Nonimmobilized Patients Research Articles

High-Accuracy Neuro-Navigation with Computer Vision for Frameless Registration and Real-Time Tracking.

For the past three decades, neurosurgeons have utilized cranial neuro-navigation systems, bringing millimetric accuracy to operating rooms worldwide. These systems require an operating room team, anesthesia, and, most critically, cranial fixation. As a result, treatments for acute neurosurgical conditions, performed urgently in emergency rooms or intensive care units on awake and non-immobilized patients, have not benefited from traditional neuro-navigation. These emergent procedures are performed freehand, guided only by anatomical landmarks with no navigation, resulting in inaccurate catheter placement and neurological deficits. A rapidly deployable image-guidance technology that offers highly accurate, real-time registration and is capable of tracking awake, moving patients is needed to improve patient safety. The Zeta Cranial Navigation System is currently the only non-fiducial-based, FDA-approved neuro-navigation device that performs real-time registration and continuous patient tracking. To assess this system's performance, we performed registration and tracking of phantoms and human cadaver heads during controlled motions and various adverse surgical test conditions. As a result, we obtained millimetric or sub-millimetric target and surface registration accuracy. This rapid and accurate frameless neuro-navigation system for mobile subjects can enhance bedside procedure safety and expand the range of interventions performed with high levels of accuracy outside of an operating room.

Spine Stereotactic Body Radiation Therapy Without Immobilization: Detailed Analysis of Intrafraction Motion Using High-Frequency kV Imaging During Irradiation

Spine SBRT requires high positioning accuracy and a stable patient to maximize target coverage and reduce excessive irradiation to organs at risk (OARs). Positional verification during spine SBRT delivery helps to ensure accurate positioning for all patients. We report our experience with non-invasive 3-dimensional (3D) target position monitoring during volumetric modulated arc therapy (VMAT) of spine metastases, in non-immobilized patients positioned using only a thin mattress and simple arm and knee supports. Fluoroscopic planar kV images were acquired at 7 frames/second using the on-board imaging system during VMAT spine SBRT. Template matching and triangulation were used to track the target in vertical, longitudinal and lateral direction. If the tracking trace deviated >1mm from the planned position in ≥1 direction, treatment was manually interrupted and 6D CBCT-based couch correction was performed. Tracking data was used to retrospectively analyze the target position. Positional data, agreement with CBCT, correlation between position of the couch and direction of any positional correction, and treatment times were analyzed. 175 fractions were analyzed. Delivery was interrupted 83 times in 66 fractions for a deviation >1mm. In 97% of cases the difference between tracking data and subsequent clinical shift performed after the CBCT match was ≤0.5mm. Lateral/longitudinal shift performed after intervention correlated with the couch roll/pitch at the start of treatment (correlation coefficient: -0.63/0.53). Mean (SD; range) time between start of first imaging and end of the last arc was 15.2 minutes (5.1;7.6-36.3). Spine tracking during irradiation can be used to prompt an intervention CBCT scan and repositioning, so that a spine SBRT target deviates by ≤1mm from the planned position, even in non-immobilized patients. kV tracking and CBCT are in good agreement. The data support verification CBCT after all 6 degrees-of-freedom positional corrections in non-immobilized spine SBRT patients.

Frameless neuronavigation with computer vision and real-time tracking for bedside external ventricular drain placement: a cadaveric study.

