Best Evidence Topics

Diagnosis

Benlolo S, Mato J, Raskine L et al.
Sternal puncture allows an early diagnosis of poststernotomy mediastinitis
Journal of Thoracic and Cardiovascular Surgery
2003;125(3):611-617.
  • Submitted by:Joel Dunning - RCS Research Fellow
  • Institution:MRI
  • Date submitted:11th April 2003
Before CA, i rated this paper: 5/10
1 Objectives and hypotheses
1.1 Are the objectives of the study clearly stated?
  Objectives: Poststernotomy mediastinitis after cardiac operations is a nosocomial infection involving the mediastinal space and the sternum, with a high mortality rate mostly related to a late diagnosis. We investigated whether sternal puncture might facilitate and shorten the delay in the diagnosis of mediastinitis.
2 Design
2.1 Is the study design suitable for the objectives
  Yes, They are looking for a diagnostic test for mediastinitis,
therefore a diagnostic study is appropriate
2.2 Who / what was studied?
  A prospective study was performed from February 1996 to September 1999 in 1024 patients undergoing sternotomy in the cardiac surgery unit in France. Of these 43 had mediastinitis and 49 had Sternal Puncture as a diagnostic procedure. (1) body temperature of greater than 38.5C or less than 35.5C; (2) heart rate of greater than 90 beats/min; (3) white blood cell count of greater than 12,000/mm3 or less than 4000/mm3; (4) tachypnea(respiratory rate >20 breaths/min or mechanical ventilation) n = 49 patients
2.3 Was this the right sample to answer the objectives?
  Seems to be the correct cohort of patients.
2.4 Is the study large enough to achieve its objectives? Have sample size estimates been performed?
  No sample size estimates done. Seems to be a small study with only 49 diagnostic tests done. This small size is seem in the wide confidence intervals (which the authors did not publish)
2.5 Were all subjects accounted for?
  1024 patients operated on.
Sternal Puncture performed on 49 patients
Epicaridial wire culture on all patients
43 cases of mediastinits
9 deaths in mediastinits groups
2.6 Were all appropriate outcomes considered?
  Outcome measure (or Gold standard) was mediastinitis defined by positive microbiology at operation. Mortality was not considered
2.7 Has ethical approval been obtained if appropriate?
  Yes
2.8 Was an independent blinded gold standard test applied to all subjects?
  The gold standard was either reoperation or 3 month follow up to exclude mediastinits, therefore the postitive cases had a different gold standard to the negative patients, although taken together this may be a reasonable Gold Standard as long as both techniques are 100% Sensitive and Specific for detecting mediastinitis.
3 Measurement and observation
3.1 Is it clear what was measured, how it was measured and what the outcomes were?
  Diagnostic Measurements are Cultures of sternal Aspirate from 3 locations per patient along sternotomy. Outcome measure is positive bacteriology on sternal debridement
3.2 Are the measurements valid?
  Their outcome measure of Mediastinitis does not correspond exactly to the Centre for Disease Control definition of Mediastinitis, although it is fairly similar. In particular some patients in this study may have been missed that count as mediastinitis by CDC definitions, who had fever or sternal instability and blood or mediastinal discharge positive microbiology, without neccessarily having a reoperation
3.3 Are the measurements reliable?
  Measurements of outcome are microbiological growth so should be reliable. However the decision to perform a reoperation may not have been as reliable or reproducible
3.4 Are the measurements reproducible?
  Measurements of outcome are microbiological growth so should be reliable. However the decision to perform a reoperation may not have been as reliable or reproducible
4 Presentation of results
4.1 Are the basic data adequately described?
  Yes. Results were as Follows :
When compared with the bacteria found during the operation, Gram stain results of sternal puncture show 12 of 23 true-positive and no false-positive results (Table 1). Bacteriologic results of sternal puncture were further improved with cultures, mostly received 24 hours later (23/23 true-positive results; Table 1). In the group of patients without mediastinitis undergoing sternal puncture (n = 26), 24 had true-negative cultured sternal puncture results, and 2 were considered to have false-positive results (Table 1) because bacteria found in the sternal puncture were Propionobacterium acnes and coagulase-negative Staphylococcus species other than S epidermidis. These 2 patients were, however, not operated on because of suspicion of skin contamination. A second puncture performed 24 hours later had negative results for both patients, and 3-month follow-up confirmed the lack of mediastinitis.
4.2 Are the results presented clearly, objectively and in sufficient detail to enable readers to make their own judgement?
  Yes. Sensitivities and specificities not given :
they are Sensitivity 52% (CI 31% to 73%)
Specificity 100% (CI 86% - 100%)
4.3 Are the results internally consistent, i.e. do the numbers add up properly?
  yes
5 Analysis
5.1 Are the data suitable for analysis?
  no real analysis was done for analysis of the diagnostic test. In particular confidence intervals were not included.
5.2 Are the methods appropriate to the data?
  For comparing Sternal Puncture group to non Sternal Puncture group appropriate tests were done
5.3 Are any statistics correctly performed and interpreted?
  A significantly smaller delay in diagnosis of mediastinitis was shown in the group of patients with mediastinitis who had Sternal Puncture compared to those who did not have puncture.
6 Discussion
6.1 Are the results discussed in relation to existing knowledge on the subject and study objectives?
  The authors could find no other studies using this technique to diagnose sternal puncture, therefore these results were compared only to previously published data on Epicardial wires and Pericardial aspiration.
6.2 Is the discussion biased?
  The discussion reads : The Rates of both true-positive and true-negative results reached 100%, with no adverse effects related to the sternal puncture.
This does not make good sense. The authors meant to say that the Positive predictive value was 100%.
However they did not discuss their results in terms of sensitivity and specificity.
7 Interpretation
7.1 Are the authors' conclusions justified by the data?
  They should have discussed their results in terms of sensitivity and specificity but their conclusions are otherwise justified
7.2 What level of evidence has this paper presented? (using CEBM levels )
  Level 2a
7.3 Does this paper help me answer my problem?
  This paper tells us that if a Sternal puncture is performed and positive culture is obtained, this rules IN the diagnosis of Mediastinitis (absolute SpIN)
However a negative result does not exclude the result
After CA, i rated this paper: 5/10
8 Implementation
8.1 Can the test be implemented in practice?
  Easily
8.2 What aids to implementation exist?
  No new equipment or skills needed
8.3 What barriers to implementation exist?
  Confidence in the findings of the study, and patients anxiety over the test
8.4 Are my patients the same as the patients tested?
  Yes
8.5 Will the test improve diagnosis in my patients?
  Yes