Insulated Offloading Provides Offloading Protection and Enhanced Skin Perfusion

Introduction. Locally and neurally mediated vasodilation of the cutaneous vasculature has been shown to occur in response to locally and systemically applied heat stresses. The resultant shunting of blood to the periphery can be upwards of 7 L/min to 8 L/min when profound heat stresses are applied. The increased cutaneous circulation from local heat stress may benefit extremities afflicted with a wound or area of compromised arterial supply. Insulating the extremity also may increase local cutaneous perfusion. Objective. This study aims to determine if increased local warmth from an insulated offloading boot or mitt (designed to protect an extremity from trauma, offload the extremity to prevent pressure ulcers, and insulate the extremity to minimize heat loss) also results in increased local cutaneous perfusion using indocyanine green fluorescence angiography (ICGFA). Materials and Methods. Nine patients from an outpatient wound care clinic with a wound or area of compromised arterial supply on the upper or lower extremity were studied prior to and following a minimum of a single 60-minute session of insulated offloading boot or mitt use utilizing ICGFA. Measurements taken were time to first onset of fluorescence (seconds) and ingress and egress rates for the area of concern and the remainder of the area imaged. Results. All 9 patients exhibited signs of increased local warmth by a mean of 3.1ºF while body temperature decreased by a mean of 1.2ºF. Local cutaneous perfusion increased with a mean change of 1 for the ingress rate to the area of concern and a mean change of 0.1 to the remainder of the area imaged. Also, ICGFA was able to demonstrate preferential shunting of the increased cutaneous perfusion to the site of most need. Conclusions. These findings suggest enhanced skin perfusion may be an additional advantage of insulated offloading boot or mitt use.

Changes in cutaneous circulation due to locally and systemically applied heat stresses have been reported to predominantly occur in response to local and neural temperature-mediated vasodilation.^1-4 Shunting of blood from the core to the periphery can be upwards of 7 L/min to 8 L/min when profound heat stresses are applied.⁴ The majority of studies demonstrating these effects have been performed in the forearm.^5,6 However, a similar response has been exhibited in the lower extremities, even those affected by peripheral arterial disease.^7,8 Increased cutaneous circulation due to local and whole-body heat stresses may assist healing in extremities afflicted with a wound or area of compromised arterial supply. The Rooke Boot (Osborn Medical Corporation, Centennial, CO) and Rooke Mitt (Osborn Medical Corporation) are designed to protect the extremity from additional trauma, offload the extremity to prevent pressure ulcers, and insulate the extremity from heat loss. Effects on local skin perfusion related to the ability of the insulated offloading products to retain heat have not previously been studied.

Indocyanine green fluorescence angiography (ICGFA) utilizes the fluorescing properties of indocyanine green (ICG) to visualize tissue perfusion. Indocyanine green is a second-generation, sterile, water soluble, nonradioactive, nontoxic, and inert tricarbocyanine dye approved by the US Food and Drug Administration for intravenous injection in adults since 1959. When administered intravenously, > 90% of ICG remains intravascular by binding to large plasma proteins in the blood. Light activated near the infrared range (760 nm–805 nm) is absorbed, and fluorescence occurs around 835 nm to 845 nm, which lies within the “optical window” of the skin (600 nm–900 nm). This fluorescence can be captured via static and video imaging with a near-infrared sensitive charge-coupled device camera. Maximum reported tissue depth is up to 20 mm, allowing for visualization of the vasculature in the subdermal plexus, at a minimum, without the risk of tissue damage.^8-11

Herein, this type of imaging was utilized on 9 patients with a wound or area of compromised arterial supply of the upper or lower extremity prior to and following at least one 60-minute session of insulated offloading product use to determine if increased local warmth also resulted in increased local cutaneous perfusion.

This was a single-center pilot study conducted with an outpatient wound care clinic at a military treatment facility. Participants were eligible for inclusion if they had a wound of any size complicated by peripheral arterial disease or an area of compromised arterial supply of the upper or lower extremity as determined by clinical examination. Exclusion criteria included pressure wounds.

Patients underwent ICGFA via the LUNA Fluorescence Angiography System (Stryker, Kalamazoo, MI) prior to and immediately following at least one 60-minute session of insulated offloading. After a session, the extremity of interest was left covered until imaging was performed to minimize any change in local skin temperature. Body temperature was taken on the forehead via standard clinical protocol with a temporal thermometer. Local temperature of the area receiving insulated offloading was recorded just prior to application and immediately after removal using a handheld infrared thermometer. Parameters recorded from each ICGFA imaging sequence included the time to first onset of fluorescence (seconds), the ingress rate (ie, arterial inflow or increase in grayscale units [0–256]/seconds from fluorescence signal onset to peak), and the egress rate (ie, venous return or decrease in grayscale units [0–256]/seconds from fluorescence signal peak to return to baseline) for Region of Interest (ROI) 1 and ROI 2. The ROI 1 incorporated the wound or area of compromised arterial supply; ROI 2 was created to incorporate the largest area of the extremity being imaged that did not include the wound to use for comparison to ROI 1.

