Venous thrombosis incidence in burn patients: preliminary results of a prospective study.

There are few prospective data on the incidence of deep venous thrombosis (DVT) in burn patients. In an on-going prospective study, hospitalized burn patients 18 years or older with an expected hospital length of stay more than 72 hours were imaged with baseline venous duplex ultrasound of all extremities within the first 48 hours after admission and weekly until discharge. Patient demographics and clinical risk factors for DVT were assessed. At the time of submission, 40 patients met screening criteria, and 30 were enrolled. Ultrasound diagnosed seven patients with 11 acute DVT for an incidence of 23%. One pulmonary embolism was documented. DVT patients had a mean age of 49 +/- 23 years with an average TBSA burn of 15 +/- 4% compared with those without thrombosis with a mean age of 44 +/- 17 years (P = NS) and TBSA burn of 18 +/- 25% (P = NS). There were no statistically significant differences for DVT patients in terms of age, number of central line days, hospital length of stay, or TBSA burned. Given the preliminary findings of this small study, we believe that all hospitalized burn patients are at risk for DVT. On-going investigation will be helpful in defining level of risk and improved prevention strategies for thromboembolic complications in burn patients.

Computed tomographic venography is specific but not sensitive for diagnosis of acute lower-extremity deep venous thrombosis in patients with suspected pulmonary embolus.

PURPOSE: Duplex ultrasound scanning (US) is the accepted standard means of diagnosis for lower-extremity suprageniculate deep venous thrombosis (LE-DVT). Computed tomographic venography (CTV) has been proposed as an alternative modality for diagnosis of LE-DVT in patients with suspected pulmonary embolism (PE). This study compared CTV with US as a means of diagnosing acute LE-DVT. METHODS: A retrospective review of US and CTV scans from 136 patients with suspected PE who underwent both studies to exclude acute LE-DVT at a single institution was performed. Studies were reviewed and coded in a blinded manner. US was considered to be the reference test. Direct costs of each study were determined by using commercial software. RESULTS: The sensitivity and specificity rates of CTV were 71% and 93%, respectively. The positive predictive value, negative predictive value, and accuracy rates of CTV were 53%, 97%, and 90%, respectively. DVT localization was the same in eight of 10 cases in which the results of both US and CTV were positive. CTV costs and charges per study were greater than those of US by $46.88 and $602.00, respectively. CONCLUSION: CTV is specific, but has a lower sensitivity rate and positive predictive value for the diagnosis of acute LE-DVT compared with US. Additionally, CTV is more costly than US scanning. Because of the lower sensitivity rate and positive predictive value and the increased cost of CTV, US remains the screening study of choice in cases of suspected acute LE-DVT.

A clinical comparison of pneumatic compression devices: the basis for selection.

PURPOSE: The five pneumatic compression devices (PCDs) that are marketed provide mechanical protection from deep venous thrombosis (DVT). They differ with respect to patterns of compression and the length of the sleeve. Evidence linking differences to clinical outcomes is lacking. Our purpose was twofold: to evaluate each of the marketed PCDs with respect to effectiveness, compliance, and patient and nursing satisfaction and to determine whether there is a clinical basis for the selection of one device over another. METHODS: Each of the marketed devices was used exclusively for a 4-week period. Patients participated in an evaluation including venous duplex ultrasound scan, DVT risk assessment, and device evaluation. Vascular laboratory records were used to document DVT. Compliance was measured by meters installed on all pumps. A ranking matrix was stratified by compression pattern: rapid graduated sequential compression, graduated compression, and intermittent compression, and each device was rated by patients and nurses. RESULTS: The PCDs were used in 1350 cases with a DVT rate of 3.5% ranging from 2% to 9.8% depending on the method of compression. Patients with DVT were older (58 vs 54 years), had better compliance (67% vs 50%), and had more compression days (11 vs 7.2). When thigh-length sleeves were used, a greater proportion of DVT occurred in the proximal segments (71%) as compared with the number of proximal DVT when the calf-length devices were used (52%; P =.21). Devices W, X, and Y had comparable rates of DVT, which were lower than those for V and Z. Compression device W, [correction] with calf and thigh sleeves, achieved the best overall ranking largely because of high scores for patient and nurse satisfaction. CONCLUSION: Our data appear at odds with commonly held beliefs. We were unable to show a difference in DVT incidence based on the length of the device or the method of compression. Randomized studies are needed to confirm our findings and evaluate hypotheses derived from this study.

