An observational cohort study was conducted on hip fracture patients admitted to a 350- and a 450-bed teaching hospital in The Hague and Delft.
Aim of the study
To determine whether anemia at admission and perioperative allogeneic blood transfusion (ABT) have an independent negative effect with mortality, occurrence of a delirium, length of hospital stay (LOS), discharge to a nursing home and 90-day readmission rate in surgically treated hip fracture patients, aged 65 years and older. Delirium has been chosen, as it is one of the most serious and most common major in-hospital complications.
Patients and methods
All patients were extracted from our digital database that contains all consecutive hip fracture patients, admitted from January 2005 to January 2010. Data were collected retrospectively for patients in the timeframe 2005-2007 and prospectively for those in the period 2008-2009.
The exclusion criteria for this study were: age < 65 years, a pathologic hip fracture, a high-energy injury and conservative treatment. Duration of follow-up in all patients was 12 months. This resulted in a cohort of 1262 admissions for a hip fracture, in 1222 patients.
From the hospital's records (both digital and paper files), age, gender, ASA classification, type of fracture, type of treatment, type of anesthesia, pre- and postoperative hemoglobin level, perioperative need for an ABT, occurrence of a delirium, LOS and discharge location were collected onto a case record form (CRF) .
Diagnosis of delirium was based on criteria of the DSM IV . Signs of a delirium are recorded in the medical and nursing records as a standard part of documentation of the daily characteristics of a patient. Delirium incidence in this series was scored based on these medical and nursing staff records. To calculate the 90-day readmission rate, all readmissions within 90 days after discharge were extracted from the digital hospital admission registration system. Postoperative mortality has been documented meticulously by repeated consultation of the population registers of the counties in the region of both hospitals as well as the hospital's patient registration systems. If present, readmissions and date of death were recorded at the CRF. As of 2008, all data were recorded prospectively in the CRF. All fore mentioned data were complete, both in the retrospective and prospective series and was performed by authors AV, BB, PP and AN.
Approval from the local ethical committee was not obtained, as this is an observational study without an intervention. Therefore, it is an evaluation of usual care as a part of good clinical practice. Since data could not be traced back to the individual patient there were no privacy issues.
Anemia and ABT policy
In all patients the hemoglobin level was measured at admission. Anemia at admission was defined based on the criteria of the World Health Organization (WHO) . These criteria classify anemia as a hemoglobin level below 7.5 mmol/L (12 g/dL) in women and below 8.1 mmol/L (13 g/dL) in men. They were tested and found sufficient for elderly by Izaks et al in their study on mortality in elderly patients .
In the Netherlands, the national CBO guideline advises ABT for subjects aged > 60 years when hemoglobin level drops below 5.0 mmol/L (8.0 g/dL) in the general population or 6.0 mmol/L (9.7 g/dL) if the patient has a serious cardiac condition or when anemia becomes symptomatic . This guideline is general practice in both hospitals. Hemoglobin level was measured on the first postoperative day as a routine and if necessary repeated thereafter based on clinical judgment.
Demographic continuous data are presented as means, with standard deviations (SD). Categorical data are presented as the number of subjects in the category, along with the percentages. Chi-square test and Fisher's exact test were used for comparing groups of categorical data.
The cohort was compared regarding differences in clinical characteristics and outcome between the anemic and non-anemic patients, based upon hemoglobin level at admission.
Univariate analysis performed to test the association between anemia and mortality (in-hospital, 3- and 12-month), delirium, LOS categories (≤ versus > 11 days), discharge to a nursing home and 90-day readmission rate. Separate logistic regression analyses were executed for each outcome, for the mortality Cox proportional hazards regression analysis was used to calculate the hazard ratio and 95% confidence interval. In these analyses, correction was performed for the possible confounders; age, gender, perioperative risk (ASA classification I/II or III/IV), receiving an ABT, type of fracture (neck of femur, (inter-) trochanteric or subtrochanteric), and type of anesthesia (general or spinal). Because of the clinical relation between the anemia and receiving an ABT collinearity diagnostics of the logistic regression models were examined.
To robustify the analysis for LOS, this parameter was changed into a binary summary outcome, i.e. ≤ or > 11 days (the median), as the distribution of the value LOS was very wide.
Patients classified ASA I or II and III or IV were combined to two groups, as the separate groups of ASA I (n = 82) and ASA IV (n = 50) classified patients were too small to be analyzed separately.
P-values lower than 0.05 were considered statistically significant. Odds ratios are displayed with a 95% confidence interval if the p-value < 0.05. All data were analyzed in SPSS 17.0 (SPSS Inc. Chicago, USA).