Win Wah

Reducing Ambulance Response Times Using Discrete Event Simulation

Abstract 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 Singapores national EMS systems for the evaluation of operational strategies to improve ambulance response times.

Housing as a Social Determinant of Health in Singapore and Its Association with Readmission Risk and Increased Utilization of Hospital Services.

Background Residence in public rental housing is an area-level measure of socioeconomic status, but its impact as a social determinant of health in Singapore has not been studied. We therefore aimed to examine the association of public rental housing with readmission risk and increased utilization of hospital services in Singapore. Methods We conducted a retrospective cohort study using retrospective 2014 data from Singapore General Hospital’s electronic health records. Variables known to affect readmission risk and health-care utilization were identified a priori and include patient demographics, comorbidities, health-care utilization in the preceding 1 year and clinical variables from the index admission in 2014. Multivariate logistic regression was used to evaluate public rental housing as an independent risk factor for admission risk, emergency department (ED), and specialist outpatient clinic attendances. Results A total of 14,457 unique patients were analyzed, and 2,163 patients (15.0%) were rental housing residents. Rental housing patients were significantly more likely to be male; required financial assistance; have chronic obstructive pulmonary disease; usage of anti-depressant and anti-psychotic medications; longer length of hospital stay during the index admission; and higher Charlson Comorbidity Index scores. After adjusting for demographics and clinical variables, staying in public rental housing remained an independent risk factor for readmission within 15 and 30 days, frequent hospital admissions and ED attendances in Singapore. Conclusion Our study showed an association between public rental housing with readmission risk and increased utilization of hospital services in Singapore. A deeper understanding of the residents’ social circumstances and health seeking behavior would be insightful.

Associations between gender and cardiac arrest outcomes in Pan-Asian out-of-hospital cardiac arrest patients☆

BACKGROUND The incidence of out-of-hospital cardiac arrest (OHCA) in women is thought to be lower than that of men, with better outcomes in some Western studies. OBJECTIVES This study aimed to investigate the effect of gender on OHCA outcomes in the Pan-Asian population. METHODOLOGY This was a retrospective, secondary analysis of the Pan Asian Resuscitation Outcomes Study (PAROS) data between 2009 and 2012. We included OHCA cases which were presumed cardiac etiology, aged 18 years and above and resuscitation attempted by emergency medical services (EMS) systems. We used multi-level mixed-effects logistic regression models to account for the clustering effect of individuals within the country. Primary outcome was survival to hospital discharge. RESULTS We included a total of 40,159 OHCA cases, 40% of which were women. We found that women were more likely to be older and have an initial non-shockable arrest rhythm; they were more likely to receive bystander cardio-pulmonary resuscitation (CPR). The univariate analysis showed that women were significantly less likely to have return of spontaneous circulation (ROSC) at scene or in the emergency department (ED), and had lower rates of survival-to-admission and discharge, and poorer overall and cerebral performance outcomes. There was however, no significant gender difference on outcomes after adjustment of other confounders. Women in the reproductive age group (age 18-44 years) were significantly more likely to have ROSC at scene or in the ED, higher rates of survival-to-admission and discharge, and have better overall and cerebral performance outcomes after adjustment for differences in baseline and pre-hospital factors. Menopausal women (age 55 years and above) were less likely to survive to admission after adjusting for other pre-hospital characteristics but not after age adjustment. CONCLUSION Differences in survival outcomes between reproductive and menopausal women highlight a need for further investigations into the plausible social, pathologic or hormonal basis.

Time series analysis of demographic and temporal trends of tuberculosis in Singapore

BackgroundSingapore is an intermediate tuberculosis (TB) incidence country, with a recent rise in TB incidence from 2008, after a fall in incidence since 1998. This study identified population characteristics that were associated with the recent increase in TB cases, and built a predictive model of TB risk in Singapore.MethodsRetrospective time series analysis was used to study TB notification data collected from 1995 to 2011 from the Singapore Tuberculosis Elimination Program (STEP) registry. A predictive model was developed based on the data collected from 1995 to 2010 and validated using the data collected in 2011.ResultsThere was a significant difference in demographic characteristics between resident and non-resident TB cases. TB risk was higher in non-residents than in residents throughout the period. We found no significant association between demographic and macro-economic factors and annual incidence of TB with or without adjusting for the population-at-risk. Despite growing non-resident population, there was a significant decrease in the non-resident TB risk (p < 0.0001). However, there was no evidence of trend in the resident TB risk over this time period, though differences between different demographic groups were apparent with ethnic minorities experiencing higher incidence rates.ConclusionThe study found that despite an increasing size of non-resident population, TB risk among non-residents was decreasing at a rate of about 3% per year. There was an apparent seasonality in the TB reporting.

