Biomedical subjects

Dimitrios Stefanidis

Publications and source records attributed to Dimitrios Stefanidis.

14 recordsLinked to original sources

PubMed2006

Construct and face validity and task workload for laparoscopic camera navigation: virtual reality versus videotrainer systems at the SAGES Learning Center.

BACKGROUND: Laparoscopic camera navigation (LCN) training on simulators has demonstrated transferability to actual operations, but no comparative data exist. The objective of this study was to compare the construct and face validity, as well as workload, of two previously validated virtual reality (VR) and videotrainer (VT) systems. METHODS: Attendees (n = 90) of the SAGES 2005 Learning Center performed two repetitions on both VR (EndoTower) and VT (Tulane Trainer) LCN systems using 30 degrees laparoscopes and completed a questionnaire regarding demographics, simulator characteristics, and task workload. Construct validity was determined by comparing the performance scores of subjects with various levels of experience according to five parameters and face validity according to eight. The validated NASA-TLX questionnaire that rates the mental, physical, and temporal demand of a task as well as the performance, effort, and frustration of the subject was used for workload measurement. RESULTS: Construct validity was demonstrated for both simulators according to the number of basic laparoscopic cases (p = 0.005), number of advanced cases (p < 0.001), and frequency of angled scope use (p < 0.001), and only for VT according to training level (p < 0.001) and fellowship training (p = 0.008). Face validity ratings on a 1-20 scale averaged 15.4 +/- 3 for VR vs. 16 +/- 2.6 for VT (p = 0.04). Ninety-six percent of participants rated both simulators as valid educational tools. The NASA-TLX overall workload score was 69.5 +/- 24 for VR vs. 68.8 +/- 20.5 for VT (p = 0.31). CONCLUSIONS: This is the largest study to date that compares two validated LCN simulators. While subtle differences exist, both VR and VT simulators demonstrated excellent construct validity, good face validity, and acceptable workload parameters. These systems thus represent useful training devices and should be widely used to improve surgical performance.

Adult↗

PubMed2006

Gallbladder perforation: risk factors and outcome.

BACKGROUND: Gallbladder perforation is difficult to diagnose and is associated with significant morbidity. This study investigates factors affecting outcome in patients with gallbladder perforation over two decades. MATERIALS AND METHODS: From 1982 to 2002 data from patients undergoing cholecystectomy at one institution were prospectively collected. Patients treated for gallbladder perforation and gangrenous cholecystitis were identified and outcomes were compared. The chi(2) test, Student's t-test, and Mann-Whitney rank sum test were used for statistical analysis. RESULTS: Two hundred eight of 11,360 patients who underwent cholecystectomy were diagnosed with gangrenous cholecystitis and 30 were diagnosed with gallbladder perforation. The perforation was contained in 9 and free in 21 patients. The diagnosis of gallbladder perforation was made preoperatively in 3% of patients. Men outnumbered women and Hispanics outnumbered Caucasians. Compared to patients with gangrenous cholecystitis, patients with gallbladder perforation presented at an older age (53 versus 60 years; P < 0.05), had more cardiovascular comorbidity (29% versus 50%; P < 0.05) and postoperative complications (19% versus 37%; P < 0.05), and required more ICU admissions (9% versus 33%; P < 0.001) and longer hospital stays (8 versus 13 days; P < 0.001). Early cholecystectomy within 24 h improved outcome (P < 0.05). CONCLUSIONS: Gallbladder perforation is a rare complication of cholelithiasis that occurs more often in men, Hispanics, and older patients. It is rarely diagnosed preoperatively. Late operative intervention is associated with increased morbidity, mortality, number of ICU admissions, and long postoperative hospital stays. An early cholecystectomy strategy may lead to improved outcomes but may be difficult to implement and may not be cost-effective.

Age Factors↗

PubMed2006

Intensive continuing medical education course training on simulators results in proficiency for laparoscopic suturing.

BACKGROUND: The purpose of this study was to determine the feasibility and effectiveness of implementing a validated suturing curriculum as a free-standing continuing medical education (CME) course. METHODS: Eighteen participants (9 practicing surgeons, 9 surgery residents) attended a 4-hour laparoscopic suturing CME course. After viewing an instructional videotape all participants had their baseline performance measured on a fundamentals of laparoscopic surgery-type videotrainer suture model. Participants then practiced on the model with active instruction from 6 proctors until a previously reported proficiency level was achieved or until the course ended. Performance was scored objectively based on time and errors. Precourse and postcourse questionnaires were collected. RESULTS: Participants trained for 2.6 +/- .8 hours and performed 37 +/- 11 repetitions. Although no participant was proficient at baseline, 72% achieved the proficiency level by the end of the course. Participants showed 44% improvement in objective scores and 34% improvement according to subjective self-rating. CONCLUSIONS: Although 4 hours may be insufficient for some trainees, an intensive half-day CME course is feasible and effective in significantly improving performance and allowing the majority of participants to achieve proficiency.

