Title: Pre-hospital critical care for out of hospital cardiac arrest. Does it work, how does it work and how much does it cost?
Funder: Department of Health and Social Care

Abstract: Background Despite remarkable efforts to improve both pre-hospital and in-hospital care, survival from out of hospital cardiac arrest (OHCA) remains poor. Certain pre-hospital interventions, such as high quality bystander cardio-pulmonary resuscitation (CPR) and early defibrillation, have been shown to improve survival from OHCA. Scientific evidence also supports the concept of pre-hospital advanced life support (ALS), and all registered paramedics in the UK are now ALS-certified. Current research regarding any further benefits from the dispatch of pre-hospital critical care teams (CCTs) to OHCA has produced conflicting results. A pilot study undertaken by the applicant suggested a potential improvement in survival to hospital discharge after OHCA from 8.9% to 13.2% when comparing ALS-trained paramedics to a CCT. Aims Given this potential for a significant benefit from CCTs, we aim to answer the following questions: - Can this effect be demonstrated to be both clinically and statistically significant in a larger sample, and across several ambulance trusts in the UK? - Which intervention(s) delivered by a CCT have the strongest survival benefit? - What is the cost effectiveness of a CCT in OHCA? - What are the barriers to a randomised clinical trial to address this research question, and how might they be overcome. Methods A number of ambulance trusts in the UK dispatch CCTs to suspected or confirmed OHCA. While the CCTs will aim to attend most cases of OHCA, they will inevitably be unavailable for some cases, due to already having been dispatched to another case of critical illness or injury, or the limitations imposed by operational duty hours and constrained funding. This results in a natural experiment where one group of patients is attended by a CCT and another is treated by ALS-trained paramedics only. Within the South Western Ambulance Trust (SWAST), the CCT attends approximately 10% of OHCA cases. All NHS ambulance trusts routinely collect data on all OHCA patients, including survival to hospital discharge, which is a national ambulance quality indicator. We will prospectively collect OHCA data from four NHS ambulance trusts over an 18-month period and analyse the effect of pre-hospital critical care on survival to hospital discharge between the two groups by matching OHCA cases with CCT care to controls treated by ALS-trained paramedics alone. This will be done using propensity score matching, variables will include location of OHCA, age of patient, bystander CPR, ambulance response time, intial cardiac rhythm and characteristics of designated receiving hospital. We will use multiple logistic regression to examine the association between the actual interventions delivered during pre-hospital care and survival to hospital discharge, with the aim to better understand the complex intervention that is pre-hospital critical care. As a next step, we will calculate the costs of providing pre-hospital critical care, following a published framework for the cost analysis of emergency medical services (EMS), in order to determine the cost-effectiveness of pre-hospital CCTs. We have explored the possibility of answering the study question through a randomised controlled trial (RCT) but the associated costs, logistical challenges, patient and public involvment (PPI) advice and ethical concerns favor an observational study design at this stage. Nevertheless, we will undertake a nested qualitative study, using focus group interviews in five key stakeholder groups, to identify the potential barriers to a RCT to address this research question, and ways to overcome these barriers. Potential benefits The results of this study will help to understand the effect of a pre-hospital CCT on survival from OHCA. They will also inform decision-making regarding the commissioning, funding and dispatch of pre-hospital CCTs with the potential to significantly improve outcomes from OHCA whilst offering clinically effective and cost-effective care.

Lay abstract: Background Despite efforts to improve the care of patients suffering out of hospital cardiac arrest (OHCA), survival rates remain poor, at around 7% in the UK. Certain pre-hospital interventions, such as early chest compressions and early attempts to re-start the heart with an electric shock (defibrillation), have been shown to improve survival from OHCA. Survival has possibly been improved further by training all registered paramedics in the UK in Advanced Life Support (ALS), which in addition to chest compression and defibrillation includes giving supported breaths to the patient's lungs and administration of drugs such as adrenaline. In a number of ambulance trusts in the UK, pre-hospital services also send a team of experienced doctors and paramedics (critical care teams, CCTs) to OHCA. They can undertake additional measures to treat OHCA but research so far has not shown a clear benefit resulting from this practice. We have undertaken a preliminary study that suggests a possible benefit from a CCT attending OHCA in the South Western Ambulance Service NHS Foundation Trust (SWAST). Aims We want to further study this possible benefit in different UK ambulance trusts and examine which of the many CCT treatments are actually beneficial. We also want to estimate the costs of CCT care for OHCA, to decide whether a pre-hospital CCT is a cost effective way of treating this condition. Methods CCTs try to attend most cases of OHCA, but sometimes they are unable to do so. Reasons for this might be that the CCT is already caring for another patient or, for example, the helicopter which carries the CCT might be unable to fly in bad weather. This means that there are two groups of patients with OHCA; one which receives CCT treatment and one which does not. We will compare survival to hospital discharge between these two groups. To make sure that any differences in survival are most likely to be due to CCT treatment, we will undertake a procedure called matching'. For each patient treated by the CCT, we will identify two patients treated by ALS-trained paramedics alone, with the same age, the same type of cardiac arrest, the same ambulance response time and so on. By matching patients' factors known to affect survival from OHCA, we will maximise the chances that the only difference between the two groups is the CCT treatment. Therefore, any survival benefit between the two matched groups is likely to be due to CCT treatment. The data needed for this matching process are routinely recorded by all English ambulance trusts. CCT treatment is actually a collection of treatments, which includes drugs, procedures and the ability to transport patients over greater distances. During OHCA treatment, the CCT might use all, none, or some of these critical care skills. We will attempt to find out which individual treatment has the biggest impact on any survival benefit. This can be done through a software-supported data analysis called multiple logistic regression. Most CCTs in the UK are using helicopters to reach the location of an OHCA. These air ambulance services are currently funded by charities. If we can demonstrate a benefit from CCT treatment, it would be a strong argument for more NHS involvement in air ambulance services and the more widespread introduction of CCTs to treat the many tens of thousands of patients who undergo resuscitation for OHCA in the UK every year. Any treatment which the NHS considers needs to not only be beneficial but also cost effective. Understanding the costs of CCT treatment will therefore be important in improving care for OHCA. We will estimate the costs of CCT care for OHCA. We will present the overall costs but also show how much of these are paid for by charities, by ambulance trusts or by hospital trusts. Whilst this study will provide very valuable information, a different type of study, called a randomised controlled trial (RCT), is generally considered to be better when trying to identify the best form of disease treatment. However, an RCT would require some OHCA patients to not receive care from a CCT, even when one is available, and this raises a number of logistical and ethical issues. We will use focus group interviews to explore these challenges, and see whether a RCT might be possible in the future. Potential benefits Overall, this project will directly influence the way the NHS and charities organise the care of patients who suffer from OHCA. We hope this research will improve survival from OHCA within five years of completion.

Research activity codes: 6.9 RESOURCES AND INFRASTRUCTURE (TREATMENT EVALUATION)
Health categories: CARDIOVASCULAR