Infections related to coronary artery bypass graft (CABG) surgery are some of the most serious infections in terms of human and financial costs, some experts believe. Due to regulations from the Centers for Medicare & Medicaid (CMS) that are effective Oct. 1, 2008, hospitals will no longer receive higher payments for the additional costs associated with treating patients for certain healthcare-acquired infections (HAIs), including those related to CABG.
Mediastinitis (a deep infection under the wound) related to Staphylococcus aureus is associated with $40,000 to $50,000 in additional costs, but these costs can differ between hospitals depending on whether they use charges or true cost, says Mohamad Fakih, MD, MPH, assistant professor of medicine at Wayne State University School of Medicine in Detroit. Fakih is board certified in internal medicine, infectious diseases and quality, and is hospital epidemiologist and medical director of infection control at St. John Hospital and Medical Center in Detroit.
The new CMS rule may make infection control issues more visible for administrators and could result in greater tools and negotiation power for infection control departments, Fakih says. I wonder if at one point these new rules may push some hospitals to evaluate whether their surgeons are taking on high-risk patients and have some criteria for who would be a surgical candidate.
CABG-related infections are devastating to patients and the healthcare system, says Vance Fowler, MD, MHS, associate professor in the department of medicine at Duke Universitys Division of Infectious Diseases and International Health.
The toll of CABG-related infections due to MRSA (methicillin-resistant Staphylococcus aureus) is significantly higher in terms of lives and healthcare-related dollars, Fowler says. Given its predominance as a cause of healthcare-associated and community-acquired infections, MRSA truly represents an unmet medical crisis in many parts of the United States and the world.
Under the CMS rules, payments will be withheld from hospitals for care concerning certain catheter-associated urinary tract infections, vascular catheter-associated infections, mediastinitis after CABG surgery, and five medical errors including blood incompatibility, air embolism, falls, bed sores and leaving objects in patients bodies after surgery.¹ CMS authorities may consider adding other HAIs and medical errors to this list. The current list complies with a 2005 law passed by Congress, and includes conditions that affect large numbers of patients, require high treatment costs, and for which there are prevention guidelines.¹ The new regulations prevent hospitals from billing patients when payments are withheld, and are intended to prevent the avoidance of patients who are perceived to be at risk for infections.¹
So far, there is not much of a buzz in the infection control industry regarding the regulation change, Fakih says. A few months ago he informed the administration at his facility about the new rules, and they understand the financial risks, he adds.
He says that he does not think the shift in reimbursement will make a big difference in how infection control issues are prioritized. The example is our hospital, Fakih says. We have incorporated all recommended infection control measures and our incentive was not really lack of reimbursement from Medicare, but aiming to improve outcomes.
What I am concerned about in this case is that it may push hospitals to question certain high-risk procedures for infection, he adds. If a patient has, lets say, diabetes, obesity, end-stage renal disease and COPD (chronic obstructive pulmonary disease), he may be a high risk of infection regardless of whether antibiotics were given on time and surgical prep was done appropriately and glucose was controlled perioperatively.
Fakih led a study that assessed what causes CABG-related infection rates to rise. (It) showed that we really did not have a significant increase of total number of cases with infection but rather the denominator has dropped over time, Fakih says. It is likely related to lower-risk cases being fewer now (because of the advances in interventional cardiology). This has pushed the cardiothoracic surgeons to accept higher-risk cases that they would not have operated on in the past.
The change in CMS reimbursement guidelines is seen in the industry as the right target, wrong tool, Fowler says.
Hopefully, the shift will lead to pronounced changes nationwide in how healthcare staffs prioritize infection prevention, especially since the involved infections are costly and potentially lethal, Fowler says. He agrees with Fakihs concern about accessibility issues that the new CMS guidelines could promote.
One potential problem from the reimbursement change is that it could make surgeons even less comfortable with caring for patients at high risk for surgical site infections (SSIs), Fowler says.
There are several risk factors that can lead to complications, and these include diabetes, peripheral vascular disease (PVD) and obesity, Fakih says. An intraoperative factor to consider is the duration of surgery. Postoperatively, the duration of intensive care unit (ICU) stay and mechanical ventilation are considerations, Fakih adds. He suggests looking at modifiable factors such as preoperative antibiotic timing, perioperative glucose control, and postoperative ICU management.
