Simon Carley

An introduction to power and sample size estimation

The importance of power and sample size estimation for study design and analysis.

Serious gaming technology in major incident triage training: A pragmatic controlled trial ☆

OBJECTIVE By exploiting video games technology, serious games strive to deliver affordable, accessible and usable interactive virtual worlds, supporting applications in training, education, marketing and design. The aim of the present study was to evaluate the effectiveness of such a serious game in the teaching of major incident triage by comparing it with traditional training methods. DESIGN Pragmatic controlled trial. METHOD During Major Incident Medical Management and Support Courses, 91 learners were randomly distributed into one of two training groups: 44 participants practiced triage sieve protocol using a card-sort exercise, whilst the remaining 47 participants used a serious game. Following the training sessions, each participant undertook an evaluation exercise, whereby they were required to triage eight casualties in a simulated live exercise. Performance was assessed in terms of tagging accuracy (assigning the correct triage tag to the casualty), step accuracy (following correct procedure) and time taken to triage all casualties. Additionally, the usability of both the card-sort exercise and video game were measured using a questionnaire. RESULTS Tagging accuracy by participants who underwent the serious game training was significantly higher than those who undertook the card-sort exercise [Chi2=13.126, p=0.02]. Step accuracy was also higher in the serious game group but only for the numbers of participants that followed correct procedure when triaging all eight casualties [Chi2=5.45, p=0.0196]. There was no significant difference in time to triage all casualties (card-sort=435+/-74 s vs video game=456+/-62 s, p=0.155). CONCLUSION Serious game technologies offer the potential to enhance learning and improve subsequent performance when compared to traditional educational methods.

A belief rule-based decision support system for clinical risk assessment of cardiac chest pain

This paper describes a prototype clinical decision support system (CDSS) for risk stratification of patients with cardiac chest pain. A newly developed belief rule-based inference methodology-RIMER was employed for developing the prototype. Based on the belief rule-based inference methodology, the prototype CDSS can deal with uncertainties in both clinical domain knowledge and clinical data. Moreover, the prototype can automatically update its knowledge base via a belief rule base (BRB) learning module which can adjust BRB through accumulated historical clinical cases. The domain specific knowledge used to construct the knowledge base of the prototype was learned from real patient data. We simulated a set of 1000 patients in cardiac chest pain to validate the prototype. The belief rule-based prototype CDSS has been found to perform extremely well. Firstly, the system can provide more reliable and informative diagnosis recommendations than manual diagnosis using traditional rules when there are clinical uncertainties. Secondly, the diagnostic performance of the system can be significantly improved after training the BRB through accumulated clinical cases.

High-Sensitivity Cardiac Troponin T Concentrations below the Limit of Detection to Exclude Acute Myocardial Infarction: A Prospective Evaluation

BACKGROUND Initial reports suggest that concentrations of high-sensitivity cardiac troponin T (hs-cTnT) (Roche Diagnostics Elecsys(®)) below the limit of blank (LoB) (3 ng/L) or limit of detection (LoD) (5 ng/L) of the assay have almost 100% negative predictive value (NPV) for acute myocardial infarction (AMI), particularly among patients without electrocardiograph (ECG) evidence of ischemia. We aimed to prospectively validate those findings. METHODS We included adults presenting to the emergency department with suspected cardiac chest pain. Standard troponin T (cTnT) and hs-cTnT (both Roche Elecsys) were tested in samples drawn on arrival. The primary outcome was AMI, adjudicated by 2 investigators on the basis of clinical data and ≥12-h cTnT testing. We also evaluated diagnostic performance when AMI was readjudicated on the basis of hs-cTnT (≥12-h) concentrations. RESULTS Of 463 patients included, 79 (17.1%) had AMI. Twenty-four patients (5.2%) had hs-cTnT concentrations below the LoB, although none had AMI. Ninety-six patients (20.7%) had hs-cTnT concentrations below the LoD, 1 of whom had AMI. Thus, diagnostic sensitivity was 98.7% (95% CI 87.5%-98.6%) and NPV was 99.0% (95% CI 94.3%-100.0%). Of the 17.3% (n = 80) patients with hs-cTnT below the LoD and no ECG ischemia, none had AMI. Thus, diagnostic sensitivity was 100.0% (95% CI 95.4%-100.0%) and NPV was 100.0% (95% CI 95.5%-100.0%). Sensitivity and NPV were maintained when AMI was readjudicated on the basis of hs-cTnT. CONCLUSIONS Our findings confirm that patients with nonischemic ECG and undetectable hs-cTnT at presentation have a very low probability of AMI, although the proportion of patients affected was smaller than in previous research.

