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Velmahos GC, Kern J, Chan L, et al. Prevention of Venous Thromboembolism After Injury. Rockville (MD): Agency for Healthcare Research and Quality (US); 2000 Nov. (Evidence Reports/Technology Assessments, No. 22.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Prevention of Venous Thromboembolism After Injury.

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3Results

Incidence of DVT and PE in Trauma Patients

Factors Affecting Reported Incidence

First, we calculated the random-effect incidences of DVT and PE after injury across all studies. Although these studies are heterogeneous in terms of their patient population and the methods used to detect DVT and PE, the technical experts believed an overall pooled estimate would still be useful, as the estimates of incidence varied widely from study to study. After preliminary analysis, we noticed that four major factors could significantly affect the reported incidences in individual studies:

  • Study design: In randomized controlled trials (RCTs), better methodologic designs often resulted in different incidences of DVT or PE relative to non-RCTs.
  • Method of diagnosis: If screening was performed routinely at predetermined time intervals, the diagnosis of DVT was made more frequently and the incidence increased relative to studies in which diagnosis was done on the basis of symptomatology or nonroutine screening.
  • Type of prophylaxis: If some form of venous thromboembolism (VT) prophylaxis was given, the reported incidence of DVT and PE was often lower than that reported in studies with no VT prophylaxis.
  • Type of trauma: Certain groups of trauma patients (e.g., spinal-cord-injured patients) had higher reported incidences of VT than did other trauma patients.

Classification of Studies According to Design, Screening, and Prophylaxis

We classified the studies according to three variables:

  • RCT or non-RCT.
  • Use of routine screening or no routine screening.
  • Type of prophylaxis.

Despite the long list of pharmaceutical and mechanical methods of prophylaxis used in the comparative studies (Table 27), the three most frequently used methods were LDH, LMWH, and mechanical devices (SCDs or AFPs). We included only these three methods in our calculations. If a study included both patients receiving prophylaxis and patients not receiving any prophylaxis, we entered data from each group separately into the appropriate category of the prophylaxis/no prophylaxis field for the calculation of DVT and PE rates. Therefore, the same study could be used in two opposite fields.

Table 27. Methods of prophylaxis employed in accepted studies.

Table

Table 27. Methods of prophylaxis employed in accepted studies.

Type of Patients Included

We also categorized the studies by patient type according to the following scheme:

1.

All studies (n=73).

2.

Studies including general trauma patients (n=33).

3.

Studies including exclusively orthopedic trauma patients (n= 0).

4.

Studies including exclusively neurosurgical trauma patients (n=26).

5.

Studies including only minor trauma patients (n=4).

Category 5 included four RCTs comparing one method of prophylaxis vs. another or vs. placebo. We retained these studies because they included patients who had lower extremity injuries not requiring operation and they did not meet our exclusion criterion of focusing on elderly patients with hip fractures. Although in a sense these studies could be grouped in the orthopedic trauma category, we decided to report them separately because of the low severity of the patients' injuries relative to average orthopedic trauma patients.

Category 2 included studies that accepted all types of trauma patients admitted in a particular trauma center and that did not focus on a certain type of injury. We attempted to differentiate severe trauma patients from general trauma patients, but the definitions of "severe trauma" in the literature varied too much to be useful for combining data. Therefore, we did not include a full analysis of incidence of DVT or PE for studies of "severe trauma" patients. However, most of the studies included patients with significant injuries. Only a few studies included the entire trauma population admitted over a period of time regardless of the severity of injury. Thus, the rates of DVT and PE given for the "general trauma" category should be close to the incidences in patients with significant injuries.

Incidence

Of 73 studies, 67 reported on DVT, 49 on PE, and 43 on both. The incidence of DVT in a total of 12,527 patients was 11.8 percent (95 percent CI: 0.104, 0.131) and the incidence of PE in 22,336 patients was 1.5 percent (95 percent CI: 0.011, 0.018). The number of patients included in the PE studies was higher than the number of patients included in the DVT studies, primarily because of one study (Winchel, Hoyt, Walsh, et al., 1994) that reported on the incidence of PE in 9,721 trauma patients discharged from one trauma center over a period of 8 years. When this study was excluded, the incidence of PE remained essentially unchanged, increasing from 1.5 percent to 1.7 percent (95 percent CI: 0.013, 0.022). For patients who received some type of prophylaxis, the rates of DVT and PE were 6.8 percent (95 percent CI: 0.053, 0.083) and 1.8 percent (95 percent CI: 0.010, 0.020), respectively. For patients who received no prophylaxis, the rates were 10.1 percent (95 percent CI: 0.062, 0.140) and 1 percent (95 percent CI: -0.008, 0.028), respectively.

