Pressure ulcer formation is a complex process that is still not clearly understood despite years of research. While the amount, duration and frequency of the applied pressure, the soft tissue’s response to loading, and the role of shear and/or friction are crucial, individual patient characteristics need to be assessed as well. Intrinsic factors such as diagnosis, history of previous tissue breakdown or surgical repair, body build, posture, muscle atrophy, nutritional status as well as magnitude and distribution of interface pressures must be considered. Extrinsic factors are also important including number of hours sitting or lying in wheelchair or bed, types of activities performed while sitting, level of functional independence, type of wheelchair, cushion and bed surface used and the support surface microenvironment, environment (climate, continence, temperature), finances; family/caregiver support; living arrangements and ease of follow up (Krouskop et al. 1983; Garber et al. 2007; Fleck & Sprigle 2007; Reger et al. 2007).
Observational study is the typical method of identifying risk factors. The analytical methodology used for each study is highly variable and makes for difficult comparisons between studies. Typically risk factors are categorized into demographic (e.g., sex, age, education, occupation, marriage), physical/medical (e.g., SCI factors, nutritional status, co-morbidities, mobility, pressure ulcer history, bowel/bladder incontinence/moisture, sensory perception, body build), and psychosocial factors such as mental status, social support, living conditions and financial status. Marin et al. (2013) conducted a systematic review and identified that clinical (e.g., spinal lesion characteristics, pre-existing history of pressure ulcers) and functional (e.g., independence in pressure ulcer management) aspects serve as risk factors specific to the SCI population compared the general population.
Many studies have found that those most likely to develop pressure ulcers fall into a typical demographic population: males who have lower levels of education and are unemployed (Byrne & Salzberg 1996; Schryvers et al. 2000; Ash 2002; Richards et al. 2004). Eslami et al. (2012) identified that lack of an intimate partner predisposed males with lower education and longer post-SCI periods to pressure ulcers.
Physical and medical factors include the biggest range of identified factors. Verschueren et al. (2011) found that the strongest risk factor for pressure ulcer occurrence was having had a pressure ulcer during acute rehabilitation; further, they noted that this is not addressed in any of the seven pressure ulcer assessment scales reviewed, including those widely adopted such as the Braden, Norton and Waterlow. Garber et al. (2000) suggested that having a pressure ulcer in the previous three years raises the risk of a subsequent ulcer, especially if the patient is younger at the age of SCI onset and self-reports as being at higher risk. Other physical/medical risk factors that have been identified most often include limitation in activity and mobility, injury completeness, moisture from bowel and bladder incontinence, lack of sensation, muscle atrophy, poor nutritional status and being underweight (DeLisa & Mikulic 1985; Salzberg et al. 1996; Krause et al. 2001). Body build, as reflected by fat infiltration, scar tissue within muscle and fat, and spasticity were considered by Sopher et al. (2011) to be risk factors for pressure ulcer development in individuals with SCI. Rabadi et al. (2011) found that only ethnicity (p=0.05) was significantly different between those with and without pressure ulcers, other than differences due to severity of the lesion. Guihan et al. (2008) suggested that difficulties for visual inspection on darkly pigmented skin may be a proxy for race, in general, as a risk factor. Gelis et al. (2009) also revealed an important difference to risk factors in the acute versus chronic care stages of SCI in that risk factors are mostly care-related in the acute SCI stage. Idowu et al. (2011) similarly found that lower nurse-patient ratios was a risk factor for pressure ulcer development and suggested an optimum ratio of one nurse to three patients. This is in contrast to the ratio of one nurse to seven patients that resulted in 50% of patients developing pressure ulcers after admission into a neurosurgical trauma unit.
Other physical/medical risk factors include smoking (Lamid & Ghatit 1993; Salzberg et al. 1996; Niazi et al. 1997; Krause et al. 2001; Smith et al. 2008), number of comorbidities especially renal, cardiovascular, pulmonary disease and diabetes (Salzberg et al. 1996; Niazi et al. 1997; Ash 2002; Smith et al. 2008; Levi et al. 1995), residing in a nursing home/hospital (Byrne & Salzberg et al. 1996), autonomic dysreflexia (Salzberg et al. 1996), anemia and hypoalbuminemia (DeLisa & Mikulic 1985; Scivoletto et al. 2004), spasticity, a history of previous ulcers (Vidal & Sarrias 1991; Byrne & Salzberg 1996; Guihan et al. 2008), an increase in tissue temperature (Fisher et al. 1978), and race and ethnicity (Guihan et al. 2008; Saladin & Krause 2009). However, Rabadi et al. (2011) did not find that modifiable vascular risk factors such as hypertension, diabetes mellitus, hyperlipidemia and current smoking, were related to the prevalence of pressure ulcer presence in a group of 87 veterans with SCI. They further showed that the groups were similar for age, gender, age of SCI onset, or SCI duration.
Although some aspects of cardiovascular disease are considered modifiable, the absence of neurogenic control of vascular activity renders blood flow occlusion secondary to unrelieved pressure unmodifiable. This reduced vascular response has been shown to have a negative correlation to the Waterlow scale resulting in early tissue damage (Li et al. 2011). Jan et al. (2011) confirmed this unmodifiable vascular characteristic in people with SCI compared to nondisabled controls. Thomas (2010) further stated that despite pressure relief diligence, tissue perfusion dysfunction in SCI is an unmodifiable intrinsic risk factor that needs special attention for more effective interventions. Wilczweski et al. (2012) identified hypotension as the strongest predictor of pressure ulcers.
Psychosocial factors are likely the most difficult to monitor but are similarly important to consider for the prevention of pressure ulcers. For example, Gelis et al. (2009) point out that behavioural factors have a bigger impact on pressure ulcer incidence and prevalence in the chronic stage (especially post-discharge) from both the care-giver and patient perspective. This is a concept that follows on the findings from a structured educational initiative to improve pressure ulcer prevention in veterans with SCI (Garber et al. 2002).
Although Saunders et al. (2010) support the notion of race as a risk factor (Guihan 2008), Saunders et al. (2010) found that African Americans with SCI are at higher risk for pressure ulcer development when they fall in a lower income level. Similar populations in Canada are not subject to this risk factor likely as a result of universal healthcare (Noreau et al. 2009). Gelis et al. (2009) also reported a similar finding and attributed the primary risk factor to the differing social-medical characteristics (e.g., level of education, access to healthcare) as proxy for the race risk factor (e.g., being African American).
Even with the numerous risk factors associated with pressure ulcers post SCI, there is limited evidence that, with more understanding of these risk factors, a decrease in pressure ulcer incidence will occur (Salzberg et al. 1996).