A major obstacle to improving bedside neurosurgical procedure safety and accuracy with image guidance technologies is the lack of a rapidly deployable, real-time registration and tracking system for a moving patient. This deficiency explains the persistence of freehand placement of external ventricular drains, which has an inherent risk of inaccurate positioning, multiple passes, tract hemorrhage, and injury to adjacent brain parenchyma. Here, the authors introduce and validate a novel image registration and real-time tracking system for frameless stereotactic neuronavigation and catheter placement in the nonimmobilized patient. Computer vision technology was used to develop an algorithm that performed near-continuous, automatic, and marker-less image registration. The program fuses a subject's preprocedure CT scans to live 3D camera images (Snap-Surface), and patient movement is incorporated by artificial intelligence-driven recalibration (Real-Track). The surface registration error (SRE) and target registration error (TRE) were calculated for 5 cadaveric heads that underwent serial movements (fast and slow velocity roll, pitch, and yaw motions) and several test conditions, such as surgical draping with limited anatomical exposure and differential subject lighting. Six catheters were placed in each cadaveric head (30 total placements) with a simulated sterile technique. Postprocedure CT scans allowed comparison of planned and actual catheter positions for user error calculation. Registration was successful for all 5 cadaveric specimens, with an overall mean (± standard deviation) SRE of 0.429 ± 0.108 mm for the catheter placements. Accuracy of TRE was maintained under 1.2 mm throughout specimen movements of low and high velocities of roll, pitch, and yaw, with the slowest recalibration time of 0.23 seconds. There were no statistically significant differences in SRE when the specimens were draped or fully undraped (p = 0.336). Performing registration in a bright versus a dimly lit environment had no statistically significant effect on SRE (p = 0.742 and 0.859, respectively). For the catheter placements, mean TRE was 0.862 ± 0.322 mm and mean user error (difference between target and actual catheter tip) was 1.674 ± 1.195 mm. This computer vision-based registration system provided real-time tracking of cadaveric heads with a recalibration time of less than one-quarter of a second with submillimetric accuracy and enabled catheter placements with millimetric accuracy. Using this approach to guide bedside ventriculostomy could reduce complications, improve safety, and be extrapolated to other frameless stereotactic applications in awake, nonimmobilized patients.

Stereotactic Neurosurgical Robotics With Real-Time Patient Tracking: A Cadaveric Study.

Robotic neurosurgery may improve the accuracy, speed, and availability of stereotactic procedures. We recently developed a computer vision and artificial intelligence-driven frameless stereotaxy for nonimmobilized patients, creating an opportunity to develop accurate and rapidly deployable robots for bedside cranial intervention. To validate a portable stereotactic surgical robot capable of frameless registration, real-time tracking, and accurate bedside catheter placement. Four human cadavers were used to evaluate the robot's ability to maintain low surface registration and targeting error for 72 intracranial targets during head motion, ie, without rigid cranial fixation. Twenty-four intracranial catheters were placed robotically at predetermined targets. Placement accuracy was verified by computed tomography imaging. Robotic tracking of the moving cadaver heads occurred with a program runtime of 0.111 ± 0.013 seconds, and the movement command latency was only 0.002 ± 0.003 seconds. For surface error tracking, the robot sustained a 0.588 ± 0.105 mm registration accuracy during dynamic head motions (velocity of 6.647 ± 2.360 cm/s). For the 24 robotic-assisted intracranial catheter placements, the target registration error was 0.848 ± 0.590 mm, providing a user error of 0.339 ± 0.179 mm. Robotic-assisted stereotactic procedures on mobile subjects were feasible with this robot and computer vision image guidance technology. Frameless robotic neurosurgery potentiates surgery on nonimmobilized and awake patients both in the operating room and at the bedside. It can affect the field through improving the safety and ability to perform procedures such as ventriculostomy, stereo electroencephalography, biopsy, and potentially other novel procedures. If we envision catheter misplacement as a "never event," robotics can facilitate that reality.

