A computer-implemented method for determining the degree of tissue hypoxia of a subject, the method comprising a) measuring and/or estimating values of blood acid-base status in a blood sample, the blood sample having been obtained from venous blood of the subject, b) providing values of measured and/or estimated arterial oxygenation (SO 2AM, SO 2AE, SpO 2) from said subject, c) converting the venous blood values by applying a venous-to-arterial conversion model for deriving blood acid-base status and oxygenation status into first estimated arterial blood values (1_ABGc), d) providing second reference acid-base status and oxygenation values of arterial blood (2_ABG) from the said subject, e) implementing a tissue hypoxia model using a measure of the total buffer base concentration and/or a measure of the total carbon dioxide content (tCO 2) in the arterial blood, said model having as input, at least, said first estimated arterial blood values (1_ABGc),and said second reference values of arterial blood (2_ABG), f) the tissue hypoxia model calculating: a. a first measure indicative of the change in the total buffer base concentration (ΔBB T) between the said first estimated arterial blood values (1_ABGc) and said second reference values of arterial blood (2_ABG), and/or b. a second measure indicative of the change in the total carbon dioxide content (ΔtCO 2,T) between the said first estimated arterial blood values (1_ABGc) and said second reference values of arterial blood (2_ABG), and g) the tissue hypoxia model being arranged to output a measure indicative of the degree of tissue hypoxia of the subject using said first and/or second measure. a) measuring and/or estimating values of blood acid-base status in a blood sample, the blood sample having been obtained from venous blood of the subject, b) providing values of measured and/or estimated arterial oxygenation (SO 2AM, SO 2AE, SpO 2) from said subject, c) converting the venous blood values by applying a venous-to-arterial conversion model for deriving blood acid-base status and oxygenation status into first estimated arterial blood values (1_ABGc), d) providing second reference acid-base status and oxygenation values of arterial blood (2_ABG) from the said subject, e) implementing a tissue hypoxia model using a measure of the total buffer base concentration and/or a measure of the total carbon dioxide content (tCO 2) in the arterial blood, said model having as input, at least, said first estimated arterial blood values (1_ABGc),and said second reference values of arterial blood (2_ABG), f) the tissue hypoxia model calculating: a. a first measure indicative of the change in the total buffer base concentration (ΔBB T) between the said first estimated arterial blood values (1_ABGc) and said second reference values of arterial blood (2_ABG), and/or b. a second measure indicative of the change in the total carbon dioxide content (ΔtCO 2,T) between the said first estimated arterial blood values (1_ABGc) and said second reference values of arterial blood (2_ABG), and a. a first measure indicative of the change in the total buffer base concentration (ΔBB T) between the said first estimated arterial blood values (1_ABGc) and said second reference values of arterial blood (2_ABG), and/or b. a second measure indicative of the change in the total carbon dioxide content (ΔtCO 2,T) between the said first estimated arterial blood values (1_ABGc) and said second reference values of arterial blood (2_ABG), and g) the tissue hypoxia model being arranged to output a measure indicative of the degree of tissue hypoxia of the subject using said first and/or second measure.