Effects of support surface relief pressures on heel skin blood perfusion

Using an alternating pressure mattress to offload heels in ICU

The heel continues to be one of the most common sites of pressure damage. This article reviews the anatomy and physiology of the heel and explores significant risk factors, including those found in the critically ill patient. Interventions to prevent heel pressure ulceration by offloading the heel are explored. An evaluation of the Nimbus 4 alternating pressure mattress was undertaken within an intensive care unit (ICU) to consider the efficacy of its unique Wound Valve Technology, which is designed to help prevent heel pressure ulceration. During the evaluation period none of the patients using the Nimbus 4 developed a pressure ulcer. Staff observed that the Wound Valves provided effective pressure redistribution and, although the cells frequently needed to be adjusted, patient safety was maintained throughout. The Wound Valves were most effective on patients who were less prone to voluntary movement.

Effect of durations of wheelchair tilt-in-space and recline on skin perfusion over the ischial tuberosity in people with spinal cord injury

OBJECTIVE

To compare the efficacy of various durations of wheelchair tilt-in-space and recline on enhancing skin perfusion over the ischial tuberosity in people with spinal cord injury (SCI).

DESIGN

Repeated-measures, intervention and outcomes measure design.

SETTING

University research laboratory.

PARTICIPANTS

Power wheelchair users with SCI (N=9).

INTERVENTIONS

Three protocols of various durations (3min, 1min, and 0min) of wheelchair tilt-in-space and recline were randomly assigned to the participants. Each protocol consisted of a baseline 15-minute sitting, a duration of 0- to 3-minute reclined and tilted, a second 15-minute sitting, and a 5-minute recovery. The position at the baseline and the second sitting was no tilt/recline of the participant and at the reclined and tilted and recovery was at 35° tilt-in-space and 120° recline.

MAIN OUTCOME MEASURES

Skin perfusion response to tilt and recline was assessed by laser Doppler and was normalized to mean skin perfusion at the baseline sitting.

RESULTS

The results showed that mean skin perfusion during recovery at the 3-minute duration was significantly higher than that at the 1-minute duration (P<.017) and mean skin perfusion was not significantly different between the 1-minute and 0-minute durations (not significant). Skin perfusion during the second sitting was significantly higher at the 3-minute duration than at the 1-minute and 0-minute durations (P<.017).

CONCLUSIONS

Our findings suggest that performing the 3-minute duration of wheelchair tilt-in-space and recline is more effective than the 1-minute duration in enhancing skin perfusion of weight-bearing soft tissues.

Heel blood flow during loading and off-loading in bedridden older adults with low and normal ankle-brachial pressure index: a quasi-experimental study

The purpose of this study was to evaluate the differences in heel blood flow during loading and off-loading in bedridden adults older than 65 years. The patients were divided into three groups based on ankle-brachial pressure index (ABI) and transcutaneous oxygen tension (tcPO₂): (1) patients with an ABI ≥ 0.8 (Group A); (2) patients with an ABI < 0.8 and heel tcPO₂ ≥ 10 mmHg (Group B); and (3) patients with an ABI < 0.8 and heel tcPO₂ < 10 mmHg (Group C). Heel blood flow was monitored using tcPO₂ sensors. Data were collected with the heel (1) suspended above the bed surface (preload), (2) on the bed surface for 30 min (loading), and (3) again suspended above the bed surface for 60 min (off-loading). Heel blood flow during off-loading was assessed using three parameters: oxygen recovery index (ORI), total tcPO₂ for the first 10 min, and change in tcPO₂ after 60 min of off-loading. ORI in Group C (n = 8) was significantly shorter than in Groups A (n = 22) and B (n = 15). Total tcPO₂ for the first 10 min of off-loading in Group C was significantly less than that in Groups A and B. Change in tcPO₂ after 60 min of off-loading in Group C was less than in Group A. Based on these findings, additional preventive care against heel blood flow decrease in older adults with an ABI < 0.8 and heel tcPO₂ < 10 mmHg might be necessary after loading.

Heel damage and epidural analgesia: is there a connection?

OBJECTIVE

To determine heel pressure injury prevalence in surgical patients prescribed epidural analgesia and identify intrinsic and extrinsic factors associated with heel damage in this patient cohort.

METHOD

A descriptive study was used to investigate intrinsic and extrinsic variables associated with recorded heel observations at a private hospital in Victoria, Australia. We recruited a sample of 29 consecutive non-emergency participants undergoing general anaesthesia for major surgery, who were prescribed epidural analgesia postoperatively. A total of 58 heel observations were made.

