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Wound Care

Alternating Pressure Overlay for Prevention of Intraoperative Pressure Injury

Joseph, Jain; McLaughlin, Dylan; Darian, Vigen; Hayes, Lillian; Siddiqui, Aamir

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Journal of Wound, Ostomy and Continence Nursing: January/February 2019 - Volume 46 - Issue 1 - p 13-17
doi: 10.1097/WON.0000000000000497
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Pressure injuries are associated with increased morbidity, hospital stay, and health care costs. In 2009, hospital-acquired pressure injuries (HAPIs) accounted for $11 billion per year in direct and indirect costs; a 2016 study found that these injuries increased hospital costs by 44% per hospital stay.1–3 Reported incidence rates vary with higher rates noted in intensive care units (ICUs) and the operating room (OR).4–7 Patients undergoing longer surgeries are postulated to have a higher risk for development of perioperative HAPIs due to prolonged, unrelieved pressure on the skin.8 The length of the procedure, regardless of the type of surgery, is a major contributing risk factor for developing HAPIs.7,9,10 Limited options are available to either reposition patients or provide pressure relief during surgeries.11

The National Pressure Ulcer Advisory Panel (NPUAP) and the Wound, Ostomy and Continence Nurses Society have published evidence-based guidelines for pressure injury prevention.12,13 In addition, the Association of periOperative Registered Nurses (AORN) has a care bundle and risk assessment tools to increase awareness and identify problems.14–16 Nevertheless, off-loading the trunk is challenging and opportunities for active intervention such as turning and repositioning are limited in the surgical suite. Therefore, a novel alternating pressure (AP) overlay was developed to mimic the concept of cyclical off-loading without impacting the surgical procedure. The overlay uses a low-profile design (less than an inch in height when fully inflated) with AP technology to provide micropressure relief while minimizing shear in the intraoperative setting. We believe that effective redistribution of pressure by dynamic support surfaces may play a role in preventing perioperative HAPIs. The purpose of this study was to determine the effect of an AP overlay system when used in the OR to prevent pressure injuries among surgical patients. Patients with HAPIs temporally related to surgical intervention (occurring within 5 days of surgery) were tracked consecutively using the AP technology. The safety, ease of use, and unobtrusiveness of the technology were also evaluated.


We complete a prospective case series of patients paced in the AP overlay and compared their outcomes with an historical control group. The study setting was Henry Ford Hospital, an urban quaternary care hospital located in Detroit, Michigan. The study focused on the OR and the neurosurgery ICU. All work performed was in accordance with institutional review board (IRB) guidelines and carried out with the ethical standards set forth in the Helsinki Declaration of 1975. Study procedures were reviewed by Henry Ford Hospital IRB and deemed exempt from individual informed consent. The study was listed at (NCT02565797) as a research study. Patient information and privacy were protected in compliance with the Health Insurance Portability and Accountability Act of 1996.


Consecutive, nonemergency, neurosurgical procedures meeting inclusion criteria were included. Our inclusion criteria were a planned surgical time longer than 2 hours, postoperative inpatient admission to the ICU, and supine positioning during surgery. Exclusion criteria were intraoperative magnetic resonance imaging (MRI) or computed tomographic scanning, patients younger than 18 years, and procedures requiring repositioning during surgery. The study was conducted over a 23-month period from January 2016 through November 2017. Results were compared to a historical control group (meeting the same inclusion and exclusion criteria) during the prior 2 years (January 2014 to December 2015) at the same institution.


The low-profile AP support system distributes the patient's weight across small nodal points of alternating contact (Dabir Micropressure Operating Table Surface; Dabir Surfaces, Chicago, Illinois). The AP overlay incorporates hundreds of patient support nodules (bulbs) arranged in rows that periodically inflate with air (Figure 1). Alternate rows are interconnected such that the overlay has 2 zones that are inflated alternatively. The inflation/deflation of the rows is computer controlled and provides temporary localized micropressure relief to body areas lying above deflated nodules. The AP overlay was placed on the OR table pad prior to the start of the surgery (Figure 2).

Figure 1.
Figure 1.:
Alternating pressure support surface. The surfaces achieve alternating support and relief utilizing independent rows of small comfort nodes. The alternating rows inflate and deflate. The inflated nodes support the body and the deflated nodes result in pressure relief. The pattern then reverses at a preprogrammed interval.
Figure 2.
Figure 2.:
Alternating support surface placed over an OR table. Support surface is placed above the OR pad and below the cover sheet. The controller unit is connected to the overlay and can be placed outside the operative field if necessary. AP indicates alternating pressure; OR, operating room.

Once the patient was in position, the AP overlay was turned on in the low-inflation and low-cycle speed (5 minutes on for each zone) setting and used throughout the surgical procedure. All team members received training concerning use of the device. Training was provided for both the perioperative team and the ICU team with in-person in-service programs for all shifts. The AP system was monitored during the procedure by the OR staff and the study coordinator (L.H.). Software audits of all devices for use and safety were performed regularly by the manufacturer.

