Human Patient Simulator

The Human Patient Simulator (HPS) system is produced by CAE Healthcare, formerly Medical Education Technologies, Inc (METI), and consists of a manikin and control rack. The model-driven manikin is a full sized lifelike body (adult or pediatric) whose pulmonary, cardiovascular and other systems respond automatically to a user's interventions and the environment. The control rack contains the physiologic and pharmacologic modeling programs and some of the simulated components.

The lab has 3 HPS manikins and 2 control racks. The original adult system was acquired jointly by Anesthesia, Nursing, and Surgery in 1994. The first pediatric manikin was originally purchased through a gift from the Eberly Foundation shortly after that. The Center has had several systems since then, with the most recent ones being scheduled for purchase in the first quarter of 2013.

Standard monitors are used to examine EKGs, blood pressures, expired breath, and oxygen saturation. Thoracic pressures are generated in real time. Pulmonary artery catheter insertion can be simulated through the computer and measurements can be displayed as the catheter progresses, including wedge and cardiac output.

Users do physical exams, airway manipulation, defibrillation / cardioversion, pharmacologic interventions, CPR and trauma procedures. Physical responses include heart and lung sounds, pulses, and real gas exchange. Real time blood gases can be read from the monitor and given to the trainees. Brain function is assessed by checking pupil size and reactivity to light. Consciousness is demonstrated by blinking or closing the eyelids.

The manikin is programmed with pharmacologic parameters for over 60 intravenous and gaseous drugs. When a drug is administered, the simulator takes into account weight and physical condition to obtain onset and offset times and dose dependent systemic effects. Drug interactions are also calculated and reflected in the vital signs.

Teaching can be approached as an instructional format, where the disease is known ahead of time and various physiologic and pharmacologic points are discussed. Trainee-led treatments can be attempted. If the outcome is not favorable, the scenario is reset and the trainees discuss which treatments may produce a better outcome. Results of multiple treatment options can be examined and compared.

Diagnosis is also taught on the simulator. Trainees are given a case history and are asked to manage the patient. They are responsible for requesting appropriate tests and monitors, interpreting results, and making a diagnosis. The trainees then manage treatments to improve the patient's condition. These scenarios can be run in real time or can be slowed down to allow discussion before proceeding.

The simulator is used for research and crisis resource management training by moving the instructor behind a one-way glass. Digital cameras are connected to a monitor in the control room. The patient's voice is produced by speakers in the manikin's head. This AV system is used for recording and archiving research projects as well as for debriefing after a training or testing session.

The cardiac system has factors which are adjusted from the computer, but which also interact with the user's interventions. When EKG leads are placed, real electrical signals are sent to a monitor. The user can palpate 6 pulses bilaterally. Individual pulses are turned off to simulate trauma to a limb. As blood pressure falls, pulses automatically disappear, indicating circulatory shock. Heart sounds are audible with standard stethoscopes, and can be changed to produce murmurs or gallops. Invasive pressures are displayed for a central line, pulmonary artery catheter or arterial line. Each has several settings corresponding to catheter advancement during insertion. Wedge pressure is obtained by inflating the balloon on a catheter that resides permanently in the manikin's chest. By injecting fluid through the computer, cardiac output is measured on a real monitor.

If the patient's circulation is not sufficient, cardiac compressions can be performed, with the pressure monitors and exhaled CO2 reflecting the effectiveness of the compressions. If the patient continues to deteriorate and a dysrhythmia develops, a defibrillator is used. Cardiac tamponade can also be simulated hemodynamically in both the child and adult manikins, as can pericardial centesis through the adult manikin's chest. As fluid is drawn off (in the pediatric manikin, pericardiocentesis is done via the computer) the hemodynamic status automatically improves. Both the adult and child manikins are responsive to defibrillation and cardioversion, with either a standard or automated external defibrillator.

The pulmonary system is self-regulating. Air movement in the lungs makes gas exchange possible. On inspiration a gas analyzer determines what the manikin is breathing (air, O2 or an anesthetic). By calculating O2 requirements and rate of CO2 production, the manikin breathes out the proper amount of CO2. Based on the body's requirements, the lung system automatically adjusts the respiratory rate and tidal volume. Breath sounds are auscultated by standard stethoscopes in several locations to detect abnormalities, such as wheezes or rales. Sound is correlated to lung movement, so the absence of sounds in one or both lungs is diagnostic.

A number of techniques can be taught using the anatomically correct airway. Bronchoscopy can be performed in the upper airway and trachea. Nasal or oral intubation can be performed. Ventilation can be compromised by tongue or upper airway swelling, bronchospasm, or laryngospasm. If an esophageal intubation is performed, the stomach swells up when ventilated.

During a tension pneumothorax, the adult manikin allows either needle decompression or chest tube placement. The treatments are performed through the computer interface for the pediatric manikin.

The adult manikin is anatomically correct for either sex and can be catheterized to obtain urine output. The urine is delivered by a peristaltic pump through the simulated bladder to the catheter. This is one of the few symptoms that is not automatically adjusted by computer models. The instructor sets a rate manually. By changing the fluid in the pump, bloody or cloudy urine can be simulated.

The new HPS fluid model has been enhanced considerably. It now models infusions of whole blood, packed cells, crystalloids and colloids independently, including the effects of each on hematocrit. The patient can lose either whole blood or plasma, to simulate the different effects of blood loss through active bleeding versus volume loss through leakage into extracellular spaces.

The patient responds to about 60 intravenous drugs (paralytics, anesthetics, opioids, reversal agents, resuscitation drugs) and several gaseous anesthetics. A barcoded syringe is automatically read on injection, which gives the computer the drug name and concentration. Volume is also measured, enabling the computer to calculate the dose. Multiple compartment models calculate the effect on each system based on the dose given, patient weight and physical condition. There is an appropriate onset and offset time, and multiple drugs will interact with each other.

The HPS manikin also has a trauma component that can be added. At this time we do not have the trauma package, but are planning to upgrade in the near future. The kit includes physical signs of trauma, such as bleeding from the eyes, ears, nose and mouth. This package also is able to portray BCW (Biological and Chemical Warfare) patients, by changing the oral / nasal bleeding to foaming, etc.