Tables 28 to 31 show the different pooled rates of DVT and PE according to the method of prophylaxis. According to results from RCTs, the incidences of DVT and PE are 14.5 percent and 2.8 percent, respectively, for patients who received LDH; 5.6 percent and 0.3 percent for patients who received LMWH; 4.9 percent and 5.2 percent for patients who received mechanical prophylaxis; and 10 percent and 0.1 percent for patients who received no prophylaxis. Most of these results were extracted from heterogeneous studies and are associated with wide confidence intervals.

Table 28. Incidence of DVT and PE in different types of trauma patients who received LDH for VT prophylaxis.

Table

Table 28. Incidence of DVT and PE in different types of trauma patients who received LDH for VT prophylaxis.

Table 29. Incidence of DVT and PE in different types of trauma patients who received LMWH for VT prophylaxis.

Table

Table 29. Incidence of DVT and PE in different types of trauma patients who received LMWH for VT prophylaxis.

Table 30. Incidence of DVT and PE in different types of trauma patients who received mechanical prophylaxis for VT.

Table

Table 30. Incidence of DVT and PE in different types of trauma patients who received mechanical prophylaxis for VT.

Table 31. Incidence of DVT and PE in different types of trauma patients who received no VT prophylaxis.

Table

Table 31. Incidence of DVT and PE in different types of trauma patients who received no VT prophylaxis.

Tables 32 to 36 show the different rates of DVT and PE according to the method of prophylaxis in the four predetermined types of trauma patients (general trauma, orthopedic trauma, neurosurgical trauma, and minor trauma), as well as in all trauma patients receiving any of the three methods of prophylaxis or no prophylaxis. Only RCTs were included in the calculation of these rates in order to produce more internally valid data. The incidence of DVT and PE for patients receiving no prophylaxis was calculated from data on the placebo group in the RCTs.

Table 32. Incidence of DVT and PE in all trauma patients, included only in RCTs, who received DH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table

Table 32. Incidence of DVT and PE in all trauma patients, included only in RCTs, who received DH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table 33. Incidence of DVT and PE in general trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table

Table 33. Incidence of DVT and PE in general trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table 34. Incidence of DVT and PE in orthopedic trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table

Table 34. Incidence of DVT and PE in orthopedic trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table 35. Incidence of DVT and PE in neurosurgical trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table

Table 35. Incidence of DVT and PE in neurosurgical trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table 36. Incidence of DVT and PE in minor trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

Table

Table 36. Incidence of DVT and PE in minor trauma patients, included only in RCTs, who received LDH or LMWH or mechanical prophylaxis or no prophylaxis for VT.

It is important to recognize that the incidences calculated in Tables 28 to 36 were derived by grouping together patients of different studies who received the same methods of prophylaxis. This analysis provides only an approximate estimate of the incidence of DVT and PE associated with each method of prophylaxis. It does not allow direct comparison among different methods of prophylaxis. Heterogeneity-as demonstrated by the results of the chi-squared heterogeneity test-among studies used in the various calculations indicates the high degree of variability in these rates. Some fields also had a limited sample of patients and studies (e.g., the "minor trauma" category). Therefore, these results should be interpreted with caution (see also Chapter 5. Conclusions).

Question 1. What Is the Best Method of VT Prophylaxis?

This question was considered to be the most important by the panel of the technical experts. We meta-analyzed RCTs that used the same methods of prophylaxis. Because the number of RCTs was limited, in a second step we also meta-analyzed studies of any design (RCT and non-RCT) that included the same methods of prophylaxis.

Meta-Analysis of RCTs

Our meta-analysis of RCTs was limited by the number of studies that were sufficiently clinically homogenous to pool. Of 19 studies with a randomized design, we were able to use only six to help answer question 1. The remaining 13 studies could not be pooled for analysis (Table 37) because they all compared different treatments. These 13 randomized studies are described in Evidence Table 1. Because we chose to require at least three studies to perform each meta-analysis, there were sufficient data to make only two comparisons: LDH vs. no prophylaxis, and mechanical prophylaxis vs. no prophylaxis.

Table 37. Methods of VT prophylaxis in the 13 RCTs that were not used in the meta-analyses.

Table

Table 37. Methods of VT prophylaxis in the 13 RCTs that were not used in the meta-analyses.

LDH vs. No Prophylaxis

Four RCTs compared LDH with no prophylaxis, two each of neurosurgical trauma (spinal patients) and general trauma patients. Two RCTs were included in the same original study (Knudson, Lewis, Clinton, et al., 1994) but were evaluated separately (see Chapter 2. Methodology: Article Screen).

