The correlation between Sub Epidermal Moisture (SEM) measurement, epidermal hydration, temperature, pain, and ultrasound, in the early detection of pressure ulcers

Background: Pressure ulcers (PU) remain an important clinical challenge which place an extensive burden on patients and on the healthcare system. Current methods of PU detection should focus on identifying injury at the very early stages, as this is when the damage is reversible if corrective methods are applied to manage the early inflammatory processes. However, current clinical practice assessments are fraught with challenges, as visual skin assessment relies on visible changes at the skin surface. PUs often originate from the deeper tissues, and visible skin injury is only present once microscopic damage during the early stages of injury has grown to involve a macroscopic cascade. Therefore, a PU that has migrated up to the visible skin surface is a sign that irreversible damage has taken place. Sub-Epidermal moisture (SEM) measurement offers a solution to this problem, in that the early inflammatory response associated with PU development can be detected. However, evidence pertaining to the significance of abnormal SEM delta values in absence of a visible skin injury is yet to be determined. This study will bridge this gap in knowledge through investigating SEM and its correlation with evidence-based technologies that assess the deep and superficial skin tissue overlying bony prominences. 

Aim: The overarching aim of this study was to explore the correlation between Sub-Epidermal moisture, epidermal hydration, temperature, pain, and ultrasound, in the early detection of pressure ulcers, within an acute patient population. 

Design: This study employed a prospective cohort study design. Participants scheduled for elective surgery, who provided written informed consent, were consecutively enrolled and followed up for three days. 

Methods: Ethical approval was granted before data collection commenced. A visual skin assessment (VSA), combined with daily measurements of SEM, epidermal hydration, temperature, pain, and ultrasound was carried out prior to and following the surgical operation. Measures were taken of the skin and deep tissue overlying bony prominences (such as the sacrum, both heels and a control site) of participants. A SEM PU was defined as two consecutive abnormal SEM delta values that succeeded a normal SEM delta value. Correlation analysis was undertaken using Pearson (R) or Spearman’s (Rs) methods. 

Results:  A total of 60 participants were included with 33.3% (n=20) of participants recruited equally into a cardiothoracic, orthopaedic, or general surgery cohort. The mean age of participants was 58 years (SD: 13.46) and 50% (n=30) were male. There was a 3.3% (n=2) incidence of PU development, and all were assessed as grade 1. The total SEM PU incidence was 61.8% (n=34), of which 26.5% (n=9) of these participants developed more than one SEM PU. A statistically significant low to moderately positive correlation was identified between SEM and ultrasound across all anatomical sites. No clear evidence of a correlation was observed between SEM, EH, and pain. Low positive and negative correlations existed across two days at the sacrum, indicating both higher and lower temperatures correlated with abnormal SEM delta values. However, temperature is highly variable, and interpretation is complex in absence of a threshold. The correlation pattern indicates that SEM and ultrasound agreed in the presence of injury, however SEM detected abnormalities before ultrasound. 

Conclusion: In this surgical cohort of participants there was a high incidence of SEM PU and a low incidence of visual PUs. The correlation between SEM, EH, temperature and pain were inconclusive across all anatomical sites and days of follow up, warranting future research evidence. However, the findings from this study provide evidence that a correlation exists between SEM and US. The correlation pattern indicates that SEM and US agreed in the presence of injury, however SEM could detect abnormalities prior to US. SEM showed superiority among the other assessments in terms of its feasibility in clinical practice.