Battle et al. Critical Care 2014, 18:R98 http://ccforum.com/content/18/3/R98
RESEARCH
Open Access
Predicting outcomes after blunt chest wall trauma: development and external validation of a new prognostic model Ceri Elisabeth Battle1,2,3*, Hayley Hutchings1, Simon Lovett1, Omar Bouamra4, Sally Jones5, Aruni Sen6, James Gagg7, David Robinson8, Jake Hartford-Beynon9, Jeremy Williams10 and Adrian Evans1,3
Abstract Introduction: Blunt chest wall trauma accounts for over 15% of all trauma admissions to Emergency Departments worldwide. Reported mortality rates vary between 4 and 60%. Management of this patient group is challenging as a result of the delayed on-set of complications. The aim of this study was to develop and validate a prognostic model that can be used to assist in the management of blunt chest wall trauma. Methods: There were two distinct phases to the overall study; the development and the validation phases. In the first study phase, the prognostic model was developed through the retrospective analysis of all blunt chest wall trauma patients (n = 274) presenting to the Emergency Department of a regional trauma centre in Wales (2009 to 2011). Multivariable logistic regression was used to develop the model and identify the significant predictors for the development of complications. The model’s accuracy and predictive capabilities were assessed. In the second study phase, external validation of the model was completed in a multi-centre prospective study (n = 237) in 2012. The model’s accuracy and predictive capabilities were re-assessed for the validation sample. A risk score was developed for use in the clinical setting. Results: Significant predictors of the development of complications were age, number of rib fractures, chronic lung disease, use of pre-injury anticoagulants and oxygen saturation levels. The final model demonstrated an excellent c-index of 0.96 (95% confidence intervals: 0.93 to 0.98). Conclusions: In our two phase study, we have developed and validated a prognostic model that can be used to assist in the management of blunt chest wall trauma patients. The final risk score provides the clinician with the probability of the development of complications for each individual patient.
Introduction Blunt chest-wall trauma accounted for over 15% of all trauma admissions to Emergency departments (EDs) worldwide [1]. Reported mortality ranges between 4 and 60%, however, no current national guidelines exist to assist in the management of this patient group unless the patient has severe, immediate life-threatening injuries [2]. The difficulties in the management of the blunt chest-wall trauma patient are becoming increasingly well recognised in the literature [3,4]. The blunt chest-wall trauma patient commonly presents to the ED initially with * Correspondence: [email protected] 1 College of Medicine, Swansea University, Swansea, Wales, UK 2 Physiotherapy department, Morriston Hospital, Swansea, Wales, UK Full list of author information is available at the end of the article
no respiratory difficulties, but can develop respiratory complications approximately 48 to 72 hours later [5,6]. Clinical symptoms are not considered an accurate predictor of outcome following non-life threatening blunt chest-wall trauma [7]. Decisions on the appropriate level of care required by the patient following discharge from the ED are therefore difficult, which is further compounded by the lack of current national guidelines. A number of well-documented risk factors for morbidity and mortality exist for blunt chest-wall trauma, including patient age, pre-existing disease, number of ribs fractured and the onset of pneumonia during the recovery phase [2,8]. A prognostic model enables the clinician to use combinations of predictor values to estimate a probability that a specified outcome will occur [9]. The resulting model may
© 2014 Battle et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Battle et al. Critical Care 2014, 18:R98 http://ccforum.com/content/18/3/R98
be used to divide the patient into categories of risk or predict probabilities of a pre-specified outcome [9]. A number of models exist for blunt chest trauma, however, most are designed for use with patients with multiple injuries and very few have been externally validated or presented in a clinically practical way [3]. For the purpose of this study, blunt chest-wall trauma was defined as blunt chest injury resulting in chest wall contusion or rib fractures, with or without non-immediate life-threatening lung injury [2]. We have developed and validated a prognostic model for the development of complications following blunt chest-wall trauma. Using the results of the prognostic model, we have also developed a simple risk score for use in the clinical setting which can assist the clinician in the management of the blunt chest-wall trauma patient.
