Devices That Accommodate Children’s Growth

A unique pediatric problem with the use of certain implanted medical devices is that they either interfere with growth or do not grow as children grow. The approved labeling for a number of orthopedic and other implants describes them as not indicated for individuals with growing bones or skeletal, skull, or other aspect of growth that is less than 90 percent of adult levels.

Some devices or their accessories or the procedures for their use are designed to take children’s growth into account. For example, when surgeons first began to insert the drainage catheter for cerebrospinal fluid shunts into the abdomen, they used tubing just long enough to enter the peritoneal cavity. As children grew these catheters had to be replaced with longer ones. Recent experience suggests that even infants can tolerate a peritoneal catheter long enough to accommodate growth to adulthood . Cardiac pacemaker leads are also implanted so that some significant amount of growth can be accommodated.

Given the risk and discomfort of replacing an implant as a child grows and given the restrictions on the use of certain devices that interfere with growth, implants that can “grow” with a child have obvious appeal. Growing children who have bone cancers removed from their limbs and prosthetic devices inserted have faced repeated surgeries to replace or expand the device to accommodate growth. FDA recently approved a device that can be expanded without surgical intervention. As described by FDA, the device employs “a coil that fits around the patient’s leg that produces an electromagnetic field. The EMF induces an electrical current and subsequent heating of an internal wire [in the implant]. The generated heat softens a polymer locking ring, allowing a slow expansion of an internal compressed spring. The spring expansion pushes the spring housing and femoral housing apart, thus increasing the overall length of the implant”. According to the manufacturer’s webpage, FDA has cleared the device for distal femur and proximal tibia implants, but implants for the humerus, proximal femur, and total femur are only available so far under compassionate use guidelines.

To cite another orthopedic example, pediatric orthopedists treating children with leg fractures have increasingly used flexible titanium nails that support the leg as the bone heals but also provide flexibility for growing bones. For children between the ages of approximately 6 and 12, the technique avoids some of the disadvantages of alternative treatments with either a body cast and traction or certain rigid nailing techniques. This technique has not been associated with problems of arrested growth in the trochanter or osteonecrosis of the head of the femur that have sometimes been reported with rigid nailing techniques.

Interest in another kind of device, the resorbable implant, is particularly strong among those who treat children with certain craniofacial and orthopedic deformities. These implants are adequately rigid to support repair or reconstruction of a deformity for several months, but they then disappear without requiring removal or replacement and without appreciably interfering with a child’s growth. In a statement to the committee, the American Academy of Pediatrics pointed to metal craniofacial fixation devices that create problems with children that are not seen in adults. AAP cited “thinning of scalp leading to annoying prominence of the device . . . subcutaneous migration of screws . . . [and] intracranial migration of the devices”. In the latter process, the device has been engulfed by the child’s growing skull such that “within a few years plates and screws were sometimes found inside the dura resting in the substance of the brain,” a location for which they clearly were not intended.

Until recently, only the results of short-term studies of resorbable implants were available, but investigators have now reported on a combined prospective and retrospective multisite analysis of nearly 2,000 patients under 2 years of age treated over a 5-year period with the same type of device. They found a lower rate of devicerelated complications requiring reoperation than for metal devices and low rates of adverse events. Consistent with a characteristic of device innovation, they noted that “the specific types of plates and screws used evolved over the study period from simple plates, meshes, and threaded screws to application-specific plates and threadless push screws whose use varied among the involved surgeons”.

In an arena that holds potentially broad promise, the emerging field of tissue engineering is exploring the development of devices such as heart valves or skin that become populated by the patient’s living cells . Such devices might grow as young patients grow and also avoid or limit immunocompatibility or biocompatibility problems that are often seen with currently used materials.

Devices That Accommodate Children’s Growth

A unique pediatric problem with the use of certain implanted medical devices is that they either interfere with growth or do not grow as children grow. The approved labeling for a number of orthopedic and other implants describes them as not indicated for individuals with growing bones or skeletal, skull, or other aspect of growth that is less than 90 percent of adult levels.

Some devices or their accessories or the procedures for their use are designed to take children’s growth into account. For example, when surgeons first began to insert the drainage catheter for cerebrospinal fluid shunts into the abdomen, they used tubing just long enough to enter the peritoneal cavity. As children grew these catheters had to be replaced with longer ones. Recent experience suggests that even infants can tolerate a peritoneal catheter long enough to accommodate growth to adulthood . Cardiac pacemaker leads are also implanted so that some significant amount of growth can be accommodated.

Given the risk and discomfort of replacing an implant as a child grows and given the restrictions on the use of certain devices that interfere with growth, implants that can “grow” with a child have obvious appeal. Growing children who have bone cancers removed from their limbs and prosthetic devices inserted have faced repeated surgeries to replace or expand the device to accommodate growth. FDA recently approved a device that can be expanded without surgical intervention. As described by FDA, the device employs “a coil that fits around the patient’s leg that produces an electromagnetic field. The EMF induces an electrical current and subsequent heating of an internal wire [in the implant]. The generated heat softens a polymer locking ring, allowing a slow expansion of an internal compressed spring. The spring expansion pushes the spring housing and femoral housing apart, thus increasing the overall length of the implant”. According to the manufacturer’s webpage, FDA has cleared the device for distal femur and proximal tibia implants, but implants for the humerus, proximal femur, and total femur are only available so far under compassionate use guidelines.

To cite another orthopedic example, pediatric orthopedists treating children with leg fractures have increasingly used flexible titanium nails that support the leg as the bone heals but also provide flexibility for growing bones. For children between the ages of approximately 6 and 12, the technique avoids some of the disadvantages of alternative treatments with either a body cast and traction or certain rigid nailing techniques. This technique has not been associated with problems of arrested growth in the trochanter or osteonecrosis of the head of the femur that have sometimes been reported with rigid nailing techniques.

