Book Text

Virtual Reality Simulators

Virtual reality refers to a set of techniques in which one interacts with a synthetic ("virtual") environment that exists solely in the computer.^[8] In the typical conception of virtual reality, representation of the synthetic environment

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**TABLE 84-2** -- Functionality of current mannequin-based simulator systems
Clinical Area	Features and Functions	Remarks
Airway	Appropriate pharyngeal and glottic anatomy	Airway often provides acceptable seal for LMA, CT, LT, etc.
	Placement of face mask, ETT, LMA, LT, Combitube
	Laryngospasm, tongue and airway swelling, cervical immobility, jaw closure, breakable teeth
	Cricothyrotomy
	Transtracheal jet ventilation
	Bronchial anatomy (to the lobar bronchus level)
Head	Eyelid movement, pupil dilatation, and reaction to light or medications	Sweating not available yet
	Patient voice and sounds such as coughing and vomiting (through built-in loudspeaker)
	Palpable carotid pulses
	Tearing
Chest	Physiologic and pathophysiologic heart and breath sounds	Breath and heart sounds through loudspeakers; sounds contain artifacts and mechanical noise
	Spontaneous breathing with chest wall movement
	Bronchospasm
	Adjustable pulmonary compliance
	Adjustable airway resistance
	Pneumothorax
	Needle thoracotomy and chest tube placement
	Defibrillation, transthoracic pacing ECG
	Chest compressions
Extremities	Palpable pulses (dependent on arterial pressure)	Very limited movement capabilities at best
	Cuff blood pressure by auscultation, palpation, or oscillometry
	Modules for fractures and wound modules
	Intravenous line placement
	Thumb twitch in response to peripheral nerve stimulation
	Arm movement
Monitoring (waveforms and/or numerical readouts)	ECG (including abnormalities in morphology and rhythm)	Simulators interface to actual clinical monitors or provide a simulated virtual vital signs display (or both)
	SpO₂
	Invasive blood pressure	Includes a virtual heart-lung machine
	CVP, PAP, PCWP
	Cardiac output
	Temperature
	CO₂ (may be actual CO₂ exhalation)
	Anesthetic gases (may have actual uptake and distribution of agents)
	Cardiopulmonary bypass
Automation and sensors	Chest compressions
	Ventilation rate and volume
	Defibrillation and pacing
	Gas analyzer (inspired O₂ , anesthetics)
	Drug recognition (drug identification and amount)
Note: The features listed are each present in some existing simulators, but not all features are present on any single device. Sets of features depend on the device and model.
CT, Combitube; CVP, central venous pressure; ECG, electrocardiogram; ETT, endotracheal tube; LMA, laryngeal mask airway; LT, Larynx tube; PAP, positive airway pressure; PCWP, pulmonary capillary wedge pressure.

is fed fairly directly to the eyes, ears, and possibly the hands. The actions of the user in the environment are translated directly from typical physical activities, not through manipulating a special pointing device. Realization of this ideal is a continuum involving compromises in these input/output modalities. At one end of the continuum, which we call a "complete virtual reality simulation," the participant is immersed in a virtual world that fully replicates at least three sensory inputs—vision, hearing, and touch (the last is more technically known as

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**TABLE 84-3** -- Desirable features of future mannequin-based simulator systems
Advanced skin signs such as
Change in skin color to cyanotic or pale
Diaphoresis
Change in skin temperature (e.g., as a result of shock or fever)
Rash, hives, or generalized edema
Regurgitation, vomiting, airway bleeding or secretions
Physical coughing (currently only sounds are simulated)
Convulsions
Purposeful movements of extremities
Support for spinal, epidural, or other regional anesthesia procedures
EEG signals (e.g., for BIS, AEP, PSI)
Intracranial pressure
Support for physical central venous cannulation
Fetal/maternal cardiotocogram (CTG)
A fully interactive simulator of a neonate or infant
Note: The table shows what features are not currently incorporated (April 2004). Some features may be under development and could be available after publication of this book. In addition, some features are currently available as third-party or homemade add-ons.
AEP, auditory evoked potential; BIS, bispectral index; EEG, electroencephalographic; PSI, patient state index.

