Cardiopulmonary resuscitation outcomes in a UK veterinary hospital: pilot study

The 2012 Reassessment Campaign on Veterinary Resuscitation (RECOVER) initiative produced evidence-based recommendations to guide professionals when performing cardiopulmonary resuscitation (CPR) on canine or feline patients (Boller and Fletcher, 2012; Yagi, 2019; Waxman, 2019). There were two main goals of the RECOVER initiative: to provide up-to-date evidence-based guidelines and to highlight the knowledge gap, at that time, in the hope of influencing future research.

Many resources specific to animals and beneficial in improving patient care were produced. These included drug dose charts and algorithm flow charts to aid decision making (Fletcher et al, 2012).

Cardiopulmonary resuscitation in practice

Although literature covers different aspects of CPR and its effectiveness, less commonly known are the mortality and survival rates for animals in veterinary care. In contrast, human medicine offers some insightful statistics in relation to survival following CPR. Patients who experience a cardiopulmonary arrest outside of the hospital setting have a survival rate of 8–10%. Those who are already within the hospital environment during cardiopulmonary arrest have a survival rate of up to 20% (Boller and Fletcher, 2012; Beyersdorf et al, 2021).

A different picture can be seen in the veterinary setting, with overall survival rates of less than 10% for in-hospital cardiopulmonary arrest, and unrecorded statistics for cardiopulmonary arrest outside the hospital (Boller and Fletcher, 2012). It is also important to consider species variations for veterinary patients. Research suggests that survival rates in felines range from 10–19%, whereas in canines survival rates after cardiopulmonary arrest may be as low as 6% (Breton, 2012; Boller and Fletcher, 2012; Smarick et al, 2012; Fletcher and Boller, 2013; McIntyre et al, 2014; Donaldson et al, 2020). Euthanasia is a valid option for some animals, which may affect the statistics on long-term patient outcomes.

An investigation into the use of the RECOVER guidelines showed that following cardiopulmonary arrest, practices that failed to use the guidelines had an overall patient survival rate of 17%, with no patients able to be discharged from their care due to death (Kawase et al, 2018). The same study found that initiating the RECOVER guidelines led to a survival rate of nearer 43% with 5% of animals able to be discharged from care (Kawase et al, 2018).

Aims

Research within veterinary medicine often focuses on common techniques, drug doses and parameters necessary for CPR (Boller and Fletcher, 2012; Boller et al, 2016; Gillespie et al, 2019; Ward et al, 2021). It rarely focuses on the influence of these factors on CPR survival rates. Therefore, the aim of this retrospective pilot study was to gain an insight into CPR outcomes within a UK veterinary teaching hospital that included a dedicated intensive care unit.

Methodology

Ethical Approval for a Veterinary Investigation through the University of Bristol was obtained: (VIN/21/034). Quantitative data was collected for the retrospective, cross-sectional study to allow analysis of 5 years' worth of data (01/01/2017 to 01/01/2022) relating to cardiopulmonary resuscitation (CPR) at one veterinary hospital.

Inclusion criteria

Animals that underwent respiratory arrest that did not lead to CPR were not included in the study (Hoehne et al, 2019). If subsequent CPR was needed within the same visit, the first cardiopulmonary arrest event was analysed as the point of first intervention (McIntyre et al, 2014; Kawase et al, 2018; Hoehne et al, 2019). When cardiopulmonary arrest occurred at a secondary visit, it was entered and analysed as a new data set because animals were considered to have survived when they were discharged (McIntyre et al, 2014; Hoehne et al, 2019).

Method

Data was collected retrospectively over 5 years: January 2017 to January 2022. Initially patient records were split by species; canine (n=89) and feline (n=25), and then anonymised to protect client and patient identity. In order to identify trends within the data, patient specific information was collected: species, breed, sex and age were recorded (Table 1). Date of arrest was recorded to help identify and organise.

The information specific to the first cardiopulmonary arrest event was recorded and statistical analysis was only carried out on data sets considered to be complete. Complete datasets consisted of all the following information:

• The time of arrest, time CPR started, duration of CPR, and location of cardiopulmonary arrest
• The use of advanced or basic life support
• Whether compressions were closed or open
• The return of spontaneous circulation for more than 20 minutes to determine whether CPR was successful
• The outcome of the first cardiopulmonary arrest event and the outcome at 24 hours and 48 hours; alive, died or euthanised, re-arrested – survived or re-arrested – died
• The animal's overall outcome; whether the animal was still alive. The definitive end point was discharge.