Merli, Herbison, Ditunno, et al. (1988) found no difference in the incidence of DVT between 16 spinal cord injured patients who received LDH and 17 similar patients who received placebo. Routine screening for DVT was performed by 125-I fibrinogen scan every week. Venography was performed if the 125-I scan was positive or at the end of the 1-month period during which each patient was studied. Patients were admitted to the study hospital within 2 weeks of injury and were excluded if they had established DVT on admission. Eight patients developed venographically proven DVT in each group (50 percent LDH vs. 46 percent placebo).

Frisbie and Sasahara (1981) included spinal-cord-injured patients received from the acute care facility within 1 week of their trauma. For 60 days, the patients were surveyed weekly by impedance plethysmography. Positive scans were confirmed by venography. The incidence of DVT was very low and equal in both groups (1/17 or 6 percent LDH vs. /15 or 7 percent no prophylaxis). This low incidence is different from that found in other reports on similar patients and suggests an unidentified prophylactic factor or difference in sensitivity in detecting DVT.

Knudson, Lewis, Clinton, et al. (1994) examined the incidence of DVT in trauma patients who had any of a number of high-risk criteria, including laparotomy, thoracotomy, ventilation greater than 24 hours, spine fracture, pelvic fracture, and femur fracture. Evaluation for DVT was performed by Duplex ultrasonography at 5- to 7-day intervals until discharge or for at least 3 consecutive weeks. Patients who could receive LDH or SCD were randomized to LDH, SCD, or no-prophylaxis (control) groups. Patients who could not receive SCD because of lower extremity fractures were randomized to LDH or control groups. Both analyses showed no difference in the incidence of DVT between patients receiving LDH and patients with no prophylaxis. In the first analysis, the incidence of DVT was 2 percent (1/44) in LDH patients and 3 percent (2/64) in controls. In the second analysis, DVT was found in 5 percent (1/19) of LDH patients and 7 percent (2/27) of controls.

The combined analysis of the pooled data from these studies (Table 38, Figure 4, Evidence Table 2) shows no difference in the incidence of DVT between patients receiving LDH and patients receiving no prophylaxis for DVT (OR: 0.965, 95 percent CI: 0.353, 2.636). The chi-squared test is not significant for heterogeneity among studies (p = 0.980).

Table 38. Rates of DVT reported in four RCTs of trauma patients, comparing LDH with no prophylaxis.

Table

Table 38. Rates of DVT reported in four RCTs of trauma patients, comparing LDH with no prophylaxis.

Figure 4. Shrinkage and funnel plots of RCTs comparing the rates of DVT in patients who received LDH or no prophylaxis.

Figure

Figure 4. Shrinkage and funnel plots of RCTs comparing the rates of DVT in patients who received LDH or no prophylaxis.

Mechanical Prophylaxis vs. No Prophylaxis

Three RCTs, two of general trauma patients and one of orthopedic trauma patients, compared mechanical prophylaxis vs. no prophylaxis. Mechanical prophylaxis was provided by SCD in all three RCTs.

Two RCTs were derived from one study (Knudson, Lewis, Clinton, et al., 1994). In trauma patients with predefined risk factors for VT, patients who could not receive LDH were randomized to either SCD or no prophylaxis. Another group of patients who did not have any contraindication to receiving LDH or SCD was randomized to LDH or SCD or no prophylaxis. Of those patients, only the ones who were randomized to SCD or no prophylaxis were included in this analysis. Duplex screening was performed weekly until discharge or for at least 3 consecutive weeks. The incidence of DVT in patients with contraindications to LDH was 0 percent for those randomized to SCD and 13 percent for those randomized to no prophylaxis (p=0.057). In patients without contraindications to LDH, the incidence was 12.5 percent for those randomized to receive SCD and 3 percent for those receiving no prophylaxis. This comparison was not statistically significant. The patients in the group who had contraindications to LDH were predominantly neurotrauma patients, whereas most patients in the group without contraindications did not have significant head or spinal-cord injuries. This study did not provide any additional data comparing patient characteristics between the two RCTs.

The dissimilar magnitudes of the differences in DVT rates between patients receiving SCD and patients receiving no prophylaxis across the two RCTs (0 percent vs. 13 percent in one RCT, but 12.5 percent vs. 3 percent in the other RCT) resulted from either or both of the following: (1) the first RCT included mostly neurotrauma patients and the other did not, and SCD offers good prophylaxis against DVT only in neurotrauma patients; or (2) the difference in DVT rates in the first RCT was almost significant, and in the other it was not; with adequate numbers to achieve statistical significance, both RCTs would show similar results.

