Pressure ulcers (PUs) have a significant impact upon patient morbidity–mortality and quality of life, and are a cause of concern for both the patients and their families, as well as for health professionals and healthcare systems. Pressure ulcers are commonly found at any healthcare level, particularly in patients with mobility problems and advanced age.1 Although the development of PUs is not intrinsically regarded as a cause of mortality during hospital admission, such lesions are associated to mortality and to other complications in the course of patient recovery: they increase the risk of infection and of in-hospital malnutrition, prolong hospital stay, increase the nursing care burden, and result in greater healthcare costs.2

Many incidence and prevalence studies have brought the problem into focus, but have been based on different indicator calculation methods, as well as on different inclusion and exclusion criteria. Patients admitted to the Intensive Care Unit (ICU) are at a high risk of developing PUs, with an incidence of between 3.3% and 52.9%.3,4 Such patients generally do not notice the increased tissue pressure or fail to react to it adequately because of sedation, analgesia and/or the use of muscle relaxants. Furthermore, the background disease and hemodynamic instability increase the risk of PUs.

Despite the magnitude of this healthcare problem, few studies have quantified the direct association between risk factors and the appearance of PUs, and some of the published articles are fundamented upon assumptions of a general nature.5 At present, ICUs use instruments for assessing the risk of PUs that have not been specifically developed for this care setting and therefore might not be adequate, since they do not take into account risk factors that are practically exclusive of such Units.6

The importance of the different aspects implicated in the appearance of PUs in critical patients is the subject of permanent controversy.5,7 It is therefore particularly important to examine the direct relationship between the risk factors and the appearance of PUs in these patients, with a view to establishing specific interventional measures. Although there are aspects upon which no direct or effective impact can be made, in some cases interventions targeted to a single element can modify the effects of the rest of the implicated factors.8

The aim of this systematic review is to identify the risk factors related to the appearance of PUs in critical patients admitted to the ICU.

A systematic review of primary studies has been carried out. The PRISMA Declaration was followed, and the review protocol was defined prior to data collection, with the purpose of reducing the impact of bias inherent to the authors and to promote transparency regarding the methods and the process.9 For the evaluation of methodological quality, we used the Critical Appraisal Skills Program España (CASPe) templates10,11 according to the type of study, with the aim of assessing the risks referred to screening, measurement, withdrawal or classification bias, as well as to confounding factors, outcome bias and other sources of bias. We selected those studies yielding a score of over 6. The studies with a score of between 6 and 8 were regarded as being of moderate quality, while those of over 8 points were taken to be of high quality.

A meta-analysis of the data was not possible, due to the heterogeneity of the designs, risk factors studied and results obtained. Since the primary objective was to identify these factors rather than to quantify the effect size of correlation to the development of PUs, we conducted a narrative synthesis in which the risk factors were categorized into domains and sub-domains, with identification of those included in the multivariate model and which were found to be statistically significant (p<0.05).

A total of 200 literature references were identified: 51 in PubMed, 102 in Scopus and 47 in WOS. After the review process, a total of 17 articles were found to meet the study inclusion criteria (Fig. 1).

Figure 1.

Study screening process.

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This systematic review shows the incidence of PUs in the ICU to be within the range 3.3–39.3%. The 17 studies included in the review evaluated an average of four risk factors for the development of PUs. The risk factors most frequently associated to the development of PUs were patient age, the length of stay in the ICU, diabetes, the duration of MBP <60–70mmHg, mechanical ventilation, continuous veno-venous hemofiltration or intermittent dialysis, vasoactive and sedative drug treatments, and postural changes.

The risk of PUs increases with age due to a number of reasons, such as reduced activity or mobility, diminished tissue tolerance and pain perception, or an increased presence of comorbidities.18,25 In 6 of the studies of our review (35.3%), patient age was identified as a risk factor for the appearance of PUs. Patients over 60 years of age were at greater risk. This evidence points to the need to incorporate patient age as a risk factor in the PU risk assessment scales.26,27

With the exception of one study18 (in which one of the inclusion criteria was the male sex), the different publications evaluated patient gender as a risk factor, with the identification of a statistically significant association in three univariate analyses20,21,24 and finally in two multivariate analyses.20,21 However, Ülker and Yapucu20 underscored that the data referred to gender must be interpreted with caution. In their study, gender as such did not pose a real risk, since the women were older than the men, and this could have caused the female population to be more vulnerable. In sum, there is little evidence to suggest that gender is a factor associated to the development of PUs.

The evidence is limited and controversial regarding the association between BMI and the development of PUs—correlations in some cases being reported with low BMI values, and with high BMI values or obesity in others. As an example, in the study published by O’Brien et al.,12 low weight was associated to the development of PUs in the multivariate analysis, while Tescher et al.3 found that patients with BMI <18kg/m2 had a 1.65-fold greater risk of developing PUs on the following day compared with patients presenting BMI 18–25kg/m2 (only in the univariate analysis). In contrast, in other studies,8,18 greater BMI was identified as a risk factor in the univariate analysis. Lastly, Catalá et al.14 considered BMI ≥40kg/m2 to be a confounding factor, since patients with morbid obesity required more days of mechanical ventilation.