Interest in another kind of device, the resorbable implant, is particularly strong among those who treat children with certain craniofacial and orthopedic deformities. These implants are adequately rigid to support repair or reconstruction of a deformity for several months, but they then disappear without requiring removal or replacement and without appreciably interfering with a child’s growth. In a statement to the committee, the American Academy of Pediatrics pointed to metal craniofacial fixation devices that create problems with children that are not seen in adults. AAP cited “thinning of scalp leading to annoying prominence of the device . . . subcutaneous migration of screws . . . [and] intracranial migration of the devices”. In the latter process, the device has been engulfed by the child’s growing skull such that “within a few years plates and screws were sometimes found inside the dura resting in the substance of the brain,” a location for which they clearly were not intended.

Until recently, only the results of short-term studies of resorbable implants were available, but investigators have now reported on a combined prospective and retrospective multisite analysis of nearly 2,000 patients under 2 years of age treated over a 5-year period with the same type of device. They found a lower rate of devicerelated complications requiring reoperation than for metal devices and low rates of adverse events. Consistent with a characteristic of device innovation, they noted that “the specific types of plates and screws used evolved over the study period from simple plates, meshes, and threaded screws to application-specific plates and threadless push screws whose use varied among the involved surgeons”.

In an arena that holds potentially broad promise, the emerging field of tissue engineering is exploring the development of devices such as heart valves or skin that become populated by the patient’s living cells . Such devices might grow as young patients grow and also avoid or limit immunocompatibility or biocompatibility problems that are often seen with currently used materials.

DEVICE DESIGN, DEVICE USE, AND DEVELOPMENTAL DIFFERENCES

Children are not small adults—a cliché but true. As described above, children, especially infants and young children, differ from adults in ways that extend beyond the obvious difference in size. These differences may have implications for the design and use of devices and for the methods to evaluate their safety and effectiveness before and after marketing.

Developmental differences between children and adults related to the safe and effective use of medical products have been most extensively analyzed and described for drugs. For drugs, scientists and clinicians have constructed a strong rationale for pediatric drug research to assure the safe and effective use of medications with children. Data indicating that some 80 percent of medications listed in the Physician’s Desk Reference lacked any prescribing information for children have also been cited to build the case for such research.

For medical devices, the committee found nothing equivalent to the pharmacology literature on developmental concerns. With drugs, one is generally considering issues along a spectrum: ingestion, bioavailability, action, untoward actions, metabolism, and disposal of metabolites. This is complex enough. With devices, one might be considering physical interactions, metabolic interactions, and growth, among other factors. Box 2.1 summarizes some of the developmental considerations for drugs compared to medical devices.

To the extent that pediatric considerations are known for a medical device, the labeling of the device should reflect that knowledge. In some cases, labeling will state that use of a device is not indicated in those under a certain age or those who are not skeletally mature. In other cases, the labeling may describe adaptations or cautions related to pediatric use.

DEVICE DESIGN, DEVICE USE, AND DEVELOPMENTAL DIFFERENCES

Children are not small adults—a cliché but true. As described above, children, especially infants and young children, differ from adults in ways that extend beyond the obvious difference in size. These differences may have implications for the design and use of devices and for the methods to evaluate their safety and effectiveness before and after marketing.

Developmental differences between children and adults related to the safe and effective use of medical products have been most extensively analyzed and described for drugs. For drugs, scientists and clinicians have constructed a strong rationale for pediatric drug research to assure the safe and effective use of medications with children. Data indicating that some 80 percent of medications listed in the Physician’s Desk Reference lacked any prescribing information for children have also been cited to build the case for such research.

For medical devices, the committee found nothing equivalent to the pharmacology literature on developmental concerns. With drugs, one is generally considering issues along a spectrum: ingestion, bioavailability, action, untoward actions, metabolism, and disposal of metabolites. This is complex enough. With devices, one might be considering physical interactions, metabolic interactions, and growth, among other factors. Box 2.1 summarizes some of the developmental considerations for drugs compared to medical devices.

To the extent that pediatric considerations are known for a medical device, the labeling of the device should reflect that knowledge. In some cases, labeling will state that use of a device is not indicated in those under a certain age or those who are not skeletally mature. In other cases, the labeling may describe adaptations or cautions related to pediatric use.

Divisions of the U.S. Government Regulating Ionizing

In the United States, no one governmental agency regulates radiation and radioactive materials. Rather, aspects of radiation regulation fall under several agencies. Some of the major agencies are listed below, although the list is not exhaustive.

Nuclear Regulatory Commission.
The Nuclear Regulatory Commission(NRC) is headed by a five-member Commission appointed by the President. The authority for the NRC comes from the Atomic Energy Act of 1954, as amended. The NRC was established by the Energy Reorganization Act of 1974. Because of the historical development of radiation regulations, the NRC formerly only exercised control over reactors and reactor byproduct materials. Thus, naturally occurring radioactive material, radioactive materials produced in particle accelerators andmachine produced radiation fell outside the purview of the NRC.

By these acts, the NRC regulates: Special nuclear material, which is uranium-233, or uranium-235, enriched uranium, or plutonium. Source material, which is natural uranium or thorium or depleted uranium that is not suitable for use as reactor fuel. Byproduct material, which is, generally, nuclear material (other than special nuclear material) that is produced or made radioactive in a nuclear reactor. Most recently, the Energy Policy Act of 2005 extendedNRC authority to include naturally occurring and acceleratorproduced radioactive materials (NARM). Before this time, the individual States regulated NARM with a somewhat non-uniform array of regulations.

