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• Authors Response
  Shane George
  Published on: 23 November 2015
• Antibiotic prophylaxis in cardiac surgery
  Graeme MacLaren
  Published on: 23 November 2015

• Published on: 23 November 2015

  Authors Response

  • Shane George
  • Other Contributors:
    • Kay Dhadwal, Sharif Al-Ruzzeh, Thanos Athanasiou, Marina Choudhury, Paris Tekkis, Pynee Vuddamalay, Haifa Lyster and Mohamed Amrani

  Dear Editor,

  We thank Drs Mclaren et al. for their interest in our study.

  Firstly, we chose Vancomycin as we wished to use an antistaphylococcal drug that had been studied in cardiac surgical patients. Additional rifampicin was used in an attempt to prevent resistance developing. Clearly the strategy was successful as we did not see any increase in resistant organisms during, or for the 2 years after,...

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  Dear Editor,

  We thank Drs Mclaren et al. for their interest in our study.

  Firstly, we chose Vancomycin as we wished to use an antistaphylococcal drug that had been studied in cardiac surgical patients. Additional rifampicin was used in an attempt to prevent resistance developing. Clearly the strategy was successful as we did not see any increase in resistant organisms during, or for the 2 years after, the study. We are interested in their statement of a change in their antibiotic prophylaxis with no difference. This statement was unpublished and is not publicly available. They have chosen to retain a unique combination of cephazolin and rifampicin as their prophylaxis. They continue to use an additional antistaphylococcal agent and their choice of rifampicin as a sole agent is unusual, with very little prior experience. Even so, we would suggest that a randomised controlled prospective study is more relevant than the observational data that is quoted.

  Secondly, they have criticised our use of vancomycin timed at induction of anaesthesia. This is frequently how vancomycin for antibiotic prophylaxis is given in many surgical centres, is seen in the study they quote (Vuorisalo) and in other studies that compare vancomycin with cephalosporins, which we have referred to. Others1 have shown that administration more than 60 mins before surgical incision surprisingly may reduce efficacy. Furthermore, our strategy was effective and a more efficacious administration regime could only make this more effective if it had any further effect at all.

  Thirdly, they advocate an even higher dose of cefuroxime but such a dose has not been published in any guideline or used by any other study. We are confident in our dosage and formulation of cefuroxime, as the incidence of infection in the low risk patients ( where cefuroxime was used) operated at the same time, as referred to in our paper and not part of our study, was extremely low.

  Fourthly, Mclaren has questioned the security of blinding in our study with the use of Rifampicin. We clearly acknowledge this limitation in our paper, but the very significant results in further infection surgical procedures, deep SSI and readmission to hospital is unlikely to be accounted for by the possibility of noticing orange colouration of the urine at the time of surgery. Lastly, we used the term ‘longer’ , referring to our 48 hr regime, as increasingly guidelines on surgical prophylaxis are limiting prophylaxis to 24hrs, with little real evidence. The 2 articles quoted in support of their criticism (Habarth & Kato) use ‘48 hours ‘as their definition of short/long term and therefore do not contradict our study.

  To reiterate, in our cohort of patients at high risk of SSI, i.e. obese, diabetic or undergoing bilateral LITA, we showed that longer and broader antibiotic prophylaxis, reduced SSI with clinical, economic and statistical significance.

  References

  1. Kevin W. Garey, Thanh Dao, Hua Chen, et al.
  Timing of vancomycin prophylaxis for cardiac surgery patients and the risk of surgical site infections.
  Journal of Antimicrobial Chemotherapy (2006) 58, 645*650

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  Conflict of Interest:
  None declared.

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• Published on: 23 November 2015

  Antibiotic prophylaxis in cardiac surgery

  • Graeme MacLaren, Intensivist
  • Other Contributors:
    • Siang Fei Yeoh and Denis Spelman

  Dear Editor,

  The recent study by Dhadwal et al. (1) has a number of weaknesses which merit discussion. The study appears to have been initiated by a “perceived increase in crude infection rates” but the organisms responsible for this increase were not presented. Unless there was a high incidence of infection with resistant organisms such as methicillin- resistant Staphylococcus aureus (MRSA) prior to study comme...

