Abstract
Compression bandaging remains the ‘gold standard’ intervention for the treatment of venous leg ulcers. Numerous studies have investigated the effect of a large variety of compression bandaging techniques and materials on venous leg ulcer healing. However, the majority of these studies failed to monitor both actual bandage application pressures and the bandaging competency of participating clinicians. A series of literature searches to explore the methods, practices, recommendations and results of monitoring compression bandaging pressures in leg ulcer research trials were undertaken. This included investigating the reliability and validity of sub-bandage pressure monitors and the degree to which compression bandaging achieves the recommended sub-bandage pressure. The literature revealed inconsistencies regarding the monitoring of sub-bandage pressure and in sub-bandage pressures produced by clinicians. This creates difficulties when comparing study outcomes and attempting to develop evidence-based practice recommendations.
Keywords
Introduction
The use of compression bandaging has long been considered the ‘gold standard therapy’ for the treatment of venous leg ulcers, with the recommended sub-bandage pressure at the ankle generally agreed to be 40 mmHg.1,2 This pressure level is open to debate as there is no empirical proof that it actually is what is required. Additionally, sub-bandage pressure can reduce significantly in the first hours after application. However, literature suggests that the majority of experienced and inexperienced clinicians fail to reliably obtain recommended sub-bandage pressures without the assistance of practice guided by the use of a sub-bandage pressure monitor.3,4 When designing research studies using compression bandaging, it is important to attempt to control for this potentially confounding variable.
Many studies reporting the effect of compression bandaging on venous ulcer healing do not monitor actual sub-bandage pressure in vivo5–7 rather they report the predicted application pressure based on the manufacturer’s proposed bandaging system instructions for use. Sub-bandage pressure shows variation dependent on the posture of the leg, bandage type, number of layers applied and stretch applied to the bandage. Conventionally, sub-bandage pressure is measured in the supine position but needs to be measured in the standing position as well, in order to calculate the static stiffness index of the bandaging system and hence whether the system is elastic or inelastic in nature. When designing a venous ulcer research trial involving lower leg compression bandaging, it is therefore necessary to be fully cognisant of current practice recommendations regarding compression bandaging pressures and to choose a reliable and reproducible method of measuring sub-bandage pressure. This permits the researcher to position resultant experimental data within a predicted continuum of variation and to report the effects of specific rather than predicted or approximate bandaging pressures.
The aim of this paper is to identify and review a reliable and valid method of measuring sub-bandage pressure in vivo and also to investigate the reported incidence of correct application pressures in the absence of the use of a sub-bandage pressure monitor. An awareness of sub-bandage pressures in the absence of monitoring and a knowledge of the reliability and validity of the various available monitoring systems facilitate the interpretation of the findings of studies investigating the outcomes of compression bandaging therapy.
Literature search methodology
In order to explore the sub-bandage pressure monitoring systems and to further investigate how such measurements have been used within clinical practice, research and education, it was necessary to explore the literature using three distinct searches.
To identify the reliability and validity of sub-bandage pressure monitoring systems. To discover how frequently correct sub-bandage pressure is achieved and To quantify the sub-bandage pressures obtained in vivo for a variety of compression bandaging systems.
Search strategy – (i) Reliability and validity of the sub-bandage pressure monitor systems
The authors had experience using the PicoPress™ (Microlab Elettronica SAS, Padua, Italy) sub-bandage pressure monitor and aimed to investigate how it compared to other sub-bandage pressure monitoring systems. An initial search of the following databases using the search term ‘PicoPress’ anywhere in the record: ProQuest, Informit, Medline, Science Direct, Springer Link, Web of Science and Wiley Online was conducted. Items not in English and veterinary articles were excluded. This returned 44 items of interest. An additional search of Google Scholar returned a further 136 items for the term ‘PicoPress’ of which 55 were of relevance and had not been captured in the previous search, leaving a total of 99 articles in which investigators had used PicoPress™ to record sub-bandage pressure values. The abstracts of these articles were then reviewed and excluded if they did not compare sub-bandage pressure measurements obtained using PicoPress™ (Microlab Elettronica SAS, Padua, Italy) and at least one other pressure monitoring device resulting in the exclusion of 89 articles. The remaining 10 articles were then reviewed in full text. None were excluded at this level. The reference lists of these articles were then hand searched and a further six articles which met the selection criteria were included (see Figure 1).
