Does the application of Opsite^⋄ Flexigrid^⋄ occlude the oxygen saturation readings in healthy individuals using the moorVMS-OXY machine?

A proportion of people who are diagnosed with peripheral arterial disease (PAD) and diabetes mellitus may develop a chronic wound [1]. A chronic wound is a break in the skin which has failed to go through each stage of wound healing (hemostasis, inflammation, proliferation and maturation) in the correct time frame [2]. This can be longer than 6 weeks or reoccurs frequently [3, 4].

Oxygen is a vital component for wound healing and a lack of oxygen can impact every stage of the healing process [2]. During wound healing, there is increased demand for energy which is provided when oxygen is readily available [5]. Energy is a fundamental requirement in wound healing due to the increased need to aid reparative processes such as, bacterial defences to prevent infection, cell proliferation and synthesis of collagen [6].

Oxygen levels need to be assessed as a decrease of oxygen in the body is associated with the development of ischemia, PAD and a reduced healing rates [2]. There are different methods for establishing arterial limb perfusion. In routine podiatric practice, this is primarily achieved via the use of a hand held Doppler, which focus’ on arterial perfusion of the foot by assessing the dorsalis pedis and the posterior tibial arteries. A study by Ladner et al., [7] showed that transcutaneous tissue oxygen tension measurement (TcPO₂) is also a suitable clinical screening tool for estimating the risk of foot ulcer non-healing in patients with diabetes and absent palpable pedal pulses. When considering the structures assessed using this device, its focus is on arteriole and capillary perfusion, which can provide vital information in relation to the perfusion of the tissues in the region of the wound. Limitations of the probes of this device are that they heat the tissues underneath, they are larger, more numerous and placed only around the wound margins. This does give useful information regarding the wound periphery but does not give actual wound bed perfusion values. The MoorVMS-OXY does provide the means of evaluating capillary oxygen saturation at the wound bed by utilizing white light reflectance spectroscopy [8]. There is only one, smaller probe to apply, which does not need to heat the tissues, therefore there is no delay prior to taking tissue measurements. The use of this device would enable clinicians to identify individuals who may have normal artery and arteriole flow but have capillary bed perfusion problems, which currently are not being assessed. These two devices mentioned are not commonly used in podiatry practice, but could provide valuable information if utilized more frequently [6, 9]. Clinicians may be concerned with applying a probe to the wound bed itself due to infection control reasons, concerns with cleaning the probe after use (as they are not disposable), causing skin stripping to the peri-wound skin on removal of a protective barrier film, if used, as well as uncertainty as to whether the protective barrier film used could affect the reliability of readings obtained from the device.

Measuring oxygen saturation percentages (SO₂%) at a wound bed could place the patient at risk of infection if performed incorrectly. All healthcare professionals are involved with infection prevention and control and must adhere to the quality standards to protect those who are vulnerable [10]. To measure ulcers, infection prevention methods must be in place. There are sterile transparent film dressings, which allow the exchange of oxygen and water vapour [11, 12], which could be used to allow devices to measure SO₂% whilst minimizing the risk of cross-infection and allowing faster probe cleaning, post use [13, 14]. However, these dressings adhere to the skin, if used in a single layer, and there is the possibility that this could leave the patient susceptible to skin stripping on it’s removal [14‐17]. Skin stripping of the peri-wound can lead to an increase in the wound size and additionally delay the healing process [14‐17]. If these dressings were used in a double layer, the skin stripping element would be removed but the thickness of the dressing may have a detrimental effect on the machine readings.

This study aims to answer this question, does the application of opsite film, as an infection control measure, in one or two layers, impact on tissue oxygenation readings obtained when using the MoorVMS-OXY? This would then allow clinicians to measure the oxygen saturation at the wound bed without the patient being at risk of cross-infection or skin stripping [14‐17], while maintaining confidence in the values that are obtained.

