Comparison of Gentleness and Reapplication Between Two Pulse Oximetry Probes in Healthy Adults in a Laboratory Setting

Abstract

Purpose

Many commonly used monitoring devices use adhesives to attach to the skin. These devices can cause avoidable skin damage, known as medical adhesive-related skin injury (MARSI). Pulse oximetry is a ubiquitous medical device used throughout care settings and, depending on the type of care, may have wear times over many hours or days. The purpose of these studies was to compare gentleness and reapplication of two pulse oximetry probes (Nellcor™ OxySoft™ neonatal-adult SpO₂ sensor, Medtronic (silicone-based probe); LNCS^® Neo, Masimo^® (acrylic-based probe)).

Patients and Methods

Institutional Review Board approval was obtained prior to study initiation and all participants provided informed consent prior to commencement of study procedures. Eighteen participants were enrolled in the gentleness trial and 19 participants were enrolled in the reapplication trial. For the gentleness trial, Trans-Epidermal Water Loss (TEWL) measurements were made at five sites on the forearm at three time points (baseline (T0), 4-hours post-initial wear (T1), 4-hours post-second wear (T2)). The total amount of protein adhered to each device was determined. For the reapplication trial, a series of 180° peel tests from the forearm were performed.

Results

For the gentleness trial, no significant differences in TEWL rates were noted between the two probes at any time point. When examining protein removal, the silicone-based probe removed approximately 75% less protein compared to the acrylic-based probe. For the reapplication trial, the silicone-based probe retained approximately 85% of initial peel-force retention after 18 reapplications, whereas after only two reapplications the acrylic-based probe retained approximately 50% of initial peel-force retention.

Conclusion

In healthy adults in a laboratory setting both probes appeared to be gentle on skin. The silicone-based probe demonstrated the ability to withstand 18 reapplications without functional loss in adhesion.

Plain Language Summary

Many medical devices and dressings use adhesives to attach to the skin. Sometimes the skin touching the adhesive can become damaged, called medical adhesive-related skin injury (MARSI). Several factors can contribute to the development of MARSI, including adhesive type. There are many types of adhesives used in medical products and dressings. Acrylic-based adhesives are widely used and provide durable and versatile attachment. Silicone-based adhesives are recommended for severe wounds and fragile skin as they allow for gentle removal and repositioning. A pulse oximeter is a commonly used medical device that measures the level of oxygen in the blood. It is used throughout hospitals, clinics, and in-home settings to monitor patients. A pulse oximetry sensor is placed on top of the skin and can be held in place with an adhesive wrap. The purpose of this study was to compare the gentleness and reapplication of two pulse oximetry probes, one with a silicone-based adhesive and one with an acrylic-based adhesive, in healthy adults in a laboratory setting.

Introduction

Medical adhesive-related skin injury (MARSI) is defined as any amount of skin damage arising from the use of medical adhesives and is recognized as a largely preventable injury.1 Though medical adhesives pervade the healthcare system, these injuries are considered to go largely unrecognized by healthcare providers, even though the downstream effects of such injuries include delayed healing, patient discomfort, and compromised skin barrier function.1,2 Individuals in the tails of the age spectrum, including premature infants and the elderly, are recognized to be at higher risk of MARSI, given thinner, more fragile skin.3,4 The compromised skin integrity inherent of MARSI can negatively impact patient’s quality of life by limiting mobility and increasing pain, while also increasing infection risk and overall healthcare costs.5 MARSIs are categorized as mechanical, dermatitis, or other and are caused by the separation of skin layers from one another, which occurs when the bond between the adhesive and outermost skin layer is greater than the bond between skin cells.1,6 As skin stripping is a common feature of MARSI, both Trans Epidermal Water Loss (TEWL) and the amount of protein removed are recommended as objective measures to assess MARSI.3

Pulse oximetry is a standard of care throughout a variety of clinical settings, most notably in intensive care units, where continuous monitoring is ubiquitous. Pulse oximetry sensors require contact with the skin for accurate readings, with many single-use sensors utilizing an adhesive for secure attachment.7 The adhesive is an important component of the pulse oximetry probe, as it must optically couple the probe to the tissue and maintain that coupling in conditions such as motion.8 Certain populations, such as premature infants and the elderly, have delicate skin and weaker skin barrier function, which can be due to a combination of factors including dryness, fewer epidermal cell layers, and less cohesion between the dermis and epidermis.9,10 As such, special care is given to avoid MARSI in these populations. To prevent MARSI, regular skin assessment, the use of skin barriers, proper application and removal techniques, and the use of silicone-based adhesive removers are recommended.11–13 In light of these recommendations, it is important to have pulse oximetry probes whose adhesive provides adequate skin adhesion while also being repositionable and gentle upon removal.