Page 2 of 8
complications (chest infection, pneumonia, haemothorax, pneumothorax, pleural effusion, or empyema), ICU admission, or a prolonged length of stay as defined as a total hospital stay of seven or more days [14,15]. Prognostic variables
For the development of the prognostic model, we considered age, number of rib fractures, chronic lung disease, cardiovascular disease, use of pre-injury anti-coagulants, smoking status and oxygen saturations and respiratory rate on initial assessment in the ED. These risk factors were based on previous research [2,8,16]. Analysis
Data were collected retrospectively from the medical notes of each patient. If there was no record in the patient’s notes of chronic lung disease, cardiovascular disease, use of preinjury anticoagulants or current smoking status, then it was assumed that these predictors were absent. The number of rib fractures was determined from the chest radiograph if not documented in the medical notes.
Baseline characteristics were presented as median and interquartile range (due to non-normal distributions) for the continuous variables and numbers and percentages for categorical variables. Differences between the baseline characteristics in the development and validation samples were analysed using the Mann-Whitney U-test (continuous variables) and Fisher’s exact test (categorical variable). Odds ratios and 95% CI were presented from the univariable analysis. All significant prognostic variables at 5% significance on the univariable analysis were included in final analysis. Multivariable logistic regression analysis using fractional polynomials (to assess linearity of the continuous variables) identified five significant predictors using the Akaike information criterion with a backward elimination approach. We quantified the predictive contribution of each variable by its z-score (the regression coefficient divided by its standard error). There was less than 2% missing data, therefore we used a simple imputation method to avoid exclusion of patients from the final analysis [17].
Patients
Performance of the model
The prognostic model was developed on a sample of 276 patients who presented to the ED of a large regional trauma centre in South Wales between 2009 and 2011, with a primary diagnosis of blunt chest-wall trauma. Patients were excluded if they were under 18 years of age or if they had sustained any immediate life-threatening injury. As eight prognostic variables were under investigation, a total of 80 blunt chest-wall trauma patients who developed complications were needed in the analysis [13].
The final prognostic model was based on five prognostic variables which were significant at the P
RESEARCH
Open Access
Predicting outcomes after blunt chest wall trauma: development and external validation of a new prognostic model Ceri Elisabeth Battle1,2,3*, Hayley Hutchings1, Simon Lovett1, Omar Bouamra4, Sally Jones5, Aruni Sen6, James Gagg7, David Robinson8, Jake Hartford-Beynon9, Jeremy Williams10 and Adrian Evans1,3
Abstract Introduction: Blunt chest wall trauma accounts for over 15% of all trauma admissions to Emergency Departments worldwide. Reported mortality rates vary between 4 and 60%. Management of this patient group is challenging as a result of the delayed on-set of complications. The aim of this study was to develop and validate a prognostic model that can be used to assist in the management of blunt chest wall trauma. Methods: There were two distinct phases to the overall study; the development and the validation phases. In the first study phase, the prognostic model was developed through the retrospective analysis of all blunt chest wall trauma patients (n = 274) presenting to the Emergency Department of a regional trauma centre in Wales (2009 to 2011). Multivariable logistic regression was used to develop the model and identify the significant predictors for the development of complications. The model’s accuracy and predictive capabilities were assessed. In the second study phase, external validation of the model was completed in a multi-centre prospective study (n = 237) in 2012. The model’s accuracy and predictive capabilities were re-assessed for the validation sample. A risk score was developed for use in the clinical setting. Results: Significant predictors of the development of complications were age, number of rib fractures, chronic lung disease, use of pre-injury anticoagulants and oxygen saturation levels. The final model demonstrated an excellent c-index of 0.96 (95% confidence intervals: 0.93 to 0.98). Conclusions: In our two phase study, we have developed and validated a prognostic model that can be used to assist in the management of blunt chest wall trauma patients. The final risk score provides the clinician with the probability of the development of complications for each individual patient.