Adult↗

PubMed2006

Extended interval for retrieval of vena cava filters is safe and may maximize protection against pulmonary embolism.

BACKGROUND: Retrieval of optional vena cava filters (VCF) has been demonstrated to be safe and feasible in injured patients in 4 recent studies. However, 2 pulmonary emboli PE were reported in these studies with mean implant durations less than 19 days. In light of these occurrences, we changed our practice for VCF retrieval when patients had recovered from their injuries and at least 30 days after their discharge, or had been stable on therapeutic anticoagulation for deep venous thrombosis (DVT) or PE for at least 2 weeks. The aim of the current study was to assess the safety of this approach. METHODS: A review of prospectively collected data on optional VCF over a 16-month period. The filters were inserted prophylactically per an institutional practice guideline or for the presence of DVT or PE with a contraindication and/or complication to anticoagulation. All patients underwent duplex imaging of the lower extremities and had pre- and post- retrieval cavagrams. Demographics, duration of implantation, and complications were recorded. RESULTS: Eighty-three patients had optional VCF inserted since the change in our clinical practice. Indications included prophylaxis for high-risk trauma patients (n = 58), DVT or PE with acute contraindication to therapeutic anticoagulation (n = 22), or complications of anticoagulation (n = 3). Two patients developed lower extremity DVT after filter insertion and 1 patient developed a vena cava thrombosis. Retrieval was successful in 47 of 54 cases (87%) attempted. Median implantation duration was 142 days (range 17-475). A filter strut fracture occurred during retrieval without further consequences. No post-insertion or post-retrieval PE occurred in this study. CONCLUSION: Extended intervals for retrieval of VCF are safe and may maximize protection against pulmonary embolism.

Adolescent↗

PubMed2006

Proficiency maintenance: impact of ongoing simulator training on laparoscopic skill retention.

BACKGROUND: Proficiency-based training in laparoscopic suturing and knot tying translates to the operating room, but little is known about the durability of acquired skill. The purpose of this study was to determine the effect of maintenance training on skill retention after demonstration of proficiency. STUDY DESIGN: Medical students (n=18) with no previous laparoscopic or simulator experience were enrolled in an IRB-approved randomized controlled trial. All subjects trained to proficiency (score of 512, based on time and errors) on a previously validated suturing model (Fundamentals of Laparoscopic Surgery videotrainer). Subjects were then randomized to a control group, which received no additional training, and an ongoing training group, which trained again to proficiency at 1 and 3 months (immediately after testing). Simulator testing was repeated at 2 weeks, 1 month, 3 months, and 6 months after initial training. No subject had interval operative experience. RESULTS: Both groups demonstrated excellent skill retention during followup; performance scores, reported as means+/-SD, were 488+/-57 versus 482+/-55 at 2 weeks (p=ns), 483+/-81 versus 491+/-64 at 1 month (p=ns), 467+/-75 versus 470+/-67 at 3 months (p=ns), and 462+/-62 versus 492+/-43 at 6 months (p=0.02) for the control versus ongoing training groups, respectively. At 6 months, the ongoing training group showed better skill retention (95% versus 90%; p=0.02) and a trend for achieving the proficiency level (33% versus 18%; p=0.2) more often than the control group. CONCLUSIONS: Although proficiency-based training results in excellent skill retention, ongoing training substantially enhances performance and minimizes skill loss. Curricula should incorporate training that fosters maintenance of proficiency.

Adult↗

PubMed2006

Psychomotor testing predicts rate of skill acquisition for proficiency-based laparoscopic skills training.

