EM · ED flow and access block

ED flow and access block — the input-throughput-output model, queuing theory, and the operational intervention ladder

Also known as Input-throughput-output model · ITO model · Asplin conceptual model of crowding · Queuing theory and Little's Law · Access block · ED flow · Patient flow · Bottleneck analysis · Emergency department boarding · Ambulance ramping · Full capacity protocol · Short-stay unit · Discharge lounge · Bed management team · Rapid assessment team

ED flow as an operations-engineering problem — the input-throughput-output model of Asplin (input = demand arriving at the emergency department; throughput = assessment and treatment inside; output = discharge or admission to an inpatient bed), with the output box as the binding constraint whose failure propagates upstream as access block and crowding. Queuing theory and Little's Law (L equals lambda times W; the number in the system equals the arrival rate multiplied by the mean time in system), which predicts that a department running at 100 per cent occupancy is mathematically unstable because waiting time rises non-linearly as utilisation approaches one. Bottleneck analysis — the rate-limiting resource defines system capacity — and Khanna's patient-journey mapping of the ED bottlenecks at triage, the doctor assessment, diagnostic turnaround and the disposition decision. Access block in the ACEM operational sense (total ED length of stay greater than 8 hours for an admitted patient) as the central operational pathology, and its burden of harm: mortality 20–35 per cent higher among crowded and boarded patients (Sprivulis, Richardson), excess mortality in critically ill patients boarded awaiting ICU (Chalfin), the dose-response of boarding length and mortality (Singer), and the full-capacity-protocol evidence that boarding in an inpatient hallway is not demonstrably worse than continued ED corridor boarding (Viccellio). The pre-hospital face — ambulance ramping (Yoon, Cook) — and left-without-being-seen as a safety signal. The differential of good versus poor flow. The operational intervention ladder: ED-internal throughput work (team triage, senior at the front door, streaming, parallel processing, fast-track), rapid assessment, short-stay units, inpatient bed-flow management (discharge lounges, early senior-led discharge before midday, predicted discharge dates, bed-management teams, whole-of-hospital bed meetings), the full-capacity protocol, ambulance-ramping mitigation, and structural capacity. The cardinal teaching is that access block is a hospital-system problem whose consequence is felt in the emergency department, and that no amount of ED-internal throughput work alone will solve chronic access block.