Central venous catheterization was introduced into China at the end of the 20th century. It has the advantages of fast infusion, high efficiency, and long retention time, so reducing patients’ pain and nurses’ workloads, and increasing nursing efficiency by removing the need for repeated puncture. In recent years, central venous catheters have been widely used in Chinese hospitals.1 However, central venous catheter-related infections (CVC-RI) have become the main hospital infections2,3 and one of the most dangerous causes of bacteremia.4,5 It has an incidence rate of (5-30)%. More attention must therefore be paid to CVC-RI.6 Transparent dressings which act as semi-permeable membranes, could reduce moisture vapor transmission, resulting in local moistness and so promoting the growth of bacteria on the skin and around the catheter. This increases the incidence of catheter-related bacteremia. In 1992, Hoffman et al7 performed a meta-analysis comparing the risks of transparent dressings and gauze dressings used for central and peripheral catheters. They showed that transparent dressings increased the relative risk of bacterial reproduction around the catheter by 53%. Meng et al8 used standard 3M transparent dressings and 3M wound dressings for central catheters in a clinical setting, and the infection rate of standard 3M transparent dressings was higher due to its lower moisture vapor transmission rate (MVTR).
Dressings with a high MVTR should reduce the catheter infection rate after venous catheterization.1 They should, therefore, be applied more widely in clinical practice as increasing attention is focused on the need to reduce catheter-related infections after venous catheterization.9-11 The MVTR is therefore an important factor influencing the choice of dressing by clinical nurses, but little information is available regarding the relative MVTRs of different dressings. In this study, we simulated the conditions of medical dressings in contact with normal skin, and with sweating skin or wounded skin with exudates. We compared the evaporation rates of a traditional gauze dressing and four different transparent dressings at different temperatures and humidities, in order to provide a theoretical basis for the clinical application of dressings in catheter nursing.
The dressings used included ordinary gauze (Shaoxing Zhende Surgical Dressing Co., Ltd (REG. No: ZYGX(Z) 20052640521)); IV3000 (Smith & Nephew (Reg. No: SFDA(I) 20071641307)); OPSITE FLEXIGRID (Smith & Nephew (Reg. No: SFDA(I) 20072641163)); 3M HP Tegaderm (American 3M company (Reg. No: SFDA(I) 20072641354)); and 3M Tegaderm (American 3M company (Reg. No: SFDA(I) 20052641019)).
Medical balance with 0.2-g gradations (Shanghai Precision Instrument Co., Ltd. (Shanghai Instrument Factory)) was used to weigh the tubes and an RXZ intellectual artificial climate cabinet (humidity controlling range: (30-95)% relative humidity (RH), humidity fluctuation range: ±5% RH, temperature controlling range: 0-50°C, temperature fluctuation range: ±1°C).
Experiments were performed in accordance with China’s medical industry standard YY/T0471.2-2004. Fifty-milliliter plastic centrifuge tubes containing 20 ml deionized water were sealed off by the dressings. The tubes were divided into five groups, according to the different dressings: Group 1 was covered with 12 layers of ordinary gauze, group 2 with IV3000, group 3 with OPSITE FLEXIGRID, group 4 with 3M HP Tegaderm, and group 5 with 3M Tegaderm.
The tubes were weighed before (Wb) and after (Wa) they were put into an RXZ intellectual artificial climate cabinet for 24 hours. The evaporation from each tube was calculated (evaporation=Wb-Wa) and the average MVTR of every dressing was calculated under different experimental conditions (MVTR=evaporation capacity/water-surface area).
In the first experiment, the tubes were put into the cabinet upright, so that the dressings did not touch the water, in order to simulate the conditions of medical dressings in contact with normal skin. The tubes were subjected to six different combinations of temperature and humidity: 20°C/30%, 20°C/60%, 20°C/90%, 37°C/30%, 37°C/60%, and 37°C/90%. Five tubes from each group were put into the cabinet under each set of conditions and the average MVTR was calculated for each dressing.
In the second experiment, tubes from groups 2, 3, 4 and 5 were laid on their sides, so that the dressings touched the water, to simulate the conditions of medical dressings in contact with sweating skin or wounded skin with exudates. Five tubes from each group were then tested under the same temperature and humidity conditions as above, and the average MVTR was calculated for each dressing.
The self-reactive ability of each dressing was calculated by comparing its MVTR when in contact with the water surface with its MVTR when not in contact with the water surface.
