By Leslie A. Hoffman, RN, PhD
Intravascular catheters are an essential component of the practice of critical care medicine. These devices are used to deliver life-sustaining intravenous fluids, antibiotics, parenteral nutrition, blood, and blood products, and to monitor the hemodynamic status of critically ill patients. However, their use is also associated with a high risk for the development of nosocomial infections. For example, central venous catheters account for an estimated 90% of all nosocomial bloodstream infections.1 There is also an increasing body of evidence that confirms that a large proportion of catheter-related bloodstream infections (CR-BSI) are preventable through careful control of factors associated with their colonization.2-5 Enhancing positive outcomes in critically ill patients requires that clinicians be aware of proven methods for preventing CR-BSI.
CR-BSI are often difficult to treat because they are caused by antibiotic-resistant organisms that implant themselves in a biofilm layer on the catheter surface or attach themselves to the thrombin sheath that forms on the internal and external surface of the catheter.3,5 Improved understanding of the pathogenesis of CR-BSI serves as the basis for appreciating the most effective management approaches.
The skin and catheter hub are the most common sources of colonization of intravascular catheters. For short-term, nontunneled, noncuffed catheters, the skin insertion site is the most common source of colonization. For long-term catheters, such as cuffed, tunneled, silicone catheters (eg, Hickman or Broviac catheters) or implantable catheters (ports), the lumen of the hub or the bell of the port is the major source of colonization.5 Because the skin of the patient and the hands of those caring for the patient are the main sources of contamination, staphylococci, particularly coagulase-negative staphylococci and Staphylococcus aureus, are the leading causes of CR-BSI.2,5 Candida albicans and Candida parapsilosis also colonize the hands of health care personnel and are emerging as important pathogens associated with catheter-related infections.5
Staphylococci, Candida, and some other microbes that commonly cause CR-BSI produce a slimy material rich in exopolysaccharide that results in the formation of a microbial biofilm. This biofilm helps microorganisms adhere to and survive on the surface of foreign bodies in the bloodstream. Bacterial growth is also aided by formation of thrombin. Following catheter insertion, a thrombin layer or sheath begins to form and eventually covers the external and internal surfaces of the intravascular segment. This sheath is rich in host proteins, such as fibrin, fibronectin, thrombospondin, and laminin, which act as adhesins.3,5 Therefore, these substances promote adherence of potential microbial pathogens to that surface. S aureus binds strongly to several of these proteins, as do coagulase-negative staphylococci and C albicans. Accordingly, it is very difficult to eradicate organisms colonizing the catheter surface because they are attached to adhesins on the surface of the catheter and covered by a protective layer of biofilm.5
Studies using quantitative electron microscopic techniques suggest that most catheters become colonized after insertion, even in the absence of symptoms. Clinically apparent infections appear to result when the number of organisms exceeds a threshold because there is a quantitative relationship between the number of organisms isolated from the catheter surface and risk for CR-BSI.5
Specific Preventive Measures
Care of the insertion site. Measures intended to remove microbes from the catheter insertion site are regarded as one of the most important measures for preventing CR-BSI. Most clinicians use providone-iodine (PI) for this purpose.3,6 An alternate solution, chlorhexidine gluconate (CHG), has also been advocated for skin disinfection. CHG has 2 potential advantages in comparison to PI. First, protein-rich biomaterials, such as blood and serum, can deactivate the microbicidal effect of PI, but not CHG. Second, the residual effect of CHG, defined as the long-term antimicrobial suppressive activity, is prolonged (at least 6 hours) whereas that of PI is minimal.6 Several studies suggested greater efficacy for CHG, but few CR-BSI were observed in each study and, until recently, it remained unclear which agent was the best choice.3,6 In 2002, Chaiyakunapruk and colleagues6 performed a meta-analysis (8 studies;4143 catheters) on these data. Among patients with a central venous catheter, CHG reduced the risk for CR-BSI by 49% compared to PI. They estimated that for every 1000 catheter sites disinfected with CHG, rather than PI, 71 episodes of catheter colonization and 11 episodes of CR-BSI would be prevented.6 Given the extent of benefit and the small incremental cost, CHG appears the agent of choice, especially in patients at high risk for CR-BSI.3,6
