Patient repositioning and pressure ulcer risk—Monitoring interface pressures of at-risk patients

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Patient repositioning and pressure ulcer risk—Monitoring interface pressures of at-risk patients

Matthew J. Peterson, PhD;1* Nikolaus Gravenstein, MD;2 Wilhelm K. Schwab, PhD;2 Johannes H. van Oostrom, PhD;1 Lawrence J. Caruso, MD2 1J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida College of Engineering, Gainesville, FL; 2Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL

Abstract—Repositioning patients regularly to prevent pres- sure ulcers and reduce interface pressures is the standard of care, yet prior work has found that standard repositioning does not relieve all areas of at-risk tissue in nondisabled subjects. To determine whether this holds true for high-risk patients, we assessed the effectiveness of routine repositioning in relieving at-risk tissue of the perisacral area using interface pressure mapping. Bedridden patients at risk for pressure ulcer forma- tion (n = 23, Braden score <18) had their perisacral skin-bed interface pressures recorded every 30 s while they received routine repositioning care for 4–6 h. All participants had spe- cific skin areas (206 +/– 182 cm2) that exceeded elevated pres- sure thresholds for >95% of the observation period. Thirteen participants were observed in three distinct positions (supine, turned left, turned right), and all had specific skin areas (166 +/– 184 cm2) that exceeded pressure thresholds for >95% of the observation period. At-risk patients have skin areas that are likely always at risk throughout their hospital stay despite repositioning. Healthcare providers are unaware of the actual tissue-relieving effectiveness (or lack thereof) of their reposi- tioning interventions, which may partially explain why pressure ulcer mitigation strategies are not always successful. Relieving at-risk tissue is a necessary part of pressure ulcer prevention, but the repositioning practice itself needs improvement.

Key words: decubitus ulcer, interface pressure, patient reposi- tioning, pressure, pressure sore, pressure ulcer, pressure ulcer risk, prevention, standard of care, triple-jeopardy area.

INTRODUCTION

Pressure ulcers are a high-risk, high-volume, and high-cost problem for hospitalized and bedridden patients. Overall pressure ulcer prevalence rates have been reported at 12.3 percent across all facilities, with prevalence being highest in long-term acute care facili- ties (22%), and facility-acquired prevalence being high- est in adult intensive care units (8.8%–10.3%) [1]. Preventing pressure ulcers and reducing their incidence is an ongoing challenge because they are associated with increased cost, length of stay, morbidity, and mortality. Managing one full-thickness ulcer can cost up to $70,000 [2], and over $17 billion is spent on pressure ulcer treat- ments annually in the United States [3].

Note: The authors would like to dedicate this article to the memory of their colleague Dr. Schwab.

Abbreviations: BMI = body mass index, HOB = head of bed, NPUAP = National Pressure Ulcer Advisory Panel, q2h = every 2 h, SLR = supine-left-right. *Address all correspondence to Matthew J. Peterson, PhD; James A. Haley Department of Veterans Affairs Medical Center (151R), HSR&D/RR&D Center of Excellence, 8900 Grand Oak Circle, Tampa, FL 33637; 813-558-3979; fax: 813-558-3990. Email: Matthew.Peterson1@va.gov http://dx.doi.org/10.1682/JRRD.2012.03.0040

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A pressure ulcer, as defined by the National Pressure Ulcer Advisory Panel (NPUAP), is a “localized injury to the skin and/or underlying tissue usually over a bony promi- nence, as a result of pressure, or pressure in combination with shear and/or friction” [4]. It is widely accepted that this mechanical loading is the main cause of pressure ulcer formation; however, the pathophysiological responses to this loading are less agreed upon [5]. Theo- ries include localized ischemia [6], reperfusion injury [7], impaired interstitial fluid flow [8], and sustained cell deformation [9]. Tissue-loading models have been devel- oped to study pressure ulcer formation, and results have shown that acute stresses and strains in the deep tissue (fat, muscle), which is more susceptible to damage than the skin, present themselves before they are apparent in the superficial tissue [5,10–11]. However, tissue pres- sures greater than capillary pressure can be endured for some time before ischemia results [12].

