But in the words of Iron Maiden, is it a case of "Be Quick Or Be Dead"?
Recent technological advances, e.g. automated dispatch services, geographic information systems and mobile intensive-care units, have allowed ambulances to reach and treat patients more quickly. At the same time providers are pushed to meet the nationally set response targets. For example, 75% and 95% of patients must be reached within 8 and 19 minutes, respectively. This applies both to patients with life-threatening conditions (Red 1 calls) and to serious but not the most life-threatening incidents (Red 2 calls). Local agreements apply to less critical conditions and to incidents that can be assessed without an ambulance response, i.e. via telephone (Hear & Treat).
However, nearly nothing is known regarding the relationship between health outcomes and ambulance response times. Primarily, this is due to the scarcity of good quality data. NHS England publishes some Ambulance Quality indicators for each one of the eleven Ambulance Services operating in the country. These are available at a monthly frequency from April 2011 onwards. They can be classified into two main categories: Systems Indicators and Clinical Outcomes. The former contain information regarding the total volume of emergency calls and the number which resulted in an emergency response arriving at the scene of the incident within 8 minutes. Other information such as the number of emergency calls closed with telephone advice, the number of patients treated and discharged on scene, re-contact rates within 24 hours and the total number of transported incidents is also available. The Clinical Outcomes monthly reports contain information about the proportion of resuscitated patients who had return of spontaneous circulation on arrival at hospital following an out-of-hospital cardiac arrest, STEMI or stroke. Also, the proportion of resuscitated patients who were discharged from hospital alive after an out-of-hospital cardiac arrest is also available.
These published data can provide a first insight regarding the trends of the efficiency of ambulance services.
Figure 1. Proportion of emergency calls (national average) responded to within 8 minutes
These trends exhibit a significant variation across regions (figure 2). In some regions the proportion of Red 1 calls reached within 8 minutes is systematically high, e.g. around 79% over the period in the West Midlands. In some other regions this proportion is systematically lower (East Midlands) and there are sharp changes in other areas, e.g. London, East of England and the South East. Moreover, there are noticeable seasonal variations, especially in the Isle of Wight, observed mostly in December, January and during the summer season.
Figure 2. Proportion of emergency calls responded to within 8 minutes, by region
Regarding the clinical outcomes, an indicative one is the cardiac arrest survival rate. This indicates the proportion of patients who had resuscitation commenced or continued by the ambulance service following an out-of-hospital cardiac arrest and who were discharged from the hospital alive. Survival rates in England seem to have been increasing between 2011 and 2013, from 6.7% to 9.2%, but they followed a downward trend in more recent years, i.e. back to 6.7% during the first quarter of 2017 (figure 3). A similar trend is observed for the proportion of resuscitated patients who had return of spontaneous circulation on arrival at hospital, although the proportions are higher, e.g. the period average is 26.1%. Again, there is substantial regional variation in clinical outcomes as well, e.g. the survival rate is high in South Central (14.4%) and in London (9.2%) and quite low in regions like East Midlands (5.8%) and the East of England (6.4%).
Figure 3. Survival rate (national average) following an out-of-hospital cardiac arrest
Apart from the evolution of performance trends, it is very interesting to examine whether there is any association between response times and health outcomes. Plotting together the percentages of Red 1 cases reached within 8 minutes and the percentage of cardiac arrest patients who were discharged from hospital alive indicates a positive correlation (figure 4). However, this could be driven by time effects, seasonal variation, differences between providers and differences in the underlying local population. A more formal analysis could indicate whether this presumed positive relationship survives when a number of factors has been controlled for. In a simple multivariate framework, we have regressed the proportion of patients discharged from hospital alive (following an emergency transfer after an out-of-hospital cardiac arrest) upon a set of year, month and provider fixed effects, interactions between providers and years and weighted the regressions by the total volume of emergency calls in order to adjust for provider size. The obtained results indicate that if the proportion of Red 1 calls responded to within 8 minutes is increased by 1 percentage point, the proportion of patients discharged alive is also higher by 0.1 percentage point; with the result being statistically significant at the 5% level. For Red 2 calls responded to within 8 minutes, the respective figure is 0.09 percentage points and it is statistically significant at the 1% level.
Figure 4. Correlation between response times and clinical outcomes
Notes: Shaded area is the 95% confidence interval for the linear fit (red line).
However, these are purely preliminary results based on published monthly time series and they may suffer from aggregation and omitted variable biases. Hence, they should be interpreted with caution. Nevertheless, they provide some first evidence about the existence of a connection between patient outcomes and response times, and they offer us a justification to look further into this issue. The use of de-identified patient record data will enable us to establish the relationship between response times and health outcomes. We are currently liaising with all Ambulance Services Trusts in England, Scotland and Wales in order to acquire access to patient record information and continue our research. People from within the NHS England and several Ambulance Services Trusts have already expressed their interest in our work and we are looking forward in obtaining and disseminating more results that we believe will be extremely interesting and useful for healthcare providers, policy makers and the public.