Mediastinal lymphadenopathy detected with an integrated positron emission tomographic/computed tomographic scan: a differential diagnosis to consider before minimally invasive staging

Integrated positron emission tomography combined with plain computed tomography is commonly employed as the diagnostic tool for patients presenting with lung opacities. This technology is non-invasive and does not put the patient at risk of contrast reaction. We report a case of a man who presented with fever, septicaemia, and a left apical lung opacity on chest radiography. His positron emission tomography and plain computed tomography scans showed increased uptake by the left apical lung opacity together with a huge anterior mediastinal mass, suggestive of lung cancer with mediastinal lymph node involvement, and a right upper lobe shadow. After an initial futile bronchoscopy, an endobronchial ultrasound-guided transbronchial needle aspiration of the mediastinal node was planned but a contrast computed tomographic scan of the thorax revealed no significantly enlarged mediastinal lymph nodes. The differential diagnoses of these findings, together with the limitations of positron emission tomography and plain computed tomography, are discussed.

Concordance between side-stream end-tidal carbon dioxide and arterial carbon dioxide partial pressure in respiratory service setting

OBJECTIVE

To explore the correlation and concordance between end-tidal carbon dioxide and arterial carbon dioxide partial pressure, and confirm the experience of the general consensus among service environments.

DESIGN

A prospective cross-sectional analysis.

SETTING

Two respiratory service units in Hong Kong.

PARTICIPANTS

Two hundred respiratory patients were recruited, in whom 219 sets of observations were recorded. Patients deemed to require arterial blood gas determination also had their end-tidal carbon dioxide partial pressure measured at that time, using two LifeSense LS1-9R Capnometers.

MAIN OUTCOME MEASURES

The agreement of end-tidal carbon dioxide partial pressure and arterial carbon dioxide partial pressure was studied by correlation coefficients, mean and standard deviation of their difference, and the Bland-Altman plot.

RESULTS

Overall, the correlation was low and insignificant (r=0.1185, P=0.0801). The mean of the difference was 7.2 torr (95% confidence interval, 5.5-8.9) and significant (P<0.001). The limits of agreement by Bland-Altman analysis were -18.1 to 32.5 torr, which were too large to be acceptable. In the sub-group on room air, the mean difference was reduced to 2.26 torr, the correlation between end-tidal carbon dioxide partial pressure and arterial carbon dioxide partial pressure was 0.2194 (P=0.0068), though statistically significant, the extent of correlation was still low.

CONCLUSION

End-tidal carbon dioxide partial pressure did not show significant correlation or concordance with arterial carbon dioxide partial pressure, especially when supplemental oxygen was used. End-tidal carbon dioxide partial pressure currently cannot replace arterial blood gas measurement as a tool for monitoring arterial carbon dioxide partial pressure. Possible reasons for the discrepancy with previous studies include small sample size in previous studies, lack of research facilities in service settings, and publication bias against negative studies.