The effects of pressure and shear on skin microcirculation in elderly stroke patients lying in supine or semi-recumbent positions.

The effects of external pressure and shear on the skin microcirculation over the sacral area, which is known as a high risk area for pressure sore formation, were studied in 30 elderly patients. The skin blood cell flux (SBF) was measured using the laser Doppler technique, with the patient first at rest in lateral position, then lying for 30 minutes in supine or semi-recumbent 45 degrees position, and finally in lateral position. Elderly high-risk patients (G2), most of them more than two years post-stroke, had a lower body mass index and a reduced sacral skin-fold compared with non-risk patients (G1). The SBF in G2 decreased 28% in supine and 14% in 45 degrees position, whereas the SBF in G1 increased 35% in supine and 13% in 45 degrees position. Spontaneous movements up to seven times per 30 minutes were registered, even during sleep, and were evident by direct observation of the recorded charts as a temporary SBF increase. The risk for skin ischaemic damage over the sacral area of elderly risk patients was evident in both positions, especially with the patients lying in supine position. When increasing the upper body slope in G2 from horizontal to 45 degrees, an inability to recover a satisfactory blood supply after the ischaemic insult was found. Discomfort from compressive and shear forces initiates changes in posture, even in elderly patients prone to tissue breakdown. Occasional relief of pressure was in most patients followed by temporary increase in skin blood flow with concomitant temperature increase. This most probably protected them from developing skin lesions.