The Manchester Acute Coronary Syndromes (MACS) decision rule for suspected cardiac chest pain: derivation and external validation

Objective We aimed to derive and validate a clinical decision rule (CDR) for suspected cardiac chest pain in the emergency department (ED). Incorporating information available at the time of first presentation, this CDR would effectively risk-stratify patients and immediately identify: (A) patients for whom hospitalisation may be safely avoided; and (B) high-risk patients, facilitating judicious use of resources. Methods In two sequential prospective observational cohort studies at heterogeneous centres, we included ED patients with suspected cardiac chest pain. We recorded clinical features and drew blood on arrival. The primary outcome was major adverse cardiac events (MACE) (death, prevalent or incident acute myocardial infarction, coronary revascularisation or new coronary stenosis >50%) within 30 days. The CDR was derived by logistic regression, considering reliable (κ>0.6) univariate predictors (p<0.05) for inclusion. Results In the derivation study (n=698) we derived a CDR including eight variables (high sensitivity troponin T; heart-type fatty acid binding protein; ECG ischaemia; diaphoresis observed; vomiting; pain radiation to right arm/shoulder; worsening angina; hypotension), which had a C-statistic of 0.95 (95% CI 0.93 to 0.97) implying near perfect diagnostic performance. On external validation (n=463) the CDR identified 27.0% of patients as ‘very low risk’ and potentially suitable for discharge from the ED. 0.0% of these patients had prevalent acute myocardial infarction and 1.6% developed MACE (n=2; both coronary stenoses without revascularisation). 9.9% of patients were classified as ‘high-risk’, 95.7% of whom developed MACE. Conclusions The Manchester Acute Coronary Syndromes (MACS) rule has the potential to safely reduce unnecessary hospital admissions and facilitate judicious use of high dependency resources.

Do risk factors for chronic coronary heart disease help diagnose acute myocardial infarction in the Emergency Department

BACKGROUND Hypertension, hyperlipidaemia, diabetes mellitus, tobacco smoking and a family history of premature coronary artery disease are known to be risk factors for the development of coronary artery disease. We sought to determine whether these traditional risk factors aid the diagnosis of acute myocardial infarction (AMI) in the Emergency Department (ED). METHODS We performed a prospective diagnostic cohort study within the ED at Manchester Royal Infirmary, a university-affiliated teaching hospital with an annual ED census of approximately 145,000 patients. We recruited 804 patients who had presented to the ED with suspected cardiac chest pain. All patients had the presence or absence of traditional cardiac risk factors documented at the time of presentation using a custom-designed clinical report form. All patients subsequently underwent 12-h troponin T testing to provide a robust gold standard for the diagnosis of AMI according to revised World Health Organisation criteria. RESULTS The absence of any traditional cardiac risk factors carried a negative likelihood ratio of 0.61 for the diagnosis of AMI. 12.2% of patients with no cardiac risk factors had AMI, compared with 21.3% of patients with four or five risk factors. The area under the receiver-operating characteristic curve was 0.49. CONCLUSIONS Traditional cardiac risk factors are not helpful for the confirmation or exclusion of AMI within the ED. Future Emergency Medicine research should focus on those clinical and diagnostic features that are likely to alter during the acute phase of illness.

Can emergency physicians ‘rule in’ and ‘rule out’ acute myocardial infarction with clinical judgement?

Objective To determine the diagnostic accuracy of emergency physician gestalt in emergency department (ED) patients with suspected cardiac chest pain, both alone and in combination with initial troponin level and ECG findings. Methods We prospectively included patients presenting to the ED with suspected cardiac chest pain. Clinicians recorded their ‘gestalt’ at the time of presentation using a five-point Likert scale, blinded to outcome. Troponin T and high-sensitivity troponin T (hs-cTnT; both Roche Diagnostics Elecsys) levels were measured in admission blood samples. All patients underwent troponin testing at least 12 h after peak symptoms. The primary outcome was acute myocardial infarction (AMI). Results 458 patients were included in this study, 81 (17.7%) of whom had AMI. Clinician gestalt alone had an area under the receiver operating characteristic curve of 0.76 (95% CI 0.70 to 0.82) for AMI. Immediately discharging patients with normal initial troponin and ECG in whom the clinician felt the diagnosis was ‘probably not’ or ‘definitely not’ acute coronary syndrome (ACS) would have avoided admission for 23.1% (95% CI 19% to 28%) patients with 100% sensitivity (95% CI 95.6% to 100%). With hs-cTnT, 100% sensitivity could have been achieved even if only patients with ‘probable’ or ‘definite’ ACS were investigated further, which would have allowed 41.7% patients to be discharged immediately. Conclusions Gestalt alone cannot be used to ‘rule in’ or ‘rule out’ ACS. By combining clinician gestalt with the admission ECG and troponin level, we found 100% sensitivity without the need for serial troponin testing. These findings have the potential to reduce unnecessary hospital admissions for suspected ACS but must be prospectively validated before considering clinical implementation.

