Determining the required size of a Clinical Decision Unit at Royal Devon & Exeter Hospital

South West PeninsulaGeneric Health Relevance
Start Date: 8 Dec 2016 End Date: 15 Apr 2017

PenCHORD - Determining the required size of a Clinical Decision Unit at Royal Devon & Exeter Hospital


The Royal Devon & Exeter Hospital (RD&E) wanted to introduce a Clinical Decision Unit (CDU) to support processes at their A&E department. Initially, it was planned that the CDU should have space for four patients at any one time; however, it was not known whether this is the most efficient size, as the number of patients who would be suitable to be referred to the CDU varied considerably at different times. 

This modelling project assessed the most suitable size of CDU and what the effect of having a CDU would be on patients’ overall length of stay in the A&E department. It also assessed the optimum opening times for the CDU.

The project developed from an HSMA project by Alaric Moore, Performance Improvement Manager at the RD&E, which worked with clinicians and patients to map out the processes involved in A&E treatment at the hospital. This research highlighted the complexity and interdependencies of the current processes, providing vital groundwork for PenCHORD’s project.

Project objectives

The project had two key objectives:

  1. To produce a decision support tool that accurately reproduced the current level of patient attendance at A&E. This tool would allow the team to test out different admission policies for admitting patients into a CDU whilst taking into account different opening hours. This tool would be a discrete event simulation model which is a common choice when modelling patient flows in hospital departments such as this one. 
  2. To identify how different strategies for admitting patients into the CDU would affect its utilisation, particularly over time. The project team would also analyse what the effect would be if the CDU was only available at certain times (e.g. between 8am and 8pm) in contrast to a 24/7 provision. The final outcome would be a risk profile which quantifies the probability that a given number of beds in the CDU would be exceeded. 


  • A highly-aggregated Discrete Event Simulation Model has been built to capture the flow of patients through ED and through a potential Clinical Decision Unit (CDU)
  • The model is parametrised with historic data in order to accurately capture the length of stay in ED
  • Admission policies into CDU have been developed together with clinicians
  • The model simulates patient flow over a year and captures the number of beds/cubicles used in the CDU at given time intervals.
  • Key outputs are a set of risk profiles which describe the probability that a given number of beds/cubicles would not be sufficient.
  • Each admission policy can be assessed and decision-makers may choose their preferred policy.
  • Overall, a number of 4 beds is deemed sufficient to accommodate all patients admitted into CDU. This will in turn reduce the length of stay in ED and also reduce the number of breaches by up to 45%.


The project team’s report to the Royal Devon & Exeter NHS Foundation Trust has fed into scoping for the CDU. This study aimed to help inform a £multi-million decision around strategic planning in A&E at the Trust.

When the CDU is implemented, PenCHORD aim to track how much it is used and the rate of admissions, and compare this to the modelling outcomes, with a view to publishing a paper on the project. 

Dr Sebastian Rachuba