Pressure ulcers result when increased pressure on the skin and subcutaneous tissues exceeds the local capillary pressure, which compromises blood flow and results in ischemia and decreased oxygen delivery [13]. Healthy capillary pressures typically range from 10 to 30 mm Hg [14]; however, capillary pressures may be lower for indi- viduals in poor health [15–16]. Studies on blood flow in response to loading vary in the amount of pressure required to stop or reduce blood flow and oxygen deliv- ery as well as by anatomical location or tissue type [17– 21]. Therefore, no widely accepted value exists that will ultimately lead to pressure ulceration [5,22]. When pres- sures exceed capillary pressure, tissue hypoperfusion, accumulation of metabolites, and impairment of tissue reperfusion may occur, all of which can damage the tis- sue [23–25]. It is well established in animal and human studies that not only is the magnitude of pressure a factor for tissue damage but the duration is important as well— the greater the pressure, the less time it takes until dam- age occurs [6,22,26–29]. Over time, prolonged high pres- sure applied to a tissue area will inevitably cause damage. Interface pressure is the perpendicular force per unit area between the support surface and the body. Interface pres- sures are greatest around the sacrum, coccyx, and ischial tuberosities, so it is not surprising that the majority of pressure ulcers develop near these locations [30–31]. How- ever, note that tissue interface pressures do not directly measure internal tissue and capillary pressures [22].

The Centers for Medicare and Medicaid Services recently designated pressure ulcers as a quality measure,

and consequently, they will not reimburse additional patient expenses resulting from a reasonably preventable condition that occurs while providing care [32–33]. Thus, pressure ulcers have become a liability for hospitals, long-term care facilities, and other healthcare providers [34–35]. However, disagreement persists about the pre- sumed inherent preventability of all pressure ulcers [36– 37]. To address this issue, the NPUAP hosted a multidis- ciplinary consensus conference in 2010 and redefined what is generally considered avoidable and unavoidable. The group unanimously agreed that most, but not all, pressure ulcers are avoidable [37]. Consensus was reached that “unavoidable pressure ulcers may develop in patients who are hemodynamically unstable, terminally ill, have certain medical devices in place, and are nonad- herent with artificial nutrition or repositioning” [37].

PATIENT REPOSITIONING

Repositioning patients regularly—every 2 h (q2h)— to prevent sustained high pressures on any particular tis- sue area is the standard of care [2,16,37–40]. However, several recent studies in which repositioning was used as the primary intervention strategy failed to reduce the incidence of pressure ulcer formation [39–41]. Addition- ally, the NPUAP conference could not reach a consensus that q2h repositioning should be the standard of care. However, they did agree that q2h repositioning should be the “guideline for care” when clinically appropriate [37]. It was also unanimously agreed that pressure-redistributing surfaces cannot replace patient repositioning care [37].

Our prior work found that standard, lateral turning by experienced nurses does not reliably relieve all areas of high skin-bed interface pressures in the perisacral region of nondisabled adult subjects [42], i.e., the collective tis- sue area around the sacrum, coccyx, and ischial tuberosi- ties. Even though subjects are repositioned and the perisacral area is no longer touching the mattress, this perisacral skin area remains exposed to significant levels of interface pressure between the pillow or wedge that is supporting the laterally turned position. Furthermore, specific skin areas remain at risk even after being placed in all three positions: supine, turned left, and turned right. These specific skin regions are termed “triple-jeopardy areas” because the same tissue remains at risk while in any of the three different positions [42]. This may help explain why pressure ulcers still develop despite implementation of

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standard preventive measures, including scheduled patient repositioning. To determine whether this is the case for at-risk patients, this study examined the effect of routine repositioning over an extended time period on the interface pressures of the perisacral skin area of bedrid- den patients at risk for pressure ulcer formation using interface pressure mapping.