181 Frameless Neuronavigation With Computer Vision and Real Time Tracking for Bedside External Ventricular Drain Placement: A Cadaveric Study

INTRODUCTION: A major obstacle to improving ventriculostomy safety and accuracy with image guidance technologies is the lack of a rapidly deployable, real-time registration and tracking system for a moving patient. METHODS: Computer vision technology was used to develop an algorithm for near continuous, automatic, and marker-less image registration. The program fuses a subject’s pre-procedure CT scan to live 3D camera images (Snap-Surface), and movement is incorporated by artificial intelligence driven recalibration (Real-Track). Surface registration error (SRE) and target registration error (TRE) were calculated for five cadaver heads that underwent serial movements (fast and slow velocity roll, pitch, and yaw motions), and several test conditions. Six catheters were placed in each cadaver (30 placements). Post-procedure CT scans allowed comparison of planned and actual catheter position for user error calculation. RESULTS: Registration was successful for all five cadaveric specimens (average SRE 0.429 mm, ±0.108). Accuracy of TRE was under 1.2mm throughout specimen movements of low and high velocities of roll, pitch, and yaw movements, with the slowest recalibration time of 0.23 seconds. There were no statistically significant differences in SRE when the specimens were draped or fully undraped (p-value = 0.336). Addition of bright light or performance under dim light did not significantly affect SRE (p-value = 0.742 and 0.859, respectively). Average TRE for catheter placements was 0.862 mm (±0.322), and average user error for the was 1.674 mm (±1.195). CONCLUSION: This computer vision-based registration system provides real-time tracking of cadaveric heads with recalibration time of less than one-quarter of a second with sub-millimetric accuracy, and enabled catheter placements with millimetric accuracy. Using this approach to guide bedside ventriculostomy could reduce complications, improve safety, and could be extrapolated to other frameless stereotactic applications in awake, non-immobilized patients.

Residual intra-fraction error in robotic spinal stereotactic body radiotherapy without immobilization devices.

Background and purposeSpinal stereotactic body radiotherapy (SBRT) involves large dose gradients and high geometrical accuracy is therefore required. The aim of this work was to assess residual intra-fraction error with a tracking robotic system for non-immobilized patients. Shifts from the first alignment (i.e. mimicking the unavailability of tracking) were also quantified.Materials and methodsForty-two patients treated for spinal metastasis (128 fractions, 4220 images) were analyzed. Residual error was quantified as the difference between translations/rotations referring to consecutive x-ray images during delivery (tracking) and to the initial set-up (no-tracking). The error distribution for each fraction/patient and the entire population was assessed for each axis/rotation angle. The impact of lesion sites, fractionation and patient’s pain (VAS score) were investigated. Finally, the dosimetric impact of residual motion was quantified in the four most affected fractions.ResultsMean overall errors (OE) were near 0 (SD < 0.1 mm). Residual translations/rotations >1 mm/1° were found in less than 1.5%/1% of measurements. Lesion site and fractionation showed no impact. The dosimetric impact in the most affected fractions was negligible. For “no-tracking”, mean OE was <1 mm/0.5°; less than 2% of displacements were >2 mm/1° within 10 min from the start of treatment with an increasing probability of shifts >2 mm over time. A significantly higher fraction of OE ≥ 2 mm was found for patients with pain in case of no-tracking.ConclusionsSpine tracking with a latest-generation robotic system is highly efficient for non-immobilized patients: residual error is time independent and close to 0. For delivery times >7–8 min, tracking should be considered as mandatory for non-immobilized patients.

PO-0973 Residual intra-fraction error in nonimmobilized patients treated with tracked robotic spinal SBRT

PO-0973 Residual intra-fraction error in nonimmobilized patients treated with tracked robotic spinal SBRT

Association between spinal immobilization and survival at discharge for on-scene blunt traumatic cardiac arrest: A nationwide retrospective cohort study

