How does lateral tilting affect the internal strains in the sacral region of bed ridden patients? - A contribution to pressure ulcer prevention

Determining frictional properties of pants and cushion cover materials using human soft tissue and a rigid sled and how they affect seated shear forces

Shear forces on the buttocks while seated are directly linked to friction, yet the frictional properties at the seat interface are unknown. Shear forces are one of the factors related to increase risk of pressure injury formation. The goals of this study included determining coefficients of friction between three cushion covers and two clothing fabrics using a mechanical system as well as human participants and to evaluate the impact of the cushion covers on shear loading on the buttocks while seated. A chair with separate seat pan tilt and back recline movements was built and instrumented with reflective markers and a load cell. A motion capture system and load cell were used to determine the angles of seat pan tilt at which the sled and participants started sliding, as well as shear forces at three recline angles for three cushion covers (vinyl, one-layer nylon, and two-layer nylon). Results showed the vinyl and two-layer nylon cushion covers respectively had the largest and smallest coefficients of friction for both pants materials. The coefficients of friction calculated with the human participants and rigid sled were within 10% of each other, demonstrating similar results. Further, increasing back recline increased shear load on the buttocks, while the two-layer nylon cover reduced shear forces seen on the buttocks. This work furthers the understanding of shear loading on the buttocks, will aid in the protocols for reducing pressure injuries, and suggests that coefficients of friction found using rigid bodies may be applied to deformable bodies.

Effect of changing the lying posture angle by changing the bed posture on the average pressure, maximum pressure, and pressure area in the hip region

BACKGROUND: An electric bed can easily change posture from a lying position and was effective in preventing pressure ulcer. OBJECTIVE: This study aimed to identify the optimal posture for the prevention of pressure ulcers by analyzing pressure changes applied to the pelvic region. METHODS: Pressure changes resulting from lateral rotations of the body using an electronic adjustable bed and changes in the posture and angles of the trunk and knees were assessed. Twelve conditions with varying angles of the trunk and knees (15–35∘ in 5∘ increments) and varying lateral angles (20–35∘ in 5∘ increments) were tested. The pressure (maximum and average) and contact area in the pelvic region of 20 individuals without disabilities were calculated. RESULTS: The conditions in which the average and maximum pressures did not increase according to the increase in angle were 25∘ for the upper body and knee angles and 35∘ for the side. CONCLUSIONS: The body pressure changed according to the posture rather than according to physical characteristics. Lateral rotation combined with changes in the angles of the trunk and knees effectively prevented pressure ulcers. Changes in the posture at various angles prevented an increased pressure on the body.

Does Sacrococcygeal Skeletal Morphology and Morphometry Influence Pressure Injury Formation in Adults?

GENERAL PURPOSE

To present a study that investigated sacrococcygeal skeletal structure as a possible nonmodifiable intrinsic risk factor for pressure injury and identify possible issues caused by its morphology.

TARGET AUDIENCE

This continuing education activity is intended for physicians, physician assistants, nurse practitioners, and nurses with an interest in skin and wound care.

LEARNING OBJECTIVES/OUTCOMES

After participating in this educational activity, the participant will:1. Recognize the background information the authors considered when planning and conducting their study of sacrococcygeal skeletal structure as a possible pressure injury risk factor.2. Identify the characteristics of the two groups of study participants.3. Choose the results of the study clinicians may consider when implementing evidence-based practice.

