Sternal wound infection revisited

Sternal wound infections (SWIs) can be subdivided into two types, superfici al or deep, that require different treatments. The clinical diagnosis of su perficial SWI is normally easy to perform, whereas the involvement of deep tissues is frequently difficult to detect. Therefore, there is a need for a n imaging study that permits the assessment of SWIs and is able to distingu ish between superficial and deep SWI. The present work was a prospective st udy aiming to evaluate the role of technetium-99m hexamethylpropylene amine oxime (Tc-99m-HMPAO) labelled leucocyte scan in SWI management. Twenty-eig ht patients with suspected SWIs were included in the study. On the basis of clinical examination they were subdivided into three groups: patients with signs of superficial SWI (group 1), patients with signs of superficial SWI and suspected deep infection (group 2) and patients with suspected deep SW I without superficial involvement (group 3). Ten patients previously submit ted to median sternotomy, but without suspected SWI, were also included in the study as a control group (group 4). All patients with suspected SWI had bacteriological examinations of wound secretion, if present. In addition T c-99m-HMPAO labelled leucocyte scan was performed in all patients. The pati ents of groups 1, 2 and 3 were treated on the basis of the clinical signs a nd microbiological findings, independently of the scintigraphic results. Th e patients of group 4 did not receive treatment. The final assessment of in fection was based on histological and microbiological findings or on long-t erm clinical follow-up. Sensitivity, specificity, accuracy and positive and negative predictive values for scintigraphic and non-scintigraphic results were calculated. In the diagnosis of superficial and deep SWI, clinical an d microbiological examination (combined) yielded, respectively, a sensitivi ty of 68.7% and 100%, a specificity of 77.3% and 80.8%, an accuracy of 73.7 % and 86.8%, a positive predictive value of 68.7% and 70.6% and a negative predictive value of 77.3% and 100%. The scintigraphic results obtained in s uperficial SWI yielded a sensitivity of 56.2%, a specificity of 90.9%, an a ccuracy of 76.3%, a positive predictive value of 81.8% and a negative predi ctive value of 74.1%, while, by contrast, in deep SWI all of these values w ere 100%. Therefore, one can conclude that Tc-99m-HMPAO labelled leucocyte scan permits accurate diagnosis of deep SWI, solving the main clinical prob lem in this field. In the present study the categorisation of patients with out taking into account Tc-99m-HMPAO labelled leucocyte planar scan finding s caused a non-negligible number of cases of superficial SWI to be treated as though they were deep SWI. This "overestimation" led to unnecessary surg ery, increased and prolonged use of antibiotics with more (higher) toxicity and additional expense.