Abstract
Knowledge of infections encountered in the setting of cardiac surgery, and their prevention and treatment, is essential for health professionals working in this area.
Knowledge of infections encountered in the setting of cardiac surgery, and their prevention and treatment, is essential for health professionals working in this area.
Endocarditis
The incidence ranges from three to seven cases per 100,000-person years. Recognized risk factors include age, pre-existing structural heart disease, prosthetic valves or devices and a history of endocarditis, with intravascular catheters or IV drug misuse also acknowledged.
Endocarditis may present acutely or indolently. Common features include fever and a new murmur.
Duke criteria (Box 40.1) are a useful method by which to attribute a likelihood of endocarditis.
Box 40.1 Modified Duke criteria
- Major
Positive blood cultures:
Two positive cultures with typical pathogen taken more than 12 hours apart, or majority of three or four taken less than 1 hour apart
Single positive blood culture for Coxiella burnetii or anti-phase 1 immunoglobulin G titre >1,800
Positive echocardiogram findings:
Oscillating intracardiac mass on valve or supporting structures, in the path of regurgitant jets, or on implanted material in the absence of an alternative anatomic explanation
Abscess
A new partial dehiscence of prosthetic valve or new valvular regurgitation
(TOE advised in patients with prosthetic valves)
Evidence of endocardial involvement
- Minor
Predisposing factor
Fever
Positive blood culture that does not meet major criteria or serological evidence of infection
Vascular phenomena:
Embolic phenomena (arterial, pulmonary), conjunctival haemorrhage, Janeway lesions, mycotic aneurysm, intracranial haemorrhage
Immunological phenomena:
Glomerulonephritis, Osler’s nodes, Roth spots, positive rheumatoid factor
Clinical diagnosis: Two major criteria, or one major criterion plus three minor criteria, or five minor criteria.
Empirical regimens are based on the likely causative organisms (Box 40.2) and patient-specific factors such as colonization with resistant organisms. Antimicrobial treatment of endocarditis varies according to the pathogen, therefore culture is essential. Serological testing may be helpful for organisms which cannot be cultured (e.g. Bartonella species, Coxiella burnetii and Brucella species). If a causative organism is not identified, antibiotic management is determined by epidemiological and risk factors that are specific to the individual patient; 16s ribosomal RNA analysis of the tissue that is subsequently excised may be helpful.
Box 40.2 Aetiology of endocarditis
Streptococcus spp.
Staphylococcus aureus
Enterococcus spp.
Coagulase negative staphylococci
HACEK (Haemophilus spp., Aggregatibacter spp.,
Cardiobacterium hominis, Eikenella corrodens, Kingella spp.)
Culture negative
Fungi
Polymicrobial
Other
Mycobacterium chimaera has recently been recognized as a cause of endocarditis amongst patients who have undergone open heart surgery. This organism is not detected by routine culture methods; therefore, specialist advice should be sought for patients with culture-negative prosthetic-valve endocarditis or endovascular graft infection.
The treatment duration for native-valve endocarditis varies from 2 weeks to 8 weeks, depending on the causative organism, and a minimum of 6 weeks for prosthetic-valve endocarditis.
A surgical consultation is advised for fungal infection, resistant organisms, prolonged bacteraemia, embolic events and left heart Gram-negative endocarditis. If surgery is performed during treatment, the duration of treatment does not change unless either an abscess is found or valve cultures are positive, in which case the day of surgery is counted as day one of treatment.
Guidelines on the management of endocarditis (American Heart Association 2015; European Society of Cardiology 2015) recommend a multidisciplinary team approach to treat patients with endocarditis, reflecting the many complications associated with this condition.
Prophylaxis against Endocarditis
Opinion is divided regarding the need for prophylaxis against infective endocarditis. NICE guidance (2008, updated July 2016) advises that prophylaxis is no longer required for high-risk procedures and only needed if a surgical procedure is being carried out in an infected site. Several studies have suggested an increase in endocarditis incidence since 2008, though a causal relationship with the implementation of the NICE guidelines has not been established. In contrast to NICE, the European Society of Cardiology (2015) continues to recommend prophylaxis for procedures requiring manipulation of the gingival or periapical region, or perforation of the oral mucosa in patients defined as high risk.
Surgical Site Infections
Surgical site infections (SSIs) are one of the most common type of healthcare-associated infections in the UK. They usually occur within 30 days in the anatomical area where surgery occurred. SSIs can be:
Superficial: limited to the skin and subcutaneous tissues
Deep: involving muscle and fascia
Organ/space: involving the anatomy opened or manipulated during the surgery e.g. bone, mediastinum, myocardium
Deep and organ/space SSIs include infections occurring up to 1 year after surgery, if an implant is in place.
The pathogens involved can be either endogenous (part of the patient’s flora) or exogenous (from the physical environment or surgical team).
Factors contributing to the likelihood of an SSI include patient-related factors (e.g. age, nutritional state) and surgery-related factors (e.g. duration of surgery, presence of foreign material).
Surgical Prophylaxis
Antibiotic prophylaxis is an important measure in preventing a postoperative SSI. For effective prophylaxis, bactericidal concentrations of antibiotic must be attained in both the serum and target tissue from the time of incision until wound closure. SSI rates increase when prophylactic antimicrobials are given either too soon or too late; antimicrobial prophylaxis should be administered an hour or less before skin incision; as close to the time of incision as possible.
Prophylaxis is recommended for rhythm-management-device insertion, open heart surgery and interventional cardiac-catheter-device placement.
A single dose is sufficient for most types of surgical procedures although for cardiac surgery there is evidence to suggest that prolonging prophylaxis to 48 hours post surgery may reduce infections.
Whether or not a further intraoperative dose of antibiotic is required depends upon the duration of surgery, blood loss and the antibiotic half-life. Re-administration of the antibiotic during surgery should be within two half-lives, with some advising within one half-life.
There is lack of consensus as to the ‘optimal’ prophylaxis regimen but, as the most common pathogen is Staphylococcus aureus, regimens should ensure activity against this pathogen in line with local resistance profiles.
Additional cover for Gram-negative organisms can be provided by adding gentamicin to narrow-spectrum regimens such as glycopeptides or flucloxacillin.
Mediastinitis
Post-sternotomy mediastinitis is a serious complication with mortality of up to 47%. It is defined as any one of the following:
Organism detected from mediastinal tissue or fluid
Mediastinitis visualized at surgery
Fever or chest pain or sternal instability in combination with either purulent discharge or mediastinal widening on imaging
Infection arises from the patient’s own flora, contamination of the surgical field or secondary to sternal wound infections. The incidence ranges from 0.4% to 5%.
The commonest pathogens are Gram-positive organisms, principally Staphylococcus aureus. Infections caused by Gram-negative organisms are less frequent and have been associated with infections at other sites (e.g. pneumonia).
There is no universal agreement on risk factors or their relative contributions, but they include:
Obesity
Diabetes mellitus
Previous sternotomy
Prolonged operative time
Infection at another site
Microbiological samples should include blood cultures, wound tissue or wound discharge. Management comprises surgical debridement in conjunction with broad-spectrum antibiotics, pending culture results.
The treatment duration depends upon the causative organism, involvement of the sternal bone and the response to therapy, but is likely to be weeks to months.
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