[Infection of sternal wound in heart surgery: analysis of 1000 operations]

Sternal wound infection (SWI) is the most important complication in cardiac surgery. The aim of this study was to describe the frequency and clinical and microbiological features of this complication.

All the cases of SWI which were observed in the authors' hospital in the first 1,000 cardiac surgery operations performed with extracorporeal circulation were retrospectively reviewed. The cases were identified through the Infectious Diseases and Cardiac Surgery Department files and were classified according to the depth of the infection. During the study period neither the prophylaxis against infection nor the surgical techniques were modified.

Forty-three patients (4.3%) presented SWI. Fourteen were superficial infections and 29 were deep infections of which 9 were classified as osteomyelitis and 20 as mediastinitis. A progressive decrease was observed in the proportion of SWI over time parallel to an increase in the number of operations performed. Staphylococcus aureus was the agent most frequently isolated (60.4%). Gram-positive aerobic cocci were found in 66.7% of the total number of isolations, being most frequent in the deep infections (83.3% of the isolations). The gram-negative aerobic bacilli were isolated more frequently in the superficial infections than in the deep infections (57.8% v.s. 16.7% of the isolations, respectively p < 0.01). In patients with SWI the predictive value of the positive blood cultures for the diagnosis of mediastinitis was 83.3%, with a sensitivity of 50% and specificity of 91.3%. Three patients with deep infection developed chronic complications and another three died (mortality by mediastinitis 15.0%). The mean postoperative stay was 52 days for the patients with deep infection and 39 days for those with superficial infection (p = NS).

The percentage of surgical wound infection during the study period showed a trend to a decrease parallel with an increase in the number of operations. The gram-positive bacteria were responsible for most of the SWI. Although the depth of SWI is difficult to clinically predict, the presence of bacteremia suggests the existence of mediastinitis. Despite their lesser clinical importance, the superficial infections carry a long postoperative stay.