Wound drainage measurements: a narrative review

Drainage from chronic wounds can significantly negatively impact a patient’s quality of life. Change in severity of wound drainage is an important measure of treatment efficacy for wounds. This study reviews existing tools used to assess wound drainage. Qualitative drainage tools are overall less burdensome, and however, differences in user interpretation may reduce inter-rater reliability. Quantitative drainage tools enable more reliable comparisons of drainage severity and treatment response between patients but sometimes require equipment to administer, increasing responder burden. Gaps in the current wound drainage measurement landscape are highlighted. Many of the existing scales have not been validated in robust studies. There is also a lack of validated global drainage measurement tools for patients with chronic inflammatory skin disorders with drainage, such as hidradenitis suppurativa or pyoderma gangrenosum. Development of a succinct drainage measurement tool for inflammatory skin diseases where drainage is a prominent symptom will improve monitoring of meaningful treatment response.


Introduction
Chronic wounds represent the largest direct medical cost of all skin conditions, costing nearly 9 billion USD in the United States annually [1]. A patient's quality of life (QOL) can be as profoundly impaired by chronic wounds as by heart and renal disease [1]. Existing, comprehensive wound assessments evaluate varying wound characteristics, including amount of drainage, pain between and during dressing changes, odor, itching, bleeding, and impact of the wound on QOL. Evaluation of change in wound drainage helps inform clinicians regarding treatment efficacy.
Many drainage assessments are currently tailored to assess post-surgical wounds. However, several other cutaneous conditions involve wound drainage, including inflammatory skin disorders such as hidradenitis suppurativa (HS) and pyoderma gangrenosum (PG), neoplastic diseases such as malignant tumors, and chronic ulcers, including vascular, 1 3 inflammatory, and rheumatologic ulcers [1]. Although studies have examined the impact of drainage on patient QOL, there is a lack of validated, targeted tools to specifically measure drainage in patients with inflammatory skin disorders such as HS and PG [2]. The aim of this study is to review existing tools used to assess drainage and highlight the lack of and need for global drainage measures in inflammatory draining skin conditions.

Assessment of drainage severity
Several measures have been created for patients to qualitatively assess drainage severity on categorical or numerical scales (Table 1). An example of a categorical scale is the Malignant Wound Assessment Tool (MWAT), a validated measure with domains including clinical wound features (i.e., wound location, classification, and edema) and physical, emotional, and social impact of the wound [3]. Regarding drainage, patients are asked to rate the severity as "dry, minimal, moderate, or heavy." Numerical rating scales ask patients to rate drainage severity, often on a scale of 0-10. Zero represents no drainage, and "10" represents the worst drainage; "10" may be defined in different ways depending on the measure. As an example, the Toronto Symptom Assessment System for Wounds (TSAS-W) defines "10" as "most severe and/or continuous drainage or exudation." [4] Some numerical scales have a descriptor that accompanies each number in the scale. Finally, another measure of drainage severity is qualitatively evaluating the amount of leakage from dressings. The Wound Symptoms Self-Assessment Chart queries how often fluid has been leaking from a patient's dressing over the last week on a scale of 0-10, with "10" defined as "constantly leaking" [5]. Similarly, the Wound Management Questionnaire asks patients whether fluid has leaked through their dressing, from "not at all," "a little," "quite a bit," to "a lot" [6].
Similarly, both categorical and numerical tools exist for healthcare providers (HCPs) to qualitatively assess drainage severity (Table 1). Categorical tools include the National Wound Assessment Form, which assesses wound moisture level as dry, moist, wet, saturated, or leaking [7]. The World Union of Wound Healing Societies' (WUWHS) Initiative Exudate Assessment uses the same categorical rating scale for drainage, but provides definitions for each rating based on qualitative estimates of fluid amount, saturation of dressing, and frequency of dressing changes [8]. Several tools grade drainage on a numerical scale with a descriptor provided for each number. For most of these measures, "0" represents no drainage. Greatest severity is defined as "severe" in the New Wound Bed Score [9], "smelly exudate" in the Tissue, Inflammation/Infection, Moisture, Edge/Epithelialization (TIME) score [10], "heavy" in the Pressure Ulcer Scale for Healing tool [11], and "copious" in the Leg Ulcer Measurement Tool [12].

