test 1 part 2

Question 1

What affects the rate of oxygen consumption?

Answer 1

 Metabolic rate

 Amount of oxygen available (i.e. delivered to tissue)

Question 2

Rate of oxygen usage

Answer 2

 As long as intracellular PO2 is ≥ 1 mmHg oxygen usage depends on [ADP] not PO2
- pO2 >1 and ADP = 1.5 normal => can produce more ATP so rate of O2 usage increases

Question 3

ADP = 0.5 normal and pO2 >1

Answer 3

• Limit amount of O2 that can be utilized because of limited ATP so rate of O2 usage decreases
• Adenine base used up

Question 4

Tissue Oxygen Gradients (Average) : Capillary to interstitial fluid

Answer 4

 95 mmHg to 40 mmHg = 55 mmHg gradient

- gradient stays relatively constant

Question 5

Tissue Oxygen Gradients (Average) : Interstitial fluid to intracellular fluid

Answer 5

 40 mmHg to 23 mmHg = 17 mmHg gradient

- gradient stays relatively constant

Question 6

What happens if arterial PO2 drops to 70 mmHg?

Answer 6

 70 mmHg – 55 mmHg = 15 mmHg Interstitial

 15 mmHg – 17 mmHg = -2 mmHg => no O2 gets inside of the cell

Question 7

importance of arterial pO2

Answer 7

• it is important to keep an adequate intracellular pO2 so we keep pO2 high

Question 8

Manage Patient’s Flow

Answer 8

• as flow rate increases, level of O2 consumption increases
   Fixed target values based on weight or body surface area (BSA)
   OR use oxygen consumption plateau

Question 9

Once flow is established, what patient parameters tell us if the target blood flow is acceptable

Answer 9

 Pressure / SvO2 / Acid-base status

- SvO2 doesn’t always tell you if all of the tissues are being perfused correctly

Question 10

Manage Patient’s Hematocrit/Hemoglobin

Answer 10

 Keep the patient’s hematocrit (HCT) above a specified value: 24 to 25%

Question 11

How to keep our hematocrit from dropping below our target

Answer 11

 Minimize prime
 RAP / VAP
 Hemoconcentrate
 Enhance urine output
 Give packed red blood cells
- Tends to be treated as if it were independent of all other physiologic parameters.

Question 12

Problems With Current Model

Answer 12

 Monitor “summary” parameters that do not tell us what is happening at the organ and/or tissue level

Question 13

Concepts of Goal Directed Perfusion

Answer 13

 Concentrate on OXYGEN DELIVERY nadir (lowest level) rather than hematocrit nadir
 Use CO2 derived variables as an indication of actual tissue perfusion
 Make treatment decisions based on the concepts and using evidence based values

Question 14

what is king

Answer 14

• Oxygen Delivery

Question 15

control components for oxygen delivery

Answer 15

 Pump flow and HCT management
 i.e. guarantee an adequate oxygen supply to the tissues
 With constant pump flow, oxygen delivery is directly related to the HCT
 Maintaining absolute values no longer the goal

Question 16

What is the optimal amount of oxygen delivery?

Answer 16

 >280 ml O2/minute/meter2

at 34 degrees

Question 17

CO2 Derived Variables – Tissue Perfusion

Answer 17

 CO2 derived variables are better than O2 derived variables at predicting “lactic shock”

Question 18

Respiratory Quotient

Answer 18

• VCO2/VO2 (volume of CO2 being produced / volume of O2 being consumed) provide an indication of the ANAEROBIC THRESHOLD
   Ratio 0.8 to 1.1 normal
   Ratio >1.1 indicates CO2 production higher than expected based on oxygen consumption
   Lactate and CO2 are products of anaerobic metabolism

Question 19

DO2/VCO2

Answer 19

• delivery of O2 / volume of CO2 production
• ratio gives an indication of quality of perfusion
   Keep ratio >5 (Oxygen delivery should be 5x greater than CO2 production)
   Treat if ratio falls below 5 (increase pump flow, increase hemoglobin content, decrease temperature, check anesthesia level)

Question 20

If DO2/VCO2 ratio too low

Answer 20

• increase anything that increases delivery of O2

- increase hemoglobin, increase BF, decrease surface area

Question 21

Background Information on Krogh’s Capillary Cylinder Model (Oxygen Pressure Field Theory)

Answer 21

• increase in metabolism => capillary dilation and flow increases
   August Krogh – Published 1918
   Rate of oxygen delivery at capillaries depends on number and distribution of capillaries
   Demonstrated change in tissue flow with change in tissue metabolism
   With increased metabolism more capillaries opened increasing the density of capillaries in a given area and thus increasing oxygen delivery
   Each capillary supplies specific volume of tissue
   Postulated the movement of oxygen out of the capillary

Question 22

radius of capillary and radius of surrounding tissue cylinder and ratios

Answer 22

• about 5 microns
• about 10 microns
  Ratio = capillary X-sectional area / cylinder X-sectional area = 1/4 (under normal resting conditions)
• area of cylinder is 4x larger than the area of the capillary

Question 23

PaO2 from arterial to venous inside capillary

Answer 23

80 mmHg to 40 mmHg

Question 24

PaO2 from arterial to venous of the interstitial fluid

Answer 24

20 mmHg to 10 mmHg (averages)

    - the pO2 close to the capillary will be higher than the pO2 farther away - greatest rate of diffusion is where there is the greatest gradient (arterial side where the gradient is equal to 80 - 20 = 60 mmHg) - rate of diffusion decreases as you go from arterial to venous end because the gradient decreases

Question 25

lethal corner

Answer 25

• there isn’t enough interstitial pO2 to keep our intracellular pO2 1 or greater

Question 26

what can we do to change the pO2 out in the lethal corner?

Answer 26

• increase BF creates a better distribution throughout the interstital fluid
• increase hemoglobin
• increase total amount of O2 being delivered
• increase pO2

Question 27

Systemic Edema Reversal On CPB

Answer 27

• during CPB, continuous ultrafiltration reverses edema and improves tissue oxygenation
• edema formation impairs capillary distribution of oxygen to the tissues
• fluid weight gain in adult CPB averages 14%

Question 28

edema causes

Answer 28

• a larger anoxic lethal corner
• larger area of less than 1 mmHg pO2
• increases the number of cells that are no longer getting the proper amount of oxygen=> anaerobic metabolism
• capillary X-section / cylinder X-section = 1/16

Question 29

what does keeping pO2s above 300 do

Answer 29

• pushes the line where anoxic lethal corner out further decreasing the size of that area
• Advantage: if you have limited blood flow and can’t increase O2 delivery, it at lease helps diffuse this problem
• dependent on how much hemoglobin is present

Question 30

arterial and venous pCO2 concentrations

Answer 30

paCO2 = 40 mmHg
pvCO2 = 60 mmHg
- movement of CO2 lowest at arterial end and highest at venous end

Question 31

how to fix the hypercapnic lethal corner (high CO2)

Answer 31

• increase blood flow
• blow off more CO2 from oxygenator
• reduce edema

Question 32

Delivery of Oxygen indexed (DO2i)

Answer 32

DO2i = ((Arterial oxygen content) x (Blood Flow)) / BSA

Question 33

Arterial oxygen content

Answer 33

Arterial oxygen content =(Oxygen bound to Hb) + (O2 dissolved in arterial
blood)