TEWL is a measure of water that evaporates across the skin barrier, providing insight into the ability of skin to continue to perform its barrier function of retaining water. This skin barrier function is reduced by removal of the outermost layers of the stratum corneum.14–16 As skin provides a physical barrier to protect against foreign bodies and infection, greater permeability can indicate degradation in integrity even if not apparent upon visual inspection.17 Disruption to the skin, which increases the amount of water vapor crossing the barrier after adhesive removal, is an indicator that an adhesive is not gentle. Higher TEWL measurements can indicate barrier disruption. Protein removal is also used as a measure of skin disruption as it is correlated to the amount of skin cells that are removed by the adhesive.18,19 The adhesive is removed from the skin and washed, then the amount of protein that was present on the surface of the removed adhesive is measured. Any protein found is assumed to have come from the skin when the probe was removed.19

Though acrylic-based adhesives are used throughout medical products and devices, including pulse oximetry probes, data suggests that silicone-based adhesives are associated with lower reported pain and skin damage compared to acrylic-based adhesives.20–22 Indeed, an expert consensus group of the Skin Tear Advisory Panel (ISTAP) recommends using silicone-based adhesives on patients considered to have fragile skin.13 Our previous work has shown the gentleness of a silicone-based probe, even on fragile skin.23 To expand on these findings, this paper presents additional data collected on healthy adults in a laboratory setting to evaluate biophysical endpoints of gentleness and reapplication of two commonly used pulse oximetry probes: the silicone-based Nellcor™ OxySoft™ neonatal-adult SpO₂ (Medtronic, Lafayette, CO) (referred to as the silicone-based probe throughout this paper) and the acrylic-based LNCS^® Neo (Masimo^®, Irvine, CA) (referred to as the acrylic-based probe throughout this paper).

Materials and Methods

Results from two separate but related studies are presented. One study evaluated probe gentleness and one study evaluated probe reapplication. Both studies enrolled adult volunteers and were performed in accordance with the Declaration of Helsinki under protocols that were duly approved by the Advarra Institutional Review Board (Columbia, MD; IRB approval numbers: Pro00057066 and Pro00057726). All participants provided written informed consent prior to study participation. Both studies were sponsored by Medtronic, the manufacturer of Nellcor pulse oximetry products, who provided all test devices, contributed to trial designs, and manuscript writing. There was no patient or public involvement in trial design, conduct, or reporting. Due to obvious differences in probe design, there was no blinding during data collection. The analysis was blinded, with probe type and randomization scheme not disclosed prior to or during the analysis. For each study, devices were applied to the forearm according to a predefined randomization scheme. The datasets used for analysis are available in Supplemental Tables 1 and 2. For each study, the procedures used have been previously described and are briefly summarized below.23

Test Devices

Both pulse oximetry probes were similar in design, consisting of an optical region that houses the probe and an associated fabric tail region, as shown in Figure 1. The primary difference between the two probes was the acrylic-based probe consisted of synthetic rubber and acrylic contacting adhesives for the skin interface, while the silicone-based probe consisted of a silicone adhesive system. Further, the fabric tail region of the acrylic-based probe was designed to be more readily disconnected from the optical region compared to the silicone-based probe. Each device was identified by participant number and test site location for tracking purposes.

Figure 1.

Image of optical (outlined in blue) and tail (outlined in orange) regions on the (a) silicone-based probe and (b) acrylic-based probe.