Diagram of literature searches.
Search strategy – (ii) Frequency with which correct sub-bandage pressure is achieved
It was apparent from the literature that compression bandages are frequently applied at non-therapeutic levels.3,4 In order to investigate whether this had been quantified and whether training involving the use of sub-bandage pressure monitors changed the accuracy of application, a second literature search was undertaken, using the term ‘bandage training’ and using the same search strategy as described above. This returned 156 articles which were screened by title and abstracts and excluded if they did not report sub-bandage pressures obtained by practitioners in a training environment. A total of 150 articles were excluded. The reference lists of the remaining six articles were hand searched and three additional articles of relevance recovered (see Figure 1).
Search strategy – (iii) Quantifying sub-bandage pressures across studies
The third literature search was conducted to determine if there was any variation in sub-bandage pressures reported for the same bandaging system between different study teams. To facilitate this initial investigation, it was decided that a four layer bandage system (Profore™, Smith & Nephew, UK) would be chosen and literature reporting the pressures obtained identified. A search of the following databases: CINAHL, Medline and Embase, was conducted using the terms ‘Profore™’ AND ‘mmHg’. Exclusion criteria were applied as in the previous searches. Six articles of interest were returned. The abstracts of these articles were examined and three were excluded as they did not report pressures obtained on human participants resulting in a further three articles being added to the search total (see Figure 1).
The results of the three searches described above were combined to contribute to the discussion and analysis below as a number of the articles contributed to more than one area of interest.
Results
Measuring sub-bandage pressure
In 2006, Partsch 8 published a list of 22 interface pressure measurement devices available at the time. This included those used in vitro and in vivo studies across a variety of disciplines (see Table 1). There are three basic modalities commonly used to directly measure sub-bandage pressure and these can be classified as pneumatic, fluid-based and electrical devices. 9 Pneumatic devices use an air-filled bladder to detect change in pressure. When a bandage is applied over the sensor, the air pressure inside the sensor increases. The change in pressure is detected by an electric or piezoelectric sensor. Most of the sub-bandage pressure sensors commonly described in clinical research practice are pneumatic and examples include: Kikuhime™ (Meditrade, Soro, Denmark), Medical Stocking Tester (MST)™ (Salzmann Medico, St Gallen, Switzerland) and PicoPress™ (Microlab Elettronica SAS, Padua, Italy).
Sub-bandage pressure monitors used in ‘in vivo’ studies.
Fluid-filled devices operate in a similar manner to the pneumatic system, except that the bladder is filled with oil or water. They are not very practical for clinical use as leakage, bulkiness and the formation of air bubbles can be problematic.8,9 Khaburi 9 describes several experimental devices using this principle, but the only commercially available monitor using fluid-filled bladders appears to be the Strathclyde Pressure Monitor™ (University of Strathclyde, Scotland) as discussed by Nelson et al. 12
Electrical pressure monitors are made of materials which change either resistance or capacitance in response to applied pressure. This change is then communicated to a monitor screen. Examples include Tactilus Human Body Interface Sensor System™ (Sensor Products Inc., Madison, NJ) and FlexiForceTM, (Tekscan, South Boston, MA, USA). However, Partsch et al. 8 described limitations with conformability of the device to the curvature of the leg due to the stiffness and bulk of the sensor. Some devices use a combination of pressure monitoring methods one example being the Strathclyde Pressure Monitor™ (University of Strathclyde, Scotland) which uses both fluid and electrical sensors.8,12
The physical construction of the sensor probes in pneumatic, fluid and electrical sub-bandage pressure monitors, due to their inherent thickness creates several difficulties when attempting to measure pressure over time. Not only can they cause pressure injuries, but the stamp they create on the skin may lead the investigator to record a reduced pressure that does not depend on the bandaging materials nor reduced leg volume but due to the indent in the leg caused by the sensor probe. As such they are unsuitable for continuous pressure measurement.
New modalities for the measurement of sub-bandage pressure are emerging. A recent study by Wang et al. 38 describes the use of a fibre optic Bragg grating encased in sports tape to record sub-bandage pressure amongst human participants; however, this device is not currently commercially available. Fong et al. 39 used PressureX Micro pressure-sensitive film (Sensor Products, Inc., Madison, N.J.) to record pressure obtained under the SNaP ™ (Acelity) negative pressure wound therapy device in a simulated model, but no study was found which used pressure sensitive film to record in vivo sub-bandage pressure measurements. Table 1 provides a list of the sub-bandage pressure monitors used to obtain in vivo measurements in the literature.
