Design and setting
This was a retrospective cohort study of adult patients who were admitted to the medical-surgical ICU of King Abdulaziz Medical City, Riyadh, Saudi Arabia from March 1999 to December 2010. The ICU is a 21-bed closed unit with a 24 hours/7 days in-house coverage by board-certified intensivists and admits approximately 900 patients per year. The hospital is a tertiary care referral center and is accredited by the Joint Commission International. The study was approved by the Institutional Review Board of the hospital. The consent was waived because of the observational nature of the study.
Transfer requests are initiated by the referring hospitals or by the patients’ families. A medical report is sent from the referring hospital detailing the medical condition and justification for the transfer. The report is then reviewed by an administrative committee to determine the eligibility of the patient for hospital admission. The concerned services and the ICU team assess eligible patients using the data in the medical report and by phone conversation with the referring physician if required, for potential benefit from the transfer and the stability for the transfer. Once the patient is accepted, the transfer process is initiated. Patients are transferred only if the clinical condition is deemed stable enough as judged by the respiratory, cardiovascular, and other clinical parameters. Transfers occur by fixed-wing airplanes, helicopters, or by ground ambulances depending on the distance from the referring hospitals. The transportation team normally consists of an intensivist or anaesthetist physician and a critical care nurse. The ambulance, helicopter, and fixed-wing airplane are equipped with life support equipments.
We extracted data for this study as a part of a quality improvement project from our ICU database, which recorded all consecutive admissions prospectively by a full-time data collector. The following variables were collected: source of admission to the ICU (other hospitals, emergency department (ED), and hospital wards), age, gender, height, weight, acute physiology and chronic health evaluation (APACHE) II score, chronic comorbidities (chronic liver, chronic cardiovascular, chronic respiratory, chronic renal, and chronic immunocompromised) as defined by APACHE II system, admission diagnosis category (respiratory, cardiovascular, neurological, other medical, nonoperative trauma, and postoperative), history of diabetes mellitus, admission postcardiac arrest, and mechanical ventilation (MV). We also documented physiologic and clinical characteristics on the first hour of ICU admission that included heart rate >150 beats/min, hypotension (defined as systolic blood pressure (SBP) <90 mmHg), and acute kidney injury (AKI) (defined as creatinine level >176.8 μmol/L). The following variables were documented during the ICU course: tracheostomy, renal replacement therapy (RRT) using continuous venovenous hemodialysis (CVVHD) or intermittent hemodialysis (HDI), and do-not-resuscitate (DNR) orders.
All consecutive patients admitted to the ICU were included in the study. Patients were divided into three groups according to the source of admission to the ICU: transfers from other hospitals, direct admissions from the ED, and admitted from hospitals wards. Patients with direct admission from hospital wards were usually nontrauma patients, because trauma patients come to ICU through ED or from other hospitals. Patients who were admitted from the operating room and recovery room were excluded because of major differences in their course and outcome from transferred patients.
The primary outcome was the hospital mortality and was available for all patients at the time of hospital discharge and refers to the outcome from King Abdulaziz Medical City. None of the patients were transferred back to the referral center. The secondary outcomes were ICU mortality, ICU and hospital length of stay (LOS), mechanical ventilation duration, and need for tracheostomy and RRT.
Continuous data were presented as means with standard deviations (SD) and categorical data as frequencies and percentages. Chi-square or Student’s t test was used to test significant differences between the patients transferred from other hospitals and each of the other two groups as appropriate. To adjust for differences in severity of illness among the groups, standardized mortality ratio (SMR) was calculated by dividing the observed mortality by that predicted by the APACHE II and was reported with its 95% confidence interval (CI). We also performed stratified analysis for the following admission categories: respiratory, cardiovascular, neurological, other medical, nonoperative trauma, and postoperative. To determine the predictors of hospital mortality among patients transferred from other hospitals, multivariate step-wise logistic regression analyses with hospital mortality as dependent variable were carried out with the following independent variables entered in the model: age, gender, APACHE II score on admission, admission diagnosis category, chronic comorbidities, mechanical ventilation, and admission physiological and clinical variables (coma, heart rate, SBP, and AKI). P < 0.05 was considered significant. Statistical analysis software (SAS, version 9.0; SAS Institute, Cary, NC) was used to analyze data.