Cath Lab Digest

C ertain sites of bony prominence are known to be at particular risk for skin breakdown and pressure ulcer development as compared with soft tissue sites under similar loading conditions. For example, pressure ulcers occur over the sacrum but are rare over the gluteus maximus.¹ To a large measure, this predilection is explainable on the basis of pressure concentration and other mechanical effects on tissue overlying the sacrum. Differences in response to short-term pressure loading of skin, overlying sacrum, and gluteus regions have been reported. Differential microvascular flow regulation involvement has been suggested.² A possible additional contributing factor that has not been widely considered is that tissue sites with greater resting levels of blood flow might be at greater risk of breakdown when weighted to levels that significantly decrease blood flow. The authors hypothesized that if resting sacral skin blood flow (SBF) was greater than in surrounding tissues, a decrease or stoppage of blood flow during loading might represent increased risk because relative tissue deficits would be greater. This hypothesis is based on the concept that for equal loading durations, the resulting tissue "flow-debt" and subsequent injury potential would be greater in more highly perfused tissue. The possible validity of this hypothesis depends, in part, on whether breakdown-prone regions do, in fact, tend to have greater resting perfusion than nearby surrounding regions.

Data describing resting blood flow in the breakdown-prone sacral region are scarce. One study of 11 healthy people suggests no significant difference exists in single point laser-Doppler measurements between sacrum and gluteus maximus.³ Data from two other studies - one including 10 young and another including 10 older healthy patients - also indicate a lack of resting perfusion difference between sacrum and gluteus maximus.^4,5 However, the combination of the small sample size and small tissue sampling area of single point laser-Doppler (~ 1 mm²) used in these studies may have obscured the presence of true differences in SBF between these sites. Because such a differential in SBF, if present, may increase understanding about the etiology of pressure ulcers, the purpose of this study was to compare ulcer-prone sacral region SBF to other less-at-risk tissue SBF using laser Doppler imaging^6-13 of larger spatial samples.

Methods

Sacral SBF with simultaneously determined resting SBF at the gluteus maximus and lower back were measured using laser Doppler imaging (LDI) to allow a large tissue area (15 cm²) to be sampled and studied for each site. Measurements were performed in 30 subjects (15 male) with an age range of 21 to 56 years (37.1 ± 2.1 years). In one subset of this group (N = 8), localized sacral skin heating to 44^o