The best magazine
Methods
Study subjects were recruited from the Urology Outpatient Clinic at the University of Rochester Medical Center between March 2009 and February 2011. All adult males age 18 years and older scheduled for outpatient flexible cystoscopy were eligible for participation, with the exception of patients using sedatives or regular analgesics and those with history of hypersensitivity to an esthetic agents, spinal cord in jury, or urethral disease. Follow ing informed consent, the study subjects were randomly assigned to receive either a 2% lidocaine gel (10 cc) or a plain lubricating gel administered with a 10 cc syringe. Experienced urologists performed the cystoscopy by using the 15.5 French Olympus flexible digital cystoscope. Immediately following the cystoscopy, each subject was asked by a nurse to rate how painful the procedure was on a visual pain scale from 0 (no pain) to 10 (agonizing pain). This approach to pain assessment was previously found to be valid and reliable in various settings, including chronic pain and pain resulting from a specific procedure (Farrar, Young, LaMoreaux, Werth, & Poole, 2001; Jensen & Karoly, 2001; Price, McGrath, Rafii, & Buckingham, 1983). In the current trial, all subjects, as well as urologists performing cystoscopy and nurses documenting the pain scores, were blinded to treatment assignment (i.e., they did not know whether pre-cystoscopy preparation contained the lidocaine gel or the plain lubricating gel). The Research Subjects Review Board at the University of Rochester approved this study.
Statistical Methods
The primary independent variable of interest in the current study was the randomly assigned treatment group (plain lubricating gel versus lidocaine gel). A randomly assigned list was generated by www.randomization.com for using either lidocaine gel or lubricant gel. Each subject had an equal probability of assignment to either group. The primary outcome variable was defined as the pain score assessed by the patient. Another variable included in the analysis was the subject's age at the time of cystoscopy. Data were also collected on 1) prep time, defined as the length of time between instillation of the gel and insertion of the cystoscope; 2) history of prior cystoscopic examinations (at least one prior cystoscopy vs. none); and 3) diagnosis of bladder tumor(s) on cystoscopy.
For the primary analysis, the treatment effect was expressed as the difference of mean pain scores between the two groups. Asymptotic confidence intervals for the difference of means were constructed using the standard approach (i.e., with variance of the mean difference estimated as the sum of the estimated variances of the means in each group) (Rosner, 2006). The null hypothesis of no difference in mean pain scores between the two groups was tested with the t-test (Rosner, 2006). In secondary analyses, the difference in median pain scores between the two groups was estimated using linear quantile regression model (SAS Institute, 2008). The frequency distributions of pain scores were examined in each group and compared using the Wilcoxon rank sum (Mann-Whitney U) test (Desu & Raghavarao, 2004).
In exploratory analyses, we also investigated whether the effect of assigned treatment on mean and median pain scores varied significantly according to age. Age was grouped in two categories: 1) less than the median age (75 years old) or 2) median age or above. To test for treatment-by-age interaction (i.e., whether the treatment effect differed in magnitude between the two age strata), treatment, age, and their product terms were included in the corresponding linear regression models. Ordinary least squares model with robust variance estimator was used in the analysis of interaction based on means and quantile regression was used in the analysis of interaction based on medians (Long & Ervin, 2000; SAS Institute, 2008). All analyses were performed in SAS version 9.2. All reported p-values are two-sided.
Sample Size
According to the study protocol, the target sample size for both groups combined was 80 patients. This sample size was considered to be both feasible in terms of accrual and adequate in terms of power for detection of clinically significant differences in average pain scores. However, accrual for the current study was stopped after 50 subjects were enrolled. This decision was based on clinical observation of consistently lower pain scores in the lidocaine group compared with the plain lubricating gel group.
Source: ...