Reduction of Surgical-site Infections in Neurosurgery
Reduction of skin flora is customarily achieved by the use of broad- spectrum antiseptics. However, the response to antiseptic agents can be highly individual in nature,25
agent is capable of removing all organisms.3
and it is also the case that no antiseptic In the absence of a known
‘minimum’ acceptable density of organisms, a reduction in number of bacteria at the wound site to as low a number as possible is indicated. Since bacterial adherence is a pivotal step in subsequent device-related infection,26–28
providing a sterile surface by using incise drapes also appears beneficial.
The results are illustrated in Figure 1 for the antimicrobial- impregnated incise drape (3M™Ioban™2).
Current evidence supports the use of a sterile incise drape with antimicrobial impregnated into the adhesive as a mechanism to reduce the risk for surgical-site infection. Assessment of the efficacy of a subset of currently available surgical incise drapes was carried out in vitro.29
For the time-dependent in vitro kill rate, expressed in logarithms of colony-forming units (CFU) killed, for an antimicrobial-impregnated incise drape (3M™Ioban™2), values are given as an average ± 1 standard deviation. Staphylococcus aureus and Staphylococcus epidermidis, both methicillin-resistant, are accentuated by enclosure (see Figure 1).
The adhesive surface of the test sample is inoculated with 50μl of a bacterial suspension (containing 5x108 [±0.5 log] CFU/ml) by dispensing 10–12 droplets across the surface. The petri dishes are covered and incubated at 35±2°C for 30 minutes plus one minute; 60 minutes plus two minutes; and 90 minutes plus two minutes (timing starts on contact with the total inoculum volume).
At the appropriate time, the sample is transferred to a blender jar containing 100ml of Difco™ D/E neutralizing broth. Samples are blended for two minutes at low speed. After blending, serial 10-fold dilutions in phosphate-buffered water are plated for each dilution in duplicate, the plates incubated, and colonies counted after 48 hours of culture (72 hours for fungal organisms).30
In a published study on the role of endogenous microflora on neurosurgical-site infections, no relationship was observed between bacterial density before or after skin antisepsis and subsequent infection.31 3M™Ioban™2™ was used in all surgical cases. In a prospective study,32 bacterial densities were measured using 3M™Ioban™2™ without disinfection prior to surgery and compared with bacterial densities with standard antisepsis (Betadine). 3M™Ioban™2™ reduced the bacterial density on the skin, although to a lesser extent than the standard antiseptic agents. The data indicate that 3M™Ioban™2™ reduced the bacterial skin count (measured as CFU) by approximately 0.70 logs. Figure 2 illustrates the relationship between the post-antisepsis and pre- antisepsis bacterial densities, given as CFU (data courtesy of Dr E Larson).
Six hundred and one patients underwent craniotomy using iodophor antisepsis.31
remaining on their skin after antisepsis.
At present, the accepted antisepsis level of a given product is determined by the tentative final monograph on antiseptic products.33
US NEUROLOGY Fifty-eight patients had only Staphylococcus epidermidis
2 3 4 5
0 1
02 3 1 4 5 Colony-forming units before antisepsis
Bacterial count 100 (2 logs) and antisepsis incomplete Bacterial counts 100 (2 logs) and antisepsis acceptable
Figure 3: Operative-site Image Demonstrating Use of a Sterile Surface Associated with the Antimicrobial-containing Incise Drape
6 7
Figure 2: Colony-forming Units Before and After Antisepsis
Staphylococcus epidermidis counts (logarithm colony-forming units): povidone iodine antisepsis
The characteristic behavior of an antiseptic appears as the diagonal line. Every data point below and to the right of the diagonal line indicates that antisepsis was acceptable by current definitions. This situation is illustrated using circles. Failure to achieve acceptable antisepsis is illustrated using squares.
The amount of bacteria necessary to lead to a prosthetic infection can be estimated34–36
at 2 logs (100 CFU), and any value that equals or exceeds this number is illustrated with a filled symbol. As indicated, 22 patients (4%) failed to undergo acceptable antisepsis and 42 patients (7%) had residual bacteria on their skin in excess of 200 CFU. Using the results described, the application of 3M™Ioban™2™ reduces those individuals who have in excess of 2 logs of Staphylococcus epidermidis on their skin to 19 (3% of all patients), effectively reducing those subjects with sufficient organisms to lead to a prosthetic infection by half.
97
Colony-forming units after antisepsis
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