CLD of Eric Wolstenholme Syst. Dyn. Rev. 23, 371–389, (2007) See IM-1008 for a stock flow version.
Medical treatment backlog (including admitted patients in the ED) has an inflow of referrals and an outflow of discharges from medical care.
A backlog can also be relieved by an outflow of people sent to non-medical wards, called outliers (or boarders).
Medical treatment backlog balances the referral rate, and also both the outlier and discharge rate. These all tend to keep the backlog steady by reducing the inflow rate when full and increasing the outflow rate when full (and vice versa).
A change in referral rate causes a buildup of medically treatable non-urgent conditions which will eventually present to hospital as unplanned emergencies rather than planned referrals. This is a reinforcing loop, which will make things worse later.
Early discharge increases the readmission rate and the backlog, another reinforcing loop.
Too many medical outliers in surgical wards crowd out surgical cases which then develop complications requiring medical treatment, another reinforcing loop.
Surgery ward occupancy puts pressure to shift patients out to discharge planning which swamps the discharge service and increases the stay in hospital. Another reinforcing loop (a fix that fails).
The buildup of patients awaiting discharge also swamps the post-acute services and the response is to buy more post-acute capacity to balance this.
This produces another fix that fails by changing the readmission rate.
The spot purchase of post-hospital services is another fix that fails. It reduces the money available for capacity and therefore the rest of the years post acute service capacity.
Note the interventions marked with a green oval outline are all fixes that fail, due to the additional reinforcing loops. Note that if these workarounds are avoided, then we can turn the vicious circles into virtuous circles.