Survival after different forms of bystander cardiopulmonary resuscitation in out-of-hospital cardiac arrest : ‛to breathe or not to breathe?’

• Background: Out-of-hospital cardiac arrest (OHCA) affects more than 6000 people per year in Sweden and only one in ten survive. One of the most important modifiable factors determining survival is early cardiopulmonary resuscitation (CPR), but different forms of CPR and their association with survival remain inadequately studied. The overall aim of this thesis was to assess the association between different forms of CPR prior to Emergency Medical Services (EMS) arrival and survival in OHCA. Methods: All patients were EMS treated OHCAs reported to the Swedish register for cardiopulmonary resuscitation. Study I-III are register based observational cohort studies. Study IV is a feasibility study of a national, investigator-initiated, multicentre, randomized clinical trial (RCT) comparing survival after dispatcher instructions of standard CPR (S-CPR) with compressions and rescue breaths vs of compressions only (CO-CPR) to trained bystanders in OHCA (TANGO2). Specific study Aims and Results: In Study I we assessed survival after CPR prior to EMS arrival compared to no CPR prior to EMS arrival. Witnessed OHCA in 1990-2011 were included (N = 30 381). CPR prior to EMS arrival was performed in 51 % of all cases. Survival to 30 days was 10.5 % for patients receiving CPR and 4.0 % when CPR was not performed, odds ratio (OR) 2.80 (95% CI, 2.47 – 3.18), adjusted OR 2.15 (95 % CI, 1.88 – 2.45). The association with survival was greater when the time to the initiation of CPR was short. In Study II we aimed to describe temporal changes in CPR rates and type of CPR prior to EMS arrival and survival in relation to three time periods of different CPR guidelines in Sweden. Witnessed OHCA in 2000 – 2017 (N = 30 455) were divided into groups reflecting guideline periods (2000 – 2005, 2006 – 2010, 2011 – 2017). Exposure was no CPR, S-CPR or CO-CPR. The proportions of patients receiving CPR prior to EMS arrival changed from 40.8 % to 68.2 % and CO-CPR changed from 5.4 % to 30.1 % between the first and the last guideline period. Adjusted OR for 30-day survival was 2.6 (95 % CI, 2.4–2.9) for S-CPR and 2.0 (95 % CI, 1.8–2.3) for CO-CPR, in comparison with no CPR. S-CPR was superior to CO-CPR (adjusted OR, 1.2; 95 % CI, 1.1–1.4). In Study III we aimed to assess survival after CPR with dispatcher instructions compared with no CPR and spontaneously initiated CPR. Lay-bystander witnessed OHCA in 2011 – 2017 were included (N = 15 471). Propensity score matched cohort were used for comparison. Using dispatcher assisted-CPR as reference, spontaneously initiated CPR was associated with higher survival, OR 1.21 (95 % CI, 1.05–1.39) and no CPR with lower survival, OR 0.61 (95 % CI, 0.52–0.72). In Study IV we aimed to assess feasibility and intermediate clinical outcomes in the TANGO2 trial. From Jan 1st to Dec 31st, 2017, a total of 729 emergency calls of suspected OHCA were randomized and 381 (51.4 %) of these were EMS treated OHCAs, 185 (48.6%) were assigned to S-CPR and 196 (51.4%) to CO-CPR. CPR instructions were provided in 89.3 % of all calls and CPR was initiated in 93.4 % of all calls. Median time to CPR instructions was 210 s in the S-CPR group (IQR 140 – 301) and 180 s in the CO-CPR group (IQR 135 – 275), this time difference was not significant (NS). Cross-over from the S-CPR group to CO-CPR instructions was found in 22.3 % (40 calls), and from the CO-CPR group to S-CPR instructions in 16.1 % (30 calls). The number of patients surviving to hospital admission were 17.3% (n = 32) versus 20.4% (n = 40) for S-CPR and CO-CPR respectively (NS). Conclusions: The current studies confirm the independent association between CPR prior to EMS arrival and survival in OHCA, irrespectively if CPR was performed with compressions and ventilation, compressions only or with dispatcher assistance. There was an almost doubled rate of CPR prior to EMS arrival in Sweden between 1990 – 2017 and a concomitant 6-fold increase in the rate of CO-CPR between 2000 – 2017. The pilot study of the TANGO2 trial was found to be feasible and safe. However, cross-over was found as a limitation.

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