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Effects of Acid-Base on Oxygenation?. James Barnett, RN, MSN Clinical Educator – Neuroscience PCC Vanderbilt University Medical Center May, 2007. Affinity. Affinity is defined as the ability of hemoglobin to combine with oxygen In other words – how much does the hemoglobin love the oxygen?
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Effects of Acid-Base onOxygenation? James Barnett, RN, MSN Clinical Educator – Neuroscience PCC Vanderbilt University Medical Center May, 2007
Affinity • Affinity is defined as the ability of hemoglobin to combine with oxygen • In other words – how much does the hemoglobin love the oxygen? • High affinity – they love to be together • Low affinity – they hate to be together
Affinity • High affinity means that… • Hemoglobin and oxygen readily combine • Hemoglobin doesn’t like to give its oxygen up – it is like a child with its blanket • Low affinity means that… • Hemoglobin doesn’t want to combine with oxygen • Hemoglobin is only too happy to give up its oxygen
OxyhemoglobinDissociation Curve (ODC) • The ODC represents the ability of hemoglobin to hold onto oxygen at various PaO2 levels • When PaO2 is high, hemoglobin is able to saturate itself with oxygen easily • When PaO2 is low, hemoglobin has a hard time holding onto oxygen
OxyhemoglobinDissociation Curve (ODC) • When PaO2 drops below 40 mmHg, hemoglobin has a hard time holding onto oxygen • The ODC is not a linear function Graphic from: http://www.rnceus.com/abgs/abgcurve.html
OxyhemoglobinDissociation Curve • So I’m sure you’re asking, “what does this have to do with acid-base balance”? • Alterations in the blood’s pH can change hemoglobin’s affinity for oxygen!!!
OxyhemoglobinDissociation Curve • Acidosis • Causes the oxyhemoglobin curve to advance to the right (remember: acid = advance) • This is known as a “shift to the right” • Affinity is reduced • More oxygen is released to the tissues, BUT • Hemoglobin is less likely to bind with oxygen in the lungs, so there is not as much to give up • De-saturation occurs at higher PaO2 than normal http://www.readylinkhealthcare.net/newsletters/0602/page2.asp
OxyhemoglobinDissociation Curve • Alkalosis • Causes the oxyhemoglobin curve to move backward to the left (remember: base = back) • This is known as a “shift to the left” • Affinity is increased • More oxygen is taken up by hgb in the lungs, BUT • Hgb is less likely to give up its oxygen to the tissues • Tissue hypoxia can occur even if PaO2 is WNL http://www.readylinkhealthcare.net/newsletters/0602/page2.asp
Finished • You have finished this inservice • Please proceed to the ABG Interpretation Post-Test at the following website