Fisher, Blachut, Salvian, et al. (1995) reported on patients with hip and pelvic fractures. According to our predetermined criteria (see Chapter 1. Introduction: Defining Trauma Patients), only the 73 patients with pelvic fractures were included in our analysis. Duplex screening was performed every 5 days until the patient was ambulating. Thirty-five patients were randomized to the SCD group and one developed DVT, whereas 38 were randomized to the no-prophylaxis group and three developed DVT (3 percent vs. 8 percent, p=0.24). It should be noted that patients with severe trauma were not managed primarily by the authors, who belonged to the orthopedic service; therefore, those patients were excluded from the study.

Overall, the analysis of the pooled data from these three RCTs (Table 39, Figure 5, Evidence Table 3) showed no difference in DVT rates between patients who received treatment with SCDs and those who did not (OR: 0.769, 95 percent CI: 0.265, 2.236). Because the confidence interval is very wide, a significant effect cannot be excluded. The chi-squared test approaches but does not reach statistical significance for heterogeneity among these studies (p=0.061).

Table 39. Rates of DVT reported in three RCTs of trauma patients, comparing mechanical prophylaxis (MP) with no prophylaxis.

Table

Table 39. Rates of DVT reported in three RCTs of trauma patients, comparing mechanical prophylaxis (MP) with no prophylaxis.

Figure 5. Shrinkage and funnel plots of RCTs comparing the rates of DVT in patients who received mechanical prophylaxis or no prophylaxis.

Figure

Figure 5. Shrinkage and funnel plots of RCTs comparing the rates of DVT in patients who received mechanical prophylaxis or no prophylaxis.

Publication Bias Evaluation of Both Analyses

Funnel plots were created for both analyses (LDH vs. no prophylaxis and mechanical prophylaxis vs. no prophylaxis). They did not show any evidence of publication bias, but the small number of studies makes it difficult to draw firm conclusions from the funnel plots.

Meta-Analysis of RCTs and Non-RCTs

Because the number of RCTs was limited, we decided to perform a meta-analysis of the data using non-RCTs. Pooled analysis including observational data is inherently more prone to bias than is analysis of RCT-only data, and these results should be viewed with caution. However, this analysis may provide additional information about the roles of different method of prophylaxis.

We were able to make four comparisons: LDH vs. LMWH, LDH vs. mechanical prophylaxis, mechanical prophylaxis vs. no treatment, and LDH vs. no treatment. In the LDH vs. LMWH comparison, the outcome was PE because one of the three studies did not report DVT; DVT was the measured outcome in the other comparisons.

LDH vs. LMWH (for PE)

Three studies-two RCTs and one non-RCT (retrospective review)-were included in this analysis. One of these studies (Geerts, Jay, Code, et al., 1996) was the highest quality RCT in the trauma literature (Quality Score of 5, the highest possible score for RCTs). The authors of this study included major trauma patients (Injury Severity Score >9) and screened all patients by venography. Evaluation for PE was based on clinical suspicion and consisted mainly of ventilation/perfusion scan and, if needed, pulmonary angiography. One hundred thirty-four patients received LDH and 129 received LMWH. The incidence of DVT was 44 percent (60/134) in the LDH group and 31 percent (40/129) in the LMWH group, whereas the incidence of proximal DVT was 15 percent (20/134) and 6 percent (8/129) in the LDH and LMWH groups, respectively. The incidence of PE was 0 percent in the LDH group and 0.7 percent (1/129) in the LMWH group. The differences in the incidence of DVT and proximal DVT, but not PE, were statistically significant and favored LMWH. There were no fatal PEs in this study.

Green, Lee, Lim, et al. (1990) evaluated 41 spinal-cord-injured patients for thrombotic events following random administration of two prophylactic regimens: LDH (21 patients) and LWMH (20 patients). The patients were screened by impedance plethysmography and Duplex ultrasonography for 8 weeks. Of LDH patients, three (15 percent) developed proximal DVT and two (10 percent) developed fatal PE. No LMWH patients developed DVT or PE.

The non-RCT (Green, Twardowski, Wei, et al., 1994) included 51 patients with spinal-cord injuries. Nine of them suffered fatal PE. The incidence of PE in 22 patients who received LDH was 32 percent (7 patients) and in 27 patients who received LMWH was 7 percent (2 patients).

The meta-analysis of the pooled data from these three studies (Table 40, Figure 6, Evidence Table 4) shows no difference in PE rates in patients receiving LDH and those receiving LMWH (OR: 3.010, 95 percent CI: 0.585, 15.485). The confidence interval is very wide; therefore, a significant effect cannot be excluded. The chi-squared test indicates that the studies are not heterogeneous (p=0.275).

