THE EFFECT OF EXTERNAL PRESSURE ON THE VASCULAR VOLUME OF THE FOREARM AND ITS RELATION TO CAPILLARY BLOOD PRESSURE AND VENOUS PRESSURE

Nonnegative matrix factorization for the identification of pressure ulcer risks from seating interface pressures in people with spinal cord injury

The purpose of this study was to predict and visualize pressure ulcer risks by using a novel approach of extracting computational features from seating interface pressures in people with spinal cord injury (SCI). In conventional clinical practice, seating interface pressure assessments rely on descriptive statistics of pressure magnitude. In this study, rank-2 nonnegative matrix factorization (NMF) was applied to the seating interface pressure maps during loading and pressure-relieving conditions in 16 people with SCI. The NMF basis images were used for visual interpretation and computational prediction of pressure ulcer risks. The two NMF basis images encapsulated pressure concentration and pressure dispersion, respectively. The first basis converged on the ischial tuberosity under both seating conditions, whereas the second basis converged anterior to the ischial tuberosity during loading and converged on the coccyx during unloading. The classification yielded 81.25% overall accuracy. In general, higher ulceration risk was associated with higher and lower activations of the first and second bases, respectively. The NMF pipeline yielded promising performance. Basis visualization affirmed the importance of lower ischial pressure and higher distribution dispersion while also revealing that clinical practice may currently be underestimating the importance of coccygeal pressure in response to pressure-relieving activities. Graphical abstract.

A new device to prevent fascial retraction in the open abdomen - proof of concept in vivo

Background

An open abdomen is often necessary for survival of patients after peritonitis, compartment syndrome, or in damage control surgery. However, abdominal wall retraction relieves delays and complicates abdominal wall closure. The principle of the newly fascia preserving device (FPD) is the application of anteriorly directed traction on both fascial edges over an external support through a longitudinal beam to relieve increased abdominal pressure and prevent fascial retraction.

Methods

Twelve pigs were randomly divided into two groups. Both groups underwent midline laparotomy under general anesthesia. Group one was treated with the new device, group two served as controls. The tension for closing the abdominal fascia was measured immediately after laparotomy as well as at 24 and 48 h. Vital parameters and ventilation pressure were recorded. Post mortem, all fascial tissues were histologically examined.

Results

All pigs demonstrated increases in abdominal circumference. In both groups, forces for closing the abdomen increased over the observation period. Concerning the central closing force after 24 h we saw a significant lower force in the FPD group (14.4 ± 3 N) vs. control group (21.6 ± 5.7 N, p < 0.001). By testing the main effects using an ANOVA analysis we found a significant group related effect concerning closing force and abdominal circumference of the FDP-group vs. control group (p < 0.001; p < 0.001). The placement of the device on chest and pelvis did not influence vital parameters and ventilation pressure. Histologic exam detected no tissue damage.

Conclusions

This trial shows the feasibility to prevent fascial retraction during the open abdomen by using the new device. Thus, it is expected that an earlier closure of the abdominal wall will be possible, and a higher rate of primary closure will be attained.

Backrest position in prevention of pressure ulcers and ventilator-associated pneumonia: conflicting recommendations

Pressure ulcers and ventilator-associated pneumonia (VAP) are both common in acute and critical care settings and are considerable sources of morbidity, mortality, and health care costs. To prevent pressure ulcers, guidelines limit bed backrest elevation to less than 30 degrees, whereas recommendations to reduce VAP include use of backrest elevations of 30 degrees or more. Although a variety of risk factors beyond patient position have been identified for both pressure ulcers and VAP, this article will focus on summarizing the major evidence for each of these apparently conflicting positioning strategies and discuss implications for practice in managing mechanically ventilated patients with risk factors for both pressure ulcers and VAP.

A chronic pressure ulcer model in the nude mouse

The pathophysiology of pressure ulcers is not yet fully understood. Widely used experimental models lead to pressure ulcers in the skin and the subcutaneous tissue only. The aim of the present study was to develop a clinically relevant deep pressure ulcer model in nude mice involving all relevant tissue layers. Balb/c nude mice were anesthetized and a steel disk was implanted under the great gluteus muscle. Full recovery was allowed for 10 days. Pressure was then periodically applied (2 hours compression, 1 hour recovery) using a Neodymium magnet in conjunction with the disk in the unanesthetized mouse. Cycles were repeated for 1, 4, 6, 8, or 10 times. Controls underwent the same procedure without placement of the magnet. The pressure ulcer grade was found to be cycle dependent,with the highest degree after 10 cycles. Histological evaluations revealed signs of necrosis in the skin and subcutaneous fat after four, and in the muscle after eight and 10 cycles of compression. Polymorphnuclear granulocyte infiltration in certain layers was found to be dependent on the number of cycles. We conclude that this clinically relevant nude mouse model can be used to investigate the mechanism of pressure ulcer development and to study new therapeutic approaches.

