Study design
This study was a prospective analysis of collected data based on OHCA patients treated by the Emergency Center in Hefei China from January 2019 to December 2020. The registry database included the OHCA patients’ demographic characteristics, as well as EMS and Emergency Department (ED) information based on the standardized Utstein style.
EMS characteristics and procedures
The Hefei Emergency Center serves a population of 5,118,200 [13]. It includes the Dispatching Department of Hefei Emergency Center and 20 sub-centers and 42 emergency stations established relying on medical institutions. All emergency personnel have the basic CPR training and passed the examination of Hefei Emergency Center and have legal practice qualification. Three or four EMS workers constitute the ambulance team, including a doctor, a driver and a nurse or an emergency personnel assistant.
The Dispatching Department of Hefei Emergency Center obtains the patient information through the emergency service number (120). After arriving at the scene, the doctor decides whether to make the CPR according to the patient’s situation, CPR is provided by the EMS personnel on scene, and then the patient is transferred to the hospital for stabilization and definitive management .
When cardiac arrest is diagnosed, chest compression and ventilation using a bag-valve mask are immediately initiated, and CPR is provided by the EMS personnel according to 2015 American Heart Association CPR and ECC guidelines [14]. If necessary, the doctor applies a semiautomated external defibrillator and AAM. After attempting defibrillation, inserting an advanced airway device, the patient is provided with advanced life support, including the administration of adrenaline by the doctor before arrival at the hospital.
Sample size
The needed sample size was calculated using the formula of sample size calculation of the experimental epidemiological study: N = [Zα \(\sqrt{2P\left(1-P\right)}\) +Zβ \(\sqrt{P_c\left(1-{P}_c\right)+{P}_e\left(1-{P}_e\right)}\)]2/(Pc- Pe)2. In this formula, Pc represented for the probability of outcome among control group, Pe represented for the probability of outcome among experimental group, P = (Pc + Pe)/2. We referred the probability of ROSC among AAM and no AAM groups [15], and set α = 0.05, β = 0.10. Finally, the required minimum sample size was 92.
Patient selection
Inclusion criteria
The patients in this study were selected from among all adult patients who had experienced OHCA and were subsequently treated with CPR and transported to a medical institution by EMS personnel in Hefei, China between 1 January 2019 and 31 December 2020.
Exclusion criteria
Patients under 18 years of age; patients with spontaneous circulation had been restored before the arrival of EMS personnel and patients who had a ‘Do Not Attempt Resuscitation’(DNAR) decision; patients whose medical records were missing data and for whom more than 60 min from the emergency call to the initiation of CPR were excluded.
Ethical approval
The Ethics Committee of Qilu Hospital of Shandong University granted ethics approval, reference number 2019012.
Exposures
The primary exposure of the study was prehospital AAM. AAM was defined as an invasive technique used for airway management, including intubation and all types of supraglottic airways. The no AAM group included patients who underwent a non-invasive technique for airway management, such as use of a bag valve mask, with or without the inclusion of the nasopharyngeal and/or oropharyngeal airways.
The second exposure of the study was administration of adrenaline. After basic life support the EMS personnel attempt to gain peripheral venous access to administer 1 mg of adrenaline intravenously every 3 to 5 min until the ROSC or arrival at the hospital.
Outcomes
The primary outcome was the probability of prehospital ROSC and ROSC at ED among all included patients. The second outcome was the probability of survival to admission and survival to hospital discharge among all included patients.
Data collection
The study is a part of the project of the incidence rate, mortality and risk factors of cardiac arrest in Chinese population which is a special project of science and technology basic resources investigation by Qilu Hospital of Shandong University.
Prehospital emergency medical records were collected through the database of Hefei Emergency Center as the Sub center of the project. Patient prognosis follow-up data is collected through the hospital where the patient were admission.
The registry included data on the OHCA patients’ socio-demographic characteristics, as well as EMS and ED information based on the standardized Utstein style, such as circumstances of the OHCA (witness status, bystander CPR), electrocardiogram (ECG) rhythm at cardiac arrest, EMS time intervals, On-site treatment measures (tracheal intubation, electrical defibrillation, adrenaline use, etc.)and patient outcomes.
Statistical analysis
The continuance data was present as mean and standard deviation (Mean ± SD) and the counting data was described as number and percentage (n,%). Missing values in EMS Scene rescue time and emergency transport rescue time were filled with multiple imputation [16]. The comparison of EMS response time and age between different groups using the independent t test. The comparison of the rate of ROSC, Survival to admission, and survival to hospital discharge between different groups using chi-square test. To explore the effects of advanced airway and adrenaline and their combined effect on outcomes of ROSC, survival to hospital admission and survival to hospital discharge, logistic regression models were constructed with or without adjusting confounders which including age, sex, prehospital time, electrical defibrillation, origin of cardiac arrest, bystander CPR and witness. All statistical analyses were performed using SPSS software 23.0, and P value < 0.05 was considered to be statistically significant.