Divisions of the U.S. Government Regulating Ionizing

In the United States, no one governmental agency regulates radiation and radioactive materials. Rather, aspects of radiation regulation fall under several agencies. Some of the major agencies are listed below, although the list is not exhaustive.

Nuclear Regulatory Commission.
The Nuclear Regulatory Commission(NRC) is headed by a five-member Commission appointed by the President. The authority for the NRC comes from the Atomic Energy Act of 1954, as amended. The NRC was established by the Energy Reorganization Act of 1974. Because of the historical development of radiation regulations, the NRC formerly only exercised control over reactors and reactor byproduct materials. Thus, naturally occurring radioactive material, radioactive materials produced in particle accelerators andmachine produced radiation fell outside the purview of the NRC.

By these acts, the NRC regulates: Special nuclear material, which is uranium-233, or uranium-235, enriched uranium, or plutonium. Source material, which is natural uranium or thorium or depleted uranium that is not suitable for use as reactor fuel. Byproduct material, which is, generally, nuclear material (other than special nuclear material) that is produced or made radioactive in a nuclear reactor. Most recently, the Energy Policy Act of 2005 extendedNRC authority to include naturally occurring and acceleratorproduced radioactive materials (NARM). Before this time, the individual States regulated NARM with a somewhat non-uniform array of regulations.

MEDICAL DEVICES WITH A HIGH OCCURRENCE OF HUMAN ERROR

Over the years, many studies have been performed to identify medical devices that have a high incidence of human error. As the result of these studies, the most errorprone medical devices were identified.

These devices include (in the order of most error-prone to least error-prone) glucose meter, balloon catheter, orthodontic bracket aligner, administration kit for peritoneal dialysis, permanent pacemaker electrode, implantable spinal cord simulator, intra-vascular catheter, infusion pump, urological catheter, electrosurgical cutting and coagulation device, nonpowered suction apparatus, mechanical/hydraulic impotence device, implantable pacemaker, peritoneal dialysate delivery system, catheter introducer, catheter guidewire, transluminal coronary angioplasty catheter, external low-energy defibrillator, continuous ventilator (respirator), and contact lens cleaning and disinfecting solutions. According to reference 29, the errors in using medical devices cause, on average, at least three deaths or serious injuries each day.

MEDICAL DEVICES WITH A HIGH OCCURRENCE OF HUMAN ERROR

Over the years, many studies have been performed to identify medical devices that have a high incidence of human error. As the result of these studies, the most errorprone medical devices were identified.

These devices include (in the order of most error-prone to least error-prone) glucose meter, balloon catheter, orthodontic bracket aligner, administration kit for peritoneal dialysis, permanent pacemaker electrode, implantable spinal cord simulator, intra-vascular catheter, infusion pump, urological catheter, electrosurgical cutting and coagulation device, nonpowered suction apparatus, mechanical/hydraulic impotence device, implantable pacemaker, peritoneal dialysate delivery system, catheter introducer, catheter guidewire, transluminal coronary angioplasty catheter, external low-energy defibrillator, continuous ventilator (respirator), and contact lens cleaning and disinfecting solutions. According to reference 29, the errors in using medical devices cause, on average, at least three deaths or serious injuries each day.

REGULATORY STANDARDS FOR RADIOACTIVE

Use of IR in medical, dental, and veterinary facilities is governed by either federal or state regulations. The NRC, drawing its authority from the Atomic Energy Act of 1954, regulates byproduct material, source material, and special nuclear material, and their uses. Here OSHA controls IR sources (X-ray machine, accelerators, accelerator-produced materials, electron microscopes, betatrons, and technology-enhanced naturally occurring radioactive materials) not covered by the Atomic Energy Act of 1954 and not regulated by the NRC.

A 1989 ‘‘Memorandum of Understanding. . .’’ defined responsibilities and authorities of each agency. Each agency has arrangements with some states for regulatory enforcement. NRC has an Agreement State Program, by which a State can sign a formal agreement with the NRC to assume NRC regulatory authority and responsibility over certain byproduct, source, and small quantities of special nuclear material. There are 33 States, listed in Table 4, with two (Pennsylvania and Minnesota) in the process of becoming Agreement States.

The Atomic Energy Act of 1954 provides a statutory basis under which NRC relinquishes to the states portions of its regulatory authority to license and regulate byproduct materials (radioisotopes); source materials (uranium and thorium); and certain quantities of special nuclear materials. The mechanism for the transfer of authority to a state is an agreement signed by the Governor of the State and the Chairman of the Commission.

The NRC has established compatibility obligations with the Agreement State regarding its current rules and future regulations that it may promulgate. Because twothirds of the states have assumed Agreement status, the NRC has provided them increasing voice in their activities. This is done through the NRC Office of Tribal and State Programs and the independent Organization of Agreement States (OAS). Both can be accessed via the URL, http:// www.nrc.gov/what-we-do/state-tribal/agreement-states. html. The NRC regulations apply in federal facilities directly holding federal licenses and in the nonagreement states. Agreement states have certain periods within which state regulations must become compliant, at certain levels of compliance, with NRC regulations. During this transition period state regulatory agencies enforce their current state regulations, based on NRC regulations in force prior to the regulatory changes, as they prepare new state regulations compliant with the recent revisions changes in federal codes. Twenty-six states have OSHA-approved state plans with their individual state standards and enforcement policies.

REGULATORY STANDARDS FOR RADIOACTIVE

Use of IR in medical, dental, and veterinary facilities is governed by either federal or state regulations. The NRC, drawing its authority from the Atomic Energy Act of 1954, regulates byproduct material, source material, and special nuclear material, and their uses. Here OSHA controls IR sources (X-ray machine, accelerators, accelerator-produced materials, electron microscopes, betatrons, and technology-enhanced naturally occurring radioactive materials) not covered by the Atomic Energy Act of 1954 and not regulated by the NRC.

