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 Affinity is defined as the ability of hemoglobin to combine with oxygen In other words – how much does the hemoglobin love the oxygen? In other words – how much does the hemoglobin love the oxygen? High affinity – they love to be together High affinity – they love to be together Low affinity – they hate to be together Low affinity – they hate to be together

Affinity High affinity means that… High affinity means that… Hemoglobin and oxygen readily combine Hemoglobin and oxygen readily combine Hemoglobin doesn’t like to give its oxygen up – it is like a child with its blanket Hemoglobin doesn’t like to give its oxygen up – it is like a child with its blanket Low affinity means that… Low affinity means that… Hemoglobin doesn’t want to combine with oxygen Hemoglobin doesn’t want to combine with oxygen Hemoglobin is only too happy to give up its oxygen Hemoglobin is only too happy to give up its oxygen

Oxyhemoglobin Dissociation Curve (ODC) The ODC represents the ability of hemoglobin to hold onto oxygen at various PaO 2 levels The ODC represents the ability of hemoglobin to hold onto oxygen at various PaO 2 levels When PaO 2 is high, hemoglobin is able to saturate itself with oxygen easily When PaO 2 is high, hemoglobin is able to saturate itself with oxygen easily When PaO 2 is low, hemoglobin has a hard time holding onto oxygen When PaO 2 is low, hemoglobin has a hard time holding onto oxygen

Oxyhemoglobin Dissociation Curve (ODC) When PaO 2 drops below 40 mmHg, hemoglobin has a hard time holding onto oxygen When PaO 2 drops below 40 mmHg, hemoglobin has a hard time holding onto oxygen The ODC is not a linear function The ODC is not a linear function Graphic from:

Oxyhemoglobin Dissociation Curve So I’m sure you’re asking, “what does this have to do with acid-base balance”? 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!!! Alterations in the blood’s pH can change hemoglobin’s affinity for oxygen!!!

Oxyhemoglobin Dissociation Curve Acidosis Acidosis Causes the oxyhemoglobin curve to advance to the right (remember: acid = advance) Causes the oxyhemoglobin curve to advance to the right (remember: acid = advance) This is known as a “shift to the right” This is known as a “shift to the right” Affinity is reduced Affinity is reduced More oxygen is released to the tissues, BUT 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 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 PaO 2 than normal De-saturation occurs at higher PaO 2 than normal etters/0602/page2.asp

Oxyhemoglobin Dissociation Curve Alkalosis Alkalosis Causes the oxyhemoglobin curve to move backward to the left (remember: base = back) Causes the oxyhemoglobin curve to move backward to the left (remember: base = back) This is known as a “shift to the left” This is known as a “shift to the left” Affinity is increased Affinity is increased More oxygen is taken up by hgb in the lungs, BUT More oxygen is taken up by hgb in the lungs, BUT Hgb is less likely to give up its oxygen to the tissues Hgb is less likely to give up its oxygen to the tissues Tissue hypoxia can occur even if PaO 2 is WNL Tissue hypoxia can occur even if PaO 2 is WNL etters/0602/page2.asp

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