Table 40. Rates of PE reported in three studies (two RCT, one non-RCT) of trauma patients, comparing LMWH to LDH.

Table

Table 40. Rates of PE reported in three studies (two RCT, one non-RCT) of trauma patients, comparing LMWH to LDH.

Figure 6. Shrinkage plot of RCTs and non-RCTs comparing PE rates in patients who received LDH or LMWH.

Figure

Figure 6. Shrinkage plot of RCTs and non-RCTs comparing PE rates in patients who received LDH or LMWH.

Two of the three studies evaluated DVT as an outcome (Geerts, Jay, Code, et al., 1996; Green, Lee, Lim, et al., 1990). In both studies, LMWH was associated with lower DVT rates relative to LDH. However, meta-analysis was not performed because we required at least three studies to perform meta-analysis.

LDH vs. Mechanical Prophylaxis

We identified four studies (two RCTs and two non-RCTs) comparing these two methods. Knudson, Collins, Goodman, et al. (1992) randomized 113 trauma patients to receive either LDH or SCD. The patients were screened by venous Doppler ultrasonography every 5 days for 3 weeks or until discharge. DVT was found in 3 of 37 LDH patients (8 percent) and 5 of 76 SCD patients (7 percent). Obviously, the discrepancy between the number of patients included in each of the two randomization groups is problematic.

In another study including three separate RCTs (as described in previous sections of this document), Knudson, Lewis, Clinton, et al. (1994) examined the incidence of DVT in trauma patients at risk for DVT. In one of these RCTs, the patients were randomized to LDH, mechanical prophylaxis, or no prophylaxis. The incidence of DVT in LDH patients was 2 percent (1 of 44 patients) and in SCD patients, 12.5 percent (4 of 32 patients). Two of 64 patients assigned to the no-prophylaxis group developed DVT (3 percent).

Dennis, Menawat, Von Thron, et al. (1993) attempted a randomized study on prophylaxis vs. no prophylaxis. Patients received prophylaxis by LDH or SCD. However, many patients were switched from their initial random assignment to the no-prophylaxis group to the SCD group at the discretion of the attending surgeon. Therefore, three nonrandom groups were created: LDH (92 patients), SCD (189 patients), and no prophylaxis (114 patients). DVT screening was done by venous Doppler or Duplex ultrasonography every 5 days. The incidence of DVT was 3 percent for LDH and SCD patients and 9 percent for the no-prophylaxis group.

Headrick, Barker, and Pate (1997) prospectively evaluated a cohort of 228 trauma patients who required bed rest of more than 3 days or had a lower extremity, pelvic, or spinal fracture with paralysis. In an nonrandom manner, patients received LDH (20 patients), SCD (130), both (54), or none (24). They were screened by venous Duplex ultrasonography on a weekly basis. The incidence of DVT for the four groups was 25 percent (5 patients), 14 percent (18 patients), 19 percent (10 patients), and 25 percent (6 patients), respectively.

Cumulatively, the meta-analysis (Table 41, Figure 7, Evidence Table 5) shows no difference in the incidence of DVT between patients receiving LDH and those receiving mechanical prophylaxis (OR: 1.161, 95 percent CI: 0.495, 2.723). The chi-squared test is not significant for heterogeneity among studies (p=0.267).

Table 41. Rates of DVT reported in four studies (two RCT and two non-RCT) of trauma patients, comparing LDH to mechanical prophylaxis.

Table

Table 41. Rates of DVT reported in four studies (two RCT and two non-RCT) of trauma patients, comparing LDH to mechanical prophylaxis.

Figure 7. Shrinkage plot of RCTs and non-RCTs comparing the rates of DVT in patients who received LDH or mechanical prophylaxis.

Figure

Figure 7. Shrinkage plot of RCTs and non-RCTs comparing the rates of DVT in patients who received LDH or mechanical prophylaxis.

Mechanical Prophylaxis vs. No Prophylaxis

In addition to the three RCTs described above in the initial meta-analysis of RCTs only, we found two more non-RCT studies comparing mechanical prophylaxis with no prophylaxis. Both of these studies (Dennis, Menawat, Von Thron, et al., 1993; Headrick, Barker, and Pate, 1997) were described in the LDH vs. mechanical prophylaxis comparison above. These two studies had LDH, SCD, and no-prophylaxis groups. The two latter groups from each study were included in this analysis.

