Emergency Cardiopulmonary Resuscitation of Out-of Hospital Cardiac Arrest: Why Should we Care

Background: Cardiopulmonary resuscitation (CPR) plays an essential role in the treatment of sudden cardiac arrest (SCA), we aimed to evaluate the inuencing factors on the effects of CPR in patients with SCA, to provide insights into the management of SCA. Methods: Patients who underwent CPR in the emergency department of our hospital from January 1, 2019 to June 30, 2021 were selected. We collected and analyzed the clinical characteristics of CPR patients. Logistic regression analyses were conducted to identify the risk factors of CPR failure. Results: A total of 308 CPR patients were included, the incidence of CPR success was 35.71%. There were signicant differences in the age, time to the start of CPR, the type of heart rhythm in the rst monitoring, duration of CPR and cumulative adrenaline dosage between CPR success and failure group (all P<0.05). No signicant differences in the gender, cause of cardiac arrest and ventilation methods were found (all P>0.05). Logistic regression analyses indicated that age ≥ 65y(OR2.132, 95CI%1.127~4.334), time to the start of CPR ≥ 12min(OR2.503, 95CI%1.015~3.583), unable to debrillation(OR1.856, 95CI%1.107~3.031), duration of CPR ≥ 40min(OR2.162, 95CI%1.242~4.178), cumulative adrenaline dosage ≥ 6mg(OR1.627, 95CI%1.151~2.472) were the independent risk factors of CPR failure(all P<0.05). Conclusions: The success and failure of CPR are affected by many factors. Early and effective interventions should be taken for these inuencing factors in clinical practice. Due to the limitation of sample size, future large-sample and multi-center studies need to further explore the relevant inuencing factors of CPR.


Background
Sudden cardiac arrest (SCA) refers to the sudden cessation of cardiac activity accompanied by hemodynamic disorders, usually caused by persistent ventricular tachycardia (VT)/ventricular brillation (VF) [1]. Most of these events occur in patients with organic heart disease especially coronary heart disease) that may not have been diagnosed before SCA [2]. In the rescue of SCA patients, cardiopulmonary resuscitation (CPR) plays a vital role, and chest compression combined with mouth-tomouth breathing is the basis of modern CPR [3]. Although CPR, de brillation and other advanced resuscitation techniques continue to develop, the survival rate of cardiac arrest is still very low [4,5]. Therefore, how to improve the effects and safety of CPR is essential to the prognosis of patients with SCA.
Cardiac arrest is a kind of clinical emergency and critical illness, the success of CPR is closely related to the cause of the cardiac arrest, the time of the arrest, and the correct rst aid measures [6,7]. With the widespread clinical application of CPR, patients with SCA have been effectively treated, but the success rate of resuscitation is still low [8]. Studies [9,10] have shown that the success rate of resuscitation in patients with cardiac arrest in different locations is also different, only 6.0-10.8% of patients with out-ofhospital SCA can survive, while about 25.8% of patients with in-hospital cardiac arrest can survive and discharge. Therefore, improving the success rate of CPR is still one of the major challenges of clinical work. To this end, we took CPR patients in the emergency department of our hospital as the research population, we retrospectively analyzed the clinical characteristics of patients with SCA in order to analyze the factors affecting the success of PCR, and to provide reference for the rescue of critically ill patients.

Ethical approval
In this study, all methods were performed in accordance with the relevant guidelines and regulations. This present study protocol had been checked and approved by the ethical committee of Hangzhou First People's Hospital(approval number:ED20180049M), and written informed consents had been obtained from the relatives of included patients.

Patients
In this study, patients who underwent CPR in the emergency department of our hospital from January 1, 2019 to June 30, 2021 were selected as the research populations. The inclusion criteria were as following: (1)patients with SCA; (2) patients underwent PCR in our department; (3)patients with age>10 years old; (4) The relatives of included patients agree to participant in this study and signed the written informed consents. The exclusion criteria were as following: (1) family members who gave up rescue and refused to perform PCR; (2) patients with incomplete or missing data on the treatment during hospitalization.