The data were analyzed using the SPSS 10.0 statistical software. Quantitative data were recorded as mean±standard deviation (SD). Differences between two groups were analyzed using t-tests, and differences among several groups were analyzed using x2 tests. Results were considered significant when P <0.05.
Simulation of medical dressings in contact with normal skin
The dressing in group 1 demonstrated the highest MVTR at 20°C, followed by group 2, group 3, group 4 and group 5. The MVTRs decreased gradually as the RH increased. The differences among some groups and humidities were statistically significant (P <0.01), as shown in Table 1.
At 37°C and RHs of 30% or 60%, the highest MVTR was demonstrated by group 1, followed by group 2, group 4, group 3, and group 5. At a humidity of 90%, however, the MVTR was higher for group 2 than group 1, followed by group 4, group 3, and group 5. MVTRs decreased gradually as RH increased (Tables 1 and 2). The MVTR differed significantly among these groups (P <0.01). The MVTR was significantly less at 90% RH than at 30% and 60% (P <0.01). The MVTRs differed significantly among groups 1, 3, and 5 at RHs of 30% and 60% (P <0.05). However, there was no significant difference in MVTRs between groups 2 and 4 at RHs of 30% and 60% (P >0.05, Table 1).
Simulation of medical dressings in contact with sweating skin or wounded skin with exudates
The dressings in group 2 demonstrated the highest MVTRs at 20°C, followed by group 4, group 3, and group 5. The MVTRs gradually decreased as the RH increased. There were significant differences among the groups and different RHs at 20°C (P <0.01, Table 2).
The highest MVTR at 37°C was demonstrated by group 2, followed by group 4, group 3, and group 5. There were significant differences among the groups (P <0.01). The MVTR gradually decreased as the RH increased. There were significant differences among the groups and among different RHs (P <0.01, Table 2).
Reactive MVTRs of different dressings
At 20°C and 37°C, the reactive MVTRs were the highest for the dressing in group 2, followed by the two 3M dressings, while the group 3 dressing had the lowest self-reactive MVTR (Table 3).
Transparent dressings have several advantages over traditional gauze dressings. These include, increased visibility of the puncture site, reduced catheter movement, reduced risk of outside contamination, faster dressing changing times, the possibility of checking the wound at an early stage, and increased patient comfort.12 For these reasons, transparent dressings have been used to cover central venous catheter puncture sites since the early 1970’s, and remain in common use. Traditional transparent dressings have low MVTRs, which means that the local wound microenvironment remains moist. On the one hand, a moist environment is conducive to wound healing,13-15 but on the other hand, it increases the risk of catheter infection.16 Standard transparent dressings are associated with a high risk of CVC-RI.16-21 There has, therefore been a recent upsurge in the clinical use of transparent dressing with higher MVTRs,22,23 such as IV3000 and 3M HP Tegaderm.
Transparent dressings with high MVTRs are preferable to traditional dressings because of the advantages conferred by their transparency. Our study therefore examined the MVTRs of different transparent dressings under different laboratory conditions. Under conditions simulating contact between medical dressings and normal skin, the traditional dressings in group 1 and the transparent dressings in group 2 both demonstrated relatively high MVTRs at different temperatures and different RHs. The dressing in group 1 performed better than that in group 2 under conditions of normal temperature (20°C) and low humidity (30%), normal temperature (20°C) and middle humidity (60%), high temperature (37°C) and low humidity (30%), and high temperature (37°C) and middle humidity (60%). However, at high temperature (37°C) and high humidity (90%), the dressing in group 2 demonstrated a higher MVTR than that in group 1, probably because the gauze dressing of group 1 absorbed water under conditions of high humidity. Although the dressing in group 2 had a similar MVTR to that in group 1, it formed a semi-permeable membrane that allowed the one-way release of moisture, without absorbing water.
The reactive MVTR of group 2 was 10.2-16.3 times greater than its MVTR, while the reactive MVTRs of groups 3, 4, and 5 were 1.4-4.3, 2.5-9.6, and 2.7-10.1 times greater than their MVTRs, respectively. Group 3 had the lowest reactive MVTR. When the skin sweats, dressings with better reactive MVTRs will increase vapor and moisture transmission substantially allowing the release of liquid and so reducing the catheter infection risk associated with increased moisture retention under the dressing.
The results of this study demonstrate that different clinically applied dressings have different MVTRs, some of which are similar to the MVTR of traditional gauze dressings. This indicates that transparent dressings need not necessarily be associated with increased infection rates due to low MVTRs, as has been previously suggested. However, further multicenter studies are needed to evaluate the MVTRs and reactive MVTRs of the different dressings used in clinical applications.
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