The biomechanics of sitting-acquired pressure ulcers in patients with spinal cord injury or lesions

Sitting-acquired pressure ulcers (SAPU) in permanent wheelchair users with traumatic or non traumatic disorders of the central nervous system (CNS) are a great medical challenge. The purpose of this review is to summarise what is currently known concerning the aetiology of SAPU, particularly in its severe form, which may now be classified as a 'deep tissue injury' according to the US National Pressure Ulcer Advisory Panel. Specifically, this review focuses on biomechanical aspects of deep SAPU and describes the relevant bioengineering methodologies and research evidence. It discusses the unique biomechanical conditions in deep tissues, which are caused by chronic sitting associated with CNS disorders, and overall, the present review indicates that avoiding interface pressures above 32 mmHg in such patients is not necessarily a 'pressure relief.'

An investigation of the uncurling forces of indwelling catheters

An elastic catheter in the male urethra produces an 'uncurling' force as it attempts to straighten itself. Where this force is sustained, it may result in some pressure necrosis, or pressure atrophy. This article describes how this in-vivo situation was modelled and the resultant pressures checked and recommends the type and size of catheter that should be used if it is needed for more than 2 days of continuous use.

In control with incontinence aids

Incontinence is a common condition affecting people of all ages. Many can be cured and all can benefit from appropriate treatment and management. Despite huge growth in this market, many products are neither appealing nor acceptable to those people who have to use them. Whenever practical, it is best that the choice of aid should be a collaborative decision between the user and the carer.

Skeletal muscle blood flow and venous capacitance in patients with severe sepsis and systemic hypoperfusion

Alterations in peripheral vascular tone are presumed to contribute to circulatory failure during severe sepsis. Decreased venous tone with venous pooling may decrease effective circulatory blood volume, while decreased arterial tone with redistribution of systemic blood may compromise tissue nutrient flow. We compared forearm arterial and venous tone and forearm blood flow in ten patients with and ten patients without sepsis. The FVT, MVC, and FBF were measured by air plethysmography. In the septic patients, MCV was 1.4 +/- 0.1 ml compared with 3.1 +/- 0.2 ml in nonseptic patients (p less than 0.01). The FVT was 13.4 +/- 1.0 mm Hg/ml in septic patients versus 7.0 +/- 0.5 mm Hg/ml in nonseptic patients (p less than 0.01). The ratio of FBF to cardiac output was 0.28 +/- 0.07 percent in septic patients and 0.31 +/- 0.07 percent in nonseptic patients. These data suggest that increased peripheral venous capacitance and redistribution of skeletal muscle blood flow are not present in patients with sepsis.

Changes in transcutaneous oxygen tension as a result of prolonged pressures at the sacrum

Prolonged pressures at the patient support interface can lead to the impairment of tissue viability resulting in tissue breakdown, particularly in debilitated individuals. However there are still few clinical guidelines to indicate safe levels of pressure and time for individual tissue areas. The effects of extended loading on transcutaneous oxygen tension (tcPO2) were examined at the sacrum of twenty debilitated subjects, prone to tissue breakdown. Each load was applied for a ten minute period through an indenter incorporating a commercial oxygen electrode. Loads were incremented until the tcPO2 levels were reduced below 2.7 kPa (20 mmHg), at which time the tissue was unloaded. The interface pressure for each applied load was measured. Results are presented in terms of relating applied pressure and time to relative changes in tcPO2. When all the results are combined it is clear that there is a range of applied pressures which significantly reduce the tcPO2 levels. The applied pressures to produce, for example, 50% reduction of the unloaded resting value, ranged from 3.0 kPa (22 mmHg) to 12.2 kPa (92 mmHg). This indicated the individual nature of the tissue response, which should be determined before clinical guidelines of safe pressure levels are established.

Management of wounds in anesthetic tissue

The management of trophic ulcers, the most common wound in hypesthetic or anesthetic tissue, is reviewed. Pressure from an extrinsic source is the most important factor leading to development of the lesion, but the threshold for ulceration is markedly lowered by impairment of protective vasomotor reflexes and metabolic responses. Prevention of severe or sustained compression of such tissue is the hallmark of proper management. The most useful surgical procedures are also discussed.

Decubitus ulcers and wheelchair cushions a review of the literature

A review of the literature is presented in this paper discussing the development of decubitus ulcers and wheelchair cushions in their management. The etiology and pathology of decubitus ulcers as well as their classification is outlined. Much research has been done in determining the amount of pressure forces that the skin can survive before becoming ischemic. This is discussed and related to the research evaluating the various cushions available on the market today. This paper is not an endorsement of any particular brand of wheelchair cushion.

Rancho flotation bed

The Rancho Flotation Bed provides hydrostatic support with maximum pressures over bony prominences of 15 to 25 mm Hg (measured with a pneumatic pressure transducer). This is generally below the levels normally quoted as conducive to the development of ischaemia. Clinical experience has shown the bed to be a successful aid to nursing by eliminating the need to turn the patients for pressure reasons, allowing patients with pressure sores to remain in a position which is more comfortable and more suitable for other nursing care. It also makes it easier for nurses to handle patients in order to care for the pressure sores.