Introduction Blunt chest-wall trauma accounted for over 15% of all trauma admissions to Emergency departments (EDs) worldwide [1]. Reported mortality ranges between 4 and 60%, however, no current national guidelines exist to assist in the management of this patient group unless the patient has severe, immediate life-threatening injuries [2]. The difficulties in the management of the blunt chest-wall trauma patient are becoming increasingly well recognised in the literature [3,4]. The blunt chest-wall trauma patient commonly presents to the ED initially with * Correspondence: [email protected] 1 College of Medicine, Swansea University, Swansea, Wales, UK 2 Physiotherapy department, Morriston Hospital, Swansea, Wales, UK Full list of author information is available at the end of the article
no respiratory difficulties, but can develop respiratory complications approximately 48 to 72 hours later [5,6]. Clinical symptoms are not considered an accurate predictor of outcome following non-life threatening blunt chest-wall trauma [7]. Decisions on the appropriate level of care required by the patient following discharge from the ED are therefore difficult, which is further compounded by the lack of current national guidelines. A number of well-documented risk factors for morbidity and mortality exist for blunt chest-wall trauma, including patient age, pre-existing disease, number of ribs fractured and the onset of pneumonia during the recovery phase [2,8]. A prognostic model enables the clinician to use combinations of predictor values to estimate a probability that a specified outcome will occur [9]. The resulting model may
© 2014 Battle et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Battle et al. Critical Care 2014, 18:R98 http://ccforum.com/content/18/3/R98
be used to divide the patient into categories of risk or predict probabilities of a pre-specified outcome [9]. A number of models exist for blunt chest trauma, however, most are designed for use with patients with multiple injuries and very few have been externally validated or presented in a clinically practical way [3]. For the purpose of this study, blunt chest-wall trauma was defined as blunt chest injury resulting in chest wall contusion or rib fractures, with or without non-immediate life-threatening lung injury [2]. We have developed and validated a prognostic model for the development of complications following blunt chest-wall trauma. Using the results of the prognostic model, we have also developed a simple risk score for use in the clinical setting which can assist the clinician in the management of the blunt chest-wall trauma patient.
Page 2 of 8
complications (chest infection, pneumonia, haemothorax, pneumothorax, pleural effusion, or empyema), ICU admission, or a prolonged length of stay as defined as a total hospital stay of seven or more days [14,15]. Prognostic variables
For the development of the prognostic model, we considered age, number of rib fractures, chronic lung disease, cardiovascular disease, use of pre-injury anti-coagulants, smoking status and oxygen saturations and respiratory rate on initial assessment in the ED. These risk factors were based on previous research [2,8,16]. Analysis
Data were collected retrospectively from the medical notes of each patient. If there was no record in the patient’s notes of chronic lung disease, cardiovascular disease, use of preinjury anticoagulants or current smoking status, then it was assumed that these predictors were absent. The number of rib fractures was determined from the chest radiograph if not documented in the medical notes.
Baseline characteristics were presented as median and interquartile range (due to non-normal distributions) for the continuous variables and numbers and percentages for categorical variables. Differences between the baseline characteristics in the development and validation samples were analysed using the Mann-Whitney U-test (continuous variables) and Fisher’s exact test (categorical variable). Odds ratios and 95% CI were presented from the univariable analysis. All significant prognostic variables at 5% significance on the univariable analysis were included in final analysis. Multivariable logistic regression analysis using fractional polynomials (to assess linearity of the continuous variables) identified five significant predictors using the Akaike information criterion with a backward elimination approach. We quantified the predictive contribution of each variable by its z-score (the regression coefficient divided by its standard error). There was less than 2% missing data, therefore we used a simple imputation method to avoid exclusion of patients from the final analysis [17].
Patients
Performance of the model
The prognostic model was developed on a sample of 276 patients who presented to the ED of a large regional trauma centre in South Wales between 2009 and 2011, with a primary diagnosis of blunt chest-wall trauma. Patients were excluded if they were under 18 years of age or if they had sustained any immediate life-threatening injury. As eight prognostic variables were under investigation, a total of 80 blunt chest-wall trauma patients who developed complications were needed in the analysis [13].
The final prognostic model was based on five prognostic variables which were significant at the P