Participants and Setting

Eighteen participants were enrolled in the gentleness study. Participants were eligible for the study if they met all of the following inclusion criteria: 1) aged 65 years or older (presumed to have more fragile skin3), 2) Fitzpatrick Skin Types I–VI, 3) refrained from exercising, drinking hot beverages, and consuming highly caffeinated products at least two hours prior to and during the day of testing, 4) refrained from showering within one hour prior to the day of testing, 5) refrained from use of moisturizing products on testing sites for a minimum of 72 hours prior to and during the day of testing, 6) agreed to removal or clipping of excessive hair at testing sites, if needed, and 7) agreed to wear clothing that provided easy, unrestricted access to testing sites. Participants were excluded if they met any of the following exclusion criteria: 1) psoriasis, active dermatitis, or a recent history of dermatitis or skin reactions or any condition that might be exacerbated by the action of removing adhesive materials, 2) currently going through menopause and experiencing hot flashes, 3) had a sunburn, skin infections(s), scars, moles, broken skin, or other blemishes on their arms that would obscure grading or measuring of the test sites, 4) had a history of a confirmed or suspected COVID-19 infection within 30 days prior to the day of testing, had contact with a COVID19-infected person or persons within 14 days prior to the day of testing, individual or a member of the individual’s household had traveled internationally within 14 days prior to the day of testing, or experienced self-reported symptoms of COVID-19 within 2 weeks prior to the day of testing, 5) any allergy or sensitivity to adhesive products or isopropyl alcohol, 6) any medical condition that, in the Investigator’s judgment, precluded the participant from participation or placed them at undue risk, 7) current participation in another clinical study or within the prior 30 days, 8) damaged skin in or around the test sites, 9) employee/contractor or immediate family member of the Investigator, cyberDERM, Dermico, or a medical device company.

Nineteen healthy participants were enrolled in the reapplication study. Participants were eligible for the study if they met all the following inclusion criteria: 1) aged 18 years or older, 2) Fitzpatrick Skin Types I–VI, 3) refrained from showering within one hour prior to the day of testing, 4) refrained from use of moisturizing products on testing sites for a minimum of 72 hours prior and during the day of testing, 5) agreed to removal or clipping of excessive hair at testing sites, if needed, and 6) agreed to wear clothing that provided easy, unrestricted access to testing sites. Participants were excluded if they met any of the following exclusion criteria: 1) pregnant, nursing, or planning a pregnancy, 2) psoriasis, active dermatitis, or a recent history of dermatitis or skin reactions or any condition that could have been exacerbated by the action of removing adhesive materials, 3) had a history of a confirmed or suspected COVID-19 infection within 30 days prior to the day of testing, had contact with a COVID-19-infected person or persons within 14 days prior to the day of testing, individual or a member of the individual’s household had traveled internationally within 14 days prior to the day of testing, or experienced self-reported symptoms of COVID-19 within 2 weeks prior to the day of testing, 4) any allergy or sensitivity to adhesive products or isopropyl alcohol, 5) any medical condition that, in the Investigator’s judgment, precluded the participant from participation or placed them at undue risk, 6) current participation in another clinical study or within the prior 30 days, 7) damaged skin in or around the test sites, 8) employee/contractor or immediate family member of the Investigator, cyberDERM, Dermico, or a medical device company.

Participants in both studies completed the following steps: 1) Pre-study visit - prior to data collection individuals were screened for study qualification. 2) Three-day conditioning – upon passing the prestudy visit, participants were instructed to refrain from use of all moisturizing products on their arms and forearms for the three-days prior to data collection. 3) Data collection – participants presented to the lab to complete their respective study procedures.

Procedures for Gentleness Study

This was a one-day study in which participants remained at the laboratory for approximately ten hours. TEWL measurements were made using a recently calibrated cyberDERM RG1 Evaporimeter System (Broomall, PA) with dual TEWL probes that were manufactured by Cortex Technology (Hadsund, Denmark). All measurements were performed in an environmentally controlled room with temperature between 20–22°C and relative humidity at 40–60%. All TEWL measurements were taken after a 30-minute acclimatization period, with the test areas on the volar forearm fully exposed. The TEWL rate was calculated as the average value over a 20 second period after steady-state conditions had been reached.

Measurements were made on five sites that had been mapped out on each arm (ten sites total).23 The assignments of the test devices to the medial or lateral sides of the right forearms were done according to a randomization map that maintained this balanced design. Control measurements were obtained from a common central area located between the two probes, where no adhesive was applied.