Assessment of drainage appearance
In addition to assessing severity of drainage, certain tools also describe other characteristics of drainage, including viscosity, color, and the presence of odor. For example, MEAS-URE and MWAT can be used to evaluate drainage viscosity in categories ranging from serous, serosanguineous, to purulent [3,13]. Drainage color is included in WUWHS, including options of red/pink, yellow/green, to brown/gray [8]. The presence of odor is a component of the TSASW and WUWHS measures [4,8]. The Bates-Jenson Wound Assessment Tool (BWAT) scores exudate type on a scale of 1 (bloody) to 5 (foul purulent) based on a composite evaluation of viscosity, color, and the presence or absence of odor [14].

Advantages and disadvantages of qualitative methods
Qualitative wound drainage measures do not require any equipment and are less burdensome to complete as compared to quantitative measures. Ease of use of these tools may encourage more frequent assessments of drainage, which is an important component of evaluating treatment efficacy for inflammatory skin conditions with drainage. Categorical and numerical scales for drainage amount can help track disease status and direction of change for individual patients. Disadvantages include the lack of specific criteria for each numerical or categorical value. Even for tools that define each possible response, user interpretations may vary since the definitions are not based on quantitative criteria, and this may reduce inter-rater reliability. Thus, comparing drainage status between patients based on qualitative responses is difficult (e.g., one patient's "severe" may be another patient's "moderate"). To this end, some clinical trials specifically track change in exudate status, as opposed to the exudate amount itself, noted as decreased, equal/ unchanged, or increased [15].

Assessment of drainage based on wound dressing
Several quantitative wound drainage tools use dressings as a means of drainage measurement ( Table 2). Most are clinician-reported outcomes. Strategies include measuring the layers of gauze a wound soaks through, the number Wound cleansed, then covered with a transparent occlusive dressing. Fluid retained within the film was withdrawn using a micropipette. Collected samples were centrifuged, and volume of supernatant was measured using a micropipette in microliters, in units of ten. Volume per day was then calculated HCP No NA of dressing changes per day, and the degree of saturation on a dressing or on clothing. In the wound exudate score, users count the layers of gauze soaked through by exudate. The score ranges from 0 to 3, with 3 defined as > 12 layers of gauze soaked through [16]. Examples of measures that count the number of dressing changes include DESIGN-R and MEASURE. DESIGN-R evaluates frequency of dressing changes from 0 (none) to 6 (more than twice a day) [17]. MEASURE takes into consideration the wear time of a dressing in days and whether nonabsorptive or absorptive dressings are required [13]. Some clinical trials calculate the mean number of dressing changes per day and the total number of dressing changes needed until a wound has completely healed [18]. The Wound Management Questionnaire is a patient tool that asks patients whether leakage has required bedding or clothes to be changed, and if so, how many times [6]. Different tools evaluate the degree of saturation on dressing or clothing. The Wound Fluid Quantification Score has an HCP rate drainage as absent, minimal, moderate, or high, based on the volume in milliliters of fluid on gauze over 24 h [19]. The Treatment Evaluation by A Le Roux's (TELER) Method evaluates whether dressings and/or clothes are damp, wet, or sodden [20]. BWAT examines the moisture of wound tissues (dry, moist, wet, saturated, or bathed in fluid) and area of drainage involvement of dressing (ranging from no measurable exudate to exudate involving > 75% of dressing) [14]. Stannard et al. quantify drainage via the size of exudate area involvement in centimeters on the removed dressing [21].

Assessment of drainage based on amount of wound affected
One tool that assesses drainage severity based on the amount of wound affected is the validated Additional treatment, Serous discharge, Erythema, Purulent exudate, Separation of deep tissues, Isolation of bacteria, and Stay (ASEPSIS) Score (Table 2). Utilizing a numerical scale of 0 to 5, it examines serous and purulent exudate separately and defines each score based on proportion of the wound affected (i.e., a score of 5 indicates > 80% wound affected) [22].

