The DGHPSim Outpatient Model

Patients who require elective care are usually admitted from a waiting list onto which they are placed after one or more outpatient consultations. The period covering the time from the GP referral to admission is the focus for the 2008 18-week Referral To Treatment (RTT) target. The DGHPSim Outpatient model simulates GP referrals and then tracks each simulated patient through outpatients to discharge or admission as an inpatient.



RTT Delays
There are three major delays in RTT for admitted patients;

1. Delay between GP referral and first Outpatient appointment with a specialist (GP-OP1)
2. Delay between specialist first appointment and later appointments (OP1-OP2)
3. Delay between decision to admit and admission (OP2-IP)

The second delay, waiting for a follow-up appointment, may be required because of diagnostic delays, and is included in the 18-week RTT target. However if patients wait for medical reasons, this is known as "watchful waiting and is not included in the 18-week RTT measurement.

Measuring RTT
Measuring RTT is still difficult for many trusts, although insights can be gained from basic information. For example, the three histograms below show a hospital's position in the three delays in 2004/2005; (Note that effects of the 17 week First Outpatient Appointment target is seen in the first graph)


The RTT State Transition Matrix
Core of the outpatient model is the RTT State Transition Matrix, which represents patient flow between 7 events.

1. GP: First referral event, generally by a GP
2. OP1: First outpatient appointment event
3. OP2: Pre-operation follow-up outpatient appointment event
4. IPDC: Inpatient as day-case admission event
5. IPOR: Inpatient as ordinary admission event
6. POP: Post-operation follow-up outpatient appointment event
7. END: Discharged from consultant's care (in OP stage)

An example RTT State Transition Matrix is shown below;