Postoperative mediastinitis in cardiac surgery - microbiology and pathogenesis.

OBJECTIVE: During 1992-2000, postoperative mediastinitis developed after 126 (1.32%) of 9557 consecutive cardiac surgery procedures. The study was done to describe the variation in clinical characteristics and microbiological etiology in mediastinitis. METHODS: The records of 126 cases of postoperative mediastinitis were reviewed. RESULTS: The median time from operation to the development of mediastinitis was 7 days. Sternal dehiscence was seen in 86 patients (68%). Coagulase negative staphylococci (CNS) were isolated in 46% of the cases with a verified microbiological etiology, Staphylococcus aureus in 26% and gram-negative bacteria in 18%. CNS were more frequently isolated in patients with sternal dehiscence (44/80, 55%) than in patients with stable sternum (10/38, 26%) (P=0.003). However, S. aureus was more frequent in patients with stable sternum (18/38, 47%) than in patients with sternal dehiscence (13/80, 16%) (P<0.001). High body mass index was associated with coagulase negative staphylococci (P<0.001) and with sternal dehiscence (P=0.008). Chronic obstructive pulmonary disease was also associated with sternal dehiscence (P<0.001) and with coagulase negative staphylococci (P=0.04). Patients who had been reoperated before onset of mediastinitis tended to have an increased risk for a gram-negative etiology (32 vs. 15% in patients not reoperated, P=0.06). The overall 90-day all cause mortality in patients with mediastinitis was 19%. High age, need for reoperation before mediastinitis, and a long primary operation time was associated with increased mortality (P=0.02, P=0.007 and P=0.001, respectively). No specific bacterial etiology was associated with increased mortality nor was the presence of bacteriemia. CONCLUSIONS: Three different types of postoperative mediastinitis can be distinguished: (1) mediastinitis associated with obesity, chronic obstructive pulmonary disease, and sternal dehiscence, typically caused by coagulase negative staphylococci; (2) mediastinitis following peroperative contamination of the mediastinal space, often caused by S. aureus, and (3) mediastinitis mainly caused by spread from concomitant infections in other sites during the postoperative period, often caused by gram negative rods. The proposed classification of mediastinitis into three groups with different pathogenic mechanisms may be useful in understanding which prophylactic counter measures have the potentials to be effective in a given situation.

Continuous ambulatory monitoring of absolute right ventricular pressure and mixed venous oxygen saturation in patients with heart failure using an implantable haemodynamic monitor: results of a 1 year multicentre feasibility study.

BACKGROUND: Implantable sensors that monitor haemodynamics over time may be useful in patients with heart failure. This multicentre study assessed the feasibility of a system that has one sensor measuring absolute pressure and another measuring mixed venous oxygen saturation (SvO(2)). Both sensors were mounted on leads that were implanted in the right ventricle. METHODS: Twenty-one patients with heart failure (NYHA II-III) were included. Comparisons were made to right heart catheterizations at implant and at 2, 6 and 12 months thereafter. Patients underwent several haemodynamic provocations during the catheterizations. RESULTS: Overall, among functioning sensors, the IHM-1 values were highly correlated with reference values for all time points during all provocations, demonstrating high reproducibility and stability (r(2)=0.91, 0.79 and 0.78 for systolic, right ventricular diastolic and SvO(2), respectively). Although IHM-1 underestimated reference pressure values by 4.5 mmHg and SvO(2)by 1.6%, this difference was consistent across provocation and stable over 12 months of follow-up. Twelve of the 21 oxygen sensors failed to function and two pressure sensors had component failures. Preliminary analysis of long-term data revealed haemodynamic patterns that may be key indicators for therapeutic interventions. CONCLUSION: This multicentre feasibility study demonstrated the accuracy and stability of sensors implanted in the right ventricle. The IHM-1, using right ventricular pressures and SvO(2), with improved performance, might be useful in the study of pathophysiological mechanisms and treatment interventions in heart failure.

Effects of cardiac surgery on some clinically used inflammation markers and procalcitonin.

