test 1 Flashcards by Marcus Chlopek

in a closed system, gas content

cannot change

- no gas fluid interface

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an increase in H+ concentration results in

-decrease in pH

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a decrease in temperature results in

increase in solubility
decrease in PPg
moves dissociation to the left
increase in pH

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pH of neutrality

-at specific temperatures there is a new pH of neutrality

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Henry’s law

 Dissolved = Solubility x Partial Pressure

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Solubility of CO2 and O2

 CO2 @ 37 degrees C = 0.06 mls CO2
/100 mls bld/mmHg
 O2 @ 37 degrees C = 0.003 mls O2
/100 mls bld/mmHg

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CO2 moved from the lungs to tissue (3)

 Dissolved
 Bound to hemoglobin
 As HCO3- (majority of CO2)
-all three determine CO2 content

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how to change the pH of blood in a closed system

1) Change total CO2 content – KEEP TEMP CONSTANT
2) Change temperature – keep total CO2 content constant
3) Change total CO2 content – change temperature

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Option one: Increase total CO2 content by ADDING additional CO2

 pCO2 will increase

 pH will decrease

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Option one: Decrease total CO2 content by REMOVING CO2

 pCO2 will decrease

 pH will increase

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Option two: Increase temperature

 Drive acid-base disassociation equilibrium to the right
 [H+] will increase
 pH will decrease

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Option two: Decrease temperature

 Drive acid-base disassociation equilibrium to the left
 [H+] will decrease
 pH will increase

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Option three: Change total CO2 content and Change temperature

 pCO2 will change producing an inverse change in pH
 Disassociation equilibrium will change causing a
corresponding increase or decrease in [H+]

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Temperature Increases:
 Gas solubility \_\_\_\_\_\_\_\_\_\_\_\_\_
 Gas partial pressure \_\_\_\_\_\_\_\_\_\_\_\_\_
 Therefore gas pressure is \_\_\_\_\_\_\_\_\_\_\_\_\_ than the
starting gas pressure
 Equilibrium of the water dissociation shifts to the
\_\_\_\_\_\_\_\_\_\_\_\_\_
 Therefore, pH will \_\_\_\_\_\_\_\_\_\_\_\_\_

 Gas solubility decrease
 Gas partial pressure increase
 Therefore gas pressure is higher than the
starting gas pressure
 Equilibrium of the water dissociation shifts to the
right
 Therefore, pH will decrease

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Draw sample

 Need: waste syringe, sample syringe, cup of ice (??)
 Draw from patient
 Draw from ECC
 Remove all air from sample – Cap tightly – Place in cup of ice

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Blood Gas Determination Via Lab

 Blood from sample injected into analyzer
 Analyzer WARMS sample to 37o C
 Analyzer determines the pO2, pCO2, and pH at 37o C

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uncorrected gases

 Report gas values determined at 37oC

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corrected gases

 Report gas values measured at 37oC but corrected back to actual body temperature

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Patient temp is 25o so analyzer will WARM the sample. pH, CO2, and O2 will be

 pH will be lower than expected (0.0147 per degree)
 CO2 will be higher than expected
 O2 will be higher than expected

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On bypass, you must look at the temperature corrected

blood gases to correctly treat the patient’s what

pO2

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where does most of the acid-base buffering in the body happen

-in the blood

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primary blood buffering system for maintaining a constant ratio of OH- to H+ (16:1) due to the changes in temp is

Imidazole moiety of the amino acid histidine

- found on most blood born proteins

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what is controled by alpha stat and pH stat management of blood gases

pH and pCO2

- arterial pO2 MUST be temperature corrected

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how do you increase pCO2

increase CO2 content

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In a normal human, what stays constant

CO2 content

intracellular pH (7.0)

- much lower than the blood pH | - more water inside the cells

as temperature increases, what happens to pH

pH decreases

pH varies from organ to organ. Why?