In relation to the time factor, the longest stays in the ICU corresponded to the studies of Cremasco et al.21 and Yepes et al.,13 who recorded a greater incidence of PUs than in the studies of Sayar et al.22 and Cox,15 with shorter stays. In the study carried out by Cremasco et al.,21 the mean stay among the patients that developed PUs was 23.39 days, versus 9.40 days among those who did not develop ulcers. In the study of Yepes et al.,13 the mean stay among the patients that developed PUs was 21.18 days, versus 8.58 days among those who did not develop ulcers. In contrast, in the case of Sayar et al.,22 the mean stay among the patients that developed PUs was 14.05 days, versus 4.66 days among those who did not develop ulcers, and in the study published by Cox,15 the mean stay among the patients that developed PUs was 11.7 days, versus 3.3 days among those who did not develop ulcers. According to this latter study, 66% of the patients developed PUs within the first 6 days of stay.

With regard to the type of admission, and although little evidence is available, those patients admitted from the emergency room had a greater risk of developing PUs.17,24 The studies carried out to date do not allow us to establish whether medical or surgical admission can be regarded as a risk factor for the development of PUs. Admission of trauma patients as a possible risk factor yielded heterogeneous results, though most studies reported no correlation to the development of PUs.

In relation to vasoactive medication and sedation, the studies were heterogeneous in terms of the variables considered. Further studies are needed to define the relationship between the development of PUs and the type of vasopressor, its dosage and the duration of treatment. In some cases, two or three vasopressors are administered, and this could increase the risk of developing PUs.28 In the case of sedation, Nijs et al.7 found sedative use to act as a protective factor – this being consistent with the observations of Roca-Biosca et al.8 referred to the number of days of sedation. In contrast, Llaurado-Serra et al.23 identified sedation as a risk factor. The evidence that some concrete medication predisposes to the development of PUs is therefore limited.

With regard to the subdomain mechanical ventilation, 6 of the 9 studies that analyzed this parameter as a risk factor confirmed its influence in the multivariate analysis. The duration of MV was evaluated in three studies that established the existence of invasive or noninvasive MV as an inclusion criterion.5,14,23 In the case of Manzano et al.,5 MV increased the risk of development of PUs by 4.2% for each day of MV, versus 7.5% for each day of MV in the study of Catalá et al.14 In the study published by Cox and Roche,16 those patients requiring MV during >72h presented a 23-fold greater probability of developing PUs.

In the case of Nijs et al.,7 a frequency of postural changes of ≥6/day and the use of alternating pressure cushions were identified as risk factors for PUs. These results are a cause for concern, since different clinical practice guides recommend precisely these measures for the prevention of PUs. The authors offer two explanations for these results. The first is that the patients at risk were adequately identified, but the preventive measures were applied too late to avoid the development of PUs. The second offered explanation is that the nursing staff only started to apply the preventive measures once the PUs became visible.

A strength of this review is that all the included studies underwent methodological quality assessment in order to identify biases and limitations. A clear limitation is the large number of variables used in the studies to describe the risk factors, which moreover did not coincide among the different publications—thereby precluding use of the data for conducting a meta-analysis. Another limitation refers to the use of different outcome variables: some studies considered PUs in stage ≥I, while others considered PUs in stage ≥II. Some authors suggested that the risk factors associated to PUs in stage I differ from those associated to stage II.29 On the other hand, in relation to the study designs involved, we included prospective and retrospective observational studies, as well as clinical trials, with the final incorporation of four retrospective studies3,12,15,16—a fact that could pose a limitation regarding the quality of the collected data.

In this systematic review, the risk factors most frequently associated to the development of PUs have been patient age, the length of stay in the ICU, diabetes, the duration of MBP <60–70mmHg, mechanical ventilation, continuous veno-venous hemofiltration or intermittent dialysis, treatment with vasoactive drugs, sedative use, and postural changes.

In most cases, the evidence is limited and does not allow the identification of risk factors intrinsically predictive of the development of PUs. Rather, the interrelation of different factors could increase the probability of ulcer development.

It would be advisable for the scientific societies to encourage definition of the minimum data set to be incorporated to studies on PUs and the risk factors independently associated to the development of such ulcers, given the heterogeneity of the existing studies.

The contributions of each of the authors in conducting this study are detailed below.

M. Isabel González-Méndez has participated in the definition of the search strategy, the screening of titles and abstracts, the retrieval of relevant articles in full text format, selection of the studies meeting the inclusion criteria, calculation of the kappa coefficient, development of the summarizing table on the characteristics of the studies and the summarizing table on evidence for risk factors, preparation of the first manuscript draft, and approval of the final version of the manuscript for publication.

Francisco Manuel Carrasco-Cebollero has participated in the screening of titles and abstracts, the evaluation of methodological quality, critical manuscript review, and approval of the final version of the manuscript for publication.

Marta Lima-Serrano designed the investigation and the systematic review protocol, and has participated in the definition of the search strategy, review of the selection of the studies meeting the inclusion criteria, checking of the evaluation of methodological quality, checking of the summarizing table on the characteristics of the studies and of the summarizing table on evidence for risk factors, review of the statistical analyses presented by the studies, critical manuscript review, and approval of the final version of the manuscript for publication.

Joaquín Salvador Lima-Rodríguez has participated in the design of the investigation, approval of the review protocol, supervision of correct conduction of the study, preparation of the final manuscript version, and approval of the final version of the manuscript for publication.

All the authors declare that they have no financial or personal ties to other people or organizations that could have an inappropriate influence upon their work.