METHODS

Study Design We performed a descriptive, observational study, col-

lecting data at a tertiary care, university-affiliated hospi- tal with 170 intensive and intermediate care beds from 2007 to 2009. Subjects were invited to enroll in the study during regular care by their physician. We hypothesized that bedridden patients undergoing q2h repositioning would demonstrate a triple-jeopardy area (i.e., triple- jeopardy area is not zero). To achieve a power of 80 per- cent, a one-tailed test with an effect size of 0.8, and an error probability of 5 percent required a minimum sample size of 12. The effect size, though seemingly large, is conservative based on results from our previous study with nondisabled subjects [42] and, since a negative area does not exist, a one-tailed test is appropriate. We enrolled participants in the study until we monitored at least 12 in all three distinct positions: supine, turned left, and turned right. To compute the power, we used G*Power 3.0 (Institut für Experimentelle Psychologie, Heinrich Heine Universität Düsseldorf; Düsseldorf, Germany).

Subjects We enrolled 23 participants in the study from a con-

venience sampling of intensive care (n = 20) and interme- diate care (n = 3) unit patients. We obtained written informed consent from the patient or his or her proxy. The patient inclusion criteria were bedridden, residing in intensive care or intermediate care unit, at risk for pres- sure ulcer formation determined by a Braden score of 18 (at time of consent), and receiving lateral reposition- ing as part of routine care. Not all patients were intubated or sedated, but none was able to reposition themselves in bed. Table 1 shows the demographics of the study cohort (sex, age, height, weight, and body mass index [BMI]) and Braden scores (on date of data collection). The subgroup of patients that we observed in all three posi-

tions will be referred to as the supine-left-right (SLR) group (n = 13).

Instrumentation We obtained interface pressure measurements using a

pressure mapping system (XSENSOR Technology Cor- poration; Calgary, Canada). The pressure sensor is a flexi- ble, thin pad with 48 × 48 half-inch sensors forming a 24 × 24 in.2 array. The 2,304 independent sensors use proprie- tary capacitive technology to discretely measure the pres- sures applied to the sensor array. The interface box relays individual pressure information from each sensor to a computer for real-time visualization and recording. We calibrated the sensor array according to the manufac- turer’s recommendations to measure pressures from 10 to 200 mm Hg, with a reported accuracy of ±10 percent, placing the sensor array between two air bladders held together in a metal frame and inflated to specific pres- sures. During calibration, sensor readings were all within ±10 percent of the measured value across the calibrated range. We used the same calibration file for all subjects. Before use in the clinical environment, we wrapped the sensor array in very thin (0.0254 mm) plastic sheeting to protect it from contamination and placed it beneath the patient’s underpads (thin, towel-like incontinence pads). We disinfected the sensor array after each use. We used a modern hospital bed with low air-loss technology for all measurements (Total Care or Total Care SpO2RT, Hill- Rom; Batesville, Indiana). The bed’s built-in ball-bearing indicator located in the side rail of the bed indicated the head of bed (HOB) elevation.

Protocol We placed the sensor array beneath the patient, span-

ning from the lower back to mid-thigh to ensure data col- lection of the perisacral area. Placing the sensor array required the nurses to roll the patient to one side and then the other so that the array could be positioned, without wrinkles, beneath the patient.

We recorded interface pressure measurements every 30 s as the patient lay in bed and received routine care, which included lateral turning by his or her nurse. The lateral turning methods included the use of pillows and/or wedges placed behind the back and thighs. The reposi- tioning technique was not prescribed by the study, and the nursing technique was unconstrained so that the results would reflect current clinical practice. Any pil- lows or wedges that were used to maintain a laterally

Patient Sex Age (yr) Height (m) Weight (kg) BMI Braden Score SLR Group 1 M 65 1.78 111 35.0 13 — 2 F 73 1.65 75 27.5 — — 3 M 69 1.83 80 23.9 16 — 4 F 84 1.57 64 25.8 10  5 M 70 1.78 86 27.3 15 — 6 M 69 1.78 110 34.8 11  7 M 60 1.65 91 33.4 10  8 F 53 1.68 70 24.9 12 — 9 M 58 1.73 120 40.1 15 —