Repositioning mattress: how a lateral tilt position reshapes the prevention of pressure ulcers in bedridden patients

Pressure ulcers have been part of tissue damage without effectiveness in medical, surgical, and intensive care units. This study aims to focus on developing lateral tilt positions for effective pressure ulcer relief for bedridden patients. A repositioning mattress was placed in the side-lying left lateral tilt position (15°, 30°, 45°), sheering (0.680, 1.323, 1.870), interface pressure (2.550, 2.290, 2.830), and placed at 1.5 m long piece of polyethylene rubber. The design strength was set at 6000 N and 2100 mm x 1105 mm (σt,0,d = 42, σc,0,d = 34). The design shows the greatest supine position at 30°, 1.323, 2.290, pressure load (Δp0 = 1.125 (1820) ≈ 2050 psi, Δp3000 = 1.125 (620) ≈ 700 psi), tensile stress (σt,0,d (MPa) = 42), compressive stress (σc,0,d (MPa) = 34), and FOS (σt,0,d = 42, σc,0,d = 34). The factor of safety illustrated that the 30° lateral tilt position is more consistent in repositioning for pressure ulcer prevention compared to the supine-to-tilt region. Further, an application of repositioning mattresses was developed to test in bedridden patients with tissue ulcers in nursing homes.

Biomechanical Changes on the Typical Sites of Pressure Ulcers in the Process of Turning Over from Supine Position: Theoretical Analysis, Simulation, and Experiment

Pressure ulcers are mainly caused by prolonged pressure on local tissues. The current method of preventing pressure ulcers is mainly to change the patient's position by turning, so it is significant to study the biomechanics of the typical site of pressure ulcers. Based on anatomical theory, a three-dimensional model of the shoulder and hip was established, and the theoretical contact pressure between the body and the bed was calculated by force analysis. Then, finite element models of typical parts of pressure ulcers were established, and the maximum stresses under different boundary conditions were obtained by finite element analysis. Finally, a human body turning experiment was conducted using a pressure distribution sensor, and the pressure distribution clouds and maximum contact pressure curves under different turning angles were obtained. The results show that the extreme point of maximum stress occurs at [Formula: see text], producing a stress concentration phenomenon; the peak stresses at the shoulder and hip are more balanced in the angular threshold range of [Formula: see text] to [Formula: see text], the stresses are more dispersed, and there exists an angular threshold for optimal integrated pressure, which can improve the efficiency of the use of assisted turning equipment. The relevant results help to explain the causes of pressure ulcer disease and can provide clinical references to improve the effectiveness of care.

Our contemporary understanding of the aetiology of pressure ulcers/pressure injuries

In 2019, the third and updated edition of the Clinical Practice Guideline (CPG) on Prevention and Treatment of Pressure Ulcers/Injuries has been published. In addition to this most up‐to‐date evidence‐based guidance for clinicians, related topics such as pressure ulcers (PUs)/pressure injuries (PIs) aetiology, classification, and future research needs were considered by the teams of experts. To elaborate on these topics, this is the third paper of a series of the CPG articles, which summarises the latest understanding of the aetiology of PUs/PIs with a special focus on the effects of soft tissue deformation. Sustained deformations of soft tissues cause initial cell death and tissue damage that ultimately may result in the formation of PUs/PIs. High tissue deformations result in cell damage on a microscopic level within just a few minutes, although it may take hours of sustained loading for the damage to become clinically visible. Superficial skin damage seems to be primarily caused by excessive shear strain/stress exposures, deeper PUs/PIs predominantly result from high pressures in combination with shear at the surface over bony prominences, or under stiff medical devices. Therefore, primary PU/PI prevention should aim for minimising deformations by either reducing the peak strain/stress values in tissues or decreasing the exposure time.

A review of foot finite element modelling for pressure ulcer prevention in bedrest: Current perspectives and future recommendations

