***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    Input: BACKGROUND Unfractionated heparin and the low molecular weight heparin , dalteparin , are used for prophylaxis against venous thromboembolism in patients undergoing craniotomy . These drugs were compared in a r and omized , prospect i ve pilot study comparing intermittent pneumatic compression devices plus dalteparin to intermittent pneumatic compression devices plus heparin . METHODS One hundred patients undergoing craniotomy were r and omly allocated to receive perioperative prophylaxis with subcutaneous ( SC heparin , 5000 units every 12 hours , or dalteparin , 2,500 units once a day , begun at induction of anesthesia and continued for 7 days or until the patient was ambulating . Entry criteria were age over 18 years , no deep vein thrombosis ( DVT ) preoperatively as judged by lower limb duplex ultrasound and no clinical evidence of pulmonary embolism preoperatively . Patients with hypersensitivity to heparin , penetrating head injury or who refused informed consent were excluded . Patients underwent a duplex study 1 week after surgery and 1 month clinical follow-up . All patients were treated with lower limb intermittent pneumatic compression devices . RESULTS There were no differences between groups in age , gender , and risk factors for venous thromboembolism . There were no differences between groups in intraoperative blood loss , transfusion requirements or postoperative platelet counts . Two patients receiving dalteparin developed DVT ( one symptomatic and one asymptomatic ) . No patient treated with heparin developed DVT and no patient in either group developed pulmonary embolism . There were two hemorrhages that did not require repeat craniotomy in patients receiving dalteparin and one that did require surgical evacuation in a patient treated with heparin . Drug was stopped in two patients treated with dalteparin because of thrombocytopenia . None of these differences were statistically significant . CONCLUSION There was no significant difference in postoperative hemorrhage , venous thromboembolism or thrombocytopenia between heparin and dalteparin . The results suggest that , given the small sample size of this trial , both drugs appear to be safe and the incidence of venous thromboembolism by postoperative screening duplex ultrasound appears to be low when these agents are used in combination with intermittent pneumatic compression devices OBJECTIVE Prophylactic therapies have demonstrated efficacy in reducing the incidence of deep venous thrombosis ( DVT ) in neurosurgical patients . Retrospective analysis of patients undergoing neurosurgical procedures at the University of Michigan demonstrated a high incidence ( 14 % ) of postoperative DVT among patients with intracranial neoplasms treated with sequential compression device ( SCD ) prophylaxis alone . Therefore , we investigated the efficacy and safety of the low-molecular weight heparin enoxaparin in preventing DVT in patients with brain tumors . The goal of the study was to compare SCD , enoxaparin , and combined SCD/enoxaparin prophylaxis among patients requiring surgery for treatment of intracranial neoplasms . METHODS Eligible patients were r and omized to SCD , enoxaparin , or combined therapy .  Treatment was initiated before the induction of anesthesia and was continued throughout the hospital stay . Patients were screened for DVT , using duplex imaging , on four occasions in the first 1 month after surgery . The incidences of DVT and serious adverse events were compared between groups using analysis of variance and the Dunnet two-sided t test . RESULTS Sixty-eight patients completed the study .  Postoperative DVT occurred in 3 of 22 ( 13.6 % ) SCD-treated patients , 1 of 23 ( 4.3 % ) enoxaparin-treated patients , and 4 of 23 ( 17.4 % ) SCD/enoxaparin-treated patients . Differences were not statistically significant . Postoperative intracranial hemorrhage did not occur in patients in the SCD-treated group , whereas 5 of 46 patients receiving low-molecular weight heparin suffered clinical ly significant intracranial hemorrhage . The study was terminated because of the increased incidence of adverse events in the enoxaparin-treated groups . CONCLUSION Enoxaparin therapy initiated at the time of anesthesia induction increases postoperative intracranial hemorrhage Forty-six patients who underwent surgery for brain tumors were studied prospect ively