Sacral skin blood perfusion: a factor in pressure ulcers?

Pressure ulcers occur over the sacrum but are rare over the gluteus maximus. This predilection is partly explained by pressure concentration effects, but other factors may be involved. The authors hypothesized that if resting sacral skin blood flow 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. Because information on sacral skin blood flow is scarce yet important to the plausibility of this hypothesis, the objective was to determine if actual sacral skin resting blood flow is, in fact, different than flow in other nearby posterior areas. Thus, skin blood flow was measured with laser Doppler imaging in 15-cm2 areas overlying the sacrum in 30 subjects (15 male) and compared to skin blood flow in other posterior sites (gluteus maximus and lower back) and to remote sites (hand and fingers). Results showed that average sacral skin blood flow (59.1 +/- 1.4 arbitrary profusion units) was significantly (P < 0.001) greater than other posterior sites (48.7 +/- 2.5 a.u.) and was significantly (P < 0.01) greater in females (63.0 +/- 1.6 vs. 55.2 +/- 1.8). These findings provide the first systematic characterization of resting sacral skin blood flow. The data are consistent with the tentative hypothesis, but more direct evidence of a linkage is clearly needed. Large spatial variability in skin blood flow (40%) suggests that comparisons of skin blood flow among sites are best done with laser Doppler imaging in contrast to standard laser Doppler monitoring.