Pressure ulcers (PUs) are a major public health challenge, having a significant impact on healthcare service and patient quality of life. Computational biomechanical modelling has enhanced PU research by facilitating the investigation of pressure responses in subcutaneous tissue and skeletal muscle. Extensive work has been undertaken on PUs on patients in the seated posture, but research into heel ulcers has been relatively neglected. The aim of this review was to address the key challenges that exist in developing an effective FE foot model for PU prevention and the confusion surrounding the wide range of outputs reported. Nine FE foot studies investigating heel ulcers in bedrest were identified and reviewed. Six studies modelled the posterior part of the heel, two included the calf and foot, and one modelled the whole body. Due to the complexity of the foot anatomy, all studies involved simplification or assumptions regarding parts of the foot structure, boundary conditions and material parameters. Simulations aimed to understand better the stresses and strains exhibited in the heel soft tissues of the healthy foot. The biomechanical properties of soft tissue derived from experimental measurements are critical for developing a realistic model and consequently guiding clinical decisions. Yet, little to no validation was reported in each of the studies. If FE models are to address future research questions and clinical applications, then sound verification and validation of these models is required to ensure accurate conclusions and prediction of patient outcomes. Recommendations and considerations for future FE studies are therefore proposed.

Is a simplified Finite Element model of the gluteus region able to capture the mechanical response of the internal soft tissues under compression?

BACKGROUND

Internal soft tissue strains have been shown to be one of the main factors responsible for the onset of Pressure Ulcers and to be representative of its risk of development. However, the estimation of this parameter using Finite Element (FE) analysis in clinical setups is currently hindered by costly acquisition, reconstruction and computation times. Ultrasound (US) imaging is a promising candidate for the clinical assessment of both morphological and material parameters.

METHOD

The aim of this study was to investigate the ability of a local FE model of the region beneath the ischium with a limited number of parameters to capture the internal response of the gluteus region predicted by a complete 3D FE model. 26 local FE models were developed, and their predictions were compared to those of the patient-specific reference FE models in sitting position.

FINDINGS

A high correlation was observed (R = 0.90, p-value < 0.01). A sensitivity analysis showed that the most influent parameters were the mechanical behaviour of the muscle tissues, the ischium morphology and the external mechanical loading.

INTERPRETATION

Given the progress of US for capturing both morphological and material parameters, these results are promising because they open up the possibility to use personalised simplified FE models for risk estimation in daily clinical routine.

Evaluating shear and normal force with the use of an instrumented transtibial socket: A case study

Patients with transtibial amputation experience ulcers on their residual limb. The loading between the device and underlying material plays a role in loads transmitted to the skin. The objective was to evaluate normal and shear forces at the socket/liner interface during walking. A 53 year old male (85.45 kg and 177.8 cm) with a transtibial amputation participated in this case study. A transtibial prosthesis was instrumented with a load cell to measure normal and shear forces at the socket interface. Three conditions were evaluated during walking: gel liner, additional three ply sock and a hole in the gel liner. Shear and normal forces were highest with the addition of a three ply. Longitudinal shear stresses ranged from 0.4-7.66 kPa, transverse shear stresses ranged from 0.01-7.79 kPa and normal stresses ranged from 2.7-61.9 kPa. Increased shear and normal forces can cause a significant decrease in blood perfusion, linked to an increased risk of ulcer formation. Experimental force results are also important for future work involving finite element modeling of the skin/liner/device interface.

Bioengineering considerations in the prevention of medical device-related pressure ulcers

BACKGROUND

In recent years, it has become increasingly apparent that medical device-related pressure ulcers represent a significant burden to both patients and healthcare providers. Medical devices can cause damage in a variety of patients from neonates to community based adults. To date, devices have typically incorporated generic designs with stiff polymer materials, which impinge on vulnerable soft tissues. As a result, medical devices that interact with the skin and underlying soft tissues can cause significant deformations due to high interface pressures caused by strapping or body weight.

METHODS

This review provides a detailed analysis of the latest bioengineering tools to assess device related skin and soft tissue damage and future perspectives on the prevention of these chronic wounds. This includes measurement at the device-skin interface, imaging deformed tissues, and the early detection of damage through biochemical and biophysical marker detection. In addition, we assess the potential of computational modelling to provide a means for device design optimisation and material selection.

INTERPRETATION

Future collaboration between academics, industrialists and clinicians should provide the basis to improve medical device design and prevent the formation of these potentially life altering wounds. Ensuring clinicians report devices that cause pressure ulcers to regulatory agencies will provide the opportunity to identify and improve devices, which are not fit for purpose.

