MI: Wound, bone and joint infections Pt.1 Flashcards
Name three major pathogens that cause surgical site infections.
- Staphylococcus aureus
- Escherichia coli
- Pseudomonas aeruginosa
List some factors affecting the severity of the disease.
- Pathogenicity of the microorganism
- Inoculum of the microorganism
- Host immune response
What threshold of contamination of a surgical site is associated with increased risk of surgical site infections?
More than 10^5 organisms per gram of tissue
How does the dose of contaminating material required to establish infection change with prosthetic material?
Reduced
What are the three levels of surgical site infections?
- Superficial incisional - skin and subcutaneous tissues
- Deep incisional - fascial and muscle layers
- Organ/space infection - any part of the anatomy that is not the incision
How is a surgical site infection caused by MRSA treated?
IV linezolid (oxazolidinone class)
List some risk factors for surgical site infections.
- Age
- ASA score of 3 or more
- Diabetes (±postop hyperglycaemia)
- Malnutrition
- Hypoalbuminaemia
- Radiotherapy and steroids
- Rheumatoid arthritis (stop DMARDs 4 weeks before and until 8 weeks after operation)
- Obesity (adipose tissue is poorly vascularised)
- Smoking (delayed wound healing)
What should patients be advised to do on the day of the operation?
Shower with soap
on day / day before surgery
Why should shaving be avoided as a method of hair removal in surgery?
It can cause microabrasians which promote bacterial multiplication (electric clipper should be used instead)
Who should be offered nasal decontamination?
Patients who are found to be carrying S. aureus
(esp. cardiothoracic surgery)
When should antibiotic prophylaxis be given for patients undergoing surgery?
At the induction of anaesthesia
List some intra-operative measures that reduce the risk of surgical site infection.
- Limit the number of people in the operating theatre
- Ventilation of the theatre (positive pressure)
ortho = laminar flow - Sterilisation of surgical instruments
- Skin preparation (using povidone-iodine or chlorhexidine in 70% alcohol)
- Asepsis and surgical technique
- Normothermia (hypothermia causes vasoconstriction and decreases oxygen delivery to the wound space thereby increasing the risk of infection)
- Oxygenation >95%
List some risk factors for septic arthritis.
- Rheumatoid arthritis
- Osteoarthritis
- Crystal arthritis
- Joint prosthesis
- IVDU
- Diabetes, chronic renal diesase, chronic liver disease
- Immunosuppression
- Trauma (e.g. intra-articular injection, penetrating injury)
Outline the pathophysiology of septic arthritis.
- Proliferation of bacteria in the synovial fluid leads to generation of a host inflammatory response
- Joint damage leads to exposure of host-derived protein (e.g. fibronectin) to which bacteria can adhere
List some bacterial factors that enable bacteria to cause septic arthritis.
- Staphylococcus aureus has receptors such as fibronectin-binding protein
- Kingella kingae have bacterial pili which adhere to the synovium (septic arthritis in children)
- Some strains of S. aureus produce Panton-Valentine Leukocidin which is associated with fulminant infections
