Bidirectional Text Compression in External Memory

Bidirectional compression algorithms work by substituting repeated substrings by references that, unlike in the famous LZ77-scheme, can point to either direction. We present such an algorithm that is particularly suited for an external memory implementation. We evaluate it experimentally on large data sets of size up to 128 GiB (using only 16 GiB of RAM) and show that it is significantly faster than all known LZ77 compressors, while producing a roughly similar number of factors. We also introduce an external memory decompressor for texts compressed with any uni- or bidirectional compression scheme

Prevention of Dabigatran-Related Gastrointestinal Bleeding With Gastroprotective Agents: A Population-Based Study

BACKGROUND & AIMS: Use of dabigatran, an inhibitor of thrombin, increases the risk of gastrointestinal bleeding (GIB). However, it is not clear whether gastroprotective agents (GPAs) prevent GIB in dabigatran users. We investigated the risk of GIB and the role of gastroprotective agents (including proton pump inhibitors and histamine type-2-receptor antagonists) in patients using dabigatran. METHODS: We performed a retrospective cohort study using a population-wide database managed by the Hong Kong Hospital Authority. Patients newly prescribed dabigatran from 2010 through 2013 were included in the analysis. Poisson regression was used to assess the risk of GIB in dabigatran users by incidence rate ratio (IRR), adjusted for patient characteristics, comorbidities, and concurrent medications. RESULTS: Among the 5041 patients newly prescribed dabigatran, 124 (2.5%) developed GIB during follow-up evaluation (4.2/100 patient-years). The risk of GIB in this population increased among patients 75 years and older (IRR, 2.47; 95% confidence interval [CI], 1.66-3.68), patients with a history of peptic ulcers or GIB (IRR, 2.31; 95% CI, 1.54-3.46), and patients who used aspirin (IRR, 1.52; 95% CI, 1.03-2.24). Concomitant use of gastroprotective agents was associated with a reduced risk of GIB (IRR, 0.52; 95% CI, 0.35-0.77). Subcategory analysis showed that use of proton pump inhibitors (IRR, 0.53; 95% CI, 0.31-0.91) or histamine type-2-receptor antagonists (IRR, 0.61; 95% CI, 0.40-0.94) were associated with a lower risk of GIB. Further analysis showed that the risk reduction by gastroprotective agents was significant for only upper GIB (IRR, 0.29; 95% CI, 0.15-0.54), and only for patients with a prior history of peptic ulcers or GIB (IRR, 0.14; 95% CI, 0.06-0.30). CONCLUSIONS: In the Hong Kong population, use of gastroprotective agents was associated with a reduced risk of GIB in patients taking dabigatran. The association was stronger for upper GIB than lower GIB, and in patients with a prior history of peptic ulcers or GIB

Gastrointestinal bleeding after liver transplantation

To investigate the causes of gastrointestinal bleeding (GIB) and its impact on patient and graft survival after orthotopic liver transplantation (OLTx), the first 1000 consecutive OLTx using tacrolimus were studied. Our patient population consisted of 834 adults. The bleeding episodes of patients with GIB (n=74) were analyzed, and patients without GIB (n=760) were used as controls. The mean age, gender, and United Network for Organ Sharing status were similar in both groups. Endoscopy was done in 73 patients with GIB and yielded a diagnosis in 60 patients (82.2%): 39 with a single, and 21 with multiple GIB episodes. In the remaining 13 patients (17.8%), the bleeding source was not identified. Of 92 GIB episodes with endoscopic diagnoses, ulcers (n=25) were the most common cause of bleeding, followed by enteritis (n=24), portal hypertensive lesions (n=15), Roux-en-Y bleeds, and other miscellaneous events (n=28). The majority (73%) of the GIB episodes occurred during the first postoperative trimester. The patient and graft survival rates were statistically lower in the GIB group compared with the control group. The adjusted relative risk of mortality and graft failure was increased by bleeding. In summary, the cumulative incidence of GIB was 8.9%. Endoscopy identified the source of GIB in most cases. Ulcers were the most common cause of GIB after OLTx. The onset of GIB after OLTx was an indicator of decreased patient and graft survival

Gastrointestinal bleeding in patients on novel oral anticoagulants: Risk, prevention and management