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  Dear Editor,

  The recent study by Dhadwal et al. (1) has a number of weaknesses which merit discussion. The study appears to have been initiated by a “perceived increase in crude infection rates” but the organisms responsible for this increase were not presented. Unless there was a high incidence of infection with resistant organisms such as methicillin- resistant Staphylococcus aureus (MRSA) prior to study commencement, the routine use of vancomycin in a multi-drug regimen is hard to justify (2, 3). The authors stated that their antibiotic regimen was based, at least in part, on Spelman et al. (4). However, it is worth noting that the prevalence of MRSA at this author’s institution fell significantly following an intensive infection control programme, prompting a return to cephazolin and rifampicin as prophylaxis against cardiac surgical-site infection (SSI). No significant increase in the incidence of SSI has been observed since the change (unpublished data).

  Dhadwal et al. (1) administered vancomycin after induction of anaesthesia. This approach is not recommended by the Centres for Disease Control and Prevention, as it does not provide adequate tissue levels of antibiotic at the time of surgical incision (2). Nonetheless, the authors documented a decrease in SSI. One explanation for this that appears not to have been considered was that the cefuroxime regimen used in the control arm was suboptimal. Other studies of cefuroxime in cardiac surgery have used considerably higher doses and a 1.5g load may be inadequate (5, 6). Moreover, a recent report highlighted significant problems with some formulations of cefuroxime (7). Dhadwal et al. (1) did not state which formulation they used.

  Blinding in the study was suboptimal both due to the orange discolouration of urine seen in patients given rifampicin and because the study required antibiotics to be given at different times and for different durations, potentially unmasking patient assignment.

  The authors concluded that longer duration of antibiotic prophylaxis reduces the incidence of SSI. However, this was not a study comparing two identical antibiotic regimens with different durations. We believe that this conclusion is both misleading and unjustified. There is substantial evidence that prolonged duration of prophylactic antibiotic therapy is detrimental to patients (8-10).

  References:

  1. Dhadwal K., Al-Ruzzeh S., Athanasiou T., et al.
  Comparison of clinical and economic outcomes of two antibiotic prophylaxis regimens for sternal wound infection in high-risk patients following coronary artery bypass grafting surgery: a prospective randomised double-blind trial.
  Heart 2007:93:1126-1133

  2. Mangram AJ., Horan TC., Pearson ML., Silver LC., Jarvis WR.
  Guideline for prevention of surgical site infection, 1999. Hospital Infection Control Practices Advisory Committee
  Infect Control Hosp Epidemiol 1999:20:250-278

  3. Vuorisalo S., Pokela R., Syrjala H.
  Comparison of vancomycin and cefuroxime for infection prophylaxis in coronary artery bypass surgery.
  Infect Control Hosp Epidemiol 1998:19:234-239

  4. Spelman D., Harrington G., Russo P., Wesselingh S.
  Clinical, microbiological, and economic benefit of a change in antibiotic prophylaxis for cardiac surgery.
  Infect Control Hosp Epidemiol 2002:23:402 -404

  5. Mandak J., Pojar M., Malakova J., et al.
  Tissue and plasma concentrations of cephuroxime during cardiac surgery in cardiopulmonary bypass- a microdialysis study.
  Perfusion 2007:22:129-136

  6. Nascimento JW., Carmona MJ., Strabelli TM., Auler JO Jr., Santos SR.
  Systemic availability of prophylactic cefuroxime in patients submitted to coronary artery bypass grafting with cardiopulmonary bypass.
  J Hosp Infect 2005:59:299-303

  7. Mastoraki E., Michalopoulos A., Kriaras I., et al.
  Incidence of postoperative infections in patients undergoing coronary artery bypass grafting surgery receiving antimicrobial prophylaxis with original and generic cefuroxime.
  J Infect 2007: Epub ahead of print.

  8. Harbarth S., Samore MH., Lichtenberg D., Carmeli Y.
  Prolonged antibiotic prophylaxis after cardiovascular surgery and its effect on surgical site infections and antimicrobial resistance.
  Circulation 2000:101:2916-2921

  9. Kato Y., Shime N., Hashimoto S., et al.
  Effects of controlled perioperative antimicrobial prophylaxis on infectious outcomes in pediatric cardiac surgery.
  Crit Care Med 2007:35:1763-1768

  10. Edwards FH., Engelman RM., Houck P., Shahian DM., Bridges CR.
  The Society of Thoracic Surgeons Practice Guideline Series: Antibiotic Prophylaxis in Cardiac Surgery, Part I: Duration.
  Ann Thorac Surg 2006:81:397-404

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  Conflict of Interest:
  None declared.

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