‘Do anti-embolism stockings fit our legs?Leg survey and data analysis’

Abstract

Background

Anti-embolism stockings are commonly used worldwide to prevent the development of thrombosis in hospitalised patients. Patients are typically measured for, and fitted with, anti-embolism stockings during extended periods of non-ambulation. Anti-embolism stockings must critically fit the leg to achieve optimum blood flow and thus success of prophylaxis. Therefore, hospitals endeavour to maintain stock of anti-embolism stockings that fit the majority of their patients.

Objectives

The objective of this study was to establish whether popular styles/brands of anti-embolism stockings “fitted” the legs of randomly selected volunteers.

Design/Methods

Volunteer’s legs were measured at ankle, calf and thigh following guidance from British nurses and in accordance with brand instructions. Leg measurements were subsequently compared to the size charts of 10 anti-embolism stocking styles made by 4 different manufacturers. Where a volunteer’s leg measurements matched all measurement points for any size, in style’s range,“fit” was achieved.

Settings

Volunteers were measured in different settings around Scotland, including private homes, work places and shopping centres.

Participants

A convenience sample of 471 volunteers (283 female, 188 male) were recruited on the basis of willingness to participate and being over 16 years old. Volunteers ranged from 17 to 82 years old with an average age of 35.

Results

The 10 different styles of anti-embolism stockings, made by 4 different brands, examined for this paper had a “fit” coefficient ranging from 0% to 100% for our volunteer’s legs. The fit coefficient is strongly influenced by the Brand’s sizing policy.

Conclusions

The proportion of legs that “fit”a particular brand of anti-embolism stockings can be increased through: 1. the reduction of the number of leg measurement points that need to be matched to the size chart of the stockings; 2. the use of open-ended size ranges; 3. the use of increased size range width and 4. the use of increased overlap between sizes. However, all but the last of these measures can have a potentially deleterious impact on the ability of the stocking to deliver the optimum graduated pressure profile to all legs that “fit” the stocking, resulting in important implications to the efficacy of prophylaxis.

Key words: Anti-embolism stockings; fit; leg shape; leg size; mechanical thromboprophylaxis; Sigel profile.

What is already known about this topic?

  • Anti-embolism stockings are commonly used worldwide to prevent thrombosis development in hospitalised patients.
  • Fitting the correct size of anti-embolism stockings to patients is critical to patient compliance and the success of thromboprophylaxis.
  • Incorrect use or fitting of anti-embolism stockings may cause skin problems, ischaema, and increased risk of thrombosis development.

What this paper adds?

  • The proportion of our sample that “fitted” different AES brands and styles ranged from 0% to 100%.
  • Good “fit” was significantly easier to achieve with knee length anti-embolism stockings compared to thigh length anti-embolism stockings.
  • Open-ended sizing and reduction of the number of measurement points on the size charts increase the proportion of patients that appear to “fit” anti-embolism stockings. However, these measures may have implications on the ability of the stockings to deliver optimum pressure profile (Sigel profile) to those patients.

Introduction

Pulmonary embolism is believed to be the most common cause of preventable death in hospitalisedpatients[Geerts et al, 2008] and approximately 25,000 people die annually as a result of venous thromboembolism in England alone [Dumbleton and Clift, 2008]. Venous thromboembolism is the collective term for pulmonary embolism and deep vein thrombosis, a pulmonary embolism often results from deep vein thrombosis [SIGN, 2010] when part of the blood clot breaks off and occludes a vein [Dumbleton and Clift, 2008]. Deep vein thrombosis has been found in between 10 and 80% of hospitalised patients not receiving prophylaxis [Dumbleton and Clift, 2008, Geerts et al, 2008] and approximately 0.1% of the general population present per year with clinical symptoms of deep vein thrombosis in the UK [SIGN, 2010]. Therefore, the majority of surgical patients and many medical patients are routinely given thromboprophylaxis in order to prevent or reduce the occurrence of venousthromboembolism [Guyatt et al, 2012, NICE, 2010, SIGN, 2010].

A range of thromboprophylaxis are available including pharmacologic and mechanical methods. The recommended thromboprophylaxis for each patient depends on their condition and risk factors [Guyatt et al, 2012, NICE, 2010, SIGN, 2010]. There are 3 different types of mechanical thromboprophylaxis: anti-embolism stockings (AES); intermittent pneumatic compression devices and venous/pneumatic foot pumps. The use of mechanical thromboprophylaxis has been shown to reduce the incidence of deep vein thrombosis by 40% and combined mechanical and pharmaceutical thromboprophylaxis reduce the incidence of deep vein thrombosis by up to 80% [Dumbleton and Clift, 2008]. This paper examines the “fit” of anti-embolism stockings (AES), the commonly used form of thromboprophylaxis for hospitalised non-ambulatory, recumbent patients.

