Methicillin resistant Staphylococcus aureus infections following cardiac surgery: incidence, impact and identifying adverse outcome traits.

OBJECTIVE: To assess the incidence and impact of Methicillin-resistant Staphylococcus aureus (MRSA) infections on cardiac surgery outcomes and to identify adverse outcome traits. METHODS: Retrospective analysis of prospectively collected data from cardiac surgical and microbiology databases between April 2000 and March 2005. The overall and yearly incidence of positive MRSA cultures was examined along with the distribution of clinical infections and the associated mortality. Pre-operative patient characteristics were analysed between non-survivors and survivors of MRSA infections. Multivariate logistic regression was used to assess the relationship between pre-operative patient characteristics and in-hospital mortality in patients with MRSA. A comparison of post-operative outcomes between non-survivors and survivors of MRSA infections was also carried out and included in the logistic regression analysis. RESULTS: There were 319 patients with positive MRSA cultures during the study period with an overall incidence of 3.9%. Yearly incidence ranged from 2.4% to 5.2%. There were 120 carriers with pre-operative positive cultures of which 25 developed clinical surgical infections leaving 224 patients as the study group. Overall mortality in patients with MRSA during the study period was 12.9%(41/319). Mortality in the study group was 17.8% (40/224). Mortality comparison between MRSA and non-MRSA mediastinitis was 26.7%(8/30) and 17.1%(13/76), respectively (p=0.26). Mortality between MRSA and non-MRSA septicaemia was 46.9% (15/32) and 52.9% (37/70) (p=0.57). Applying the logistic EuroSCORE to the MRSA patients revealed that non-survivors had a significantly higher pre-operative risk of 10.4% compared to survivors with a pre-operative risk of 6.2% (p=0.003). Renal dysfunction and poor ejection fraction were found to be pre-operative factors associated with mortality in MRSA patients following the multivariate logistic regression analysis. Non-survivors had longer stays on intensive care, longer ventilation times, and were more likely to require support with balloon pumps and haemofiltration. MRSA septicaemia and length of ventilation were significantly associated with mortality in MRSA patients ahead of pre-operative characteristics. CONCLUSIONS: The incidence of MRSA is low, but carries a high mortality. MRSA septicaemia and mediastinitis have the highest associated mortality; however, this is not significantly different from non-MRSA infections. Patients with MRSA who die have higher pre-operative risk and have a poorer post-operative course than survivors.

Does off-pump surgery offer benefit in high respiratory risk patients? A respiratory risk stratified analysis in a propensity-matched cohort.

OBJECTIVE: The role of off-pump surgery in high respiratory risk patients remains unclear. In this study, we aim to evaluate the effect of off-pump surgery on high respiratory risk patients. METHODS: To achieve comparative groups, a five digit propensity score matching with 18 pre-operative variables was performed on 4406 consecutive CABG patients operated between January 2000 and September 2003. Respiratory risk stratification was performed with the following variables: (1) FEV(1)<65% of predicted, (2) patients>75 years old, (3) history of current smoking, (4) body mass index more than 40 kg/m(2) and (5) NYHA class IV dyspnoea in combination with current respiratory medication. The presence of two or more variables defined high risk. The primary end point was post-operative ventilation time. We also compared alveolar arterial gradients (A-a gradient) on admission to ITU, 2 and 4h using Friedman rank time analysis. RESULTS: We matched 1353 off-pump patients with 1353 unique on-pump patients. Respiratory risk stratified selection resulted in 73 off-pump and 55 on-pump high-risk patients. In the off-pump group, four (5.5%) patients had more than two selection criteria, compared to one (1.8%) for on-pump patients (p=0.29). The off-pump group had more patients with FEV1<65% compared to on-pump: 65 (89.0%) versus 40 (72.7%); p=0.017. The median ventilation time was significantly shorter for off-pump patients (7h [IQR: 5-14] vs 12h [IQR: 7-18], p=0.003). In the off-pump group, three (4.1%) patients had a ventilation time>48 h compared to eight (14.6%) in the on-pump group, p=0.037. A-a gradient measurements on admission to ITU were lower in off-pump patients (median: 182.3 [IQR: 126.6-216.2]) compared to on-pump patients (median: 194.7 [IQR 139.7-245.4], p=0.064). CONCLUSION: Off-pump surgery offers benefit to high respiratory risk patients by reducing post-operative ventilation time. Off-pump patients also have lower A-a gradients in the early post-operative period but this failed to reach significance.

Mechanical versus medical bridge to transplantation in children. What is the best timing for mechanical bridge?