IntroductionSpinal immobilization has been indicated for all blunt trauma patients suspected of having cervical spine injury. However, for traumatic cardiac arrest (TCA) patients, rapid transportation without compromising potentially reversible causes is necessary. Our objective was to investigate the temporal trend of spinal immobilization for TCA patients and to examine the association between spinal immobilization and survival. MethodsWe conducted a retrospective cohort study using the Japan Trauma Data Bank 2004–2015 registry data. Our study population consisted of adult blunt TCA patients encountered at the scene of a trauma. The primary outcome was the survival proportion at hospital discharge, and the secondary outcome was the proportion achieving return of spontaneous circulation (ROSC). We examined the association between spinal immobilization and these outcomes using a logistic regression model based on imputed data sets with the multiple imputation method to account for missing data. ResultsAmong 4313 patients who met the inclusion criteria, 3307 (76.7%) were immobilized. The proportion of patients that underwent spinal immobilization gradually decreased from 82.7% in 2004–2006 to 74.0% in 2013–2015. 1.0% of immobilized and 0.9% of non-immobilized patients had severe cervical spine injury. Spinal immobilization was significantly associated with lower survival at discharge (odds ratio [OR], 0.64; 95% confidence interval [CI], 0.42 to 0.98) and ROSC by admission (OR, 0.48; 95%CI, 0.27 to 0.87). There was no significant sub-group difference of the association between spinal immobilization and survival at discharge by patients with or without cervical spine injury (p for interaction 0.73). ConclusionSpinal immobilization is widely used even for blunt TCA patients, even though it is associated with a lower rate of survival at discharge and ROSC by admission. According to these results, we suggest that spinal immobilization should not be routinely recommended for all blunt TCA patients.

Comparison of Radial Forearm Free‐Flap Donor Site Dressing Modalities with Temporary Forearm Immobilization

Objectives: 1) Compare the success and complication rates of two dressing techniques for radial forearm free-flap donor sites in patients undergoing short term limb immobilization. 2) Recognize the observed benefit of short-term donor limb immobilization in this population. Methods: This was a prospective, randomized, controlled study of patients undergoing radial forearm free flap reconstruction of head and neck oncologic post-ablative defects from 2010 to 2013 at a single tertiary care center. Participants’ donor sites were covered with split-thickness skin grafts and were randomized into two arms: static pressure dressing and negative pressure dressing groups. All participants underwent immobilization of the donor arm using a custom-fit removable volar splint for 30 days. Data were collected at 2 postoperative time points. Results: Fifty-four patients underwent radial forearm and were enrolled in the study. Twenty-seven patients (50%) received negative pressure dressings, and 27 patients (50%) received static pressure dressings. 100% of enrolled patients were immobilized with custom volar splints. Follow-up data were available for 40 (74%) patients at the time of this writing. The overall complication rate was 20% (n = 8). Within the group of patients with medical co-morbidities, 25% (n = 2) demonstrated donor site morbidity. Conclusions: This study reaffirms both techniques as viable methods for covering radial forearm donor sites; however, there are differences between them in cost and convenience for the patient. Additionally, this follow-up study demonstrates that 30-day immobilization may improve donor site outcome regardless of dressing strategy, as evidenced by an overall decrease in donor site morbidity compared to previously published results on non-immobilized patients.

Spine Immobilization in Penetrating Trauma: More Harm Than Good?

Previous studies have suggested that prehospital spine immobilization provides minimal benefit to penetrating trauma patients but takes valuable time, potentially delaying definitive trauma care. We hypothesized that penetrating trauma patients who are spine immobilized before transport have higher mortality than nonimmobilized patients. We performed a retrospective analysis of penetrating trauma patients in the National Trauma Data Bank (version 6.2). Multiple logistic regression was used with mortality as the primary outcome measure. We compared patients with versus without prehospital spine immobilization, using patient demographics, mechanism (stab vs. gunshot), physiologic and anatomic injury severity, and other prehospital procedures as covariates. Subset analysis was performed based on Injury Severity Score category, mechanism, and blood pressure. We calculated a number needed to treat and number needed to harm for spine immobilization. In total, 45,284 penetrating trauma patients were studied; 4.3% of whom underwent spine immobilization. Overall mortality was 8.1%. Unadjusted mortality was twice as high in spine-immobilized patients (14.7% vs. 7.2%, p < 0.001). The odds ratio of death for spine-immobilized patients was 2.06 (95% CI: 1.35-3.13) compared with nonimmobilized patients. Subset analysis showed consistent trends in all populations. Only 30 (0.01%) patients had incomplete spinal cord injury and underwent operative spine fixation. The number needed to treat with spine immobilization to potentially benefit one patient was 1,032. The number needed to harm with spine immobilization to potentially contribute to one death was 66. Prehospital spine immobilization is associated with higher mortality in penetrating trauma and should not be routinely used in every patient with penetrating trauma.