BACKGROUND: Laparoscopic simulator training translates into improved operative performance. Proficiency-based curricula maximize efficiency by tailoring training to meet the needs of each individual; however, because rates of skill acquisition vary widely, such curricula may be difficult to implement. We hypothesized that psychomotor testing would predict baseline performance and training duration in a proficiency-based laparoscopic simulator curriculum. METHODS: Residents (R1, n = 20) were enrolled in an IRB-approved prospective study at the beginning of the academic year. All completed the following: a background information survey, a battery of 12 innate ability measures (5 motor, and 7 visual-spatial), and baseline testing on 3 validated simulators (5 videotrainer [VT] tasks, 12 virtual reality [minimally invasive surgical trainer-virtual reality, MIST-VR] tasks, and 2 laparoscopic camera navigation [LCN] tasks). Participants trained to proficiency, and training duration and number of repetitions were recorded. Baseline test scores were correlated to skill acquisition rate. Cutoff scores for each predictive test were calculated based on a receiver operator curve, and their sensitivity and specificity were determined in identifying slow learners. RESULTS: Only the Cards Rotation test correlated with baseline simulator ability on VT and LCN. Curriculum implementation required 347 man-hours (6-person team) and 795,000 dollars of capital equipment. With an attendance rate of 75%, 19 of 20 residents (95%) completed the curriculum by the end of the academic year. To complete training, a median of 12 hours (range, 5.5-21), and 325 repetitions (range, 171-782) were required. Simulator score improvement was 50%. Training duration and repetitions correlated with prior video game and billiard exposure, grooved pegboard, finger tap, map planning, Rey Figure Immediate Recall score, and baseline performance on VT and LCN. The map planning cutoff score proved most specific in identifying slow learners. CONCLUSIONS: Proficiency-based laparoscopic simulator training provides improvement in performance and can be effectively implemented as a routine part of resident education, but may require significant resources. Although psychomotor testing may be of limited value in the prediction of baseline laparoscopic performance, its importance may lie in the prediction of the rapidity of skill acquisition. These tests may be useful in optimizing curricular design by allowing the tailoring of training to individual needs.

Adult↗

PubMed2006

Colorectal cancer in Hispanics: a population at risk for earlier onset, advanced disease, and decreased survival.

BACKGROUND: While colorectal cancer (CRC) incidence and mortality rates have declined slightly over the past decade, there remain marked differences by ethnicity. Our aim was to investigate ethnic differences in occurrence, clinical presentation and outcome of CRC at a tertiary university center that serves a predominantly Hispanic population. METHODS: Prospectively collected data from the tumor registry on patients diagnosed with colorectal cancer from 1985 through 2001 was examined. Age at diagnosis, mode of presentation, sex, tumor location, ethnicity, TNM stage, and survivals were assessed and ethnic differences were sought. RESULTS: Records from 453 patients with CRC were reviewed. There were 296 (65%) patients that were Hispanics, 112 (25%) non-Hispanic Whites, 37 (8%) African Americans, and 8 (2%) of other or unknown ethnicity. Compared with non-Hispanic Whites, Hispanics presented at a younger age (58.5 +/- 14 versus 53.6 +/- 12.73, respectively; P < 0.01), with a significantly greater incidence of stage IV disease (19% versus 32%, respectively; P = 0.02). They had significantly poorer age-adjusted survival (median survival of 92 months for <55 years and 77 months for >55 years versus 48 months for <55 years and 48 months for >55 years, respectively; adjusted log rank P = 0.045). There were no differences in tumor location, mode of presentation or adjuvant treatment received. CONCLUSIONS: Hispanic patients with CRC in our catchment area present at a younger age with more metastatic disease and have a poorer survival than non-Hispanic Whites. Modification of screening criteria and treatment paradigms may be required for Hispanics.

Adult↗

PubMed2005

Robotic Laparoscopic Fundoplication.

Gastroesophageal reflux disease is a very common disorder, and both medical and surgical treatments have shown outstanding results. Whereas proton pump inhibitors are the mainstay of treatment, laparoscopic fundoplication has become a very attractive alternative due to its efficacy and low morbidity. There are defined patient categories that may benefit more from laparoscopy than medical therapy, but a conclusive comparison between the two is lacking. Robotic laparoscopic fundoplication can be performed safely without increased morbidity. Potential advantages include enhanced precision, improved dexterity, and remote telesurgical applications. Disadvantages include increased cost and prolonged operative times. Further studies and more long-term outcome data are needed to fully evaluate the procedure. Robotic surgery is currently in its infancy and not cost effective but has a very promising future. With further development of automatization and miniaturization features, robotic surgery may prove more efficient than conventional laparoscopy.

Journal Article↗

PubMed2005

Skill retention following proficiency-based laparoscopic simulator training.