TEWL measurements were taken at baseline (T0), after four hours of wear (T1), and after an additional four hours of wear (T2). At T1, after the devices had been worn for approximately four hours, the devices were manually removed and retained for reapplication for the second wear period. After the 30-minute post removal TEWL measurements were completed, the same devices were reapplied to the same sites as at the baseline visit. In a few cases, there were concerns that the acrylic-based probe may become detached completely during the trial, these probes were replaced during the second wear period in accordance with the randomization scheme. At T2, the devices were again manually removed and then sent to Nelson Labs (Salt Lake City, UT) where the total amount of protein adhered to each device was determined using the Micro BCAtm Protein Test. Another series of TEWL measurements were then obtained from the ten mapped sites.

Procedures for Reapplication Study

This was a one-day study in which the participants remained at the laboratory for approximately two hours. The previously described computerized cyberDERM 180° peel tester was used for reapplication testing.23 Briefly, the peel tester uses a stepper motor attached to uniaxial lead screw to pull the stressing clamp at a constant rate of 5.0 + 0.2 mm/sec and a calibrated digital force gauge records the resulting tension. The scale range is such that the expected mean test level falls between 20 to 80% of the full scale. Both probes were run in a pairwise fashion according to a randomized treatment map. Dwell time for each run was approximately 30 seconds, which is notably different than what would be experienced in a clinical setting, where probe repositioning may occur over multiple days after dwell times of several hours. One caveat with the 180° peel test is that observed forces arise not only from detaching the adhesive device from the skin but also from the device bending back upon itself. Since both test devices consist of a flexible tail region and a stiffer section containing the optical sensor, the observed force plot is more complex than typically seen with a uniformly coated homogenous adhesive test strip. Therefore, two peel adhesion values were calculated for each run, one for the tail region and one for the optical region. For the tail region, the mean peel adhesion value was calculated using at least 50 data points from the initial plateau of a given run (typically data points 20–110) and the peel force of the optical region was calculated by summing the area under the curve of a given run (typically data points 120–220).

As the adhesive under the optical region is the same as the adhesive on the tail for both devices, the increase in values seen in the optical region is not an increase in adhesion, but rather an increase in force of removal due to the work required to bend the stiff components. Thus, in addition to confirming visually that the probe was still firmly attached to the skin, we also determined the work required to remove the optical region by using the Riemann-Liouville left sum24 as an approximation of the area under the curve within the optical region.

Statistical Analysis

The data was processed using GraphPad statistical software. A two-sided p-value of ≤0.05 was considered statistically significant in all tests. Continuous variables are presented as mean ± standard deviation, unless otherwise noted.

For the TEWL results, the appropriate values were pooled by individual participant to provide a mean value for the optical region and tail regions of the two probes and the corresponding control for each time point. A repeated measures ANOVA with Tukey-Kramer Multiple Comparisons Test was then run on the net change from baseline to determine the degree of significance at T1 and T2.

For protein adhered to each device, a paired t-test was employed. A value of 2.5μg/cm² for the silicone-based probe and 2.6 μg/cm² for the acrylic-based probe was given to samples falling below the detection limits of the Micro BCAtm assay. The subtle difference in detection limit between the two probes is due to slight differences in surface area. For analysis, any measurement below the test detection limit were given the respective detection limit value (2.5 µg/cm² or 2.6 µg/cm²). Though several analysis methods have been proposed to handle left-censored data,25 a simple, conservative approach was selected for this study as it was deemed to provide adequate information on degree of protein removal to meet study objectives.

For the peel test, the appropriate values for the optical and tail regions were calculated from profiles obtained from both devices for each of the 18 serial cycles of removal and reattachment from each participant. These were then compiled, and the mean values plotted as a function of cycle number to create a decay curve suitable for analysis. The resulting trendlines, which show the dynamics of decreasing adhesion with increased number of reapplications, were analyzed for goodness of fit using the MS-Excel toolbox. Since the decay curve dynamics appeared different between the two probes, a milestone analysis was performed after two reapplications to compare resistance to peeling at a fixed time point.