Comparison of paediatric major incident primary triage tools

Objectives: To determine the sensitivity and specificity of paediatric major incident triage scores. The Paediatric Triage Tape (PTT), Careflight, Simple Triage and Rapid Treatment (START), and JumpSTART systems were tested. Methods: In total, 3461 children presenting to a South African emergency department with trauma were scored using the four different methods. The sensitivity and specificity of the four scores was calculated against the Injury Severity Score (ISS), New ISS (NISS), and a modification of the Garner criteria (a measure of need for urgent clinical intervention). We also performed a Bayesian analysis of the scores against three different types of major incident. Results: None of the tools showed high sensitivity and specificity. Overall, the Careflight score had the best performance in terms of sensitivity and specificity. The performance of the PTT was very similar. In contrast, the JumpSTART and START scores had very low sensitivities, which meant that they failed to identify patients with serious injury, and would have missed the majority of seriously injured casualties in the models of major incidents. Conclusion: The Careflight or PTT methods of triage should be used in paediatric major incidents in preference to the jumpSTART or START methods.

Diagnosis of pulmonary embolism with CT pulmonary angiography: a systematic review

Objective: To appraise the evidence on the diagnostic accuracy of CT pulmonary angiography and the prognostic value of a negative CT pulmonary angiogram in the diagnosis of pulmonary embolism. Methods: Medline, EMBASE, and grey literature were systematically searched by two researchers. Any study which compared CT pulmonary angiography to an acceptable reference standard or prospectively followed up a cohort of patients with a normal CT pulmonary angiogram was included. Study methods were appraised independently by two researchers, and data were extracted independently by three researchers. Results: Thirteen diagnostic and 11 follow up studies were identified. Studies varied in prevalence of pulmonary embolism (19–79%), patient groups, and method quality. Few studies recruited unselected emergency department patients. There was heterogeneity in the analysis of sensitivity (53 to 100%), specificity (79 to 100%), and false negative rate (1.0 to 10.7%). The pooled false negative rate of combined negative CT pulmonary angiography and negative deep vein thrombosis testing was 1.5% (95% CI 1.0 to 1.9%). Conclusion: Diagnostic studies give conflicting results for the diagnostic accuracy of CT pulmonary angiography. Follow up studies show that CT pulmonary angiography can be used in combination with investigation for deep vein thrombosis to exclude pulmonary embolism.

Can a modified thrombolysis in myocardial infarction risk score outperform the original for risk stratifying emergency department patients with chest pain

Background: The thrombolysis in myocardial infarction (TIMI) risk score has been shown to risk stratify patients with suspected acute coronary syndromes (ACS) effectively in the emergency department (ED) but cannot be used to guide patient disposition. We aimed to evaluate whether modifying the TIMI risk score to give greater weighting to ischaemic ECG changes and troponin elevations would enhance its risk stratification and thus potentially facilitate safe patient discharge after 12-h troponin testing. Methods: A prospective diagnostic cohort study was performed within the ED at Manchester Royal Infirmary, a university-affiliated teaching hospital with an annual ED census of approximately 145 000 patients. 804 patients who had presented to the ED with suspected cardiac chest pain were recruited. All patients underwent 12-h troponin T testing and were followed up by telephone and chart review after 30 days for the composite primary outcome of death, acute myocardial infarction (AMI) or urgent coronary revascularisation. Results: The modified TIMI risk score outperformed the original (area under the receiver operator characteristic curve 0.87 versus 0.77, p<0.001). Using a cut-off of more than 2 points the score had a sensitivity of 96.4% for the prediction of 30-day events. The specificity of the score was only 51.0%, suggesting that in practice over 40% of patients would be ineligible for discharge even after troponin testing. Conclusions: Modifications to the TIMI risk score can improve its performance in the risk stratification of patients presenting to the ED with chest pain. However, a lack of specificity may still limit its use for guiding patient disposition after troponin testing.