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Wei Lam S.S.,Health Services Research and Biostatistics Unit | Zhang Z.C.,Singapore General Hospital | Oh H.C.,Singapore Health Services Pte Ltd | Ng Y.Y.,Singapore Civil Defence Force | And 2 more authors.
Prehospital Emergency Care | Year: 2014

Objectives. The objectives of this study are to develop a discrete-event simulation (DES) model for the Singapore Emergency Medical Services (EMS), and to demonstrate the utility of this DES model for the evaluation of different policy alternatives to improve ambulance response times. Methods. A DES model was developed based on retrospective emergency call data over a continuous 6-month period in Singapore. The main outcome measure is the distribution of response times. The secondary outcome measure is ambulance utilization levels based on unit hour utilization (UHU) ratios. The DES model was used to evaluate different policy options in order to improve the response times, while maintaining reasonable fleet utilization. Results. Three policy alternatives looking at the reallocation of ambulances, the addition of new ambulances, and alternative dispatch policies were evaluated. Modifications of dispatch policy combined with the reallocation of existing ambulances were able to achieve response time performance equivalent to that of adding 10 ambulances. The median (90th percentile) response time was 7.08 minutes (12.69 minutes). Overall, this combined strategy managed to narrow the gap between the ideal and existing response time distribution by 11-13%. Furthermore, the median UHU under this combined strategy was 0.324 with an interquartile range (IQR) of 0.047 versus a median utilization of 0.285 (IQR of 0.051) resulting from the introduction of additional ambulances. Conclusions. Response times were shown to be improved via a more effective reallocation of ambulances and dispatch policy. More importantly, the response time improvements were achieved without a reduction in the utilization levels and additional costs associated with the addition of ambulances. We demonstrated the effective use of DES as a versatile platform to model the dynamic system complexities of Singapore's national EMS systems for the evaluation of operational strategies to improve ambulance response times. © 2014 National Association of EMS Physicians. Source


Yang K.K.,Singapore Management University | Lam S.S.W.,Health Services Research and Biostatistics Unit | Low J.M.W.,Singapore Management University | Ong M.E.H.,Singapore General Hospital | Ong M.E.H.,National University of Singapore
Operations Research for Health Care | Year: 2016

Long waiting times in emergency departments (EDs) not only reduce patients' perceived quality of care, but also increase crowding which can adversely affect patients' outcomes. Waiting time has been found to affect patients' outcomes and is closely associated with delays in the provision of ancillary services to ED patients by the diagnostic/treatment laboratories. The focus of this study is to improve the flow of ED patients by testing alternative triage processes and capacity of physicians, triage nurses and laboratories. Three alternative triage processes are examined for managing the flow of ED patients through shared and dedicated laboratories across different utilization of physicians, triage nurses, and laboratories using a discrete event simulation (DES) model that captures the pertinent characteristics of EDs operating in tertiary acute care hospitals under conservative assumptions. Our results show that choosing the appropriate triage process and adding extra capacity to the triage and dedicated laboratory can significantly improve ED performance, especially when physician utilization is high. In contrast, adding extra capacity to a shared laboratory improves performance only slightly. Our results also show that shared laboratory generally provides better support to EDs than dedicated laboratory. © 2016 Elsevier Ltd. Source


Lam S.S.W.,Health Services Research and Biostatistics Unit | Nguyen F.N.H.L.,Health Services Research and Biostatistics Unit | Ng Y.Y.,Singapore Civil Defence Force | Lee V.P.-X.,Health Services Research and Biostatistics Unit | And 3 more authors.
Accident Analysis and Prevention | Year: 2015

Objectives Time to definitive care is important for trauma outcomes, thus many emergency medical services (EMS) systems in the world adopt response times of ambulances as a key performance indicator. The objective of this study is to examine the underlying risk factors that can affect ambulance response times (ART) for trauma incidents, so as to derive interventional measures that can improve the ART. Material and methods This was a retrospective study based on two years of trauma data obtained from the national EMS operations centre of Singapore. Trauma patients served by the national EMS provider over the period from 1 January 2011 till 31 December 2012 were included. ART was categorized into "Short" (<4 min), "Intermediate" (4-8 min) and "Long" (>8 min) response times. A modelling framework which leveraged on both multinomial logistic (MNL) regression models and Bayesian networks was proposed for the identification of main and interaction effects. Results Amongst the process-related risk factors, weather, traffic and place of incident were found to be significant. The traffic conditions on the roads were found to have the largest effect - the odds ratio (OR) of "Long" ART in heavy traffic condition was 12.98 (95% CI: 10.66-15.79) times higher than that under light traffic conditions. In addition, the ORs of "Long ART" under "Heavy Rain" condition were significantly higher (OR 1.58, 95% CI: 1.26-1.97) than calls responded under "Fine" weather. After accounting for confounders, the ORs of "Long" ART for trauma incidents at "Home" or "Commercial" locations were also significantly higher than that for "Road" incidents. Conclusion Traffic, weather and the place of incident were found to be significant in affecting the ART. The evaluation of factors affecting the ART enables the development of effective interventions for reducing the ART. ©2015 Elsevier Ltd. All rights reserved. Source