Sample size calculations were completed for both studies. Available data from previous trials were used to inform sample size calculations.23 For the gentleness study, for comparison of TEWL, a sample size of three participants was determined necessary to detect a difference of 3.0g/m² between the null hypothesis mean of 3.8g/m² and the alternative hypothesis mean of 0.8g/m² with a known standard deviation of 0.8g/m² and significance level of 0.02500 using a one-sided Wilcoxon test assuming that the actual distribution is normal. For protein removal, a group sample size of 35 per probe was determined necessary to achieve 90% power to detect superiority using a one-sided, Mann–Whitney test assuming normal distribution. The margin of superiority was assumed to be −6.0 µg/cm³ and the true difference between the means was assumed to be −7.528 µg/cm³. The significance level was set at 0.025. The data are drawn from populations with standard deviations of 0.2 and 2.6 µg/cm³. As each participant had two of each probe applied during study procedures, a sample size of 18 participants was determined (18 participants X 2 of each probe = 36 samples per probe). For the reapplication study, peel force values after the 18th removal at one measurement site were used and values were reduced by 20% to account for repositioning the probe to another measurement site. The following distribution was assumed: mean = 22.584g, SD=5.594g, 95% CI = (19.887g, 25.280g). The 95% upper confidence limit of the mean peel force was selected as the value for the alternate hypothesis. The mean peel force was tested to the specification limit of > 0g. A sample size of eight participants was needed to achieve 97% power to detect a difference of −8.0g between the null hypothesis mean of 0g and the alternative hypothesis mean of 8.0g with a known standard deviation of 5.6 and with a significance level of 0.02500 using a one-sided Wilcoxon test, assuming that the actual distribution is normal. To include a larger sample of tissue variability, a sample size of 18 participants was selected.

Results

Gentleness Study

When assessing the optical region, TEWL rates were statistically significantly greater for both probes at each time point when compared to control sites (p < 0.05, Figure 2). No statistical differences in TEWL rates were noted between the two probes at either time point (T0 to T1: silicone-based probe: 0.29 g/m²hr ± 0.65 g/m²hr, acrylic-based probe: 0.25 g/m²hr ±0.79 g/m²hr, p > 0.05; T1 to T2: silicone-based probe: 0.19 g/m²hr ± 0.68 g/m²hr, acrylic-based probe: 0.13 g/m²hr ±0.97 g/m2hr, p > 0.05). When assessing the fabric tail region, there were no statistically significant differences in TEWL rates for silicone-based probe compared to control at either time point (p > 0.05). TEWL rates were found to be statistically significantly greater for the acrylic-based probe at T1 (p < 0.01) but not at T2 (p > 0.05), when compared to control sites. There were no statistical differences noted between the two probes at either time point (T0 to T1: silicone-based probe: 0.06 g/m2hr ± 0.82 g/ m2hr, acrylic-based probe: 0.50g/m2hr ± 1.19 g/m2hr, p > 0.05; T1 to T2: silicone-based probe: −0.14 g/m²hr ± 0.69 g/m²hr, acrylic-based probe: 0.26 g/m²hr ± 1.49 g/m²hr, p > 0.05).

Figure 2.

Mean TEWL rates for the respective optical and fabric tail regions of the silicone-based and acrylic-based probes at baseline (T0) and after the first four-hour wear period (T1) or the second four-hour wear period (T2).

As seen in Figure 3, the amount of protein removed was greater for the acrylic-based probe (silicone-based probe: mean = 2.59±0.23 µg/cm², acrylic-based probe: mean = 11.01±2.35 µg/cm², p<0.001). The silicone-based probe removed approximately 75% less protein compared to the acrylic-based probe when removed from the skin. This result is likely an underestimate of the true difference, as 14 of the 18 measurements for the silicone-based probe were below the test detection limit of 2.5 µg/cm². These cases were given a value of 2.5 µg/cm² in our statistical analysis.

Figure 3.

Box plot comparing the amount of keratin protein adhered to the removed device. The detection limit of the test was 2.5μg/cm² for the silicone-based probe and 2.6 μg/cm² for the acrylic-based probe.

Reapplication Study

Representative results of the reapplication study are depicted in Figure 4, which shows the differences in peel profile between the fabric tail and optical regions, as well as the differences in profiles between the probes. For the silicone-based probe (Figure 4a), the pattern of each profile is consistent between each trial, with peaks within the optical regions appearing at approximately the same position, with the most notable difference being the more elevated heights of the first two or three trials. However, when evaluating the acrylic-based probe (Figure 4b) only the first nine runs are shown to better illustrate that each profile differs not only in elevation but also in peak location. Further, it is noted that peel resistance dramatically decreases with increasing number of peels in both the tail and optical regions. While increasing number of peels, the position of the major peaks tended to appear earlier in the profile.