According to Fowler, the best way to treat a CABG-related infection is to prevent it in the first place.
With the growing number of re-do and other high-risk patients undergoing CABG, the need for preventive strategies for CABG is greater than ever, Fowler says. The growing population of high-risk patients receiving CABG and other surgeries represents an opportunity for the pharmaceutical industry to develop novel therapeutics aimed at preventing post-surgical infections and also a mandate to healthcare providers to redouble their efforts to reduce these devastating complications of medical progress.
Evaluating Sternal SSI Rates
In order to evaluate factors related to a gradual rise in sternal SSI rates, Fakih and colleagues conducted a study of all patients who underwent CABG surgery from 2000 to 2004 at a 608-bed, tertiary care teaching hospital. Of 3,578 patients who underwent CABG, 144 (4 percent) had sternal SSI.²
Infection rates increased, even though there was a marked reduction in the number of operations per year. The percentage of patients with PVD increased from 12 percent to 24.3 percent, and the percentage with congestive heart failure increased from 17 percent to 22 percent.²
Between 2002 and 2004, the mean duration of surgery increased from 233 to 290 minutes, the percentage of patients with a National Nosocomial Infections Surveillance system (NNIS) risk index of 2 increased from 14.3 percent to 38 percent, and the percentage of patients with a postoperative stay in the intensive care unit of greater than 72 hours increased from 29 percent to 40.6 percent, the authors write.
Analysis showed that diabetes mellitus, PVD, obesity, duration of surgery, and postoperative stay in the intensive care unit of greater than 72 hours were independently associated with infection.² The conclusion was that an increase in infection in the CABG population not associated with an outbreak may be a reflection of a change in the severity of illness, the authors wrote. Preoperative, intraoperative, and postoperative markers for increased infection risk may be used, in addition to the NNIS risk index, to assess the patient population risk.
Predicting Risks for Major Infection After CABG
Major infections are infrequent but important complications of cardiac surgery and predicting their occurrence is essential for future prevention, cite the authors of the study, Surgery for coronary artery disease, clinical predictors of major infections after cardiac surgery.
They note that cardiac surgery infections increase morbidity, mortality and cost, and can require prolonged treatment with antibiotics, additional surgery, or both. The researchers believe that the proportion of coronary artery bypass patients who are at a high risk for infection is increasing because the U.S. population is aging, a growing number of patients are undergoing redo procedures, and there is a frequency of conditions conferring both cardiovascular and infectious risks (obesity, diabetes mellitus) among this population. Thus, there is a critical need to identify patients undergoing cardiac surgery who are at risk for major infections and to develop effective interventions to prevent these infections.
The research objective was to create and validate a bedside scoring system that could estimate a CABG patients likelihood of acquiring a major infection, such as mediastinitis, thoracotomy or vein harvest site infection, or septicemia.³ More specific objectives were to identify the frequency of major infection after CABG, identify determinants of major infection among CABG patients, and convert these determinants into a bedside scoring system.³ The researchers used the Society of Thoracic Surgeons National Cardiac Database to analyze 331,429 CABG cases from Jan. 1, 2002, to Dec. 31, 2003, to identify risk factors for major infection.
The first model was referred to as the preop model and was limited to preoperative characteristics.
The second included preoperative and intraoperative characteristics and was referred to as the combined model. Major infection occurred in 11,636 patients (3.51 percent): (25.1 percent mediastinitis, 32.6 percent saphenous harvest site, 35.0 percent septicemia, 0.5 percent thoracotomy, 6.8 percent multiple sites).³ Patients with major infection had a significantly higher mortality rate (17.3 percent versus 3.0 percent) and had a postoperative length of stay longer than 14 days (47.0 percent versus 5.9 percent) than patients who did not have a major infection.³ Both the preop model and combined model successfully discriminated between high- and lowrisk patients, the authors write. A simplified risk scoring system of 12 variables accurately predicted risk for major infection.