Thromboprophylaxis in an academic medical center.

INTRODUCTION: Questions regarding which patients require prophylaxis for thromboembolism, what methods should be used and the appropriate duration of treatment remain unanswered. METHODS AND MATERIALS: A retrospective review from a single academic medical center was undertaken to evaluate prophylactic strategies. Multiple sources of data were used to identify patients who were prophylaxed and those who developed deep vein thrombosis or pulmonary embolism. These data were analyzed to determine factors associated with successful prophylaxis including age, type of prophylaxis and admitting services. RESULTS: A total of 22,030 patients were admitted of whom 7520 (36%) received prophylaxis and there were 523 thromboembolic events. Pneumatic compression devices and antiembolic stockings had the lowest incidence of failure, 2.2% and 3.2% respectively. There were significant differences in the rates of prophylaxis used by the five admitting services, being highest in surgery (40.8%) and lowest in gynecology (11.4%). However, these groups had the lowest incidence of venous thromboembolism (4.3%, 2.3%). Both of these groups used pneumatic compression as the method of choice (64.3% and 65.2%). CONCLUSIONS: Thromboembolism prophylaxis reduces the incidence of DVT and PE, however, our study demonstrates the variable effectiveness of each method in different types of patients. Our data suggest that patient risk of DVT should be individually assessed and an appropriate method of prophylaxis should be applied when warranted.

Nitric oxide inhibition increases matrix metalloproteinase-9 expression by rat aortic smooth muscle cells in vitro.

OBJECTIVE: The hypothesis to be tested was that diminished bioavailable nitric oxide (NO) affects matrix metalloproteinase (MMP) expression and activation in vascular smooth muscle cells (SMCs). METHODS: Cultivated rat aortic SMCs (RA-SMCs) were exposed to increasing concentrations of L-N-monomethyl arginine (L-NMMA), a nonselective inhibitor of NO synthase, in the presence of proinflammatory cytokines (50 ng/mL interleukin [IL]-1beta, 50 ng/mL interferon-gamma, and 30 microg/mL lipopolysaccharide). Nitrite and nitrate, two of the final end products of NO metabolism, were measured in media collected at 48 hours with the use of the Saville assay (n = 4). MMP activity was measured with 1% gelatin zymography (n = 4). In separate experiments in which 2 ng/mL of IL-1beta and L-NMMA was used, MMP protein and messenger RNA (mRNA) levels were determined with Western blot analysis (n = 3) and semiquantitative reverse transcriptase-polymerase chain reaction (n = 3), respectively. Data were analyzed with nonparametric analysis of variance. RESULTS: Increasing concentrations of the NO synthase inhibitor L-NMMA caused a dose-dependent decrease (P <.05) in nitrite and nitrate production by RA-SMCs after cytokine exposure. Zymography documented an early dosedependent increase (P <.05 compared with cytokines alone) in 92-kd MMP activity, with no significant changes in 72-kd MMP activity after treatment with L-NMMA (P >.05 compared with cytokines alone). Reverse transcriptase-polymerase chain reaction and Western blot analysis revealed that the addition of L-NMMA to IL-1beta-stimulated RA-SMCs led to significant increases in MMP-9 mRNA (n = 3, P <.01 for 1.0 mmol/L L-NMMA) and MMP-9 protein levels (n = 3, P <.05), respectively. No differences in MMP-2 mRNA or protein levels were demonstrated. CONCLUSIONS: Inhibition of cytokine-induced NO expression in RA-SMCs is associated with a selective, dose-dependent increase in MMP-9 expression and synthesis. These findings suggest that alterations in local NO synthesis may influence MMP-9-dependent vessel wall damage.

Outcomes after surgery for thoracic outlet syndrome.