Use of antimicrobial-coated catheters. After insertion, a thrombin layer forms and eventually covers the external and internal surface of the catheter. The thrombin layer facilitates the microbial pathogenesis of CR-BSI via: 1) extraluminal infection that occurs primarily via direct migration of cutaneous bacteria to the catheter tip; and 2) intraluminal infection that occurs via spread from the catheter hub.3 A novel strategy for prevention of CR-BSI involves the use of catheters impregnated with the antiseptic combination of chlorhexidine and sliver sulfadiazine (CS). Several randomized clinical trials have compared efficacy of CS impregnated and noncoated catheters in preventing CR-BSI, as has a recent meta-analysis.7 In the meta-analysis (11 studies; 2603 catheters) findings indicated that patients who received catheters impregnated with CS had a statistically significant decrease of approximately 40% in the incidence of CR-BSI.7 An additional clinical trial (12 hospitals; 738 catheters) compared the efficacy of CS impregnated catheters with catheters impregnated with minocycline/rifampin (MR). CS and MR had similar efficacy for the first week of use. However, MR impregnated catheters were more effective in decreasing the incidence of CR-BSI after this time point.8 There has also been a formal economic evaluation that indicated that use of CS-coated catheters produced significant clinical and economic benefits when used in patients at high risk for catheter-related infections.9 The analysis suggested that for every 300 CS-impregnated catheters used, approximately $59,000 would be saved, 7 cases of CR-BSI would be avoided, and 1 death would be prevented.9 Both minocycline and rifampin are used as systemic antimicrobial agents. For this reason, their use on catheters creates the potential for increased antibiotic resistance. Therefore, CS-impregnated catheters appear the better choice.3
Selection of insertion site. The location of catheter placement is an important risk factor for complications, whether infections, mechanical, or thrombotic.10 A number of studies support that catheters inserted into the subclavian site are colonized less often than those inserted into the jugular site.2-4 Potential causes include proximity of the jugular site to oropharyngeal secretions, a higher skin temperature and problems maintaining an optimal dressing, particularly in men.4 Conversely, mechanical complications are more common with subclavian insertion. The most frequent major complication, pneumothorax, occurs in 1.5-2.3% of cases.10 Generally, the femoral site is also viewed as increasing risk for infection but, until recently, randomized data supporting this assertion were not available. In 2001, Merrer and associates10 reported findings from patients admitted to 8 ICUs (4 university-affiliated; 4 community) who were randomized to undergo central venous catheterization at the femoral (n = 145) or subclavian (n = 144) site. Only patients undergoing their first central venous catheterization were eligible and none required emergency catheterization. Femoral insertion resulted in a significantly higher incidence of overall infections (19.8% vs 4.5%) and major infections (sepsis with or without CR-BSI) (4.4% vs 1.5%). There was also a higher incidence of overall thrombotic complications (21.5% vs 1.9%) but no difference in mechanical complications (17.3% vs 18.8%). Thus, evidence supports that the femoral site should be avoided when possible and decisions regarding other sites should be made on the basis of patient-related factors and operator skill.3
Use of maximum sterile barriers. Both submaximal and maximal sterile barrier (MSB) protection may be used during catheter insertion. Mermel and associates11 compared risk for CR-BSI in 297 patients who had pulmonary artery catheters inserted with and without MSB protection; risk for CR-BSI was almost twice as high when MSB technique was not used. In a prospective study, central venous or pulmonary artery catheters inserted in the operating room using submaximal barrier protection (gloves, small fenestrated drape) were more likely to be associated with subsequent BSI than those inserted on the ward or ICU with MSB precautions (sterile gloves, long-sleeved gown, full-size drape, and nonsterile mask).2 Sherertz and colleagues12 reported a significant reduction in CR-BSI associated with increased use of MSB during catheter insertion. These data provide strong evidence that MSB use reduces the risk for CR-BSI, regardless of where the catheter is inserted.2
Duration of catheterization. Although some clinicians also advocate routine replacement of central venous catheters as a measure to reduce infection, available data do not support this practice.2,3 Eyer and associates13 randomized 112 patients with central venous, pulmonary artery, or systemic arterial catheters for more than 7 days into 3 groups: 1) weekly change, new site; 2) weekly guidewire exchange, same site; and 3) no routine weekly change. No significant differences were noted in the incidence of local or bacteremic infection. Similar findings were reported by Cobb and colleagues14 when 160 ICU patients were randomized to catheter changes every 3 days at a new site, over a guidewire, or replacement when clinically indicated. Patients who underwent routine replacement at new sites did not have lower rates of infection, and guidewire replacement was associated with a trend (6% vs 0%; P = 0.06) toward more CR-BSI. A subsequent meta-analysis found no data to support routine removal of catheters on a scheduled basis in the absence of clinical indications.15
