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Ann Thorac Surg 2002;74:1195-1200
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

A retrospective review of three antibiotic prophylaxis regimens for pediatric cardiac surgical patients

^a Division of Pediatric Cardiology, University of Michigan Medical Center, and Michigan Congenital Heart Center, Ann Arbor, Michigan, USA
^b Division of Infection Control and Epidemiology, University of Michigan Medical Center, and Michigan Congenital Heart Center, Ann Arbor, Michigan, USA
^c Division of Cardiac Surgery, University of Michigan Medical Center, and Michigan Congenital Heart Center, Ann Arbor, Michigan, USA

Accepted for publication June 13, 2002.

* Address reprint requests to Dr Maher, Department of Cardiology, Connecticut Children’s Medical Center, 282 Washington St, Hartford, CT, USA 06106.
e-mail: kmaher{at}nemours.org

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
BACKGROUND: Optimal antimicrobial prophylaxis for the pediatric cardiac surgical patient is unknown. We have reviewed our experience with more than 4,000 pediatric cardiac surgical patients at the University of Michigan to evaluate antibiotic prophylaxis regimens.

METHODS: Three antibiotic prophylaxis protocols were serially used during a 6-year period: Protocol 1 (n = 786): cefazolin was administered before operation and continued as long as thoracostomy tubes or central venous catheters were present; Protocol 2 (n = 1095): cefazolin was discontinued 48 hours postoperatively, regardless of the presence of tubes or catheters; Protocol 3 (n = 2039): cefazolin was continued as long as thoracostomy tubes were present, but not for central venous catheters. Patients with an open chest postoperatively received vancomycin and gentamicin until chest closure. This was identical during all three protocols. We retrospectively determined the rate of surgical site infections and unrelated bloodstream infections (the latter for both cardiac medical and surgical patients) for the three protocols.

RESULTS: Surgical site infections per 100 operations for protocols 1, 2, and 3 was 2.04, 6.58, and 1.67, respectively (p < 0.05 for protocol 2 versus protocols 1 and 3). The mean age of patients with a surgical site infection ranged from 12 to 15.4 months. Patients with an open chest had a higher rate of surgical site infection (18.8% for protocol 2 and 9.3% for protocol 3). Bloodstream infections per 1,000 patient days for protocols 1, 2, and 3 were 2.18, 6.51, and 5.02, respectively (p < 0.05 protocol 1 versus protocols 2 and 3).

CONCLUSIONS: These data suggest that pediatric cardiac surgical patients may benefit from prophylactic antibiotics as long as thoracostomy tubes are in place.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Antimicrobial prophylaxis (AP) for surgical procedures represents one of the most common reasons for prescribing antibiotics in hospitals. Antimicrobial prophylaxis was first used in the 1950s with significant controversy [1–4]. In 1961, a study by Burke clearly demonstrated the effectiveness of antibiotic prophylaxis in an animal model of dermal lesions [5]. Antimicrobial prophylaxis has now become the standard of care for patients undergoing cardiac surgical procedures [6]. Although it is well accepted that AP should be initiated before starting an operation, the optimal duration of prophylaxis after operation is unclear for pediatric cardiac surgical patients, as reflected in the variation in prescribing practices at pediatric cardiac centers [7, 8]. In the most recent survey [8], 43 pediatric cardiac surgical centers reported AP protocols. Antimicrobial prophylaxis was continued by 29 (67%) of the centers if a thoracostomy tube was present and by 31 (72%) of the centers if a mediastinal tube was present. A smaller number of centers continued AP for indwelling arterial lines, central venous catheters, pacing wires, or endotracheal tubes. Multiple studies of adult cardiac surgical patients suggest that continuing prophylactic antibiotics for 48 hours or less postoperatively may be optimal [9–12], but empirical data relevant to pediatric cardiac patients is very limited.

