• Javier Tercero, Isabel Gracia, Paola Hurtado, Nicolás de Riva, Enrique Carrero, Marta Garcia-Orellana, Isabel Belda, José Rios, Felipe Maldonado, Neus Fàbregas, and Ricard Valero.
• From the Department of Anaesthesiology, Hospital Clínic de Barcelona, University of Barcelona (JT, IG, PH, NdR, EC, MG-O, IB, NF, RV), Institut d'Investigacions Biomédiques August Pi i Sunyer (IDIBAPS) and Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM) (RV), Medical Statistics Core Facility, IDIBAPS and Hospital Clinic de Barcelona (JR), Biostatistics Unit, Faculty of Medicine, Universitat Autònoma de Barcelona, Barcelona, Spain (JR) and Department of Anaesthesiology, Faculty of Medicine, Hospital Clínico Universidad de Chile, University of Chile, Santiago, Chile (FM).
• Eur J Anaesthesiol. 2021 Jan 1; 38 (1): 49-57.

BackgroundMaintaining adequate blood pressure to ensure proper cerebral blood flow (CBF) during surgery is challenging. Induced mild hypotension, sitting position or unavoidable intra-operative circumstances such as haemorrhage, added to variations in carbon dioxide and oxygen tensions, may influence perfusion. Several of these circumstances may coincide and it is unclear how these may affect CBF.ObjectiveTo describe the variation in transcranial Doppler and regional cerebral oxygen saturation (rSO2), as a surrogate of CBF, after cardiac preload and gravitational positional changes.DesignObservational study.SettingOperating room at Hospital Clínic de Barcelona.VolunteersTen healthy volunteers, white, both sexes.InterventionsMeasurements were performed in the supine, sitting and standing positions during hyperoxia, hypocapnia and hypercapnia protocols and after a Valsalva manoeuvre.Main Outcome MeasuresCardiac index (CI), haemodynamic and respiratory variables, maximal and mean velocities (Vmax, Vmean) (transcranial Doppler) and rSO2 were acquired. Results were analysed using a generalised estimating equation technique.ResultsCI increases more than 16% after a preload challenge were not accompanied by differences in rSO2 or Vmax - Vmean. With positional changes, Vmean decreased more than 7% (P = 0.042) from the supine to the seated position. Hyperoxia induced a cerebral rSO2 increase more than 6% (P = 0.0001) with decreases in Vmax, Vmean and CI values more than 3% (P = 0.001, 0.022 and 0.001) in the supine and standing position. During hypocapnia, CI rose more than 20% from supine to seated and standing (P = 0.0001) with a 4.5% decrease in cerebral rSO2 (P = 0.001) and a decrease of Vmax - Vmean more than 24% in all positions (P = 0.001). Hypercapnia increased cerebral rSO2 more than 17% (P = 0.001), Vmax - Vmean more than 30% (P = 0.001) with no changes in CI. After a Valsalva manoeuvre, rSO2 decreased more than 3% in the right hemisphere in the upright position (P = 0.001). Vmax - Vmean decreased more than 10% (P = 0.001) with no changes in CI.ConclusionCBF changes in response to cerebral vasoconstriction and vasodilatation were detected with rSO2 and transcranial Doppler in healthy volunteers during cardiac preload and in different body positions. Acute hypercapnia had a greater effect on recorded brain parameters than hypocapnia.

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