The meta-analysis of the pooled data from these four studies (Table 42, Figure 8, Evidence Table 6) shows no difference in the incidence of DVT between patients using SCD and those not receiving any DVT prophylaxis (OR: 0.527, 95 percent CI: 0.190, 1.460). The chi-squared test is not significant for heterogeneity among studies (p=0.092).

Table 42. Rates of DVT reported in five studies (three RCT and two non-RCT) of trauma patients, comparing mechanical prophylaxis to no prophylaxis.

Table

Table 42. Rates of DVT reported in five studies (three RCT and two non-RCT) of trauma patients, comparing mechanical prophylaxis to no prophylaxis.

Figure 8. Shrinkage plot of RCTs and non-RCTs comparing the rates of DVT in patients who received mechanical prophylaxis or no prophylaxis.

Figure

Figure 8. Shrinkage plot of RCTs and non-RCTs comparing the rates of DVT in patients who received mechanical prophylaxis or no prophylaxis.

LDH vs. No Prophylaxis

In this analysis, we included the four RCTs described in the previous section of meta-analysis dealing with RCTs only and three additional non-RCTs. Two of these non-RCTs are described above (Dennis, Menawat, Von Thron, et al., 1993; Headrick, Barker, and Pate, 1997). Of the three nonrandomized groups of patients found in these studies (LDH, SCD, no prophylaxis), the LDH and no prophylaxis groups were used for this analysis.

In the third non-RCT, Ruiz, Hill, and Berry (1991) prospectively evaluated 100 multiple trauma patients with an Injury Severity Score greater than or equal to 10 and followed up these patients by venous Duplex ultrasonography on days 1, 3, 6, 10, and 21 or until discharge. At the discretion of the surgeon, 50 patients received LDH and 14 of them developed DVT (28 percent); 50 patients received no prophylaxis and one of them developed DVT (2 percent). Obviously, the patients who were selected to receive prophylaxis were at greater risk for the development of DVT.

This meta-analysis (Table 43, Figure 9, Evidence Table 7) shows that there is no difference in the incidence of DVT between patients receiving LDH and those receiving no prophylaxis (OR: 1.033, 95 percent CI: 0.360, 2.965). The chi-squared test for heterogeneity shows that these studies are heterogeneous (p=0.020).

Table 43. Rates of DVT reported in seven studies (four RCT and three non-RCT) of trauma patients, comparing LDH to no prophylaxis.

Table

Table 43. Rates of DVT reported in seven studies (four RCT and three non-RCT) of trauma patients, comparing LDH to no prophylaxis.

Figure 9. Shrinkage plot of RCTs and non-RCTs, comparing rates of DVT in patients who received LDH or no prophylaxis.

Figure

Figure 9. Shrinkage plot of RCTs and non-RCTs, comparing rates of DVT in patients who received LDH or no prophylaxis.

Publication Bias

We produced funnel plots for all four comparisons described in the RCT and non-RCT meta-analysis, which indicated that there may have been publication bias in comparisons of LDH versus no prophylaxis. However, reliable conclusions cannot be drawn because of the limited number of studies. These funnel plots are not reported here.

Question 2: What Groups of Patients Are at High Risk of Developing VT?

We considered all studies including risk factors for analysis, regardless of study design. Different authors reported numerous risk factors, but we only analyzed risk factors reported in at least three studies.

We treated the risk factors as either dichotomous or continuous variables according to the data provided. For instance, if three or more studies provided data on VT incidence for patients who were younger or older than 55 years old, then the risk factor of "age >55" was considered a dichotomous value. Other studies provided only the age (mean and standard deviation) of patients with and without DVT but did not use a specific age cutoff point. We combined these data and examined the risk factor "age" as a continuous variable.

Risk Factors as Dichotomous Variables

We analyzed the following variables:

A number of studies included age as a risk factor, but the different cutoff points used in each study (age >30, 40, 50, 55, etc.) did not allow analysis of this variable. For the above six risk factors, Tables 44 to 49 report the DVT rates and Figures 10 to 15 provide the graphic representation of the meta-analysis of these studies with the corresponding funnel plots. The six corresponding evidence tables (Evidence Tables 8 to 13) describe these studies. The only risk factors found to place the patient at higher risk for development of DVT are spinal fracture (OR: 2.260, 95 percent CI: 1.415, 3.610) and spinal-cord injury (OR: 3.107, 95 percent CI: 1.794, 5.381). The chi-squared heterogeneity test indicates that only the studies used to evaluate long-bone fractures are heterogeneous (p=0.000). For all other comparisons, the chi-squared test is not significant for heterogeneity among studies.

Table 44. Rates of DVT reported in four studies comparing male vs. female patients (using gender as a risk factor).

