Emergency Room Simulation
As a renowned simulation expert you have been asked by a hospital to perform a study at its Emergency Room. This is usually a hectic environment. Large numbers of patients arrive and each time a decision has to be taken concerning treatment. Is a major surgery inevitable or will a plaster do? The purpose of this study is to support the management in their decision making. Because the hospital management consists of doctors who have grown into management, they seem to be unable to explain clearly what their ideas and targets are. You have been contacted because net ears goernment funding ill be loered significantl. The onl thing they know for sure is that waiting times should be limited to avoid that patients die or that their symptoms exacerbate.
First, ou need to formulate a problem definition hich ou could present to the hospitals management. Thereafter, you are advised to create a conceptual model and to supplement this subsequently with quantitative data to obtain a quantitative model. The models can be developed in a number of phases by gradually decreasing the abstraction level.
System description
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Have a look at the map of the emergency room which is given to you by the management (case- map.doc). Patients arrive by car at the parking lot. On average one patient arrives every 3.5 minutes, according to an exponential distribution. Patients walk from the parking lot, through the entrance to a waiting area near the reception, which requires between 2 and 8 minutes (uniformly distributed). The patient sits down on a chair in the waiting area until it is his/her turn at the reception. The receptionist determines the appropriate specialisation based upon the nature of the injury. This takes on average 2 minutes, normally distributed with a standard deviation of 0.5 minutes. There are three possibilities:
1. Major injuries; these require an immediate complex operation elsewhere in the hospital. This concerns 5% of the patients. They go straight to another part of the hospital (out of the model).
2. Medium injuries; these require immediate operation; however, this can be performed at the Emergency Room. This concerns 7% of the patients. They go to one of the operating rooms where they will be treated by a surgeon. If all surgeons are busy, the patient must wait. The estimated time required to perform an operation is with an
. As you may have noticed, there is only one chair for patients who wait for an operation. After all, if the waiting line would increase, then the injuries may become fatal. Assume that the receptionist has sufficient information to decide whether to send a patient to the operating rooms or if necessary to prevent a waiting line length of two patients to send that
patient to another part of the hospital (out of the model).
3. All other patients are sent to a doctor in one of the treatment rooms. The time required for
a treatment is
. The doctor, who works from 9:00 until 17:00, is fairly inexperienced. Therefore, (s)he is 30% slower than his/her colleagues. The standard
deviation remains the same.
Patients walk from the reception to their appropriate destination. It takes a patient about 2 minutes to leave the reception area (and the model) when going to another part of the hospital. To go from the reception to (the waiting room of) the treatment rooms takes between 3 and 4 minutes. To go from the reception to the operating rooms takes between 4 and 5 minutes.
A patient who has been treated by a surgeon has a 75% probability that (s)he can go home instantly after the operation. This patient then walks to the exit in about 4 minutes. Otherwise, the patient must recover in another part of the hospital. These patients walk after the operation to the door that leads to the other parts of the hospital in about 12 minutes. Patients who were
expected value of 30 minutes and a standard deviation of 6 minutes
variance of 0.25 minutes2
estimated as normally distributed with an expected value of 3 minutes and a
case – page 2
normally distributed
treated by a doctor can always go home after the treatment. It takes these patients about 4 minutes to walk to the exit.
There are 4 surgeons, 4 doctors and 3 receptionists. The receptionists work for 8 hours each (including breaks), from 7.00 until 15.00, from 15.00 until 23.00 and from 23.00 until 7.00. The receptionists take a 15-minute break every even hour. So the receptionist who starts at 7.00 takes breaks from 8.00 until 8.15, from 10.00 until 10.15, and so on. The surgeons work as follows. Three surgeons work in shifts, from 6.00 until 14.00, from 14.00 until 22.00 and from 22.00 until 6.00. The fourth surgeon works from 9.00 until 17.00. Each surgeon takes a 15- minute break every odd hour. So the breaks of the surgeon who starts at 6.00 are from 7.00 until 7.15, from 9.00 until 9.15, and so on. The fourth surgeon starts to work at 9.00 and therefore starts his/her day by taking a break. The schedules of the four doctors are identical to the schedules of the surgeons. Note that this is an Emergency Room, so if it is time for somebody to take a break, that person will first finish the patient (s)he is working on, before taking the break. Furthermore, the break will end at the scheduled time anyway.
Problem definition
Question 1
Formulate a problem definition (step 1 of a simulation project) which you could present to the hospitals management.
Conceptual model
Question 2
Create a conceptual model of the process as described so far. Add quantitative data to obtain a quantitative model.
Implementation, Verification, Validation
Create a Witness model from the quantitative model you made at question 2. Simulate the system for 5 days. Start the simulation at 0.00.
Use the supplied map of the Emergency Room in your Witness model. Also think of the following in the animation of your model:
The routes that patient walk along,
It must be visible when a receptionist, doctor, or surgeon takes a break.
Furthermore, you get the following hints to make your model:
Build the model gradually and check the functionality of each extension before you continue building.
Model the surgeons and doctors with SETS. That will save you a lot of work at level 2.
Think carefully about the SCHEDULES before you enter them into Witness. You only need 3 schedules, each schedule consisting of just a few (at most 9) ROWS.
Check very very carefully (lives are at stake!) that there can never be more than 1 patient in the waiting line for the operating rooms. Also prevent sending patients to another part of the hospital if they would not cause the waiting line length to exceed 1. Examine the related processes carefully and find out all options that might occur. Before implementing, it might be wise to first write down a logic formulation that includes all of these options.
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