A 1989 ‘‘Memorandum of Understanding. . .’’ defined responsibilities and authorities of each agency. Each agency has arrangements with some states for regulatory enforcement. NRC has an Agreement State Program, by which a State can sign a formal agreement with the NRC to assume NRC regulatory authority and responsibility over certain byproduct, source, and small quantities of special nuclear material. There are 33 States, listed in Table 4, with two (Pennsylvania and Minnesota) in the process of becoming Agreement States.

The Atomic Energy Act of 1954 provides a statutory basis under which NRC relinquishes to the states portions of its regulatory authority to license and regulate byproduct materials (radioisotopes); source materials (uranium and thorium); and certain quantities of special nuclear materials. The mechanism for the transfer of authority to a state is an agreement signed by the Governor of the State and the Chairman of the Commission.

The NRC has established compatibility obligations with the Agreement State regarding its current rules and future regulations that it may promulgate. Because twothirds of the states have assumed Agreement status, the NRC has provided them increasing voice in their activities. This is done through the NRC Office of Tribal and State Programs and the independent Organization of Agreement States (OAS). Both can be accessed via the URL, http:// www.nrc.gov/what-we-do/state-tribal/agreement-states. html. The NRC regulations apply in federal facilities directly holding federal licenses and in the nonagreement states. Agreement states have certain periods within which state regulations must become compliant, at certain levels of compliance, with NRC regulations. During this transition period state regulatory agencies enforce their current state regulations, based on NRC regulations in force prior to the regulatory changes, as they prepare new state regulations compliant with the recent revisions changes in federal codes. Twenty-six states have OSHA-approved state plans with their individual state standards and enforcement policies.

Introduction of Ultrasonic Imaging

Medical imaging has many modalities and most of themprovide clinicians with unique features of a
volume ofinterest (VOI) resulting from a chosen modality. Ultrasonicimaging is one technique for
collecting anatomical andphysiological information from within the human body.It can be used for
diagnosis (imaging) and for image-guidedtherapy, where therapeutic intervention can be appliedwith
direct image-based feedback. Other modalitiesinclude X ray (roentgen radiation), CT (computed
tomography),MRI (magnetic resonance imaging), PET or PET/CT (positron emission tomography), and
SPECT (singlephoton emission computed tomography).

In contrast tomost other imaging techniques, ultrasonic imaging is veryattractive to professionals
because it is cheap, real time(with>100 full frame images per second, >100 Hz), and ituses
nonionizing radiation. Moreover, current clinicalultrasound machines can be integrated into laptop
computerswith very little external hardware for maximum portabilityand versatility. These combined
features allow theuse of ultrasonic imaging in a wide variety of settings, fromprivate physician
practices, to ambulances with on-siteparamedics, to battle field situations, where very robustand
lightweight equipment is required. Many other uses ofultrasonic imaging are found in science and
industry theseinclude, for example, ultrasonic microscopy, nondestructivetesting and touch sensitive
screens.

Introduction of Ultrasonic Imaging

Medical imaging has many modalities and most of themprovide clinicians with unique features of a
volume ofinterest (VOI) resulting from a chosen modality. Ultrasonicimaging is one technique for
collecting anatomical andphysiological information from within the human body.It can be used for
diagnosis (imaging) and for image-guidedtherapy, where therapeutic intervention can be appliedwith
direct image-based feedback. Other modalitiesinclude X ray (roentgen radiation), CT (computed
tomography),MRI (magnetic resonance imaging), PET or PET/CT (positron emission tomography), and
SPECT (singlephoton emission computed tomography).

In contrast tomost other imaging techniques, ultrasonic imaging is veryattractive to professionals
because it is cheap, real time(with>100 full frame images per second, >100 Hz), and ituses
nonionizing radiation. Moreover, current clinicalultrasound machines can be integrated into laptop
computerswith very little external hardware for maximum portabilityand versatility. These combined
features allow theuse of ultrasonic imaging in a wide variety of settings, fromprivate physician
practices, to ambulances with on-siteparamedics, to battle field situations, where very robustand
lightweight equipment is required. Many other uses ofultrasonic imaging are found in science and
industry theseinclude, for example, ultrasonic microscopy, nondestructivetesting and touch sensitive
screens.

PHYSICAL PRINCIPLES of Ultrasound

Ultrasonic imaging is based on ultrasound, which is soundproduced at frequencies beyond those detectable in humanhearing, that is, >20 kHz. In the same way that ultraviolet(UV) light is invisible to the human eye, ultrasound isinaudible to the human ear. Often objects that serve ascarriers for ultrasound waves need to be treated as waveguides.Nonlinear effects become apparent for ultrasoundpropagation when leaving the range of elastic deformationduring the propagation of waves through a medium.Physical material constants form ultrasound parameters,for example the speed of sound or the attenuation ofsound. Very high frequency sound waves are treated byquantum acoustic laws. Historically, ultrasound wasproduced by oscillating platelets, or pipes.

Magnetostrictionand the piezoelectric effect followed, and are still very much relevantmechanisms for medical and industrial ultrasound. In1918, it was found that the use of oscillating crystals couldbe used to stabilize frequencies. The upper frequency forsound in a given solid material is determined by theseparation of neighboring atoms in the host medium. Thisupper frequency limit is met when neighboring atoms,assuming the linear chain model, oscillate with a 1808phase shift, the so-called optical branch of oscillations ina solid.

