OXYHEMOGLOBIN DISSOCIATION CURVE Chemeketa Community College.
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Transcript of OXYHEMOGLOBIN DISSOCIATION CURVE Chemeketa Community College.
OXYHEMOGLOBIN DISSOCIATION
CURVE
Chemeketa Community College
Oxygen-hemoglobin dissociation curve
Oxy/hemo Curve
The ability of oxygen to bind with and dissociate from hemoglobin
How shifts change affinity
Oxy/hemo Curve
97% O2 on Heme of Hgb 3% in plasma
–3% is available in anemia
–Harmful in toxicity
Oxy/hemo Curve
O2 is “loosely” attached to heme
Easily formed and dissolved
Oxy/hemo Curve
Heme can carry 4 O2 molecules
Each site is affected by the other 3
As they bind, space is decreased
Oxy/hemo Curve
The more they bind, the harder it becomes to bind
Oxy/hemo Curve
Two transfer sites exist Alveolar-capillary site Capillary-tissue site
O2 Saturation Monitoring
ABGs, pulse oximetry
Venous sats
O2 Sat. Monitoring
Does not tell tissue oxygenation
Patient may have tissue hypoxia in spite of monitors
Oxy/hemo Curve
Normal curve uses O2 Sats and PaO2 to reflect amount of oxygen available to the tissues
Oxy/hemo Curve-Normals
37 degrees, pH 7.40, PaCO2 40 mm/hg
Deviation causes a shift
Oxygen-hemoglobin dissociation curve
Oxy/hemo Curve
Upper-flat portion is lungs Steep portion is tissues Body can hold 96-97% down
to 80 mm/hg
Oxy/hemo Curve
Results of tissue transfer-
–Venous blood at 63%
–At 27 mm/hg the Sat is 50%
Changes in Affinity
pH, PaCO2, carbon monoxide, abnormal Hgb., temp, intracellular compounds, 2,3-DPG
The Bohr effect
Oxygenated Hgb = stronger acid than deoxygenated Hgb
Change in pH facilitates release of oxygen
The Bohr effect
Acid becomes weaker
Blood picks up CO2
Transports to lungs and
process reverses
Relationship of hemoglobin sat. and pH
Temperature
Decrease causes increased affinity–Shift to left
Increase causes decreased affinity–Shift to right
Relationship of hemoglobin sat. and Temperature
2,3 DPG (diphosphoglycerate)
An enzyme that affects binding directly
Competes with oxygen
2,3 DPG (diphosphoglycerate)
More 2,3 DPG =decreased affinity
Less = increased affinity
Carbon Monoxide (CO)
CO has > 200 times greater affinity than oxygen
Always causes lower oxygen sats
Abnormal Hemoglobin
May have greater or lesser affinity
Left Shift
Increased affinity for O2 At any PaO2, % is higher
Left Shift
Easier to “hook-on” Harder to “un-hook”
Left Shift-clinical situations Alkalosis, hypocapnia,
hypothermia Decreased DPG, CO
poisoning Blood transfusion,
fetal Hgb
Clinical example
56 yo woman with ICP elevated
Craniotomy for CVA bleed/ aneurysm
Hyperventilated to vasoconstrict
Her ABGs
pH = 7.53, Pa CO2 = 21 mm/hg
PO2 = 118 mm/hg, HCO3 = 17.8 mEq/L
O2 Sat = 99.1%, Temp =37.6
What does it mean? Left shift makes it
hard to “un-hook” Tissue hypoxia must
be watched for-even if readings indicate high sats
Right shift
Decreased affinity for O2 At any PO2, sat % is
decreased Harder to “hook-on” Easy to “un-hook”
Clinical situations
Acidosis, hypercapnia, hyperthermia
Elevated DPG Hyperthyroidism, anemia,
chronic hypoxia
Clinical example
25 yo with ARDS Secondary to staph
pneumonia 100% O2, PPV
ABGs
pH = 7.27, PaCO2 = 51.2 mm/hg
PO2 = 40 mm/hg, HCO3 = 23.6 mEq/L
O2 Sat = 76.2%, Temp =39.7
Clinical example
Right shift is protective if-additional O2 is given
Summary
The curve helps us appreciate factors that affect the oxygenation status of critical patients.
http://www.ventworld.com/resources/oxydisso/oxydisso.html
Summary
Diseases or treatments shift the curve
Understanding allows for more appropriate interventions