Peter Slasor | PubMed Health

PubMed2003

Joint models for efficient estimation in proportional hazards regression models.

In survival studies, information lost through censoring can be partially recaptured through repeated measures data which are predictive of survival. In addition, such data may be useful in removing bias in survival estimates, due to censoring which depends upon the repeated measures. Here we investigate joint models for survival T and repeated measurements Y, given a vector of covariates Z. Mixture models indexed as f (T/Z) f (Y/T,Z) are well suited for assessing covariate effects on survival time. Our objective is efficiency gains, using non-parametric models for Y in order to avoid introducing bias by misspecification of the distribution for Y. We model (T/Z) as a piecewise exponential distribution with proportional hazards covariate effect. The component (Y/T,Z) has a multinomial model. The joint likelihood for survival and longitudinal data is maximized, using the EM algorithm. The estimate of covariate effect is compared to the estimate based on the standard proportional hazards model and an alternative joint model based estimate. We demonstrate modest gains in efficiency when using the joint piecewise exponential joint model. In a simulation, the estimated efficiency gain over the standard proportional hazards model is 6.4 per cent. In clinical trial data, the estimated efficiency gain over the standard proportional hazards model is 10.2 per cent.

Algorithms↗

PubMed2003

Does the sedative agent facilitate emergency rapid sequence intubation?

OBJECTIVES: To ascertain whether the sedative agent administered during neuromuscular-blocking agent-facilitated intubation (rapid sequence intubation [RSI]) influences the number of attempts and overall success at RSI. METHODS: Records were drawn from an ongoing, prospective multicenter registry of emergency department intubations. Conditional logistic regression stratified by institution was used to identify factors associated with multiple intubation attempts and unsuccessful RSI. RESULTS: Of 3,407 intubations over 33 months in 22 institutions, 2,380 involved RSI. After correcting for the specialty and experience of the intubator and for the presence of airway aberrancy, the sedative agent was significantly associated with the number of attempts at intubation (p = 0.002). Specifically, the use of etomidate (adjusted odds ratio [OR] 0.35 [95% CI = 0.17 to 0.72]), ketamine (OR 0.27 [95% CI = 0.11 to 0.65]), a benzodiazepine (OR 0.47 [95% CI = 0.23 to 0.95]), or no sedative agent (OR 0.51 [95% CI = 0.23 to 1.13]) prior to neuromuscular blockade was associated with a lower likelihood of successful intubation on the first attempt, as compared with thiopental, methohexital, or propofol. The adjusted odds ratios for the likelihood of overall success had similar point estimates, but did not reach statistical significance due to lack of power (p = 0.2, with 36 unsuccessful intubations). Among patients receiving etomidate, intubation was more likely to be successful on the first attempt with increasing doses of either etomidate or succinylcholine. CONCLUSIONS: Thiopental, methohexital, and propofol appear to facilitate RSI in emergency department patients, independent of patient characteristics or intubator training. A deeper plane of anesthesia may improve intubating conditions in emergency patients undergoing RSI by complementing incomplete muscle paralysis.

Adolescent↗