Other quantitative measures of drainage
Some clinical trials seek to measure the exact volume of drainage. These methods may include measurement in cubic cm of drainage collected in surgical drains [23] or calculating the weight difference of a saturated dressing [24]. The ESTimation method uses a micropipette to recover fluid from a dressing that was occluded over the wound. The sample is centrifuged to remove cell debris, and then, the volume of supernatant is measured in microliters. The  [25]. Recent studies have examined whether skin impedance values, which reflect the response of skin regions to applied electrical currents, may help characterize drainage. Kekonen et al. described the utility of using electrodes to generate skin impedance values to assess degree of skin humidity [26]. Low skin impedance was correlated with higher exudate production. Henricson et al. described using a moisture sensor to assess exudate levels to guide when to change wound dressings [27].

Advantages and disadvantages of quantitative methods
Quantitative tools for wound drainage severity measurement have less inter-rater variability as compared to qualitative methods. They not only enable the evaluation of drainage status and drainage response to treatment of individual patients, but also allow more reliable comparisons regarding drainage severity and treatment response across different patients. However, quantitative methods impart greater responder burden on the clinician and patient, sometimes requiring physical equipment. In addition, unless exact measurement of drainage is sought, surrogate methods of measurement may still impart inter-rater variability. For example, measures based on number of dressing changes per day may differ depending on different thresholds patients have for changing their dressing. Measures that examine dressing saturation depend on how the dressing is affixed and the type of dressing used. Of the measures discussed in this paper, only DESIGN-R, TELER, and BWAT have been validated in studies.

Lack of global drainage measures in chronic inflammatory skin conditions
Using HS as an example of a chronic inflammatory draining skin disease, there is one study in the literature that evaluates efficacy of wound dressings in HS patients, which asked participants to rate drainage severity from 1 to 4, defined as 1 (no), 2 (a little), 3 (moderate), or 4 (a lot of drainage) [28]; however, this was not a validated measure. Another measure, the Hidradenitis Suppurativa Odor and Drainage Scale (HODS), asks patients to rate both the usual amount and worst amount of drainage from their HS for specific anatomic locations, including head/neck, armpits, trunk, groin, buttocks, genital/perianal area, and other areas. The 5-point categorical scale for HODS ranges from "no drainage" to "very severe drainage," and each is defined based on the wear time of dressings. Though specific for HS, HODS does not include a simple global drainage measure. PG, another chronic draining inflammatory skin condition, also lacks a specific global measure for drainage.

Discussion
Draining skin lesions greatly influence the morbidity of patients and constitute a significant clinical problem. However, the clinimetrics of drainage are overall poorly developed. Although there are various qualitative and quantitative wound drainage measurements that are in use as clinical tools or have been used in clinical trials, many of the existing scales have not been validated in robust studies.
There is currently a lack of a global, validated tool assessing wound drainage in inflammatory skin disorders. Several of the existing wound drainage measures are designed for surgical wounds and pressure ulcers, and these measures are not readily applicable to inflammatory skin conditions. For instance, measuring the distribution of drainage in a wound bed is difficult in a disease like HS where drainage is often sequestered in tunnels. Characterizing drainage viscosity as a measure of drainage severity is also less relevant for noninfectious, inflammatory skin conditions.
The lack of a specific and validated global drainage tool for inflammatory skin diseases is a barrier to assessment of this important outcome. More studies should investigate the development of a succinct drainage measure in skin diseases where drainage is a prominent, burdensome symptom. This would allow for improved monitoring of meaningful treatment response in clinical trials as well as in clinical settings. dradenitis Suppurativa Foundation. AbbVie: Consultant, Speaker, Advisory Board (Honoraria), ChemoCentryx, Incyte, Janssen, Novartis, UCB: Consultant (Honoraria). BMG has received fees from Novartis. GBJ reports grants and personal fees from AbbVie, personal fees from Coloplast, personal fees from Chemocentryx, personal fees from LEO pharma, grants from LEO Foundation, grants from Afyx, personal fees from Incyte, grants and personal fees from InflaRx, grants from Janssen-Cilag, grants and personal fees from Novartis, grants and personal fees from UCB, grants from CSL Behring, grants from Regeneron, grants from Sanofi, personal fees from Kymera, personal fees from VielaBio, outside the submitted work. There was no financial transaction for the preparation of this manuscript. All other authors report no conflicts of interest.
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