Study Design
The Calgary Health Region (CHR) (population 1,197,848 as of 2006) contains three closed medical-surgical ICUs, each in academic centers affiliated with the University of Calgary. While all units manage critically ill medical and surgical patients, certain services have been regionalized. One unit is a trauma/neurosurgical referral centre with 25 beds, the second a vascular surgery referral centre that has 14 beds, and finally a 10-bed medical-surgical unit. Each ICU is staffed by attending physicians who are board-certified in critical care medicine, and do one week shifts at a time. Registered nurses are typically assigned one patient each, but may look after two patients if short-staffed.
When on service, Intensivists perform daily bedside rounds. While residents and fellows have input on the decision-making process, attending Intensivists have full responsibility for development and implementation of the daily healthcare plan on each patient in the ICU. Intensivists are on-call 24 hours per day, with call being performed from home at night. They regularly return during the night to oversee trainees. Residents from nearly every training program in the CHR, ranging from Postgraduate Year (PGY) 1 to PGY 4, complete rotations in each ICU and perform in-house overnight call. Every night has resident coverage, with residents averaging call once every fourth night. Approximately 50% of the year, an ICU fellow will also be on service at each of the sites, and will complete call from home once every three nights. Decisions to perform invasive procedures are made in conjunction with the Intensivist and depending on the experience level of the trainee, the Intensivist may or may not directly supervise the procedure. A record of all procedures is documented in the ICU electronic database, TRACER.
All patients admitted to CHR ICUs between August 1, 2002 and July 31, 2007 were identified from TRACER. If a patient was admitted to ICU more than once during the study period, one of the visits was randomly selected to be included in the analysis. During the study period, there were no major changes to the Regional Healthcare System that affected how care was delivered in the ICU.
ICU physicians were classified by their base specialty of training into one of three groups: Internal Medicine (Internal Medicine Group), Internal Medicine plus a fellowship in Pulmonary Medicine (Pulmonary Group), or Anesthesia, General Surgery and Emergency Medicine, which due to small numbers were analyzed together (AGSEM group). Over the study period three Intensivists left Calgary and six were hired.
Patients were grouped according to the base specialty of the Intensivist who admitted them to the ICU, and outcomes were compared between these groups. The primary outcome measures were ICU mortality and length of stay (LOS). We elected to use these as primary outcomes instead of the more traditional hospital mortality and LOS in order to focus on the outcomes that would maximally reflect the care provided by Intensivists and attempt to minimize effects of other variables that may influence outcomes outside of the ICU. Secondary outcomes consisted of in-hospital mortality, hospital LOS, number of invasive procedures performed and limitation of life support therapies, as judged by the number of patients changed from full care to do not resuscitate (DNR) during their ICU admission. The following invasive procedures were tracked: endotracheal intubation, chest tube, thoracentesis, central line, arterial line, pulmonary artery catheter insertion, lumbar puncture, bone marrow biopsy and paracentesis. Most procedures are done by housestaff, but direct or indirect supervision is provided by the attending Intensivist in the majority of cases.
In analysis of the entire cohort, only the identities of the admitting physicians were accounted for, despite the fact that many patients were cared for by more than one Intensivist while in ICU. A priori, we made the decision to also complete a subgroup analysis on those patients who were admitted and managed by a single Intensivist for their entire ICU admission in order to provide a more specific analysis of the impact that each Intensivist group may have on patient outcomes.
Analysis
Means for continuous data were compared using the Kruskal-Wallis test or one-way analysis of variance (ANOVA) where appropriate. Categorical data was compared with use of Fisher's Exact test.
Given the significant heterogeneity in baseline patient and Intensivist characteristics, the use of regression analysis was appropriate. However, typical regression models are unable to account for clustering of patients, so we utilized generalized estimating equations (GEE) to control for correlation between individual observations. For these analyses, two sources of correlation were identified and accounted for in each model: those related to the hospital site the patient was admitted to and those related to the individual physician who cared for the patient. To evaluate variables associated with ICU and hospital mortality, we used a model built on a binomial distribution with a logit link function. As ICU and Hospital LOS were skewed, they were natural-log transformed to approximate statistical normality, and subsequently entered into separate linear scale response models with identity as the link function. Evaluation of number of procedures performed utilized GEE based on a Poisson distribution, while the model for change in level of care was built on a binomial distribution.
Given the size of the cohort, all relevant variables felt to potentially impact the dependent variable in each of the models were included [7]. Therefore, the following independent variables were included in all of the models: patient age, gender, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, mean Therapeutic Intervention Scoring System (TISS) over first 24 hours of admission to ICU, year of admission, time of year of admission (by 28-day block to coincide with trainees' length of rotation), level of care at time of admission (full care or DNR) and discharge, admission diagnosis, Intensivist gender, Intensivist base specialty of training, years since completion of Critical Care Medicine Fellowship, and ICU occupancy at admission and at discharge. In addition, the number of invasive procedures performed per patient was included as an independent variable in all models except the one where it was the dependent variable, and ICU LOS was included as an independent variable in models assessing ICU and hospital mortality, number of invasive procedures performed, and the change in level of care. Separate analyses with adjustment for the variables listed above were completed for the entire cohort and the subgroup of patients who were admitted and managed by a single Intensivist. Detailed results of these analyses are provided in Additional file 1.
All P values < 0.05 were considered significant. Statistical analysis was done using Stata version 8.0 (College Station, Texas, USA) and SUDAAN version 9.0 (RTI International, Raleigh, North Carolina, USA). Prior to initiation of this study, ethical approval was obtained from the Conjoint Health Research Ethics Board at the University of Calgary. Permission for waiver of consent was obtained as this was a retrospective review of a database and all data was made anonymous at the time of acquisition from TRACER.