All patients were examined preoperatively and tracked through their hospital stay. Preoperative skin check to document the absence of preexisting pressure injury was performed by the preoperative care nurse. All patients were transferred postoperatively directly to the ICU. As part of usual nursing assessment, all patients were evaluated every shift via a skin survey performed by the unit staff nurse. At-risk areas were assessed daily for pressure injuries based on NPUAP guidelines.12 The Braden Scale for Pressure Sore Risk was used to stratify low- and high-risk patients requiring additional monitoring and skin care plus off-loading (Braden Scale score >12).17 The Braden Scale was chosen in order to allow comparison to the historical control population. This information was recorded in the electronic medical record and transferred to the research database by the study coordinator.

Data Collection

Demographic and risk factor data were abstracted from the electronic medical records. These included age, gender, weight, body mass index, Braden Scale score on postoperative day 1, history of tobacco use, diabetes mellitus, paralysis, nutrition consult, duration of surgery, type of surgery, use of OR pads and warming blankets, and history of previous pressure injury. Patients were evaluated daily for pressure injuries postsurgery, with the perioperative pressure injury period being defined as up to 5 days postsurgery. The time the AP overlay was turned on and off was recorded. A questionnaire developed specifically for this study was given to all members of the care team involved in the study population. The questionnaire was designed to determine workflow changes, documented or undocumented morbidity, unintended consequences, and elicit general feedback. The questionnaire was completed in writing, electronically via e-mail, and verbally in person. The questionnaire was given at the completion of the study. Retrospective data were collected on consecutive patients with similar selection criteria from the prior 2 years using the electronic health record. All study data were recorded and stored on a secured and safe computer per IRB requirements.

Sample Size

An adaptive clinical trial process was employed for calculating the sample size. The adaptive design uses accumulating data to decide on how to modify aspects of the study without undermining the validity and integrity of the trial. Based on a historical pressure injury incidence rate of 6% in the target population, and an assumed reduction of 50% (3% incidence) in patients undergoing surgery with the AP overlay, initial sample size calculations indicated the need for 400 patients in the historical control group and 200 patients in the AP group (2 to 1 proportion). Interim analysis of the AP group data (at n = 80) indicated that the incidence rate in the AP group was 0%. As part of the adaptive design, the sample size was recalculated using χ2 statistics (α= .05, β= .20) for an incidence rate of 6% in the historical control group and 0.05% in the AP group. A 3 to 1 proportion was used for sample size allocation. The recalculated sample size (without continuity correction) was 292 patients in the historical control group and 100 patients in the AP group. This revised sample size assumed 18 pressure injuries in the historical control group and no pressure injury in the AP group. The analysis presented in this study is based on the revised sample size.

Data Analysis

Categorical data are presented as counts and percentages, whereas continuous data are presented as means and/or medians, standard deviations, and ranges. Analyses were based on admissions (as compared to individual patients); no adjustments were made for patients with multiple admissions. The proportion of patients in each group with pressure injuries was analyzed by the χ2 test. All data were analyzed by using SAS 9.2 software (SAS Institute Inc, Cary, North Carolina), and statistical significance was set at P less than .05.


Three hundred ninety-two patients (292 in the historical control group and 100 in the AP group) were entered into the study based on selection criteria. Demographic factors were compared for the historical control and AP groups and found to be similar (Table).

TABLE. - Comparison of Baseline Demographic and Clinical Factors
Overlay Group Control P
Number of patients 100 292
Age 58 ± 14 59 ± 12 .492
Male gender 54% 52% .737
Body mass index 30 ± 8 29 ± 9 .325
Tobacco use 19% 23%
American Society of Anesthesiologist physical status classification score 3 ± 1 3 ± 1 1.000
Surgery duration, h 3.8 ± 1.2 3.9 ± 1.1 .444
NICU days 2.2 ± 0.6 2.4 ± 1.2 .111
Mean Braden Scale postoperative day 1 16 ± 2 16 ± 2 .692
History of spinal cord injury 32% 26% .249
History of previous pressure injurya 14% 2% .002
Perioperative HAPIa 0 18 .001
Abbreviations: HAPI, hospital-acquired pressure injury; NICU, neonatal intensive care unit.
aP < .05.

Clinical characteristics were also compared for the 2 populations (Table). The 2 populations were similar in regard to potential pressure injury risk factors. There was statistically significant higher incidence of a history of previous pressure injury in the control group. In addition, there were no significant differences between the 2 groups for use of warming blanket, type of OR pad, use of general anesthesia, core temperature, hypotension, serum albumin, OR position, use of microclimate beds postoperative, incontinence, and history of diabetes mellitus.

No patients in the prospective AP group developed a perioperative HAPI during the study, whereas 18 HAPIs occurred in the historical control group. Specifically, there were 10 stage 1, 7 stage 2, and 1 stage 3 perioperative pressure injuries (per NPUAP staging guidelines) in the historic group (n = 292). This difference was statistically significant (0% vs 6%, P = .004).

