Measurements of oxygen saturation of brain, liver and heart areas in the supine and sitting position using near infrared spectrophotometry.

Background and aims: Regional oxygen saturation (rSO₂) monitoring of the brain by near-infrared spectroscopy (NIRS) has been mainly used during carotid endarterectomy. The present study was conducted in volunteers and investigates the rSO₂ values of the brain, heart and liver tissue as assessed by NIRS in the supine and the sitting position.

Methods: After obtaining written informed consent from forty-nine healthy volunteers, rSO₂ values were recorded in the heart and liver areas in the supine and the sitting position, while simultaneously the rSO₂ values of the brain.

Results: The rSO₂ brain values in the supine and the sitting position were 69 ± 6.0 and 66 ± 6.1 respectively (p = 0.0001). The rSO₂ values in the supine and the sitting position were 76 ± 10.5 and 79 ± 6.7 for the heart (p > 0.05) and 85 ± 6.8 and 82 ± 7.2 for the liver, (p = 0.007). Heart rSO₂ values were higher than the brain rSO₂ values in both the supine (76 ± 10.4 versus 69 ± 6.6; p = 0.0001) and the sitting position (79 ± 6.7 versus 66 ± 6.1; p = 0.0001). The liver rSO₂ values were also higher than the brain rSO2 values in the supine (85 ± 6.8 versus 69 ± 6.0; p = 0.0001) and in the sitting position (82 ± 7.2 versus 66 ± 5.7; p = 0.0001). Arterial blood pressure and arterial oxygen saturation (SpO₂) did not differ between the two positions but the heart rate was higher in the sitting position (p = 0.030).

Conclusions: We conclude that brain and liver (but not heart) rSO₂ values are higher in the supine than sitting position. Additionally, NIRS may be used to assess oxygenation of the heart and liver.