Cardiac arrest is one of the most critical and dangerous clinical conditions. Although the level of medical treatment has made great progress in recent decades, the prognosis of cardiac arrest is still poor[13]. A report[14] analyzed the outcomes of more than 12,000 patients, these patients were the patients treated by Emergency Medical Service (EMS) staff in Seattle, USA during the 24 years, the patients treated in 1998-2001 and the patients treated in 1977-1981 were compared, the ratio of survival to discharge did not improve significantly (15.7% vs 17.5%). The United States Improved Survival Cardiac Arrest Registry (CARES) registry study prospectively included 70,027 American patients with out-of-hospital SCA from 2005 to 2012, and found that the discharge survival rate increased significantly from 5.7% in 2005 to 2012 8.3% of the year[15]. The success rate of CPR in our study was 35.71%. All patients in this study treated in the department of emergency of our hospital and received timely and correct treatment. Therefore, the success rate of CPR is higher than that of previous reports[16-18]. And we have found that age≥65y, time to the start of CPR≥12min, unable to defibrillation, duration of CPR≥40min, cumulative adrenaline dosage≥6mg are the independent risk factors of CPR failure, early alert and preventions are needed for those patients.
The ratio of men to women in SCA patients in this preset study is 1.46:1, but the univariate analysis showed that gender had no significant effect on the success rate of cardiopulmonary resuscitation. Age is an independent factor affecting the success rate of CPR. Younger patients have a higher success rate of CPR. This is consistent with the results of previous related studies[19-21]. The reason may be that most elderly patients have circulatory and respiratory diseases, and the body function is poor[22]. Once cardiac arrest occurs, the tolerance of various organs to ischemia and hypoxia is poor[23]. For patients with emergency cardiac arrest, medical staff can effectively monitor their initial heart rhythm type. The results of this article have found that the success rate of CPR is higher in patients with defibrillating heart rhythm than in patients with non-defibrillating heart rhythm, and the initial heart rhythm type is the influencing factor of CPR success. Studies[24, 25] have found that in patients with cardiac arrest in the hospital, if the initial heart rhythm type is a defibrillating heart rhythm, their CPR success rate, survival rate after discharge, and neurological recovery at discharge are all improved than those who cannot defibrillate, which is in line with the findings of our study .The reason may be that when the initial heart rhythm is ventricular fibrillation or ventricular tachycardia, the heart is in a weak and irregular contraction state, and there is weak tissue perfusion in the body, so the effect of CPR is better[20, 26].
In the process of CPR, chest compressions are the primary rescue method, but the choice of ventilation methods is still controversial. In this study, compared with balloon masks, tracheal intubation has no positive effect on the success rate of cardiopulmonary resuscitation. Previous study[27] has pointed out that compared with balloon mask-assisted ventilation, the establishment of advanced airway will increase the adverse effect on the long-term prognosis. This may be because cardiac arrest patients are usually accompanied by irritability, vomiting, difficult tracheal intubation, longer length of intubation process[28-30]. Besides, it is inevitable to terminate the heart compression during the intubation process, so that the coronary artery blood perfusion is interrupted for too long[31, 32]. However, there are also reports[33, 34] suggesting that for patients with pulmonary disease, tracheal intubation may be a favorable factor for the success of CPR, so it is necessary to choose a suitable ventilation method according to the specific situation.
Regarding the dose of epinephrine used, the CRP group had a larger amount of epinephrine, but it is not clear whether the prolonged resuscitation time caused the larger epinephrine use, or whether the large amount of epinephrine used adversely affect the resuscitation process[35]. Studies[36-38] have shown that adrenaline can increase myocardial oxygen consumption and reduce blood perfusion of other organs, which will adversely affect the long-term survival rate of discharged patients and the recovery of neurological function. Therefore, further research is needed to clarify the dose and timing of epinephrine in the CPR process.