Because of the retrospective nature of the study, variables were selected in line with the veterinary hospital's recording system. All variables were considered equally important. Future prospective studies may allow for focus on particular variables onces they have been highlighted as important.

Statistical analysis

A Chi-squared test was used to test for an association between the measured variable (for example, return of spontaneous circulation) and CPR outcome. For continuous data, a Mann-Whitney U test for difference was used. The independent variable (time of arrest) was compared to the dependant variable (outcome of CPR – dead or alive) to calculate difference.

Results

Of 253 patients that received CPR, 172 patients met the inclusion criteria, 114 of those had complete data sets and were analysed. Of those analysed, 72.8% used the hospital-specific recording sheet to appropriately document CPR.

Descriptive statistics

Time taken to start CPR ranged from immediately (77.5% [n=89] canines and 60% [n=25] felines) to one hour.

When reviewing all patients, the intensive care unit was the most frequently used location for CPR (78.1%) and theatre was the second most common area (9.6%). Other locations such as during CT, MRI, and in the car park recorded 0.9% of cases for each. Basic life support was used in 14% of cases. Advanced in combination with basic life support, with a range of techniques, was used in 86% of cases. Closed compressions were more commonly used (95.6%) when performing CPR.

Animals varied in their length of stay in the hospital, so the outcome measured was time of death or discharge; 6.1% of patients survived and were discharged. Patients that died during their stay in hospital (73.7%) did so because CPR was unsuccessful or because a ‘do not resuscitate’ order existed. A total 20.2% of cases were euthanised (Figure 1).

Statistical analysis

Following a Chi-squared test significant outcomes were determined for location of resuscitation (P=0.003), type of compression used (P=0.005) and return of spontaneous circulation of more than 20 minutes (P=0.001) against outcome of CPR. No significance was reported for the use of advanced/basic life support (P=0.696) and outcome of CPR. Canine and feline patients were analysed together.

The Mann-Whitney U test elicited no significant differences for age at CPR (U=1188.500, P=0.603), time of arrest (U=1028.500, P=0.565) and duration of CPR (U=1119.000, P=0.964).

Discussion

The main research aim was to determine whether outcomes of CPR within a UK veterinary hospital could be investigated. Initial outcomes following CPR after cardiopulmonary arrest were recorded, along with the collection of variables that may influence the outcome of CPR.

Outcomes of cardiopulmonary resuscitation

The current study reported that 6.1% of animals survived to discharge, which is in agreement with previous research (Breton, 2012; Boller and Fletcher, 2012; Fletcher and Boller, 2013). Evaluation of the effectiveness of CPR, at different sites internationally, suggests that between 5.3% and 9.5% of dogs and cats survive until discharge (McIntyre et al, 2014; Kawase et al, 2018; Hoehne et al, 2019).

After the initial CPR outcome, the current study reported 21.9% of animals were alive and had achieved sustained return of spontaneous circulation; 10.1% lower than reported by McIntyre et al (2014) and 5.9% lower than reported by Hoehne et al (2019). Current results agreed with previous literature that at 24 hours after initial recorded cardiopulmonary arrest 10.5% of animals were still alive. After 48 hours outcomes were no longer recorded for previous studies, while the current study indicated that 8.8% of patients remained alive. To understand how trends continue it may be beneficial to suggest recording of patient outcomes past the 24-hour period. Sustained return of spontaneous circulation was found to be statistically significant and associated with CPR outcome. It is an accurate presumption that in order to be alive the individual must have achieved sustained return of spontaneous circulation. Compliance with and use of the RECOVER guidelines should help in achieving sustained return of spontaneous circulation (Kawase et al, 2018; Hoehne et al, 2019).

Within this study most cases of CPR (78.1%) were reported to occur in the intensive care unit. Typically this area contains more systemically unwell animals that require continual monitoring and more specialised care when compared to those on the wards (Goldhill and Sumner, 1998). Hoehne et al (2019) also found that CPR was most common in the emergency room/intensive care unit or theatre; areas which are well equipped to deal with CPR. Results from this study and Hoehne et al (2019) reflect hospitals with a dedicated intensive care unit. However, all practices will manage patients who require high levels of care and monitoring. A comparative study in UK veterinary practices without a dedicated intensive care unit would help generalise the results to all veterinary practices.

