Wound, Bone and Joint Infections Flashcards
What are the major pathogens in surgical site infection?
Staph.aureus (MSSA and MRSA)
E.coli
Pseudomonas aeruginosa
What is the pathogenesis of a surgical site infection?
- Contamination of wound at operation
- Pathogenicity and innoculum of microorganisms
- Host immune response
If surgical site is contaminated with > 10^5 microorganisms per gram of tissue, risk of SSI is increased. The dose of contaminating bacteria required to cause infection is much lower if there is foreign material present e.g silk suture.
What are the three levels of surgical site infection?
Superficial incisional: Affect skin and subcutaneous tissue.
Deep incisional: Affect fascial and muscle layers.
Organ/space infection: Any part of anatomy other than incision.
A patient is admitted in February, with a subarachnoid and subdural haemorrhage after a fall. Decompressive craniectomy. In April, they had a cranioplasty with titanium plate.
Patient was readmitted in October with large subdural collection with midline shift and had a subsequent abscess evacuation. Titanium plates removed. Underneath there was severe infection with 1-1.5cm thick pus.
What is the likely organism?
MRSA
Patient was given linezolid
What are three different phases where surgical site infections can be prevented?
Pre-operative phase
Intra-operative phase
Post-operative phase
What is the relationship between age and developing a surgical site infection?
An independent risk factor.
A direct linear trend of increasing risk until 65 years of age.
A prospective study examining patient undergoing total hip replacement. Age over 75 was found to be a significant risk factor.
Which underlying illnesses are risk factors for a surgical site infection?
ASA score of 3 or more
Diabetes: Two to three fold increased risk. Association with post-op hyperglycaemia. Control blood glucose. HbA1C < 7.
Malnutrition
Low serum albumin
Radiotherapy and steroid use: Taper steroids.
Rheumatoid arthiritis: Stop disease modifying agents for 4 weeks before and 8 weeks post-op.
Why is obesity a risk factor for surgical site infections?
Adipose tissue is poorly vascularised. Poor oxygenation of tissues and functioning of the immune response increases the risk of SSIs.
Risk increased by 2 to 7 in patients with a BMI of 35 or more.
How is smoking a risk factor for surgical site infections?
Smoking duration and number of cigarettes smoked.
Nicotine delays primary wound healing.
Peripheral vascular disease.
Vasocontrictive effect of reduced oxygen-carrying capacity of blood.
Encourage tobacco cessation.
How can pre-operative showering affect the risk of surgical site infections?
Microorganisms colonising the skin may contaminate exposed tissues and cause an SSI. There is no difference in SSI incidence when chlorhexidine or detergent/bar soap is used.
Patients should be advised to shower or bath using soap or on the day of surgery or the day before.
How can hair removal affect the risk of surgical site infections?
Micro-abrasions caused by shaving with a razor may lead to multiplication of bacteria. Use electric clippers on the day of surgery with single-use head.
Hair should not be removed unless it will interfere with the operation.
How can nasal decontamination affect the risk of surgical site infections?
S.aureus is carried in the nares of 20-30%.
A multivariate analysis demonstrated that S.aureus carriage was the most powerful independent risk factor for SSI following cardiothoracic surgery.
How can antibiotic prophylaxis affect the risk of surgical site infections?
Antibiotic prophylaxis should be given at induction of anaesthesia.
Bactericidal concentration of the drug should be established in serum and tissues at time of incision.
Additional doses may be necessary if there has been significant blood loss or if the operation has been prolonged.
How can ventilation affect the risk of surgical site infections?
Maintain positive pressure ventilation.
Maintain around 20 air changes per hour (of which at least 3must be fresh air).
Filter all air.
Keep operating room doors closed.
Consider laminar flow for orthopaedic implant surgery.
How can sterilisation affect the risk of surgical site infections?
Sterilise all surgical instruments.
Inadequate sterilisation of surgical instruments has resulted in SSI outbreaks.
How should skin be prepared to reduce the risk of surgical site infections?
When skin is incised microorganisms may contaminate tissues and cause an SSI.
Prepare skin at surgical site using antiseptic preparation: povidine-iodine or chlorhexidine.
Chlorhexidine in 70% alcohol is used.