modalities being used to diagnose PE. Thus, the increase in the incidence of diagnosed PE is a relative phenomenon because a large number of patients being diagnosed with PE currently would have not been diagnosed in the past because of not having an imaging investigation or having imaging with a less sensitive modality. We are confident regarding the latter statement because we have, despite implementing a much more stringent followup in recent years, not noted an increase in the incidence of fatal PE.
It is established that imaging tests such as MDCT with a relatively high sensitivity (90%, 96%, and 100%) and specificity (86%, 89%, and 94)6,34,50 are more likely to detect an embolus than an older imaging modality such as VQ scan. Multidetector CT currently is the preferred imaging modality for investigation of suspected PE.3,10,37,43
Multidetector CT has an exponential improvement in volume coverage speed with greater diagnostic image quality when compared with conventional spiral CT.17 It is capable of detecting and localizing small radiodense objects, which easily can be missed on axial CT.46 The fact is some of these objects, labeled as emboli, may in fact not be thrombotic in nature.16 Although the diagnosis of fat embolism by CT has been described,25 we were not able to elucidate the exact nature of the emboli seen in the segmental and subsegmental pulmonary vasculature on the CT images because no contrast medium was administered to all the patients.
We should be aware of the challenges sophisticated imaging modality in general, and modern imaging for PE in particular, will introduce to the surgical community. The introduction of MDCT started a new era in the diagnosis of PE. Computed tomography pulmonary angiography with high sensitivity and specificity is becoming the preferred imaging modality for evaluation of patients with suspected PE.40,42,47,51 Numerous institutions may witness an increase in the incidence of diagnosed PE that may be attributable to the marvel of modern imaging.
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