Knee Immobilization for Pain Control after a Hamstring Tendon Anterior Cruciate Ligament Reconstruction

Background This study will attempt to evaluate the efficacy of knee immobilization on patient pain levels after an anterior cruciate ligament reconstruction. Hypothesis There is no difference in visual analog scale pain scores 2 days after anterior cruciate ligament reconstruction between patients who wear a knee immobilizer and those who do not wear a knee immobilizer. Study Design Randomized clinical trial; Level of evidence, 1. Methods Patients aged 18 to 40 years who met study inclusion criteria were eligible. Patients meeting intraoperative inclusion critiera were randomized (immobilizer or no immobilizer) after wound closure. The immobilizer used was a soft, unhinged brace with Velcro® straps. Preoperative, intraoperative, and postoperative protocols were standardized. The primary outcome was patient self-assessed pain using a 0-to-100-mm visual analog scale at day 2 after surgery. Secondary outcomes included pain and analgesic use in the first 14 days after surgery, complications, and range of motion (approximately 3 weeks postoperatively). A sample size estimate was calculated and resulted in the need for 44 patients per group. Results A total of 102 patients were enrolled; 88 patients were randomized, and 14 were excluded intraoperatively. There was no difference in mean visual analog scale pain scores at 2 days after surgery between immobilized and nonimmobilized patients (32.6 and 35.2, respectively; P = .59; difference, —2.6; 95% confidence interval, —12.2 to 6.9). There were no differences between groups in medication consumed, range of motion, or complications. Pain and analgesic use were the same for both groups at 7 and 14 days postoperatively. Conclusion No differences in pain or any of the secondary outcomes were detected between immobilized and nonimmobilized patients at any point during the first 14 days after anterior cruciate ligament reconstruction.

Prospective Performance Assessment of an Out-of-Hospital Protocol for Selective Spine Immobilization Using Clinical Spine Clearance Criteria

We determine whether the use of an emergency medical services (EMS) protocol for selective spine immobilization would result in appropriate immobilization without spinal cord injury associated with nonimmobilization. A 4-year prospective study examined EMS and hospital records for patients after the implementation of an EMS protocol for selective spine immobilization. EMS personnel were trained to perform and document a spine injury assessment for out-of-hospital trauma patients with a mechanism of injury judged sufficient to cause a spine injury. The assessment included these clinical criteria: altered mental status, evidence of intoxication, neurologic deficit, suspected extremity fracture, and spine pain or tenderness. The protocol required immobilization for patients with a positive assessment on any of those criteria. Outcome characteristics included the presence or absence of spine injury and spine injury management. The study collected data on 13,483 patients; 126 of the patients were subsequently excluded from the study because of incomplete data, leaving a study sample of 13,357 patients with complete data. Spine injuries were confirmed in the hospital records for 3% (n=415) of patients, including 50 patients with cord injuries and 128 patients with cervical injuries. Sensitivity of the EMS protocol was 92% (95% confidence interval [CI] 89.4 to 94.6%) resulting in nonimmobilization of 8% of the patients with spine injuries (33 of 415). None of the nonimmobilized patients sustained cord injuries. The specificity was 40% (95% CI 38.9 to 40.5%). The use of our selective immobilization protocol resulted in spine immobilization for most patients with spine injury without causing harm in cases in which spine immobilization was withheld.

