Medical Device and Prosthesis Infection

Prosthesis Infection

How to suspect one has a medical device or prosthesis Þ Note scars on patient and ask them about the cause

If one finds acute inflammation associated with a prosthetic device which has been implanted over a year ago Þ suspect a prosthetic associated infection

Thrombotic accumulation on a prosthetic aortic valve Þ thromboembolism Þ TIA Þ brain infarct

Cardiovascular Devices - Incidence of infections Þ heart valves (1-4%); pacemakers (0.5-2%); peripheral vascular grafts (1-6%); total artificial hearts (25-100%)

Virchow’s Triad - thrombogenicity

Pathogenesis of device-centered infections Þ (triad) Host – pathogen – medical device

Pathways of Infections

Facilitation of Infections by Implant Devices

Early implant Infections (< 2 mo postoperatively) Þ Intraoperative contamination from airborne sources, asterile surgical techniques; Early postoperative complications, e.g., wounds; Immunocompromised status of host

Late implant Infections (> 2 mo postoperatively) Þ Hematogenous seeding from transient bacteremia, other infection sites; Therapeutical dental procedures, infection of catheters, surgery

Sources of vascular cannula-related infections Þ contaminated disinfectants, hands of medical personnel, autoinfection, patient’s microflora

Bacteria form a BIOFILM of slime which protects them in their adhesions Þ protective against inflammatory cells; it’s a diffusion barrier against infused antibiotics

Prosthetic valve endocarditis (mitral valve) Þ STAPHYLOCOCCI – most prominent Þ can manifest as an annulus invasion, myocardial abscess, valve obstruction, or pericarditis

Important medical device and prothesis infections

(1) Prosthetic valve endocarditis

(2) Vascular graft infections

(3) Orthopaedic prosthesis infections

(4) Pacemaker infections

(5) Catheter-associated infections

(6) CSF shunt infection

Unique features of biomaterial-centered infections

(1) Adhesive bacterial colonization of substrata

(2) A biomaterial, damaged tissue, or relatively acellular tissue substratum

(3) Infection caused by smaller bacterial inoculi

(4) Bacterial resistance to host defense mechanisms and antibiotic therapy

(5) Characteristic bacteria such as Staph. aureus, Strep. epidermidis, and Pseudomonas aeruginosa

(6) The transformation of nonpathogens or opportunistic pathogens into virulent organisms by the presence of a biomaterial substratum

(7) Polymicrobiality

(8) Specificity of phenomena (material, organisms, host location)

(9) Persistence of infection until implant (substratum) removal

(10) The presence of inflammation, tissue cell damage, and necrosis at the implant tissue interface (the immunoincompetent, fibroinflammatory zone)

(11) The absence of tissue integration at the biomaterial interface

(12) Probable alteration of host cellular and humoral immune responses by the biomaterials and bacteria