Where is the bottleneck in our emergency department throughput?

ED throughput bottlenecks are identified by measuring four timestamps: door-to-triage, triage-to-provider, provider-to-disposition, and disposition-to-departure. In most hospitals, the longest segment is disposition-to-departure (averaging 97 minutes for admitted patients) because inpatient bed availability — not ED clinical capacity — is the rate-limiting step. Boarding hours — total hours of ED occupancy by admitted patients awaiting inpatient beds — is the most accurate single measure of ED throughput constraint.

Each ED throughput segment has a different rate-limiting factor. Door-to-triage should be less than 10 minutes for ESI 2-3 patients by ACEP standards; most hospitals achieve this more than 90% of the time, and it is rarely the primary throughput bottleneck except during surge events. Triage-to-provider averages 38 minutes nationally; the key variable is the provider coverage model — split-flow and fast-track designs that redirect ESI 4-5 patients to a separate low-acuity track reduce this segment by 40–50% for those patients. Provider-to-disposition averages 2–3 hours and is driven by diagnostic turnaround time (laboratory 45–90 minutes, imaging 30–120 minutes by modality), specialist consultation availability, and clinical decision-making time. None of these are primarily addressable by ED operations — they require coordinated improvement with laboratory, radiology, and specialty services.

Disposition-to-departure is the segment where boarding lives. The average admitted patient waits 97 minutes after the admission decision is made before an inpatient bed is available. During peak census periods, this number extends to four to eight hours for individual patients. The mechanism is straightforward: inpatient beds do not turn over until discharges are processed, and discharges depend on physician rounds, pharmacy medication reconciliation, transport availability, and family notification — all of which are compressed into the morning window. When rounds run late, the discharge cascade delays bed availability for afternoon admissions from the ED, creating the afternoon boarding surge that most EDs experience without recognizing its structural cause.

ED directors and hospital administrators typically report average door-to-disposition time as the primary throughput metric. This number has several problems. It averages together discharged and admitted patients, whose throughput paths diverge significantly at the provider-to-disposition segment. It does not capture boarding — the time after disposition decision for admitted patients — which is the largest contributor to total length of stay in the ED. And it smooths the bimodal daily distribution: ED throughput is typically fast in the morning, acceptable in the afternoon, and severely delayed in the evening when boarding accumulates.

Boarding hours — the total ED bed-hours occupied by admitted patients during a given week — is a metric that few EDs calculate routinely but that accurately represents the true throughput constraint. A week with 142 boarding hours means that 142 ED bed-hours were consumed by patients who had completed their clinical care but were waiting for inpatient placement. At 4–5 ED beds blocked simultaneously during peak boarding periods, this is equivalent to closing 15–18% of ED capacity for several hours per day — a capacity reduction that would trigger emergency operations if it happened due to physical infrastructure failure.

Establish boarding hours as the primary ED throughput metric, tracked daily and reviewed in capacity management huddles. This reframes the ED boarding problem as a hospital-wide capacity problem — which it is — rather than an ED operational problem, enabling the cross-departmental interventions that actually address it. A bed expediter role during peak census hours (10:00 am–4:00 pm) whose sole function is advancing inpatient bed assignment for admitted patients in the ED has demonstrated 30–45 minute reductions in average disposition-to-departure time in multiple implementations.

Discharge lounge programs — comfortable waiting areas where clinically ready inpatients can wait for final discharge instructions, medication counseling, and transport — free inpatient beds earlier in the day by decoupling clinical readiness from physical bed occupancy. Patients who are clinically ready but waiting for paperwork or family pickup can vacate the inpatient bed without leaving the building, enabling that bed to be cleaned and reassigned for an ED admit 60–90 minutes earlier than standard discharge workflow allows. Facilities implementing discharge lounge programs combined with bed expediter roles have reduced ED boarding hours by 30–40% within 90 days of implementation.