Individuals with leg ulcers enrolled in a randomized controlled trial between 2004 and 2008 formed the study sample . The primary outcome of the original study was time to ulcer healing (fully epithelialized, no scab, no drainage), with pain and health-related quality of life (HRQL) as secondary outcomes. Healing measures were collected as close to the first observation of healing as possible, typically the same day or the following visit. Baseline and healing assessment data from the trial formed the dataset for the current study. Ethics approval for the trial was received from Queen's University Research Ethics Board, Kingston, Ontario, Canada (REB# NURS-140-03).
As a pragmatic nursing trial several procedures are noteworthy. All participants received a comprehensive evidence-based assessment by their specially trained attending registered nurses in the community care settings located in multiple regions across Canada, including urban centers as well as remote/rural areas. Inclusion criteria for the study were: adult (≥18 years), English-speaking or with access to translation, able to provide written informed consent, clinical presentation of venous insufficiency with an ankle brachial pressure index (ABPI) ≥0.8, and a leg ulcer with minimum duration of one week that measured at least 0.7 cm in any one dimension. Ulcers smaller than 0.7 cm were excluded. Very small ulcers may be difficult to distinguish from skin erosions due to varicose eczema, and are likely to heal rapidly and may not require treatment with compression. Given the reality in community nursing care with this population, an ulcer could be either a first occurrence or recurrent ulcer. Those with medication-controlled diabetes mellitus were excluded. Full trial protocol details are described elsewhere .
For the current study the primary outcome was the prevalence of pain at time of healing. Prevalence was defined as the percent of participants with pain at time of healing. The secondary outcome was the incidence of pain at time of healing. Incidence was defined as the percent of participants with pain at time of healing of those who were free of pain at treatment initiation. Pain specific to the leg ulcer was assessed using the short form McGill Pain Questionnaire (SF-MPQ) [30–32]. The McGill Pain Questionnaire consists of 15 pain descriptors (11 sensory and 4 affective), a visual analogue scale (VAS), and the Present Pain Intensity (PPI). Each pain descriptor can be valued either as “0=none”, “1=mild”, “2=moderate”, or “3=severe”. For the purposes of the analysis values 1 through 3 were recoded as “1-3=present” versus “0=not present”. From the descriptors, sensory, affective, and total pain index scores were generated and standardized out of 100. The VAS is a 100mm scale anchored with “0=no pain” and “10=worst possible pain”. Due to the highly skewed nature of the VAS score, pain was classified in two ways: i) present (VAS>0/10) or absent (VAS = 0); and ii) none/mild (VAS≤3/10) or moderate/severe (VAS>3/10). The PPI is comprised of six number-word combinations ranging from “0=no pain” to “5=excruciating pain”. The SF-MPQ is designed to assess the multidimensional nature of the pain experience and has been demonstrated to be a reliable, valid, and consistent measurement tool . Importantly, it has been used in studies of individuals with leg ulcers and other chronic wounds and found to be a sound approach for clinically assessing the quality of pain with this population .
Predictive factors captured on admission for nursing care (baseline) included demographic and clinical characteristics, and HRQL. Demographic characteristics included age, sex, and circumstance(s) of living. Clinical characteristics included size and duration of ulcer at baseline, time to healing of current ulcer, and mobility and medications for pain control. Baseline characteristics were collected during the comprehensive baseline assessment using interviews and the Leg Ulcer Assessment Tool (LUAT) . HRQL was measured at baseline using the Medical Outcomes Survey Short Form-12 (SF-12) . The SF-12 produces two scores, the Physical Component Summary (PCS) and the Mental Component Summary (MCS). The PCS and MCS are standardized to a mean of 50, with a score above 50 representing better than average and below 50 indicating poorer than average function . A two to three point difference in summary scores is considered clinically meaningful . Individual missing items for the SF-12® were imputed using assignment of mean score (AMS) [35, 36].
Chi-square tests were used to assess the association between categorical variables and the 2-level VAS pain measures at baseline and at time of healing, while independent t-tests were used for continuous variables. Variables with a non-normal distribution were analyzed with appropriate non-parametric procedures, Mann–Whitney U test for unpaired data and Wilcoxon signed ranks test for paired data. Multivariable logistic regression was then used to identify the subset of significant predictors of pain at healing. The primary outcome for the predictive model was defined as pain present at time of healing (VAS>0/10). All regression procedures used simultaneous entry. Variables were eliminated one at a time in successive regressions if p≥0.10, and retained if p<0.10 so as not to miss clinically important trends. Odds ratios (OR) and 95% confidence intervals (CI) are reported for the final multivariable model. Analyses were conducted using IBM© SPSS© (version 20 for Windows).