Why did our 4-hour A&E standard drop below 78% last week?

Single-week drops in A&E performance almost always trace to one of three causes: a surge in ambulance conveyances without corresponding bed availability, delayed discharges blocking downstream flow, or staff sickness creating coverage gaps in assessment areas during peak hours (typically 14:00–20:00).

Three distinct mechanisms drive single-week performance drops. Ambulance surge occurs when AMPDS category 2 conveyance volumes spike — often due to weather events, community care failures, or care home incidents — without a corresponding escalation in A&E staffing or bed availability. The surge creates a handover queue that extends into corridor care, consuming clinical time and delaying assessment for walk-in patients simultaneously. When more than 40% of hourly attendances arrive via ambulance, 4-hour performance degrades non-linearly.

Delayed discharge is the mechanism most frequently misidentified as arrival volume. When delayed transfer of care patients occupy admission beds for 48–72 hours beyond clinical readiness, the downstream effect is that A&E patients wait for beds that technically exist but are functionally unavailable. Social care assessment delays, particularly on Mondays following weekend reduced staffing, create predictable DTOC spikes that drive Tuesday–Wednesday A&E performance drops. Staff sickness creating band 5–6 nursing shortfalls during 14:00–20:00 triage periods compounds both mechanisms by reducing the throughput capacity of the assessment area itself.

Standard A&E SitRep data reports arrival volume, breach count, and 4-hour percentage. Arrival volume almost always appears elevated in a breach week, which creates the misleading impression that demand exceeded capacity. In reality, arrival volume is rarely the true cause. Bed availability is the actual binding constraint in approximately 80% of breach weeks — the patients were ready to be admitted but there was nowhere for them to go, and the 4-hour clock expired while they waited.

The data that would identify the true cause — inpatient bed occupancy at hourly intervals, ambulance handover queue length, DTOC patient count, nursing staffing level by shift — lives in separate operational systems that are almost never joined to A&E breach data in real time. When the medical director asks "why did performance drop this week?", the answer produced is typically arrival volume because that is the only number readily available, even though it explains a minority of cases.

Implement hourly bed state monitoring that tracks available inpatient beds by specialty alongside A&E breach risk in real time. When the morning bed state shows occupancy above 92% before 10:00, this is a reliable predictor of afternoon 4-hour breach pressure. The bed management team needs this data before the problem develops, not in the post-incident review. Pairing the bed state with an automated discharge prediction (patients expected to discharge today by ward) gives a 4–6 hour forward view of available capacity.

Flag DTOC patients at day 2 of admission and implement same-day social care assessment protocols for high-risk patients identified at admission. Most DTOC episodes are predictable from admission data: age 75+, social care needs, no confirmed discharge destination, and previous DTOC history are reliably present. Triggering social care referral on day 1 for this cohort rather than waiting for clinical confirmation of discharge readiness reduces average DTOC duration by 1.8–2.4 days — directly releasing the bed capacity that prevents afternoon breach accumulation.