Evaluation of antidecubitus mattresses

Skin stiffness determined from occlusion of a horizontally running microvessel in response to skin surface pressure: a finite element study of sacral pressure ulcers

Pressure ulcers occur following sustained occlusion of microvessels at bony prominences under skin surface pressure (SSP). However, the mechanical conditions of the surrounding soft tissue leading to microvascular occlusion are not fully understood. This study determined the stiffness of homogenized skin with microvasculature at the sacrum that occludes microvessels at an SSP of 10 kPa (consistent with a standard mattress) and recovers from occlusion at 5 kPa (consistent with a pressure-redistribution mattress). We conducted two-dimensional finite element analyses under plane stress and plane strain conditions to determine the stiffness of the skin. The results for plane stress conditions show that the microvessel was occluded with a Young's modulus of 23 kPa in response to an SSP of 10 kPa at the center of the sacrum and that the circulation recovered following a reduction in the SSP to 5 kPa. The resulting Young's modulus is consistent with reported data. Our study indicates that the critical value of the SSP for microvascular occlusion is determined not only by the stiffness of homogenized skin with microvasculature but also by the intraluminal pressure, microvascular wall stiffness, and body support conditions.

Microclimate and development of pressure ulcers and superficial skin changes

This study aims to evaluate the microclimate and development of pressure ulcers and superficial skin changes. A prospective cohort study was conducted in an acute care ward in Indonesia. Risk factors for pressure ulcers and superficial skin changes were identified based on the Bergstrom Braden conceptual model. Microclimate data were collected every 3 days for 15 days while the development of pressure ulcers and superficial skin changes was observed every day. Pressure ulcers and superficial skin changes were developed in 20 of the 71 participants. Total mean difference in skin temperature was higher for patients with pressure ulcers and superficial skin changes (0·9 ± 0·6°C) compared with controls (0·6 ± 0·8°C) (P = 0·071). Binary logistic regression predictor values for pressure ulcers and superficial skin changes were 0·111 for type of sheet and 0·347 for Braden Scale results. In conclusion, difference in skin temperature seems to be a predictor for pressure ulcer development and superficial skin changes, while synthetic fibre sheets are able to maintain a beneficial microclimate.

Modelling the effect of repositioning on the evolution of skeletal muscle damage in deep tissue injury

Deep tissue injury (DTI) is a localized area of tissue necrosis that originates in the subcutaneous layers under an intact skin and tends to develop when soft tissue is compressed for a prolonged period of time. In clinical practice, DTI is particularly common in bedridden patients and remains a serious issue in todays health care. Repositioning is generally considered to be an effective preventive measure of pressure ulcers. However, limited experimental research and no computational studies have been undertaken on this method. In this study, a methodology was developed to evaluate the influence of different repositioning intervals on the location, size and severity of DTI in bedridden patients. The spatiotemporal evolution of compressive stresses and skeletal muscle viability during the first 48 h of DTI onset was simulated for repositioning schemes in which a patient is turned every 2, 3, 4 or 6 h. The model was able to reproduce important experimental findings, including the morphology and location of DTI in human patients as well as the discrepancy between the internal tissue loads and the contact pressure at the interface with the environment. In addition, the model indicated that the severity and size of DTI were reduced by shortening the repositioning intervals. In conclusion, the computational framework presented in this study provides a promising modelling approach that can help to objectively select the appropriate repositioning scheme that is effective and efficient in the prevention of DTI.

Keeping vulnerable elderly patients free from pressure ulcer is associated with high caregiver burden in informal caregivers

RATIONALE AND OBJECTIVES

The effect of the presence of pressure ulcers on burden of caregivers is unknown. We investigated the relationship between the state of pressure ulcers in vulnerable elderly patients and the burden on their informal caregivers.

METHODS

This cross-sectional study enrolled 137 patients aged > or = 40 years with limited activity and mobility at 10 home care service facilities in Japan. We assessed pressure ulcer status from medical records and caregiver burden using scores from both the Burden Index of Caregivers (BIC) and the Japanese short version of the Zarit Burden Interview (ZBI).

RESULTS

Among patients, mean age was 80.9 years, 31.4% were men, and 83.9% were free from pressure ulcers. Multivariable analysis showed that caregivers whose patients were free from pressure ulcers had significantly higher caregiver burden as assessed by both the BIC [beta-coefficient = 3.18, 95% confidence interval (CI): 1.42-4.95, P = 0.003] and ZBI scores (beta-coefficient = 1.94; 95%CI = 0.30-3.58; P = 0.03).

CONCLUSIONS

Our results suggest that the continuous effort involved in keeping patients free from pressure ulcers may be associated with high caregiver burden in informal caregivers.