Novel oral anticoagulants (NOACs), which include direct thrombin inhibitor (dabigatran) and direct factor Xa inhibitors (rivaroxaban, apixaban and edoxaban), are gaining popularity in the prevention of embolic stroke in non-valvular atrial fibrillation as well as in the prevention and treatment of venous thromboembolism. However, similar to traditional anticoagulants, NOACs have the side effects of bleeding, including gastrointestinal bleeding (GIB). Results from both randomized clinical trials and observations studies suggest that high-dose dabigatran (150 mg b.i.d), rivaroxaban and high-dose edoxaban (60 mg daily) are associated with a higher risk of GIB compared with warfarin. Other risk factors of NOAC-related GIB include concomitant use of ulcerogenic agents, older age, renal impairment, Helicobacter pylori infection and a past history of GIB. Prevention of NOAC-related GIB includes proper patient selection, using a lower dose of certain NOACs and in patients with renal impairment, correction of modifiable risk factors, and prescription of gastroprotective agents. Overt GIB can be managed by withholding NOACs followed by delayed endoscopic treatment. In severe bleeding, additional measures include administration of activated charcoal, use of specific reversal agents such as idarucizumab for dabigatran and andexanent alfa for factor Xa inhibitors, and urgent endoscopic management.published_or_final_versio

An old problem with a new therapy: GI bleeding in VAD patients and deep bowel enteroscopy (Double balloon. Spiral enteroscopy).

An old problem with a new therapy: GI Bleeding in VAD patients and deep bowel enteroscopy (Spiral and Double Balloon Enteroscopy) Purpose: Evidence suggests that patients treated with non-pulsatile ventricular assist devices (VAD) are at an increased risk for gastrointestinal bleeding (GIB) beyond what is expected from routine anticoagulation. Diagnostic and treatment algorithms are currently undefined. We reviewed our experience of GIB in VAD patients and propose a new algorithm utilizing deep bowel enteroscopy (DBE) aimed to speed diagnosis and limit transfusions. (471) Methods & Procedures From 2004 to 2011, we studied 62 patients who received a non-pulsatile VAD at our center for episodes of GIB. GIB was defined as heme-positive stool, hematemeisis, or drop in Hgb\u3e1gm. All patients were anticoagulated and no patient had any previous bleeding history. The diagnostic and treatment modalities utilized consisted of standard GIB tests but evolved into an algorithm based primarily on DBE. DBE consists of double-balloon and spiral enteroscopy that allow us to see and treat pathology in the small bowel upt o 400 cm beyond the Ligament of Treitz. (723) Results: There were 41 individual episodes of GIB in 14 patients. Separating the episodes into two groups based on days to diagnosis and days to treatment, we found that when the diagnosis was made and treated within 2 hospital days, patients received half (3.53 v. 7.33 with

An old problem with a new therapy: gastrointestinal bleeding in ventricular assist device patients and deep overtube-assisted enteroscopy.

Conventional algorithms for diagnosis and treatment of gastrointestinal bleeding (GIB) in patients with nonpulsatile ventricular assist devices (VADs) may take days to perform while patients require transfusions. We developed a new algorithm based on deep overtube-assisted enteroscopy (DOAE) to facilitate a rapid diagnosis and treatment. From 2004 to 2012, 84 patients who underwent VAD placement in our institution, were evaluated for episodes of GIB. Our new algorithm for the management of GIB using DOAE was evaluated by dividing the episodes into three groups: group A (traditional management without enteroscopy), group B (traditional management with enteroscopy performed \u3e24 hours after presentation), and group C (new management algorithm with enteroscopy performedpresentation). Gastrointestinal bleeding was observed in 14 (17%) of our study patients for a total of 45 individual episodes of which 28 met our criteria for subanalysis. Forty-one (84%) lesions were confined to the upper gastrointestinal tract with more than 91% of these lesions being arteriovenous malformations. Average number of transfusions in groups A, B, and C were 4.1, 6.3, and 1.3, respectively (p = 0.001). The number of days to treatment was significantly shorter in group C than group B (0.4 vs. 5.3 days, p = 0.0002). Our new algorithm for the management of GIB using DOAE targets the most common locations of bleeding found in this patient population. When performed early, DOAE has the potential to decrease the need for transfusions and allow for an early diagnosis of GIB in VAD recipients