AES apply graduated compression to the leg, which increases blood flow [Dumbleton and Clift, 2008], reduces stasis [Geerts et al, 2008]and venous distension [NICE, 2010] in the legs, thereby lowering the risk of thrombosis formation and embolism [Dumbleton and Clift, 2008]. The ideal compression profile is generally agreed to be the ‘Sigel profile’ [Dumbleton and Clift, 2008, NICE, 2007, Sigel et al, 1975] and most manufacturers design theirAES to deliver this pressure profile to legs properly “fitted” with their stockings [ArjoHuntleigh, 2012, Carolon, 2009, Preventex, 2012]. A stocking that exerts the Sigel profile would exert 18mmHg to the ankle, 14mmHg to calf, 8mmHg at the knee (popliteal break), 10mmHg at the lower thigh and 8mmHg at the upper thigh. This level of compression has been shown to increase blood flow in the deep veins by 75% [Sigel et al, 1975].

The pressure exerted by AES is rarely measured in a clinical environment due to lack of time and availability of an appropriate pressure sensor. Instead stockings are tested using laboratory methods through the measurement of tension and subsequent calculation of pressures that would be exerted on a range of limb circumferences. A number of test methods and devices exist for measuring anti-embolism stockings [BSI, 1993, RAL, 2008] but all measure the tension of the stocking at the ankle, calf and thigh area (if present) for particular extensions or circumferences. The pressures that would be exerted by that stocking at particular circumference of ankle, calf andor thigh are then calculated using an equation based on the Laplace Law [BSI, 1993]. The simple form of the Laplace Law states that pressure is equal to tension divided by the radius of curvature (which is easily calculated from the circumference). Therefore, if a particular stocking is put on a leg that is thicker or thinner than that for which it was designed, both the tension and circumference change and it is likely that a different pressure profile will be exerted. Thomas, Toyick and Fisher(2000) measured changes in pressure (referred to as % stiffness) of up to 36% when stockings were tested in accordance with the standard BS 7672,“Specification for Compression, stiffness and labelling of anti-embolism hosiery”, atone size larger andsmaller than that recommended by the manufacturer. Moreover, MacLellan(2002) showed that the pressure exerted on the maximum recommended leg measurement was frequently 4 to 5mmHg higher than on the minimum recommended leg measurement for commercially available AES. He further demonstrated that the pressure profiles exerted on the minimum and maximum recommended leg dimensions were frequently different [MacLellan, 2002]. Therefore, the match between stocking size and leg size is critical to achieving the ideal pressures at ankle, calf and thigh and the ideal positive pressure gradient from ankle to the proximal part of the leg.

Guidelines on thromboprophylaxis stress the importance of measuring legs carefully and correctly, and fitting the correct size of AES in order to ensure good fit, optimum benefit and compliance with anti-embolism stockings [Geerts et al, 2008, NICE, 2010, SIGN, 2010] as well as minimising the risks associated with their use [Dumbleton and Clift, 2008, NICE, 2010]. It is also recommended that staff be trained in the use and fitting of AES and that stocking use be “closely monitored” and patients’ legs be re-measured and re-fitted if oedema develops [NICE, 2010] or leg size changes. Further, the NICE guideline 92 cautions against fittingAES to “unusual leg size or shape” due to the risks associated with poorly fitted stockings. They cite the risks of potential tourniquet effects at the proximal part of the leg leading to ischaemia and increased risk of thrombosis development if stockings are the wrong size or shape for the leg [NICE, 2010]. However, the judgement of what constitutes an “unusual leg size or shape” is normally left to the nurse fitting the stockings and may be influenced by the size charts of AES stocked by that hospital.

Each brand has its own size ranges at a variety of measuring points and its own methods of communicating the sizes. Some brands offer fewer measurement points than others and some have open-ended sizing (where the upper or lower limit of a size range is not specified), both of which give the impression that they are appropriate for use on a wider range of patients than brands with narrower or more specific size ranges and or more measurement points. This can result in confusion as to which products are most suitable for an individual patient.

Given the critical nature of the fit of AES on the leg in achieving optimum venous return and maximum protective benefit we turn to the question of whether the AES currently available in our hospitals is available in the correct sizes for our patient’s legs. To the best of the author’s knowledge no survey of patient’s leg sizes could be found and the British Standards committee members for compression hosiery were unaware of a survey having been conducted. Therefore, since any member of the public could be admitted to hospital for many of the surgical and medical conditions for which AES is recommended a survey of randomly selected volunteer’s legs around Scotland was undertaken. These measurements were compared to the size charts of 10 styles of AES produced by 4 major brands in order to determine how many of our volunteer’s legs would fit a standard AES and how many had "unusual leg size or shape” according to the current AES provision.

Method

Measures: The circumferential leg measurements, also called girths, at the ankle, calf and thigh of 471 volunteers were measured in a variety of locations around Scotland. Both legs of each volunteer were measured to the nearest cm at the ankle, largest calf girth and largest thigh girth as indicated by the measurement instructions for anti-embolism stockings (AES) and following training provided by 2 Scottish National Health Service nurses.