We have made some observations at our institution that may be useful in determining appropriate antibiotic prophylaxis for pediatric cardiac surgical patients. Before March 1994, for routine prophylaxis, patients received preoperative cefazolin, which was continued as long as thoracostomy, mediastinal, or central venous catheters were in place (Protocol 1). Given observations in adult cardiac surgical patients suggesting that limiting antibiotics to 48 hours postoperatively may be prudent, we instituted a change in our AP protocol: prophylactic antibiotics were discontinued 48 hours after operation, regardless of the presence of transthoracic tubes, central venous catheters, or intracardiac catheters (Protocol 2). With the initiation of Protocol 2, an increase in the number of surgical site infections (SSI) was observed. Because this increase in the number of infections was also approximately coincident with the initial utilization of recently refurbished operating rooms, it was thought that the increase in infections might be related to this or other unappreciated changes in practice. An intensive effort was made to identify the source of these infections, and to generally optimize clinical practice to minimize the risk of infection. These efforts neither yielded an explanation for the increase in SSI, nor appeared to have had an appreciable impact on the rate on infection. In January 1996, again we altered our antibiotic prophylaxis protocol. Patients received antibiotics for a minimum of 48 hours postoperatively, and AP was continued as long a thoracostomy or mediastinal tube was present (Protocol 3). We observed a substantial decrease in surgical wound infections after the reinitiation of AP for thoracostomy tubes, suggesting that AP in pediatric cardiac surgical patients may be appropriate for as long as chest/mediastinal tubes are in place.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
This research was approved by the Investigational Review Board at the University of Michigan on March 8, 2001.

Data procurement
The Michigan Congenital Heart Center at the C.S. Mott Children’s Hospital, which is a part of the University of Michigan Hospitals, is a large referral center for congenital heart operations with more than 800 cardiac operations performed annually. Pediatric cardiac patients are admitted to a dedicated pediatric cardiac intensive care unit. A dedicated nursing and physician staff provides medical care for the unit. Children less than 1 year of age represent the largest single group operated (approximately 55%), although a wide age range was represented, with approximately 6% of the patients being 18 years of age or older.

For cardiac surgical patients admitted between January 1993 and December 1998, medical records, infection control records, and other hospital data were reviewed. The total number of patients, the number of surgical procedures performed, and the number of SSIs were obtained. Patients included in the study were patients who had undergone cardiopulmonary bypass, as well as thoracotomy or sternotomy patients. For patients who had a SSI, the following were ascertained: the age of the patient, the type of AP, the length of time from operation to infection, the type of infection, the organism isolated, and whether the sternotomy wound was closed or left open postoperatively.

In addition, we obtained the number of bloodstream infections (BSIs) from all pediatric cardiac patients in the pediatric cardiac intensive care unit, including those who had a surgical procedure and those who did not. Patients identified with a BSI did not have a concomitant SSI for the purposes of this study.

Three faculty surgeons operated upon the patients: one throughout the entire time period, one from January 1993 to July 1993, and one from July 1993 until the end of the time period reviewed.

SSI case ascertainment
Infections were separated into two groups: (1) superficial incisional and (2) deep incisional/mediastinitis. A modification of the Center for Disease Control definition for SSI was used [13], summarized as follows:

1. Superficial incisional: A superficial SSI must meet the following criterion: Infection occurs within 30 days after the operative procedure and involves only skin and subcutaneous tissue of the incision and patient has at least one of the following:

1. purulent drainage from the superficial incision
   
2. organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision
   
3. at least one of the following signs or symptoms of infection: pain or tenderness, localized swelling, redness, or heat, and superficial incision is deliberately opened by surgeon, unless incision is culture-negative
   
4. diagnosis of superficial incisional SSI by the surgeon or attending physician
   
5. not reported as superficial SSI: stitch abscess, infection of an episiotomy or newborn circumsicion site, infected burn wound, incisional SSI that extends into the fascial and muscle layers.
   

2a. Deep incisional must meet the following criterion: Infection occurs within 30 days after the operative procedure if no implant is left in place or within 1 year if implant is in place and the infection appears to be related to the operative procedure and involves deep soft tissues (eg, fascial and muscle layers) of the incision and patient has at least one of the following:

1. purulent drainage from the deep incision but not from the organ/space component of the surgical site
   
2. a deep incision spontaneously dehisces or is deliberately opened by a surgeon when the patient has at least one of the following signs or symptoms: fever (> 38°C) or localized pain or tenderness, unless incision is culture-negative
   
3. an abscess or other evidence of infection involving the deep incision is found on direct examination, during reoperation, or by histopathologic or radiologic examination
   
4. diagnosis of a deep incisional SSI by a surgeon or attending physician
   

2b. Mediastinitis/organ space SSI must meet the following criterion: Infection occurs within 30 days after the operative procedure if no implant is left in place or within 1 year if implant is in place and the infection appears to be related to the operative procedure and infection involves any part of the body, excluding the skin incision, fascia, or muscle layers, that is opened or manipulated during the operative procedure and at least one of the following:

