Oxygenation Flashcards
Hemoglobin (HbA)
2 alpha globins
2 beta globins
-each bound to a Heme
-4 O2 binding sites
T form: taut
- low affinity for O2, give up to tissues
- conditions favoring form: CO2, H+/acidosis, high temp, 2,3-DPG
- cause unloading of O2 into tissues
R form: relaxed
-high affinity for O2
Positive cooperativity
once one Hb binds O2, more likely for the others to bind O2
Causes sigmoid shape to oxygen-hemoglobin dissociation curve
What shifts the oxygen-hemoglobin dissociation curve to the right
“CADET face Right”
CO2 Acidosis high 2,3-DPG increased Exercise increased Temp
Oxygen unloads
R –> T form shift
What shifts the oxygen-hemoglobin dissociation curve to the left
decreased CO2 Alkalosis Low 2,3-DPG decreased metabolic need lower temp
Methemoglobin
toxic form
can’t carry O2 as well –> tissue hypoxia
oxidized form of iron - ferriC form, Fe3+
-c third letter
Higher affinity to cyanide
Substances known to cause methemoglobiemia
Nitrates, nitrites antimalarials - cloroquin, primaquine Dapsone Sulfonamides Local anesthetics - lidocaine metoclopramide
Treatment of methemoglobinemia?
Methylene blue
Vit C
If need to give med that causes it long term, give cimetidine (gradually lowers)
Cyanide antidote kit
amyl nitrite
sodium nitrite
-form methemoglobin to transport cyanide
Thiosulfate - binds cyanide –> thiocyanate –> renal excretion
Carboxyhemoglobin
hemoglobin bound to CO
Hb affinity to CO 200-250X greater than O2
Decreased O2 binding capacity
Shifts O2 dissociation curve to left
Can’t dx w/ pulse oximetry - will look normal as Hb is saturated
Total blood O2 content
dissolved O2 + (hemoglobin binding capacity x O2 saturation)
Conceptual, not a calculated equation
Anemia effect on blood O2 content
Decreases total O2 content
Causes:
Decrease RBC syntehsis
Increased RBC destruction
loss of RBCs
Pulse Ox will be normal - saturation of hemoglobin present is normal
Chronic lung disease effect on blood O2 content
decreased PaO2
Physiologic shunt –> low O2 extraction ratio
Low blood O2 content
Exercise/activity effect on blood O2 content
decreases venous PO2
Increases O2 demand
Increases O2 extraction
Alveolar gas equation
PAO2 = PIO2 - (PaCO2/R)
PAO2 = 150 - PaCO2/0.8
As PaCO2 goes up, PAO2 goes down and vice versa
A-a gradient
PAO2 - PaO2
normal 10-15 mmHg
Things increasing A-a gradient
- shunting or V/Q mismatch
- pulmonary fibrosis - diffusion limitation
- increased FiO2 - flood alveoli w/ O2 but physiologic limit to amount that can diffuse, artificially increased
- advanced age
PaO2/FiO2
normal: 300-500 mmHg
less than 300 - gas exchange deficit
less than 200 - severe hypoxia
Mechanisms of oxygen deprivation
Inadequate PaO2 (hypoxemia)
- high altitude
- hypoventilation
- high A-a gradient
- –diffusion limitation (pulmonary fibrosis)
- –Right to Left cardiac shunt
- –V/Q mismatch
Inadequate O2 delivery to organs/tissues (hypoxia)
- hypoxemia
- anemia
- CO poisoning
- Low Cardiac Output
Inadequate perfusion (ischemia)
- obstruction of arterial flow (MI or stroke)
- reduced venous drainage
Ventilation
O2 from outside body to the alveoli
Oxygenation
O2 from alveoli to the blood
CO2 transport in blood
- converted to HCO3- by carbonic anhydrase
- bound to N terminus of globin as carbaminohemoglobin
- dissolved in blood (measured w/ ABG)
Response to exercise
Increased O2 consumption
Increased CO2 production
Higher ventilation rate
V/Q in apex and base more uniform - dilated pulmonary capillaries in apex
Increased pulmonary blood flow d/t increased cardiac output
decreased pH - lactic acid
No change in PaO2 and PaCO2
Increased venous CO2 content