PHYSICAL PRINCIPLES of Ultrasound

Ultrasonic imaging is based on ultrasound, which is soundproduced at frequencies beyond those detectable in humanhearing, that is, >20 kHz. In the same way that ultraviolet(UV) light is invisible to the human eye, ultrasound isinaudible to the human ear. Often objects that serve ascarriers for ultrasound waves need to be treated as waveguides.Nonlinear effects become apparent for ultrasoundpropagation when leaving the range of elastic deformationduring the propagation of waves through a medium.Physical material constants form ultrasound parameters,for example the speed of sound or the attenuation ofsound. Very high frequency sound waves are treated byquantum acoustic laws. Historically, ultrasound wasproduced by oscillating platelets, or pipes.

Magnetostrictionand the piezoelectric effect followed, and are still very much relevantmechanisms for medical and industrial ultrasound. In1918, it was found that the use of oscillating crystals couldbe used to stabilize frequencies. The upper frequency forsound in a given solid material is determined by theseparation of neighboring atoms in the host medium. Thisupper frequency limit is met when neighboring atoms,assuming the linear chain model, oscillate with a 1808phase shift, the so-called optical branch of oscillations ina solid.

Spectrum of Medical Device Use with Children

The use of medical devices with children spans a wide spectrum, includingdevices that are used uniquely with children, devices that are reduced insize or otherwise modified for use with children, and devices that do notdiffer for adult and pediatric use. Use with children is explicitly precluded for some devices.Box 2.2 and the following discussion illustrate the spectrum of pediatricdevice use. The use of particular devices as examples does not necessarilyimply a committee judgment that the devices have been adequatelystudied for short- or long-term safety or effectiveness in use with children.Sometimes children, especially infants, have unique needs or conditionsfor which specialized devices are developed. The infant incubator is anobvious example.

In addition, children may so dominate the target population in need ofa device that the consideration of adult users is secondary rather thanprimary. One example of a device initially developed for children is theatrial septaloccluder. It was originally intended to treat children who havea hole in the wall separating the inflow chambers of the left and right sidesof the heart, but it has also been used to treat adults with that condition. To cite another example,FDA recently granted limited approval for a pulmonary valved conduit (akind of heart valve) that is, again, primarily intended to correct congenitalheart defects in children but can be used with adults. Although congenital heart disease is sometimes regarded as acondition of children, estimates suggest that there are at least as manyadults living with congenital heart disease as there are children.

Spectrum of Medical Device Use with Children

The use of medical devices with children spans a wide spectrum, includingdevices that are used uniquely with children, devices that are reduced insize or otherwise modified for use with children, and devices that do notdiffer for adult and pediatric use. Use with children is explicitly precluded for some devices.Box 2.2 and the following discussion illustrate the spectrum of pediatricdevice use. The use of particular devices as examples does not necessarilyimply a committee judgment that the devices have been adequatelystudied for short- or long-term safety or effectiveness in use with children.Sometimes children, especially infants, have unique needs or conditionsfor which specialized devices are developed. The infant incubator is anobvious example.

In addition, children may so dominate the target population in need ofa device that the consideration of adult users is secondary rather thanprimary. One example of a device initially developed for children is theatrial septaloccluder. It was originally intended to treat children who havea hole in the wall separating the inflow chambers of the left and right sidesof the heart, but it has also been used to treat adults with that condition. To cite another example,FDA recently granted limited approval for a pulmonary valved conduit (akind of heart valve) that is, again, primarily intended to correct congenitalheart defects in children but can be used with adults. Although congenital heart disease is sometimes regarded as acondition of children, estimates suggest that there are at least as manyadults living with congenital heart disease as there are children.

Machine-Produced Radiation

While much of machine-produced radiation is coveredby state regulations, when used on humans applicationsmanufacture of the units falls under the auspicesof the FDA. The FDA rules can be found in 21 CFR 1020.For the most part, the state regulations follow the FDAguidances when applicable, but sometimes with a sizabledelay.

Mammography forms a notable exception to thegeneral lack of federal control over machine-producedradiation in medicine. Based on the MQSA, as notedabove, the FDA sets requirements for practitioners onmammography, and failure to satisfy the requirementsprevents providers from obtaining reimbursement fromgovernment sources. The requirements for mammographyequipment are given below in the section onDiagnostic Units. In addition, there are considerablerequirements placed on the training and experience ofthe persons involved: the radiologist, the radiographer, and the medical physicist.

Radiation producing machines fall into three maincategories discussed in the following sections.

Machine-Produced Radiation

While much of machine-produced radiation is coveredby state regulations, when used on humans applicationsmanufacture of the units falls under the auspicesof the FDA. The FDA rules can be found in 21 CFR 1020.For the most part, the state regulations follow the FDAguidances when applicable, but sometimes with a sizabledelay.

Mammography forms a notable exception to thegeneral lack of federal control over machine-producedradiation in medicine. Based on the MQSA, as notedabove, the FDA sets requirements for practitioners onmammography, and failure to satisfy the requirementsprevents providers from obtaining reimbursement fromgovernment sources. The requirements for mammographyequipment are given below in the section onDiagnostic Units. In addition, there are considerablerequirements placed on the training and experience ofthe persons involved: the radiologist, the radiographer, and the medical physicist.

Radiation producing machines fall into three maincategories discussed in the following sections.

MEDICAL EQUIPMENT CLASSIFICATION

As the health care system uses a large variety of electronic equipment, it can be grouped into three major classifications:

A, B, and C.

Classification A includes medical equipment/devices that are directly and immediatelyresponsible for the patient’s life or may become so in emergencies. Morespecifically, when this type of equipment fails, there is seldom sufficient time forrepair. Therefore, this equipment must always operate at the moment of need. Itmust have high reliability. Some examples of the Classification A equipment are cardiac pacemakers, cardiac defibrillators, respirators, and electro-cardiographicmonitors.

