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"Shier, David"
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Predicting the difficult laparoscopic cholecystectomy: development and validation of a pre-operative risk score using an objective operative difficulty grading system
BackgroundThe prediction of a difficult cholecystectomy has traditionally been based on certain pre-operative clinical and imaging factors. Most of the previous literature reported small patient cohorts and have not used an objective measure of operative difficulty. The aim of this study was to develop a pre-operative score to predict difficult cholecystectomy, as defined by a validated intra-operative difficulty grading scale.MethodTwo cohorts from prospectively maintained databases of patients who underwent laparoscopic cholecystectomy were analysed: the CholeS Study (8755 patients) and a single surgeon series (4089 patients). Factors potentially predictive of difficulty were correlated to the Nassar intra-operative difficulty scale. A multivariable binary logistic regression analysis was then used to identify factors that were independently associated with difficult laparoscopic cholecystectomy, defined as operative difficulty grades 3 to 5. The resulting model was then converted to a risk score, and validated on both internal and external datasets.ResultIncreasing age and ASA classification, male gender, diagnosis of CBD stone or cholecystitis, thick-walled gallbladders, CBD dilation, use of pre-operative ERCP and non-elective operations were found to be significant independent predictors of difficult cases. A risk score based on these factors returned an area under the ROC curve of 0.789 (95% CI 0.773–0.806, p < 0.001) on external validation, with 11.0% versus 80.0% of patients classified as low versus high risk having difficult surgeries.ConclusionWe have developed and validated a pre-operative scoring system that uses easily available pre-operative variables to predict difficult laparoscopic cholecystectomies. This scoring system should assist in patient selection for day case surgery, optimising pre-operative surgical planning (e.g. allocation of the procedure to a suitably trained surgeon) and counselling patients during the consent process. The score could also be used to risk adjust outcomes in future research.
Journal Article
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
BackgroundA reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.MethodsPatient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendall’s tau for dichotomous variables, or Jonckheere–Terpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.ResultsA higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both p < 0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROC = 0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all p < 0.001).ConclusionWe have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty.
Journal Article
Can Human Rationality Be Defended \A Priori\?
In this paper, I develop two criticisms of L. Jonathan Cohen's influential a priori argument that human irrationality cannot be experimentally demonstrated. The first is that the argument depends crucially on the concept of a normal human but that no such concept suitable for Cohen's purposes is available. The second is that even if his argument were granted, his thesis of an unimpeachable human capacity for reasoning is not a defense of human reasoning, but rather amounts to the claim that we cannot make any meaningful evaluative claims about human reasoning whatsoever.
Journal Article
The Temporal Stage Fallacy: A novel Statistical Fallacy in the medical literature
Celebrated for disproving the traditional view that lack of oxygen at birth (perinatal asphyxia) contributes significantly to cerebral palsy, a 1986 New England Journal of Medicine article by Karin Nelson and Jonas Ellenberg engineered a new consensus in the medical community: that lack of oxygen at birth rarely causes cerebral palsy. We demonstrate that the article's central argument relies on straightforwardly fallacious statistical reasoning, and we discuss significant implications--e.g. how carefully fetuses are monitored during labor and delivery, expert testimony in malpractice cases, and public policy decisions.
Journal Article