**TABLE 84-4** -- Characteristics of currently available simulator systems for anesthesia (as of July 2003)
Type/Manufacturer	Patient Simulator (Eagle-MedSim)	HPS and PediaSim (METI)	ECS (METI)	SimMan (Laerdal)	ASC (Anesoft)
External representation of the patient	Mannequin	Mannequin	Mannequin	Mannequin	Computer
					Screen
Internal control logic	Model based	Model based	Model based	Script based	Model based
Interface to actual physiologic monitors	+	+	- (+ECG)	- (+ECG)	-
Simulated physiologic monitors	-	- (+)	+	+	NA
Automated drug recognition	+	+	-	-	NA
Hands-on training	+	+	+	+	-
Easy transport	-	-	+	+	++
Price (approx) in U.S. dollars	(210,000)	200,000	40,000	40,000	200–800 (depending on type of license)
	No longer produced
Systems in the U.S.	55	200 (+70)	46	600
Systems in Europe	10	30 (+10)	5	100
Total systems (world)	75	271 (+90)	60	900	10,000
Note: This table shows only simulators available for anesthesia training. Most of them can also be used for intensive care medicine or emergency medicine training. The human patient simulator of METI is also available with a mannequin resembling a child around 8 years old. There are a variety of screen-based simulators, especially for resuscitation training (e.g., ResusSim, MicroSim, Inhospital, Sophus Medical), and lower-fidelity mannequin-based skills trainers (e.g., mega-code trainer) available in adult, child, infant, and neonate models.
ASC, anesthesia simulator consultant; ECS, emergency care simulator; HPS, human patient simulator; NA, not available.

a haptic/kinesthetic system)^[8] —and allows complete physical interaction with the world. At the other extreme of the continuum is a screen-based simulator that generates a limited virtual world, but it restricts its output to a screen display and provides interaction with the virtual world only through a pointing device. Screen-based simulators provide an interface to the human sensory system that is very far from physical reality, whereas a complete virtual reality simulation may be, in its most advanced form, nearly indistinguishable from the real world. A "partial" virtual reality simulator would replicate fewer senses (or less complete replication, such as a three-dimensional visual representation on a two-dimensional screen) or could restrict physical interaction with the world, or both. Finally, one can imagine hybrids of realistic simulators and virtual reality simulators in which the virtual reality representation is overlaid onto a real physical environment.

A complete virtual reality patient simulator would be very complicated because it requires the following:

A complete computer model of the patient, the environment, and the function of every object in the environment that could be used (e.g., monitoring devices, carts)
A means of tracking visual, audio, and touch fields of the user to determine what is to be displayed and to identify what physical actions are being performed
Appropriate display hardware for every sensory modality and appropriate input hardware for each action pathway (e.g., touch, speech)
Hardware to compute all the models, to conduct the tracking, and to produce all the output to the display hardware in real time

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Virtual reality is a rapidly developing field. It has stimulated intense interest in a number of domains, particularly the military and entertainment. Although the potential of this approach is very exciting, virtual reality is still under development.

Prototype virtual reality patient simulators (and so-called three-dimensional virtual worlds) have been discussed informally, but as of this writing, there is no published experience with any meaningful virtual reality patient simulation system, although work has been published in areas of partial-task virtual reality and single-procedure virtual reality simulators (e.g., intravenous access^[9] and bronchoscopy,^[10] as well as endoscopic surgery).

Even though virtual reality simulators have many theoretical advantages over screen-based and realistic simulators (e.g., realism, virtual "hands-on" interaction, instantaneous reset of the environment), these advantages are currently offset by the immaturity of the field. In spite of considerable "hype" about virtual reality, such systems are now either very limited in capability or very expensive, and in most cases, they are both limited and expensive. A true virtual reality "immersion" experience in a patient care setting comparable to that obtainable with a realistic simulator is not yet on the horizon.

Nonetheless, it is likely that virtual reality techniques will eclipse other types of simulators within 10 to 20 years.^[11] In the interim, we believe that virtual reality will be used primarily to augment the display representation of current screen-based simulators.