The aim of the present study was to evaluate baseline regional cerebral oxygen saturation (rSO₂) values and identify factors influencing preoperative rSO₂ in elective minor surgery.

Observational analysis post-hoc.

Observational post-hoc analysis of data for the patient sample (n=50) of a previously conducted clinical trial in patients undergoing tumourectomy for breast cancer or inguinal hernia repair. Exclusion criteria included pre-existing cerebrovascular diseases, anaemia, baseline pulse oximetry <97% and low quality rSO₂ sensor signals. Demographic data, comorbidities, and ASA physical status as well as height and weight were collected prospectively from all patients. Baseline rSO₂ values were recorded while the patient breathed room air, using the INVOS 5100C monitor™ (Covidien, Dublin, Ireland).

Thirty-seven women (72%) and 13 men (28%) 48±13 years of age were enrolled in this study. Baseline rSO₂ was 62.01±10.38%. Baseline rSO₂ was significantly different between men (67.6±11.2%) and women (60±9.4%), (P=0.023). There were also differences between baseline rSO₂ and ASA physical status (ASA I: 67.6±10.7%, ASA II: 61.6±8.4%, ASA III: 55.8±13.9%, P=0.045). Baseline rSO₂ had a positive correlation with body weight (r=0.347, P=0.014) and height (r=0.345, P=0.014). We also found significant differences in baseline rSO₂ among patients with and without chronic renal failure (P=0.005). No differences were found in any other studied variables.

Non-modifiable patient characteristics (ASA physical status, sex, chronic renal failure, body weight and height) influence baseline rSO₂.