Infections associated with medical devices
There are several concerns that healthcare professionals must consider when selecting a medical device. This selection is essentially based on the treatment effectiveness and cost, as well as on the risk of infection. Catheters (central venous and urinary catheters) and endotracheal and feeding tubes (Table 4.1) are considered the commonly used medical devices (Cooper et al., 2014).
There are an enormous variety of intravascular devices that are inserted through the skin into vessels of the respiratory system to deliver medication, fluids, or nutritional products. These devices can also measure blood and pulmonary artery pressure and allow access to withdraw blood samples for analysis (Raad et al., 2007). The infections associated with this type of devices can occur locally at the site of insertion until the vein and surrounding tissue to cause phlebitis. If the microorganism reaches the circulatory system, it can potentially cause systemic sepsis. To avoid severe infections, the intravascular device for long-term use is initially inserted into a tunnel in the skin before entering a central vein. In this case the wound healing reduces the risk of infection through microorganism migration from the outside of the device (Khardori and Yassien, 1995; Cooper et al., 2014). The biofilm formation can occur both in the outer part of the catheter and in the lumen (Cooper et al., 2014). During the first week of catheterization, extraluminal biofilm is considered the main cause of bloodstream infections associated with catheters (Percival et al., 2015; Donlan, 2011). Contrarily, vascular catheters that remained in situ for 30 days demonstrated predominantly luminal colonization (Raad et al., 1993). Therefore, patients that require long-term catheters for intravenous access have a higher risk of bloodstream infection. Anaissie et al. (1995) observed that early infection occurs within one day of catheter insertion. In fact, they stated that this was a universal occurrence (Anaissie et al., 1995). Central vascular catheters are more likely to promote sepsis since they are preferably long-term medical devices (Raad et al., 1993).
Urinary catheters are tubular devices of latex or silicone, which are used to measure urine output, collect urine, and prevent its retention and also to control urinary incontinence (Percival et al., 2015; Donlan, 2001b). In the case of patients undergoing catheterization, the risk of an infection associated with the catheter increases 10% each day that the device is in place. This type of catheter has a higher risk once ascending colonization and consequently infection can occur. In fact, 80% of urinary tract infections are related to the use of urinary catheters (Percival et al., 2015; Cooper et al., 2014).
Endotracheal tubes are manufactured using polyvinylchloride that is easily contaminated (Khardori and Yassien, 1995). Therefore, when a patient is intubated with endotracheal tubes and is on mechanical ventilation, ventilator-associated pneumonia (VAP) can occur in 48-72 h. This infection has major implications for the healthcare system since it leads to longer stays in hospitals and also higher costs of hospitalization (Palmer, 2009). The risk of developing VAP after the intubation procedure has a mortality rate of 24-76%. VAP can be classified based on the risk of infection in early-onset or late-onset if the hospitalization is inferior or superior to 5 days, respectively (Percival et al., 2015). The main factor in acquiring VAP is the endotracheal tubes since biofilms proliferate really fast (within 24 h) on these materials (Tarquinio et al., 2014; Adair et al., 1999).
The enteral tubes are used in patients that are unable to masticate due to neurological or pharyngeal disease, and require this support for long periods of time. The enteral nutrition is chosen over parenteral route since it is associated with lower risks of sequelae, so it preserves the barrier, absorptive, and immunological functions of the gut (Hu and Zheng, 2003). Independent of the type of tube used, these feeding tubes can be used for the migration of the microorganism through the tube until the stomach. In consequence an abnormal microflora as well as biofilms can develop in the tubes (Peters et al., 2012; Bankhead et al., 2009). Several innate mechanisms of resistance of the stomach flora break down when the patients are with artificial feeding. One of the consequences of these tubes is the absence of certain stimuli associated with food intake that results in inhibition of saliva and peristaltic movements and consequently in pH increase and reduction of gastric nitrite concentrations. The effect of all these events results in a microbial overgrowth in stomach and duodenum, which are also recalcitrant to antibiotic therapy (Peters et al., 2012).