In this study, we analyzed the different prognostic factors for OHCA for different age groups. Compared with the older group, we found that bystander CPR and prehospital defibrillation by AED were independent prognostic factors for younger OHCA patients.
Many previous studies have demonstrated that prehospital factors are associated with the outcomes of OHCA, such as location of OHCA [3, 13], EMS response time [15, 16], attended by EMT-Paramedic , and witness of OHCA . Some studies attempted to exam the influence of bystander CPR on OHCA outcomes, but the results were inconclusive. Girotra et al. showed that bystander CPR was positively correlated with survival and neurological outcome . However, Handel et al. did not find a positive association between bystander CPR and survival to hospital discharge in OHCA . There could be several possible explanations for this discrepancy. First, there could be a difference in the quality of CPR provided by bystanders. Axelsson et al. revealed that OHCA witnessed by EMT had a higher chance of survival than bystander-witnessed OHCA . Second, the time between cardiac arrest and initiation of CPR might impact the outcome. Sasson et al. reviewed 79 studies and concluded that the survival rate might increase if a bystander initiated CPR early . A study by Sladjana et al demonstrated that CPR performed within four minutes of the cardiac arrest would have a better prognosis . Third, response time could also affect the outcome. Rajan et al. showed that the ratio of the standardized 30-day survival rate between bystander CPR and non-bystander CPR increased as response time was prolonged; at response time of 5 minutes, bystander CPR was associated with a 2.3 times greater survival rate compared with that of non-bystander CPR and a 3.0 times greater survival rate at 10 minutes response time . Fourth, the differences in age and communities of patients included in these studies might influence the impact of bystander CPR on OHCA outcomes. In the present study, we found that bystander CPR was associated with a higher chance of survival for the younger group than that of the older group.
Prehospital defibrillation was also a prognostic factor for OHCA [2, 10]. Our study found that prehospital defibrillation was associated with a higher chance of survival for the younger group than that for the older group. One possible reason was the different causes of OHCA among the different age groups. Winther-Jensen et al. revealed that the number of cardiogenic OHCA was higher in younger patients than in older patients , and cardiogenic OHCA seemed to have better prognosis . Early defibrillation is an effective treatment for ventricular fibrillation (VF), and VF is a common presentation for cardiogenic OHCA . Furthermore, younger OHCA patients had a higher probability of accepting invasive post-resuscitation procedures, such as coronary angiography, than older patients . Coronary angiography is known to reduce mortality and improve neurological recovery in patients with ST elevation myocardial infarction (STEMI) complicated with OHCA . Shavelle et al. collected data on 422 STEMI OHCA patients who underwent coronary angiography, and 263 (62%) survived to hospital discharge, and 193 (46%) patients had a favorable neurological outcome, which was much better than that of generalized OHCA patients . However, older OHCA patients had more comorbidities than the younger group. In our study, the older group had a higher ratio of diabetes, previous stroke, and respiratory diseases than that of younger patients. The preserved organ function, such as heart function, might be poorer than that of the younger group; therefore, prehospital defibrillation for the older group did not improve outcomes in the present study.
Location of cardiac arrest is a prognostic factor for OHCAs [3, 13]. OHCA occurred at different counties, public/resident or urban/rural area also influenced the outcome [3, 10, 13]. OHCA occurring in public locations are usually associated with a shorter response time, younger age, and more often occur during the daytime . OHCAs occurring in different areas might impact the EMS response time, and might reflect different socioeconomic status of the countries [3, 10]. Shorter response time, younger age, OHCA occurring during the daytime, urban areas, and socioeconomic status are usually associated with better prognosis [15, 16, 24, 25]. However, people who have OHCAs in public locations tend to be healthier, are able to move freely, and probably have less comorbidity, and thus have better outcomes . The current study also supported this finding. In the current study, OHCAs occurring in public locations had better prognosis in both the younger and older groups.
EMS response time was defined as the duration of time from when a call is made to the EMS to the point when the EMT arrive at the scene. Recently, several studies revealed that shorter EMS response time could improve outcome of OHCA [15, 16, 21, 27]. Shorter EMS response time was associated with a higher rate of survival to discharge and of 1 year survival . For bystander witnessed OHCA, Ono et al. collected 204,277 episodes of OHCA and reported that a response time of ≤ 6.5 minutes was correlated to favorable neurological outcomes . With bystander CPR, the response time could be prolonged to 7.5 minutes. For OHCAs of cardiac origin, response time less than 7.5 minutes was found to increase the odds of survival to discharge and had better neurological outcome . In the present study, when response time was prolonged by 1 minute, we found decreased odds of survival to discharge in both the older (OR = 0.833, 95% CI: 0.742–0.928) and younger groups (OR = 0.860, 95% CI: 0.811–0.909). Reduced EMS response time reflect earlier advanced cardiovascular life support (ACLS) interventions and higher quality CPR by EMT and thus improves prognosis.
In Taiwan, an EMS agent can be classified into EMT-I, EMT-II and EMT-P. The difference between EMT-I, EMT-II, and EMT-P are mainly in the training program and training time received and what they are authorized to do. The total training time for EMT-I, EMT-II and EMT-P qualifications are 40, 280, and 1280 hours, respectively. The training programs for cardiac arrest include the BLS, but only EMT-P undergo the program with ACLS being held in the hospital. Attendance by EMT-P was associated with a good prognosis of OHCA in our study, both for the younger and older groups. One possible reason for this could be the difference in experience. Usually EMTs enter the workplace after undergoing EMT-I training. After a period of time, they complete EMT-II training and EMT-P if necessary. Therefore, both the training programs and experience of the EMTs differ. Gold et al. also discovered that every additional year of experience for a paramedic was associated with 2% increased odds of survival for OHCA patients . Another possible explanation is earlier intervention using advanced life support (ALS). In Taiwan, only EMT-P are allowed to perform ALS, such as the placement of an endotracheal tube and limited drug administration, including epinephrine and amiodarone. Another study performed in Taiwan revealed that EMT-P intervention was related to a higher rate of survival to hospital admission . Furthermore, recent studies also showed that prehospital physician involvement was associated with improved return of spontaneous circulation, survival to hospital admission, and survival to hospital discharge [4, 29]. These results suggest that high quality CPR and early ALS, even ACLS, involvement were associated with better outcomes of OHCA.
Pre-existing comorbidities might be a prognostic factor for OHCA, but previous studies showed inconclusive results. Hirlekar, et al. demonstrated that renal disease, diabetes, congestive heart failure, and metastatic carcinoma were poor prognostic factors for 30-day survival rate, after adjusting for prehospital factors . Andrew, et al. revealed that diabetes, congestive heart failure, renal disease, and chronic obstructive pulmonary disease were associated with reduced odds of survival to hospital discharge for initial shockable OHCA patients ; additionally, another study did not find a statistically significant association between diabetes and survival to hospital discharge after adjusting for prehospital and demographic factors . However, Lai et al. found that cardiac comorbidities, such as valvular heart diseases and cardiomyopathy, were independent factors that improve survival . The current study did not find significant differences between effects of comorbidities, including diabetes, hypertension, previous stroke, and liver disease, on survival of OHCA patients. A recent systemic review of 29 observational studies, attempted to find a relationship between pre-arrest comorbidity and outcomes of OHCA . However, a meta-analysis was not performed in this review due to the clinical and statistical heterogeneity across the included studies. The authors concluded that among the 29 studies, 42% (40/94) outcomes of survival showed statistically significant association between comorbidities on OHCA survival. In other words, although some studies revealed a negative association between comorbidities and survival of OHCA, the overall result was still inconclusive.