One hundred and ten patients were investigated prospectively in a study aimed at creating reference curves for inflammation markers (serum C-reactive protein (CRP), blood leukocyte count, iron, transthyretin and procalcitonin). Blood samples were taken daily and the patients were monitored for signs of infection. Ninety-six patients had no postoperative infections. CRP and leukocyte counts peaked on the third and second postoperative days, respectively. Neither patients operated on off-pump (n = 4) nor patients with minor infections (n = 11) differed from the non-infected group. Two out of three patients with major postoperative infection exhibited a secondary peak in CRP and leukocyte count. Iron and transthyretin decreased initially, followed by a slow increase without any difference between the groups. Procalcitonin was high in some non-infected patients and low in some infected patients. CRP and leukocyte count had a predictable course with a secondary peak in major infections but the other markers did not provide any valuable information.

Spread of coagulase-negative staphylococci during cardiac operations in a modern operating room.

BACKGROUND: Coagulase-negative staphylococci cause 33% to 62.5% of wound infections after cardiac operations. The aim of this study was to investigate the sources of coagulase-negative staphylococci in the sternal wound. METHODS: Twenty operations performed in zonal ventilated operating rooms were investigated prospectively. Cultures were taken from all persons present in the room, the sternal wound, and the air. Isolates macroscopically judged to be coagulase-negative staphylococci were metabolically classified, and similar isolates were investigated by pulsed-field gel electrophoresis. RESULTS: Bacterial counts in the operating room air were very low. Wound contamination was found in 13 of 20 operations. Six wound isolates could be traced, three to the patients' sternal skin, one to the patient's groin, one to the surgeon's nose, and one to the surgeon's arm and forehead and the assistant's nose. Three operating field air cultures could be traced to the scrubbed theatre staff. The single case of superficial sternal wound infection was caused by Staphylococcus aureus, which was not isolated from the wound at operation. CONCLUSIONS: In an ultraclean environment, bacteria in the sternal wound originated from the patients' own skin and from the surgical team.

Computed tomography of the sternum and mediastinum after median sternotomy.

BACKGROUND: Computed tomography is used in our hospital to diagnose complications after median sternotomy, but its efficiency is unknown. Nor is the computed tomographic appearance of normal healing of a median sternotomy known. Computed tomography was evaluated for its ability to diagnose mediastinitis and sternal dehiscence, and a reference material of normally healing median sternotomies was created. METHODS: In a prospective study, 20 patients with a normally healing median sternotomy were examined 1 week, 1 month, 3 months, and 6 months after operation. In a retrospective study, 87 scans from 65 patients that were made because a postoperative complication was suspected were reviewed. RESULTS: In the prospective study, all patients had clinically uneventful healing. None of the computed tomographic scans showed radiologic signs of healing at 3 months. At 6 months, half of the patients had healed completely. In the retrospective study, 49 scans were performed on suspicion of infection; 7 of them indicated mediastinitis, 2 were false-positive, while mediastinitis was present in a total of 16 of the scans. Thirty-eight scans were made because of sternal pain or suspected dehiscence; after 21 of the scans, recovery was uneventful, and in 11, the definite diagnosis was dehiscence or pseudarthrosis. CONCLUSIONS: Clinical healing of the sternotomy does not correlate with the computed tomographic image. Computed tomography is not a sensitive tool for diagnosing mediastinitis, and in patients with sternal pain, it adds little information.

Continuous ambulatory haemodynamic monitoring with an implantable system. The feasibility of a new technique.

AIMS: This study evaluates the feasibility and safety of a completely implantable system for long-term ambulatory monitoring of important haemodynamic parameters in patients with severe cardiopulmonary disease. METHODS: The design of the implantable monitoring system is similar to a conventional single lead pacemaker. A lead with incorporated biosensors for the continuous recording of pressure and oxygen saturation signals is positioned in the right ventricle and connected to a monitor and memory device subcutaneously implanted like an ordinary pacemaker can. RESULTS: Five patients with implanted haemodynamic monitoring systems have been followed for from 7 to 16 months. Continuous measurements of activity, heart rate, mixed venous oxygen saturation and estimated pulmonary artery diastolic pressure were registered with variable resolution during daily living and predefined provocations. The memory covered a maximum of 3 weeks at low resolution. The monitored parameters showed an adequate and significant response to various haemodynamic situations. Except for the demand of recalibration of two oxygen sensors, there were no technical problems and the quality of data were excellent. CONCLUSION: Long-term ambulatory haemodynamic monitoring is feasible and potentially useful for the management of patients with severe cardiopulmonary disease.

Mediastinitis after cardiovascular operations: a case-control study of risk factors.

