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Paper text:
although cardiac surgery procedures fall into the category of so - called  clean procedures  , they remain burdened with the risk of infectious complications .
postoperative sternal wound infection ( swi ) occurs in 0.5 - 8% of patients and is associated with high mortality ( 14 - 47% ) , especially in the event of deep sternal wound infection ( dswi ) , which is the most serious form of sternal wound infection .
the reasons behind the complications are multifactorial and may be endogenous or exogenous in nature .
the occurrence of postoperative infection may be related to patient characteristics ( advanced age , diabetes , generalized atherosclerosis , circulatory insufficiency ) or surgery parameters ( duration lasting several hours , use of extracorporeal circulation , operative wound extent , necessity of employing electrocoagulation during hemostasis , peri- and postoperative blood loss requiring blood product transfusion ) .
applying antibiotic locally in the form of collagen - gentamicin sponge appears to be the perfect solution .
notwithstanding , although the sponge is used in cardiac surgery in more than 50 countries , its efficacy in preventing swi is still being disputed .
gram - positive and gram - negative bacteria , such as staphylococcus aureus , staphylococcus epidermidis , pseudomonas aeruginosa , and escherichia coli , are the most commonly encountered microorganisms that infect bone and soft tissue . in cardiac surgery ,
being able to adhere to foreign material , such as catheters or stainless steel wires used for sternal closure , they synthesize an extracellular polysaccharide , producing a biofilm that is difficult to eliminate . in such cases ,
the foreign body has to be removed in order to allow proper treatment of the infection .
other pathogens isolated from sternal wounds include escherichia coli , klebsiella , 
 enterobacter cloacae , and acinetobacter .
propionibacterium acnes has also been identified as a microbal agent of swi , which can influence sternal instability after fixation [ 2 , 6 ] .
this natural antibiotic produced by micromonospora purpurea is characterized by a wide spectrum of bactericidal action with regard to oxidative gram - negative bacteria and some gram - positive microorganisms .
as has been demonstrated , staphylococci are sensitive to high concentrations of gentamicin [ 59 ] .
its bactericidal action is dependent on the concentration of the agent at the infection site .
the mechanism of action is based on the blocking of protein biosynthesis , as aminoglycosides bind permanently to subunit 30s of the bacterial ribosome .
biological distribution is dependent on factors including age , obesity , renal function , or the presence of ascites in patients .
gentamicin , like other aminoglycosides , is not well absorbed when administered orally due to its cationic nature ; therefore , its administration needs to be parenteral  intravenous or intramuscular [ 7 , 10 ] . in the case of intravenous administration ,
the agent 's bioavailability is 100% , and its maximum serum concentration is reached as early as 30 minutes after injection .
its biological half - life time is 2 hours for adults , and therapeutic concentration is achieved at the range of 4 - 10 mg / l ; however , intravenous administration of > 2 mg / l is considered to be toxic for the patient .
the bioavailability of gentamicin administered intramuscularly is the same as in the case of intravenous administration , but a longer period of time ( 30 - 90 minutes ) is required to reach maximum serum concentration . within 24 hours , gentamicin is expelled by the kidneys in unchanged form , accumulating in the lysosomes of kidney proximal tubular cells and causing their apoptosis in clinically relevant doses
aminoglycosides have good chemical stability and do not commonly cause allergic reactions . in comparison to -lactam antibiotics , which are widely used in perioperative prophylaxis
, aminoglycosides have a significantly narrower operating range , but they rarely induce bacterial resistance . if bacterial resistance to gentamicin does occur , it mostly consists in the breaking down of the antibiotic by various enzymes .
an important characteristic of aminoglycosides is their ability to act in synergy with other antibacterial agents .
the synergy effect and the ability to rapidly kill microorganisms can be observed in combination therapy , substantiating their clinical efficacy . combining them with -lactam antibiotics
can be employed in the treatment of serious infections by gram - negative bacteria or in the treatment of infections caused by gram - positive bacteria , such as staphylococcus aureus , enterococci , or streptococcus viridans endocarditis .
combining gentamicin with ultrasound is being successfully used to kill biofilm - producing bacteria , such as escherichia coli and pseudomonas aeruginosa , which are commonly found on implants , dialysis catheters , cardiac pacemakers , as well as on artificial vascular prostheses and heart valves .
the therapeutic capabilities of systemic antibiotic administration are limited , while the local application of antibiotics is associated with numerous advantages .
most importantly , high agent concentration at the implantation site is ensured and minimum inhibitory concentration ( mic ) is retained during the treatment , while adverse effects are minimized without reaching a toxic blood concentration . at present , various biodegradable and nondegradable antibacterial agent carriers are being used .
one of the first biomaterials available on the market was poly(methyl methacrylate ) ( pmma ) used in the form of bone cement or granules ; the currently employed materials include hydroxyapatite ( granules or porous scaffold ) , the natural polymer chitosan ( membranes , microgranules , thermosensitive gel , sponges ) , and bovine tendon collagen ( sponges ) [ 7 , 1215 ] .
collagen sponges resorbed after the release of the drug are widely used as carriers for active substances .
some of the conducted in vitro studies demonstrate that the kinetics of releasing the antibiotic from this matrix may reach as much as 95% after as little as 1.5 hours , in comparison to 8% achieved by pmma carriers . local application results in the achievement of a high concentration of the therapeutic agent within several hours , which is then retained for up to 4 days .
owing to these kinetic properties and to the activity of the antibiotic within a set time period , the development of microorganism resistance progresses very slowly .
moreover , collagen may produce scaffolds for fibrin deposition , which results in the healing of tissue defects and acceleration of wound healing .
gentamicin - collagen sponge ( gmcs ) is frequently used in surgery in order to prevent wound infections and to treat local infections of bone and soft tissue [ 1 , 4 ] .