The eighteen participants included undertook the protocol without complications and no participants withdrew from the study. The data was obtained from 29 of the available 36 participant limbs. For the purposes of calculating the results n = the number of participant limbs included in the study will be used, thus n = 29. The data was normally distributed, as assessed by box plotting, see Fig. 1, and performing a Shapiro-Wilk test on the results, p-value is greater than 0.05 (no Opsite Flexigrid: p = 0.267, single Opsite Flexigrid: p = 0.331, double Opsite Flexigrid: p = 0.148) respectively. Mauchly’s test of sphericity showed that the assumption of sphericity had not been violated.

Descriptive Statistics showed that the highest measure of SO₂% occurred at the 1st MTPJ with no Opsite Flexigrid (mean: 49.1241, SD: 11.59990), followed by a slight SO₂% decrease with a single layer of Opsite Flexigrid (mean: 48.7241, SD: 12.77298). However, an even further SO₂% decrease with a double Opsite Flexigrid at the 1st MTPJ (mean: 45.2069, SD: 12.46208).

Figure 1 shows the mean SO₂% of each participant from the samples across the independent variables. This shows that as the OF layers increase the SO₂% decrease. The SO₂% ranges from layer to layer; no Opsite Flexigrid ranges from 24.0–67.8%, single Opsite Flexigrid ranges from 23.6–72.0% and double Opsite Flexigrid ranges from 13.2–64.9%.

After performing the one way repeated ANOVA, it was shown that SO₂% was statistically significant at the different layers; F (2,56) = 4.501, p < 0.05, p = 0.015. Pairwise comparisons further showed the mean differences in SO₂% between each of the layers and whether it is statistically significantly different or not. See Table 1. A single layer of Opsite Flexigrid compared to no Opsite Flexigrid has a decreased mean difference of 0.400, however was not statistically significant different because p > 0.05, p = 1.000 (95% confidence interval, − 4.584 to 3.784). The mean differences for a double layer of Opsite Flexigrid versus no Opsite Flexigrid decreased by 3.917, and double layer of Opsite Flexigrid versus a single layer of Opsite Flexigrid decreased by 3.517. This shows that mean values for double Opsite Flexigrid versus no Opsite Flexigrid (p = 0.037, 95% confidence interval, − 7.640 to − 0.195), and double Opsite Flexigrid versus single Opsite Flexigrid (p = 0.016, 95% confidence interval, − 6.484 to − 0.551) have a statistically significant difference (p < 0.05).

The purpose of this study was to investigate whether applying a sterile transparent film wound dressing would occlude the SO₂% value collected by the MoorVMS-OXY and it has been proved that it does, but not significantly. However, the application of a double layer of Opsite Flexigrid does significantly alter the results obtained. It also endeavored to consider how this may assist in its clinical application when considering preventing cross infection and / or skin stripping, on the most common weight-bearing ulceration site of the foot [24, 25].

The MoorVMS-OXY has been used in a range of studies proving it is a functional and reliable device to use. It has been used on the following; Wistar rats [26], Sprague-Dawley rats [27], mice [28], pigs [29], and humans; on the forearm [30] and forehead [31]. It is not limited to measuring specific body parts and has the potential to be utilized in clinical practice more frequently than it is at present. This device has been validated as reliable and accurate in measuring SO₂% in a skin phantom and human skin [32]. Alongside this, results have shown that measuring oxygen and tissue perfusion can be an early indicator of compromised tissue function [30]. Otherwise, there is limited literature on the use of the Moor VMS-OXY and wound healing, with the majority of the previous research focusing on comparing oxygen measurement using this device and others, such as, Near infra-red Spectroscopy (NIRS), pulse oximetry and TcPO₂. The human studies identified were to; predict results for wound healing with Hyperbaric Oxygen Therapy [33], detect stages of chronic arterial insufficiency of lower extremities [34], and to determine lower limb oxygenation values [35]. These studies each have different limitations, ranging from the participants, measurement sites and comparison devices used. For example, to measure capillary oxygenation using TcPO₂, the transducer needs to heat to 42 °C, which is not suitable for long-term monitoring and is invasive [33]. NIRS cannot measure oxygen values through adipose tissue, thus limiting its use, [35] and pulse oximetry can only measure capillary SO₂% on the peripheries; limiting its clinical use [34].

