A total of 223 episodes of cardiac arrest occurred in 219 patients, yielding an incidence of 77 per 1000 beds per year. During the period, approximately 2860 patients died and 882 200 patients-days were spent at the hospital, indicating that CPR was instituted in 8% of in-hospital deaths; at a rate of 1.76 per 1000 admissions, or 0.25 episodes per 1000 patient-days. Two episodes were excluded from further analysis as being very atypical and not providing useful information: One patient died from VF in the ED when the defibrillator repeatedly malfunctioned. Another patient arrested in the ED from hypothermia, received cardiopulmonary bypass, and survived.
Among the remaining 217 patients and 221 episodes, the median age was 75 years, 66% were male, and three patients were < 18 years. Cardiac aetiology, i.e. no other obvious cause, was presumed present in 179 patients (81%). The outcome was determined in all patients (table ). One patient arrested four times and was discharged twice two months apart. Another patient arrested twice, survived for 24 hours but died before hospital discharge. Only the first episode per hospital admission was included in the models to avoid statistical dependency problems.
Episode and time characteristics vs. outcome
In almost half of the patients there was no response, whereas 12% showed signs of life during resuscitation but eventually died on scene. ROSC was achieved in 40% of the patients, half of whom died within 24 hours. Among the 217 patients, 29 survived to hospital discharge (13%, 95% CI: 9 to 19%); two of whom had presented with asystole or PEA. One-year survival was 9.7% and five-year survival 7.8%. CPR quality was found to be good in about half of the episodes (table ). Figure presents the observed relation between outcome, time, and CPR quality.
Figure 1 Relation between outcome, CPR quality and time to first defibrillation (≤ 10 minutes), in patients presenting with VF/VT (a, upper); or asystole/PEA (b, lower). Note that the BLS phase may extend beyond the first defibrillation. CPR quality scale: (more ...)
Presenting rhythm VF/VT
Median Tdefib was 4 minutes (IQR: 82 – 412 s). We found a negative correlation between outcome and Tdefib (Spearman's rho = -0.38, 95% CI: -0.58 to -0.18, p < 0.001), but not with TCPR (Spearman's rho = -0.0127, 95% CI: -0.23 to 0.21, p = 0.90), or with CPR quality (Somer's d = -0.02, 95% CI: -0.18 to 0.15, p = 0.85). In the statistical models, the variables log (Tdefib), CPR quality, and their interaction (i.e. product term) were found to be statistically significant (coefficients given in Figures and ). This phenomenon is visualized in figure : with Tdefib less than about 3 minutes (figure , grey line), survival is better among those who did not receive BLS CPR. When Tdefib exceeds this value, all patients with ROSC appear in the upper two strata of figure , corresponding to CPR of increasing quality. The time point (Tdefib) at which BLS impact changes from negative to positive was calculated to be 2.72 minutes with CPR quality scale 0–2 (Figure ) or 3.85 min with CPR quality scale 0–1 (Figure ). Figure shows the response surface derived from the statistical model, with the expected probability of survival according to CPR quality scale 0–2 and time to defibrillation. At Tdefib = 1 minute, the baseline probability of survival is about 70%. If no defibrillator is immediately available and CPR is not provided, survival rapidly decreases to about 3% at Tdefib = 10 minutes. Providing CPR in conjunction with defibrillation at this time increases the probability of survival to about 33%. Immediate CPR at Tdefib = 1 in conjunction with defibrillation is associated with a drop in survival to approximately 25%. The interaction between time and CPR, i.e. how CPR impact changes from negative to positive, can be seen as a twist of the surface. Figure illustrates the same phenomenon when CPR is treated as a binary variable (0–1); the curves intersect close to 4 min.
Figure 2 Estimated probability surface of survival among patients with VF/VT, according to time to first defibrillation (≤ 10 minutes), and BLS CPR quality. CPR quality scale: 0 – No CPR; 1 – Intermediate quality; 2 – Compression (more ...)
Figure 3 Estimated probability of survival among patients with VF/VT, according to time to first defibrillation (≤ 10 minutes), and to whether BLS CPR was provided or not. Logistic regression coefficients with 95% confidence intervals in parentheses: Model (more ...)
Presenting rhythm PEA or ASY
Among the 131 patients with presenting rhythms of asystole and PEA (Figure ), 19 (15%) had not received BLS but were resuscitated by the resuscitation team; among these were eight episodes witnessed by the team. Seven of the 19 achieved ROSC and one was discharged. We found no relation between outcome and TCPR (Spearman's rho = -0.002, 95% CI: -0.18 to 0.17, p = 0.98), or with CPR quality (Somer's d = -0.04, 95% CI: -0.21 to 0.12, p = 0.58).
A total of 43 patients with a presenting rhythm of asystole or PEA received DC shocks. Among these, 19 had converted to a shockable rhythm during resuscitation and were properly defibrillated; one of them survived to discharge. These episodes were retained and analysed in the PEA/ASY group.