Statewide Method of Measuring Ambulance Patient Offload Times

UMMS Affiliation

Department of Population and Quantitative Health Sciences

Publication Date


Document Type



Biostatistics | Emergency Medicine | Health and Medical Administration | Health Services Administration | Health Services Research | Statistics and Probability


OBJECTIVE: Ambulance patient offload time (APOT) also known colloquially as "Wall time" has been described in various jurisdictions but seems to be highly variable. Any attempt to improve APOT requires the use of common definitions and standard methodology to measure the extent of the problem.

METHODS: An Ambulance Offload Delay Task Force in California developed a set of standard definitions and methodology to measure APOT for transported 9-1-1 patients. It is defined as the time "interval between the arrival of an ambulance at an emergency department and the time that the patient is transferred to an ED gurney, bed, chair or other acceptable location and the ED assumes responsibility for care of the patient." Local EMS agencies voluntarily reported data according to the standard methodology to the California EMS Authority (State agency).

RESULTS: Data were reported for 9-1-1 transports during 2017 from 9 of 33 local EMS Agencies in California that comprise 37 percent of the state population. These represent 830,637 ambulance transports to 126 hospitals. APOT shows significant variation by EMS agency with half of the agencies demonstrating significant delays. Offload times vary markedly by hospital as well as by region. Three-fourths of hospitals detained EMS crews more than one hour, 40% more than two hours, and one-third delayed EMS return to service by more than three hours.

CONCLUSION: This first step to address offload delays in California consists of standardized definitions for data collection to address the significant variability inherent in obtaining data from 33 local agencies, hundreds of EMS provider agencies, and 320 acute care hospital Emergency Departments that receive 9-1-1 ambulance transports. The first year of standardized data collection of ambulance patient offload times revealed significant ambulance patient offload time delays that are not distributed uniformly, resulting in a substantial financial burden for some EMS providers in California.


ambulances, crowding, emergency service, health services accessibility, hospitals, statistics and numerical data

DOI of Published Version



Prehosp Emerg Care. 2019 May-Jun;23(3):319-326. doi: 10.1080/10903127.2018.1525456. Epub 2018 Oct 25. Link to article on publisher's site

Journal/Book/Conference Title

Prehospital emergency care : official journal of the National Association of EMS Physicians and the National Association of State EMS Directors

PubMed ID


Related Resources

Link to Article in PubMed