Since 2015, all Danish prehospital EMS have used the nationwide Prehospital Electronic Medical Record (PEMR). In 2023, the investigators developed the Danish Drowning Formula (DDF), a text-search algorithm designed to search the unstructured text fields in the electronic medical records with comprehensive search criteria to identify all potential water-related incidents. This protocol describes the first study to analyse the prehospital data from a nationwide Danish cohort of patients treated by the EMS from 2016 to 2023 following non-drowning aquatic rescues.

Purpose The purpose of this study is to establish recommendations towards specific educational, preventative, or rescue strategies to reduce the number of aquatic rescues in Denmark (e.g., campaigns targeting high-risk groups, or fencing, allocating rescue equipment, or establishing lifeguard stations in high-risk areas). This may not only enhance prevention of aquatic rescues but also decrease the mortality and the total number of drowning incidents in Denmark.

Objectives The primary objective is to estimate the yearly incidence of patients treated by the Danish EMS following a non-drowning aquatic rescue from 2016 to 2023 and calculate the aquatic rescue to drowning ratio. The secondary objectives are to characterise the rescues (e.g., lay rescuer or professional rescuer, use of equipment) and to report the spatial distribution.

Study design This study is a nationwide registry-based study with data from the Danish nationwide PEMR from 2016 to 2023.

Methods Since 2015, all Danish prehospital EMS have used the nationwide Prehospital Electronic Medical Record (PEMR). In 2023, the investigators developed the Danish Drowning Formula (DDF), a text-search algorithm designed to search the unstructured text fields in the electronic medical records with comprehensive search criteria to identify all potential water-related incidents. This study will be the first to analyse the prehospital data from a nationwide Danish cohort of patients treated by the EMS from 2016 to 2023 following non-drowning aquatic rescues.

Inclusion Criteria:

• All the patients registered in the Danish Prehospital Electronic Medical Record from 2016-2023 will be screened by the Danish Drowning Formula and the medical records containing one or more trigger words will be extracted for manual validation.
• All records where the patient was immersed or submersed in liquid but did not experience mild, moderate, or severe respiratory impairment following the drowning process will be included.

Exclusion Criteria:

• All records where the patient was immersed or submersed in liquid and did experience mild, moderate, or severe respiratory impairment following the drowning process).
• All records where the patient was not immersed or submersed in liquid.

Patients treated by the Danish EMS following an aquatic rescue are identified from the Danish Prehospital Electronic Medical Record using the Danish Drowning Formula and extensive manual validation.

We used the WHO definition of drowning supported by the "Clarification and Categorisation of Non-fatal Drowning" statement to differentiate between drowning and non-drowning aquatic rescues.

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