Geographic factors are associated with increased risk for out-of hospital cardiac arrests and provision of bystander cardio-pulmonary resuscitation in Singapore

BACKGROUND Bystander Cardio-Pulmonary Resuscitation (BCPR) can improve survival for Out-of-Hospital Cardiac Arrest (OHCA). This study aimed to investigate the geographic variation of BCPR provision and survival to discharge outcomes among residential OHCA cases, evaluate this variation with individual and population characteristics and identify high-risk residential areas with low relative risk (RR) of BCPR and high RR of OHCA at the development guide plan (DGP) census tract levels in Singapore. METHODS This was a retrospective, secondary analysis of two prospectively-collected registries in Singapore from 2001 to 2011. We used Bayesian conditional autoregressive spatial models to examine predictors at the DGP level and calculate smoothed RR to identify high-risk areas. We used multi-level mixed-effects logistic regression models to examine the independent effects of individual and neighborhood factors. RESULTS We found a total of 3942 OHCA with a BCPR rate of 20.3% and a survival to discharge rate of 1.9% and 3578 cases eligible for BCPR. After adjusting for age, witnessed status, presumed cardiac etiology and longer response time, the risk of BCPR provision significantly increased by 0.02% for every 1% increase in the proportion of household size 5 and above in the DGP area (odds ratio 1.02, 95%CI=1.002-1.038, p<0.026). We identified 10 high-risk residential areas with low RR of BCPR and high RR of OHCA. CONCLUSION This study informed that neighborhood household size could have played a significant role in the provision of BCPR and occurrence of high-risk areas. It demonstrates the public health potential of combining geospatial and epidemiological analysis for improving health.

Conversion to shockable rhythms during resuscitation and survival for out-of hospital cardiac arrest.

Background: In out of hospital cardiac arrest (OHCA), the prognostic influence of conversion to shockable rhythms during resuscitation for initially non‐shockable rhythms remains unknown. This study aimed to assess the relationship between initial and subsequent shockable rhythm and post‐arrest survival and neurological outcomes after OHCA. Methodology: This was a retrospective analysis of all OHCA cases collected from the Pan‐Asian Resuscitation Outcomes Study (PAROS) registry in 7 countries in Asia between 2009 and 2012. We included OHCA cases of presumed cardiac etiology, aged 18‐years and above and resuscitation attempted by EMS. We performed multivariate logistic regression analyses to assess the relationship between initial and subsequent shockable rhythm and survival and neurological outcomes. 2‐stage seemingly unrelated bivariate probit models were developed to jointly model the survival and neurological outcomes. We adjusted for the clustering effects of country variance in all models. Results: 40,160 OHCA cases met the inclusion criteria. There were 5356 OHCA cases (13.3%) with initial shockable rhythm and 33,974 (84.7%) with initial non‐shockable rhythm. After adjustment of baseline and prehospital characteristics, OHCA with initial shockable rhythm (odds ratio/OR = 6.10, 95% confidence interval/CI = 5.06–7.34) and subsequent conversion to shockable rhythm (OR = 2.00,95%CI = 1.10–3.65) independently predicted better survival‐to‐hospital‐discharge outcomes. Subsequent shockable rhythm conversion significantly improved survival‐to‐admission, discharge and post‐arrest overall and cerebral performance outcomes in the multivariate logistic regression and 2‐stage analyses. Conclusion: Initial shockable rhythm was the strongest predictor for survival. However, conversion to subsequent shockable rhythm significantly improved post‐arrest survival and neurological outcomes. This study suggests the importance of early resuscitation efforts even for initially non‐shockable rhythms which has prognostic implications and selection of subsequent post‐resuscitation therapy.