10 M 71 1.80 65 20.1 16 — 11 F 61 1.63 77 29.0 17  12 M 54 1.82 120 36.2 16  13 M 43 1.85 125 36.3 11  14 M 76 1.75 79 25.7 11 — 15 F 74 1.60 71 27.7 15 — 16 F 67 1.40 55 28.2 12 — 17 F 69 1.60 80 31.3 10  18 F 47 1.63 62 23.3 11  19 F 80 1.65 64 23.4 12  20 M 46 1.70 110 38.0 10  21 M 64 1.75 80 26.1 17  22 M 72 1.73 68 22.7 19  23 M 32 1.83 114 34.0 13 

Total 14 M, 9 F 63.3 ± 12.7 1.70 ± 0.11 85.9 ± 21.9 29.3 ± 5.6 13.3 ± 2.8 — SLR Group 8 M, 5 F 60.1 ± 15.2 1.71 ± 0.09 89.6 ± 23.2 30.3 ± 5.5 12.8 ± 3.2 

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turned position were placed beneath the sensor array to allow continuous measurement of interface pressures between the patient and the supporting device. The sensor array was inspected after each turn to confirm that the patient’s perisacral area was recorded. If the sensor array got bunched up or if the patient’s perisacral area moved off the array, adjustments were made only when the patient was already in the process of being repositioned to avoid interfering with patient care.

We monitored patients for 4 to 6 h. We chose this time frame to allow for observation of the three distinct positions (supine, turned left, and turned right) during the q2h repositioning protocol. The same investigator (M.P.) recorded the general positioning of the patient (direction

of turn and HOB elevation) for all of the data collection periods for all patients. We obtained demographic infor- mation from the patients’ charts.

Data Variables Definitions of four data variables of interest and how

we calculated them include— • At-risk areas (centimeters squared) for pressure ulcer

formation are the skin areas exposed to various inter- face pressure thresholds (32 mm Hg—a historical and contested value [5,16,20,22]—used for statistical analyses, 40 mm Hg, and 50 mm Hg). We calculated at-risk areas for every position experienced by each patient, as well as for how long these particular skin

Table 1. Patient demographics and Braden score data. These data represent mean ± standard deviation for demographic and Braden score data for study cohort and for supine-left-right (SLR) group.

 = included in SLR group, BMI = body mass index, F = female, M = male.

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areas were at risk. At-risk areas could be located over any load-bearing tissue, such as the greater trochanter while laterally turned.

• Always-at-risk areas (centimeters squared) are the skin areas at risk for >95 percent of the total observa- tion period, regardless of the number of positions experienced. We used >95 percent of the patient’s monitoring time rather than 100 percent to provide a more realistic representation of what the patients actu- ally experienced. For example, if a patient momen- tarily rolled to one side and then back during a recording, the pressure profile could indicate that spe- cific tissue areas were relieved, though just briefly.

• Triple-jeopardy areas (centimeters squared) refer to the same always-at-risk areas of skin that coincide in all three positions. This term only applies to the patients observed in all three distinct positions and to areas in the perisacral region.

• Peak pressure over time (millimeters of mercury) was calculated by averaging the peak interface pressure measurement of each pressure profile obtained over the duration of each position (supine, turned left, or turned right). This value demonstrates the constancy of the maximal pressures experienced, rather than just a one-time value experienced for 30 s of a 2 h time period.

Data Analysis We used MATLAB (MathWorks; Natick, Massachu-

setts) and Excel (Microsoft; Redmond, Washington) to image, align, analyze, compile, plot, and compare the interface pressure data. Each pressure profile provided the interface pressure (millimeters of mercury) at each of the 2,304 discrete sensors. We determined peak interface pressures and confined them to the tissues surrounding the perisacral area, buttocks, and greater trochanters. We also calculated the skin areas that were subjected to various pressure thresholds over time. In addition to the 32 mm Hg threshold, we also analyzed the data using more strin- gent at-risk area interface pressure thresholds of 40 and 50 mm Hg, an increase of 25 and 56 percent, respectively.

