Changes in Blood Volume and Oxygenation in Lower Limb Tissue in Patients Maintaining the Lithotomy Position Under General Anaesthesia

To investigate the effect of the lithotomy position on lower limb circulation under general anaesthesia, near-infrared spectroscopy (NIRS) was used to measure changes in blood volume and oxygenation in thigh tissue in patients (n = 35) under general anaesthesia in the lithotomy position. The NIRS measurement items, including total haemoglobin concentration (total-Hb), tissue haemoglobin index (nTHI), and tissue oxygenation index (TOI) in the thigh, were recorded for 60 min, while the patients were in the lithotomy position. The correlation between changes in each measurement item and patient characteristics, elevation of the lower extremities, and cardiorespiratory indices were evaluated. Data obtained from 24 patients were analysed. The median values (quartile deviation) of changes in total-Hb, nTHI, and TOI during the 60-min period from baseline were + 3.09 (1.99) μmol/L, +0.08 (0.03) a.u., and + 2.25 (1.75) %, respectively, all of which were significantly increased (p < 0.05). Regression analysis showed that no factor was significantly associated with the increase in any measurement item. The present results suggest that circulation in thigh tissue tends to shift towards hyperaemia during 60 min of general anaesthesia in the lithotomy position, regardless of patient background factors or changes in cardiorespiratory conditions.