Some early research explored the use, choice and relative efficacy of sub-bandage pressure monitors, but only one study was identified 40 which discussed the application and technological differences between the devices. Without direct comparison between monitoring devices and in the absence of a ‘gold standard’, it is difficult to infer the superiority of one over another.
In 2010, Partsch and Mosti 41 addressed this gap in the literature and published a study which compared three different commercially available, portable, sub-bandage pressure monitors. They examined the performance of Kikuhime™ (Meditrade, Soro, Denmark), SIGaT tester™ and PicoPress™ (Microlab Elettronica SAS, Padua, Italy) in a simulated model. The three sensors were attached to a cylinder and simultaneously subjected to pressure created by a sphygmomanometer cuff as the reference point. They found PicoPress™ (Microlab Elettronica SAS, Padua, Italy) to have superior accuracy and reproducibility. Despite the simulated testing model employed, their findings have been widely adopted in in vivo investigations. Howse, 33 Lattimer et al. 42 and Protz et al. 35 among others have used PicoPress™ (Microlab Elettronica SAS, Padua, Italy) in their compression studies and found it suitable for monitoring pressures in vivo.
The choice of an accurate and reliable monitor does not, however, ensure accurate and reliable measurements. Finnie 40 isolated eight factors contributing to variability in sub-bandage pressure measurement and they were: leg shape, patient posture, the length of time the bandage has been in place, ambient temperature, skin humidity, patient weight, sensor probe placement and calibration of the monitoring equipment. Many of these parameters can be manipulated by the researcher; however, leg shape, skin humidity and patient weight remain variables. Correct equipment calibration is to be assumed as a given in the conduct of good research. The remaining two factors warrant further discussion.
Positioning the sensor probe
A lack of standardisation of sensor probe positioning makes it difficult to compare results between studies. A survey of studies for which sensor placement data was available identified a wide variation in location and terminology regarding the probe placement. These findings are reproduced in Table 2. In 2003, Partsch 43 produced an international consensus document entitled Measurement of Lower Leg Compression In Vivo: Recommendations for the Performance of Measurements of Interface Pressure and Stiffness and although no agreement was reached regarding the recommended placement of sensors, the document does promote the systematic recording of sensor position by anatomical location. The consensus document adopts the abbreviations for anatomical locations favoured by the Comite Europeen de Normalisation (CEN) European Prestandard for Medical Compression Hosiery (2001), (CEN), 8 which are reproduced in detail in the consensus document. These standards allocate an alphanumeric identifier to specific anatomical locations. Position B1 is described as the junction of the Achilles tendon and the calf muscle, proximal to the medial malleolus. In addition to recording anatomical locations by standardised abbreviations, the recommendations suggest researchers further clarify the position as medial, ventral, dorsal or lateral thus maximising the experimental reproducibility. Table 2 shows an increase in the use of this location system and a trend to the adoption of B1 as the standard placement for the ‘ankle’ sensor in papers later than 2006.
Sensor probe positions.
Frequency with which correct sub-bandage pressure is achieved
Most clinicians, after initial training, aim to apply compression therapy to target pressure,30,37 but studies investigating application pressure show that target pressure is frequently not achieved unless practitioners have access to a sub-bandage pressure monitor.4,12,25 In 2003, Feben 3 undertook a literature review to discover if formal instruction was required to produce effective sub-bandage pressure. Her review revealed a paucity of studies investigating this phenomenon. At this time only three quasi experimental studies were found which documented compression bandaging pressures achieved by nurses during the pre and post compression bandaging training.4,12,13
In 2003, sub-bandage pressure monitors were not generally affordable, portable or readily available. This situation has altered over the intervening period. Investigation was undertaken to see if bandage application had improved since the availability of portable and affordable sub-bandage pressure monitoring devices, and a literature search was conducted which included articles published up to 2016. A summary of the resultant studies (including secondary data where the original studies were not obtainable) is provided in Table 3 (see Table 5 for manufacturers of bandages stated).
Compression bandage pressures pre and post training.