We used the pressure profiles of the various positions obtained for each patient to determine how repositioning affected the patients’ interface pressures. We anatomi- cally aligned the pressure profile images by maximizing normalized two-dimensional cross-correlation, as con- ducted in previous work [42], and then adjusted them fur- ther, if necessary, by visual inspection to ensure that skin

areas from one position were compared with the same skin areas of another position. We used a one-sample Wilcoxon signed rank test to test the hypothesis that the triple-jeopardy area was not zero. Wilcoxon rank sum and signed rank tests were used, as appropriate, to com- pare interface pressures, at-risk areas, and triple-jeopardy areas between positions. We also compared these at-risk patients with the nondisabled subject findings from Peterson et al. [42] using similar statistical techniques; we considered p < 0.05 significant.

RESULTS

Pressure Profiles and Patient Positioning We recorded a total of 15,784 pressure profiles from

more than 131 h of patient monitoring; each patient was monitored an average of 5.7 ± 1.0 h. We could not ana- lyze some of the pressure profiles (<8%) because data were recorded during patient repositioning or because the perisacral area had moved off the sensor array. After removing these profiles, we analyzed 14,527 pressure profiles from 121 h of monitoring. The SLR group con- sisted of 8,028 profiles from 66.9 h of monitoring time.

Table 2 shows the specific positions observed for each patient. We recorded the HOB elevations for each of the positions periodically throughout the study. For the supine position, the average HOB elevation was 30° (range: 15–65°); for the turned-left position, the average HOB elevation was 26° (range: 18–40°); and for the turned-right position, the average HOB elevation was also 26° (range: 15–45°).

Interface Pressures and At-Risk Areas The peak interface pressures, peak pressures over

time, and at-risk areas did not differ significantly by posi- tion (Table 3). However, on an individual basis, the peak interface pressures and specific areas of at-risk skin were susceptible to significant changes upon patient reposi- tioning. For example, the peak interface pressures for one patient upon being turned to the left from a supine posi- tion increased nearly threefold due to shifting of the patient’s body weight directly over the greater trochanter (Figure 1).

Always-at-Risk and Triple-Jeopardy Areas All 23 patients demonstrated always-at-risk areas,

with a mean always-at-risk area of 206 ± 182 cm2 (Table 2).

Patient Positions No. of Positions Always-at-Risk Area (cm2) Triple-Jeopardy Area

(cm2) 1 R, L, R, L 4 297 — 2 R, L 2 5 — 3 S, L 2 469 — 4 S, L, R, L 4 8 8 5 S, L, S 3 73 — 6 S, R, S, L 4 108 108 7 S, L, R 3 119 119 8 S, L 2 169 — 9 S 1 261 —

10 R 1 247 — 11 S, R, L, R 4 110 110 12 R, S, L 3 456 456 13 S, R, L 3 613 613 14 S, Sit, S, R 4 516 — 15 S, L 2 427 — 16 R, L, R, L 4 105 — 17 S, L, S, R 4 76 76 18 R, S, L 3 15 15 19 R, L, R, S 4 195 195 20 S, L, R 3 248 248 21 S, R, L 3 2 2 22 S, L, R 3 15 15 23 S, L, R 3 194 194 Mean ± SD — 3.00 ± 0.95 206 ± 182 166 ± 184

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Accordingly, all 13 patients in the SLR group demon- strated triple-jeopardy areas as well and had a mean tri- ple-jeopardy area of 166 ± 184 cm2 (Table 2). These unambiguous results support our hypothesis that bedrid- den, at-risk patients do demonstrate a triple-jeopardy area (SLR group, p < 0.001) or always-at-risk area (all patients, p < 0.001). To view the areas of skin that were always-at-risk and for how long, we compiled the at-risk areas from every pressure profile from each patient’s entire monitoring period. Figure 2 illustrates the typical interface pressure profiles for the three different positions and how the at-risk skin areas were affected over time.

We also analyzed the data with more stringent inter- face pressure thresholds. At 40 mm Hg, 18 of 23 patients (9 of 13 in SLR group) had always-at-risk areas, and at

50 mm Hg, 10 of 23 patients (3 of 13 in SLR group) still had always-at-risk areas. Since the at-risk patients dif- fered in age, Braden score, and body type, we also ana- lyzed the data to see whether any of these factors affected the results. However, no trend emerged upon analyzing always-at-risk or triple-jeopardy areas with respect to age, height, weight, BMI, or Braden score.