1. purulent drainage from a drain that is placed through a stab wound into the organ space
   
2. organisms isolated from an aseptically obtained culture of fluid or tissue in the organ space
   
3. an abscess or other evidence of infection involving the organ space that is found on direct examination, during reoperation, or by histopathologic or radiologic examination
   
4. diagnosis of an organ space SSI by a surgeon or attending physician
   

Patients were evaluated by the Infection Control and Epidemiology staff, this included review of medical records and microbiologic data (culture results, serial cultures, antimicrobial sensitivities), type of wound discharge, location, signs and symptoms on infection, operating surgeon, assistants, operating room used, case number that day, and interviewing of medical care providers for the patient. No routine surveillance cultures of surgical sites were obtained in asymptomatic patients except for patients with an open chest, where mediastinal cultures were obtained at the time of chest closure. The SSIs are reported per 100 operations.

Bloodstream infections (unrelated to SSI)
Blood cultures were obtained primarily by peripheral venipuncture; occasionally samples were obtained from arterial or central venous catheters. Indications for obtaining blood cultures included one or more of the following: fever, leukocytosis, hypotension, tachycardia, acidosis, cardiovascular instability, purulent drainage, or other signs and symptoms of infection. A modification of the Center for Disease Control definition for nosocomial BSI was used [13]. Patients who had only one bottle positive with a common skin contaminant instead of two bottles drawn on separate occasions were defined as having a BSI if other signs and symptoms were present. Surveillance blood cultures were not obtained. The BSIs are reported as the number of infections per 1,000 patient-days.

Antibiotic prophylaxis protocols
Protocol 1 (January 1993–march 1994)
Cefazolin (50 mg/kg) was administered intravenously approximately 1 hour before skin incision and continued intravenously (25 mg/kg every 8 hours) until central venous catheters, intracardiac catheters, thoracostomy tubes, and mediastinal tubes were removed. Vancomycin was used for patients allergic to penicillin.

Protocol 2 (April 1994–december 1995)
Cefazolin was administered preoperatively as above, but was discontinued 48 hours postoperatively, regardless of the presence of central venous catheters, intracardiac catheters, thoracostomy tubes, or mediastinal tubes.

Protocol 3 (January 1996–December 1998)
Cefazolin was administered preoperatively as above, but it was continued until 48 hours after thoracostomy tubes and mediastinal tubes were removed. Antibiotics were not continued for the presence of central venous or intracardiac catheters. None of the protocols used AP for endotracheal tubes, arterial catheters, or indwelling urinary catheters.

Most patients had complete closure of the surgical wound before leaving the operating room. However, for some patients (mostly neonates) the sternum was left open and a silastic patch is used to cover the wound. Approximation of the sternum and skin closure usually took place 3 to 7 days postoperatively. Antimicrobial prophylaxis for these open-chest patients was the same for all three protocols. Antimicrobial prophylaxis consisted of preoperative intravenous cefazolin (50 mg/kg), with intravenous vancomycin (10 mg/kg/dose every 12 hours) and intravenous gentamicin (2.5 mg/kg/dose every 8 hours) started upon arrival to the intensive care unit. These antibiotics were continued until 48 hours after chest closure. Cefazolin was readministered if indicated by the protocol following chest closure. Occasionally, patients would have their chest opened postoperatively in the intensice care unit due to complications (tamponade, cardiac arrest). These patients also received vancomycin and gentamicin upon chest opening, which was continued until 48 hours after chest closure. Patients with open chest postoperatively are included in the totals for SSI patients, as well as being evaluated separately as a subgroup.

Statistical analysis
The ² analysis or Fisher’s exact test was used to compare results between protocols.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
SSI
The number of patients operated on during protocols 1, 2, and 3 were 786, 1,095, and 2,039, respectively. Total SSI rates were 2.04%, 6.58%, and 1.67% during protocols 1, 2, and 3, respectively. Superficial infections and deep incisional/mediastinal infections were evaluated as subgroups. They also followed a similar rate pattern with each protocol (Fig 1 and Table 1). The average length of time from operation to diagnosis of infection was 16, 12.6, and 15 days for protocols 1, 2, and 3, respectively. The average age of patients diagnosed with a SSI was 12, 14.2, and 15.4 months during protocols 1, 2, and 3, respectively. Patients who were less than 1 year of age represented 78% of SSI, and infants less than 3 months of age represented 43% of SSI.