How consistent and effective are current repositioning strategies for pressure ulcer prevention?

AIM

To examine the inter-practitioner variability of repositioning for pressure ulcer prevention, the effectiveness of the intervention, and whether the provision of written guidance influenced the repositioning technique.

METHODS

A pre-test post-test study design was utilised. Descriptive data regarding the work history of participants was collected. Participants were invited to reposition a healthy volunteer before and after reviewing guidance detailing the 30° side-lying technique. The researchers measured the resulting turn angles and assessed offloading of bony prominences.

RESULTS

The repositioning technique varied considerably in the sample of nurse participants. Turn angles decreased following the guidance, but offloading of body sites vulnerable to pressure damage remained sporadic.

CONCLUSION

Pressure ulcer prevention training should include practical demonstrations of repositioning. Clear guidance regarding the optimal repositioning technique for pressure ulcer prevention is needed.

Visualizing Tissue Strain Under the Sacrum and Coccyx in Different Supine Postures: A Case Series

OBJECTIVE

To visually assess and report the influence of supine positioning and sacrum and coccyx anatomy on tissue deformation.

METHODS

A convenience sample of three participants was scanned using MRI. All participants were scanned in a supine position with a rig oriented in a flat or horizontal position and with the torso portion of the rig elevated to 30° to simulate head-of-bed elevation. Representative images were identified to visualize and depict (1) the differences in tissue thickness and deformation in response to changes in supine positioning (0° and 30°), (2) the relative displacement of the skeleton relative to the skin during 30° incline, and (3) differences in sacrococcygeal morphology.

RESULTS

The tissue thickness under the sacrum stayed the same or increased when torsos were elevated. Skeletons were displaced relative to the skin when the rig was elevated regardless of the pelvis location. Further, in the elevated position, coccyges flexed when pelvises were placed on the elevated segment but did not flex when pelvises were placed on the horizontal segment.

CONCLUSIONS

This case series is useful in defining new areas of research that can (1) identify the deformation induced by normal and frictional forces resulting from different positions of the bed chassis, (2) assess the impact of positioning the pelvis on elevated versus horizontal segments of the bed chassis, and (3) define the association between sacral and coccyx morphology and pressure ulcer occurrence in hospitalized patients.

Understanding Displacements of the Gel Liner for Below Knee Prosthetic Users

Many people with amputation utilize a prosthetic device to maintain function and ambulation. During the use of the prosthetic device, their residual limbs can develop wounds called pressure ulcers. The formation of these wounds has been linked to deformation and loading conditions of the skin and deeper tissues. Our research objective was to develop a complete profile of displacements on the gel liner at the interface with the socket during walking in transtibial amputees. Displacements for seven regions along the limb were quantified in addition to six calculations of displacement and three rotations relative to the prosthetic socket. The largest displacements were observed in the distal region of the gel liner, near the pin locking mechanism on the gel liner. Displacements were uneven throughout the liner with distal regions showing higher displacements. This mechanics-based information, combined with clinical information, will allow us to understand the local skin and muscle displacements, and will provide insights regarding localized tissue breakdown. Knowledge of how the liner displaces within the prosthetic socket can also help prosthetists modify designs to reduce these displacements, and reduce the potential for shear on the skin and in deeper tissues.

