Structure

In DPS a patient is simulated through parameters. The course of the parameters in time differs for every case and determines the manifestation of the illness of the patient.

After a student has come to a diagnoses he can select appropriate treatment. This treatment can have a positive or even negative effect on the course of the parameters in time.

During a case the program provides students with feedback on their performance.

Patient

Each DPS patient is built up form a standard patient database that is changed and extended to simulate an illness. The patient condition changes in time due to a change in the parameters caused by the program or the student.

Standard patient

Within the standard patient the state of the patient is recorded in parameters. Parameters are continues variables. Some parameters can be measured directly by the student and some only come to light in what we call the symptoms of the patient (discrete variables).

An example of a parameter that can be measured directly is the systolic blood pressure. This parameter can also be distracted from the symptoms of the patient. Low blood pressure can cause dizziness, while high blood pressure can cause headaches. 

An example of a parameter that can not be measured is the blood circulation in a leg. The value can only be distracted by looking at the symptoms it influences, such a the color of the skin, for example red, pink or white and the temperature, hot or cold.  

In addition to the parameters, all the treatment that is available in medical practice is recorded in the standard patient. An operation is defined as a change it causes to a parameter in time when selected by the student. This change or effect of the operation is recorded in time. Effects can be absolute or relative. When an artery is closed by an operation, the effect on the blood supply is absolute. Medication that influences the blood pressure can for example have a relative effect on the blood pressure because the blood pressure can still be influenced by other therapies.  

Case patient

A case patient will consist partly of parameters and operations from the standard patient (some with different settings) and partly of new parameters and operations that are specific for the patients illness.

A case can be defined as a collection of effects that are selected by the program and are invisible to the student. In the case of a pneumothorax for example there are effects on parameters, such as: decline of the blood pressure and the oxygen saturation in time and an increase of the respiration frequency. The effect is stored in the effect-time table.

An operation that is selected by a student can influence the parameters in time. In the case of the pneumothorax a thoracic drain can have a positive effect on the parameters blood pressure, oxygen saturation and respiration frequency. This operation might have already existed in the standard patient, but for this case the effect on the parameters is added and the score is changed from negative to positive.

In every case stop criteria are defined, which a student should reach before a case can be finished. The stop criteria are different for every case. The duration of a case is therefore dependent on the actions of the student. A blood pressure that drops under 40 mmHg can be a stop criteria when the student is performing poorly, or, in case of the pneumothorax, the decision to put in a thoracic drain can end the case positively.

Patient condition

At the start of a simulation all the parameters are initialized between minimal and maximal normal values for healthy people.

The patient condition is simulated by influencing the parameters during the simulation. This influence can be executed by the program or by the student by appropriate therapy. The influence on the parameters can be seen in changes of the lab values or the symptoms that are linked to the parameters, such as medical history and physical examination.

At all times a patient will answer a question when asked. The author can however help the student when a patient gets critically ill, by warnings to the student. These warnings are dependent on the state of the patient, the location of the patient and the preceding actions of the student. When a patient is at home, talking to you on the phone, you will for example not be able to assess the physical condition of the patient as accurately as when the patient is with you in hospital.

Case

The state of a patient during a case will be reflected in the parameters that are sometimes directly measurable and sometimes have to be estimated through the linked symptoms. Parameters can change in time during a case due to effects that are executed on them. The change of the parameters in time bring about the dynamic course of a case.

Parameters

The state of the patient at any moment in time during a simulation is determined by parameters. Parameters are continues variables, but can also be used as discrete variables. Some parameters are directly measurable and some are hidden and can only be estimated by looking at the symptoms that are dependent on the parameter. More than one symptom can be linked to a parameter. For example the blood supply for a leg can be the parameter that influences the symptoms temperature, color and even ankle-arm index of that leg.

In DPS parameters are not automatically dependent on one another, this in contrast to physiological simulations. This choice has caused a drastic simplification of the model, which has made it practically unusable for physiological simulations. The advantage for DPS is that simulations can be build with less effort in less time, a disadvantage is the extra work it costs to make one effect influence the course of many different parameters.

Effects

Effects are defined as interventions to the state of the patient, such as medication or operations, that can influence the course of the parameters that determine the illness in time. This effect can be relative or absolute. An absolute effect will overwrite all the preceding effects, a relative effect will be added to the preceding effects on a parameter. 

An effect is determined in an effect-table in which parameter values on different point in time are stored. An effect is therefore not a formula, but a series of point the parameter will reach in time. This inaccurate way of determining the effect of interventions in time justifies the choice of the effect in DPS  without much research into the effect of interventions.

Dynamic course

Time is essential in DPS. The state of the patient can change rapidly or slowly during a simulation. First aid cases can be simulated through rapid changes in the state of the patient. Students are then forced to intervene quickly to save a patients life. Follow-up situations, for example intermittend claudication, that can take years can be simulated with a very slow change of the state of the patient in time. In all cases the student can speed up time between sessions with the simulated patient.

To make DPS simulations as realistic as possible the results of any examinations, such as EKG and x-rays, are given only after an appropriate time of delay. This delay sometimes forces students to decide what to in an acute situation without having all the information provided.
All measurements, such as blood pressure or lab values, are initialized between normal maximal and minimal values at the start of every simulation. During a simulation the values are additionally measured with a normal deviation from the actual value. These factors cause DPS to perform a little different every time a students starts up a new simulation.

Dynamic course

Time is essential in DPS. The state of the patient can change rapidly or slowly during a simulation. First aid cases can be simulated through rapid changes in the state of the patient. Students are then forced to intervene quickly to save a patients life. Follow-up situations, for example intermittend claudication, that can take years can be simulated with a very slow change of the state of the patient in time. In all cases the student can speed up time between sessions with the simulated patient.

To make DPS simulations as realistic as possible the results of any examinations, such as EKG and x-rays, are given only after an appropriate time of delay. This delay sometimes forces students to decide what to in an acute situation without having all the information provided.
All measurements, such as blood pressure or lab values, are initialized between normal maximal and minimal values at the start of every simulation. During a simulation the values are additionally measured with a normal deviation from the actual value. These factors cause DPS to perform a little different every time a students starts up a new simulation.