Where's the way out? Access block, boarding and hospital overcrowding: a narrative review.

Emergency department (ED) overcrowding is a persistent global challenge associated with adverse patient outcomes and system inefficiencies. Boarding and access block, which delay the transfer of admitted patients to inpatient beds, represent its most critical manifestations. While overcrowding has traditionally been attributed to rising demand and ED inefficiencies, growing evidence identifies downstream constraints in hospital capacity and patient flow as major drivers. A non-systematic literature search was conducted using PubMed and Web of Science focusing on studies published between January 1990 and December 2025 related to ED overcrowding, boarding, hospital overcrowding, access block, patient flow, and hospital capacity. The literature was narratively synthesized and organized according to the input-throughput-output framework to examine system-level determinants and interventions and to explore overcrowding as a hospital-wide phenomenon. Interventions targeting input and throughput processes improve local ED performance metrics but often fail to reduce overcrowding when output capacity remains constrained. Conversely, high inpatient-bed occupancy, delayed discharge processes, and inefficient hospital-wide patient flow are frequently associated with access block and boarding. Overall, the literature supports the interpretation of ED overcrowding as a manifestation of hospital-wide dysfunction. High-performing hospitals prioritize patient flow as an institutional focus and adopt a system-level approach, characterized by executive leadership involvement, real-time data monitoring, and shared accountability across departments. Boarding may be better understood as the clinical manifestation of system-level failure in hospital patient flow rather than an ED-specific issue. The way out requires a shift from ED-centered interventions to coordinated, hospital-wide strategies, recognizing that the responsibility for timely and safe patient flow lies with the entire organization.