Technologies to monitor the health of loaded skin tissues

There are many situations where the skin and underlying soft tissues are compromised by mechanical loading in the form or pressure, or pressure in combination with shear. If sustained, this can lead to damage in the tissues particularly adjacent to bony prominences, resulting in chronic wounds. An array of bioengineering technologies have been adopted to assess the integrity of loaded soft tissues. This paper aims to review these approaches for the quantification, simulation and early detection of mechanically-induced skin damage. The review considers different measurements at the interface between the skin and support surface/medical device, involving pressure, shear, friction and the local microclimate. The potential of the techniques to monitor the physiological response of the skin to these external stimuli including biophysical measurement devices and sampling of biofluids are critically analysed. In addition, it includes an analysis of medical imaging technologies and computational modelling to provide a means by which tissue deformation can be quantified and thresholds for tissue damage defined. Bioengineering measurement and imaging technologies have provided an insight into the temporal status of loaded skin. Despite the advances in technology, to date, the translation to clinical tools which are robust and cost effective has been limited. There is a need to adapt existing technologies and simulation platforms to enable patients, carers and clinicians to employ appropriate intervention strategies to minimise soft tissue damage.

Development and psychometric validation of a questionnaire to evaluate nurses' adherence to recommendations for preventing pressure ulcers (QARPPU)

AIM OF THE STUDY

The main objective of this work is the development and psychometric validation of an instrument to evaluate nurses' adherence to the main recommendations issued for preventing pressure ulcers.

MATERIAL AND METHODS

An instrument was designed based on the main recommendations for the prevention of pressure ulcers published in various clinical practice guides. Subsequently, it was proceeded to evaluate the face and content validity of the instrument by an expert group. It has been applied to 249 Spanish nurses took part in a cross-sectional study to obtain a psychometric evaluation (reliability and construct validity) of the instrument. The study data were compiled from June 2015 to July 2016.

RESULTS

From the results of the psychometric analysis, a final 18-item, 4-factor questionnaire was derived, which explained 60.5% of the variance and presented the following optimal indices of fit (CMIN/DF: 1.40 p < 0.001; GFI: 0.93; NFI: 0.92; CFI: 0.98; TLI: 0.97; RMSEA: 0.04 (90% CI 0.025-0.054).

CONCLUSIONS

The results obtained show that the instrument presents suitable psychometric properties for evaluating nurses' adherence to recommendations for the prevention of pressure ulcers.

Adaptation of a MR imaging protocol into a real-time clinical biometric ultrasound protocol for persons with spinal cord injury at risk for deep tissue injury: A reliability study

BACKGROUND

High strain in soft tissues that overly bony prominences are considered a risk factor for pressure ulcers (PUs) following spinal cord impairment (SCI) and have been computed using Finite Element methods (FEM). The aim of this study was to translate a MRI protocol into ultrasound (US) and determine between-operator reliability of expert sonographers measuring diameter of the inferior curvature of the ischial tuberosity (IT) and the thickness of the overlying soft tissue layers on able-bodied (AB) and SCI using real-time ultrasound.

MATERIAL AND METHODS

Part 1: Fourteen AB participants with a mean age of 36.7 ± 12.09 years with 7 males and 7 females had their 3 soft tissue layers in loaded and unloaded sitting measured independently by 2 sonographers: tendon/muscle, skin/fat and total soft tissue and the diameter of the IT in its short and long axis. Part 2: Nineteen participants with SCI were screened, three were excluded due to abnormal skin signs, and eight participants (42%) were excluded for abnormal US signs with normal skin. Eight SCI participants with a mean age of 31.6 ± 13.6 years and all male with 4 paraplegics and 4 tetraplegics were measured by the same sonographers for skin, fat, tendon, muscle and total. Skin/fat and tendon/muscle were computed.

RESULTS

AB between-operator reliability was good (ICC = 0.81-0.90) for 3 soft tissues layers in unloaded and loaded sitting and poor for both IT short and long axis (ICC = -0.028 and -0.01). SCI between-operator reliability was good in unloaded and loaded for total, muscle, fat, skin/fat, tendon/muscle (ICC = 0.75-0.97) and poor for tendon (ICC = 0.26 unloaded and ICC = -0.71 loaded) and skin (ICC = 0.37 unloaded and ICC = 0.10).

CONCLUSION

A MRI protocol was successfully adapted for a reliable 3 soft tissue layer model and could be used in a 2-D FEM model designed to estimate soft tissue strain as a novel risk factor for the development of a PU.