When emergency medicine isn’t there: a scoping review of global acute care substitutes and complements for disaster response and surge capacity

BACKGROUND: Disasters and everyday gaps in emergency care force acute illness and injury to be managed outside of formal emergency medicine (EM) and emergency medical services (EMS) systems. Because EM capacity varies substantially worldwide, this scoping review applies a substitutes-and-complements framework to the mechanisms that deliver acute care in and around formal EM or EMS, classifying their roles as substitutes, complements, or both across levels of EM system maturity and disaster conditions. The resulting typology serves as an inventory of latent disaster surge capacity. MAIN TEXT: Following the PRISMA extension for scoping reviews, five databases (PubMed, Scopus, Web of Science, Embase, and CINAHL) were searched, yielding 11,161 records. After title and abstract screening, 758 full-text articles were assessed for eligibility and 115 studies were included. We charted study type, country, and EM system maturity, using a codebook derived from American College of Emergency Physicians' (ACEP) International Ambassador country reports, the primary acute-care mechanism, care-delivery context, and COVID-19 relevance. Mechanisms were then classified by whether they substituted for or complemented formal EM. Publications were concentrated in the COVID-19 era (82/115, 71% from 2020 or later) and in high-income, mature-EM settings (United States 30%; 64/115 mature-EM). The most common mechanisms were lay and community first-responder programs (n = 18), hospital-at-home and remote monitoring (n = 15), and telehealth-based emergency and behavioral-health services. Overall, substitutes predominated (75/115), whereas complements (18/115) clustered in mature-EM systems. CONCLUSIONS: Our inventory of latent surge capacity reframes each mechanism as a potential candidate for transfer across the EM-maturity spectrum: routine substitutes used in low-maturity systems may offer pre-planned crisis capacity for mature systems, while lower-infrastructure telehealth models may provide decision support or partial substitution where formal EM is limited. The substitute-complement balance tracks maturity, but the opportunity lies in translating mechanisms to the settings where they are not currently used as such.