-temperature of each organ is different therefore changing the pH form organ to organ

Advantages of keeping CO2 content constant

 Maintains constant pH difference across cell membranes  Maintains constant ratio of negative to positive charges on proteins  Allows enzyme systems to work at optimal level regardless of temperature

what stays constant and what changes for pH stat

- constant- pH | - changes- temperature CO2 content

what stays constant and what changes for alpha stat

- constant- CO2 content | - changes- temperature and pH

consequences of hypothermia for pH stat

 blood more acidic (b/c of increase in CO2 content)  hydrogen ion gradient across the cell membrane changes  acidity alters metabolic activity (metabolic rate goes down)  cells do not maintain electroneutrality  added CO2 influences blood flow regulation (increase CO2> increase vasodilation)

consequences of hypothermia for alpha stat

 maintain constant charge on alpha-imidazole side chain  hydrogen ion gradient across cell does not change  cellular enzyme functions are maintained  cells maintain electroneutrality  auto-regulation of blood flow maintained (flow depends on metabolism)

alpha-stat for peripheral perfusion

-studies suggest improvement of peripheral | perfusion

alpha stat cerebral blood flow

-less than normal because it is based on metabolic need of tissue

pH stat cerebral blood flow and management

- greater than normal because pressure dependent - go from metabolism controlling CBF to a change in pressure controlling CBF - lose autoregulation

Cerebral blood flow normally autoregulated

 flow tightly coupled to cerebral metabolism  flow independent of blood pressure  flow regulated by PCO2

luxury flow

- flow is greater than the metabolic rate | - as blood flow through a tissue goes up, potential for embolic injury goes up

lose autoregulation at what temp

20 decrees C

pH-stat uncouples flow and metabolism

 greater blood flow – pressure dependent  improved cooling – more homogeneous  luxury flow – predispose to risk of embolic injury, high intracranial pressure, edema

Alpha-stat maintains autoregulation

 lower blood flow – based on metabolism |  predispose to adverse distribution of blood flow – risk of ischemic injury

kids are more susceptible to

-ischemic injury rather than embolic injury

adults more susceptible to

-embolic injury rather than ischemic injury

regular bypass adult strategy

 With little or no hypothermia might not make any difference. -With mild to moderate alpha-stat might be better

PROFOUND WITH ARREST ADULTS best strategy

 Combination (cross-over) best approach – use pH stat while cooling to ensure maximal cerebral metabolic suppression – switch to alpha-stat to remove acidosis

INFANTS best strategy

 Appears pH-stat may offer better outcomes (major cause of brain injury may relate more to hypoperfusion rather than emboli (might switch to alpha stat)

manage pH stat

* Always keep temperature corrected PCO2 at 40 mmHg | * Always keep temperature corrected pH at 7.40

You are on bypass and the patient is at 28o. Your last blood gas came back with the following temperature corrected values: PO2=98 mmHg; PCO2=30 mmHg; pH=7.53; bicarb=24; SvO2=74. Assuming you are practicing pH stat, which of the following best describes the patient’s total CO2 ontent?

Total CO2 content lower than it should be

You are on bypass and the patient is at 28o. Your last blood gas came back with the following temperature corrected values: PO2=98 mmHg; PCO2=30 mmHg; pH=7.53; bicarb=24; SvO2=74. Assuming you are practicing pH stat, how would you bring the CO2 content back to where it should be?

Add CO2 to the patient

You are on bypass and the patient is at 28o. Your last blood gas came back with the following temperature corrected values: PO2=98 mmHg; PCO2=30 mmHg; pH=7.53; bicarb=24; SvO2=74. Which of the following best describes how you would “fix” the PO2? [pH stat]

Increase FiO2

You are on bypass and the patient is at 28o. Your last blood gas came back with the following temperature corrected values: PO2=98 mmHg; PCO2=30 mmHg; pH=7.53; bicarb=24; SvO2=74. Which of the following best describes how you would “fix” the SvO2? [pH stat]

Make no change

You are on bypass and the patient is at 32o. Your last blood gas came back with the following temperature corrected values: PO2=350 mmHg; PCO2=60 mmHg; pH=7.15; bicarb=20; SvO2=60. Assuming you are practicing pH stat, which of the following best describes the patient’s total CO2 content?

