Additional blood-gas variables for the rational control of oxygen therapy. With allowance for shifts of the oxygen dissociation curve.
When a sample of arterial blood is analysed for oxygen tension and, using a modern oximeter, for haemoglobin concentration and saturation, it is possible to calculate the position of the oxygen dissociation curve and two new variables: "P95" and "C(a-x)O2". P95 is the tension at which the haemoglobin would be 95% saturated and can, therefore, constitute a target tension for near-maximum arterial content of oxygen. C(a-x)O2 (the "conditional extraction" of oxygen) is the amount of oxygen, in ml/dl blood, which can be extracted from the arterial blood for a hypothetical mixed-venous oxygen tension PxO2. It is explained how it is possible to estimate the adequacy of tissue oxygenation by comparing any available estimate of the required extraction (normally about 5 ml dl-1) with conditional extractions calculated for three hypothetical values of PxO2 covering the clinical range. Methods of calculation are given. For accurate results at high arterial saturations, a peripheral venous sample may be required in addition to the arterial sample.
Willis
N
N
Department of Medical Biochemistry, University Hospital of Wales, Cardiff.
Clapham
M C
MC
Mapleson
W W
WW
D002302:Cardiac Output; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008433:Mathematics; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010102:Oxygen Inhalation Therapy / Q000379:methods*; D010313:Partial Pressure
D006454:Hemoglobins; D010100:Oxygen