RESULTS

Heel damage prevalence in the study sample was 13.8% (n=8).

CONCLUSION

Intrinsic factors associated with this complication included intra- and postoperative hypotension, vascular disease, smoking, chronic obstructive pulmonary disease, and multiple disease burdens. Extrinsic factors associated with heel damage included thromboembolic deterrent stockings and the postoperative ward use of heel protectors designed for use in operating theatres. It is hoped that the study findings will assist improvements in the assessment of heel damage risk and promote the pressure prevention strategies required by this patient cohort.

Effect of wheelchair tilt-in-space and recline angles on skin perfusion over the ischial tuberosity in people with spinal cord injury

OBJECTIVE

To investigate the efficacy of wheelchair tilt-in-space and recline on enhancing skin perfusion over the ischial tuberosity in wheelchair users with spinal cord injury (SCI).

DESIGN

Repeated-measures, intervention, and outcomes-measure design.

SETTING

A university research laboratory.

PARTICIPANTS

Wheelchair users with SCI (N=11; 9 men, 2 women; mean ± SD age, 37.7±14.2y; body mass index, 24.7±2.6kg/m(2); duration of injury, 8.1±7.5y).

INTERVENTIONS

Protocols (N=6) of various wheelchair tilt-in-space and recline angles were randomly assigned to participants. Each protocol consisted of a 5-minute sitting-induced ischemic period and a 5-minute wheelchair tilt-in-space and recline pressure-relieving period. Participants sat in a position without tilt or recline for 5 minutes and then sat in 1 of 6 wheelchair tilted and reclined positions, including (1) 15° tilt-in-space and 100° recline, (2) 25° tilt-in-space and 100° recline, (3) 35° tilt-in-space and 100° recline, (4) 15° tilt-in-space and 120° recline, (5) 25° tilt-in-space and 120° recline, and (6) 35° tilt-in-space and 120° recline. A 5-minute washout period (at 35° tilt-in-space and 120° recline) was allowed between protocols.

MAIN OUTCOME MEASURES

Laser Doppler flowmetry was used to measure skin perfusion over the ischial tuberosity in response to changes in body positions caused by performing wheelchair tilt-in-space and recline. Skin perfusion response to wheelchair tilt-in-space and recline was normalized to skin perfusion of the upright seated position (no tilt/recline).

RESULTS

Combined with 100° recline, wheelchair tilt-in-space at 35° resulted in a significant increase in skin perfusion compared with the upright seated position (no tilt/recline; P<.05), whereas there was no significant increase in skin perfusion at 15° and 25° tilt-in-space (not significant). Combined with 120° recline, wheelchair tilt-in-space at 15°, 25°, and 35° showed a significant increase in skin perfusion compared with the upright seated position (P<.05).

CONCLUSIONS

Our results indicate that wheelchair tilt-in-space should be at least 35° for enhancing skin perfusion over the ischial tuberosity when combined with recline at 100° and should be at least 25° when combined with recline at 120°. Although smaller angles of wheelchair tilt-in-space and recline are preferred by wheelchair users for functional purposes, wheelchair tilt-in-space less than 25° and recline less than 100° may not be sufficient for effective pressure reduction for enhancing skin perfusion over the ischial tuberosity in people with SCI.

Are pressure redistribution surfaces or heel protection devices effective for preventing heel pressure ulcers?

BACKGROUND

Heel pressure ulcers are recognized as second in prevalence only to pressure ulcer (PU) on the heel among hospitalized patients, and recent studies suggest their incidence may be higher than even sacral ulcers.

OBJECTIVES

We systematically reviewed the literature to identify and evaluate whether pressure redistribution surfaces or heel protection devices are effective for the prevention of heel ulcers.

SEARCH STRATEGY

We searched CINAHL and MEDLINE databases, using the keywords "pressure ulcer" and "heel," which we also searched the Cochrane Library, using the key terms "pressure ulcer," "heel," and "support surface." We hand searched the ancestry of pertinent research reports and review articles in order to identify additional studies. Inclusion criteria were (1) any study that compared one or more pressure redistribution surfaces or heel protection devices designed specifically to prevent heel PU and (2) any study comparing 2 or more pressure redistribution surfaces designed to prevent PU that specifically reported differences in the incidence of heel PU. Exclusion criteria were (1) studies that did not measure heel PU incidence as an outcome, (2) studies without an English language abstract, and (3) studies that reported overall PU incidence but did not analyze heel PU incidence separately.