Figure 4.

Representative set of 18 peel pest profiles for (A) silicone-based probe and (B) acrylic-based probe obtained sequentially from the mid volar forearm of the same individual.

Figure 5 displays the decay curves of the fabric tail region for both probes. A slight but noticeable drop in adhesion during the first two runs was noted in the silicone-based probe, with minimal change thereafter. A drop in adhesion was noted within the first five or six runs for the acrylic-based probe, with minimal change thereafter in either region.

Figure 5.

Mean peel force (g), as measured at the fabric tail region, required to remove the silicone-based probe and the acrylic-based probe during the 180° peel test at each test run. The grey line represents the mean peel force for each test run of the acrylic-based probe. The black line represents the mean peel force for each test run of the silicone-based probe.

The entire series of 18 peel profiles for the silicone-based probes were completed with no issues with adherence. The silicone-based probes appeared to have no appreciable drop in peel-force retention and were easily reapplied to the test site without issue throughout the subsequent peels. In contrast, several problems arose during the repetitive peel test of the acrylic-based probe, with the most common problem being the separation of the fabric tail region from the optical region, which remained attached to the skin. When this occurred, the optical region was manually removed, and the probe reconstructed by re-adhering the fabric tail region to the optical region. For five participants, no further separations were experienced in subsequent tests. Two participants did experience additional separations in some of the subsequent peel tests. Most likely this was due to the design of the acrylic-based probe which allows for the fabric tail region to be replaced.

Regardless of whether the probe remained intact or needed to be reconstructed after three or four runs, most of the acrylic-based probes were only very loosely attached even after being pressed with a roller. In two individuals, the acrylic-based probes would loosely adhere to the skin such that the probe would fall off due to gravity when the forearm was rotated. In these cases where the probe adherence was less than the force of gravity, the peel force testing was terminated prior to completing all 18 runs.

After 18 runs, the silicone-based probe retained approximately 85% of initial peel-force retention (Run 1: 33.92±8.05, Run 18: 28.53±6.60, % remaining: 85.17±14.25%). In contrast, after two repositions, on average, the acrylic-based probe had retained approximately 50% of initial peelforce retention (Run 1: 57.8±19.5, Run 2: 28.0±9.4, % remaining: 49.5±11.9%). After two repositions, some of the probes no longer adhered to the peel test device, thus resulting in data from only the first two repositions being used for analysis. No attempt was made to statistically compare these devices based on the work required to remove the optical region, as the stiffness differed between these two devices.

Discussion

The silicone-based probe demonstrated greater repositionability and less skin removal compared to the acrylic-based probe. Though the TEWL rates were significantly raised for both probes compared to control, this increase was minimal and not a clinical indicator of a large change in barrier function.19 Though these results are based off data collected from healthy adults in a laboratory setting, they are consistent with previous literature that shows that silicone adhesives are strong and gentle, based on their physical properties that limit strain on the skin.2,3,23 One study examining the incidence of MARSI in elderly spinal surgery patients found that those who received silicone-based dressings after surgery had lower incidence and shorter duration of MARSI compared to patients receiving acrylic-based dressings.26 Further, a randomized controlled trial evaluating silicone- and acrylic-based medical tape on adult surgical patients deemed at-risk for skin injury found a decreased incidence of visualized skin injury in those who received the silicone-based tape.27 Patients in the silicone group also reported higher satisfaction scores compared to those in the acrylic group. Neonates are at high risk of MARSI, given their delicate skin, especially those born prematurely, with silicone-based adhesives recommended to help reduce risk of skin injury.28,29 Given that this patient population experiences reduced skin barrier function, some treatment plans include high humidity incubators to reduce TEWL.30 In this setting, silicone-based adhesives are preferable not only because of their gentleness but also their ability to wick away moisture to prevent excessive skin moisture which can cause maceration.

