the prevalence of pressure ulcers in the usa is about 25% ( 3 ) . in iran , pressure ulcers are usually developed secondary to insufficient blood supply , ischemia , and tissue necrosis over bony prominences . tissue necrosis happens due to the compression of soft tissue between bony prominences and external pressure ( 5 - 7 ) . moreover , pressure ulcers also increase the length of hospital stay and the health care costs ( 8 - 11 ) . since 1993 to 2006 , the prevalence of pressure ulcers in hospitalized adult patients has increased by 80% , imposing about us$11 billion on healthcare systems ( 12 ) . the cost of treating a pressure ulcer in the uk varies from  1064 ( stage i ulcer ) to  10551 ( stage iv ulcer ) and the total cost is about  1.4 - 2.1 billion a year . it is also estimated that pressure ulcers can increase the cost of nursing cares up to 50% ( 13 , 14 ) . one of the new interventions developed to treat pressure ulcers is transdermal or topical wound oxygen therapy ( twot ) . studies show that delivering oxygen directly to the wound site accelerates the angiogenesis , the collagen synthesis , the fibroblast growth processes , and suppresses the bacterial growth , which in turn facilitate tissue regeneration ( 3 , 15 , 16 ) . this method has several advantages , including fewer complications and lower costs and more safety ( 17 ) . despite the potential effects of twot on wound healing , therefore , there is a literature reporting the application of topical oxygen to heal wounds ( 15 ) , and the results of researches declared that twot positively affected the pressure ulcers healing process ( 18 - 20 ) or had less significant effect on healing the pressure ulcers ( 21 ) . although there were not such researches in iran ; and well - designed clinical trials are needed to prove this notion . the current study aimed to evaluate the effects of twot on the healing of pressure ulcers . it was a single - blind multi - center randomized controlled trial conducted in 2009 . a convenient sample of 100 adult patients hospitalized in two general state university - affiliated medical - surgical intensive care units and one neurology unit located in qazvin the inclusion criteria were being at least 18 years old with a stage ii - iv pressure ulcer , according to the university of texas wound classification system ( 5 ) , on the sacral or ischial areas . the exclusion criterion was having any kind of peripheral vascular diseases such as diabetes and mellitus - induced vascular complications . the coin - tossing method and block randomization technique ( five blocks and ten samples in each block ) were used to randomly assign the patients to either the control or the experimental groups . the participants consisted of 100 patients with pressure sore enrolled in the study based on convenient sampling method . one patient from the intervention group and two patients from the control group were excluded . patients or their families were blind for allocation ; therefore , it is a single blind research . the sample size was calculated based on the prior studies considering 95% confidence level ; 80% power , d = 1 and  = 1.8 . the sampling formula was : patients in the control group received only the routine care of the study setting . patients in the experimental group received the routine care of the study setting in addition to twot . twot consisted of direct application of humidified high pressure ten liters per minute oxygen to the wound site for 20 minutes , three times a day for 12 days . this type of dressing was used to minimize wound site irritation and to promote patients comfort . all the interventions were implemented by a nurse holding b. sc . and experienced in wound care . the wound status the pressure ulcers scale for healing ( push ) was employed ( 22 , 23 ) . the validity and reliability of push were confirmed in previous studies ( 17 , 23 ) . wound status was assessed before and every 48 hours after the beginning of the intervention . accordingly , wound status was assessed seven times , i.e. , before the intervention ( t1 ) , as well as two days ( t2 ) , four days ( t3 ) , six days ( t4 ) , eight days ( t5 ) , ten days ( t6 ) , and twelve days ( t7 ) after the intervention . according to the average patient stay in the units ( 12 days ) and limited resources , the intervention was carried out for 12 days . and wound assessment was performed by two educated nurses . the statistical package for social sciences version 17.0 ( spss v.17.0 ; spss inc . , chicago , il , usa ) was employed for data analysis . to analyze the study data , descriptive statistics measures such as percentage , mean , and the study groups were compared in terms of the study variables by the independent - sample t - test , the binominal , and the chi - square tests . moreover , the repeated measures analysis of variance ( anova ) test was used to compare changes in the wound status across the seven assessment time - points . the effect of other variables such as gender , age and other confounding factors were transferred into the model . ethical consideration ( including plagiarism , research misconduct , data fabrication or falsification , redundancy , double submission , etc . ) the university - affiliated institutional review board and ethics committee approved the study ( no : k 2635/20/28 ) . finally , they were asked to read and sign the informed consent form of the study . the ethical code number and further ethical consideration is in irct website ( the registration number : irct138708051407n1 ) . a convenient sample of 100 adult patients hospitalized in two general state university - affiliated medical - surgical intensive care units and one neurology unit located in qazvin , iran were recruited . the inclusion criteria were being at least 18 years old with a stage ii - iv pressure ulcer , according to the university of texas wound classification system ( 5 ) , on the sacral or ischial areas . the exclusion criterion was having any kind of peripheral vascular diseases such as diabetes and mellitus - induced vascular complications . the coin - tossing method and block randomization technique ( five blocks and ten samples in each block ) were used to randomly assign the patients to either the control or the experimental groups . the participants consisted of 100 patients with pressure sore enrolled in the study based on convenient sampling method . one patient from the intervention group and two patients from the control group were excluded . patients or their families were blind for allocation ; therefore , it is a single blind research . the sample size was calculated based on the prior studies considering 95% confidence level ; 80% power , d = 1 and  = 1.8 . patients in the experimental group received the routine care of the study setting in addition to twot . twot consisted of direct application of humidified high pressure ten liters per minute oxygen to the wound site for 20 minutes , three times a day for 12 days . this type of dressing was used to minimize wound site irritation and to promote patients