PURPOSE: This study determined whether there is an association between psychological and socioeconomic characteristics and the long-term outcome of operative treatment for patients with sensory neurogenic thoracic outlet syndrome (N-TOS). METHODS: Clinical records, preoperative psychological testing results, and long-term follow-up questionnaire data were reviewed for consecutive patients who underwent surgery for N-TOS from 1990 to 1999. Multivariate logistic regression models were developed as a means of identifying independent risk factors for postoperative disability. RESULTS: Operative decompression of the brachial plexus via a supraclavicular approach was performed for upper extremity pain and paresthesia with no mortality and minimal morbidity in 170 patients. After an average follow-up period of 47 months, 65% of patients reported improved symptoms, and 64% of patients were satisfied with their operative outcome. However, 35% of patients remained on medication, and 18% of patients were disabled. Preoperative factors associated with persistent disability include major depression (odds ratio [OR], 15.7; P =.02), not being married (OR, 7.9; P =.04), and having less than a high school education (OR, 8.1; P =.09). CONCLUSION: Operative decompression was beneficial for most patients. Psychological and social factors, including depression, marital status, and education, are associated with self-reported disability. The impact of the preoperative treatment of depression on the outcome of TOS decompression should be studied prospectively.

Recurrent thromboembolism in patients with vena cava filters.

BACKGROUND: Patients with venous thromboembolic disease are treated with anticoagulation or vena cava filter placement to prevent pulmonary embolism. A recent report suggested that filter placement may increase the risk of recurrent deep venous thrombosis (DVT) and prompted a review of our experience. METHODS: Prospectively collected data on 2109 consecutive patients receiving filters were evaluated for recurrent thromboembolism, vena cava occlusion, or venous stasis ulceration. Outcomes were stratified and analyzed according to the use of anticoagulants at the time of insertion and at follow-up. Incidence rates were also compared with reports in the literature. RESULTS: Of 1191 patients with DVT at filter placement, complete follow-up data at a mean of 9 years were available for 465. Recurrent DVT was found in 12% of the 241 patients who were given anticoagulants and 15% of the 224 who were not (P >.05). We also failed to find a significant association between the use of anticoagulation and the incidence of pulmonary embolism (2%), stasis ulceration (2%), and vena cava occlusion (0.0). CONCLUSIONS: Recurrent DVT in patients with existing thromboembolic disease is not an unexpected event, which, in our experience, is not associated with anticoagulant or filter use. Anticoagulation should be used when possible to treat existing DVT to reduce thrombus progression and potentially to reduce subsequent complications but does not seem to reduce the rate of recurrent DVT. Rates of recurrent thromboembolism were consistently less than the 20% to 50% reported in the literature.

Rapid recovery of photosystems on rewetting desiccation-tolerant mosses: chlorophyll fluorescence and inhibitor experiments.

In the mosses Racomitrium lanuginosum, Anomodon viticulosus and Rhytidiadelphus loreus, after a few days air dry, F:(v)/F:(m) reached, within the first minute of remoistening in the dark, two-thirds or more of the value attained after 40 min. A fast initial phase of recovery was completed within 10-20 min after which further change was slow. Initial recovery of Phi(PSII) in the light was somewhat slower, but was generally substantially complete within a similar time. Remoistening with 0.3 mM cycloheximide (CHX) or 3 mM dithiothreitol (DTT) made little difference to this short-term (40 min) recovery of either F:(v)/F:(m) or Phi(PSII); 3 mM chloramphenicol (CMP) had little effect on recovery of F:(v)/F:(m), but resulted in substantial (though not total) depression of Phi(PSII) and (14)CO(2) uptake. Effects of the protein-synthesis inhibitors and DTT were much more clearly apparent in longer-term experiments (>20 h) but only in the light. In the dark, the three inhibitors had at most only slight effects over periods of 60-100 h. In the light, CMP-treated samples of all three species showed a progressive decline of dark-adapted F:(v)/F:(m), falling to zero within 1-5 d (possibly due to blocking of the turnover of the D1 protein of PSII) and accelerated by DTT. CHX-treated samples showed a similar but slower decline. In the shade-adapted and relatively desiccation-sensitive Rhytidiadelphus loreus, slow recovery of F:(v)/F:(m) continued in the dark even in the presence of CMP and CHX for much of the 142 h of the experiment. The results indicate that in desiccation-tolerant bryophytes recovery of photosynthesis after periods of a few days air dry requires only limited chloroplast protein synthesis and is substantially independent of protein synthesis in the cytoplasm.

