The Effect of Ambulance Response Time on Survival Following Out-of-Hospital Cardiac Arrest

Abstract

Background: Out of hospital cardiac arrest (OHCA) is one of the more common causes of death in Germany. Ambulance response time is an important planning parameter for emergency medical services (EMS) systems. We studied the effect of ambulance response time on survival after resuscitation from OHCA.

Methods: We analyzed data from the German Resuscitation Registry for the years 2010-2016. First, we used a multivariate logistic regression analysis to determine the effect of ambulance response time (defined as the interval from the alarm to the arrival of the first rescue vehicle) on the hospital-discharge rate (in percent), depending on various factors, including resuscitation by bystanders. Second, we compared faster and slower EMS systems (defined as those arriving on the scene within 8 minutes in more than 75% of cases or in ≤ 75% of cases) with respect to the frequency of resuscitation and the number of surviving patients.

Results: Our analysis of data from a total of 10 853 patients in the logistical regression model revealed that the rate of hospital discharge was significantly affected by the ambulance response time, bystander resuscitation, past medical history, age, witnessed vs. unwitnessed collapse, the initial heart rhythm, and the site of the collapse. The success of resuscitation was inversely related to the ambulance response time; thus, among patients who did not receive bystander resuscitation, the discharge rate declined from 12.9% at a mean response time of 1 minute and 10 seconds to 6.4% at a mean response time of 9 minutes and 47 seconds. Twelve faster EMS systems and 13 slower ones were identified, with a total of 9669 and 7865 resuscitated patients, respectively. The faster EMS systems initiated resuscitation more frequently and also had a higher discharge rate with good neurological outcome in proportion to the population of the catchment area (7.7 versus 5.6 persons per 100 000 population per year, odds ratio [OR] 0.72, 95% confidence interval [0.66; 0.79], p<0.001).

Conclusion: Rapid ambulance response is associated with a higher rate of survival from OHCA with good neurological outcome. The response time, independently of whether bystander resuscitation measures are provided, ha^ a significant independent effect on the survival rate. In drawing conclusions from these findings, one should bear in mind that this was a retrospective registry study, with the corresponding limitations.

Figure 1

The effect of ambulance response time on the percentage hospital discharge rates of OHCA patients in emergency medical services (N = 10 853) depending on cardiopulmonary resuscitation performed by a bystander. Patients were assigned to five time categories; these categories were defined according to the time interval between “Raising of the alarm and arrival of the first vehicle.” The dashed lines show the discharge rates of these patients adjusted using a multivariate logistic regression model. Further statistical analyses was performed using the Chi² test with Bonferroni correction, odds ratio, and confidence interval; statistical significance was set at p<0.01. CPR, cardiopulmonary resuscitation; OHCA, out-of-hospital cardiac arrest; OR, odds ratio; 95% CI; 95% confidence interval

Figure 2

Multivariate logistic regression analysis with the binary outcome measure “Discharge following OHCA.” A total of 10 853 patients with OHCA that was not observed by the emergency medical services were included. Resuscitation success declines with increasing ambulance response time, higher age, and severe pre-existing disease. In contrast, bystander resuscitation, a shockable rhythm, or the fact that the collapse was witnessed or occurred in public or a medical practice, improve the prognosis following resuscitation by emergency medical services. CPR, cardiopulmonary resuscitation; OHCA, out-of-hospital cardiac arrest; ref., reference

eFigure 1

The number of patients that survive annually following resuscitation by EMS systems as a projection and simulation on the basis of the logistic regression model. At a measured hospital discharge rate of 13%, this means that 7091 patients survive per year in Germany. By reducing the individual ambulance response times by 10%, 20%, or 30%, the number of survivors increases annually by 370, 515, or 634 patients, respectively. If the rate of bystander CPR could be raised by 20 or 40 percentage points to 47% or 67%, an additional 245 or 426 patients could be saved every year. By simulating a 20% reduction in ambulance response time combined with an increase in the rate of bystander CPR to 47%, as many as 771 more patients/year could be saved, amounting to an annual total of 7862 patients saved in Germany by EMS systems following sudden OHCA and resuscitation. ART, ambulance response time; CPR, cardiopulmonary resuscitation; EMS, emergency medical services; OHCA, out-of-hospital cardiac arrest; SIM, simulation

eFigure 2

The effect of ambulance response time at the EMS systems level on CPR incidence and resuscitation success in a comparison of 12 faster (9669 resuscitation patients) and 13 slower (7865 resuscitation patients) EMS systems. A faster EMS system reaches >75% of patients with the first vehicle within 8 min after raising of the alarm, a slower system reaches = 75% of patients. The incidences and mortality were calculated as number/100 000 population/year; the percentages given relate to the number of resuscitation patients; statistical analysis was performed using the Chi² test; and statistical significance was set at p<0.05. CPC, cerebral performance categories; CPR, cardiopulmonary resuscitation; EMS, emergency medical services; OHCA, out of hospital cardiac arrests; RACA, ROSC after cardiac arrest; ROSC, return of spontaneous circulation; RTR, response time reliability