Physiological measurements of tissue health; implications for clinical practice

Abstract

Pressure mapping alone insufficiently describes tissue health. Comprehensive, quantitative non invasive assessment is crucial. Interface pressures (IPs) and transcutaneous blood gas levels [transcutaneous tissue oxygen (T(c) PO(2) )] were simultaneously assessed over both ischia and the sacrum to investigate the hypotheses: (i) tissue oxygenation decreases with sustained applied pressure; (ii) tissue oxygen and IP are inversely correlated in loaded soft tissues; (iii) multisite assessments are unnecessary because healthy individuals are symmetrical. Measurements were taken at 5-minute intervals for 20 minutes in both sitting and supine lying for a cohort of 20 able-bodied adults. There were no statistically significant changes over time for either variable in 96% of timepoint comparisons. Specifically, no significant differences were seen between 10 and 20 minutes in either position. These findings imply that a 10-minute assessment can reliably indicate tissue health and that tissue may adapt to applied load over time. No statistically significant correlations between T(c) PO(2) and IP were observed. However, the left and right ischia were significantly different for both variables in supine lying (P < 0.001) and for sitting IP (P < 0.010). Thus, even in this healthy cohort, postural symmetry was not observed and should not be assumed for other populations with restricted mobility. If a multisite technique cannot be used, repeated tissue health assessments must use the same anatomic location.

The physiological response of soft tissue to periodic repositioning as a strategy for pressure ulcer prevention

“…This result was also shown by Kim et al (2012) who reported values for interfaces pressures that are similar in magnitude and distribution to the present study (median = 46, range 27-84 mm Hg). In addition, their evaluation of transcutaneous tissue oxygen values at the sacrum was reported to remain stable during 20 minutes of static supine lying, with mean values of TcPO2 between 31 and 37 mm Hg.…”

“…However, it is well established that interface pressures alone do not alert the clinician to risk of pressure ulcers and the imprecise relationship between pressure magnitude and duration limits the predictive or prognostic value of the measured parameter (Reenalda et al, 2009). Accordingly, much research has utilised measures of tissue viability, often in the form of transcutaneous gas monitoring, to examine the tissue response to mechanical loads (Chai and Bader, 2013;Kim et al, 2012;Makhsous et al, 2007). These studies have shown distinct changes in tissue oxygen (TcPO 2 ) and carbon dioxide (TcPCO 2 ) tensions when measured at differing skin sites subjected to representative external pressures (Knight et al, 2001).…”

Back to basics: biophysical methods in tissue viability research

“…They found no difference between time point measurements and no significant correlations between interface pressure and TcPO 2 . However, they did find some asymmetries in measures taken from the left and right side of the ischium highlighting that multiple sites of evaluation should be taken (Kim et al, 2012). There are however, some questions as to whether 20 minutes is sufficient to evaluate physiological response to pressure given the known association of time.…”

“…A recent study was conducted by Kim et al (2012), where interface pressures and transcutaneous blood gas measurements were taken during sitting and lying. Here they took measurements every 5 minutes for a total of 20 minutes.…”

Effects of conventional and alternating cushion weight-shifting in persons with spinal cord injury

“…Detailed spectral analysis also reveals component contributions to blood flow [16–17]. LDF blood flow assessment combined with T c PO 2 measurement can thus reveal tissue health information that cannot be provided by IP measurement alone [18–20]. …”