Study design. This intervention study was conducted from January 2011 to December 2013. Participants were followed from the time they began using an air mattress until hospital discharge or death.
Setting and participants. This study was conducted in an 832-bed university hospital in Japan. At this hospital, PU preventive care is provided in accordance with the guidelines of the Japanese Society of Pressure Ulcers by a PU control team that includes nurses certified in WOC care.17 All terminal-stage cancer patients referred to a palliative care team for pain were invited to participate and were considered eligible for participation if they were at least 20 years old, had a Japan Coma Scale (JCS)27 score of I, and a Glasgow Coma Scale (GCS)28 score >15. Patients who refused to provide consent or had an existing PU were excluded. All procedures, from participant eligibility and selection to completion of randomization, were performed by the researchers.
Randomization and blinding. The participants were randomized to the intervention group or the control group by one of the researchers using an alternate randomization schedule.
Blinding was difficult because participants could identify the type of air mattress by removing the bedsheet, and nurses could identify the type when setting up the air mattress. Therefore, after consent to participate in the study was obtained, patients were given an explanation of the type of air mattress they would be using. Once enrolled, participants were given a unique identification number to ensure anonymity.
Intervention. The air mattress used in the intervention group was an alternating, exchange-type, dual-fit, air-cell mattress (NEXUS; Cape Co, Ltd, Kanagawa, Japan). The bottom part has a single layer base mat. The structure of the upper part consists of 24 air cells in a bottom supporting layer and an upper layer with 48 separated air cells. The accompanying pump has 2 pressure settings to adjust firmness that were controlled by a nurse. The amount of firmness is related to patient stability and movement in bed, movement while getting into and/or out of bed, and sitting on the bed; the firmness of the air cells is adjusted according to the user’s activity. The height of the mattress is 13 cm, including the base mat and upper layer of air cells.
The air mattress for the control group was an alternating, 2-layer overlay, air-cell mattress (TRICELL; Cape Co, Ltd Kanagawa, Japan), which has a standard mattress base. The upper part of the mattress consists of 24 integrated air cells in the top and bottom layers. This mattress has 1 setting for the accompanying pump to raise the internal pressure for firmness and stability. The height of the cells in the upper part of the mattress is 10 cm.
Procedure. Nurses at the study facility were provided basic knowledge and skills for PU prevention. Nurses on the study ward also received an explanation regarding mattress pressure adjustment using the accompanying pump before the start of the study, and the mattress manual was available at bedside. The researchers checked the mattress pressure adjustment once a day.
At the start of the study, participants were switched from the hospital’s usual thin foam mattress to the assigned air mattress. The air mattress pressure setting was based on the participant’s most recent weight and was adjusted as necessary to achieve an interface pressure in the sacral area of ≤40 mm Hg per manufacturer specifications and the standard value for mattress assessment for PU prevention in Japan.29
Data collection. Participant characteristics were collected at the start of the study from patient records and included age, gender, cancer diagnosis, treatment history (eg, chemotherapy and radiotherapy), presence of pain (Yes/No), pain numeric rating scale (NRS) rating (0 = no pain, 10 = the most intense pain30), performance status (PS) rating (0 = fully active; 4 = cannot carry out any self-care such as standing/sitting, bathing, and toileting; 5 = dead31), Palliative Performance Scale32 (PPS; a validated and reliable tool used to assess a patient’s progressive decline in functional performance), activity score rating (100% = normal activity with no evidence of disease, 0% = death), and body mass index (BMI). In addition, interface pressure29 in the sacral region as measured by the researcher using a multipad pressure evaluator,29 Braden Scale score33 (0 = low risk, 23 = high risk), and K scale34 rating (an assessment used in Japan; 0 = low risk, 6 = high risk) for PU risk were assessed and recorded. Data on the duration of air mattress use also were collected. Patients were assessed once a week by the researchers. The nurses and researchers determined whether PUs had developed. PU variables were assessed using DESIGN-R35 rating, where d0 = no particular skin lesion and no redness; d1 = persistent redness; d2 = lesion extends into dermis; D3 = lesion extends into the subcutaneous tissue; D4 = lesion extends to muscle, tendon, and bone; D5 = lesion extends into the articular or body cavity; and DU = it is impossible to measure the depth for the PU severity assessment.
For patients who developed a PU, information obtained included the Braden Scale score; presence of urinary incontinence, fecal incontinence, or a urinary catheter; interface pressure measured at the time of entry to the study, ulcer depth, and symptoms (eg, pain and/or redness, the latter assessed by the researchers and a WOC nurse).
Mattress comfort was assessed subjectively after the air mattress had been used. Pain was assessed every 24 hours as previously described. Researchers also interviewed the study participants about comfort using Yes/No questions from previous studies23,26 that addressed mattress noise, sinking into the bed, slipping on the bed, being affected by motion, sticky feeling, temperature, and feeling pressure from the air cells. Comfort related to activity was assessed by asking patients direct Yes/No questions about their experiences getting out of bed, getting into a sitting position, and walking to the bed and whether movement induced pain, unstable posture when moving, or a feeling of floating in the buttocks.
Outcomes. The primary outcome was development of a PU. The secondary outcome was air mattress comfort.
Data analysis. Survey data and responses to descriptive questions were entered into a spreadsheet. Scores on the Palliative Prognostic Index (PPI)36 were calculated based on PPS scores while noting the presence of edema, dyspnea at rest, and delirium. Participant characteristic numerical data were compared using the Mann-Whitney U test, and categorical data were compared using the chi-squared test and Fisher’s exact test. PU development data were compared using the chi-squared test and Fisher’s exact test, and ulcer depth was compared qualitatively using DESIGN-R.35 Comfort at rest and while moving was evaluated by comparing categorical data using the chi-squared test and Fisher’s exact test. Statistical analysis was conducted using JMP 11.0 software (SAS Institute, Tokyo, Japan). P <.05 indicated a statistically significant difference.
Ethical considerations. This study was approved by the ethical review board of the Kanazawa University Ethics Committee (No. 883). Any participant who developed a PU was promptly reported to his/her physician and certified WOC nurse, and appropriate measures were taken.