Set-up error in supine-positioned patients immobilized with two different modalities during conformal radiotherapy of prostate cancer

Background: Conformal radiotherapy requires reduced margins around the clinical target volume (CTV) with respect to traditional radiotherapy techniques. Therefore, high set-up accuracy and reproducibility are mandatory. Purpose: To investigate the effectiveness of two different immobilization techniques during conformal radiotherapy of prostate cancer with small fields. Materials and methods: 52 patients with prostate cancer were treated by conformal three- or four-field techniques with radical or adjuvant intent between November 1996 and March 1998. In total, 539 portal images were collected on a weekly basis for at least the first 4 weeks of the treatment on lateral and anterior 18 MV X-ray fields. The average number of sessions monitored per patient was 5.7 (range 4–10). All patients were immobilized with an alpha-cradle system; 25 of them were immobilized at the pelvis level (group A) and the remaining 27 patients were immobilized in the legs (group B). The shifts with respect to the simulation condition were assessed by measuring the distances between the same bony landmarks and the field edges. The global distributions of cranio-caudal (CC), posterior-anterior (PA) and left-right (LR) shifts were considered; for each patient random and systematic error components were assessed by following the procedure suggested by Bijhold et al. (Bijhold J, Lebesque JV, Hart AAM, Vijlbrief RE. Maximising set-up accuracy using portal images as applied to a conformal boost technique for prostatic cancer. Radiother. Oncol. 1992;24:261–271). For each patient the average isocentre (3D) shift was assessed as the quadratic sum of the average shifts in the three directions. Results: Group B showed a better accuracy and reproducibility than group A for PA shifts (2.6 versus 4.4 mm, 1 SD), LR shifts (2.4 versus 3.6 mm, 1 SD) and CC shifts (2.7 versus 3.3 mm, 1 SD). Furthermore, group B showed a rate of large PA shifts (>5 mm) equal to 4.4% with respect to the 21.6% of group A ( P<0.0001). This value was also better than the corresponding value found in a previously investigated group of 21 non-immobilized patients (Italia C, Fiorino C, Ciocca M, et al. Quality control by portal film analysis of the conformal radiotherapy of prostate cancer: comparison between two different institutions and treatment techniques (abstract). Radiother. Oncol. 1997;43(Suppl. 2):S16, 16.8%, P=0.001). For both groups there was no clear prevalence of one component (systematic or random) with respect to the other. The average isocentre shifts (averaged on all patients) were 3.0 mm (±1.4 mm, 1 SD) for group B and 5.0 mm (±2.8 mm, 1 SD) for group A against a value of 4.4 mm (±2.4 mm, 1 SD) for the previously investigated non-immobilized patient group. Conclusions: Immobilization of the legs with an alpha-cradle system seems to improve both the accuracy and reproducibility of the positioning of patients treated for prostate cancer with respect to alpha-cradle pelvic-abdomen immobilization. Based on these data, we decided to use the legs immobilization system and to reduce the margin around the CTV (from 10 to 8 mm) in the PA direction.

