Control of infection after thoracic and cardiovascular surgery

Postoperative infection in cardiac surgery: the influence of a change in prophylactic antibiotic regimen

A total of 448 patients undergoing cardiovascular surgery were followed for the development of postoperative infection. Non-extracorporeal procedures were assigned to group 1 and open-heart procedures to group 2. The incidence of infection was compared in two groups who received prophylactic antibiotics. Patients (n = 253) received ampicillin alone (group 1) or in combination with gentamicin (group 2) for 7 days starting 1 day before the operation (period A). One hundred and ninety-five patients (period B) received cefazolin starting preoperatively 30 min before induction, alone (group 1) or in combination with gentamicin (Group 2) for 3 days. The percentage of patients developing infection in periods A and B for group 1 patients was 4.2% and 3.5% and for group 2 it was 25.8% and 18.7% respectively. The overall infection rate was 13%. The number of infection sites involved were 1.5 per infected patient. Urinary tract infections were the most frequent followed by endocarditis and other deep infections, wound infections and respiratory infection. Gram-negative rods were the predominant pathogens (Klebsiella spp. and Pseudomonas aeruginosa) during both periods (47 out of 70 isolates). Wound infections due to Gram-positive cocci were higher in period A (4/8) as compared to period B (1/5). During period B there were three cases of fungal endocarditis whereas no case occurred during period A. Although the incidence of infection was reduced during the period of cefazolin prophylaxis, the difference was not statistically significant.

Infection following coronary artery surgery. Comparison of two antibiotic prophylaxis regimens

A prospective randomized study was conducted in 200 patients undergoing coronary artery bypass surgery. All patients received intravenous (IV) cephalothin prophylaxis for 48 hours beginning with anesthetic induction. Group A (99 eligible patients) received cephalexin 500 mg po, qid for three extra days. Group B (94 eligible patients) received no oral therapy. The overall infection rate was 9.3 percent (18 patients). Six patients had multiple sites of involvement. There was no difference between group A (9.0 percent, nine patients) vs B (9.5 percent, nine patients) (p greater than 0.5). The median sternotomy infection rate, superficial or deep, was 2.6% (five patients). The surgical wound infection rate was 4.7 percent (nine patients). The overall infection rate compares favorably with that of high risk groups for clean surgical procedures defined in SENIC study. There was no advantage to prolonged oral cephalexin prophylaxis following coronary artery bypass (CAB) surgery.

Staphylococcus epidermidis as a cause of postoperative wound infection after cardiac surgery: assessment of pathogenicity by a wound-scoring method

Wound infection after clean surgery prolongs hospital stay but the organism most commonly isolated from wound discharge, Staphylococcus epidermidis, is often dismissed as a contaminant or commensal. The wounds of 517 patients were assessed, after cardiac surgery, by a wound-scoring method ('ASEPSIS') and a close comparison was made of the appearance and clinical outcome of 89 wounds, from which bacteria were isolated. There was no significant difference in the scores of 49 wounds, where S. epidermidis was the sole isolate (9.5 per cent of all wounds, 95 per cent CI 6.9-12.0 per cent), and 13 wounds infected with Staphylococcus aureus (2.5 per cent, 95 per cent CI 1.2-3.9 per cent). Repeat cultures were obtained from 21 of the 49 wounds and, in 16 of these, the second isolate showed the same biochemical reactions and antibiotic resistance pattern as the first. Infection of sternal wounds is commoner with coagulase-negative staphylococci than with S. aureus and, clinically, is just as severe.

Study of cardiothoracic wound infection at St. Thomas' Hospital

Wound infection occurred after 14.3 per cent of 433 open heart operations. In 309, saphenous veins were harvested for coronary artery bypass grafting (CABG) and 8.7 per cent of sternal wounds and 12.9 per cent of leg wounds were infected. Only 1.6 per cent of the remaining 124 patients who had open heart operations without leg surgery suffered sternal wound infections. In the CABG group sternal infection was theatre-related and significantly associated with length of pre-operative stay, diabetes and re-operation. Similar organisms were isolated from both leg and sternal wounds which suggest that organisms were transferred from legs to sternum with the veins. No clinically relevant cross infection was demonstrated. Skin disinfection and surgical technique seem more important than antibiotic prophylaxis in the control of these infections.

The prophylactic use of antimicrobials in surgery

During the period August 1976 to June 1982, there were 98 reports of antimicrobial prophylaxis in human surgery that were judged unevaluable. Our review, coupled with that of Chodak and Plaut, identified studies of 126 antibiotic regimens that were considered evaluable and a total of 205 studies considered unevaluable. A decrease in infection rate in antibiotic-treated patients compared to non-antibiotic-treated patients was seen in 120 (95%) of the evaluable regimens. Ninety-nine (79%) of these 120 regimens produced statistically significant reductions in the infection rate (P less than .05, chi 2 analysis). The majority of the antibiotic regimens were tested in procedures that were classified as clean-contaminated. Of the regimens that yielded a statistically significant reduction in infection rate with antimicrobial therapy, in 66 (67%) the agents were used for 24 hours or less. Five regimens were identified in which a higher infection rate occurred in specific patient groups when prophylactic antibiotics were used, but the differences were not statistically significant. In the overwhelming majority of evaluable studies, antibiotics decreased the incidence of surgical infection compared with non-antibiotic groups. The available data also support the effectiveness of short prophylactic antibiotic courses of 24 hours' duration or less. The duration necessary for antibiotic prophylaxis was specifically tested in nine regimens. In all nine, a short course (less than 24 hours) of antibiotic prophylaxis was as effective as longer periods of therapy (24 hours to 5 days) in preventing infection.

Evaluation and management of prosthetic valve endocarditis

Despite improved operative technique and sophistication in managing patients undergoing cardiac valve replacement, prosthetic valve endocarditis (PVE) remains a source of major morbidity (overall recent incidence approximately 2.1%), and these patients have a high case-fatality rate (58% overall). Early PVE (less than 60 days postoperative) has a worse prognosis (78% case-fatality rate) and is usually caused by staphylococcal species, gram-negative rods, and fungi; whereas the case-fatality rate in late PVE is 46%, owing to the lower fatality of streptococcal species infections that tend to occur late. Risk factors that portend a poor clinical response to medical therapy alone include the presence of congestive heart failure, paravalvular leakage, systemic embolic, early PVE, nonstreptococcal etiology, aortic location in a nonheterograft valve, as well as persistent fever (greater than 10 days). Given the frequently dismal outcomes in the medical management of these patients, the case is made for early surgical intervention in most cases of PVE (except for late streptococcal disease), especially if any of the aforementioned risk factors are present.

Opportunistic endocarditis following open-heart surgery

The incidence of endocarditis following open-heart operations is declining, but the relative incidence of endocarditis by the opportunistic organisms, both bacterial and fungal, has increased. These "opportunists" require careful identification and sensitivity testing so that appropriate therapy can be planned. In cases of candida endocarditis, a positive precipitin test and elevated candida antibody titer may provide an earlier means of diagnosis than blood cultures. These patients should be treated promptly with adequate dosages of specific antimicrobial or antifungal agents. Reoperation should be considered early if there is evidence of valve dehiscence or embolic phenomena or if drug therapy fails to control the infection.