In theatre, the majority of cases are considered non-emergency, systemically well patients, having a low American Society of Anaesthesiologists (ASA) physical status classification grade, reducing the probability of CPR (Bille et al, 2012; Portier and Ida, 2018). If these animals were to undergo cardiopulmonary arrest and then CPR, their chances of survivial increases, because of the ready supply of oxygen, having a secure airway, being continuously monitored and having secure intravenous access to administer any appropriate reversal agents (Braz et al, 2009; Grubb et al, 2020). Interventions can therefore be carried out immediately. To determine if these factors do influence the number of patients achieving ROSC, future studies could focus more closely on the individual areas of the practice. By understanding the percentage of patients that are surviving in different areas of the practice, further variables could be added, such as ready access to an oxygen supply. Within a practice, staff may focus on different areas and specialisms, and despite regular training may not be practiced at providing CPR (McMicheal et al, 2012; Kruppert et al, 2020). To improve, biannual training with practical simulations, recommended by the RECOVER guidelines, would support individuals lacking confidence or experience (McMicheal et al, 2012; Waxman, 2019; Ward et al, 2021).

Collecting historical data provided an understanding of CPR effectiveness and highlighted potential areas for improvement. This study would be most beneficial to the veterinary hospital involved, but could support similar practices when recording CPR cases and auditing the outcomes.

Limitations

The study has highlighted the importance of using the hospital recording sheet to record what interventions were provided once cardiopulmonary arrest was diagnosed. These recording sheets ensure that all aspects of the animals care have been documented to support the practice incase of clincial auditing, legal repercussions or interest in understanding trends and occurances at a later date (RCVS, 2023). Of the 172 patients who matched the inclusion criteria, 33.7% of the animals' cases could not be used because their data sets were incomplete. CPR situations can be fast-paced and clinical staff will react to the conditions they find themselves in while putting the welfare of the animal first (RCVS, 2012a). However, record keeping is important not only for the accurate logging of events but also for time keeping, as a prompt for clinical goals and to evidence gold-standard techniques to those that are still learning (RCVS, 2012a).

Owner perceptions were not recorded, as the study was conducted in retrospect. It should be considered that euthanasia has been reported as a leading cause of death after CPR, with poor prognosis and financial issues being cited (McIntyre et al, 2014; Kawase et al, 2018). It is important to understand the decision making process of owners in order for veterinary professionals to gain consent about CPR and be fully informed about individual clients circumstances and beliefs. A prospective study would allow full and detailed data collection in the additional areas that this study has highlighted.

Future studies

Investigating owner perceptions of CPR may highlight why animals are given a do not resuscitate order or euthanised and explain some of the discrepancy in CPR survival rates within this study (6.1%) compared to human medicine (20%) (Boller and Fletcher, 2012; Beyersdorf et al, 2021).

The RECOVER initiative is currently being reviewed and, while the current retrospective study has highlighted variables that are associated with CPR outcome, a more impactful prospective study would provide useful information. Recreating the study would allow all the required variables to be collected every time CPR was performed, increasing links to CPR outcome which are useful for clinical audits, as well as developing evidence-based practice for patients requiring CPR (RCVS, 2012a; RCVS, 2012b).

Boller et al (2016) investigated the use of the Utstein-style guidelines to standardise the recording of CPR cases, concluding that its use would improve and encourage detailed research. A modern approach to this with the use of a digital questionnaire may help data collection, storage and analysis of patient CPR records which would support clinical auditing.

Conclusion

CPR outcomes recorded were in line with previously reported data. This project has highlighted areas that could be focused on in a detailed prospective study, the results of which would enable better practice auditing. Further understanding of the relationship between the variables of significance and the outcomes of CPR could help veterinary professionals improve survival rates more in line with those seen in human medicine and educate owners on reasonable expectations.

Despite the study's limitations, it has provided scope for further research, highlighted areas of best practice, such as detailed record keeping, and outlined a need for standarisation across the industry. The study has the possibility of benefitting and influencing similar practices within the UK to audit their CPR cases and consider whether improvements can be made.

KEY POINTS

• On average 6% of canine patients survive CPA to discharge.
• Following RECOVER guidelines should help when trying to achieve sustained return of spontaneous circulation.
• Recording CPR outcomes can help with clinical auditing and add to patient outcome data.