###### Abstract  
Pressure injuries (PIs) are typically characterized by lesions of the dermis and subcutaneous tissue; they result from a downward force exerted on the area between a bony prominence and an external surface. Transcutaneous oxygen pressure (TcPO2) measurements are a standardized method for measuring tissue oxygen pressure. Standardized TcPO2 measurement data are lacking in regions susceptible to pressure injury. It is unclear whether the absence of data can be attributed to the unreliability and variability of the measurements obtained. This study aimed to assess the reliability and repeatability of TcPO2 measurements conducted using a fluorescence-sensitive photo-optical sensor at three sites on the foot where PIs can occur but for which no data are available. Thirty volunteers participated in this study. TcPO2 was measured in two sessions, one week apart, at the lateral of the fifth metatarsal head, the styloid process, and the lateral malleolus of both feet. TcPO2 (mmHg) exhibited moderate reliability for the left fifth metatarsal and right fifth metatarsal styloid process (ICC: 0.575 and 0.624, respectively). The right fifth metatarsal and the right and left lateral malleoli demonstrated good and excellent reliability of the styloid process of the left fifth metatarsal, with ICC values of 0.810, 0.816, 0.763, and 0.900, respectively. The implementation of a fluorescence-sensitive photo-optical sensor for the measurement of TcPO2 in the designated regions yielded reliable and reproducible measurements. p <concept>  
infection, insufficient nutrition, prolonged hospitalization, and increased workload and medical expenses [3; 4; 5]. In Europe, the prevalence of PIs among hospitalized adults has been estimated to be approximately 12.8%, with an incidence of 5.4 per 10,000 patients [6]. In Spain, the Sixth National Study conducted by the National Group for the Study of and Advice on Pressure Ulcers and Chronic Wounds found a prevalence of hospital-acquired PIs of 7.7%, a figure that rises to 6.05% in nursing homes and social healthcare centers [7; 8]. Prolonged pressure on the PI region is typically characterized by injury to the skin and subcutaneous tissue, resulting from the downward force exerted on the area between a bony prominence and an external surface, such as a mattress or wheelchair cushion. Sustained pressure exerted by medical devices has also been identified as a contributing factor. The prolonged application of pressure on the affected area can result in the occlusion of blood vessels, leading to tissue damage due to a decrease in the supply of oxygen and nutrients to the tissue [9]. The impact of pressure on anatomical sites that are prone to PIs, as well as its effect on tissue viability, has been the subject of extensive research. The effect on tissue varies according to anatomical location, with a more significant impact observed in the heel and ankle regions when a 50 mmHg(g) increase in pressure is recorded, as opposed to the sacrum and trochanter, where an increase of 140 mmHg is required to elicit a comparable effect. This finding underscores the notion that an alteration in cutaneous blood flow, in conjunction with the tissue ischemia that it engenders due to a decline in tissue perfusion and oxygenation within a designated area, can be modulated by the quantity of tissue separating the surface from the bone, thereby facilitating the dissipation of the load [10]. Transcutaneous oxygen pressure (TcPO2) measurements are a standardized method of measuring oxygen pressure in tissues [11]. This technique has been demonstrated to be effective in assessing microcirculation, and, as such, it can be utilized as a predictive value for the wound healing process [12]. In cases of severe ischemia or diabetes, TcPO2 has been shown to be more sensitive than the ankle brachial index. This is due to its ability to detect changes in blood flow caused by both macrovascular and microvascular disease.