The researchers concluded that they had identified and validated a model that can preoperatively identify which cardiac surgery patients are at a high risk for major infection. To reduce rates of major infections, these highrisk patients could be targeted for perioperative intervention strategies.³
Prior studies have identified risk factors for postoperative mediastinitis, but many of these characteristics could not be determined before surgery, which is the time that intervention strategies could be most important, the researchers claim. They also contend that no study to date has developed a simplified scoring system that can be used to estimate a patients risk for major post- CABG infection.
They considered major infection to be defined as one or more of the following: surgical site infection (deep sternal wound, thoracotomy, or leg vein harvest site, septicemia before discharge, readmission within 30 days of surgery for deep sternal wound infection, leg wound infection, or septicemia. Infection was documented by at least one of the three following factors: a wound opened with excision of tissue (incision and drainage), positive culture, or if the patient was treated with antibiotics.³
The researchers of this study claim that infection is an uncommon, but potentially devastating complication of cardiac surgery. To learn more about this complication, they used clinical information from about two thirds of all U.S. bypass procedures that were performed during the study period.
Major infection was relatively uncommon in the Society of Thoracic Surgeons (STS) database (3.5 percent of patients developed an infection after CABG).³ Rates of leg wound infection and septicemia in the study were similar to prior reports and rates of mediastinitis (0.6 percent in the STS database) are consistent with some reports, but are lower than others.³
The difference in mediastinitis rates could be related to the geographically diverse population of the STS database, and lower rates of mediastinitis in the STS database may reflect differences in identification of infectious complications of CABG.³
The rates of mediastinitis could be higher in centers with active infection control surveillance rather than voluntary reporting, and the lower rate of mediastinitis may reflect the fact that the STS database primarily captures acute events, whereas some infections dont become apparent until weeks after surgery.³
Several variables in the investigation were important risk factors for infectious complications after cardiac surgery. Obesity was a significant risk factor in the preop and combined model.
The presence of BMI >40 kg/m2 alone conferred a 2.6 percent risk for major infection in the preop model, a finding that agrees with some, but not all prior reports, the researchers write. Potential explanations for the impact of obesity include inadequate serum levels of prophylactic antibiotics, technical difficulties in maintaining sterility of tissue folds, and poor perfusion of adipose tissue. The importance of diabetes mellitus as an independent risk factor for major infection was again demonstrated.
Cardiogenic shock, perfusion time of 200 to 300 minutes, and placement of an intraarterial balloon pump were associated with the highest risk for major infection, but their overall impact on the models was limited because they occurred infrequently.³
For example, all three variables occurred in less than 10 percent of the study population, the authors write. By contrast, the impact of obesity, diabetes and congestive heart failure was significant because of the frequency of several conditions: Over one third of study patients had a BMI >30 kg/m2, one third had diabetes mellitus, and 18 percent had congestive heart failure.
Because obesity is epidemic in the United States, it is likely that the risk factors for major infection after CABG will increase, the researchers conclude. This could lead to important clinical implications, because it suggests that a relatively small proportion of patients who undergo CABG bear the majority of risk for major infection. It also suggests that high-risk patients are identifiable before surgery, and that several of these risks could be modified.³
Before this study, it was difficult to preoperatively estimate an individual patients risk for infectious complications, the researchers share. For example, continuous intravenous insulin therapy designed to maintain blood glucose levels <150 mg/dL reduces the risk of deep sternal wound infection by 66 percent among diabetic patients.
Some solutions include clinical process improvements, weight loss, smoking cessation efforts, and interventions (including nasal decolonization and vaccines) that target Staphylococcus aureus.³ The researchers of this study believe that preoperative risk assessments could be used to identify at-risk populations in whom clinical trials are cost-effective.
In the mean time, most healthcare professionals will continue to use any tool available to prevent infections related to CABG surgery. And for the tiny minority of healthcare professionals who wont take appropriate measures, there will be consequences in the fall.
2. Fakih MG, et al. Increase in the rate of sternal surgical site infection after coronary artery bypass graft: a marker of higher severity of illness. Infection Control Hospital Epidemiology, May 2007.
3. Fowler VG, et al. Surgery for coronary artery disease, clinical predictors of major infections after cardiac surgery. American Heart Association, Inc. 2005.