Classification B contains a vast majority of medical equipment used for routineor semi-emergency diagnostic or therapeutic purposes. Failure of such equipmentdoes not result in the same emergency as in the case of Classification A equipmentbecause there is time for repair. Some of the devices that fall under this classificationare ultrasound equipment, spectrophotometers, electrocardiograph andelectroencephalographrecorders and monitors, gas analyzers, colorimeters, and diathermyequipment.
Classification C contains equipment that is not critical to a patient’s life orwelfare but simply serves as a convenience equipment. Two examples of the ClassificationC equipment are wheelchairs andbedside television sets.

All in all, there could be some overlap between these three classifications ofequipment, particularly between Classifications A and B.After the passage of the Medical Device Amendments of 1976, the FDA classifieddevices marketed prior to 1976 into the following three categories:

Category I
This contained devices in which general controls such as
good manufacturing practices were considered satisfactory with respect
to safety and efficacy.

Category II
This contained devices in which general controls were
considered insufficient with respect to safety and efficacy and in which
performancestandards could be established.Medical Device Reliability and Associated Areas

Category III
This contained devices in which the manufacturer isrequired to submit evidence of safety and efficacy with the aid of welldesignedstudies. More specifically, the devices included in this categorysupport life, prevent health impairment, or present an unreasonable riskof injury or illness and need FDA approval prior to their marketing.

MEDICAL EQUIPMENT CLASSIFICATION

As the health care system uses a large variety of electronic equipment, it can be grouped into three major classifications:

A, B, and C.

Classification A includes medical equipment/devices that are directly and immediatelyresponsible for the patient’s life or may become so in emergencies. Morespecifically, when this type of equipment fails, there is seldom sufficient time forrepair. Therefore, this equipment must always operate at the moment of need. Itmust have high reliability. Some examples of the Classification A equipment are cardiac pacemakers, cardiac defibrillators, respirators, and electro-cardiographicmonitors.

Classification B contains a vast majority of medical equipment used for routineor semi-emergency diagnostic or therapeutic purposes. Failure of such equipmentdoes not result in the same emergency as in the case of Classification A equipmentbecause there is time for repair. Some of the devices that fall under this classificationare ultrasound equipment, spectrophotometers, electrocardiograph andelectroencephalographrecorders and monitors, gas analyzers, colorimeters, and diathermyequipment.
Classification C contains equipment that is not critical to a patient’s life orwelfare but simply serves as a convenience equipment. Two examples of the ClassificationC equipment are wheelchairs andbedside television sets.

All in all, there could be some overlap between these three classifications ofequipment, particularly between Classifications A and B.After the passage of the Medical Device Amendments of 1976, the FDA classifieddevices marketed prior to 1976 into the following three categories:

Category I
This contained devices in which general controls such as
good manufacturing practices were considered satisfactory with respect
to safety and efficacy.

Category II
This contained devices in which general controls were
considered insufficient with respect to safety and efficacy and in which
performancestandards could be established.Medical Device Reliability and Associated Areas

Category III
This contained devices in which the manufacturer isrequired to submit evidence of safety and efficacy with the aid of welldesignedstudies. More specifically, the devices included in this categorysupport life, prevent health impairment, or present an unreasonable riskof injury or illness and need FDA approval prior to their marketing.

B-Mode Ultrasound

B-mode is one of the most commonly used operation modesof a clinical ultrasound scanner. As explained earlier,ultrasound is a reflection or scattering based imagingmodality, and the sophisticated generation of a sound waveallows the focusing of the sound to a specific location. Eachtransmission yields one scan line around the targeted focalpoint. If only one focal point is selected, one scan lineextends over the total depth range, which is user definedin the current imaging settings. In order to record a fullimage frame using a linear array, the imaging software ofthe scanner electronically moves the active aperture of thearray across the physical aperture to transmit and receive at a given line density.

Typically, hundreds of scan linesare generated this way and displayed on a monitor.Figure 12 shows the cross-sectional sagittal (front to back,vertical slice) image of a fetus in utero. She is sucking onher thumb, as real-time video reveals. On the left of Fig. 12one can see the head and the strong reflection of the skullbone. The very left side of the image is black, an artifactthat could be due to maternal bowel gases that scatter thesound away from the transducer. The remainder of theskull is clearly visible from the forehead to the chin andfrom the back of the head to the neck area. Bones reflectsound waves well and result in a bright signal in the image.The black surroundings of the fetus are regions of amnioticfluid, which does not scatter sound due to the homogeneousnature of the fluid. .

In front of the mouth, one can see the hand of the fetus.Once again the bones of the hand, namely, the knuckles,are pronounced since they scatter more ultrasound thanthe soft tissue of the hand. In the same fashion one can seethe reflections of the spine.

B-Mode Ultrasound

B-mode is one of the most commonly used operation modesof a clinical ultrasound scanner. As explained earlier,ultrasound is a reflection or scattering based imagingmodality, and the sophisticated generation of a sound waveallows the focusing of the sound to a specific location. Eachtransmission yields one scan line around the targeted focalpoint. If only one focal point is selected, one scan lineextends over the total depth range, which is user definedin the current imaging settings. In order to record a fullimage frame using a linear array, the imaging software ofthe scanner electronically moves the active aperture of thearray across the physical aperture to transmit and receive at a given line density.

Typically, hundreds of scan linesare generated this way and displayed on a monitor.Figure 12 shows the cross-sectional sagittal (front to back,vertical slice) image of a fetus in utero. She is sucking onher thumb, as real-time video reveals. On the left of Fig. 12one can see the head and the strong reflection of the skullbone. The very left side of the image is black, an artifactthat could be due to maternal bowel gases that scatter thesound away from the transducer. The remainder of theskull is clearly visible from the forehead to the chin andfrom the back of the head to the neck area. Bones reflectsound waves well and result in a bright signal in the image.The black surroundings of the fetus are regions of amnioticfluid, which does not scatter sound due to the homogeneousnature of the fluid. .

