Disadvantages of Robotic Surgery
THE QUESTION OF SAFETY
In comparison to robots used in the industrial sector, medical robots present designers with much more complicated safety problems. Some of the most important factors which lead to such complexity are described below:
- Human presence: In an industrial situation, there are no humans present in
the application environment. Should that be necessary, safety regulations
specify that the robot be de-activated while humans are in the vicinity.
This greatly simplifies the safety requirements and their satisfaction. In
the medical sector, however, robots are required to assist rather than to
replace humans. In that respect, they must be able to work in close
proximity to humans and perform well in a chaotic, time-varying environment.
This requires medical robots to have rich sensory and reasoning capabilities
concerning their environment, something that both pushes the current
technology to the limits and presents robot designers with insurmountable
obstacles.
- Fault consequences: This is closely related not only to the presence of
humans near the robot, but also to the nature of the task of the robot,
which typically involves a human patient. In the industrial sector, a fault
can mean at most some loss of physical equipment. In the medical sector,
where lives are at stake, the implications are of profound importance.
- Non-generic task: In the industrial sector, the robot is required to perform a series of movements in some pre-defined order. The object it is operating on, be it as simple as a metal pipe or as complex as a car, is not distinguished in any way, that is, the robot is not required to take account of differences on an object-by-object basis, but treats them all as being equal. When dealing with patients, however, this is not possible. Each patient has their own distinguishing characteristics, making a uniform approach inappropriate. In safety terms, this requires testing, or at least reasoning about infinitely many scenarios.
Possible reasons that can lead to unsafe operation of a medical unit include flawed design, malfunction of hardware and software components, misinterpretation and incorrect or inadequate specification. As in many other applications, improving some of these parameters results in a degraded performance in other areas, while an overall increased level of safety is accompanied by an increase in cost, complexity, or both.
The idea of total safety is a fallacy. Instead, different safety strategies offer different advantages (and, or course, disadvantages). The overall probability of error must be always kept at very low levels. Perhaps even more important than the probability of a fault is the ability to detect that a fault has indeed occurred and prevent hazards resulting from it, that is, allow the robot to "fail safely". This usually involves shutting the robot down and removing it from the patient, and having the operation manually completed by a surgeon.
As the task which the robot undertakes becomes more and more complicated, there is an increasing need for more complex hardware and software components (faster response, better accuracy, more degrees of freedom). This increases the probability of error exponentially. Software is notoriously difficult to reason about, while hardware reliability never ceases to be of prime importance.
A final consideration concerning safety is, perhaps surprisingly, size. Both patients and doctors feel uncomfortable working next to medical robots which tower above the surgeon at over 7 feet and weigh in at several tens of kilograms. There is some logic behind that, however. A larger robot can usually exert more force than a smaller one, resulting in an increased amount of damage in case of a fault.