Systemic Oxygenation Flashcards
What is the equation for Hb bound oxygen?
1.34 (O2 binding capacity of hemoglobin in ml) X Hb X SO2 (ml/DL)
What is oxygen content?
The amount of oxygen that is Hb bound and dissolved in plasma
What happens to oxygen solubility in plasma as the body temperature rises?
The oxygen solubility will decrease
What is the equation for dissolved O2 in plasma?
0.003 X PO2
What is the arterial O2 content (CaO2)?
CaO2 = (1.34 X Hb x SaO2) + 0.003 X PaO2
What is normal arterial O2 content?
20 ml/DL
What is normal venous o2 content?
15 ml/DL
What is the O2 extracted for a normal person?
5 ml/DL or 50 ml/L
250 ml/min with a cardiac output of 5L/min
What is DO2?
The rate of oxygen delivery
What is the equation for DO2?
CO x CaO2 X 10
What is normal DO2?
900-1100 ml/min
What’s VO2?
The rate of O2 transport from the systemic capillaries to the tissues
What is the equation for VO2?
VO2 = CO X (CaO2-CvO2) X 10
What is the VO2 in healthy patients?
200-300 ml/ min
What does DO2 depend on?
Cardiac output
Oxygen content of the blood (Hb concentration and O2 sat)
What does VO2 depend on?
Cardiac output
o2 sat
SvO2
Hb concentration
What is whole body VO2?
Accounts for O2 uptake in the lungs
VO2 = VE X (FiO2-FeO2)
What is the normal O2 consumption of the lungs?
Less than 5%
What are the two conditions associated with low VO2?
- Decreased metabolism
2. Inadequate tissue oxygenation
What is oxygen debt?
The cumulative deficit in tissue oxygenation
What lab value correlates with a low VO2?
Lactate levels (begin to rise after 6 hours lag time)
What is the oxygen extraction ratio?
O2ER = VO2/DO2
Or
O2ER = (SaO2 - SvO2)/SaO2
What is normal O2ER?
.25
What is the equation for the control of VO2?
VO2 = DO2 X O2ER
What is the point at which VO2 begins to decrease?
When O2 extraction is maximal at 50%
How is SaO2 monitored?
By pulse oximetry
How is SvO2 monitored?
By the pulmonary artery catheter
What is normal SaO2-SvO2 or oxygen extraction?
20-30%
What does an increase in the oxygen extraction above 30% indicate?
A decrease in O2 delivery
What does an increase in O2 extraction that approaches 50% indicate?
Inadequate tissue oxygenation
What does a decrease in oxygen saturation below 20% mean?
A defect in O2 utilization (usually sepsis)
What is the simplified equation for O2 extraction?
1 - SvO2
What is the equation for SvO2 (mixed venous oxygen saturation?
SvO2 = SaO2 -(VO2/ CO X 1.34 X Hb)
What is the simplified equation of SvO2 is the arterial blood is fully saturated?
SvO2 = 1 - VO2/DO2
What is the normal range for SvO2?
65-75%
A change in SvO2 is only significant when….
It changes by more than 5% and lasts longer than 10 minutes
What does a decrease in SVO2 mean?
There is a decrease in oxygen delivery (cardiac output or anemia)
What does an increase in SvO2 mean?
A defect in O2 utilization
What is the normal range for central venous oxygen saturation?
70-89%
How is central venous oxygen saturation monitored?
By a central line in the SVC
What are the oxygen markers for impaired tissue oxygenation?
VO2 less than 200 ml/min or 110 ml/m2/min
SaO2 - SvO2 approaching 50%
SvO2 less than 50%
What are the chemical markers of impaired tissue oxygenation?
Lactate over 2 mM/l
Base deficit over 2
How is lactate used for prognosis?
- The initial value of lactate
2. The amount of time is takes to return to normal
What is the mechanism of lactate accumulation in sepsis?
Inhibition of pyruvate dehydrogenase which inhibits the movement from glycolysis to the Krebs cycle in mitochondria and therefore o2 utilization
What is arterial base deficit?
The amount of base that must be added to one liter of blood to raise the ph to 7.4
What is a normal arterial base deficit?
Less than 2
