This document discusses factors that can influence the risk of postoperative infection and the role of anaesthetists in prevention. It notes that surgical site infections occur in 5-20% of surgeries and outlines several strategies anaesthetists can employ, including proper administration of antibiotic prophylaxis before incision, maintaining normothermia, and using maximal sterile barriers for invasive procedures like central line insertion. The timing of antibiotic prophylaxis is particularly important to reduce infection risk.

1. Preventing postoperative infection:
the
anaesthetist’s role
By
Dr. Chamika Huruggamuwa

2. Key points
• Surgical site infection is common (5–20%) and
may be associated with significant morbidity and
even mortality.
• Crucial immune mechanisms such as neutrophil
phagocytosis 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.

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

4. • 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 aureus
bacteraemias, antibiotic-related Clostridium difficile
enteritis, and intravascular cannulaerelated infections

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

6. • When a neutrophil ingests bacteria (or any
foreign debris), it undergoes a ‘respiratory burst’,
temporarily increasing its oxygen consumption
which results in the production of anti-microbial
oxygen free radicals. Oxygen free radicals such as
superoxide ions and hydrogen peroxide are
produced by the enzymes superoxide dismutase
and myeloperoxidase. Variables that affect tissue
oxygen delivery or enzyme function can impair
the production of oxygen free radicals and allow
bacteria to survive and infection to become
established.

7. respiratory burst
During 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

8. Well-known variables that influence surgical
site infection include
surgical 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.)

9. Factors that can be optimized in the
perioperative period can be divided into
(i) Well-established interventions (supported
by good evidence)
(a) antibiotic prophylaxis,
(b) hand hygiene,
(c) aseptic technique during invasive
procedures,
(d) perioperative thermoregulation.
(ii) Less certain interventions (some supporting
evidence)
(a) face masks and theatre traffic,
(b) regional anaesthesia techniques,
(c) inspired oxygen,
(d) glycaemic control.
(iii) Speculative interventions (no supportive
evidence as yet)
(a) goal-directed fluid management,
(b) minimizing blood transfusions,
(c) enhanced recovery after surgery
(ERAS),
(d) avoidance of selected opioids

10. 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.

11. Clean’ surgery involves
no break in aseptic technique and the respiratory,
gastrointestinal, or genitourinary tracts not being breached.
‘Clean-contaminated’ surgery involves
the 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.

12. Prophylactic antibiotic administration reduces the bacterial
inoculum at the time of surgery and significantly decreases the rate
of 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

13. 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 if
antibiotics were administered either after incision or .60
min before incision .
hospitals should have locally published guidelines for
surgical 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.

14. 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 recommended
for clean, non-prosthetic, uncomplicated surgery.

15. Hand hygiene
The 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 perform
hand hygiene before and after every patient contact and
is an accepted method to prevent transmission of
resistant organisms between patients.

16. Aseptic technique during invasive
anaesthetic procedures
Anaesthetists regularly insert central venous catheters (CVCs) and
epidural catheters which may be portals of entry for bacteria.
Guidelines in the UK, USA, and Australia recommend maximal
barrier 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.

17. 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 bloodstream
infections when compared with the internal jugular and femoral
sites.
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 insertion
of peripheral nerve catheters.

18. Perioperative thermoregulation
Hypothermia triggers thermoregulatory vasoconstriction, thereby
decreasing subcutaneous tissue oxygen tension. This can significantly
reduce neutrophil function and collagen deposition in healing
wounds.
Hypothermia can also directly impair immune function.
Mild perioperative hypothermia (28C below normal core
body temperature) has been shown to,
Increase wound infection rates,
Delay wound healing,
Increase transfusion requirements, and
Lengthen hospital stay

19. Face masks and theatre traffic
The 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.

20. Regional anaesthesia
Epidural analgesia results in a lower incidence of some postoperative
respiratory 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.

21. 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.

22. Inspired gas composition: oxygen vs nitrous
oxide and volatile anaesthetic agents
Increasing the partial pressure of oxygen in the blood and tissues
beyond that which is required to fully saturate haemoglobin has
been postulated to improve the oxidative bactericidal activity of
neutrophil.
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 nitrous
oxide intraoperatively reduced the incidence of postoperative
infection.

23. In vitro and animal studies have suggested that volatile
anaesthetic agents may cause
a dose-dependent inhibitory effect on neutrophil function,
cytokine release,
lymphocyte proliferation.

24. 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.

25. Studies have shown that tight glycaemic control [blood glucose
(BG) maintained between 4.5 and 6 mmol dl21] reduces bloodborne
infection rates and hospital mortality.
Tight glycaemic control may be at the expense of an increase in the
number of hypoglycaemic episodes which themselves
can also be deleterious to physiology and even life threatening.
It has therefore been suggested that maintaining BG below 10 mmol
dl21 and reducing BG variability is likely to be both safe and effective.

26. 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.

27. Allogeneic blood transfusion
Immunomodulation and immunosuppression are known consequences
of 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 products
where possible.
METHODS OF AVOIDING BLOOD TRANSFUSION....?

28. 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.

29. 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.

31. THANK YOU.