OBJECTIVE: Precise timing of mechanical circulatory support as a bridge to transplantation is crucial for successful outcome. In our practice, increasing metabolic injury resulting from third organ (renal/gut) dysfunction is an indication for mechanical circulatory support. It is not known how metabolic injury would influence the outcomes in these patients. In this study we compared biochemical and clinical parameters between children who received mechanical circulatory support and those who were treated with medical management alone as a bridge to transplantation. METHODS: Data from 24 patients were retrospectively analysed from their records. There were 11 patients in the mechanical group. In this group, five patients received biventricular assist device, five received veno arterial extra corporeal membrane oxygenation and one received left ventricular assist device. In the medical group, there were 13 patients who received various levels of inotropic support before transplantation. Five clinical and three biochemical parameters were identified and compared between the mechanical and medical groups. Mortality prior to transplantation was also compared between the two groups. Transplantation was the end point of the study. RESULTS: Serum creatinine and serum lactate levels were significantly higher in the mechanical group (P=0.006 and 0.001, respectively), reflecting advanced metabolic injury in these patients. Mean fractional shortening in the mechanical group was 8.4%, compared to 14.5% in the medical group which was statistically significant (P=0.02). All of the 11 patients in the mechanical group were ventilated compared to 7 of the 13 (53.8%) in the medical group. Need for renal support was higher in the mechanical group (83.3%) in comparison to none in the medical group (P=0.023). Mortality in both groups was comparable with two patients in each group. 11 patients in the medical group (84.6%) and 9 in the mechanical group (81.8%) reached transplantation. CONCLUSION: This study confirmed that patients in the mechanical group were considerably worse in metabolic terms when compared to the medical group. Final outcome of bridging them to transplantation was comparable. This study seem to support the justification of reserving the mechanical circulatory support to those who are metabolically more injured without adversely affecting their outcomes.

First report of no-react bovine internal mammary artery performance and patency.

BACKGROUND: No-React treatment is known to render tissues resistant to calcific degeneration and to reduce early inflammatory response. No-React bovine internal mammary artery (NR-IMA) is available for restricted use in Europe. In this first study, our aim was to use magnetic resonance imaging (MRI) to investigate the clinical performance and patency rates of this conduit. METHODS: Seven patients received 8 grafts with NR-IMA. Approval from the Medical Devices Agency of the United Kingdom was obtained for use of this material. One patient needed salvage coronary artery bypass grafting (CABG). Graft patency was investigated with cardiac MRI. One patient was excluded from the MRI study because of the presence of intracerebral metal clips. The mean follow-up period was 2.5 years with a range of 1 to 4.5 years. RESULTS: There was no mortality in this group. After treatment 6 patients were asymptomatic, and 1 patient had class II anginal symptoms. Four (57%) of the 7 NR-IMA grafts remained patent. The longest patency was 4.5 years in a patient who underwent salvage CABG. Other associated grafts in this cohort of patients were 5 left internal mammary arteries (all patent), 1 radial artery graft (patent), and 7 saphenous vein grafts (4 [57%] of 7 patent). There were no occluded NR-IMA grafts in a patient with patent vein grafts. CONCLUSION: We concluded that at 2.5 year follow-up, NR-IMA had a patency rate of 57% (4 of 7 cases). This rate matched the vein graft patency rate in this cohort of patients. With the longest patency of 4.5 years, use of NR-IMA seems to hold promise for the future.

Logistic risk model for prolonged ventilation after adult cardiac surgery.

BACKGROUND: The aim of this study was to develop a multivariate risk prediction model for prolonged ventilation after adult cardiac surgery. METHODS: This is a retrospective analysis of prospectively collected data on 12,662 consecutive patients undergoing adult cardiac surgery between April 1997 and March 2005. Data were randomly split into a development dataset (n = 6,000) and a validation dataset (n = 6,662). A multivariate logistic regression analysis was undertaken using a forward stepwise technique to identify independent risk factors for prolonged ventilation (defined as ventilation greater than 48 hours). The area under the receiver operating characteristic (ROC) curve and the Hosmer-Lemeshow goodness-of-fit statistic were calculated to assess the performance and calibration of the model, respectively. Patients were split into low-, medium-, and high-risk groups based on their predicted probability of prolonged ventilation. RESULTS: Three hundred thirty-three patients had prolonged ventilation (5.5%). Independent variables, identified with prolonged ventilation, are shown with relevant coefficient values and p values as follows: (1) age 65 to 75 years, 0.7831, p < 0.001; (2) age 75 to 80 years, 1.5605, p < 0.001; (3) age greater than 80 years, 1.7115, p < 0.001; (4) forced expiratory volume less than 70% predicted, 0.3707, p = 0.013; (5) current smoker, 0.5315, p = 0.001; (6) serum creatinine 125 to 175 micromol/L, 0.6371, p < 0.001; (7) serum creatinine greater than 175 micromol/L, 1.3817, p < 0.001; (8) peripheral vascular disease, 0.6212, p < 0.001; (9) ejection fraction less than 0.30, 0.7839, p < 0.001; (10) myocardial infraction less than 90 days, 0.7415, p < 0.001; (11) preoperative ventilation, 1.3540, p = 0.004; (12) prior cardiac surgery, 0.8946, p < 0.001; (13) urgent surgery, 0.4414, p = 0.004; (14) emergency surgery, 0.7421, p = 0.005; (15) mitral valve surgery, 0.7715, p < 0.001; (16) aortic surgery, 1.7043, p < 0.001; and (17) use of cardiopulmonary bypass, 0.4052, p = 0.025; intercept, -4.7666. The ROC curve for the predicted probability of prolonged ventilation was 0.79, indicating a good discrimination power. The prediction equation was well-calibrated, predicting well at all levels of risk. A simplified additive scoring system was also developed. In the validation dataset, 5.1% of patients had prolonged ventilation compared with 5.4% expected. The ROC curve for the validation dataset was 0.75. CONCLUSIONS: We developed a contemporaneous multivariate prediction model for prolonged ventilation after cardiac surgery. This tool can be used in day-to-day practice to calculate patient-specific risk by the logistic equation or a simple scoring system with an equivalent predicted risk.