DISCUSSION

Regular q2h repositioning of patients is the standard of care that is routinely implemented to reduce the risk of pressure ulcer formation. Our results clearly demonstrate that bedridden, at-risk patients have substantial areas of

Table 2. At-risk patient positions observed and corresponding always-at-risk and/or triple-jeopardy areas.

Note: In “Sit” position, head of bed was 65°. L = left, R = right, S = supine, SD = standard deviation.

Peak Interface Pressures (mm Hg) PositionSupine Left Right At-Risk Patients with HOB Elevation Peak Pressures*† 122.5 ± 45.1 134.2 ± 43.7 119.8 ± 33.8 Peak Pressures Over Time* 99.1 ± 34.3 99.5 ± 30.0 88.9 ± 17.1 Nondisabled Subjects — 69.2 ± 12.8 64.8 ± 9.1 Supine Measurement Prior to Turning to 

Left Side 68.6 ± 19.5 — —

Supine Measurement Prior to Turning to  Right Side

65.8 ± 11.7 — —

Turned with 30 HOB Elevation — 84.5 ± 17.5 80.4 ± 11.4

At-Risk Areas (cm2) PositionSupine Left Right At-Risk Patients with HOB Elevation‡ 716 ± 290 742 ± 304 744 ± 287 Nondisabled Subjects — 468 ± 151 434 ± 147 Supine Measurement Prior to Turning to 

Left Side 470 ± 170 — —

Supine Measurement Prior to Turning to  Right Side

480 ± 170 — —

Turned with 30 HOB Elevation — 569 ± 192 558 ± 159 Triple-Jeopardy and Always-at-Risk

Areas (cm2) Triple-Jeopardy Area Always-at-Risk Area

At-Risk Patients 166 ± 184 206 ± 182§ Nondisabled Subjects 60 ± 54 —

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skin that do not get relieved and remain at risk despite repositioning by experienced nurses. This observation was not isolated to only a few patients—all 23 patients monitored in this study demonstrated always-at-risk areas. We monitored patients for approximately 6 h con- secutively, and they had specific skin areas that remained at risk during the entire observation period. Based on these results, we can reasonably assume that these skin areas are at risk for the majority of time a patient is bed- ridden. These results mirror those of the nondisabled sub- ject study that first described the triple-jeopardy area phenomenon [42] and confirm that at-risk patients also have substantial always-at-risk skin areas despite routine repositioning.

Since there is no widely accepted value for an inter- face pressure threshold for tissue risk or damage, we also

used more stringent interface pressure thresholds. Upon evaluation with greater interface pressure thresholds, the results revealed that always-at-risk areas and triple-jeopardy areas still continued to exist in a significant subset of at- risk patients, which suggests that the current standard of care is not sufficient. However, of the patients that dem- onstrated an always-at-risk area, the fraction of those patients that were from the SLR group decreased as the interface pressure thresholds increased. Furthermore, the mean always-at-risk area was less for the SLR group (tri- ple-jeopardy area) than for the overall study population as a whole. These results provide objective support that routine patient repositioning, when done properly, reduces always-at-risk areas, which should, in turn, reduce pressure ulcer risk. Accordingly, future studies are needed to assess whether patients with always-at-risk

Table 3. Comparison of interface pressure (mm Hg), at-risk areas (cm2), triple-jeopardy areas (cm2), and always at-risk areas (cm2) between patients at risk for pressure ulcer formation and nondisabled subjects. Data presented as mean  standard deviation, and all measurements were taken on same brand of modern hospital bed. Nondisabled subject data from Peterson et al. [42].

*At-risk patient values were significantly larger than nondisabled subjects for corresponding supine and laterally turned positions (p < 0.001). †At-risk patient values were significantly larger than nondisabled subjects for corresponding turned with HOB elevation positions (p < 0.001). ‡At-risk patient values were significantly larger than nondisabled subjects for corresponding supine and laterally turned positions (p < 0.003). §At-risk patient values were significantly larger than nondisabled subjects (p < 0.006). HOB = head of bed.

