Survival in Out-of-Hospital Cardiac Arrest After Standard Cardiopulmonary Resuscitation or Chest Compressions Only Before Arrival of Emergency Medical Services: Nationwide Study During Three Guideline Periods
Authors: Riva G, Ringh M, Jonsson M, et al.
Published in: Circulation, 2019 Apr 1.
For over a decade, in hopes of increasing bystander CPR, we have been transitioning from standard CPR, which included chest compressions and rescue breathing, to compression-only CPR. As previous research has shown, this transition has been successful in increasing bystander CPR. However, we have not previously discussed the impact of this transition on survival.
This month we look at a national study that described changes in the rates and types of CPR performed before EMS arrival over three consecutive guideline periods. The authors also assessed the association between the type of CPR performed and 30-day survival. This was an observational nationwide register-based cohort study performed in Sweden. For context, Sweden has a population of close to 10 million, which is similar to Georgia, North Carolina, Michigan, and New Jersey.
Sweden was an ideal place to perform this study because the authors had access to data from the Swedish CPR registry. This is a nationwide registry for reporting of out-of-hospital cardiac arrest. It’s a wonderful resource because not only does it have data dating back to 2000, but it’s a very robust data set. It contains standardized data based on the Utstein template for cardiac arrest reporting. Data are reported by EMS crews after responding to an OHCA. These data include patient characteristics, location of the arrest, probable cause of the arrest, and if the arrest was witnessed. For witnessed arrests, data are collected indicating if bystander CPR was performed, the method of CPR (standard or compression-only), and highest medical education level of the person(s) performing CPR before EMS arrival.
The study period was from 2000–2017. The authors evaluated data over the entire study period and separately for each guideline period. From 2000–2005 the guidelines recommended a compression-to-ventilation ratio of 15:2. From 2006–2010 the Swedish national CPR guidelines recommended a compression-to-ventilation ratio of 30:2, and compression-only CPR was introduced as an option if bystanders were unwilling to perform rescue breaths. From 2011–2017 the guidelines recommended compression-only CPR for dispatcher-assisted CPR or standard CPR with a 30:2 ratio. The authors classified patients as receiving no CPR, standard CPR, or compression-only CPR. The study outcome of interest was 30-day survival.
There were 68,126 cases of OHCA that had an EMS response during the study period. Of these, 34,680 were witnessed by a bystander. One of the most impressive things about this study is the lack of missing data: Out of over 34,000 cases, only about 2,719 were excluded due to missing data on CPR type, and 605 were excluded because they had missing outcome data. Not everyone has access to outcome data on more than 98% of their patients! After excluding OHCAs that were unwitnessed, EMS-witnessed, or where only rescue breaths were provided, there were 3,445 cases included in the analysis.
Forty percent of patients included in the study did not receive CPR, 39.2% received standard CPR, and 20.8% received compression-only CPR. There was an impressive increase in rates of bystander CPR over the different guideline periods. The initial proportion of patients receiving any type of CPR before EMS arrival increased from 40.8% in the first guideline period to 58.8% in the second guideline period and 68.2% in the final guideline period. The proportion of patients receiving standard CPR changed from 35.4% to 44.8% to 38.1% over the three periods. The proportion of patients receiving compression-only CPR changed from 5.4% to 14.0% to 30.1%. Over the entire study period, standard CPR was performed at a higher percentage by bystanders with a medical education (2,736, 25.1%) when compared to compression-only CPR (929, 15.3%).
More patients survived after 30 days in the later guideline periods, and both standard CPR and compression-only CPR were associated with increased 30-day survival percentages. Over the entire study period, 30-day survival was 5.8% among patients who did not receive CPR, 13.8% among patients who received standard CPR, and 13.5% among patients who received compression-only CPR.
When specifically comparing standard CPR to compression-only CPR, there was no statistically significant difference noted (OR 1.03; 95% CI, 0.94–1.13). However, when adjusting for baseline characteristics and other important resuscitation factors, standard CPR was associated with a statistically significant increase in 30-day survival (OR 1.20; 95% CI, 1.10–1.40). Just a quick reminder on the interpretation of odds ratios: An odds ratio of 1.00 means there is no difference between the groups. If 1.00 is between the lower and upper bounds of a 95% confidence interval, the result is not statistically significant.
This was a very interesting and important study that showed almost double the rate of bystander CPR following the introduction of compression-only CPR. Further, the results indicated that compression-only CPR is associated with much higher percentages of patients who survive after 30 days.
While it appears we should continue to have appropriately trained individuals perform standard CPR, compression-only CPR is clearly a valuable method to increase patient survival when performed by those unwilling to provide rescue breaths.
As with every study, this one has some limitations, including an inability to evaluate neurological function. This study period also included a time when a randomized controlled trial was being performed in Sweden, which could have impacted the increased rates of bystander CPR.
As always, I hope you can read this entire manuscript. There are a lot of subanalyses we couldn’t discuss here, as well as some interesting methods for working with missing data.
Antonio R. Fernandez, PhD, NRP, FAHA, is research director at the EMS Performance Improvement Center and an assistant professor in the Department of Emergency Medicine at the University of North Carolina–Chapel Hill. He is on the board of advisors of the Prehospital Care Research Forum at UCLA.