Case summary: Kelly Sydell paid us a visit this morning to tell us about a great case– a 74M with PMH aortic stenosis s/p recent aortic valve replacement, who presented with mild hyponatremia with a difficult volume exam, as well as mild incisional erythema and was found to have post-operative Salmonella mediastinitis.
- The most common cause of mediastinitis in the modern era is a post-operative complication of thoracic or cardiac surgery; the majority are monomicrobial and nosocomial.
- Chest CT scan with contrast is the radiologic test of choice in diagnosing mediastinitis, as symptoms and exam findings can be subtle (as in this patient), and mediastinal widening on CXR is not sensitive in post-operative mediastinitis (but interestingly IS more sensitive in mediastinitis from other causes!).
- LT and Goop reminded us that during the AIDS epidemic, we learned that non-typhoidal Salmonella has a predilection for aortitis and mycotic aneurysm, particularly in the setting of atherosclerosis.
- In the olden days, most mediastinitis arose from esophageal perforation, contiguous spread of oropharyngeal infection, penetrating trauma or hematogenous spread
- Now, most cases are the consequence of cardiac or thoracic surgery
- Incidence post-operatively ranges from 0.5-4% and depends on both patient factors (e.g. DM, obesity) and operative characteristics (e.g. how long the sterum is open)
- Bacteriology (majority nosocomial and mono microbial):
- More atypical causes: fungi, Legionella, Mycoplasma hominis, or Nocardia and Mycobacterium tuberculosis
- Presentation can be fulminant and acute or mild and subacute-to-chronic
- Patients present with:
- chest pain
- sternal instability
- signs of sternal wound infection
- purulent discharge
- majority with leukocytosis and 50% with +BCx
- Physical exam findings can be subtle; if suspicious, mediastinal widening on CXR is insensitive for post-operative mediastinitis (more sensitive for non-post-op causes), so radiologic test of choice is CT chest with contrast
- surgical debridement with either primary or secondary closure
- antibiotics for 2-6 weeks (vanc/zosyn–> narrow pending intra-operative cultures)
Dubert M, Pourbaix A, Alkhoder S, Mabileau G, Lescure F-X, Ghodhbane W, et al. (2015) Sternal Wound Infection after Cardiac Surgery: Management and Outcome. PLoS ONE 10(9): e0139122.
Salmonella and the vasculature
- Vascular infections due to Salmonella can involve the thoracic and abdominal aorta, as well as coronary arteries, peripheral arteries, or vascular grafts and prosthetic valves.
- Aortic infections are much more frequent, and the majority of these involve the abdominal aorta.
- Nearly all cases of aortitis due to Salmonella result in formation of an aneurysm or, less commonly, in enlargement of a previously existing aneurysm
- Most patients with aortitis due to Salmonella have preexisting atherosclerotic disease at the site of the subse- quently infected aneurysm
- Mediastinitis due to Salmonella is rare and morbid, as it is strongly associated with concomitant aortitis, mycotic aneurysm, and rupture.
Soravia-Dunand, VA et al. Aortitis Due to Salmonella: Report of 10 Cases and Comprehensive Review of the Literature. Clinical Infectious Diseases 1999;29:862–8.
Fernández-Ayala M1, Nan D, Gutierrez JA, Fariñas MC. Postoperative mediastinitis due to Salmonella. Scand J Infect Dis. 2003;35(1):67-8.
Approach to hyponatremia
Just a reminder that until robots take over medicine and improve our volume exams, there exists a very nifty volume-independent hyponatremia algorithm found here (Rabih version) and here (Rachel Stern version)!