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.