BACKGROUND: An analysis of risk factors for postoperative mediastinitis can lead to a better understanding of the pathogenesis of this complication and to more effective preventive measures. METHODS: This case-control study of 37 patients and 74 matched controls evaluated 54 potential risk factors. RESULTS: Nine variables were significantly associated with increased risk of postoperative mediastinitis: total operation time (p = 0.0013), high body-mass index (p = 0.0033), use of beta-adrenergic drugs before the onset of infection (p = 0.0037), long cardiopulmonary bypass time (p = 0.0072), long aortic cross-clamp time (p = 0.0075), presence of diabetes (p = 0.0122), high body weight (p = 0.0130), and use and duration of temporary pacing wires (p = 0.0293 and p = 0.0241 respectively). In a conditional logistic regression analysis, use of beta-adrenergic drugs before the onset of infection (p = 0.0058; odds ratio 19.7; 95% confidence limits, 2.37 and 163.7) and body mass index (p = 0.0082; odds ratio 1.27; 95% confidence limits, 1.06 and 1.52) were independently associated with a significantly increased risk of postoperative mediastinitis. CONCLUSIONS: Obesity and use of beta-adrenergic drugs, which is indicative of obstructive respiratory problems, were the most important risk factors suggesting that mechanical strain on the sternotomy and sternal instability may precede infection. Targeted preventive measures for these groups could be justified.

Long-term recording of cardiac output via an implantable haemodynamic monitoring device.

Long-term monitoring of central haemodynamics with implanted monitoring systems might be valuable in managing heart failure patients. Such systems offer an opportunity for repeated 'semi-invasive' cardiac output determinations according to the Fick principle. Five patients, four with chronic heart failure and one with chronic pulmonary disease, underwent supine exercise testing during cardiac catheterization at 0, 2, 6 and 11 months after implantation of a right ventricular mixed venous oxygen saturation sensor connected to an implantable haemodynamic monitor. The monitor provided a continuous measure of oxygen saturation via a radio-telemetry link to a metabolic cart capable of measurement of breath-by-breath oxygen consumption. Cardiac output was computed using oxygen consumption, mixed venous oxygen saturation, arterial oxygen saturation by pulse oximetry and haemoglobin oxygen capacity. Biosensor-derived oxygen saturation compared to blood samples from the pulmonary artery showed an excellent correlation over time, r2 = 0.94 (implant), r2 = 0.91 (6-11 months). There was a strong correlation between semi-invasive-determined cardiac output using the biosensor and the invasive technique, which persisted over the entire follow-up period. Repeated semi-invasive cardiac output measurements using an implanted haemodynamic monitoring system in chronic heart failure patients is feasible and the data may be of value for optimizing therapy.

Diagnosing sternal wound infections with 99mTc-labeled monoclonal granulocyte antibody scintigraphy.

BACKGROUND: Postoperative mediastinitis is a serious complication of thoracic operations. The diagnosis can sometimes be difficult, especially in cases with subacute clinical presentation. The aim of this study was to assess the clinical use of granulocyte scintigraphy and tomography in the diagnosis of postoperative wound infection and mediastinitis. METHODS: Twenty-nine patients after cardiothoracic operations were included, of whom 5 patients with a normal postoperative course formed the control group. We injected technetium 99m-monoclonal antigranulocyte antibodies and performed single-photon emission computed tomography after 4 and 20 hours. RESULTS: Twenty-three patients had both the early and the later scan; the remaining 6 had only the early scan. Seven scans indicated infection: 3 cases of mediastinitis, 2 cases of superficial wound infection, 1 case of infection in a synthetic aortic graft, and 1 case of osteitis. All were verified by bacterial culture. There was one false-negative scan; this patient had only the early registration and then was explored. CONCLUSIONS: This method when combined with the tomographic scan option is able to distinguish between deep and superficial infections. Two registrations must be made for optimal results.

Surviving resuscitation: successful repair of cardiac rupture.

An 83-year-old man was found unconscious and was successfully resuscitated. Progressive cardiac failure developed. After 42 hours of observation echocardiography revealed cardiac tamponade and a discontinuity in the left atrial wall. Exploration showed a laceration of the left atrium at the junction of the left pulmonary veins, which was closed with a direct suture on cardiopulmonary bypass. The postoperative course was uneventful.