CPR
The CPR program referred to the American Heart Association(AHA) cardiopulmonary resuscitation and cardiovascular rst aid guidelines [11,12], speci cally as follows: (1) we performed chest compressions at a rate of 100~120 times/min, and kept the depth of chest compressions at 5~6 cm; (2) The airway was opened at the same time as the chest compressions were started. A balloon mask was usually used to maintain su cient oxygen supply. If necessary, tracheal intubation would be performed. The ventilation rate was maintained at 10 breaths per minute; (3) For patients with ventricular brillation or pulseless ventricular tachycardia detected at the beginning or midway would receive electrical de brillation immediately; (4) For patients who did not need electrical de brillation, epinephrine would be used as soon as possible, 1 mg each time, An intravenous injection is given in 3 to 5 minutes intervals; (5) Patients with cardiac arrest caused by different reasons would be treated as soon as possible to remove the risk factors. After completing 5 cycles, we evaluated the patient's condition. The criteria for successful CPR were: (1) palpable aortic pulsation or audible heart sounds; (2) measurable blood pressure, blood pressure maintained above 90/60 mmHg, and it could be maintained for 24 hours (3) The patient regained his light re ex.

Data collection
We collected the patient's name, gender, age, time of cardiac arrest, place of onset, main cause of cardiac arrest, type of heart rhythm monitored for the rst time, whether to receive electrical de brillation, whether to accept tracheal intubation, cumulative epinephrine dosage, total duration of CPR according to the registration content of Utstein model registration form.

Statistical method
We used SPSS25.0 statistical software to analyze the collected data. All measurement data are rst tested for normality. Data conforming to the normal distribution were expressed as mean ± standard deviation, and independent sample t test is used for comparison between groups; count data was expressed as frequency or percentage, and comparison between groups was used χ2 test. Logistic regression analyses were conducted to identify the risk factors of CPR failure. The tests were all twosided, and P<0.05 indicated that that the difference was statistically signi cant.

Results
The characteristics of included patients A total of 308 CPR patients were enrolled in this study, including 185 males and 123 females. As presented in Figure 1, the average age was (66.34±16.62) years ole, of which 71-80 years old had the largest number of patient, followed by 61-70 years old. And the main causes of cardiac arrest in patients with CPR were presented in Table 1. Table 1 The main causes of cardiac arrest in patients with CPR(n=308)  The risk factors of CPR failure The variable assignments of multivariate logistic regression were showed in Table 3. As presented in  Cumulative adrenaline dosage (mg) X 5 ≥6=1, <6=2 Table 4 The logistic regression analysis on the risk factors of CPR failure

Discussion
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 [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][17][18]. And we have found that age≥65y, time to the start of CPR≥12min, unable to de brillation, 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 signi cant 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][20][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 de brillating heart rhythm than in patients with non-de brillating heart rhythm, and the initial heart rhythm type is the in uencing 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 de brillating heart rhythm, their CPR success rate, survival rate after discharge, and neurological recovery at discharge are all improved than those who cannot de brillate, which is in line with the ndings of our study .The reason may be that when the initial heart rhythm is ventricular brillation 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, di cult tracheal intubation, longer length of intubation process [28][29][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 speci c 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][37][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.

Conclusions
In summary, cardiogenic disease is the main cause of cardiac arrest, and age≥65y, time to the start of CPR≥12min, unable to de brillation, duration of CPR≥40min, cumulative adrenaline dosage≥6mg are the independent risk factors of CPR failure, clinical early alert and targeted preventions are needed for those patients to increase the success rate of CRP, to improve the prognosis of SCA patients. However, limited by sample size, future studies with larger sample size and multi-centers are needed for further con rmation on the in uencing factors of PCR, to provide more reliable evidences to the management and treatment of SCA. In this study, all methods were performed in accordance with the relevant guidelines and regulations. This present study protocol had been checked and approved by the ethical committee of Hangzhou First People's Hospital(approval numb er:ED20180049M), and written informed consents had been obtained from the relatives of included patients.

Consent for publication
Not applicable.

Availability of data and materials
All data generated or analyzed during this study are included in this published article.

Competing interests
The authors declare that they have no competing interests.  Age distribution of patients with CPR

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