Forty-eight members of the care team were asked to complete the study questionnaire, representing a 75% response rate (Figure 3). Over 80% of respondents agreed that they were adequately trained and the device functioned as intended. Six respondents (14%) identified questions about fitting the support surface to the OR table. These concerns were referred to the coordinator who rectified the issues. The broad opinion of the group was positive. They were appreciative to have an intervention that could influence pressure injury occurrences in the OR. Technical and operational issues with using the AP overlay system in the OR were monitored by the study coordinator. There were no device failures, and discussion with the caregivers and the OR support staff indicated no difficulties or concerns regarding the AP overlay. We also evaluated unintended consequences from use of the AP overlay technology and found no increase in morbidity, length of stay, or readmission in the AP group.

Figure 3.
Figure 3.:
Questionnaire for the health care team regarding use of the alternating pressure overlay.


Significantly fewer patients placed on the AP overlay experienced HAPI when compared to the historic comparison group. Responses to a brief questionnaire administered found that the AP overlay was not considered intrusive by the support staff or surgeons. In addition, there were no complaints related to workflow, interference with other technologies, or difficulty with use. We assert that staff engagement and education were integral to the success of this study, as knowledge deficits in pressure injury prevention are significant hurdles in enacting successful initiatives.18 Multiple staff members stated they were encouraged by the fact that the OR staff could have a positive impact on HAPIs in the OR. It is possible that increased focus and education may have contributed to the improved outcome, beyond just the technology.

We compared these outcomes with a historical control cohort regarding perioperative complications, surgery time, and wound complications. We found no evidence of increases in morbidity, OR time, or infection for the AP group.

Identifying pressure injuries as related to a surgery can be challenging. They do not manifest in the OR, and their attribution must be deduced. If a patient develops an HAPI, care providers must retrospectively examine a period of 24 to 72 hours for likely contributing factors. Such a period of confinement may include an acute period of immobility at home due to trauma or unconsciousness, a prolonged period of immobility related to change in health status, loss of a caregiver, a prolonged emergency department stay, and testing or treatment requiring sedation or immobilization (such as cardiac catheterization, MRI). If timing and location make it more likely, then the OR can be considered the likely source for the HAPI. Nevertheless, this manner of reverse engineering makes it difficult to be completely confident regarding the origin of surgery-related HAPIs. These challenges in attribution probably contribute to the variability in published incidences that range from 5% to almost 40%.19–23 In addition, postoperative prevention bundles partially rely on validated scales for assessing pressure injury risk such as the Braden Scale for Pressure Sore Risk that do not consider intraoperative factors such as surgical time and positioning. The retrospective nature of this study makes it difficult to clearly identify any such confounding factors for surgery-related HAPIs. All patients with HAPI identified in the control group did undergo surgery within 72 hours of identifying the pressure injury.

The AORN has developed a focused and evidence-based program for pressure injury prevention in the OR setting.14 This is an important step toward better understanding the problem and developing treatment options. This program and the care bundle focus on appropriately padding as much as possible prior to the procedure and off-loading as much as possible after the procedure. Clinicians have comparatively limited opportunity for active intervention during many surgical procedures. The AP overlay system evaluated here is one of the few options available for actively managing pressure on the support surface during surgery. Other pressure redistribution systems have been adapted for use in the OR. Additional research on the optimal strategy for pressure injury prevention in the OR is necessary including comparative effectiveness studies.


To our knowledge, this is the first study to examine low-profile AP technology in an OR setting. Limitations of the study include lack of randomization to a treatment or comparison group. Based on study selection criteria, only 30% of patients undergoing neurosurgical surgical procedures qualitied for study participation. In an effort to maximize device use within the surgical department, we felt it important to use all appropriate cases for this study. Therefore, we elected to use historical controls as an appropriate method for comparison. Future studies will need to look at concurrent control subjects or a randomized clinical trial design to account for any changes in clinical protocol and care in the intraoperative or perioperative period. The Braden Scale was used to stratify pressure injury risk in our study. Other tools such as Scott Triggers may be better suited for the OR.24 We decided to use the Braden Scale in order to better compare the treatment group with our historical control group. Although we could have applied the Scott Triggers tools to the control group via the medical records, we were unable to retrospectively apply this instrument to our historic control group. We therefore selected consistency in our pressure injury risk scale to eliminate this confounding factor.


Study findings suggest that an AP overlay system can safely and reliably be used during neurological surgeries. It was also shown that using this AP product may improve outcomes with respect to perioperative HAPIs, including patients evaluated to be at high risk for pressure injury development. The device functioned as expected, and there were no unintended consequences. Further studies are underway to evaluate the use of this AP overlay system beyond the OR for more comprehensive care.


Research support was provided by Dabir Surfaces, Inc, Chicago, Illinois.


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Critical care; Neurosurgery; Perioperative pressure ulcers; Pressure injury; Pressure ulcer; Quality improvement; Technological innovations

© 2018 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the Wound, Ostomy and Continence Nurses Society