Pressure variation supine to standing by bandage type.
aDSI or dorsiflexion stiffness index with patient supine for both pressures.Note: Figure 8 refers to a method of applying a bandage.
Manufacturers of bandages.
The percentage of practitioners who obtained target pressures in vivo pre training ranged from 9.3% 35 to 65.1%. 30 However, it is of note that in the Protz et al. 35 study, the target range was 50–60 mmHg. Following training with a sub-bandage pressure monitor, this improved from a minimum of 78% to a maximum of 91% and improvements were maintained or increased in the short term. In 2014, Schollum 46 conducted a literature review to identify research which supported training or assessment methodologies that ensured sustained compression competency. No method was identified that achieved this aim.
It is interesting to note that Zarchi and Jemec 37 found years of professional experience, wound care education or previous work in an advanced complex wound care clinic were not significant predictors of achievement of satisfactory sub-bandage pressure. This is further evidenced by data collected by Protz et al. 35 amongst participants in a series of seminars on compression therapy when participants were offered the chance to test their bandaging pressure after the seminar. Inclusion criteria included seminar participation, a minimum of two year’s work experience and knowledge of the principles of venous leg ulcer management. Surprisingly, only 9.3% correctly applied short stretch bandages to target pressure.
Quantifying sub-bandage pressure in compression bandaging systems
Few manufacturers list the working and resting pressures of their compression systems in commercial literature. At best, they provide a recommended supine application pressure at the ankle, generally in the order of 40 mmHg for high compression, but offer no indication as to what the standing or walking pressures could be, either immediately post application or during the extended wear. In contrast, Partsch et al., 47 Protz et al. 45 and Jünger et al. 48 recommend the application pressures of up to 50–60 mmHg. Table 4 summarises the compression values evident in the available literature.
Variations in sub-bandage pressure with changes in posture have been discussed in the literature, most notably by Partsch 23 who related variation in pressure to the resultant elasticity of the combination of bandages applied, a quality he termed ‘stiffness’. Sub-bandage pressure increases as the patient changes posture from supine to sitting then standing and ambulating. The amount of change is dependent on the elasticity of the bandage or elastomeric properties in the bandage system used.5,26,44 The change in pressure with change in posture is termed the ‘static stiffness index’ (SSI) of the system. Although both Mosti and Mattaliano 26 and Benigni et al. 27 tested multiple bandaging systems and measured at B1 (8 and 10 combinations respectively), no comprehensive list of in vivo SSI values for a range of bandage systems was discovered during the literature search.
In 2005, Partsch 23 undertook to name and quantify the change in sub-bandage pressure, developing a calculation based on the theoretical change in leg circumference at the junction of the gastrocnemius muscle and the Achilles tendon (B1) when a patient changes from supine to active standing posture (to which he assigned the value of 1cm), and the change in sub-bandage pressure at the same point. The choice of 1 cm change was selected based on earlier work by Wienert and Hanson 49 (n = 110) and his own data collection (n = 20) 23 and relates to the increase in leg circumference due to muscle contraction when the individual is standing. He termed this value the ‘static stiffness index’ (SSI), which can be defined as the “difference between the interface pressure when standing and lying (mm Hg) divided by 1 cm” (Mosti and Mattaliano26, p.627). Partsch then defined elastic and inelastic bandaging systems. The bandaging system was applied to a supine person, at a pressure of 40 mmHg at point B1. The person then rose to a standing position and the pressure was recorded again. Elastic systems were those which showed a difference between supine and standing pressure of less than 10 mmHg and inelastic systems those with a pressure difference of more than 10 mmHg. 23 Prior to the 2005 research by Partsch,23,44 the terms ‘elastic’ and ‘inelastic’ in relation to compression bandaging systems were defined only by in vitro tests assuming maximal extensibility of >100% as elastic and of <100% as inelastic. 47 It should be noted that Mosti and Mattaliano 26 showed that even without an individual correction to 1 cm circumference increase, the static stiffness index is a valuable parameter differentiating elastic from inelastic bandages in vivo (see Table 5 for manufacturers of bandages stated).