RESULTS

Clinical evidence concerning the efficacy of pressure redistribution surfaces or heel protection devices is sparse. Existing evidence suggests that pressure redistribution surfaces vary in their ability to prevent heel pressure ulcers, but there is insufficient evidence to determine which surfaces are optimal for this purpose. A single study suggests that a wedge-shaped viscoelastic foam cushion is superior to standard foam pillows for preventing heel PU, but further research is needed before a definitive conclusion concerning this issue can be reached. There is insufficient evidence to determine whether heel protection devices are more effective than a standard hospital foam pillow for the prevention of heel PU. Research is urgently needed to determine the effectiveness of available heel protection devices for the prevention of heel PU. Studies should address efficacy among the available products and compare efficacy to standard foam pillows.

IMPLICATIONS FOR PRACTICE

Given the paucity of clinical evidence, clinical decisions about the selection of an optimal device for preventing heel PU rely on a combination of existing evidence and clinical experience. While pressure redistribution devices may reduce tissue interface pressures at the heels, expert opinion and clinical experience concur that elevation of the heel is indicated to both reduce pressure and prevent shear and friction caused by frequent movement of the heel due to restlessness, reflex movements of the legs, or voluntary movement. A variety of heel protection devices are available that are designed to both relieve tissue interface pressure and protect the heel from shear and friction. Considerations for selecting an optimal heel protection device include its ability to elevate the heel off the underlying support surface while preventing foot-drop and rotation of the leg, the boot's ability to wick away temperature, its ability to be cleaned, whether it allows patient ambulation, its ability to remain in place despite patient movement, and its ability to remain in place without causing pressure to other surfaces of the foot.

Wavelet-based spectrum analysis of sacral skin blood flow response to alternating pressure

OBJECTIVES

To provide insight into the physiologic mechanisms associated with alternating pressure, using wavelet analysis of skin blood flow (SBF) oscillations, and to determine whether the application of alternating pressure induces myogenic responses, thereby enhancing SBF as compared with constant loading.

DESIGN

Repeated-measures design.

SETTING

University research laboratory.

PARTICIPANTS

Healthy, young adults (N=10; 5 men, 5 women; mean age +/- standard deviation, 30.0+/-3.1 y).

INTERVENTION

Alternating pressure for 20 minutes (four 5-min cycles with either 60 mmHg or 3 mmHg) and constant loading for 20 minutes at 30 mmHg on the skin over the sacrum.

MAIN OUTCOME MEASURES

A laser Doppler flowmeter was used to measure sacral SBF response to both alternating pressure and constant loading. Wavelet-based spectrum analysis of SBF oscillations was used to assess underlying physiologic mechanisms including endothelium-related metabolic (.008-.02 Hz), neurogenic (.02-.05 Hz), and myogenic (.05-.15 Hz) controls.

RESULTS

Alternating pressure stimulated an increase in sacral SBF of compressed soft tissues as compared with constant loading (P<.01). SBF during the high-pressure phase of 4 alternating pressure cycles showed an increasing trend. An increase in power in metabolic frequency range and a decrease in power in the myogenic frequency range during alternating pressure were observed compared with SBF prior to loading. Power increased in the myogenic frequency range during the low-pressure phase of alternating pressure and decreased during the high-pressure phase.

CONCLUSIONS

SBF control mechanisms, as assessed by the characteristic frequencies embedded in SBF oscillations, show different responses to 2 loading pressures with the same average pressure but different patterns. Our study suggests that optimization of operating parameters and configurations of alternating pressure support surfaces to compensate for impaired SBF control mechanisms in pathologic populations may be possible using wavelet analysis of blood flow oscillations.

Comparison of Two Pressure Ulcer Preventive Dressings for Reducing Shear Force on the Heel

OBJECTIVE

We compared the shear forces exerted over the heel between a pressure ulcer preventive dressing and a thin-film dressing in a clinical setting. Interface pressures were measured as well.

DESIGN

Quasi-experimental clinical trial.

SETTING AND SUBJECTS

Participants were 30 elderly patients (5 men, 25 women; mean age, 86.4 +/- 8.0 years) hospitalized in a geriatrics hospital in Japan; all had a Braden score of less than 14 (mean, 10.1 +/- 1.1). Informed consent was obtained from all the patients.A shear force and pressure sensor including a strain gauge, and an oval airbag-type pressure sensor were used.