comfort . all the interventions were implemented by a nurse holding b. sc . and experienced in wound care . the primary outcome measure was the wound status . to assess the wound status the pressure ulcers scale for healing ( push ) was employed ( 22 , 23 ) . the validity and reliability of push were confirmed in previous studies ( 17 , 23 ) . wound status was assessed before and every 48 hours after the beginning of the intervention . accordingly , wound status was assessed seven times , i.e. , before the intervention ( t1 ) , as well as two days ( t2 ) , four days ( t3 ) , six days ( t4 ) , eight days ( t5 ) , ten days ( t6 ) , and twelve days ( t7 ) after the intervention . according to the average patient stay in the units ( 12 days ) and limited resources , the intervention was carried out for 12 days . and wound assessment was performed by two educated nurses . the statistical package for social sciences version 17.0 ( spss v.17.0 ; spss inc . , chicago , il , usa ) was employed for data analysis . to analyze the study data , descriptive statistics measures such as percentage , mean , and standard deviation were used . the study groups were compared in terms of the study variables by the independent - sample t - test , the binominal , and the chi - square tests . moreover , the repeated measures analysis of variance ( anova ) test was used to compare changes in the wound status across the seven assessment time - points . the effect of other variables such as gender , age and other confounding factors were transferred into the model . ethical consideration ( including plagiarism , research misconduct , data fabrication or falsification , redundancy , double submission , etc . ) was completely observed by the authors . the university - affiliated institutional review board and ethics committee approved the study ( no : k 2635/20/28 ) . finally , they were asked to read and sign the informed consent form of the study . the ethical code number and further ethical consideration is in irct website ( the registration number : irct138708051407n1 ) . totally , 100 patients , 50 patients ( males 48% and females 52% ) in the intervention group and 50 patients ( males 52% and females 48% ) , participated in the control group in the study ( figure 1 ) . the results of the independent - samples t - test and chi - square test showed that the control and the experimental groups did not differ significantly in terms of age , gender , previous history of cerebrovascular accident , level of consciousness , mobility , and baseline wound stage and wound area ( p value > 0.05 ; table 1 ) . data are presented as mean  sd . the result of the independent samples t - test . ( % ) . on the other hand , after 12 days of twot , the number of patients with complete wound healing , defined as complete epithelialization of the wound with the absence of drainage , in the experimental group ( sixteen patients ) was greater than that of the control group ( only one patient ) . the results of the binominal test revealed that this difference was statistically significant ( p value < 0.001 ) . moreover , the results of the repeated measure anova test for the within subjects factor of time showed that the wound area differed significantly across the seven assessment time - points in the experimental group ( p < 0.001 ; table 2 ) . however , the results of this test in the control group indicated that , the wound area did not differ significantly across the assessment time - points ( p value = 0.16 ; table 2 ) . data are presented as mean  sd . the result of the repeated measure test . the result of the independent samples t - test . on the other hand , the results of the independent - samples t - test showed that the study groups significantly differed in terms of wound area on sixth , eighth , and twelfth days ( p value < 0.01 ; table 2 ) . moreover , the results of this test revealed that the total mean of wound area in the experimental group was significantly lower than that of the control group ( p value < 0.001 ; table 2 ) . the current study aimed to evaluate the effects of twot on the healing of pressure ulcers . the study findings revealed that twot positively affected the pressure ulcers healing process . this finding is in line with the findings of the previous studies ( 3 , 4 , 24 - 26 ) . it was also found that the number of patients with complete wound healing was greater in the experimental group than the control group . tawfick and sultan also evaluated the effects of twot on the healing of venous ulcers and reported that 80% of the patients in the experimental group and only 35% of patients in the control group experienced complete wound healing ( 20 ) . evaluated the cost - effectiveness of transdermal oxygen therapy in the treatment of necrotic ulcers and reported that in the experimental group , the wound healing rate was significantly higher than that of the control group ( 19 ) . compared to the expensive wound management approaches , using a simple catheter to deliver oxygen to the wound site bears no considerable cost . therefore , transdermal wound oxygen therapy is a cost - effective method to treat pressure ulcers . however , further studies are still needed to provide more evidence on the effectiveness of transdermal wound oxygen therapy . therefore , conducting studies to assess the effect of twot on diabetic foot ulcers is recommended . moreover , the current study only assessed the effectiveness of twot in the healing of pressure ulcers located on the sacral and ischial areas . consequently , further studies are recommended to examine the effectiveness of twot to treat pressure ulcers located on the other parts of the body . finally , according to the relatively small sample size of the current study ,
background : although healthcare quality has considerably improved in many countries , pressure ulcer is still a major health challenge worldwide.objectives:the current study aimed to evaluate the effects of twot on the healing of pressure ulcers.patients and methods : this study was a randomized controlled trial , and the convenient sample including 100 patients hospitalized in two university - affiliated medical - surgical intensive care units and one neurology unit located in qazvin , 
 iran were studied . 
 patients with stage ii - iv pressure ulcer on the sacral or ischial areas were randomly assigned to either the control or the experimental groups . 
 the experimental group received a 12-day transdermal wound oxygen therapy . 
 wound status was assessed seven times before the intervention , as well as two , four , six , eight , ten , and twelve days after the intervention.results:after 12 days of wound oxygen therapy , the number of patients with complete wound healing in the experimental group was significantly greater than that of the control group . moreover , the total mean of wound area in the experimental group was significantly lower than that of the control group.conclusions:transdermal wound oxygen therapy can effectively promote wound healing in patients with pressure ulcers .