Discussion
The aim of this literature review was to investigate the various devices available to measure sub-bandage pressure and explore the reported application pressures obtained both in the treatment of venous leg ulcers, and the training of health practitioners who apply compression bandaging systems. We found there were several commercial systems available, none of which had been established against an in vivo, validated gold standard. This makes it difficult to determine a superior product for either research or practice applications. This discovery is broadly in agreement with Partsch et al. 8 who made no specific recommendation regarding the absolute superiority of any specific system. However, these authors listed 18 desirable characteristics of a sub-bandage pressure measurement device including size, flexibility, accuracy, cost and electronic simplicity.
Despite the limitations and lack of consensus regarding the best method for measurement of sub-bandage pressure, it became apparent that application pressure was not a static concept, but varied with the posture of the patient and the skill of the individual applying the bandaging system.
Measuring sub-bandage pressure
Sub-bandage pressure is dependent on the strength and stretch of the bandage material combined with the curvature of the leg. Mathematically, this can be calculated using Laplace’s Law. 50 However, the application of Laplace’s Law to the clinical environment is problematic as it is necessary to make allowance for the fact that the curvature of the leg is irregular, and hence the pressure at any given point on the limb may be higher or lower dependent on the radius of curvature at that point. This finding reveals a gap in the literature with regard to comparative efficacy of sub-bandage pressure monitors in vivo and has implications when comparing research findings between studies, particularly if the readings were not obtained from similar sites on all subjects.
The consensus document “Measurement of lower leg compression in vivo: Recommendations for the performance of measurements of interface pressure and stiffness” 8 recommends position B1 as the most appropriate site at which to measure sub-bandage pressure 43 and the use of the B1 position in compression research is becoming increasingly common. Position B1 is described as the junction of the Achilles tendon and the calf muscle, proximal to the medial malleolus. 43 The B1 level has been chosen by the European Committee of Normalisation as the level at which compression hosiery measurements should be calculated. 43 The adoption of this convention contributes to the development of an evidence base as it permits a more robust comparison of study outcomes. It must also be stated that leg architecture varies between individuals, but a randomised study with sufficient power will control for this variable.
Frequency with which correct sub-bandage pressure is achieved
The sub-bandage pressure obtained by clinicians is subject to a great degree of variability and cannot be predicted by the experience or education of the practitioner. 37 It must be confirmed by measurement using a sub-bandage pressure monitor. In any experimental study, it is important to control the variables. If one of the variables is sub-bandage pressure, it is necessary to standardise bandage application (both technique and position of patient). It appears that this is best achieved by providing training to participating clinicians, which involves the use of a sub-bandage pressure monitor and then regularly monitoring application technique to ensure effective and sustained pressures are obtained.
It is critical to get the pressure right both in the clinical setting and in a research context. From a clinical perspective, compression remains the gold standard for the treatment of venous leg ulcers 51 and the current recommended application pressure is at least 40 mmHg at the ankle on application32,52 The literature revealed that actual pressures obtained by practitioners vary greatly from that recommended and are influenced by the skills of the practitioner and the type of bandage and its SSI.35,37 Within a research environment, an accurate record of the ongoing sub-bandage pressures applied by practitioner/s during an interventional study is imperative if one is to ensure rigour in research methodology. It should be considered prudent for researchers to undertake pilot studies to ascertain bandage SSI is achieved in the specific research context.
Variation in sub-bandage pressure with posture
The standardisation of terminology regarding SSI allowed for direct comparison between various compression systems, permitting clinicians to more precisely tailor their bandage choices to patient need. For example, it may be necessary to apply modified compression bandaging to a patient with a degree of arterial insufficiency in order to facilitate healing of an ulcer of mixed aetiology, but this may generate concerns about the possibility of high working pressures. By choosing to apply a bandage system with a low static stiffness, the risk of high working pressure and hence iatrogenic ischemia is low. Recent research by Mosti et al. 53 defined circumstances in which inelastic compression may be used safely in the treatment of leg ulcers of mixed aetiology. Other authors discuss the relative merits of elastic or inelastic bandages for promoting patient tolerance of compression bandaging 54 and the avoidance of excessively high standing pressures. 55 However, some increase in compression pressure when the patient is upright is desirable in order to counteract the effects of gravity.