Determination of “fit”: The girths of each volunteer’s left and right legs were separately compared to the size charts of 4 major brands of AES: Covidien’s (Kendall) T.E.D.; ArjoHunteigh’sFlowtron; Urgo’sPreventex; H&R Healthcare’s Carolon. For below knee AES, each volunteer’s ankle girth was matched to the size chart and size matches were noted; this was repeated for the calf girth. Where both ankle and calf matched the same size of below knee stocking the volunteer’s leg was said to match, or “fit”, a particular size. If no ankle girth range was specified then the match to the brand was determined based on calf girth only. If the ankle and calf did not match the same product size, e.g. the ankle was ‘small’ but the calf was ‘medium’, then no stocking in that range would be deemed to “fit” the volunteer. This process was repeated for thigh length stockings using ankle, calf and thigh girths. The percentage of our volunteers’ legs to “fit” each size of stocking in the range is presented, as is the percentage of volunteers’ legs that “fitted” no size in the range. The “fit” coefficient for a brand is defined as the percentage of our volunteers’ legs that fitted any one or more sizes in a range at all relevant measurement points. Legs may not “fit” any size in a brands’ range because the leg is too thin or too thick for the sizes available or because the leg has a different profile to the size charts, being either too conical (e.g. larger calves) or too cylindrical (e.g. larger ankles), for example.

Participants and recruitment: Volunteers were recruited to the survey using convenience sampling methodsin a variety of locations and settings around Scotland including: private homes, work places, shopping centres and a nursing home. Attempts were made to cover different social/economic demographics in the choice of measurement locations and measurements were made on all days of the week and at different times of day in an attempt to avoid bias. However, measurement setting was largely determined by the researchers’ ability to obtain permission to measure thus the sample may not be representative of the wider population.

In shopping centres, researchers set up a screen to enable private measurements. During quiet periods all passers-by were approached until someone agreed to participate, at busy periods the researchers approached as many passers-by as possible. Once a volunteer showed interest in participation the terms and purpose of the research and the measurement process were explained using a standardised script. All willing volunteers were taken behind the screen in order to have both legs measured for this study, the only exclusion criteria were absence of legs or being younger than 17 years old. All volunteers signed an ethical consent form prior to being measured. Their sex was noted by the researcher on the measurement form and each participant was asked their age, no other demographic information was requested or noted.

In work places and the nursing home, all available employees or residents were asked whether they wished to participate in the study, if they were willing to participate they were measured in a private room. In the nursing home a member of staff was also present. The same exclusion criteria, script, ethical consent form and measurement form were used for all measurements in all locations and settings.

Data analysis: All leg measurements were recorded in a Microsoft Excel spreadsheet. Separate copies of this spreadsheet were made for each AES brand and style evaluated in this study. Each leg measurement was manually matched to sizes according to the size chart of each brand and style at ankle, calf and thigh. Microsoft excel functions were then used to determine whether all measurement points for each leg “fitted” all measurement points for each size of stocking. Where a leg matched the same size of stocking at ankle and calf for below knee AES or at ankle, calf and thigh for above knee AES it was deemed to “fit”. The unit of measurement for analysis was legs and 942 legs were measured and analysed in total.

Note: Each brand of AES evaluated in this study provided a range of sizes in 2 or 3 leg lengths for each of their products. Three of the 4 brands examined provided open-ended leg length ranges, such as a short thigh length AES being suitable for patients with a leg length “less than 74cm”; therefore all of our volunteers would be said to “fit” these AES in terms of length. Carolon was the only brand to set upper and lower limits for its AES lengths; this may have further reduced the proportion of our volunteers to “fit” their products. However, leg length was not included in this evaluation as it is less critical in determining the pressure gradient delivered to legs than circumferential measurements and most brands utilise an open-ended sizing policy. All brands require that leg length and a number of circumferential measurements be taken before selecting the correct size of AES for a patient. For the rest of this paper however, only the circumferential measurements required will be discussed.

Results

Survey volunteers ranged from 17 to 82 years of age, with an average age of 35 and standard deviation of 14. 283 of the volunteers were female and 188 were male.

Table 1 shows that different brands of anti-embolism stockings (AES) vary significantly in terms of the number of sizes available and the proportion of our volunteers whose measurements “fit” a particular size. The size ranges and reasons for these differences of percentage“fit” are explored in later in this paper. Note that the percentage of volunteers “fitting” each size for somestyles adds up to more than 100% because some of the volunteers “fitted” 2 sizes. The “fit” coefficient is defined as the percentage of our volunteers who “fitted” any one, or more, sizes in a range of AES at all relevant measurement points and is found by subtracting the percentage of volunteers who did not fit any sizeof AES in Table 1 from 100%.

Table 1 shows that, according to the manufacturer’s size charts, Covidien’s below knee T.E.D. stockings had a “fit” coefficient of 100%, meaning that they “fitted” all of our volunteer’s legs, with 10% (n=95) “fitting” 2 sizes of below knee stocking. Urgo’sPreventex brand below knee stockings had a “fit” coefficient of 82% (n=776), Flowtron AES “fitted” 74% (n=701) and Carolon “fitted” 62% (n=583) of our sample.