METHODS

The sensor was attached to one heel using double-sided tape; then the target dressing was applied over the sensor and on the opposite heel to avoid the influence of the opposite heel on the shear force measurement. Interface pressures were measured with the patient in a stationary supine position; shear force was then measured at 0.2-second intervals, while the sheet was manually pulled at a velocity of around 5 cm/second. Shear force was determined by averaging the stable shear force lasting for 10 measurement points.

RESULTS

The mean interface pressures with the PPD and the film dressings were 70.7 +/- 16.5 and 70.2 +/- 15.2 mmHg, respectively; this difference was not statistically significant. The shear force produced during the pulling of the sheet was 2.2 +/- 1.4 and 11.7 +/- 5.8 N, respectively (P < .001, Wilcoxon signed-rank test).

CONCLUSIONS

The results of this study suggest that a dressing with a low-friction external surface (such as the pressure ulcer preventive dressing) can significantly reduce shear force. However, results also suggest that external dressings do not significantly reduce interface pressures and cannot be used as a substitute for heel elevation in an immobile patient.

Effects of Support Surface Relief Pressures on Heel Skin Blood Flow in Persons with and without Diabetes Mellitus

OBJECTIVE

To investigate the effects of pressure relief magnitude on heel blood hyperemia in persons with and without diabetes mellitus.

DESIGN

Study participants (1 group of persons with diabetes and 1 group without diabetes) lay on a support surface for 70 minutes with 1 heel on an end cell of a support surface. Cell pressure was computer controlled to be 20 mm Hg during support and 5 or 0 mm Hg during relief. Heel skin blood perfusion was monitored by laser Doppler on the heel and foot dorsum. Heel hyperemia was determined as ratios of skin blood perfusion areas during hyperemia to preloading (AR) and peak hyperemia to mean skin blood perfusion during preload (QR).

SUBJECTS

13 persons with diabetes mellitus (6 females, 7 males; age 65.2 +/- 3.0 years) and no known diabetes-related complications, and 15 persons without diabetes mellitus (7 females, 8 males; age 54.7 +/- 3.1 years)

SETTING

University research center.

RESULTS

For the nondiabetes mellitus group, hyperemia was significantly greater with complete pressure-relief compared with partial relief (P < .001). In contrast, the diabetes mellitus group showed no significantly increased response to full relief, and the hyperemia achieved during full relief, measured by AR and QR, was significantly less than with the nondiabetes mellitus group.

CONCLUSIONS

These results suggest that a diabetes-related reduced microvascular vasodilatory capacity is not exceeded during partial pressure relief, but is exceeded during complete pressure relief. Accordingly, differences in hyperemic response would become unmasked only when maximum hyperemia could be established during complete heel off-loading. This would suggest that a diminished hyperemia during complete off-loading, as found in the present diabetes mellitus group, may be problematic if widely present in the diabetic (or possibly older) population, under conditions in which heel loading occurs for sustained intervals.

Evaluation of alternating pressure air mattresses: one laboratory-based strategy

Although many different type of alternating pressure air mattresses (APAMs) are used for the prevention and treatment of pressure ulcers, few high quality randomised controlled trials are available on which to base purchasing decisions. Faced with this situation, physiological measurements are increasingly being used as a surrogate. Laboratory evaluation techniques have centred largely on interface pressure (IP) measurement, typically analysing discrete maximum and minimum levels, or average pressure. However, since pressure relief is time varying, a time-based analysis technique may be more suitable for performance assessment. Measurements of IP, mattress air cell pressure (AP), skin tissue perfusion using laser Doppler fluxmetry (LDF), transcutaneous oxygen (tcPO2) and carbon dioxide (tcPCO2) were taken simultaneously on the sacrum, heels, trochanters and buttock over at least two alternating cycles. Duration of IP below three thresholds (30, 20, and 10 mmHg) as well as the area under the tcPO2, tcPCO2 and LDF curves were calculated automatically. Ten healthy volunteers were recruited to evaluate the pressure-relieving characteristics of two different designs of APAMs. Results indicated significant differences between the products. During the deflation phase of the cycle contact pressures on the heel were significantly lower (p < 0.0001) on the device whose inflation pressure was significantly higher, although there was no significant difference in deflation pressure. Therefore, it is important to note that low APs do not necessarily produce lower IPs under the heel, contrary to the intuitive classical notion. These techniques could assist in the selection of alternating or dynamic surfaces of any description confirmed by further clinical validation.