Deep Venous Thrombosis and the Risk of Pulmonary Embolism: A Systematic Study

The Influence of several diseases and clinical conditions on the presence oí pulmonary embolism (PE) in a large series of patients with deep venous thrombosis (DVT) in the lower extremities was analyzed prospectively. Lung scan findings from a series of 434 consecutive patients with DVT (with and without symptoms of PE) were studied and then correlated to five clinical variables: age, sex, elapsed time since clinical symptoms had appeared in the leg to diagnosis, degree of proximity of venous thrombus, and the presence or not of several risk factors that could have predisposed to thrombus development. According to scintigraphic findings, 164 patients were considered to have PE (asymptomatic in 76 of them), while 200 patients were classified as having only DVT. Lung scan was considered to be indeterminate for PE in 70 patients, and they were not included in the study. No differences were found in terms of age, sex, interval of time elapsed since onset of symptoms to diagnosis, or in the degree of proximity of the thrombus. However, several differences between groups were found when comparing the presence or absence of several predisposing factors for thrombosis: DVT developing in immobilized patients was associated with a significantly lower incidence of PE as compared with nonimmobilized patients (p = 0.005). Conversely, patients with a history of venous thromboembolism (VTE) had a significantly higher rate of embolism (31/51 vs 133/313; p = 0.01). On logistic regression analysis, a history of VTE showed a statistically significant association with more than a twofold higher risk of having PE for patients with such an antecedent. Our findings suggest that different pathophysiologic pathways could perhaps explain differences in embolic potential. The Influence of several diseases and clinical conditions on the presence oí pulmonary embolism (PE) in a large series of patients with deep venous thrombosis (DVT) in the lower extremities was analyzed prospectively. Lung scan findings from a series of 434 consecutive patients with DVT (with and without symptoms of PE) were studied and then correlated to five clinical variables: age, sex, elapsed time since clinical symptoms had appeared in the leg to diagnosis, degree of proximity of venous thrombus, and the presence or not of several risk factors that could have predisposed to thrombus development. According to scintigraphic findings, 164 patients were considered to have PE (asymptomatic in 76 of them), while 200 patients were classified as having only DVT. Lung scan was considered to be indeterminate for PE in 70 patients, and they were not included in the study. No differences were found in terms of age, sex, interval of time elapsed since onset of symptoms to diagnosis, or in the degree of proximity of the thrombus. However, several differences between groups were found when comparing the presence or absence of several predisposing factors for thrombosis: DVT developing in immobilized patients was associated with a significantly lower incidence of PE as compared with nonimmobilized patients (p = 0.005). Conversely, patients with a history of venous thromboembolism (VTE) had a significantly higher rate of embolism (31/51 vs 133/313; p = 0.01). On logistic regression analysis, a history of VTE showed a statistically significant association with more than a twofold higher risk of having PE for patients with such an antecedent. Our findings suggest that different pathophysiologic pathways could perhaps explain differences in embolic potential. The Tip of the Thromboembolism IcebergCHESTVol. 102Issue 3PreviewThe article by Monreal et al in this issue (see page 677 ) reminds us how much we have learned about venous thromboembolism, as well as how much we have yet to discover. Despite a serious effort to study 500 patients with thromboembolic disease using clinical information as well as both venography and ventilation-perfusion lung scan results, the study is a demonstration of how our understanding of this spectrum of elusive and dangerous conditions remains limited and how, even today, our clinical decisions have to be made in a setting of considerable uncertainty. Full-Text PDF

Deep venous thrombosis and the risk of pulmonary embolism. A systematic study.

The influence of several diseases and clinical conditions on the presence of pulmonary embolism (PE) in a large series of patients with deep venous thrombosis (DVT) in the lower extremities was analyzed prospectively. Lung scan findings from a series of 434 consecutive patients with DVT (with and without symptoms of PE) were studied and then correlated to five clinical variables: age, sex, elapsed time since clinical symptoms had appeared in the leg to diagnosis, degree of proximity of venous thrombus, and the presence or not of several risk factors that could have predisposed to thrombus development. According to scintigraphic findings, 164 patients were considered to have PE (asymptomatic in 76 of them), while 200 patients were classified as having only DVT. Lung scan was considered to be indeterminate for PE in 70 patients, and they were not included in the study. No differences were found in terms of age, sex, interval of time elapsed since onset of symptoms to diagnosis, or in the degree of proximity of the thrombus. However, several differences between groups were found when comparing the presence or absence of several predisposing factors for thrombosis: DVT developing in immobilized patients was associated with a significantly lower incidence of PE as compared with nonimmobilized patients (p = 0.005). Conversely, patients with a history of venous thromboembolism (VTE) had a significantly higher rate of embolism (31/51 vs 133/313; p = 0.01). On logistic regression analysis, a history of VTE showed a statistically significant association with more than a twofold higher risk of having PE for patients with such an antecedent. Our findings suggest that different pathophysiologic pathways could perhaps explain differences in embolic potential.