BACKGROUND: Proficiency-based curricula using both virtual reality (VR) and videotrainer (VT) simulators have proven to be efficient and maximally effective, but little is known about the retention of acquired skills. The purpose of this study was to assess skill retention after completion of a validated laparoscopic skills curriculum. METHODS: Surgery residents (n=14) with no previous VR or VT experience were enrolled in an Institutional Review Board-approved protocol and sequentially practiced 12 Minimally Invasive Surgical Trainer-VR and 5 VT tasks until proficiency levels were achieved. One VR (manipulate diathermy) and 1 VT (bean drop) tasks were selected for assessment at baseline, after training completion (posttest), and at retention. RESULTS: All residents completed the curriculum. Posttest assessment occurred at 13.2 +/- 11.8 days and retention assessment at 7.0 +/- 4.0 months. After an early performance decrement at posttest (17%-45%), the acquired skill was maintained up to the end of the follow-up period. For VR, scores were 81.5 +/- 23.5 at baseline, 33.3 +/- 1.8 at proficiency, 48.4 +/- 9.2 at posttest, and 48.4 +/- 11.8 at retention. For VT, scores were 49.4 +/- 12.5 at baseline, 22.0 +/- 1.4 at proficiency, 25.6 +/- 3.6 at posttest, and 26.4 +/- 4.2 at retention. Skill retention was better for VT, compared with VR (P < .02). The extent of skill deterioration did not correlate with training duration or resident level. CONCLUSIONS: Although residents do not retain all acquired skills (more so for VR than for VT) according to simulator assessment, proficiency-based training on simulators results in durable skills. Additional studies are warranted to further optimize curriculum design, investigate simulator differences, and establish training methods that improve skill retention.

Adult↗

PubMed2005

Reactivity of valganciclovir in aqueous solution.

The rates of hydrolysis of valganciclovir to ganciclovir and L-valine and isomerization of the R and S diastereomers of valganciclovir in aqueous buffer solution from pH 3.8 to 11.5 were determined at 37 degrees C. The kinetics of hydrolysis were first order for at least two half-lives in neutral and basic solutions. In acidic solutions where less than 10% degradation occurred, the rate of hydrolysis was determined assuming a first-order loss in drug. At 37 degrees C and pH 7.08, the half life is 11 h. The maximum stability at the pH values studied occurred at pH 3.81 with a half life of 220 days. The kinetics of the approach to equilibrium for the isomerization were first order and the ratio of the R:S isomer at equilibrium was 52:48. Isomerization was approximately 10 fold faster than hydrolysis over the pH range studied with a half-life at pH 7.01 of 1 h. The maximum stability toward isomerization (t1/2>533 h) occurs at a pH below 3.8. The pH-rate profile for the hydrolysis and the isomerization reaction are best described by hydroxide ion catalyzed mechanisms. In acidic and neutral solutions, the hydroxide reacts with the protonated form of the drug, while in basic solutions, the hydroxide reacts with the neutral form of the drug.

Buffers↗

PubMed2004

Evidence and consequence of porcine endogenous retrovirus recombination.

The genetic nature and biological effects of recombination between porcine endogenous retroviruses (PERV) were studied. An infectious molecular clone was generated from a high-titer, human-tropic PERV isolate, PERV-A 14/220 (B. A. Oldmixon, et al. J. Virol. 76:3045-3048, 2002; T. A. Ericsson et al. Proc. Natl. Acad. Sci. USA 100:6759-6764, 2003). To analyze this sequence and 15 available full-length PERV nucleotide sequences, we developed a sequence comparison program, LOHA(TM) to calculate local sequence homology between two sequences. This analysis determined that PERV-A 14/220 arose by homologous recombination of a PERV-C genome replacing an 850-bp region around the pol-env junction with that of a PERV-A sequence. This 850-bp PERV-A sequence encompasses the env receptor binding domain, thereby conferring a wide host range including human cells. In addition, we determined that multiple regions derived from PERV-C are responsible for the increased infectious titer of PERV-A 14/220. Thus, a single recombination event may be a fast and effective way to generate high-titer, potentially harmful PERV. Further, local homology and phylogenetic analyses between 16 full-length sequences revealed evidence for other recombination events in the past that give rise to other PERV genomes that possess the PERV-A, but not the PERV-B, env gene. These results indicate that PERV-A env is more prone to recombination with heterogeneous backbone genomes than PERV-B env. Such recombination events that generate more active PERV-A appear to occur in pigs rather frequently, which increases the potential risk of zoonotic PERV transmission. In this context, pigs lacking non-human-tropic PERV-C would be more suitable as donor animals for clinical xenotransplantation.

Animals↗

PubMed2003

Differentiation-dependent up-regulation of p47(phox) gene transcription is associated with changes in PU.1 phosphorylation and increased binding affinity.

