VA PA Sim Center

The MedSim-Eagle Patient Simulator

The MedSim-Eagle Patient Simulator is a realistic, hands-on simulator of the anesthetized or critically ill patient. A "hands-on" simulator is one in which the clinical environment and the patient are represented as real physical objects. A specially instrumented patient mannequin stands in for the patient, and real clinical equipment is used to make up the work environment.

The modern anesthesia simulator was invented here at Stanford in 1986 by a group led by David M. Gaba, M.D., Professor of Anesthesia. The MedSim-Eagle Patient Simulator is an outgrowth of two generations of patient simulators designed and built here known as C.A.S.E. (Comprehensive Anesthesia Simulation Environment).

Features of the MedSim-Eagle Patient Simulator available at the VA/Stanford Simulation Center:

Regional Anesthesia Option. To simulate administration of regional anesthesia.

Drug recognition system. Detects type and amount of drug administered to patient.

Cardiopulmonary Bypass Module. Provides a virtual bypass pump for simulation of placing a patient on bypass and removing the patient from bypass.

Computer-controlled eyes. Eyes open and close and eye reflexes respond to stimulus.

Arm movement. Arm moves in response to stimulus when patient is not paralized.

Arm/Leg swelling. Arm and Leg can swell to simulate trauma.

Drug Editor. Allows user customization of drug default names, concentrations, pharmacokinetics, and pharmacodynamics.

More complete airway management training head and neck. Allows use of LMA, Combitube, and transtracheal jet ventilation or cricothyrotomy.

Better breath sounds and heart sounds.

Built-in gas analyzer. Allows automated quantitation of inspired gases and better servo control of VCO2.

Improved patient editor and library of pre-defined "abnormal" patients. Generic events can be customized to trigger and resolve by predefined clinical intervensions and rare events can be easily programmed.

New arrhythmias supported. (e.g. A Fib, A Flutter, Mobitz type II 2nd degree block) (NOTE: The following refers to Version 2.3 of the MedSim-Eagle Patient Simulator)

The three components of the simulator are:

The Patient Mannequin

The mannequin is based on a commercially available medical training patient mannequin. This mannequin supports many clinical activities. Complete airway management can be practiced including mask ventilation, endotracheal and endobronchial intubation, cricothyrotomy and transtracheal jet ventilation. The airway can be made "difficult" in several ways including changes in the neck/head alignment, incorporation of an intrapharyngeal mass, and laryngospasm. Other clinical features supported by the mannequin include ability to placeme of peripheral and central intravenous lines, a thumb that can be stimulated by real clinical nerve stimulators (and responds appropriately depending on what drugs have been given), palpable radial and carotid pulses, heart sounds and breath sounds. ECG leads place at appropriate electrode locations pick up the mannequin's electrocardiogram.

The mannequin's electromechanical computer controlled lungs are embedded in its chest (just like a person) and breathe spontaneously as well as by hand or mechanical ventilation. Lung mechanics can be adjusted by the computer in real time as appropriate. Incoming gases are detected and quantitated and their concentrations fed to the physiologic and pharmacologic computer models. The gases actually ventilate the mannequin, which itself produces CO2 (as determined by the mathematical models of metabolism and the circulation) which is expired by the lungs. Thus, any respiratory gas analyzer can be used to physically quantitate inspired and expired gases.

Drugs must be injected into working IV lines. We like to say "there are no magic drugs in the simulator -- you have to actually draw them up and give them". Their identity is input to the to the computer by the instructor. A standard anesthesia drug/supplies cart is in the simulator OR

The Interface Cart

The mannequin's electrical and pneumatic components are controlled by an interface cart which sits on casters underneath the OR table, or at the foot of the patient's bed. The cart also supplies the input cables for electronic monitors such as invasive blood pressures and pulse oximeters. The cart receives it's directions from the simulator main computer.

The Simulator Computers and the Instructor's Control Station

The simulator contains two computers working in parallel. One computer, a single board microprocessor computer, executes all the physiologic models in real time. There are complex mathematical models of the cardiovascular system, the pulmonary system, metabolism, fluid and electrolyte balance, thermal regulation. For example, the cardiovascular model tracks "mathematical blood" moved from chamber to chamber and vessel to vessel by updating its differential equations hundreds of times per second. There are pharmacokinetic and pharmacodynamic models of more than 75 drugs which might be given. It is important to remember that these models are true mathematical models, not "rules" or artificial intelligence. What happens in one model affects all the others.

The second (main) computer, a Sun Microsystems SparcStation, provides the graphical user interface for the Instructor's Control Station. The simulator is totally operated with a mouse and keyboard similar to the interface used on Macintoshª or Windowsª computers. Most commands or selections are made by pointing and clicking on virtual buttons and sliders, or by selecting from menus

The software of the simulator is extremely flexible. One can call up different underlying patients to be used. A patient file gives the values of hundreds of parameters in the mathematical model that defines a patient -- things like "baseline myocardial contractility", "maximum possible contractility", "pulmonary dead space", "pulmonary shunt fraction", etc. There are several default patients, or one can construct hundreds of variations.

Similarly, the simulator comes with over twenty abnormal "events" which can be triggered. These include things like, "hypoxemia", "malignant hyperthermia", "anaphylaxis", "myocardial ischemia". For each event there are a variety of settings possible, governing how it is triggered, how severe it is and how quickly it will come on, and the relative intensity of the various possible manifestations. For example, for anaphylaxis one can set how much vasodilation there will be, how much bronchospasm, and whether there will be a rash. One can also set the responsiveness of the patient to various treatments for that event, for example whether the anaphylaxis will respond to small doses of epinephrine or only to massive doses. Once the event's characteristics are tailored, it can be saved away under a new name. This enables instructors to create huge libraries of variants of the standard events. Up to three abnormal events can be running simultaneously. Thus, when different patients can be used, with hundreds of different events or their variants, there is nearly an infinite ability to replicate simple or challenging clinical situations.

The simulator software provides other nice features. For example, Snap and Restore allows one to capture a scenario at any point in time and save it under a name. Thus, one can come back to that exact point at any time, picking up the simulation exactly where it left off.

Hundreds of people have undergone training sessions with this type of patient simulator. Although it is not exactly a real human being, the experience is extremely realistic. In particular, the simulator has been used for special training in Anesthesia Crisis Resource Management. This is an intense training course similar to that given to airline pilots concerning the technical and behavioral aspects of managing critical situations that might arise during anesthesia.

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