This section outlines the key surgical attributes for which performance parameters can be quantitatively validated. The skills cannot be validated in this way, since (a) a complete validation system is needed capable of recognising and dealing with other parameters that are difficult to measure and (b) what is straightforward to measure is not necessarily useful, and vice versa.
The human attribute set is a list of attributes that needs to be modelled so as to develop databases. These must be both compatible and comprehensive. An accurate primary attribute set is important. The tools should be fit for purpose. The interaction between this attribute set and the system (the so-calledAttribute – Performance Analysis Engineinterface) is specific to the system being designed and the sub-skills being tested. In this case, the attributes are proficiency in orientation, navigation and pattern recognition.
3.5.1 Visual interfaces for surgery
The surgeon in their operating environment usually depends upon a good visual field. Ideally simulation would match human performance. For a human to fix on a point, the central foveal Field of view (FOV) region of the eye has the greatest concentration of light-registering receptors, designed to detect light of wavelengths that are perceived as colours. These are termed cones since this is the point that is used to look at in detail
(reading textetc.). It therefore produces the highest resolution. There are 147000 cones per square millimetre in the fovea. This part of the eye and the associated visual mapping in the cerebral cortex limits the ideal performance for the human-computer interface. In fact, true colour requires '24 bit' data. In the Exeter Virtual Worlds (SIM1) model, a compromise of 3-colour 16-bit was adopted, allowing up to 106 images using 25:1 JPEG compression. The size of the image is limited by the band width and supported frame recording rate. The rate was 7 frames per second. This limited the number of frames that could be recorded in the time available using fresh cadaveric material (see page 54). Users were satisfied with the colour quality of the images. Viewing is on a high definition television monitor in operating theatres and so a display resolution of at least 72 dpi is appropriate.
3.5.2 Haptic and auditory interfaces for surgery
The haptic and auditory feedback in simulation require a relatively narrower bandwidth and so are not considered a problem for present calculations regarding data storage, needing only approximately 10% of the storage space of visual data. It is important to consider background noise levels and other distractions that can impair performance of the individual. Open surgery is often performed wearing lead jackets (γ- radiation protection) for long periods under intense lighting at a raised temperature to achieve the optimum environment for the patient, not necessarily for the surgeon. Arthroscopy is somewhat easier in this respect, not requiring lead jackets and usually not lasting more than one hour per case. Since the purpose of the simulation development is to focus upon the vision aspects for training pattern recognition skills, the detailed issues surrounding haptic and auditory feedback are not addressed here.
3.5.3 Psychology in the clinical environment
It is sensible to explore the possible methods for the introduction of simulation into clinical practice. By considering the qualities of a training environment and current proposals, this indicates the prototype training environment limitations. Surgery can be viewed as an interaction between 3 particular elements:
The surgeon - training, expertise, and competence.
The patient - their expectations, pathology, anatomy and physiology.
Decision Making: For successful surgery, elements of decision making need to be properly integrated and mutually supported. Human technical competency is probably still the most significant factor that affects outcome, because of the human capacity for sensory and perceptual discrimination and also speed of response to stimuli. Surgeons are still the best agents for decision-making. Through our evolutionary past, we have developed an intrinsic ability for pattern recognition, decision-making and construction of plans, more flexible than any existing robotic hardware. With respect to our senses however, our performance generally is inferior for the detection and processing of incoming signals and, most importantly, for detecting small variations in the signals and the time to respond (47). In spite of being able to operate through two channels (thinking and acting simultaneously), humans are primarily single channel sequential recorders with a wide base and low sensitivity input/output capacity, with respect to their cost (48). The flexibility of the human response is limited and so operator-induced delay is of concern with respect to complex systems. Fortunately, however, there are few procedures in surgery where it is not possible to stop and apply an appropriate algorithm for analysis of the situation before proceeding.
Effects of fatigue: It is more critical to be able to recognise the need to apply such processes since, if the initial perception is absent or aberrant, then the appropriate path is unlikely to be followed. Humans are quite adept at storing multiple units of information, selecting, interpreting and acting upon this information. These functions are, however, decreased when fatigued or stressed and much of the input/output capacity is compromised. The natural predilection then is to revert to a more primitive mode, dealing with stimulating responses singly and sequentially, such that the competing signals need to wait for attention and a defined action. Sleep disturbance, a common problem in operating surgeons, can have major effects with malaise and a temporary reduction in intelligence quotient predominating, with consequential operating impairment (49). The fatigue, once established, is associated with a reduction in skill proficiency, psychological stress, resulting decrements of motivation and performance, often with slow, irregular and distorted performance. Experience suggests that decision- making requires cognitive information with the following components:
Prior knowledge of the data source
Memories of past or similar occurrences
Inherent bias (50;51) suggests that heuristic rules and knowledge may be adapted and modified through training whilst memories are unlikely to be significantly effected.
3.5.4 User interface design considerations
Developing an original approach to surgical simulation involves accurately modeling the specific skills and requirements of surgeons. Those factors above outline the human side of the ‘Human Computer Interface’ (HCI) equation. The human performance aspects of this have far-ranging implications for the potential way that surgeons are screened in future for their training. The traditional teaching was that a surgeon should possess the'Eyes of a hawk, the hands of a lady and the heart of a lion'.
This eloquent description by the fictional character Sir Lancelot Sprat in novels and on film (52) represents a romantic picture of the qualities required to make a surgeon, emphasizing high fidelity sensors and actuators.
The minimum entry criteria currently employed for surgeons, specify Basic Surgical Training skills as the only demonstration of physical and psychomotor ability required. Therefore the simulator design efforts have until recently been directed towards mastering these skills.e.g.VR MIST (17;43;53).
As detailed in Chapter 4, the planned evolution of simulation must take into consideration the educational application for which it is intended, closely linked to the surgeon’s experience in clinical posts and their individual learning agreements with their mentors. Once familiar with an interface, the user wishes to maintain a degree of autonomy, modifying it and adapting it to their special needs and considerations. This process of customization should relate to theuser profile. This should be integrated into both the evolving educational requirements and the development process for standards by which the systems are to be judged. Seymour (54) has recently developed evaluation methodologies for users, though this needs to be seen within the context of Higgins and Satava’s (Figure 4.1) (20) work from the San Diego group. This is referred to as the validation model.