Sex-unique Disparities in Survival and Resuscitation After Out-of-hospital Cardiac Arrest - a Danish Analysis
Conditions: Out-Of-Hospital Cardiac Arrest
Sponsor: Prehospital Center, Region Zealand

05-10-2022 
Study protocol: 
 
Sex-unique disparities in survival and 
resuscitation after out-of-hospital cardiac 
arrest – a Danish analysis 
  
Study type 
Observational study  
 
Unique protocol identification number 
ohcagd2022 
 
Background 
With the recent emphasis on research in womens´ health, sex differences in OHCA are nowadays more 
often investigated worldwide and mounting evidence revealed sex as a possible modifier of outcome in 
cardiovascular disease (CVD)1 2 3 4 5. Cardiovascular disease (CVD) is the leading cause of death in women, 
although conventionally, it has been considered as a male dominated disease6. In contrast to common 
beliefs, heart attacks occur almost as frequently in women as in men, but at an older age and with clinical 
manifestations that vary between, younger, premenopausal and older postmenopausal women7 8 9.  
Previous studies have investigated sex differences in OHCA, but with limited comprehensiveness and 
conflicting results regarding reported survival between sexes10 11 12 13 14. These discrepancies may be 
explained by the fact that data is assessed in different countries with different health care systems, with 
divergent inclusion criteria and subgroups of age, e.g. selection for only shockable initial rhythm (SIR)14. This 
suggests further investigations and cohesion to a standardized and comprehensive view on sex differences 
in OHCA outcomes.  

In 2016 the Danish Emergency Medical Services introduced a nationwide electronic reporting system. This 
registry allows electronic searches to evaluate subgroups of OHCA (out-of-hospital cardiac arrest).  Hence, 
it became possible to investigate characteristics in OHCA related to sex differences. Therefore, with this 
population-based cohort-study, we plan to analyze all emergency medical services treated resuscitations in 
Denmark between 2016 and 2021.  This serves to achieve a better understanding and enhanced knowledge 
of the epidemiology of OHCA in between different sexes.  
Aim 
In this study we aim to describe possible differences in help provision by bystanders, cardiopulmonary 
resuscitation (CPR), pre-hospital treatment by emergency medical services (EMS), presence of SIR and 
survival rates after OHCA at successive stages of treatment for a six-year period in a Danish setting.  
Methods 
This study is a registry-based follow-up, including data on OHCA collected in the electronical prehospital 
medical registrations recorded by the Danish Emergency Medical Service over a 6-year period from 2016 to 
2021. 
Data 
This analysis will be based on data from the national electronic based Danish OHCA registry. Data on OHCAs 
with resuscitative attempts in Denmark have been collected in the electronic based Danish Medical Service 
report system since 2016. The registry covers detailed data including the EMS report, executive entries, and 
advanced text searches of prehospital charts. All cases go through an elaborate validation process where all 
identified events are read through manually by an external verification team. This ensures high quality of 
data, collected according to the Utstein recommendations, throughout the approximately 5400 cases of 
OHCA in Denmark annually. During this verification process, supplementary sources of data are linked to 
each OHCA, among others information about survival, localization, initiation of bystander CPR and EMS 
personnel operation.  
Variables included 
• 
Age: Age will be defined as the patient´s age at the time of the event. Subjects will be stratified 
into six age-groups, including <40 years of age, 40-49 years of age, 50-59 years of age, 60-69 years 
of age, 70-79 years of age, over 80 years of age. 
• 
Sex: Sex will be stated as either male, female or undetermined and derived from personal 
identification numbers. Gender will be defined based on EMS-charts, in cases where an 

identification number is not found. 
• 
Initial rhythm: The initial rhythm recorded by manual defibrillator or AED (whichever first) will be 
defined as the first rhythm observed by EMS personnel and categorized as either shockable initial 
rhythm ((SIR), ventricular tachycardia, ventricular fibrillation), non-shockable (asystole, pulseless 
electrical activity), non-shockable (other) or undetermined. 
• 
Etiology of cardiac arrest: Presumed causes will be stated as either presumed cardiac, other 
medical cause, trauma, drug overdose, drowning, electrocution, or hypoxemia (external).  
• 
Location of Incidence: Location will be characterized as either: privat home, public space, outdoor 
nature or other. 
• 
Observation of occurrence: OHCAs will be defined as either unwitnessed, bystander witnessed or 
EMS-witnessed. 
• 
Cardio-pulmonary-resuscitation (CPR): CPR will include bystander-initiated CPR and EMS 
treatment with CPR. 
• 
Deployment of automatic external defibrillators (AEDs): Defibrillation will include defibrillation by 
bystanders and/or EMS personnel. This includes using publicly available AEDs, which are fitted to 
the patient, have analysed the rhythm, but did not deliver a shock. 
• 
EMS-response time: This will be defined as the time between a dispatcher receiving the 
emergency call and the arrival of the first EMS-personnel. 
• 
Hospitalization: Hospitalization will be considered as either: transported to hospital or declared 
dead by EMS-personnel. 
• 
Return-of-spontaneous-circulation (ROSC): ROSC will be classified as the achievement of ROSC 
anytime between recognition of the event and termination (defined as either hospital admission 
or declaration of death by EMS-personnel). 

• 
State at hospital admission: State of the case upon arrival at the hospital will be defined as either 
ROSC or ongoing CPR. 
• 
Survival: Survival will be defined as ROSC at the time of hospital admission, additionally 30-day 
survival will be included, this derived from data from the National Patient Registry. Survival will be 
calculated in total, per age decade and after selection for SIR. Survival will also be stratified 
according to location of OHCA (at non-public versus public location).  
Analysis 
Data is collected using the STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) 
statement. All percentages will exclude missing values. Descriptive statistics includes the above-mentioned 
variables identified with absolute numbers and percentages. Comparative analyses will be carried out using 
non-parametric testing to examine subgroups. Forward logistic regression analysis will be performed for 
multivariate analysis. Odds ratio for survival will be calculated stratified by localization, bystander, SIR and 
EMS-actions.  
Data storage 
Data is stored on secure drive according to the regional instructions for safe conduct of data management. 
Overall recruitment status 
Completed. 
Ethical considerations 
GDPR will be followed according to Danish law, and the study is registered and approved at the Danish Data 
Protection Agency, capital region of Denmark. Since it is a registry-based study, no ethical approval is 
required.  
Perspectives  
This study will provide updated information regarding OHCA for the association of sex, bystander actions 
and survival, based on a reviewed, high-quality database. Findings might contribute to enhanced 
knowledge upon circumstances and potential modifiable factors associated with increased survival. Thus, it 
is our hope that this study will contribute to improve handling this type of arrests. This, eventually using 
educational campaigns targeted laypersons and healthcare personnel. 

List of Abbreviations  
AED: Automatic External Defibrillator 
CPR: Cardio Pulmonary Resuscitation  
EMS: Emergency Medical Services 
GDPR: General Data Protection Regulation 
OHCA: Out-of-Hospital Cardiac Arrest  
ROSC: Return of Spontanous Circulation 
SIR: Shockable Initial Rhythm 
STROBE: STrengthening the Reporting of OBservational studies in Epidemiology 
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