View larger version (46K): [in this window] [in a new window]   Fig 1. The incidence of surgical site infection in relation to the time period and antibiotic prophylaxis protocol used.

SSI after hospital discharge
Infections diagnosed after discharge from the hospital accounted for 29% of all SSI over the time period studied. Of these infections, 63% were readmitted for antibiotic treatment, 27% were treated as outpatients.

Organisms associated with SSI
Coagulase-positive Staphylococcus was the predominant organism identified for SSIs during all three protocols; however, considerable variation between the three protocols was present (Table 2).

	Comment

Top Abstract Introduction Patients and methods Results Comment References

We observed an increase in SSI and BSI shortly after reducing our postoperative prophylaxis from coverage for transthoracic tubes and central venous catheters to limiting antibiotics to the first 48 hours postoperatively. Shortly after changing our protocol back to providing antibiotics as long as transthoracic tubes were in place, the SSI rate decreased to the level initially observed when longer postoperative coverage was used (Fig 1). This suggests that for pediatric patients undergoing an operation for congenital heart lesions, antibiotic prophylaxis until removal of transthoracic drainage tubes may be indicated. Consistent with this, a meta-analysis of experience with thoracostomy tubes placed for a variety of reasons in adults suggests that antibiotic prophylaxis for chest tubes is beneficial [15].

Our retrospective review suffers from the same limitations that any such review does, and the difference in the rate of SSI between the three protocols may have been due to factors other than the antibiotic protocol per se. It is possible, for example, that differences in sterile technique could account for the findings. However, intensive efforts to improve sterile technique in the operating room and the intensive care unit, starting soon after implementation of protocol 2, failed to reduce the rate of SSI, whereas institution of protocol 3 was temporally associated with a reduction in SSI (Fig 1). It is also possible that risk factors for infection were greater during the protocol 2 "era," relative to the time periods before and after it, although this seems unlikely. In fact, if anything, the complexity of the patients most recently operated seems to be greater than for those operated during the second protocol. Perhaps most important, although a relatively long course of antibiotic prophylaxis may be optimal for some institutions, for others a shorter course may be appropriate. A potential limitation of this study is the occasional patient who is diagnosed at a referring institution with a SSI that does not become part of the data set. Therefore, the total number of infections for each period may be slightly underestimated.

A report by Dagan and co-workers [16] from the University of Toronto differs somewhat from our findings. They compared two cohorts of pediatric cardiac surgery patients who underwent operation in 1987 to 1988 (n = 310 patients) and 1991 to 1992 (n = 410 patients). In the 1987 to 1988 cohort, antibiotic prophylaxis for thoracostomy tubes was used. In the 1991 to 1992 cohort, no antibiotic prophylaxis was used for thoracostomy tubes; patients received prophylactic cefazolin only until 48 hours after operation. The rate of SSI was 7% in the 1987 cohort, and 4.3% in 1992. Although this data might suggest that prophylaxis for only 48 hours postoperatively is optimal, the Toronto group had introduced a number of infection control measures designed to decrease the risk of nosocomial infection after 1988 but before 1991, complicating interpretation of the data. It is also important to note that differences in the absolute rate of SSI between our center and that in Toronto may reflect differences in case ascertainment or other factors, and not necessarily indicate a true difference in the rates of infection.

The number of BSI was greater during the periods of time covered by protocols 2 and 3 compared to protocol 1. Although it is possible that this increase was related to the lack of antibiotic coverage while central venous and intracardiac catheters were in place, there are other possible explanations. Most especially, it could be that the risk of bacteremia was greater, owing to more complex patients, greater use of indwelling catheters, and other factors, in the patients most recently cared for. Unfortunately, we do not have data regarding indwelling catheters, nor could readily compare the patient groups in terms of risk for bacteremia.

Patients with an open chest postoperatively had the same prophylaxis while the chest was open; however, during protocol 2 patients would not have antibiotic prophylaxis after chest closure, whereas during protocol 3 patients would be placed on cefazolin after chest closure for as long as chest tubes were present. This may account for the decrease in the SSI rate from 18.8% to 9.3% for open chest patients, which was observed from protocol 2 to protocol 3.

In summary, our recent experience with antibiotic prophylaxis in pediatric cardiac patients suggests that provision of antibiotic prophylaxis for as long as thoracostomy tubes are in place may reduce the rate of SSI (relative to discontinuing antibiotics sooner). Well-controlled, prospective studies, however, will be required to more definitively determine the optimal duration of antibiotic prophylaxis in this setting.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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