Chapter 21: Product Issues Design of Biomedical Devices and Systems By: Paul H. King Richard C. Fries

Product Safety & Legal Issues  Risk Assessment What failure could cause harm to the patient or user? What failure could cause harm to the patient or user? What misuse of the device could cause harm? What misuse of the device could cause harm?  Liability Assessment Have all possible failure modes been explored and designed out? Have all possible failure modes been explored and designed out? Have all possible misuse situations been addressed? Have all possible misuse situations been addressed?

Safety  Freedom from accidents or losses  A function of the situation in which it is measured Drinking water & kidney failure Drinking water & kidney failure  A measure of the degree of freedom from risk in any environment

Safety  Accident – unwanted or unexpected release of energy (old definition, see history of gunpowder, TNT manufacture, etc.)  Mishap – unplanned event or series of events that result in death, injury, occupational illness, damage to or loss of equipment or property, or environmental harm

Mishap  Multiple factors that flow in series until the system is out of control and a loss is produced Anticipation of simpler problems needed! Anticipation of simpler problems needed! Opportunities for interruption –study! Opportunities for interruption –study!

How Do Engineers Deal With Safety Problems?  Operational or Industrial Safety Examination during operational life Examination during operational life Correcting unacceptable hazards Correcting unacceptable hazards  Goal: design an acceptable safety level into the system before actual production or operation Examine Accidents Determine Causes Correct

Safety and Reliability  Safety – only concerns itself with failures that introduce hazards  Reliability – probability of failure of a device to meet its requirements

Safe System  One in which damage to persons or property doesn’t happen often or, when it does, the damage is minor  Small damage potential Able to occur more often Able to occur more often Still considered Safe Still considered Safe  Large damage potential Chance for mishap small Chance for mishap small  System that fails all the time can still be safe  System can be up and running all the time and consistently put people at risk Reliable system, but not Safe Reliable system, but not Safe

Example: Pacemaker  Pacemaker that paces at 110 beats per minute continuously no matter what is very RELIABLE  If patient is in cardiac failure, high pacing rate is medically inappropriate. UNSAFE  Reliable but Unsafe device

MTTF & MTBF  Mathematical laws of probability used to estimate reliability  Published values for reliability measures: Mean Time To Failure Mean Time To Failure Mean Time Between Failure Mean Time Between Failure

Legal Aspects of Safety  3 Most Common Theories of Liability: Negligence Negligence Strict liability Strict liability Breach of warranty Breach of warranty

Negligence  One should pay for injuries that he causes when acting below the standard of care of a reasonable, prudent person participating in the activity of the action in question  People have the right to be protected from unreasonable risks of harm  A manufacturer that does not exercise reasonable care or fails to meet a reasonable standard of care in the manufacture, handling, or distribution of a product may be liable for any damages caused.

Strict Liability  Focus on product  One who sells any product in a defective condition unreasonably dangerous to the user or consumer or to his property is subject to liability for physical harm thereby caused to the ultimate user or consumer or to his property if the seller is engaged in the business of selling such a product, and it is expected to and does reach the user or consumer without substantial change to the condition in which it is sold.  Risk/benefit analysis

Breach of Warranty  3 Types Breach of implied warranty of merchantability Breach of implied warranty of merchantability Breach of the implied warranty of fitness for a particular purpose Breach of the implied warranty of fitness for a particular purpose Breach of an express warranty Breach of an express warranty

System Safety  Fail-safe – designed to fail into a safe and harmless state  Enter safe states by terminating or preventing hazardous conditions (lockouts or shutdown systems)  Should be able to work despite failure of other functions

Hardware Safety  Techniques for reducing failure of component: Component derating Component derating Safety margin Safety margin Load protection Load protection

Software Safety  Safety is a concern when used to control potentially unsafe systems  Safety needs to be considered in the design of software packages, especially when considering the “crash” of a system  Software failures are a major source of recalls…

Verification & Validation of Safety  Proof of Safety –fault cannot occure or if a fault occurs it is not unsafe…  Verification – capture the semantics of the hardware, software code, and the system behavior  Fault-tree analysis

Effective Safety Program  Implementation of internal hazard analysis procedures, a firm grasp of regulatory and other standards, and an awareness of the current industry practice regarding safety controls  Figure 21-1 Safety Analysis Checklist

Accident Reconstruction & Forensics  Biomedical Engineers may be used to analyze accidents  Analysis of Medical Device accidents  Discussion on biomechanics and accident investigation

Medical Device Accidents  Process for a medical device accident investigation: accident/contact/data collection(MAUDE, DHF, other)/hypothesis/report/court or settle  Examples follow:

Medical Cases:  Enteral feeding tube complication  Pressure limited respiration system  IM Nail accident  Penile implant  Blood oxygenator  Failure to monitor  Failure to perform (car/ventilator/child)

Biomechanics & Traffic Accident Investigations  Data Collection National Highway Transportation Safety Administration (NHTSA) National Highway Transportation Safety Administration (NHTSA)  Injury Estimation Abbreviated Injury Scale (AIS) Abbreviated Injury Scale (AIS)  Impact Analyses Accident report, crush patterns, etc to estimate probable outcome Accident report, crush patterns, etc to estimate probable outcome  Generally collaborate with Orthopedics …

Safety or lawsuit!