with 125I labeled Fibrinogen leg scans to detect postoperative venous thrombosis . The incidence of thrombosis was 72 % for meningioma patients , 60 % for glioblastoma patients , and 20 % for brain metastasis patients .Correlation between the occurrence of venous thrombosis and the various clinical factors thought to be responsible for the high incidence of thrombosis generally failed to show statistical significance . This finding , along with the marked variation in the incidence of venous thrombosis between the different brain tumor groups , strongly suggests that biological factors play a more important role than clinical factors in determining which brain tumor patient will suffer a postoperative thrombosic event By the use of 125I-labeled fibrinogen test , the incidence of postoperative deep vein thrombosis ( DVT ) and the effectiveness of prophylactic low-dose heparin treatment were investigated in 110 patients who underwent elective neurosurgical procedures . Fifty patients were appointed r and omly to a  control group and 50 to a heparin group ( 10 patients were excluded since they had DVT before surgery ) . The incidence of DVT was reduced from 34 % in the control group to 6 % in the heparin group ( p less than 0.005 ) . No statistically significant differences were observed in transfusion requirements , postoperative hemoglobin concentration , and the occurrence of postoperative hematomas between the two groups . Positive correlation was observed between DVT and motor deficit ( p less than 0.05 ) . Preoperative assessment of patients ' sensitivity to the st and ard 5000-unit dose of heparin was performed in all treated patients and is thought an important factor in improving the safety of heparin prophylaxis Objective Venous thromboembolism ( VTE ) after spinal surgery affects a patients ' postoperative recovery and also carries a mortality risk . Some studies recommended chemical prophylaxis for high-risk patients and for those after complex spinal surgeries . However , chemoprophylaxis for VTE in spinal surgery is underemployed and there is no agreement on the use of VTE prophylaxis in spinal surgery . The aim of this study was to document the incidence of VTE after an elective instrumental spinal surgery , among those receiving preoperative chemoprophylaxis as compared with patients who did not receive it . Methods This study was carried out on eighty-nine patients allocated r and omly to receive either low molecular weight heparin ( LMWH ) or no prophylaxis before elective instrumental spinal surgery .  All patients received postoperative compression stockings . A compression Doppler ultrasonography was performed for all patients to detect postoperative deep vein thrombosis . In addition , further imaging studies were performed for patients suspected of VTE . Results Three ( 3.3 % ) patients were diagnosed with VTE . One of them had received preoperative chemoprophylaxis . There were no significant difference in incidence of VTE between the two groups ( p>0.95 ; 95 % confidence interval , 0.06 - 8.7 ) . Laterality of gender and postsurgical recumbence duration were all independent predictors of VTE ( p=0.01 and p<0.001 , respectively ) . Conclusion The difference in the incidence of thromboembolic complications between the two groups was not significant . Moreover , we found that preoperative prophylactic LMWH injection has no major bleeding complications altering postoperative course ; still , the issue concerning the initiation time of chemoprophylaxis in spinal surgery remains unclear Although there are alternative methods and drugs for preventing venous thromboembolism ( VTE ) , it is not clear which modality is most suitable and efficacious for patients with severe ( stable or unstable ) head/spinal injures . The aim of this study was to compare intermittent pneumatic compression devices ( IPC ) with low-molecular-weight heparin ( LMWH ) for preventing VTE . We prospect ively r and omized 120 head/spinal traumatized patients for comparison of IPC with LMWH as a prophylaxis modality against VTE . Venous duplex color-flow Doppler sonography of the lower extremities was performed each week of hospitalization and 1 week after discharge . When there was a suspicion of pulmonary embolism ( PE ) , patients were evaluated with spiral computed tomography . Patients were analyzed for demographic features , injury severity scores , associated injuries , type of head/spinal trauma , complications , transfusion , and incidence of deep venous thrombosis ( DVT ) and PE . Two patients ( 3.33 % ) from the IPC group and 4 patients ( 6.66 % ) from the LMWH group died , with their deaths due to PE . Nine other patients also succumbed , unrelated to PE . DVT developed in 4 patients ( 6.66 % ) in the IPC group and in 3 patients ( 5 % ) in the LMWH group . There was no statistically significant difference regarding a reduction in DVT , PE , or mortality between groups ( p = 0.04 , p > 0.05 , p > 0.05 , respectively ) . IPC can be used safely for prophylaxis of VTE in head/spinal trauma patients CONTEXT Venous thromboembolism ( VTE ) is the most frequent complication following craniotomy for brain tumors . At Brigham and Women 's Hospital , VTE after craniotomy for brain tumor is the leading cause of deep vein thrombosis ( DVT ) and pulmonary embolism ( PE ) among patients hospitalized for conditions other than VTE . OBJECTIVE To minimize VTE among patients undergoing craniotomy for brain tumor . DESIGN R and omized , prospect i ve , double-blind clinical trial . SETTING Brigham and Women 's Hospital . PATIENTS One hundred fifty patients undergoing craniotomy for brain tumor r and omized to enoxaparin , 40 mg/d , vs heparin , 5,000 U bid , with all patients receiving graduated compression stockings and intermittent pneumatic compression . MAIN OUTCOME MEASURES The rate of DVT detected by venous ultrasonography prior to hospital discharge . RESULTS Symptomatic DVT or PE developed in none of the patients . The overall rate of asymptomatic VTE was 9.3 % , with no significant difference in the rates between the two prophylaxis groups . Ten of the 14 patients identified with VTE had thrombus limited to the deep veins of the calf . CONCLUSIONS Enoxaparin , 40 mg/d , or unfractionated heparin , 5,000 U bid , in combination with graduated compression stockings , intermittent pneumatic compression , and predischarge surveillance venous ultrasonography of the legs , result ed in 150 consecutive patients without symptomatic VTE . The low 9.3 % frequency of asymptomatic VTE comprised mostly isolated calf DVT . Therefore , this comprehensive , multimodality approach to VTE prophylaxis achieved excellent efficacy and safety Perioperative anticoagulant prophylaxis for  postoperative venous thromboembolism ( VTE ) in neurosurgical patients has not gained wide acceptance due to the fear of intracranial bleeding . Physical methods give a worthwhile reduction of postoperative VTE but there still remains a substantial residual incidence . In other clinical indications , low molecular weight heparins have proven to be effective for prophylaxis of VTE when administered postoperatively , with the advantage of no bleeding enhancement during surgery . Therefore , we performed a multicentre , r and omized , double-blind trial in neurosurgical patients to investigate the efficacy and safety of adding a low molecular weight heparin ( LMWH ) , nadroparin , initiated postoperatively , to graduated compression stockings in the prevention of VTE . Deep-vein thrombosis was detected by m and atory venography . Bleeding was determined according to pre-defined objective criteria for major and minor episodes . An adequate bilateral venogram was obtained in 166 of 241 LMWH patients ( 68.9 % ) and 179 of 244 control patients ( 73.4 % ) . A total of 31 of 166 LMWH patients ( 18.7 % ) and 47 of 179 controls patients ( 26.3 ) had VTE up to Day 10 postoperatively ( p = 0.047 ) . The relative risk reduction ( RRR ) was 28.9 % . The rates for proximal deep-vein thrombosis/pulmonary embolism were 6.9 % and 11.5 % for the two groups , respectively ( RRR : 40.2 % ; p = 0.065 ) . Secondary analyses involved all VTE up to day 56 post-surgery which was detected in 33 patients of 241 in the LMWH group ( 13.7 % ) and 51 of 244 control patients ( 20.9 % ; RRR 34.5 % ; p = 0.018 ) . The corresponding percentages for proximal deep-vein thrombosis/pulmonary embolism were 5.8 % and 10.2 % for the two groups , respectively , giving a RRR of 43.3 % ; p = 0.36 . Major bleeding complications , during the treatment period , occurred in six low molecular weight heparin treated patients ( 2.5 
    Output:
    
Based on moderate-to-good quality of evidence , chemoprophylaxis is beneficial in preventing VTE , with no significant increase in either major or minor bleeding complications in patients undergoing cranial and spinal procedures .