Composite Measures of Individual and Area-Level Socio-Economic Status Are Associated with Visual Impairment in Singapore

Purpose To investigate the independent relationship of individual- and area-level socio-economic status (SES) with the presence and severity of visual impairment (VI) in an Asian population. Methods Cross-sectional data from 9993 Chinese, Malay and Indian adults aged 40–80 years who participated in the Singapore Epidemiology of eye Diseases (2004–2011) in Singapore. Based on the presenting visual acuity (PVA) in the better-seeing eye, VI was categorized into normal vision (logMAR≤0.30), low vision (logMAR>0.30<1.00), and blindness (logMAR≥1.00). Any VI was defined as low vision/blindness in the PVA of better-seeing eye. Individual-level low-SES was defined as a composite of primary-level education, monthly income<2000 SGD and residing in 1 or 2-room public apartment. An area-level SES was assessed using a socio-economic disadvantage index (SEDI), created using 12 variables from the 2010 Singapore census. A high SEDI score indicates a relatively poor SES. Associations between SES measures and presence and severity of VI were examined using multi-level, mixed-effects logistic and multinomial regression models. Results The age-adjusted prevalence of any VI was 19.62% (low vision = 19%, blindness = 0.62%). Both individual- and area-level SES were positively associated with any VI and low vision after adjusting for confounders. The odds ratio (95% confidence interval) of any VI was 2.11(1.88–2.37) for low-SES and 1.07(1.02–1.13) per 1 standard deviation increase in SEDI. When stratified by unilateral/bilateral categories, while low SES showed significant associations with all categories, SEDI showed a significant association with bilateral low vision only. The association between low SES and any VI remained significant among all age, gender and ethnic sub-groups. Although a consistent positive association was observed between area-level SEDI and any VI, the associations were significant among participants aged 40–65 years and male. Conclusion In this community-based sample of Asian adults, both individual- and area-level SES were independently associated with the presence and severity of VI.

Derivation of indices of socioeconomic status for health services research in Asia.

Background Environmental contexts have been shown to predict health behaviours and outcomes either directly or via interaction with individual risk factors. In this paper, we created indexes of socioeconomic disadvantage (SEDI) and socioeconomic advantage (SAI) in Singapore to test the applicability of these concepts in an Asian context. These indices can be used for health service resource allocation, research and advocacy. Methods We used principal component analysis (PCA) to create SEDI and SAI using a structured and iterative process to identify and include influential variables in the final index. Data at the master plan geographical level was obtained from the most recent Singapore census 2010. Results The 3 areas with highest SEDI scores were Outram (120.1), followed by Rochor (111.0) and Downtown Core (110.4). The areas with highest SAI scores were Tanglin, River Valley and Newton. The SAI had 89.6% of variation explained by the final model, as compared to 67.1% for SEDI, and we recommend using both indices in any analysis. Conclusion These indices may prove useful for policy-makers to identify spatially varying risk factors, and in turn help identify geographically targeted intervention programs, which can be more cost effective to conduct.

Frequent attenders to the ED: patients who present with repeated asthma exacerbations.

BACKGROUND Asthma has been reported as one of the main causes of frequent attendance to the emergency department (ED), and many of those visits are potentially preventable. Understanding the characteristics of frequent attender (FA) patients with asthmatic exacerbations will help to identify factors associated with frequent attendance and improve case management. The aim of this study is to describe the characteristics of FA who present multiple times to the ED for asthma exacerbations. METHODS This study was a retrospective review of cases presented to Singapore General Hospital ED in 2010. Patients who attended the ED for 4 times or more with at least 1 visit attributable to asthma exacerbations in 2010 were included. They were then categorized as FA with multiple exacerbations (FAME) and those with fewer exacerbations. RESULTS Of 105616 ED patients, 155 patients attending the ED in 2010 were identified as FA with asthma, and 26 (17%) of these patients were classified as FAME, resulting in 213 visits (45% of total visits). Compared with FA with fewer exacerbations group, FAME were more likely to be men (P = .002), unemployed (P < .000), bad debtors (P = .045), substance abusers (P = .022), previously known to medical social workers (P = .002), and were found to spend a longer amount of time in the ED (>6 hours) (P = .03). CONCLUSION We found that a small number of FAME patients accumulated a large number of ED visits and spent a significantly longer time in the ED. This group tended to be males with social, financial, and addiction problems.

Effect of known history of heart disease on survival outcomes after out-of-hospital cardiac arrests

We aimed to investigate the effect of known heart disease on post‐out‐of‐hospital cardiac arrest (OHCA) survival outcomes, and its association with factors influencing survival.