Sacral positioning and interface pressure in the beach-chair position during shoulder surgery: a retrospective, observational study

Background Intraoperative pressure-related skin injuries remain a concern during surgery under general anaesthesia. Although interface pressures have been evaluated in various surgical positions, sacral pressure in the beach-chair position has not been reported. Aim To investigate sacral interface pressure and sacral skin changes during shoulder surgery in the beach-chair position. Methods We retrospectively analysed 28 patients who underwent shoulder surgery in the beach-chair position. Sacral interface pressure was measured in the supine and beach-chair positions. Patients were classified by sacral positioning: Group A, sacrum over the flat bed base; Group B, sacrum over the flexion hinge. Sacral skin findings, raw maximal contact pressure, sacral pressure normalised to body weight (P/W index), and changes in maximal pressure location after repositioning were assessed. Results Group A comprised 17 patients and Group B comprised 11 patients. All patients showed transient sacral erythema immediately after surgery, which resolved within 30 min without pressure injury. In the supine position, mean P/W index was higher in Group B than in Group A. In the beach-chair position, raw maximal contact pressure was significantly higher in Group A immediately after positioning, whereas P/W index did not differ significantly between groups. Maximal pressure location changed after repositioning in 4/17 patients in Group A and 8/11 in Group B. Conclusions Flat bed-base sacral positioning was associated with less frequent changes in maximal pressure location during repositioning. As no pressure injuries occurred, these findings should be interpreted as changes in intraoperative pressure distribution rather than evidence of pressure injury prevention.