Preventing postoperative infection: the

anaesthetist’s role

By

Dr. Chamika Huruggamuwa

Key points

• Surgical site infection is common (5–20%) and may be associated with significant morbidity and even mortality.

• Crucial immune mechanisms such as neutrophilphagocytosis of bacteria may be impaired during the perioperative period.

• For effective prophylaxis, appropriate antibiotics should be given before skin incision as recommended by the recent WHO Safe Surgery Saves Lives surgical safety checklist.

• Potentially modifiable perioperative factors under control of the anaesthetist can influence the incidence of surgical site infection.

• Postoperative surgical patients are at risk of developing multiple types of hospital-acquired infections.

• These include surgical site infections which are relatively common (incidence 5–20%), can prolong hospital stay, cause morbidity, increase the cost of health care, and even lead to mortality.

• Other hospital-acquired infections affecting surgical patients include respiratory and urinary tract infections, methicillin-resistant Staphylococcus aureusbacteraemias, antibiotic-related Clostridium difficileenteritis, and intravascular cannulaerelated infections

• progression from wound contamination to clinical infection is largely determined by the adequacy of host defence, the most important immune mechanism of which is neutrophilphagocytosis which occurs during a crucial few hours intraoperatively and after operation.

• When a neutrophil ingests bacteria (or anyforeign debris), it undergoes a ‘respiratory burst’,temporarily increasing its oxygen consumptionwhich results in the production of anti-microbialoxygen free radicals. Oxygen free radicals such assuperoxide ions and hydrogen peroxide areproduced by the enzymes superoxide dismutaseand myeloperoxidase. Variables that affect tissueoxygen delivery or enzyme function can impairthe production of oxygen free radicals and allowbacteria to survive and infection to becomeestablished.

respiratory burstDuring phagocytosis the phagocytic cell undergoes an increase in glucose and oxygen consumption termed the respiratory burst. The respiratory burst generates several oxygen-containing compounds that kill the bacteria undergoing phagocytosis – oxygen-dependent intracellular killing. Bacteria can also be killed by pre-formed substances released from granules or lysosomes upon bacterial fusion with the phagosome – oxygen-independent intracellular killing

Well-known variables that influence surgicalsite infection includesurgical factors(e.g. haematoma, anastomotic leak, poor surgical

technique, choice of antiseptic, prolonged or technically difficult procedure)

patient factors (immunosuppression, age, ASA status comorbidities, colonization by S. Aureus.)

Factors that can be optimized in the perioperative period can be divided into

(i) Well-established interventions (supportedby good evidence)(a) antibiotic prophylaxis,(b) hand hygiene,(c) aseptic technique during invasiveprocedures,(d) perioperative thermoregulation.(ii) Less certain interventions (some supportingevidence)(a) face masks and theatre traffic,(b) regional anaesthesia techniques,(c) inspired oxygen,(d) glycaemic control.(iii) Speculative interventions (no supportiveevidence as yet)(a) goal-directed fluid management,(b) minimizing blood transfusions,(c) enhanced recovery after surgery(ERAS),(d) avoidance of selected opioids

Antibiotic prophylaxis

• The UK National Institute of Clinical Excellence (NICE) issued guidelines in 2008 recommending a single dose of prophylactic antibiotics i.v. On starting anaesthesia (i.e. before skin incision), or earlier if a tourniquet is to be used.

• NICE recommends antibiotic prophylaxis for the following types of surgery:

• clean surgery involving the placement of a prosthesis or implant,

• clean-contaminated surgery,• contaminated surgery.

Clean’ surgery involves no break in aseptic technique and the respiratory,gastrointestinal, or genitourinary tracts not being breached.‘Clean-contaminated’ surgery involvesthe oropharynx, sterile genitourinary or biliary tract, the gastrointestinal or respiratory tracts, or where there has been a minor breach in aseptic technique.‘Contaminated’ surgery is defined as the presence of acute inflammation, infected bilious secretions, infected urine, or gross contamination from the gastrointestinal tract.‘Dirty’ surgery is where an established infection exists and therapeutic antibiotics are administered based on the susceptibility of bacterial isolates grown from culture.

Prophylactic antibiotic administration reduces the bacterialinoculum at the time of surgery and significantly decreases the rateof bacterial contamination of the surgical site.For effective prophylaxis, evidence has shown that the minimum inhibitory concentratio of the antibiotic agent at tissue level must be exceeded for, at least, the period from incision to wound closure. Hence the timing of the prophylactic antibiotics is crucial.

This is an area where anaesthetists can have a significant impact on reducing patient risks of infection

Observational studies have shown that the infection rate is lowest if antibiotics are administered within 30 min of incision, with the odds of infection increasing two-fold ifantibiotics were administered either after incision or .60 min before incision .

hospitals should have locally published guidelines forsurgical antibiotic prophylaxis based on local infective microbes and their antibiotic resistance patterns

For antibiotics with a relatively short half-life , a second dose of antibiotics is often recommended for prolonged procedures. Prolonged antibiotic prophylaxis extending after the surgical procedure has not been shown to be more effective than short-term prophylaxis.

Antibiotics have risks and commonly identified adverse effects of antibiotic therapy include gastrointestinal symptoms (nausea, vomiting, or diarrhoea), minor allergic reactions such as skin rashes myalgias and arthralgias. Rare adverse effects include pancytopenia, kidney or liver dysfunction, and life-threatening anaphylaxis.

Routine antibiotic prophylaxis is therefore not recommendedfor clean, non-prosthetic, uncomplicated surgery.

Hand hygieneThe impact of disinfection of hands on infection rates was first demonstrated by Semmelweis in the 1840s and the requirement for the surgical scrub is a well established principle for surgeons entering the operating theatre. The advent of disinfection with alcohol-based hand rub has reduced the time required to performhand hygiene before and after every patient contact and is an accepted method to prevent transmission of resistant organisms between patients.

