Table 1 Feedback loops in the HDU model

R1: Crowding impedes coordination

With limited space, an increase in patients causes an increase in crowding, which impedes communication and coordination, reducing the appropriateness of treatment. Patient conditions are slower to improve, slowing the rate of discharge and thus maintaining crowding.

R2: Crowding impedes documentation

Crowding also reduces the space available for documentation and storage of patient records. This reduction in monitoring and documentation reduces providers’ ability to properly identify and communicate patient needs, thus reducing appropriateness of treatment and slowing patient discharge.

B1: Deaths drive space availability

With rapidly deteriorating patient conditions comes a higher rate of patient mortality. This mortality reduces HDU crowding, forcing an uncontrolled and undesirable balancing mechanism to regain equilibrium in the HDU.

B2: Crowding drives discharge

An increase in crowding forces decisions about how to maintain the operation of the HDU, meaning the risk of discharging patients in order to reduce crowding and maintain functioning capacity of the HDU.

R3: Hygiene and parental cooperation

Increases in crowding reduce the efficacy of hygiene control procedures. Lower hygiene means that parents are less willing to support nurses and physicians in care delivery, increasing the work burden on clinicians and accelerating the adverse effects of crowding.

B3: Parental peer learning and support

Counteracting the adverse impact of crowding on hygiene and coordination, crowding creates opportunities for peer learning and peer support among parents, reducing work burden on clinicians as parents support the care process.

R4: Worker burden

A higher patient/provider ratio increases work burden for clinicians, which increases risk of burnout that further increases the patient/provider ratio.

R5: Nurse word of mouth

A higher patient/provider ratio increases the work burden on clinicians, which makes it harder to find nurses to improve adequacy of staffing. This forms a reinforcing loop where difficult working conditions perpetuate that worker burden through barriers to hiring.