the site of surgical access , such as sternotomy , is rarely affected by infection ; however , if it does take place , it is associated with the risk of further serious complications .
for this reason , additional prophylaxis is crucial , particularly in the case of high - risk patients .
the local application of gentamicin in the form of an absorbable collagen sponge ensures gradual release of the agent within a short time period , which improves wound healing without the nephrotoxic or ototoxic effect of aminoglycosides [ 1 , 14 ] .
one of the studies by friberg et al . has demonstrated that administering 260 mg of gentamicin in between the parts of the closed sternum results in a high antibiotic concentration within 8 - 12 hours after the surgery .
it may be applied substernally , presternally , or in between the parts of the cut sternum .
substernal implantation allows a high gentamicin concentration to be achieved in this region , with concurrent lower antibiotic concentration in the presternal area .
this results in a significant reduction in mediastinal deep sternal wound infections ( dswi ) and a slight reduction in superficial sternal wound infections ( sswi ) . in turn , in presternal application , the wires are partially covered , which prevents the adhesion of coagulase - negative staphylococci present in the physiological flora of the skin .
it appears , therefore , that the best option is to place the matrix in between the halves of the cut sternum , which allows for a balanced release of the antibiotic in the vicinity of the sternal closure .
there remains , however , a risk of reoperation due to sternal dehiscence and bleeding .
literature data indicate that additional cardiac surgery interventions due to bleeding were required by approximately 4% of patients with sponges applied in this manner and by 2.3% of controls .
certainly , a too thick layer of the sponge applied during sternal closure may lead to such complications ; therefore , in order to reduce the high risk of postoperative bone marrow bleeding and sternal instability , a single antibiotic matrix , properly cut to match the margins of the wound , should be used ( figs . 1 and 2 ) [ 1 , 5 , 9 ] .
scheme  a gentamicin - collagen sponge , properly cut to size and placed in between the halves of the sternum and substernally ( longitudinal and cross section ) [ 5 , 17 ] 
  a gentamicin - collagen sponge cut with sterile scissors to fit the shape of the wound , inserted under and in between the halves of the sternum after a cabg procedure the literature presents the advantages of the local application of antibacterial agents in surgery .
efficacious use of sponges in prophylaxis provided to cardiac surgery patients has been presented by friberg et al . , who examined 2000 patients undergoing coronary artery bypass grafting ( cabg ) .
in the group implanted with the sponges , postoperative complications in wound healing occurred in 4.3% of patients , as compared to 9% of patients in whom only standard perioperative antibiotic prophylaxis was used .
reports from a hospital in germany also corroborate the advantageous effect of gmcs ( 2.54% vs. 6.5% ) , especially with regard to dswi reduction ( 0.56% vs. 3.52% ) .
a medical center in the czech republic also reported a positive effect of this type of prophylaxis on the incidence of swi ( 8.3% vs 19.8% ) . by applying a gentamicin - collagen sponge locally in between the parts of the surgically cut sternum and modifying the sternal closure procedure ,
a significant reduction has been observed with regard to swi cases caused primarily by cons bacterial strains , with the exception of propionibacterium acnes bacteria refractory to aminoglycoside treatment .
furthermore , redness and secretion at the surgical access site were reduced during the wound healing process in comparison with the control group .
reported 12.3% of surgical site infections within 5 years in a clinical hospital in france .
reoperation due to dswi was required by 13.8% of patients , in comparison to 12.6% of patients implanted with gmcs .
therefore , the use of the sponges did not significantly limit the development of deep infection .
similar observations were made by raja et al . ; in their study , gentamicin did not limit the occurrence of dswi ( 2.1% vs. 3.1% ) , but it did influence the reduction of sswi ( 2.1% vs. 6.2% ) .
data collected from as many as 48 hospitals in the usa indicate the lack of a significant difference in terms of reducing infection between the study group and controls ( 8.4% vs. 8.7% ) with regard to both superficial and deep sternal wound infection .
as underscored by the authors , multicenter studies often do not reflect results obtained in individual cases .
the differences in the results may also be explained by ethnic and regional differences , as well as by the associated distribution of pathogens with varying mechanisms of resistance .
for example , the american studies included a small percentage of bacterial strains that turned out to be resistant to gentamicin , including staphylococcus epidermidis .
therefore , the differences in bacterial strains distribution condition the efficacy of agents used in prophylaxis .
despite advanced surgical techniques , a body of science concerning the pathogenesis of surgical site infections , and the use of perioperative antibiotic prophylaxis , the incidence of these infections remains unchanged .
thus , more effective methods of prevention are required , particularly because of the rising population age and obesity , the number of type 2 diabetes patients , and the rapid emergence of resistant microorganisms . while evidence indicating that local prophylaxis administered in the form of gentamicin - collagen sponge implanted at the end of cardiac surgery procedures may reduce the incidence of swi does exist , it appears crucial for clinical practice to conduct further observation and assessment of the capabilities of gmcs due to differing opinions .
although their use is recommended for all adult patients undergoing heart surgery , it can be of greatest benefit to high - risk patients ( e.g. with diabetes and/or bmi > 25 ) .
the frequency of sternal wound infection ( swi ) after cardiac surgery ranges from 0.5% to 8% and is associated with significant morbidity , mortality , and treatment cost . 
 perioperative antibiotic prophylaxis is not sufficient to fully prevent the contamination of the surgical access site . 
 one of the most effective methods for the prevention of wound infection seems to be the use of gentamicin - impregnated collagen sponge , which is successfully used in abdominal and orthopedic surgery . 
 surgically implantable topical antibiotics can reduce wound infection in cardiac patients as well , but the efficacy of swi prevention in cardiac surgery still raises many questions .