Hand hygiene. Hand-washing is the single most important step that can be taken to prevent transmission of microorganisms. However, poor compliance is common and, in the ICU, compliance typically does not exceed 40%.4 Several factors have been implicated as causes, including high patient workload, inconvenient placement of hand-washing facilities, allergy or intolerance to solutions, and reliance on gloves.4 However, 5-10% of hands remain contaminated after glove removal.17 When properly performed, hand-washing can require 1-2 minutes, including time to walk to the sink, wash and dry the hands, and walk back to the patient.16 In a 14-bed ICU, this equated to 16 hours per shift.16 There are consistent reports of improved compliance when ICU personnel used an alcohol-based handrub as an alternate to hand-washing. Handrubbing required 20 seconds to complete, was equal or more effective in removing organisms, and had fewer adverse effects.16 Given these benefits and poor compliance with hand-washing, substituting an alcohol-based handrub seems a logical and practical choice.
Adequate nurse staffing. Understaffing has been reported to increase risk for errors, iatrogenic complications, nosocomial infections, and death.4,18 Needleman and associates18 analyzed data from 799 hospitals in 11 states (> 5 million medical discharges; > 1 million surgical discharges) to determine the relationship between the amount of care provided by nurses and patient outcomes. A higher proportion of hours of care by registered nurses was associated with lower rates of urinary tract infection and pneumonia. When analyzing causes of a protracted outbreak of CR-BSI in SICU patients, Fridkin and colleagues19 found the nurse-to-patient ratio significantly increased in the outbreak period and was an independent risk factor for these infections. Findings suggested that nursing staff reductions below a critical level likely contributed to the increased infection rate by making adequate catheter care difficult. Harbath and Pittet20 attributed an outbreak of Enterobacter cloacae infections to understaffing (57% of required) and overcrowding (166% of capacity). Given the current nursing shortage, these findings provide compelling support for efforts to improve ICU staffing.
Surveillance protocols. Surveillance has been recognized to be a critical component of infection control for more than 30 years. Surveillance should be broad-based and include: 1) epidemiologic surveillance defined as the continuous collection, tabulation, analysis, and dissemination of information relating to the occurrence of nosocomial infections; 2) monitoring of device use and updating of procedures, as required; 3) educational programs that reinforce the need for compliance with infection control procedures, teach new technologies, and monitor compliance; and 4) specific recommendations for change developed from these data.5 Surveillance of infection patterns in ICUs may help to detect particular problems and design targeted interventions. In response to an observation that, despite conventional bedside and didactic instruction, physicians-in-training were not using optimal infection control practices, Sherertz et al12 developed a 1-day course that included lectures on basic infection control practices and a series of 1-hour stations with hands-on practice. After the course, the use of maximum sterile barrier precautions increased significantly (from 44% to 65%), and the rate of CR-BSI significantly decreased by 28%. Cost savings over the study period ranged from $63,000 to $800,000 after deduction of course costs depending on the method used to estimate the cost of each infection.
CR-BSI due to central venous catheters are a common complication in ICU patients and a major contributor to increased health care costs and patient morbidity and mortality. Emerging evidence suggests that risk for CR-BSI can be reduced if several practices are implemented. These include: 1) use of CHG to prepare the insertion site; 2) avoiding the femoral site when possible; 3) choosing a catheter coated with CHG; 4) using MSB during catheter insertion; and 5) avoiding removal of catheters on a scheduled basis in the absence of clinical indications. Meticulous attention to good hand hygiene, insuring appropriate nurse staffing levels, and implementation of surveillance protocols are additional important steps that can be used to prevent catheter colonization and subsequent CR-BSI.
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