This study aims to 1) describe patient-, setting-, and dispatcher-related characteristics in drowning-related emergency calls to the Emergency Medical Dispatch Centre (1-1-2 emergency phone) and 2) factors associated with 30-day survival. The investigators will separately analyse drowning-related out-of-hospital cardiac arrest (OHCA) and drowning-related non-OHCA. If feasible, the investigators will qualitatively analyse the calls to identify and describe potential barriers for an optimal handling strategy.

Previous studies have explored emergency priority levels, emergency call categorisations, barriers to assessing an emergency call, and the effects on the outcome. However, this has never been done specifically for drowning patients. Drowning presents a rare and special circumstance that may be particularly complex for laypeople and medical dispatchers for several reasons. Despite this complexity and medical dispatchers' potential to optimize treatment and improve outcomes in drowning incidents, the characteristics of drowning-related emergency calls have never been explored.

This protocol presents a registry-based cohort study of drowning-related emergency medical calls to the EMDC (1-1-2 emergency phone) with 30-day follow-up.

Data from the national Danish Prehospital Drowning Data will be linked with audio files and electronic data from the EMDC database using the patient's unique civil registration numbers.

The investigators will construct two lists of variables: one list for OHCA and one for non-OHCA emergency calls. Data collection from the EMDC database will consist of three phases.

In phase 1, three independent reviewers will listen to 20 emergency calls on drowning (10 OHCA and 10 non-OHCA) to identify relevant variables from the calls (e.g., presence of key symptoms [since an emergency call often does not contain information regarding the absence of symptoms], communication barriers [anything that comes in the way of receiving and understanding information], pre-arrival instructions to callers etc.).

In phase 2, the same reviewers will listen to 20 other emergency calls (10 OHCA and 10 non-OHCA) and use the lists for data collection to determine the data availability and completeness. This may result in modifications to the lists of variables. The investigators will use the results as a basis for reviewer training and calculate inter-rater reliability.

Once the reviewers' performances are satisfying (defined as Fleiss kappa ≥0.8), the investigators will move to phase 3 and collect data for all the drowning calls. Emergency calls will be stratified as OHCA or non-OHCA calls.

Inclusion Criteria:

• Patients at all ages registered in the Danish Prehospital Drowning Data are eligible.

Exclusion Criteria:

• Obvious clinical signs of irreversible death (decapitation, decomposition, post-mortem lividity, post-mortem rigidity)
• A valid Do-Not-Attempt-Resuscitation (DNAR) order or other code status orders limiting life-sustaining therapies
• Missing or corrupted audio files
• Missing identification number
• Missing 30-day survival

All validated drowning cases registered in the Danish Prehospital Drowning Data will be linked with data from the EMDC database according to a data minimisation principle. Patients are included in the Danish Prehospital Drowning Data if they have experienced a drowning incident between 2016 and 2023, defined as experiencing respiratory impairment from submersion or immersion in liquid.

The datasets used and analysed during the current study are available from the corresponding author upon reasonable request.