Total CO2 content higher than it should be

You are on bypass and the patient is at 320. Your last blood gas came back with the following temperature corrected values: PO2=350 mmHg; PCO2=60 mmHg; pH=7.15; bicarb=20; SvO2=60. Assuming you are practicing pH stat, how would you bring the CO2 content back to where it should be?

Remove CO2 from the patient

You are on bypass and the patient is at 320. Your last blood gas came back with the following temperature corrected values: PO2=350 mmHg; PCO2=60 mmHg; pH=7.15; bicarb=20; SvO2=60. Which of the following best describes how you would “fix” the PO2? [pH stat]

Decrease FiO2

You are on bypass and the patient is at 320. Your last blood gas came back with the following temperature corrected values: PO2=350 mmHg; PCO2=60 mmHg; pH=7.15; bicarb=20; SvO2=60. Which of the following best describes how you would “fix” the PCO2? [pH stat]

Increase gas-to-blood flow ratio

You are on bypass and the patient is at 320. Your last blood gas came back with the following temperature corrected values: PO2=350 mmHg; PCO2=60 mmHg; pH=7.15; bicarb=20; SvO2=60. Which of the following best describes how you would “fix” the bicarb? [pH stat]

Add bicarb

You are on bypass and the patient is at 320. Your last blood gas came back with the following temperature corrected values: PO2=350 mmHg; PCO2=60 mmHg; pH=7.15; bicarb=20; SvO2=60. Which of the following best describes how you would “fix” the SvO2? [pH stat]

Increase cardiac index

You are on bypass at 300. You have just received the following blood gas results: PO2 [@ 37 = 100; @ 30 = 91] PCO2 [@ 37 = 40; @ 30 = 29.4] pH [@ 37 = 7.40; @ 30 = 7.51] You are using alpha stat. Which PO2 value do you use for your analysis?

91 mmHg

40 mmHg

7.40

Total CO2 content where it should be

Increase FiO2

Make no change

You are on bypass at 300. You have just received the following blood gas results: PO2 [@ 37 = 100; @ 30 = 91] PCO2 [@ 37 = 40; @ 30 = 29.4] pH [@ 37 = 7.40; @ 30 = 7.51] You are using pH stat. Which PO2 value do you use for your analysis?

91 mmHg

29.4 mmHg

7.51

Increase FiO2

Decrease gas-to-blood flow ratio

You are on bypass at 250. You have just received the following blood gas results: PO2 [@ 37 = 275; @ 25 = 250] PCO2 [@ 37 = 75; @ 25 = 55] pH [@ 37 = 7.13; @ 25 = 7.23] SvO2 = 65% You are using pH stat. Which of the following values will you use for your PCO2 analysis?

55 mmHg

Make no change

Increase gas-to-blood flow ratio

Increase cardiac index

You are on bypass at 250. You have just received the following blood gas results: PO2 [@ 37 = 275; @ 25 = 250] PCO2 [@ 37 = 75; @ 25 = 55] pH [@ 37 = 7.13; @ 25 = 7.23] SvO2 = 65% You are using alpha stat. Which of the following values will you use for your PCO2 analysis?

75 mmHg

Make no change

Increase gas-to-blood flow ratio

Increase cardiac index

You are on bypass at 250. You have just received the following blood gas results: PO2 [@ 37 = 275; @ 25 = 250] PCO2 [@ 37 = 67.6; @ 25 = 40] pH [@ 37 = 7.22; @ 25 = 7.40] SvO2 = 84% You used pH-stat to cool the patient. You now want to convert to alpha-stat. Which of the following best describes how you would adjust the pO2?

Make no change

Increase gas-to-blood flow ratio