Of these studies, only one [33] mentions using methods to prevent cross-infection occurring which were; sterilizing or sanitizing the device, the participants skin, or using a sterile barrier.

This study illustrated that a double layer of Opsite Flexigrid decreases SO₂% values and this is likely due to the thickness of Opsite Flexigrid itself and the probe being able to only measure up to a depth of 1-2 mm [8].

When considering the use of a sterile barrier to protect the wound bed, there are many sterile transparent film dressings on the market other than Opsite Flexigrid. Each of these film dressings may have different thicknesses, therefore, the authors recommend trying to identify the thinnest film dressing on the market to establish if this affects the oxygen saturation values obtained.

Currently the results indicate that a double layer of Opsite Flexigrid cannot be used when measuring SO₂% in wounds because it occludes the probe and affects the values obtained. Using a single layer of Opsite Flexigrid marginally decreases the SO₂% value compare to no Opsite Flexigrid, however this was shown to have no statistical significant difference, suggesting a single layer of Opsite Flexigrid could be used in clinical practice. It would be beneficial if the study were repeated with a larger sample size to consolidate the findings and provide results more representative to the larger population.

It is acknowledged that skin stripping could occur using a single Opsite Flexigrid, if placed directly on the skin, when measuring SO₂% in wounds. Therefore, a future study using a single Opsite Flexigrid with the adhesive side stuck to the probe, compared to the single Opsite Flexigrid being stuck on the patient would provide evidence on whether there is a difference in readings or not. This would in turn prevent skin stripping and/or cross infection occuring in patients.

Strong skin pigmentation can cause compromised results [19]. Using the Fitzpatrick Scale [18] allowed elimination of the participants which had a higher skin score. However, limiting the study participants to skin types 1 and 2. This does not allow a true clinical representation of SO₂% amongst the entire population and its use in participants with a higher Fitzpatrick Skin score should be avoided. However, if measuring SO₂% at a wound bed, there is no Melanin present at that point, therefore, further research is required into whether this device can be used in higher Fitzpatrick skin scores if measuring the base of open ulcerations. This would expand its use further in clinic and make it a more versatile machine.

A limitation of the study was that participants were in a rested seated position, rather than laying supine or prone. Being supine or prone may have given more accurate results because it allows the effects of gravity to be eliminated at the foot / probe interface [36, 37]. Previous studies implemented this in their methods so it was not considered a confounding variable [30, 31, 33‐35, 37].

To conclude, there are very few MoorVMS-OXY studies done on humans, but from the literature found, it is used widely showing it is reliable and clinically applicable [26‐32]. Oxygen is vital to ensure wound healing, and a lack of oxygen can delay the healing process [2]. Monitoring SO₂% in patients with ulcers, whom may have PAD and diabetes mellitus, [1] is very important because SO₂% can be used as a predictor for healing times [2, 6, 9], consequently allowing health professionals to form management plans for each patient. Continuous monitoring of SO₂% provides tracking of progression and/or regression of wound healing.

From this study’s findings, the application of double Opsite Flexigrid significantly decreases the SO₂% values obtained compared to when no Opsite Flexigrid is applied, therefore occluding readings generated by the MoorVMS-OXY. This suggests that double Opsite Flexigrid cannot be used when measuring SO₂%. However, a single Opsite Flexigrid marginally decreases the SO₂%, but still partially occludes the readings. It is recommended that a single layer could be used, when obtaining measurements from the wound bed, in order to allow easier cleaning of the probe and to minimise cross infection risk. The single layer of Opsite Flexigrid can be applied directly to the probe or to the skin, however the clinician needs to be aware of potential skin stripping, if used on the skin. The results obtained with a single Opsite Flexigrid layer will impact on the results minutely, but not significantly, so should provide some reassurance that the values are as close to those obtained with no Opsite Flexigrid, but while providing greater infection control measures.