Robotic challenges in surgical electronics
27 July 2011
Surgical robotic systems exist to maximise the chances of successful surgery by providing operating room staff with reliable, rock-steady and untiring assistants.
And, because robotic equipment can be made with more degrees of freedom and greater finesse than the human hand can employ, it can be deployed through smaller incisions, thus reducing the physical trauma to the patient and improving the subsequent recovery time.
Surgical robots, however, are just part of a family of medical electrical systems that demand special care with their design, as Alistair Fleming describes...
Operating rooms are quite unlike any other environment because of the complexity and criticality of procedures that take place. All electrical systems that are used in this space, therefore, need to perform at a high level of precision, reliability and safety.
A key consideration with surgical robotic equipment, for example, is that since some of the moving parts will be working inside a living human body, a small malfunction could cause serious harm to the patient, or even prove fatal. For this reason, electrical systems used in the medical field can’t just be imported from other industries but rather need to be designed and validated from the ground up.
When considering the design of any electronic equipment, it is always tempting to see which standard off-the-shelf components can be used in order to accelerate development and keep costs down. But, while this makes sense for some industries, in the field of medical electrical systems you can’t easily redeploy commercial assemblies.
For example, industrial circuit boards can be manufactured with positive and negative poles as close together as 2mm but medical equipment requires a gap of at least 5mm. Use of non-medically approved systems could make sense when prototyping ideas, but if you want to proceed to actual product development, you will need to take a more robust approach. Here are some of the reasons why…
Risk management
Regulation requires that medical device development take a risk-based approach to design. At a high level, this is woven into the standards that govern medical quality systems, whilst methodologies are defined in the detailed risk management standard, ISO 14971. The intention is to identify risk and to avoid harm to the patient, the user, other equipment and the environment, even in the event of a single fault occurring. These risk principles flow into all of the particular standards that are further addressed below.
Each geographical region has its own regulatory framework for medical device design. The major markets are increasingly harmonising on the standards that can be used to demonstrate regulatory compliance. Medical regulatory frameworks exist to ensure that products of all kinds meet quality standards and are safe and effective for patients and users alike. But, rather than simply conforming to the standards where they apply, it makes far more sense to de-risk the entire process of equipment design and manufacture. This means exerting control over every line of software code, every material component and every manufacturing step from the outset of the development.
Design strategy
To minimise both project and product risk, different disciplines (electronic, software, mechanical) and all the interrelating component elements (PLCs, motors, communications ...) need to be coordinated under a single system architecture design strategy. This has to span the function of, and interactions between, the various sub-systems. It has to consider how these will be specified, detailed, validated and maintained in the field. Careful planning and a clear understanding of the issues up front can eliminate costly redesigns and/or hugely burdensome validation cycles later on.
The operation of the system as a whole has to be validated. A good design, whether medical or industrial, will adopt the same general strategy but tighter standards apply to the development of medical products. It is important that understanding how these affect both the product design and also the development process itself are considered at the same time as the planning of the system architecture.
Hardware design
The overarching standard for the safety of medical electrical systems is IEC 60601. With a focus on hardware and mechanical design, the latest (third) edition of this standard adopts risk-based principles and extends to several hundred pages (plus at least nine collateral standards). When compared to their industrial equivalents, these standards require more stringent isolation requirements and can mean that industrial board layouts are non-compliant with medical applications.
Apart from conforming to the standards, designers and developers need to control the quality of all component parts, through specification, choice of suppliers and the manufacturing process. The failure of a single component to meet defined specifications could threaten the integrity of the entire system.
Software design
IEC 62304 is the main standard for medical device software. It describes the set of processes, activities and tasks that comprise the software development and maintenance lifecycle. It includes sections on safety classification, risk management, testing, problem resolution, change management and documentation. Apart from meeting its intended purpose, the primary focus is on safety because a software bug can have repercussions out of all proportion to the triviality of the coding error. Testing, validation and documentation of each module and how they work together are vital steps to minimise the risk of a system malfunction.
Another purpose of thorough documentation is to show your intent and details of your development and testing to regulatory bodies and, indeed, anyone else who needs to know. With such products, especially those with a software element, it is otherwise difficult if not impossible to demonstrate that all measures have been taken to ensure safety after the development is complete. Medical design history files show the due diligence that went into the design throughout the development cycle to ensure compliance.
Transparency and traceability
A key benefit of this holistic design approach is that if your team or an external supplier ever proposes a change to a component, you will know exactly the context and its likely ramifications. Such transparency and traceability is absolutely vital in medical systems and its absence is one of the major reasons why off-the-shelf PLCs, for example, are unlikely to fit the bill. Without this level of control, suppliers are at liberty to make individual component changes that can slip under the radar. As a consequence, the system would over time start to drift away from the configuration that was validated and the manufacturer would be forced into a costly sequence of assessment, adaptation and revalidation of the entire system (assuming they are even aware of the change).
What’s our experience?
A number of companies have come to us with innovative product concepts that perform well, but can’t progress to market in the form they have been presented. Software may not have been written to medical standards, testing may not have been documented sufficiently, or hardware may fall short of requirements. This makes it monumentally difficult to verify and validate inner workings. Understanding these limitations enables us to help plan corrective strategies and redress the shortcomings, but the better approach is always to get it right first-time. Consistently, our approach at Sagentia is to take an up-front risk-based approach with systematic planning and execution across all areas, including mechanical, electronic and software.
As an example of our experience in such complex systems, we were asked by Prosurgics to lead the product development programme for a 'next generation' robotic camera holder. It had to ensure that stringent specification requirements for performance, safety, size and ergonomics were all met. We also had to manage and co-ordinate the involvement of Prosurgics’ other partners. Our team comprised mechanical, electronics and software engineers and we delivered working prototypes in six months. The result, FreeHand, is the first product on the market to bring affordable robotic assistance in minimally invasive abdominal surgery.
While 'getting on with the job' is always more attractive to developers than detailed architecture and validation planning and conformance to standards, in the long run such a systematic approach will pay massive dividends.
Peace of mind
Practically and commercially, the best way to achieve the effectiveness and safety requirements of medical electronic systems is to design from the ground up. This means laying out a solid plan for the design, development, validation, manufacture and maintenance of these devices within the framework of the various standards. This is the only sensible way to proceed, not least because it provides developers, regulators and customers with confidence and control every step of the way.
Alistair Fleming is Surgical Sector Specialist at Sagentia
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