Table

Table 44. Rates of DVT reported in four studies comparing male vs. female patients (using gender as a risk factor).

Table 45. Rates of DVT reported in eight studies comparing patients with head injury vs. patients without head injury (using head injury as a risk factor).

Table

Table 45. Rates of DVT reported in eight studies comparing patients with head injury vs. patients without head injury (using head injury as a risk factor).

Table 46. Rates of DVT reported in 12 studies comparing patients with long-bone fractures vs. patients without long-bone fractures (using long-bone fractures as a risk factor).

Table

Table 46. Rates of DVT reported in 12 studies comparing patients with long-bone fractures vs. patients without long-bone fractures (using long-bone fractures as a risk factor).

Table 47. Rates of DVT reported in eight studies comparing patients with pelvic fractures vs. patients without pelvic fractures (using pelvic fractures as a risk factor).

Table

Table 47. Rates of DVT reported in eight studies comparing patients with pelvic fractures vs. patients without pelvic fractures (using pelvic fractures as a risk factor).

Table 48. Rates of DVT reported in 10 studies comparing patients with spinal fractures vs. patients without spinal fracture (using spinal fracture as a risk factor).

Table

Table 48. Rates of DVT reported in 10 studies comparing patients with spinal fractures vs. patients without spinal fracture (using spinal fracture as a risk factor).

Table 49. Rates of DVT reported in five studies comparing patients with spinal-cord injury vs. patients without spinal-cord injury (using spinal-cord injury as a risk factor).

Table

Table 49. Rates of DVT reported in five studies comparing patients with spinal-cord injury vs. patients without spinal-cord injury (using spinal-cord injury as a risk factor).

Figure 10. Shrinkage and funnel plots of four studies comparing rates of DVT between male and female patients (using gender as a risk factor).

Figure

Figure 10. Shrinkage and funnel plots of four studies comparing rates of DVT between male and female patients (using gender as a risk factor).

Figure 11. Shrinkage and funnel plots of eight studies comparing rates of DVT between patients with and patients without head injuries (using head injuries as a risk factor).

Figure

Figure 11. Shrinkage and funnel plots of eight studies comparing rates of DVT between patients with and patients without head injuries (using head injuries as a risk factor).

Figure 12. Shrinkage and funnel plots of 12 studies comparing rates of DVT between patients with and patients without long-bone fractures (using long-bone fractures as a risk factor).

Figure

Figure 12. Shrinkage and funnel plots of 12 studies comparing rates of DVT between patients with and patients without long-bone fractures (using long-bone fractures as a risk factor).

Figure 13. Shrinkage and funnel plots of eight studies comparing rates of DVT between patients with and patients without pelvic fractures (using pelvic fractures as a risk factor).

Figure

Figure 13. Shrinkage and funnel plots of eight studies comparing rates of DVT between patients with and patients without pelvic fractures (using pelvic fractures as a risk factor).

Figure 14. Shrinkage and funnel plots of 10 studies comparing rates of DVT between patients with and patients without spinal fractures (using spinal fractures as a risk factor).

Figure

Figure 14. Shrinkage and funnel plots of 10 studies comparing rates of DVT between patients with and patients without spinal fractures (using spinal fractures as a risk factor).

Figure 15. Shrinkage and funnel plots of five studies comparing rates of DVT between patients with and patients without spinal-cord injuries (using spinal cord injuries as a risk factor).

Figure

Figure 15. Shrinkage and funnel plots of five studies comparing rates of DVT between patients with and patients without spinal-cord injuries (using spinal cord injuries as a risk factor).

Risk Factors as Continuous Variables

We examined three continuous variables: age, Injury Severity Score (ISS), and units of blood transfused.

Age

We examined the mean age in seven studies. The meta-analysis of the pooled data (Figure 16) shows that patients with DVT are significantly older than those without DVT by an average of 8.133±1.504 years (95 percent CI: 5.115, 11.141). The corresponding funnel plot does not show evidence of publication bias. The seven studies are described in Evidence Table 14. The Q-statistic of the heterogeneity test shows that the studies are not heterogeneous (p=0.323).

Figure 16. Shrinkage and funnel plots of seven studies comparing patients with and patients without DVT with regard to patient age.

Figure

Figure 16. Shrinkage and funnel plots of seven studies comparing patients with and patients without DVT with regard to patient age.

ISS (Injury Severity Score)

Similarly, the meta-analysis of the data from six studies on ISS (Figure 17) shows that patients with DVT have a significantly higher ISS than patients without DVT by 1.430±0.747 (95 percent CI: 0.000, 2.924). Although this difference isstatistically significant, it does not carry clinical significance. The corresponding funnel plot shows possible publication bias. The studies are described in Evidence Table 15. The Q-statistic of the heterogeneity test shows that the studies are not heterogeneous (p=0.843).

