8. Pulse Oximetry Flashcards
how many hemoglobin per RBC
300 million
hemoglobin subunits
4 subunits
each subunit contains a heme group
heme group
porphyrin ring
iron (site of oxygen binding)
how may oxygen molecules can 1 hemoglobin bind?
4 subunits
each bind 1 oxygen
= 4 total oxygen per hemoglobin
how many oxygen molecules per RBC
over 1 billion oxygen molecules
hematocrit
(Hct)
percentage of blood that is red blood cells
blood components
plasma
white blood cells (thrombocytes)
red blood cells (RBCs)
normal male hematocrit
45%
normal female hematocrit
39%
hematocrit vs hemoglobin lab values
Hct = 3xHb
hematocrit units
percentage
hemoglobin units
concentration (g/dL)
anemia
decrease in hemoglobin and/or hematocrit
- decr Hct will result in decr Hb (directly proportional)
anemia Hb
<6.5 g/dL
<65 g/L
anemia Hct
<20%
Causes of anemia
fluid administration
- dilutes [Hb]
blood loss
- decr Hb
lysed RBCs
- destroyed Hb
renal insufficiency/failure
-decr erythropoietin (EPO) production. –> less RBCs
PAO2
partial pressure of O2 in the alveoli
cannot measure
can calculate
PAO2 factors
primarily determined by pt FiO2
- incr FiO2 = incr PAO2
- decr FiO2 = decr PAO2
barometric pressure
- higher alt: decr press = decr FiO2
minute ventilation (minimally)
- changing breathing rate does not really help
PaO2
partial pressure of O2 in the arteries
portion of O2 that dissolves in blood
1.5% of all O2 in body
measured by blood sample
what percentage of O2 in the body is bound to hemoglobin?
98.5%
PaO2 factors
determined by PAO2
- decr PAO2 = decr PaO2 (room air)
- incr PAO2 = incr PaO2 (supp O2)
not affected by Hct (RBC levels) or SaO2
normal PaO2
80-100 mmHg (room air)
decreases w/age
normal PaO2 for healthy pts calculation
PaO2 ~ 5x FiO2
low PaO2 causes
lung disease
problems w/alveolar capillary gas exchange
PaO2 can be a quick indicator of
if the pt has healthy or unhealthy lungs
SaO2
% of Hb that is saturated w/O2
directly measured: blood sample
indirect measure: pulse ox
SaO2 factors
Primarily determined by PaO2
- lower PaO2 = lower SaO2
- higher PaO2 = higher SaO2
supplementary O2 impacts to SaO2
supp O2 incr PAO2
(incr FiO2)
incr PAO2 = incr PaO2
(incr diffusion of O2 into blood)
incr PaO2 = incr SaO2
( Hb can soak up more O2)
Other factors that impact SaO2
pH
Co2
Temp
Anemia
2,3 DPG
Carboxyhemoglobin levels
Methemoglobin levels
these alter the way Hb soaks up O2
A-a Gradient
difference in PAO2 and PaO2
- PAO2 (lungs) vs PaO2 (blood)
should be small in healthy pts w/good lung diffusion
normal A-a Gradient
room air: 5-15mmHg
100% FiO2: 10-110mmHg
widened A-a Gradient
expected w/lung disease
-impaired alveolar/capillary diffusion
PAO2 = normal
- O2 can still get into alveoli
PaO2 = decreased
- more difficult to get O2 into blood
Oxyhemoglobin Dissociate Curve
(HbO2)
shows how PaO2 determines SaO2