The risk assessment profile score identifies trauma patients at risk for deep vein thrombosis.

BACKGROUND: The identification of trauma patients at risk for the development of deep venous thrombosis (DVT) at the time of admission remains difficult. The purpose of this study is to validate the risk assessment profile (RAP) score to stratify patients for DVT prophylaxis. METHODS: All patients admitted from November 1998 thru May 1999 were evaluated for enrollment. We prospectively assigned patients as low risk or high risk for DVT using the RAP score. High-risk patients received both pharmacologic and mechanical prophylaxis. Low-risk patients received none. Surveillance duplex Doppler scans were performed each week of hospitalization or if symptoms developed. Hospital charges for prophylaxis were used to determine the savings in the low-risk group. Statistical differences between the risk groups for each factor of the RAP and development of DVT were determined by the chi-squared test, with significance at a probability value of less than .05. RESULTS: There were 102 high-risk (64%) and 58 low-risk (36%) individuals studied. Eleven of the high-risk group (10.8%) experienced the development of DVT (asymptomatic, 64%). None of the low-risk group was diagnosed with DVT. Five of the 16 RAP factors were statistically significant for DVT. Eliminating prophylaxis and Doppler scans in low-risk patients resulted in a total savings of $18,908 in hospital charges. CONCLUSIONS: The RAP score correctly identified trauma patients at increased risk for the development of DVT. Despite prophylaxis, the high-risk group warrants surveillance scans. Withholding prophylaxis in low-risk patients can reduce hospital charges without risk.

The percutaneous greenfield filter: outcomes and practice patterns.

OBJECTIVE: The percutaneous steel Greenfield filter (PSGF) is similar in appearance to the titanium Greenfield filter (TGF) but differs in the length and orientation of the attachment hooks and in the over-the-wire delivery system. Because these differences improve ease of insertion and attachment, they may affect patient outcomes and physician practices. The purpose of this study was to evaluate the performance of the PSGF relative to the TGF and to determine whether there had been a change in physician practices. METHODS: The Michigan Filter Registry contains data for a prospective cohort of 2188 patients with Greenfield filters. Procedural and long-term outcomes for patients with a PSGF were abstracted. These events were compared with rates for Registry patients who had a TGF. Trends for indication for placement, delivery route, and filter location were also compared with published series. RESULTS: Since 1995, 600 PSGFs have been placed in 599 patients. A 1-year mortality rate of 42% left 349 patients available for annual follow-up, and studies were completed for 231 (66%). Periprocedural events occurred in 2.5% of cases with associated morbidity in 1.5%. The rate of new pulmonary embolism was 2.6%, and vena caval patency was 98.3%. The combined rate of new venous thromboembolic events was 12.5%. Left-sided femoral vein placements increased to 20%, and the major indication for filter placement has become prophylaxis (46%). CONCLUSIONS: The PSGF is similar to the TGF with respect to patient outcomes, and it provides decreased rates of asymmetry along with excellent fixation. The flexible carrier system has allowed more frequent access through the left femoral vein. The ease of use and favorable patient outcomes have resulted in more frequent placement for prophylactic indications.

Current status of pulmonary embolism and venous thrombosis prophylaxis.

Prophylaxis for venous thromboembolism is an area that has received intense study in certain conditions, but less than adequate coverage in other areas. In considering who needs prophylaxis, patients are categorized into levels of risk. Clinical venous thromboembolism can be correlated to these levels of risk. Methods of prophylaxis include pharmacologic, mechanical, and combinations of these. Each category of surgical and medical patient requires specific types of prophylaxis. In certain orthopedic indications, the length of prophylaxis outlasts the inpatient hospital stay and may be as long as 1 month after discharge. Even with the best prophylaxis today, the incidence of deep venous thrombosis (DVT) and pulmonary embolism (PE) is decreased by only approximately 70% to 80%. Further developments should allow for greater declines in the rates of venous thromboembolism, with its subsequent short-term consequence of pulmonary embolism and lower extremity morbidity and long-term consequence of the disabling syndrome of chronic venous insufficiency (CVI).