In front of the mouth, one can see the hand of the fetus.Once again the bones of the hand, namely, the knuckles,are pronounced since they scatter more ultrasound thanthe soft tissue of the hand. In the same fashion one can seethe reflections of the spine.

Adjustments in Medical Device Size

Sometimes the physical size of a medical device is the main issue withpediatric use. Infant or child versions exist for many common medicaldevices such as hospital beds, bandages, and scales.

More complex devices can often be manufactured in sizes to fit all ormost pediatric uses without compromising their structure or function. Forexample, leads for implanted cardiac pacemakers used with children can bemade shorter than adult leads without compromising their function, althoughsurgical implantation techniques may vary, especially with infants.To cite another example, a saline-filled testicular prosthetic implant thathas been tested in adults and children with a congenitally absent or surgicallyremoved testicle is now available in an extra small size. For this and other implanted devices, replacement with alarger size may be anticipated to accommodate a child’s growth. Intraocular lens replacement, which has long benefited adults sufferingfrom cataracts, can also help children with certain vision problems. Thesizes of the replacement lenses developed for adults are not, however, appropriatefor young children. In addition, the surgicalprocedure must accommodate developmental considerations such as lowerscleral rigidity, greater elasticity of the anterior capsule, and higher vitreouspressure.

For certain implanted devices, reductions in size have brought benefitsto both children and adults. The cardiac pacemaker is a notable example. Figure show the difference in size between an externalpacemaker that was designed to provide short-term life supportand a recent implantable pacemaker that offers long-term support.

In some cases, sizing of a device is done at the time of use. For example,cardiac shunts or tubes that are used to connect two blood vessels come indifferent diameters. The appropriate length is determined by the surgeonwho cuts them to size just before insertion.

Size adjustments may not be straightforward, even for relatively simpledevices. A case in point involves tracheostomy tubes, which are adjusted tofit different size windpipes by creating an array of sizes that vary by incrementsof 0.5 mm in diameter and simultaneously differ in length. In a childwith an abnormally narrow airway, the tube with the appropriate diametermay be too short, which can cause it to become dislodged. Specially constructedtubes can be ordered from the manufacturer, but this option is notfeasible in an emergency situation.

Lack of a device in sizes appropriate for the full range of pediatricpatients may limit the use of certain interventions. For example, in intracardiacechocardiography (an imaging technique used to guide certain cardiacprocedures), the size of the catheter used in the procedure has limited use with very young patients. The technique, which has not been fully tested inrandomized clinical trials, avoids an imaging procedure that requires intubation and general anesthesia.

Adjustments in Medical Device Size

Sometimes the physical size of a medical device is the main issue withpediatric use. Infant or child versions exist for many common medicaldevices such as hospital beds, bandages, and scales.

More complex devices can often be manufactured in sizes to fit all ormost pediatric uses without compromising their structure or function. Forexample, leads for implanted cardiac pacemakers used with children can bemade shorter than adult leads without compromising their function, althoughsurgical implantation techniques may vary, especially with infants.To cite another example, a saline-filled testicular prosthetic implant thathas been tested in adults and children with a congenitally absent or surgicallyremoved testicle is now available in an extra small size. For this and other implanted devices, replacement with alarger size may be anticipated to accommodate a child’s growth. Intraocular lens replacement, which has long benefited adults sufferingfrom cataracts, can also help children with certain vision problems. Thesizes of the replacement lenses developed for adults are not, however, appropriatefor young children. In addition, the surgicalprocedure must accommodate developmental considerations such as lowerscleral rigidity, greater elasticity of the anterior capsule, and higher vitreouspressure.

For certain implanted devices, reductions in size have brought benefitsto both children and adults. The cardiac pacemaker is a notable example. Figure show the difference in size between an externalpacemaker that was designed to provide short-term life supportand a recent implantable pacemaker that offers long-term support.

In some cases, sizing of a device is done at the time of use. For example,cardiac shunts or tubes that are used to connect two blood vessels come indifferent diameters. The appropriate length is determined by the surgeonwho cuts them to size just before insertion.

Size adjustments may not be straightforward, even for relatively simpledevices. A case in point involves tracheostomy tubes, which are adjusted tofit different size windpipes by creating an array of sizes that vary by incrementsof 0.5 mm in diameter and simultaneously differ in length. In a childwith an abnormally narrow airway, the tube with the appropriate diametermay be too short, which can cause it to become dislodged. Specially constructedtubes can be ordered from the manufacturer, but this option is notfeasible in an emergency situation.

Lack of a device in sizes appropriate for the full range of pediatricpatients may limit the use of certain interventions. For example, in intracardiacechocardiography (an imaging technique used to guide certain cardiacprocedures), the size of the catheter used in the procedure has limited use with very young patients. The technique, which has not been fully tested inrandomized clinical trials, avoids an imaging procedure that requires intubation and general anesthesia.

CRCPD Model Regulations

Since the CRCPD model program serves as the basis formany of the state rules, we will consider the provisionshere for regulations dealing with ionizing radiation notfrom byproduct material. Because of the compatibilityrequirement to become an agreement state, those parts ofthe CRCPD model regulations that deal with materialunder NRC oversight follow the federal rules as discussedabove. Thus, these need not be considered here.

The FDAdoes impose some requirements on the manufacturers ofradioactive materials and radiation-producing machinesintended for human use, but that leaves the use ofmachine-produced radiation and naturally occurring andaccelerator-produced radionuclides only under the controlof individual states.