Figure 17. Shrinkage and funnel plots of six studies comparing patients with and patients without DVT with regard to Injury Severity Score.

Figure

Figure 17. Shrinkage and funnel plots of six studies comparing patients with and patients without DVT with regard to Injury Severity Score.

Blood Transfusion

The difference in the amount of blood transfused for patients with or without DVT, as shown by the meta-analysis of the data from three studies (Figure 18), is not statistically significant (mean ± standard deviation [SD]: 1.882±2.815 units of blood, 95 percent CI: -3.637, 7.401). The funnel plot shows no publication bias, but the sample size is small. The studies are described in Evidence Table 16. The Q-statistic for the test of heterogeneity shows that the studies are not heterogeneous (p=0.935).

Figure 18. Shrinkage and funnel plots of three studies comparing patients with and patients without DVT with regard to units of blood transfused.

Figure

Figure 18. Shrinkage and funnel plots of three studies comparing patients with and patients without DVT with regard to units of blood transfused.

Question 3: What Is the Best Method of Screening for VT?

After reviewing the 73 studies included for the final analysis, we realized that the evidence on the best method of screening was very limited. Only three studies (Evidence Table 17) were found that compared tests for screening asymptomatic trauma patients for DVT. Todd, Frisbie, Rossier, et al. (1976) reported on 20 spinal-cord-injured patients and compared the 125-I fibrinogen test, impedance plethysmography, and venography on 17 limbs. The authors reported that impedance plethysmography was superior to the fibrinogen scan when compared with venography. Another study (Brach, Moser, Cedar, et al., 1977) compared the 125-I fibrinogen test and impedance plethysmography with venography and found similar sensitivities. A third study (Engel, Evans, Mikk, et al., 1993) compared D-dimer level accuracy against venous Doppler ultrasonography and found a good correlation between the two.

None of the studies compared Duplex ultrasonography against venography in all patients included in the study. The technical experts determined that the real question of interest is whether bedside ultrasonography can substitute for venography to reliably detect DVT in patients with severe trauma who are clinically unevaluable or asymptomatic. Although there are studies comparing these methods in other types of patients, the trauma literature provides no relevant evidence. For this reason, Question 3 cannot be answered in this Evidence Report.

Question 4: What Is the Role of VCFs in Preventing PE?

The evidence that we identified on VCFs derived entirely from nonrandomized, uncontrolled trials. Although many studies on VCFs have been published that include trauma patients along with other types of patients, we could not isolate the data referring to the trauma patients alone. For this reason, we restricted our literature analysis for this issue to studies that included only trauma patients.

The study designs frequently included historical controls and presented multiple outcomes, including PE, fatal PE, DVT, VCF-insertion-site DVT, and VCF-related complications. Different periods of time were used for followup. For these reasons, comparison of these studies was very difficult, and our results should be considered as generating, rather than proving, hypotheses related to the use of VCF.

Tables 50 and 51 and Evidence Table 18 present the incidence of PE and fatal PE in patients who had a VCF placed, patients who were managed contemporaneously without a VCF, and historical controls who were managed without a VCF. A total of 321 severely injured patients in these studies received a VCF prophylactically. Two patients developed PE with no fatal PEs, for a random-effects estimate for PE of 0.2 percent (95 percent CI: -0.007, 0.010). In 1,083 patients who were managed contemporaneously without a VCF, 7 developed a PE and 1 a fatal PE, for a random-effects estimate for PE of 1.5 percent (95 percent CI: 0.011, 0.041). In 1,806 historical controls, 57 developed a PE and 24 a fatal PE for a random-effects estimate for PE of 5.8 percent (95 percent CI: 0.020, 0.096). The incidence (random-effects estimates) of fatal PE was 0 percent in prospectively followed patients with VCF, 0.1 percent (95 percent CI: -0.009, 0.011) in prospectively followed patients without VCF, and 3 percent (95 percent CI: 0.002, 0.064) in historical controls. In most fields of comparison, the studies were heterogeneous, as shown by the chi-squared heterogeneity test in Tables 50 and 51.

Table 50. Incidence of pulmonary embolism in patients with and without vena cava filters.

Table

Table 50. Incidence of pulmonary embolism in patients with and without vena cava filters.

Table 51. Incidence of fatal pulmonary embolism in patients with and without vena cava filters.

Table

Table 51. Incidence of fatal pulmonary embolism in patients with and without vena cava filters.

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