Nine patients were enrolled in this pilot study. The median age of the 9 patients (8 men, 1 woman) was 69.0 ± 10.8 years (range, 56–79 years). Six patients utilized insulated offloading during a single 60-minute session, and 4 patients used insulated offloading for a greater period of time: 10 days (1), 2 weeks (1), 1.5 months (1), and 5.5 months (1).

The median body temperature of all 9 patients was relatively unchanged from prior to and following a single 60-minute session of insulated offloading (98.5 ± 2.2ºF vs. 97.3 ± 1.5ºF, respectively). The median local temperature increased only slightly following a single 60-minute session (85.7 ± 8.3ºF to 88.8 ± 7.3ºF) (Table 1). Median time to onset of fluorescence decreased by a mean of 1 second following one 60 minute session, signifying a quicker time to arterial inflow. Local temperature was not recorded in enough patients who continued use to assess the outcome (Table 2).

The median ingress rate to the area with a wound or limited arterial supply increased by 1.4-fold, while the median ingress rate to the uncompromised area decreased by the same amount following a single 60-minute session of insulated offloading. The median egress rate to the area with a wound or limited arterial supply increased by 1.3-fold, while the egress rate to the uncompromised area remained unchanged. For the 4 patients that continued insulated offloading therapy, both the median ingress and egress rates to the area with a wound or limited arterial supply increased. The median ingress rate to the uncompromised area did increase slightly, while the median egress rate remained relatively unchanged from baseline to last follow-up (Tables 3, 4).

This pilot study found that while local temperature and tissue perfusion is not greatly changed after a single 60-minute session of insulated offloading boot or mitt use, continued use results in a local temperature increase. This increased temperature appears to result in increased local cutaneous perfusion (Figures 1, 2, 3, 4). The findings of this study are in line with others that have found local skin perfusion increases with an application of greater whole-body and local heat stresses.^1,2

Application of local heat measuring ~37ºC, ~39ºC, and ~41ºC to the forearm significantly increased tissue oxygenation and skin perfusion independent of perfusion or metabolic changes to the underlying musculature.^5-7 This change in cutaneous perfusion is postulated to occur due to several cardiovascular adjustments made to assist with heat dissipation.⁸ Previous studies^1-8 on the relationship of local heat and cutaneous perfusion have not assessed patients with an open wound or area of compromised arterial supply. However, reductions in transcutaneous oxygen pressure measurements (TCOM) have been documented to the plantar aspect of the diabetic foot when local heat stress is applied.⁹ These reductions in TCOM were hypothesized to occur due to increased oxygen consumption, though the results of the present study suggest the increased local cutaneous perfusion is preferentially shunted to the area of most need, as seen by the increase in ingress rates to the area of need with accompanying decrease in the uncompromised area after use of the insulated offloading boot or mitt. With the composition of the cutaneous vasculature being 90% to 95% thermoregulatory, this is not altogether unexpected, though it must be confirmed with larger, high-quality studies.

Limitations of this study include the small number of patients and the lack of standardized parameters for perfusion assessment provided by the ICGFA. The primary goal of this study was to determine if an increase in local skin temperature would be observed and if this increase resulted in vasodilation and an increased local cutaneous perfusion. While the ICGFA has no validated ranges for the parameters obtained, ICGFA has been used in surgical specialties to assess the presence of perfusion.^9,10 Given the properties of ICG and the ease and ability to rapidly perform visual assessment of the cutaneous vasculature, ICGFA was utilized as the method of vascular assessment in this study. Larger, high-quality studies with inclusion of routine methods of vascular assessment are required to confirm the results of this study.

The insulated offloading boot and mitt are made to protect, offload, and insulate the extremity. Findings of this pilot study suggest continued insulated offloading therapy increased local skin temperature and tissue perfusion. This increased tissue perfusion appears then to be preferentially shunted to the area of most need, ie, wounds or ischemia. Increased local skin temperature and cutaneous perfusion may be an added benefit of the insulated offloading boot and mitt. Larger, high-quality studies, including the use of standardized vascular assessments in addition to ICGFA, are needed to confirm these findings.

Affiliations: Madigan Army Medical Center, Tacoma, WA; and Scriptum Medica, University Place, WA

Correspondence: Valerie Marmolejo, DPM, Scriptum Medica, PO Box 65965, University Place, WA 98466; www.scriptummedica.com;
vlsdpm@gmail.com

Disclosure: The authors disclose no financial or other conflicts of interest. The views expressed are those of the author(s) and do not reflect the official policy of the Department of the Army, the Department of Defense, or the United States government.