Infections Related to the Use of Medical Devices and Changes in the Oropharyngeal Flora

Abstract: Background: Humans exist in mutualistic balance with a large range of microbiota. Illness and hospitalization can disturb this balance and contribute to hospital-acquired infections (HAIs), which occur most often in critically ill patients. The use of medical devices such as central venous catheters (CVCs) and endotracheal tubes (ETTs) is essential in the care of critically ill patients. At the same time, they increase the risk of HAI by forcing or disrupting the normal barriers in the human body. All such devices eventually become colonized with microbes (usually normal flora), that form biofilms on the surface of the foreign material and subsequently lead to infection. The three types of devices related to the majority of HAIs in the intensive care unit are ETTs, urinary catheters, and CVCs.Aim: The present research was conducted to study: (i) changes in oropharyngeal microbial flora during hospitalization; (ii) compare biofilm formation on widely used ETTs with different surface properties and to explore factors potentially predictive of biofilm formation; (iii) the incidence of catheter-related infections and the impact of implementing a simple hygiene insertion bundle; (iiii) compare the blood compatibility of widely used CVCs.Paper I: In a clinical observational study, oropharyngeal cultures were collected from 487 individuals: 77 controls, 193 ward patients, and 217 critically ill patients. The results indicated that occurrence of an abnormal oropharyngeal flora is an early and frequent event in hospitalized patients, particularly the critically ill. Also, colonization with gut flora in the oropharynx was common in critically ill patients. Treatment with proton pump inhibitors was associated with colonization of gut flora in the oropharynx. The result of paper I reinforces the hypothesis that proton pump inhibitor use increases the risk of pneumonia by changing the oral flora, harboring gut bacteria which then may be micro aspirated into the lungs.Paper II: In a clinical observational study, biofilm formation on three widely used ETTs was compared in critically ill patients. Biofilm formation on the tubes was found to be an early and frequent event, and high-grade biofilm formation on the ETTs was associated with development of VAP. Compared to uncoated polyvinyl chloride (PVC) ETTs, silicone-coated and noble-metal-coated PVC ETTs were independently associated with reduced high-grade biofilm formation. Methods aimed at the continuous monitoring of biofilm formation are warranted. Routines for biofilm removal need further study.Paper III: This retrospective study compared the incidence of catheter-related infections and catheter-related bloodstream infections during a 2-year period starting 1 year before and ending 1 year after the implementation of a simple hygiene insertion bundle. A total of 1,722 catheter insertions were included. The incidence of catheter-related infections and catheter-related bloodstream infections in this Scandinavian cohort was low. Thus, it seems that the implementation of a simple hygiene insertion bundle was effective in reducing catheter-related infections. The use of multiple-lumen catheters was associated with increased risk of catheter-related infections.Paper IV: In an experimental study, the blood compatibility of three coated and three uncoated CVC materials was evaluated in a modified Chandler loop model imitating the flow of blood in a vein. When in contact with blood, all the tested catheters had some impact on blood cells, contact coagulation, the complement system, or inflammatory markers, although the effects varied significantly. A polyurethane catheter coated with chlorohexidine and silver sulfadiazine showed the most unfavorable blood compatibility profile. A silicone dialysis catheter exhibited the greatest variation in the blood compatibility tests. Poor blood compatibility could cause inflammation and facilitate the development of catheter-related thrombosis in patients receiving these central venous catheters, but clinical significance has to be studied further.