Background/Aims: Enterocutaneous fistulas are associated with prolonged hospital stay, high morbidity/mortality, and increased hospital costs. This study aims to describe the use of a vacuum system and normal oral diet in dealing with this problem. Methods: Seventy-four consecutive patients with recent and defined external postoperative fistulas were analyzed. Abdominal imaging was used to exclude abscess and distal obstruction. The fistula tract was sealed with Foley catheter, connected to a negative pressure flask, changed daily for 5, 10 or 15 days, as necessary. A normal oral diet was permitted. Results: No patient died. Serum albumin and transferrin showed significantly higher levels at the end of treatment than at the beginning. The moderate and low-output fistulas had the best results (97% closed). Forty-eight (65%) fistulas closed after 5 days, 16 (22%) after 10 days and 4 (5%) after 15 days. Treatment failed in 6 (8%) patients, who subsequently underwent surgery. The fistula did not close in 1 patient with a low output. The cost of the treatment was USD 41.75/day and it was considered cost-effective. Conclusions: The vacuum system demonstrated good results in the treatment of fistulas. It included simplicity, low cost, short hospital stay, absence of skin breakdown, normal eating, good nutrition and activity patterns.
In survival studies with families or geographical units it may be of interest testing whether such groups are homogeneous for given explanatory variables. In this paper we consider score type tests for group homogeneity based on a mixing model in which the group effect is modelled as a random variable. As opposed to hazard-based frailty models, this model presents survival times that conditioned on the random effect, has an accelerated failure time representation. The test statistics requires only estimation of the conventional regression model without the random effect and does not require specifying the distribution of the random effect. The tests are derived for a Weibull regression model and in the uncensored situation, a closed form is obtained for the test statistic. A simulation study is used for comparing the power of the tests. The proposed tests are applied to real data sets with censored data.
In this paper we study the cure rate survival model involving a competitive risk structure with missing categorical covariates. A parametric distribution that can be written as a sequence of one-dimensional conditional distributions is specified for the missing covariates. We consider the missing data at random situation so that the missing covariates may depend only on the observed ones. Parameter estimates are obtained by using the EM algorithm via the method of weights. Extensive simulation studies are conducted and reported to compare estimates efficiency with and without missing data. As expected, the estimation approach taking into consideration the missing covariates presents much better efficiency in terms of mean square errors than the complete case situation. Effects of increasing cured fraction and censored observations are also reported. We demonstrate the proposed methodology with two real data sets. One involved the length of time to obtain a BS degree in Statistics, and another about the time to breast cancer recurrence.
Este trabalho apresenta um estudo de confiabilidade em dados relativos ao tempo de vida de poços petrolíferos terrestres da Petrobras, produtores de óleo na Bacia Potiguar (RN/CE). O objetivo do estudo foi, com base em um conjunto de dados sobre ocorrências de falhas, verificar a existência do relacionamento entre o tempo de vida dos poços e algumas de suas características, como método de elevação, nível de produção, BSW (Basic Sediments and Water), razão gás óleo (RGO), unidade operacional de origem, entre outras. Os dados foram obtidos de um estudo retrospectivo de uma amostra com 450 poços-colunas que se encontravam em funcionamento no período de 2000 a 2006, escolhida de forma a representar todos os poços da bacia RN/CE. Foi realizada uma modelagem probabilística dos dados relativos à primeira falha através do ajuste do modelo de regressão Weibull. O modelo se mostrou apropriado para ajustar os dados e foi possível identificar, através do teste da razão de verossimilhança, quais e de que forma algumas características influenciam o tempo até a falha dos poços.
The use of control charts for monitoring schemes in medical context should consider adjustments to incorporate the specific risk for each individual. Some authors propose the use of a risk-adjusted survival time cumulative sum (RAST CUSUM) control chart to monitor a time-to-event outcome, possibly right censored, using conventional survival models, which do not contemplate the possibility of cure of a patient. We propose to extend this approach considering a risk-adjusted CUSUM chart, based on a cure rate model. We consider a regression model in which the covariates affect the cure fraction. The CUSUM scores are obtained for Weibull and log-logistic promotion time model to monitor a scale parameter for nonimmune individuals. A simulation study was conducted to evaluate and compare the performance of the proposed chart (RACUF CUSUM) with RAST CUSUM, based on optimal control limits and average run length in different situations. As a result, we note that the RAST CUSUM chart is inappropriate when applied to data with a cure rate, while the proposed RACUF CUSUM chart seems to have similar performance if applied to data without a cure rate. The proposed chart is illustrated with simulated data and with a real data set of patients with heart failure treated at the Heart Institute (InCor), at the University of São Paulo, Brazil.
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