Lam S.S.W.,Health Services Research and Biostatistics Unit | Zhang J.,Singapore General Hospital | Zhang Z.C.,Singapore General Hospital | Oh H.C.,Health Services Research | And 3 more authors.
American Journal of Emergency Medicine | Year: 2015

Abstract Objectives Dynamically reassigning ambulance deployment locations throughout a day to balance ambulance availability and demands can be effective in reducing response times. The objectives of this study were to model dynamic ambulance allocation plans in Singapore based on the system status management (SSM) strategy and to evaluate the dynamic deployment plans using a discrete event simulation (DES) model. Methods The geographical information system-based analysis and mathematical programming were used to develop the dynamic ambulance deployment plans for SSM based on ambulance calls data from January 1, 2011, to June 30, 2011. A DES model that incorporated these plans was used to compare the performance of the dynamic SSM strategy against static reallocation policies under various demands and travel time uncertainties. Results When the deployment plans based on the SSM strategy were followed strictly, the DES model showed that the geographical information system-based plans resulted in approximately 13-second reduction in the median response times compared to the static reallocation policy, whereas the mathematical programming-based plans resulted in approximately a 44-second reduction. The response times and coverage performances were still better than the static policy when reallocations happened for only 60% of all the recommended moves. Conclusions Dynamically reassigning ambulance deployment locations based on the SSM strategy can result in superior response times and coverage performance compared to static reallocation policies even when the dynamic plans were not followed strictly. © 2014 Elsevier Inc. All rights reserved. Source


Boh C.,National University of Singapore | Li H.,Health Services Research and Biostatistics Unit | Finkelstein E.,National University of Singapore | Haaland B.,National University of Singapore | And 4 more authors.
Academic Emergency Medicine | Year: 2015

Objectives This study aimed to determine which factors contribute to frequent visits at the emergency department (ED) and what proportion were inappropriate in comparison with nonfrequent visits. Methods This study was a retrospective, case-control study comparing a random sample of frequent attenders and nonfrequent attenders, with details of their ED visits recorded over a 12-month duration. Frequent attenders were defined as patients with four or more visits during the study period. Results In comparison with nonfrequent attenders (median age = 45.0 years, interquartile range [IQR] = 28.0 to 61.0 years), frequent attenders were older (median = 57.5 years, IQR = 34.0 to 74.8 years; p = 0.0003). They were also found to have more comorbidities, where 53.3% of frequent attenders had three or more chronic illnesses compared to 14% of nonfrequent attenders (p < 0.0001), and were often triaged to higher priority (more severe) classes (frequent 52.2% vs. nonfrequent 37.6%, p = 0.0004). Social issues such as bad debts (12.7%), heavy drinking (3.3%), and substance abuse (2.7%) were very low in frequent attenders compared to Western studies. Frequent attenders had a similar rate of appropriate visits to the ED as nonfrequent attenders (55.2% vs. 48.1%, p = 0.0892), but were more often triaged to P1 priority triage class (6.7% vs. 3.2%, p = 0.0014) and were more often admitted for further management compared to nonfrequent attenders (47.5% vs. 29.6%, p < 0.001). The majority of frequent attender visits were appropriate (55.2%), and of these, 81.1% resulted in admission. For the same number of patients, total visits made by frequent attenders ($174,247.60) cost four times as much as for nonfrequent attenders ($40,912.40). This represents a significant economic burden on the health care system. Conclusions ED frequent attenders in Singapore were associated with higher age and presence of multiple comorbidities rather than with social causes of ED use. Even in integrated health systems, repeat ED visits are frequent and expensive, despite minimal social causes of acute care. EDs in aging populations must anticipate the influx of vulnerable, elderly patients and have in place interventional programs to care for them. © 2015 by the Society for Academic Emergency Medicine. Source

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