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areas are more likely to develop (1) pressure ulcers, (2) more severe pressure ulcers, and/or (3) pressure ulcers at these specific

Figure 1. Interface pressure changes by position. Peak interface pressures over time are displayed for two different patients. Peak pressures were located around perisacral area and greater trochanters. Repositioning at times resulted in large sustained changes in peak pressures (bottom graph) but not always (top graph). (a) Peak interface pressures for patient 6 initially in supine posi- tion, turned right at minute 7, supine at minute 210, and turned left at minute 325. (b) Peak interface pressure for patient 18 initially turned right, supine at minute 147, and turned left at minute 268.

tissue locations. Despite the standard of care (q2h), repositioning

intervals varied between patients (Table 2, “Positions”) and none was effective in relieving all at-risk tissue areas. For example, two patients were not repositioned during

the entire monitoring period. It was not clear why the repositioning procedures were different, but we believe our observations mirror typical interoperator reposition- ing technique differences. All the same, it may not matter exactly how repositioning is accomplished, but rather that the at-risk tissue gets relieved regularly from pres- sure. To put our observations in perspective, the average always-at-risk area was over 200 cm2; therefore, an area one-third the size of an 8.5 × 11 in. sheet of paper is not getting relieved and remains at risk for pressure ulcer for- mation. Hence, future research is needed to establish how pressure mapping, implemented as a patient monitoring device or as a means to educate caregivers to improve their repositioning techniques, can further reduce or elim- inate high skin-bed interface pressures, at-risk areas, and always-at-risk areas (including triple-jeopardy areas) in at-risk patients to reduce pressure ulcer risk.

We are not aware of any prior work examining the interface pressures of a cohort of patients during an inter- val of care that covers the spectrum of positions experi- enced by patients who typically have the highest prevalence of pressure ulcer formation. Comparing the at-risk patients of this study with nondisabled subjects [42] (for values and statistical significance, see Table 3), we found the peak interface pressures were 49 to 59 per- cent and 85 to 94 percent higher for the at-risk patients than for nondisabled subjects, with and without HOB ele- vation, respectively. The peak pressures over time of at- risk patients were 11 to 18 percent and 37 to 51 percent greater than the peak pressures of nondisabled subjects, with and without HOB elevation, respectively. The at-risk areas were 30 to 33 percent and 52 to 71 percent larger for the at-risk patients than nondisabled subjects in the supine and laterally turned positions, with and without HOB elevation, respectively. The triple-jeopardy and always-at-risk areas were also considerably larger for the at-risk patients than for nondisabled subjects, 277 and 343 percent, respectively. Perhaps due to pain, frailty, medical condition, or the reservation of nurses to not dis- turb the patient too much, bedridden at-risk patients experience higher interface pressures and larger at-risk and always-at-risk areas (including triple-jeopardy areas) than nondisabled subjects. These results that demonstrate at-risk patients have higher interface pressures than non- disabled subjects are consistent with data reported by Berjian et al. [43].

Our study had a few limitations. First, tissue interface pressures do not directly measure internal tissue and cap- illary pressures. We are not implying that an at-risk area

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is ischemic, but we feel these areas are at-risk due to ele- vated interface pressures. Moreover, interface pressure mapping is currently the best noninvasive method to measure pressures applied to the skin. The use of peak interface pressures has been reported to be unreliable for test-retest scenarios [44], but this did not affect our always-at-risk and triple-jeopardy results. Second, patient shifting and/or raising the HOB could result in a patient moving off the sensor array, generating unusable pressure profiles

Figure 2. Interface pressure profiles by position and triple-jeopardy areas. (a) Typical perisacral interface pressure profiles from one intensive care unit patient; color bar is in millimeters of mercury with color denoting at-risk areas. (b) Total amount of triple-jeopardy (always-at- risk) area. (c) Schematic of patient lying in bed on pressure sensor. Pressure profiles should be viewed as if you are facing patient. (d) Amounts of time specific areas of skin were at risk across all positions experienced by patient. Color bar indicates time (in hours) that specific skin areas were at risk. Areas at risk for maximal amount of time (dark red) were always at risk and never relieved.