It can be seen, from the historical experimental data, that variation in sub-bandage pressure with posture can range between 2.2 (Rimaud, 36 Biflex 16) and 28.3 (application of 2 Rosidal K obtained by Partsch 44 ) depending on the bandage type, combination and application method. It can also be noted that there is variation in recorded changes between studies even when the application method and bandage type are the same. For example, Biflex 16™ applied at 30% stretch and 50% overlap was reported by Benigni et al. 27 to have a variation of 6 mmHg and the same bandage findings by Rimaud et al. 36 were 2.2 mmHg. The variation in probe position is a potential contributing factor.
With regard to the Profore™ bandage system, the results obtained by various authors differ markedly. Wong et al. 6 applied Profore ™ at a supine pressure of 58 mmHg, obtained a standing pressure of 80 mmHg and hence an SSI of 18.0. This result is greater than 10.0 and therefore classified as inelastic according to Partsch. 23 Dale et al. 21 reported a mean supine pressure of 44 mmHg, a mean standing pressure of 60 mmHg and an SSI of 16.0, also considered inelastic by Partsch’s 23 classification. Both studies report supine application pressures of greater than 40 mmHg. In contrast, Protz et al. 45 with a supine application pressure of 40 mmHg record a difference in sub-bandage pressure (supine to standing) of 8.5 mmHg and Hafner et al., 18 with a supine application pressure of 38 mmHg, a difference of 6.0 mmHg. However, this variation cannot properly be considered SSI as these authors used different measuring points not relevant to the calculation of SSI. Profore acts as an inelastic bandage due to the friction of the layers and the adhesive outer layer. 56 These results show a trend towards a higher initial application pressure being associated with a higher SSI; however, the relationship cannot be assumed to be linear due to the small sample size.
Conclusion
The purpose of this investigation was to identify a criteria for the accuracy and reliability amongst the sub-bandage pressure monitors, and to explore the frequency with which correct sub-bandage pressure is achieved. We found an absence of robust studies validating the performance of sub-bandage pressure monitors in vivo. Furthermore, there was a paucity of literature directly comparing the performance of the various commercially available sub-bandage pressure monitors. The one study to do so found PicoPress ™ (Microlab Elettronica SAS, Padua, Italy) superior to Kikuhime™ (Meditrade, Soro, Denmark) and SIGaT tester™. 41 However, there is a need for further comparative research regarding both commercially available sub-bandage pressure monitors and the use of emergent technologies such as pressure sensitive films 39 and fibre optic manometry 38 as potential modalities for the measurement of sub-bandage pressure.
The sub-bandage pressure obtained by clinicians is subject to a great degree of variability and cannot be predicted solely by the experience or education of the practitioner, 37 but must be confirmed by the measurement using a reliable sub-bandage pressure monitor. Those studies reporting sub-bandage pressures obtained by clinicians showed that in many cases the desired pressure was not obtained and reported findings varied from 9.3% 35 to 91%. 9
Additionally, although the change in sub-bandage pressure associated with alteration in posture is not constant for a given bandaging system, nor practitioner application, being dependent on patient morphology and the degree of stretch applied to the bandage, the performance of bandaging system as inelastic or elastic remains a constant. It would therefore appear necessary to measure this variance under bandages applied to each patient and by each practitioner to ascertain actual pressure changes and confirming the use of an elastic or inelastic system. This may prove challenging in the clinical environment due to time constraints and the availability, portability and cost of currently available sub-bandage pressure monitoring devices, but it would add to the quality of evidence obtained in the research environment and is inevitable in future publications investigating the compression therapy.
Footnotes
Authors' Note
Sharon L Boxall is also affiliated with Silver Chain Group, Osborne Park, WA, Australia and Heart and Vascular Research Institute, Harry Perkins Institute of Medical Research, Perth, WA, Australia. Keryln Carville is also affiliated with School of Nursing, Midwifery and Paramedicine, Curtin University, Bentley, WA, Australia.
Shirley J Jansen is also affiliated with Curtin Medical School, Curtin University, Perth, WA, Australia and Heart and Vascular Research Institute, Harry Perkins Institute of Medical Research, Perth, WA, Australia.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/ or publication of this article: The authors wish to acknowledge the funding support for Project Officer & PhD student Ms Sharon Boxall from the Wound Management CRC.
Ethical approval
Not required – literature review.
Guarantor
KC.
Contributorship
SB researched the literature, analysed the data and wrote the first draft. All authors reviewed and edited the manuscript and approved the final version of the manuscript.
Acknowledgements
Nil.