The viability of soft tissues in elderly subjects undergoing hip surgery

Exploring the effects of lateral pressure to the soft tissue of the buttocks during seating to preserve tissue perfusion

AIM

Pressure-ulcer occurrence in the seated patient is understudied. Preventative devices have been developed and are prescribed commonly, but there is little quantitative evidence of their effectiveness. This study explores the concept of a lateral pressure device, a prevention device that applies pressure to the sides of the seated buttocks, to reduce the amount of tissue distortion and blood-vessel occlusion. It is hypothesized that this device will reduce deep tissue injury by reducing the pressure at the bone-muscle interface, as demonstrated computationally in previous research. This study aimed to use oximetry to investigate the efficacy of the device in maintaining transcutaneous gas tensions of the tissue as close to baseline as possible.

METHODS

Oximetry electrodes were attached to participants' ischial tuberosity and greater trochanter for different amounts of lateral pressure. The amount of lateral pressure is a given percentage of the pressure due to the participants' underbody pressure.

RESULTS

The results show that 50 % lateral pressure is sufficient to produce an improvement in participants' gas tensions at their ischial tuberosity, without negatively impacting the tissue at their greater trochanter, relative to the control of sitting with no application of lateral pressure.

CONCLUSION

Despite a rudimentary prototype device design, and that participants each placed their own oximetry sensors, results support the application of lateral pressure as a method to maintain transcutaneous gas tensions. Further work should be carried out on a larger sample to consolidate these findings.

A Phantom-Based Method to Assess X-Ray Table Mattress Interface Pressures

BACKGROUND

Pressure redistribution performance of x-ray table mattresses can influence the development of pressure ulcers in at-risk populations. Interface pressure analysis, with human participants, is a common method to assess mattresses. This approach has limitations that relate to the lack of standardisation between and within humans.

AIM

This study aimed to develop and validate an anthropomorphic phantom-based method to assess x-ray table mattress interface pressures as an index of mattress performance.

METHODS

A three dimensional phantom simulating an adult's head, pelvis, and heels was printed from x-ray computed tomography image data and attached to a metal frame 175 cm in length. Dry sand was added to the phantom head, pelvis, and heels to represent a range of human weights. Pressure distribution was assessed using XSensor. Phantom validation was achieved by comparing phantom mattress interface pressure characteristics, for five human equivalent weights, against 27 sets of human mattress interface pressure data.

RESULTS

Using the correlation coefficient R, phantom and human pressure data showed good correlation for the five phantom weights (R values: head = 0.993, pelvis = 0.997, and heels = 0.996).

CONCLUSION

A novel method to test x-ray mattresses for interface pressure was developed and validated. The method could have utility in the testing of x-ray mattresses that are in routine use and for new mattress development. Phantom interface pressure data could be provided by manufacturers to help inform procurement decisions when matching mattress characteristics to medical imaging demands and the underlying patient populations.

An ex vivo porcine skin model to evaluate pressure-reducing devices of different mechanical properties used for pressure ulcer prevention

Pressure ulcers are complex wounds caused by pressure- and shear-induced trauma to skin and underlying tissues. Pressure-reducing devices, such as dressings, have been shown to successfully reduce pressure ulcer incidence, when used in adjunct to pressure ulcer preventative care. While pressure-reducing devices are available in a range of materials, with differing mechanical properties, understanding of how a material's mechanical properties will influence clinical efficacy remains limited. The aim of this study was to establish a standardized ex vivo model to allow comparison of the cell protection potential of two gel-like pressure-reducing devices with differing mechanical properties (elastic moduli of 77 vs. 35 kPa). The devices also displayed differing energy dissipation under compressive loading, and resisted strain differently under constant load in compressive creep tests. To evaluate biological efficacy we employed a new ex vivo porcine skin model, with a confirmed elastic moduli closely matching that of human skin (113 vs. 119 kPa, respectively). Static loads up to 20 kPa were applied to porcine skin ex vivo with subsequent evaluation of pressure-induced cell death and cytokine release. Pressure application alone increased the percentage of epidermal apoptotic cells from less than 2% to over 40%, and increased cellular secretion of the pro-inflammatory cytokine TNF-alpha. Co-application of a pressure-reducing device significantly reduced both cellular apoptosis and cytokine production, protecting against cellular damage. These data reveal new insight into the relationship between mechanical properties of pressure-reducing devices and their biological effects. After appropriate validation of these results in clinical pressure ulcer prevention with all tissue layers present between the bony prominence and external surface, this ex vivo porcine skin model could be widely employed to optimize design and evaluation of devices aimed at reducing pressure-induced skin damage.

