P50 Determinations: Techniques and Clinical Importance
The oxyhemoglobin dissociation curve demonstrates the relationship between the partial pressure of oxygen and the percent hemoglobin carrying oxygen. The decrease in this percentage as blood passes from the arterial to venous side of tissue is indicative of the amount of oxygen delivered to that tissue. The four controlling factors governing oxygen delivery to tissue are: oxyhemoglobin concentration, blood flow, tissue PO2 and hemoglobin affinity for oxygen.1 If the affinity of hemoglobin increases, then compensation must occur or there will be a corresponding decrease in oxygen delivery to the tissue. The forms of compensation are increased blood flow (cardiac output), increased oxyhemoglobin concentration or decreased tissue PO2.1 P50 is the PO2 at which hemoglobin is 50% saturated with oxygen. It’s value defines relative changes in oxygen-hemoglobin affinity. To test the hypothesis that decreases in P50 are potentially harmful to an acutely ill individual, we developed procedures for rapidly and easily determining P50.
KeywordsMajor Abdominal Surgery Mixed Venous Oxygen Saturation Venous Side Blood Pass Oxyhemoglobin Dissociation Curve
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