It is worth noting that the difference in protein removal between the two probes is potentially larger than calculated in the current study, as protein removed was, at times, below test detection limit, creating left censored data. In the future, lower dilution ratios would increase the concentration of protein and allow for more complete data. Though not a primary outcome of the gentleness study, it was observed that the two probes may differ in how well they remain attached when reapplied to the skin. Approximately 22% of the acrylic-based probes showed some signs of lifting after eight hours of use, while this was not observed with any of the silicone-based probes. These observations were not statistically evaluated, and further clinical testing would need to be undertaken to confirm this observation.

After 18 repositions the adhesion of the silicone-based probe was only reduced by approximately 15%. This suggests that the probe would be able to withstand frequent repositioning, every three hours, for over two days. In contrast, the acrylic-based probe rapidly lost adhesion, 50% after two repositions, with many probes unable to complete all 18 rounds of testing.

It should be pointed out that the silicone adhesive does not build adhesion over time, as it fully wets into the skin morphology when applied.31 In contrast, traditional adhesives like those used in the acrylic-based probe build adhesion over time as they wet into the morphology of the skin and gain surface area.32 Therefore, the dwell time used in this study would benefit the acrylic-based probe over the silicone-based probe. However, with the longer dwell times seen in the clinical setting, the acrylic-based probe would be expected to remove more skin cells than reported here, though specific testing in the clinical setting would be needed to confirm this hypothesis. Further, the skin that is removed remains on the adhesive and reduces its future adhesion by reducing the available surface area for bonding.

The results seen in the protein removal and reapplication trials are most likely connected. Waring et al show this effect on a silicone adhesive, with higher protein assay results correlated to higher contamination on the adhesive.33 Less skin cells removed and adhered to the silicone-based probe, which would allow for continued repositioning with similar adhesion to its first removal. In contrast, the high amount of skin cells removed by the acrylic-based probe would physically block the adhesive from adhering to the skin on future repositions, leading to its precipitous decline in peel force. This decline appears to be a power function which is consistent with this type of decay where each reposition would block a similar percentage of adhesive that was still available.

Limitations

For gentleness, there were several protein assay results below the test detection limit, specifically for the silicone-based probe, resulting in left-censored data. Challenges in handling censored data, especially left-censored data, is well-recognized and several analysis methods have been proposed in response. In the analysis presented here, values falling below the detection limit were assigned the detection limit value. This approach provides a conservative value of protein removed, as the actual values were lower than the detection limit. During the reapplication portion of the study the differences in the stiffness of the optical region could not be accounted for so only the fabric tail region of the probe was discussed. The probe dwell time during the gentleness study was four hours, timing that may be seen in the clinical setting. However, due to the time restraints of completing 18 reapplication trials, the dwell time of the probes during the reapplication study was approximately 30 seconds per run, which is not reflective of clinical practice. The short dwell time would be expected to increase the repositionability of the acrylic-based adhesive but have no similar effect on the silicone-based adhesive. Given the laboratory setting and healthy adult sample, these studies do not reproduce clinical experience and therefore did not allow for assessment of relevant clinical outcomes such as incidence of MARSI, patient comfort, or probe utilization over time. Though these results are consistent with previous work, independent validation of these results would be of value.

Conclusion

In healthy adults in a laboratory setting, the silicone-based probe demonstrated greater repositionability and less protein removal compared to the acrylic-based probe. Neither probe appeared to impede skin barrier function, as indicated by similar TEWL values. Validation of these findings by other research teams would be valuable. Future studies based in clinical settings, specifically intensive care units, examining patient related incidence of MARSI and probe reapplication over longer wear times in silicone- and acrylic-based probes would be of interest. Further, understanding the economic impact of using probes with greater reapplication capacity would provide an important and interesting perspective on device selection.

Funding Statement

This study was sponsored and funded by Medtronic, the manufacturer of Nellcor pulse oximetry products. All authors received research support from, or are employees of, Medtronic. Medtronic was involved in the study design, interpretation of data, and writing of the manuscript, and in the decision to publish the results.

Disclosure

We disclose that Gary Grove is Vice President of Research and Development of cyberDERM, inc., Timothy Houser is an employee of Dermico, LLC, and Jacob Dove and Derek Moody are employees of Medtronic. This study was sponsored and funded by Medtronic. All authors received research support from Medtronic to conduct this study. The authors report no other conflicts of interest in this work.