Complicações decorrentes do posicionamento cirúrgico de clientes idosos submetidos à cirurgia de quadril

Este estudo de revisão sistemática da literatura, segundo as recomendações sugeridas pela Colaboração Cochrane, teve como objetivo buscar nas publicações das bases de dados consultadas as evidências disponíveis sobre complicações decorrentes do posicionamento cirúrgico em idosos submetidos à cirurgia de quadril. Nesta revisão, os estudos identificados e discutidos apresentaram aspectos importantes no desenvolvimento de uma prática efetiva, possibilitando maior compreensão da necessidade de elaboração de pesquisas melhores delineadas que proporcionem validade interna de estudos futuros, para que seus resultados possam ser utilizados na prática clínica.

Pressure sores and hip fractures

Development of pressure sores during hospital admission causes morbidity and distress to the patient, increases strain on nursing resources, delaying discharge and possibly increasing mortality. A hip fracture in elderly patients is a known high-risk factor for development of pressure sores. We aimed to determine the current incidence of pressure sores and identify those factors which were associated with an increased risk of pressure sores. We retrospectively analysed prospectively collected data of 4654 consecutive patients admitted to a single unit. One hundred and seventy-eight (3.8%) of our patients developed pressure sores. Patient factors that increased the risk of pressure sores were increased age, diabetes mellitus, a lower mental test score, a lower mobility score, a higher ASA score, lower admission haemoglobin and an intra-operative drop in blood pressure. The risk was higher in patients with an extracapsular neck of femur fracture and patients with an increased time interval between admission to hospital and surgery. Our studies indicate that while co-morbidities constitute a substantial risk in an elderly population, the increase in incidence of pressure sores can be reduced by minimising delays to surgery.

Role of ischemia and deformation in the onset of compression-induced deep tissue injury: MRI-based studies in a rat model

A rat model was used to distinguish between the different factors that contribute to muscle tissue damage related to deep pressure ulcers that develop after compressive loading. The separate and combined effects of ischemia and deformation were studied. Loading was applied to the hindlimb of rats for 2 h. Muscle tissue was examined using MR imaging (MRI) and histology. An MR-compatible loading device allowed simultaneous loading and measurement of tissue status. Two separate loading protocols incorporated uniaxial loading, resulting in tissue compression and ischemic loading. Uniaxial loading was applied to the tibialis anterior by means of an indenter, and ischemic loading was accomplished with an inflatable tourniquet. Deformation of the muscle tissue during uniaxial loading was measured using MR tagging. Compression of the tissues for 2 h led to increased T2 values, which were correlated to necrotic regions in the tibialis anterior. Perfusion measurements, by means of contrast-enhanced MRI, indicated a large ischemic region during indentation. Pure ischemic loading for 2 h led to reversible tissue changes. From the MR-tagging experiments, local strain fields were calculated. A 4.5-mm deformation, corresponding to a surface pressure of 150 kPa, resulted in maximum shear strain up to 1.0. There was a good correlation between the location of damage and the location of high shear strain. It was concluded that the large deformations, in conjunction with ischemia, provided the main trigger for irreversible muscle damage.

Validation of the mobility subscale of the Braden Scale for predicting pressure sore risk

BACKGROUND

The Braden Scale for Predicting Pressure Sore Risk has been tested extensively for reliability and validity, but the validity of each subscale has not been evaluated. Because subscale scores are intended to guide patient care decisions, validity is an important issue.

OBJECTIVE

: To establish the convergent construct validity of the mobility subscale of the Braden Scale.

METHODS

The study evaluated 16 members at a veterans' home (4 members representing each score on the mobility subscale). Movement, as recorded by a Motionlogger Actigraph, a wristwatch-sized accelerometer and microprocessor that measures physical movement (activity), was measured continuously. Each person wore an Actigraph on the nondominant ankle for 72 hours.

RESULTS

The mean activity for each of the four subscale score groups was plotted, producing a histogram in which higher scores were associated with greater activity (F[3, 15] = 31.69;p <.001, one-way analysis of variance), as expected. Pair wise multiple comparisons between groups showed that only the subgroup with a score of 4 was significantly different in mean activity (p <.001) from the other three score groups.

CONCLUSIONS

Convergent construct validity for the Braden mobility subscale was supported. A larger sample and establishment of a threshold to eliminate minor, ineffective movements from Motionlogger Actigraph measures may distinguish between significant and nonsignificant movement.

The measurement of interface pressure and its role in soft tissue breakdown

This paper describes the effect of applied pressure on soft tissue and its possible role in the development of pressure ulcers. It concentrates on the quantification of the applied pressure at the patient-support interface and the limitations and variability of current techniques, measurement systems and data presentation. It then describes the effects of interface pressures at the tissue and cellular level, and attempts that have been made to describe and model the tissue mechanics. Finally it sets a challenge to medical engineers to improve the present measurement systems and tissue models, thus increasing understanding, both clinically and at the cellular level, so that the incidence of pressure ulcers can be reduced.