Thirty-five studies were reported in the review: 20 randomised controlled trials (n= approximately 4,526); 13 experimental studies (n=258); one prospective study; and one retrospective study. Sample size ranged from 10 to 1,971 patients.
Study quality: 18 randomised controlled trials either had insufficient power or did not estimate the required sample size; 11 randomised controlled trials had unclear or inadequate randomisation; and four randomised controlled trials did not report baseline comparability of treatment groups. The sample size of laboratory studies was small (10 to 57) and nine such studies involved only healthy people.
Randomised controlled trials assessing effectiveness (15 randomised controlled trials, n=4,366)
One randomised controlled trial (n=600) reported a significantly lower incidence of pressure ulcers associated with alternating pressure air overlays compared to a standard hospital mattress (4.2 per cent versus 13 per cent, p<0.01). Seven of 10 studies reported no significant difference between alternating pressure air overlays or alternating pressure air replacements and different types of constant low-pressure mattresses; three randomised controlled trials reported that alternating pressure air overlays or alternating pressure air replacements were significantly more effective than constant low-pressure mattresses. Four randomised controlled trials compared different types of alternating pressure air mattresses (results were reported). One retrospective study reported that alternating pressure air replacements were more effective than standard hospital mattresses in reducing pressure ulcer in burns patients.
Experimental studies assessing contact interface pressure and blood perfusion (13 studies, n=258)
Two studies compared alternating pressure air mattresses versus standard hospital mattress; one reported significantly lower contact interface pressure with the alternating pressure air overlays and the other reported significantly higher tcPO2 with the alternating pressure air overlays. Four studies compared alternating pressure air mattresses with different constant low-pressure surfaces and seven studies compared different types of alternating pressure air mattresses; findings were inconsistent.
Comfort: Four randomised controlled trials compared alternating pressure air mattresses with constant low-pressure mattresses. Studies variously reported problems with hardness and noise (one study), few problems with either mattress (one study), no significant difference in comfort scores (one study) and more problems with alternating pressure air overlays compared to alternating pressure air replacements (one study). The authors stated that findings on comfort were inconsistent due to different types of mattresses used and outcomes reported. Results from other laboratory studies and randomised controlled trials that compared different types of alternating pressure air overlays were also reported.
Mechanical reliability and user errors were also reported in the review.