The model regulations fall into many sections, with eachsection covering a particular part of radiation safety.General rules that apply to all applications and followthe NRC notably Parts 19 and 20 come in sections in thebeginning. In addition to the general provisions, each ofthe parts that deal with particular applications all havesections addressing shielding and survey requirements forthe modality (such that the radiation levels satisfy Part 20limits), safety requirements for operation (such as doorinterlocks to prevent walking in during irradiation),ventilation if airborne radionuclide production is possible,record retention requirements and training andexperience.

CRCPD Model Regulations

Since the CRCPD model program serves as the basis formany of the state rules, we will consider the provisionshere for regulations dealing with ionizing radiation notfrom byproduct material. Because of the compatibilityrequirement to become an agreement state, those parts ofthe CRCPD model regulations that deal with materialunder NRC oversight follow the federal rules as discussedabove. Thus, these need not be considered here.

The FDAdoes impose some requirements on the manufacturers ofradioactive materials and radiation-producing machinesintended for human use, but that leaves the use ofmachine-produced radiation and naturally occurring andaccelerator-produced radionuclides only under the controlof individual states.

The model regulations fall into many sections, with eachsection covering a particular part of radiation safety.General rules that apply to all applications and followthe NRC notably Parts 19 and 20 come in sections in thebeginning. In addition to the general provisions, each ofthe parts that deal with particular applications all havesections addressing shielding and survey requirements forthe modality (such that the radiation levels satisfy Part 20limits), safety requirements for operation (such as doorinterlocks to prevent walking in during irradiation),ventilation if airborne radionuclide production is possible,record retention requirements and training andexperience.

NEED OF RELIABILITY IN MEDICAL DEVICES

A modern hospital uses more than 5000 types of medical devices, ranging from asimple tongue depressor to a complex pacemaker. The criticality of their reliabilitymay vary from device to device. The failure of medical devices in the past due tohardware and other reasons has been very costly in terms of fatalities, injuries, dollars and cents, etc.

Furthermore, some of today’s medical devices have becomevery complex and are expected to operate under a stringent environment, thus puttingmore pressure on their reliability assurance during the design phase. Other instrumentalfactors requiring better reliability of medical devices include:? Liability suits? Public pressure? Government regulations: one typical example of such regulations is theMedical Device Amendments to the Federal Food, Drug and CosmeticAct in 1976, thus empowering the Food and Drug Administration (FDA)to regulate medical devices during their design and development phases.

Since 1976, the FDA demands that all medical devices be safe and effectivefor their intended purpose and in fact in the mid 1980s, the FDAadded the term reliability to its original demand. Subjecting a medicaldevice to a reliability program provides a systematic approach to theproduct development process and assures that the regulatory requirementsare adequately satisfied. It also gives confidence to a certain degree thatinspection by regulatory bodies will not lead to major discrepancies. Allin all, improved reliability medical devices will be safe, cost-effective,and easy to maintain.

NEED OF RELIABILITY IN MEDICAL DEVICES

A modern hospital uses more than 5000 types of medical devices, ranging from asimple tongue depressor to a complex pacemaker. The criticality of their reliabilitymay vary from device to device. The failure of medical devices in the past due tohardware and other reasons has been very costly in terms of fatalities, injuries, dollars and cents, etc.

Furthermore, some of today’s medical devices have becomevery complex and are expected to operate under a stringent environment, thus puttingmore pressure on their reliability assurance during the design phase. Other instrumentalfactors requiring better reliability of medical devices include:? Liability suits? Public pressure? Government regulations: one typical example of such regulations is theMedical Device Amendments to the Federal Food, Drug and CosmeticAct in 1976, thus empowering the Food and Drug Administration (FDA)to regulate medical devices during their design and development phases.

Since 1976, the FDA demands that all medical devices be safe and effectivefor their intended purpose and in fact in the mid 1980s, the FDAadded the term reliability to its original demand. Subjecting a medicaldevice to a reliability program provides a systematic approach to theproduct development process and assures that the regulatory requirementsare adequately satisfied. It also gives confidence to a certain degree thatinspection by regulatory bodies will not lead to major discrepancies. Allin all, improved reliability medical devices will be safe, cost-effective,and easy to maintain.

CAUSES OF PATIENT INJURIES AND MEDICAL DEVICE ACCIDENT CLASSIFICATION

Before we discuss the topic of human error further, let us examine the causes ofpatient injuries and medical device accident classification because both subjectsdirectly or indirectly relate to the occurrence of human error.

Over the years, professionals working in the medical field have identified eightfundamental mechanisms, as shown in Figure, through which patients (or Medical Device Reliability and Associated Areaspersonnel) may be injured or killed.


The understanding of these mechanisms orcauses is essential to determine the extent to which a device’s design or use mayhave contributed to the occurrence of an accident.

Medical device accidents may be classified into seven categories: operator orpatient error,manufacturing defect, design deficiency, abnormal or idiosyncraticpatient response, faulty preventive maintenance, repair or calibration, random componentfailure, and sabotage or malicious intent.

CAUSES OF PATIENT INJURIES AND MEDICAL DEVICE ACCIDENT CLASSIFICATION

Before we discuss the topic of human error further, let us examine the causes ofpatient injuries and medical device accident classification because both subjectsdirectly or indirectly relate to the occurrence of human error.

Over the years, professionals working in the medical field have identified eightfundamental mechanisms, as shown in Figure, through which patients (or Medical Device Reliability and Associated Areaspersonnel) may be injured or killed.


The understanding of these mechanisms orcauses is essential to determine the extent to which a device’s design or use mayhave contributed to the occurrence of an accident.

Medical device accidents may be classified into seven categories: operator orpatient error,manufacturing defect, design deficiency, abnormal or idiosyncraticpatient response, faulty preventive maintenance, repair or calibration, random componentfailure, and sabotage or malicious intent.