Indications for filter placement.

Indications for placement of a vena caval filter reflect the perception of efficacy and safety of these devices. The traditional indications include contraindications to or complications of anticoagulation. Over time, physicians have expanded these indications to include prophylactic placement in patients at high risk of pulmonary embolism. The decision to place a filter should be made only after weighing the risks and benefit in each situation. Long-term outcomes should be carefully evaluated.

Filter complications and their management.

Complications from the use of vena caval filters are rare but can occur at placement, during other procedures, or late in follow-up. Placement problems such as bleeding from the insertion site or embolism from thrombus manipulation are largely avoidable. Technical difficulties with introduction, positioning, or misplacement have been minimized by use of flexible carriers and guidewires. However, later insertion of guidewires without fluoroscopy for line changes can lead to problems of entrapment. Filter capture of emboli can result in further thrombus propagation at that site or in filter obstruction. Management of these events requires adequate visualization to determine whether to use lytic therapy or a second filter. Late complications include filter strut fracture in 0.05% of cases and filter penetration, of even rarer functional significance. Pain that can be attributed to the filter has been found only in a single case of pelvic misplacement. The limited consequences of mechanical changes in the filter argue strongly against unnecessary interventions, which frequently result in an increase in morbidity.

Prophylactic vena caval filters in trauma: the rest of the story.

OBJECTIVE: The purpose of this study was to describe outcomes for patients with trauma who had vena caval filters placed in the absence of venous thromboembolic disease (group P) and compare them with outcomes for patients with trauma who had filters placed after either deep venous thrombosis or pulmonary embolism (group T). DESIGN: The study is a case series of consecutive patients who received vena caval filters after traumatic injury. Data were collected prospectively at the time of filter placement from reports of diagnostic studies obtained for clinical indications and during the annual follow-up examinations. Event rate findings are based on objective tests. Data were obtained from the Michigan Vena Cava Filter Registry. RESULTS: Filters were placed in 385 patients with trauma; 249 of these filters were prophylactic (group P). Event rates were similar in the two groups. New pulmonary embolism was diagnosed in 1.5% of the patients in group P and 2% of the patients in group T. Caval occlusion rates were 3.5% for group P and 2.3% for group T. In all, 15.6% of the patients in group P had deep venous thrombosis or pulmonary embolism after placement. The frequencies of lower extremity swelling and use of support hose were higher in group T than in group P (43% vs 25% and 25% vs 3.5%, respectively; P <.005). Outcomes were comparable in the two groups with respect to mechanical stability of the filter. CONCLUSIONS: The prophylactic indication for vena caval filter placement in patients with trauma is associated with a low incidence of adverse outcomes while providing protection from fatal pulmonary embolism. The current challenge is to limit the number of unnecessary placements through improved methods of risk stratification.

In vivo evaluation of vena caval filters: can function be linked to design characteristics?

PURPOSE: To compare the five vena caval filters marketed in the United States and one investigational vena caval filter and to determine whether there is an association between their design and their in vivo function. METHODS: Four of each type of filter--Simon Nitinol (SN), Bird's Nest (BN), Vena Tech (VT), Greenfield stainless steel (PSGF), Greenfield titanium (TGF), and the investigational stent cone filter (NGF)--were studied for 60 days in 12 sheep. Radiographic and pathologic outcomes to be assessed included clot capture and resolution, vena caval penetration, position of the filter, thrombogenicity, and vessel wall reaction. RESULTS: Filters differed with respect to the number of clot-trapping levels and the interdependence of the legs. All devices were successfully placed. Intentionally embolized clot was captured. One VT and two SN filters migrated in response to clot capture. Resolution of thrombus was variable, and related to the design of the device. Fibrin webbing was widely present with the VT, BN, and SN filters but limited in the others. The VT and NGF filters demonstrated the most stable filter base diameter. CONCLUSIONS: The performance of vena caval filters differs with respect to clot resolution and mechanical stability. Interdependent filter limbs and single-stage conical capture sites appear to result in more favorable performance in in vivo studies.

