The roles of surveillance and epidemiology

Effective surveillance of medical devices may include collecting adequate information on the materials involved. Other chapters in this book discuss in more detail the importance of data on the exact identity of devices used; this information can be cross-referenced to find the particular materials.

Epidemiologic studies of devices can be designed to take advantage of knowledge about the device materials. For example, devices made of different materials can be compared against each other to study performance and safety characteristics. When such studies are designed, a common bias to consider is 'confounding by indication'. For example, a cemented hip prosthesis offers quick recovery time but is susceptible to cracking and failure over time; it might be appropriate for a person with an expected remaining life of less than 10 years, but inappropriate for a heavy or active person [38];

Table 19.2 Reported adverse events related to device materials, by tissue reaction, device involved, and specific description

Tissue reaction

Examples of devices involved

Description

Irritant contact dermatitis

Allergic contact dermatitis, allergic contact hypersensitivity, or delayed hypersensitivity Immediate allergic local contact hypersensitivity Immediate allergic general hypersensitivity, anaphylaxis type

Anaphylactoid reaction

Gloves

External part of cochlear implant system

Latex gloves

Latex gloves

Latex

Polyurethane-elastomeric hydrogel composite midline venous catheters Dialysis membranes that have been improperly prepared for their first use Polyacrylonitrile (PAN)

hemodialysis membranes Leukocyte filters Low-density lipoprotein filtering columns

Dried, cracked, or split skin is caused by the physical irritation of the glove, glove powder, or moisture [5] Skin irritation can be caused by rubbing, necessitating changing the magnet strength (the magnet holds the external part in place on the skin) or temporary removal of the external part [6,7] Blistering, itching, crusting, or oozing skin lesions appear 1-3 days after the exposure [5,8]

Skin urticaria (hives) occurs immediately and can progress to a generalized reaction [5,9,10]

Symptoms include allergic rhinoconjunctivitis and can progress rapidly to asthma, swelling of lips and airways, shortness of breath, shock, and death. This can occur with contact on the skin, a mucous membrane, the lungs (via airborne particles), or surgically exposed tissue [5,9]

The hydrogel, meant to soften after insertion and make the catheter more comfortable, has been reported to cause immediate severe allergic reaction [11,12]

This is called 'First Use Syndrome' and is an anaphylactic reaction to sterilizing substances left on the membrane after production [13,14]

The reaction is clinically similar to anaphylaxis, but is caused by a different mechanism (bradykinin pathway) and is potentiated by angiotensin-converting enzyme (ACE) inhibitor medications [15-25]

(Continued)

Table 19.2 (Continued)

Tissue reaction

Examples of devices involved

Description

Blood coagulation

Neurotoxicity

Foreign body reaction, granulomatous type

Mercury toxicity

Liver toxin

Ulcer

Prosthetic heart valves

At least 10 year-old cellulose acetate hemodialysis membranes

Silicone gel breast implants, either intact or ruptured

Hip prostheses

Mercury amalgam tooth fillings

Polyurethane breakdown products

Soft hydrophilic polymer contact lenses

Unless anticoagulants are taken, the prosthesis can cause blood coagulation, increasing the risk of blood clots [26] Severe neurologic symptoms, including decreased vision and hearing, conjunctivitis, and headache, developed in seven patients within 7-24 hours after being exposed to the cellulose acetate breakdown products in membranes that were over 11 years old [27,29] Granulomatous reactions to the silicone membrane and to the escaped gel have been noted in surgical specimens. The result of the process is scarring around the implant that forms a capsule, which can contract, resulting in hardness and pain (see Chapter 27) Wear can cause particles to be ground off the prosthesis, provoking a granulomatous reaction in the joint, which leads to aseptic loosening [30] There are controversial claims that enough mercury vaporizes or is ground off the surface of the fillings to gradually poison the patient or the patient's fetus. Reported effects have included impaired neurologic development during childhood, neurotoxicity, kidney dysfunction, and reduced immunocompetence [31,32]

Polyurethane foam has been used to cover implanted electric lead wires [34], silicone breast implants [35], and as a potting material in hemodialyzers [33]. It has been shown to be hepatotoxic in humans [33] These reduce oxygen flow to the cornea; if wear is prolonged, an ulcer can form [36,37]

the outcomes that are assessed in a study that compares these two types of hip joints may be affected more by the different patient characteristics than by the hip joints used. Another example is surgical gloves: vinyl is much less allergenic than latex, but latex has much better performance characteristics. Studying latex sensitivity among users of vinyl, compared to users of latex, could be confounded by the users' actual or feared latex sensitivity. Latex has many interesting features that impact epidemiologic study design, as discussed in the following section.

Figure 19.2 Latex medical or surgical gloves. Photograph by S. LoriBrown, PhD, MPH, used with her permission
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