A technique based on laser Doppler flowmetry and photoplethysmography for simultaneously monitoring blood flow at different tissue depths

The aim of this study was to validate a non-invasive optical probe for simultaneous blood flow measurement at different vascular depths combining three photoplethysmography (PPG) channels and laser Doppler flowmeter (LDF). Wavelengths of the PPG were near-infrared 810 nm with source-to-detector separation of 10 and 25 mm, and green 560 nm with source-to-detector separation of 4 mm. The probe is intended for clinical studies of pressure ulcer aetiology. The probe was placed over the trapezius muscle, and depths from the skin to the trapezius muscle were measured using ultrasound and varied between 3.8 and 23 mm in the 11 subjects included. A provocation procedure inducing a local enhancement of blood flow in the trapezius muscle was used. Blood flows at rest and post-exercise were compared. It can be concluded that this probe is useful as a tool for discriminating between blood flows at different vascular tissue depths. The vascular depths reached for the different channels in this study were at least 23 mm for the near-infrared PPG channel (source-to-detector separation 25 mm), 10-15 mm for the near-infrared PPG channel (separation 10 mm), and shallower than 4 mm for both the green PPG channel (separation 4 mm) and LDF.

Sitting can cause ischaemia in the subcutaneous tissue of the buttocks, which implicates multilayer tissue damage in the development of pressure ulcers

A better understanding of how pressure ulcers develop in the buttocks will improve prophylactic measures. Our aim was to investigate signs of reduced perfusion and ischaemia in the subcutaneous fat in the buttocks during sitting. A microelectrode was used to quantify oxygen (pO(2)). Metabolites that indicate aerobic or anaerobic metabolism (glucose, lactate, pyruvate, and glycerol) were quantified using microdialysis. Sixteen healthy people were studied while they sat on a wheel chair cushion, and a hard surface. Sitting pressures were mapped, and the thickness of the subcutaneous fatty layer was measured. The results showed that pO(2) and glucose were significantly reduced during sitting, and for pO(2) the effect is significantly more profound during sitting on a hard surface. After loading, both glucose and pO(2) increased significantly. We conclude that the subcutaneous adipose tissue covering the ischial tuberosities becomes ischaemic during sitting. This finding supports the theory that not only is the skin involved in early development of pressure ulcers, but also the deeper tissues.

Periodically relieving ischial sitting load to decrease the risk of pressure ulcers

OBJECTIVE

To investigate the relieving effect on interface pressure of an alternate sitting protocol involving a sitting posture that reduces ischial support.

DESIGN

Repeated measures in 2 protocols on 3 groups of subjects.

SETTING

Laboratory.

PARTICIPANTS

Twenty able-bodied persons, 20 persons with paraplegia, and 20 persons with tetraplegia.

INTERVENTIONS

Two 1-hour protocols were used: alternate and normal plus pushup. In the alternate protocol, sitting posture was alternated every 10 minutes between normal (sitting upright with ischial support) and with partially removed ischial support (WO-BPS) postures; in the normal plus pushup protocol, sitting was in normal posture with pushups (lifting the subject off the seat) performed every 20 minutes.

MAIN OUTCOME MEASURE

Interface pressure on seat and backrest.

RESULTS

In WO-BPS posture, the concentrated interface pressure observed around the ischia in normal posture was significantly repositioned to the thighs. By cyclically repositioning the interface pressure, the alternate protocol was superior to the normal plus pushup protocol in terms of a significantly lower average interface pressure over the buttocks.

CONCLUSIONS

A sitting protocol periodically reducing the ischial support helps lower the sitting load on the buttocks, especially the area close to ischial tuberosities.

Measuring tissue perfusion during pressure relief maneuvers: insights into preventing pressure ulcers

BACKGROUND/OBJECTIVE

To study the effect on tissue perfusion of relieving interface pressure using standard wheelchair pushups compared with a mechanical automated dynamic pressure relief system.

DESIGN

Repeated measures in 2 protocols on 3 groups of subjects.

PARTICIPANTS

Twenty individuals with motor-complete paraplegia below T4, 20 with motor-complete tetraplegia, and 20 able-bodied subjects.

METHODS

Two 1-hour sitting protocols: dynamic protocol, sitting configuration alternated every 10 minutes between a normal sitting configuration and an off-loading configuration; wheelchair pushup protocol, normal sitting configuration with standard wheelchair pushup once every 20 minutes.

MAIN OUTCOME MEASURES

Transcutaneous partial pressures of oxygen and carbon dioxide measured from buttock overlying the ischial tuberosity and interface pressure measured at the seat back and buttocks. Perfusion deterioration and recovery times were calculated during changes in interface pressures.

RESULTS

In the off-loading configuration, concentrated interface pressure during the normal sitting configuration was significantly diminished, and tissue perfusion was significantly improved. Wheelchair pushups showed complete relief of interface pressure but incomplete recovery of tissue perfusion.

CONCLUSIONS

Interface pressure analysis does not provide complete information about the effectiveness of pressure relief maneuvers. Measures of tissue perfusion may help establish more effective strategies. Relief achieved by standard wheelchair pushups may not be sufficient to recover tissue perfusion compromised during sitting; alternate maneuvers may be necessary. The dynamic seating system provided effective pressure relief with sustained reduction in interface pressure adequate for complete recovery of tissue perfusion. Differences in perfusion recovery times between subjects with spinal cord injury (SCI) and controls raise questions about the importance of changes in vascular responses to pressure after SCI.