(<8% of total data collected). However, active movements (absent shear) are likely beneficial because they redistribute the patient’s weight similar to nondisabled people, for example, when shifting weight

while sitting in a chair. Third, we anatomically aligned patient interface pressure profiles when necessary to ascertain that specific areas of skin were correctly tracked over time. We needed alignment for half of the patients we observed. This adjustment, or any patient movement, could have led to minor errors in tracking specific skin areas, but we found no significant difference in triple-jeopardy or always-at-risk areas between patients who had their pressure profiles aligned compared with those who did not. Last, we placed the sensor array beneath the patient’s underpads to protect it from the patient and additional contaminants and so that it would not be used in place of the underpads to help lift and reposition the

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patient. The underpads may aid in slight pressure relief, thus resulting in lower measured pressures.

CONCLUSIONS

Bedridden patients at risk for pressure ulcer forma- tion exhibit high skin-bed interface pressures and specific skin areas that are likely always at risk (i.e., triple-jeopardy and always-at-risk areas) for the vast majority of the time patients are in bed despite routine repositioning care. Healthcare providers are unaware of the actual tissue- relieving effectiveness (or lack thereof) of their reposi- tioning interventions, which may partially explain why pressure ulcer mitigation strategies are not always suc- cessful. Relieving at-risk tissue is a necessary part of pressure ulcer prevention, but the repositioning practice itself needs improvement. Further research is needed to determine how pressure mapping can be used to develop better patient repositioning techniques and improve at- risk tissue pressure relief to help prevent pressure ulcer formation.

ACKNOWLEDGMENTS

Author Contributions: Study concept and design: M. J. Peterson, N. Gravenstein,  W. K. Schwab, J. H. van Oostrom, L. J. Caruso. Data collection: M. J. Peterson, W. K. Schwab, L. J. Caruso. Data analysis: M. J. Peterson. Data interpretation: M. J. Peterson, N. Gravenstein, W. K. Schwab,  J. H. van Oostrom, L. J. Caruso. Drafting of manuscript: M. J. Peterson. Critical revision of manuscript for important intellectual content:  M. J. Peterson, N. Gravenstein, W. K. Schwab, J. H. van Oostrom,  L. J. Caruso. Financial Disclosures: The authors have declared that no competing interests exist. Funding/Support: This material was based on work supported by the Department of Anesthesiology, University of Florida College of  Medicine; J. Crayton Pruitt Family Department of Biomedical  Engineering, University of Florida College of Engineering; Shands Hospital, University of Florida College of Medicine; and Health  Services Research & Development/Rehabilitation Research &  Development Center of Excellence, James A. Haley Department of Veterans Affairs Medical Center. Additional Contributions: This work was presented in part at the 2010 National Patient Safety Foundation Patient Safety Congress, Orlando, Florida (May 17–19, 2010), and the NPUAP Biennial Con- ference, Las Vegas, Nevada (February 25–26, 2011). Dr. Peterson is now with the Health Services Research & Development/Rehabilita-

tion Research & Development Center of Excellence, James A. Haley Department of Veterans Affairs Medical Center, Tampa, Florida. Institutional Review: This study received institutional review board approval and all patients or their proxies provided informed consent. Participant Follow-up: The authors have no plans to inform the par- ticipants of the publication of this study. Disclaimer: The contents of this manuscript are those of the authors alone and do not represent the views of the Department of Veterans Affairs, the University of Florida, or the U.S. Government.

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Submitted for publication March 5, 2012. Accepted in revised form September 10, 2012.

This article and any supplementary material should be cited as follows: Peterson MJ, Gravenstein N, Schwab WK, van Oostrom JH, Caruso LJ. Patient repositioning and pressure ulcer risk—Monitoring interface pressures of at-risk patients. J Rehabil Res Dev. 2013;50(4):477–88. http://dx.doi.org/10.1682/JRRD.2012.03.0040

ResearcherID/ORCID: Johannes H. van Oostrom, PhD: B-1407-2008

This content is in the Public Domain.

This content is in the Public Domain.