This prospective study aimed to identify clinical and laboratory predictors of return of spontaneous circulation (ROSC), 28-day survival, and favorable neurological outcomes in adult patients experiencing out-of-hospital cardiac arrest (OHCA) and brought to the emergency department (ED) by emergency medical services (EMS). Specifically, the prognostic value of hematologic, biochemical, and blood gas parameters on admission was assessed for ROSC, 28-day survival, and favorable neurological recovery. Additionally, the study investigated the influence of key patient-centered and prehospital variables, including demographic features, initial cardiac rhythm, and the timeliness and type of cardiopulmonary resuscitation (CPR), defibrillation, and airway interventions, on overall survival and neurological status.

This prospective, observational, and cross-sectional study was conducted in the ED of a tertiary urban hospital between May 2023 and May 2024. Adult patients (aged ≥18 years) who experienced OHCA and received attempted resuscitation by EMS personnel were screened for eligibility. All patients received advanced cardiac life support (ACLS) in accordance with the 2021 European Resuscitation Council (ERC) and 2020 American Heart Association (AHA) guidelines.

Patients were initially categorized into survivors and non-survivors based on ROSC and 28-day survival status. Furthermore, 28-day survivors were stratified into two subgroups based on their neurological status using the Cerebral Performance Category (CPC) score. Favorable neurological outcome was defined as CPC 1-2 (good to moderate cerebral performance with independence), while CPC 3-5 (severe disability, coma, or death) constituted unfavorable outcome.

Prior to the initiation of the study, a standardized and pre-piloted data collection form was developed based on current literature to ensure consistency and reproducibility. During the study period, patient data were initially recorded by board-certified emergency medicine specialists who were on duty in the ED at the time of each patient's arrival. These attending physicians were directly responsible for patient management and completed the data forms either during the resuscitation process or immediately thereafter. All physicians involved in data entry were blinded to the study hypothesis. Subsequently, all collected data were extracted, cross-checked, and verified for accuracy and completeness by an emergency medicine specialist with eight years of clinical experience, who was also blinded to the study hypothesis.

Patient data were obtained from multiple sources, including hospital's automated systems and ED's archives, prehospital EMS reports, and the national digital healthcare database of Türkiye (e-Nabız), which was used to verify survival status and neurological outcomes at 28 days.

Collected data includes, demographics (age, sex), comorbidities (hypertension, diabetes mellitus, coronary artery disease, chronic kidney disease, or malignancy), and prehospital variables such as whether the cardiac arrest was witnessed, whether bystander CPR was performed, the time from collapse to the initiation of CPR, the time from collapse to EMS arrival, the durations of no-flow (time without CPR) and low-flow (time with CPR but no ROSC), and the initial cardiac rhythm, categorized as ventricular fibrillation or pulseless ventricular tachycardia (VF/pVT), asystole, or pulseless electrical activity (PEA). The airway management method used by EMS was also recorded, including BVM, SGD, or ETI. Other recorded interventions included prehospital defibrillation, epinephrine administration (including total dose), and the use of mechanical chest compression devices. Whether ROSC was achieved in the field prior to ED arrival was also documented.

On arrival to the ED, clinical examination findings included the patient's body temperature, the Glasgow Coma Score (if measurable), the presence or absence of pupillary light reflex, and the requirement for vasopressor support within the first hour.

Laboratory data obtained upon admission included hematological parameters such as white blood cell count (WBC), hemoglobin level, platelet count, mean platelet volume (MPV), neutrophil count, monocyte count, and eosinophil count. Biochemical measurements included creatinine, urea, lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), sodium, potassium, chloride, calcium, and troponin-I levels. Arterial blood gas analysis results included pH, partial pressure of carbon dioxide (pCO₂), bicarbonate, lactate concentration, carboxyhemoglobin percentage, and methemoglobin percentage.

Clinical outcomes, including ROSC, 28-day survival or mortality, and neurological status, were also recorded.

Patients' demographics, initial rhythm, prehospital intubation status, and hematological, biochemical, and blood gas parameters on admission were compared to identify factors associated with 28-day survival and neurological status between the groups. Independent predictors of survival were determined via multivariate logistic regression analysis of variables that significantly differed between survivors and non-survivors.

Inclusion Criteria:

- This study included 420 adult patients (aged ≥18 years) who were brought to our hospital's ED due to OHCA and who had initiated attempted resuscitation by EMS were initially screened for inclusion between May 2023 and May 2024.

Exclusion Criteria:

• Patients aged < 18 years
• Patients with in-hospital cardiac arrest
• Patients who have suffered cardiac arrest due to major trauma, drowning, drug overdose, or known terminal illness
• Patients with active hematologic malignancy
• Patients with incomplete data regarding primary outcomes or admission laboratory tests

This study included 420 adult patients (aged ≥18 years) who were brought to our hospital's ED due to OHCA and who had initiated attempted resuscitation by EMS were initially screened for inclusion between May 2023 and May 2024.

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