Mosses and alternative adaptation to life on land.

It is easy to dismiss bryophytes as 'lower' plants, mere primitive precursors long since left behind in the evolutionary race, and of only rather esoteric and incidental biological interest. But this is to let oneself be led astray by a simplistic image of a tidy evolutionary tree - an image that served Darwin well a century and a half ago (Desmond & Moore, 1992), but which we should now see as an intricately branched evolutionary bush with innumerable shoots reaching out from all depths to the growing apices that represent the present day. The earliest land plants may indeed have been at a bryophyte level of organization, but modern bryophytes, no less than vascular plants, are the product of some 450 million years' evolution since that time (Edwards et al., 1998). Raven (1977, 1984) has emphasized the importance of the evolution of supracellular transport systems in the origin of vascular land plants. Bryophytes, on the other hand, evolved desiccation tolerance and represent an alternative strategy of adaptation to life on land, photosynthesizing and growing when water is available, and suspending metabolism when it is not. They are limited by their mode of life, but also liberated : they are prominent on hard substrates such as rock and bark, which are impenetrable to roots and untenable to vascular plants. Bryophytes (in species numbers the second biggest group of green land plants) may be seen as the mobile phones, notebook computers and diverse other rechargeable battery-powered devices of the plant world - not direct competitors for their mains-based equivalents, but a lively and sophisticated complement to them.

Assessment of apparent vena caval penetration by the Greenfield filter.

PURPOSE: To examine and elucidate the mechanisms for apparent "penetration" by Greenfield vena caval filters. METHODS: Two filters were placed in the inferior venae cavae (IVC) of four immature sheep and followed with cavography for 1 year. Two animals underwent computed tomography (CT) and laparoscopic examination. At necropsy, the vena cava and adjacent structures of all four animals were examined grossly and histologically. RESULTS: Based upon cavography and CT imaging, all filters appeared to penetrate the vena cava at 12 months. However, at laparoscopy, no hooks or limbs were exposed, and the pericaval tissues remained intact; each hook or limb was within the adventitia or encapsulated in scar tissue. Histology of the tissue at the hook sites revealed remodeling of the intimal surface of the IVC and thinning of the adventitia. CONCLUSIONS: Based upon these data, we hypothesize that the vena cava gradually adapts by medial and adventitial thinning and myointimal remodeling to the radial force exerted by a filter. This process allows increase in the filter base diameter while maintaining the integrity of the cava and protecting adjacent structures.

Suprarenal filter placement.

PURPOSE: This study was undertaken to determine the clinical outcomes for patients with Greenfield filters placed in the suprarenal (SR) inferior vena cava (IVC). METHODS: We collected data prospectively from annual follow-up evaluations of patients with filters. Patients underwent venous color-flow duplex examinations of the IVC and lower extremities, abdominal radiographs, and physical assessment. The outcomes for those patients with filters in the SR IVC were compared with the outcomes previously reported and with the outcomes for patients with filters in the infrarenal cava. RESULTS: SR placement accounted for 7.6% (148/1932) of all filter placements. Follow-up data were available for 73 placements, or 49%. No cases of renal dysfunction were related to filter placement. The rate of recurrent pulmonary embolism (PE) was 8%, and the rate of long-term caval occlusion was 2.7%. These rates did not differ statistically from the rates for patients with infrarenal filters (P > .05). Male patients tended to be older by 15 years, to have more recurrent PE, and to experience more filter migration (6 vs 2 mm). Failure of SR filters to prevent PE was associated statistically with the primary indication for placement. Recurrent PE was the indication in 5 of 6 patients who sustained PE after SR filter placement (P = .007). Filter limb fracture was seen only with the stainless-steel Greenfield filter. CONCLUSION: Greenfield filters placed above the renal vein provide protection from PE with a minimal risk of occlusion. Twenty-five years of experience with Greenfield filters shows that they are safe and effective both in young female patients of child-bearing potential and in all patients with appropriate indications for SR placement.