Aseptic technique during invasiveanaesthetic procedures

Anaesthetists regularly insert central venous catheters (CVCs) andepidural catheters which may be portals of entry for bacteria.

Guidelines in the UK, USA, and Australia recommend maximalbarrier precautions for the insertion of CVCs, epidural, and nerve block catheters.

This is often considered as part of an ‘insertion bundle’ approach together with the use of chlorhexidine antisepsis,careful selection of site, avoidance of unnecessary lines or lumens (and prompt removal when appropriate), and hand hygiene.

They also recommend using 2% chlorhexidine in alcohol as this has higher efficacy than povidone-iodine when used for skin antisepsis.

The subclavian site is associated with fewer CVC-related bloodstreaminfections when compared with the internal jugular and femoralsites.

There is also some evidence that the use of real-time ultrasound-guidance during insertion may reduce CVC-related infections, due to fewer needle insertions and increased speed of insertion, with reduced incidence of haematoma formation.

Infections involving epidural catheters are reported as rare. Epidurals should generally be removed within 72 h.

Ultrasound-guidance is now commonly used for insertionof peripheral nerve catheters.

Perioperative thermoregulationHypothermia triggers thermoregulatory vasoconstriction, therebydecreasing subcutaneous tissue oxygen tension. This can significantlyreduce neutrophil function and collagen deposition in healing wounds.Hypothermia can also directly impair immune function.

Mild perioperative hypothermia (28C below normal corebody temperature) has been shown to,Increase wound infection rates, Delay wound healing, Increase transfusion requirements, andLengthen hospital stay

Face masks and theatre trafficThe practice of wearing face masks is believed to minimize the transmission of oropharyngeal and nasopharyngeal bacteria from operating theatre staff to patients’ wounds, thereby decreasing the likelihood of postoperative surgical site infections.

In fact, the largest and best conducted study reviewed showed no statistically significant difference in infection rates even if the surgical team were unmasked.

HOWEVER, it is reasonable and considered good medical practice to continue wearing face masks in the operating suite.

Regional anaesthesiaEpidural analgesia results in a lower incidence of some postoperativerespiratory complications, such as pneumonia, in patients undergoing laparotomy. This is generally considered to be as a result of superior analgesia, when compared with systemic opioids, allowing an increased ability for patients to cough and clear secretions.

In a recent epidemiological study, the use of neuraxial anaesthesia rather than general anaesthesia has been proposed as an approach for preventing surgical site infection after lower limb arthroplasty.

Proposed mechanisms of reduction in postoperative surgical infections are via ,

modulation of the inflammatory response,

vasodilation leading to improved tissue oxygenation,

And/Or improved postoperative analgesia, particularly with epidural techniques.

Inspired gas composition: oxygen vs nitrousoxide and volatile anaesthetic agents

Increasing the partial pressure of oxygen in the blood and tissuesbeyond that which is required to fully saturate haemoglobin hasbeen postulated to improve the oxidative bactericidal activity ofneutrophil.There is some evidence that giving 80% inspired oxygen rather than 30% inspired oxygen reduces wound infections in colorectal surgery.

The Enigma Trial revealed that avoidance of inhaled nitrousoxide intraoperatively reduced the incidence of postoperative infection.

In vitro and animal studies have suggested that volatileanaesthetic agents may cause

a dose-dependent inhibitory effect on neutrophil function,

cytokine release,

lymphocyte proliferation.

Glycaemic control

Acute hyperglycemia has many deleterious effects.

Reduced vasodilation, Impaired reactive endothelial nitric oxide generation, Decreased complement function, Increased expression of leucocyte and endothelial adhesion molecules Increased concentrations of cytokines Impaired neutrophil chemotaxis and phagocytosis.

These in turn could lead to increased inflammation, vulnerability to infection, and multiorgan system dysfunction.

Studies have shown that tight glycaemic control [blood glucose(BG) maintained between 4.5 and 6 mmol dl21] reduces bloodborneinfection rates and hospital mortality.

Tight glycaemic control may be at the expense of an increase in the number of hypoglycaemic episodes which themselvescan also be deleterious to physiology and even life threatening.

It has therefore been suggested that maintaining BG below 10 mmoldl21 and reducing BG variability is likely to be both safe and effective.

Fluid management

More recently, evidence has begun to emerge, suggesting that a more restrictive approach to fluid management reduces complications which include surgical wound site infections and other forms of sepsis (e.g. pneumonia-related).

Goal-directed’ fluid therapy, requiring invasive monitoring of central venous pressure, pulmonary artery occlusion pressure, or stroke volume via oesophageal Doppler probes, has gained some evidence for improved outcomes.

Allogeneic blood transfusion

Immunomodulation and immunosuppression are known consequencesof allogeneic blood transfusion in humans.

The effect appears to be dose-related, that is, the greater the number of blood units and products used, the greater the risk of infection.

Consideration also needs to be given to other methods of resuscitation and haemostasis, and also the use of fresh blood productswhere possible.

METHODS OF AVOIDING BLOOD TRANSFUSION....?

Opioid-induced immunosuppression

The majority of opioids in current clinical practice have the propensity to suppress the immune system in humans.

Morphine, Fentanyl, Remifentanil, and Meperidine, and to a lesser extent methadone have been shown to possess significant immunosuppressive properties.Oxycodone, Buprenorphine, and Hydromorphone have been shown to have no significant effects on the immune system, and Tramadol, due to its complex mechanism of actions, has been shown to have immuno-enhancing properties.

It would seem good practice to consider avoiding the use of known immunosuppressive opioids in the critically ill patient, particularly those known to have any degree of immunosuppression.

THANK YOU.