The p47(phox) gene encodes a cytosolic component of the phagocytic NADPH oxidase complex. Expression of p47(phox) is both tissue-specific and developmentally regulated. Stable transfection of the myeloid cell lines PLB985 and HL60, with reporter gene constructs containing as little as 58 bp of proximal promoter sequence, was capable of directing significant reporter gene activity in myeloid cells, which increased significantly on induction of myeloid differentiation. EMSA analysis of a binding site for the Ets family member, PU.1, located at positions -39 to -44 revealed that the pattern of complex formation changed significantly on induction of myeloid differentiation. All EMSA complexes were competed by a functional PU.1 binding site and could be supershifted in the presence of polyclonal anti-PU.1 antibody. Reaction of EMSA complexes with anti-phosphoserine antibody, treatment with phosphatase, or Western blotting of proteins captured on the PU.1 binding site, was used to demonstrate that the changes in PU.1 complex formation dependent on myeloid differentiation were associated with increased levels of PU.1 phosphorylation. Furthermore, the more highly phosphorylated forms of PU.1 were shown to have a greater affinity for the p47(phox) PU.1 consensus binding site. Up-regulated transcriptional activity in response to myeloid differentiation can therefore be correlated with increased levels of PU.1 phosphorylation and a greater binding affinity.

Base Sequence↗

PubMedDate not supplied

Gangrenous cholecystitis in the decade before and after the introduction of laparoscopic cholecystectomy.

BACKGROUND: Gangrenous cholecystitis is a severe form of acute cholecystitis with high morbidity. This study investigate the outcomes for patients undergoing cholecystectomy for gangrenous cholecystitis in the decade before and after the introduction of laparoscopic technology at our institution. METHODS: From 1982 to 2002, all patients undergoing cholecystectomy for gangrenous cholecystitis were prospectively entered into a database. Demographic data, method of surgery, and outcome variables were assessed and compared over time. RESULTS: Cholecystectomy was performed to treat gangrenous cholecystitis in 238 patients (mean age, 54 years). From 1982 to 1992, 98 patients underwent cholecystectomy for gangrenous cholecystitis, and from 1992 to 2002, 140 patients underwent the procedure. Ninety-seven patients underwent laparoscopic cholecystectomy, and 33 patients (34%) required conversion. The open and laparoscopic cholecystectomy group differed in the number of intensive care unit admissions (13% vs. 5%, P < 0.05), overall length of hospital stay (10 vs. 5.7 days, P < 0.001) and rate of intraabdominal abscesses (8% vs. 0.7%). CONCLUSION: Gangrenous cholecystitis remains a disease with high morbidity. Laparoscopic cholecystectomy shortened hospital stay and can be offered without increasing morbidity. Methods to decrease intraabdominal abscess formation in patients undergoing laparoscopic cholecystectomy for gangrenous cholecystitis are needed.

Aged↗

PubMedDate not supplied

Safety and efficacy of metallic stents in the management of colorectal obstruction.

BACKGROUND: The use of self-expandable metallic stents in the management of obstructing colorectal cancer has been described with increasing frequency in the literature. Our goal was to evaluate the efficacy and associated morbidity of the use of self-expandable metallic stents to relieve colorectal obstruction at our institution. METHODS: A retrospective chart review of patients who underwent colorectal stent placement between December 2001 and December 2003 in a tertiary referral center was performed. RESULTS: Stents were placed successfully in 17 of 21 patients (81%) with colorectal obstruction. Placement was achieved endoscopically in 13 patients and radiologically in 4. Ten self-expandable metallic stents were used as a bridge to surgery, and 7 were used for palliation. The obstructions were located in the sigmoid colon (11 patients), the rectosigmoid (3), the splenic flexure, the hepatic flexure, and the rectum. Malignant obstruction was noted in 14 patients. One patient with malignancy experienced a sigmoid perforation, and 2 patients with benign disease had complications (1 stent migration and 1 re-obstruction). Stent patency in obstruction secondary to colonic adenocarcinoma was 100% in our follow-up period (range, 5 to 15 months). CONCLUSIONS: The use of stents as a bridge to surgery is associated with low morbidity, allows for bowel preparation, and thus avoids the need for a temporary colostomy. Long-term patency suggests that stents may allow for the avoidance of an operation in patients with metastatic disease and further defines their role in the palliation of malignant obstruction. Further prospective randomized studies are necessary to fully elucidate the use of stents in the management of colorectal cancer.

Adenocarcinoma↗