Topic 7

Question 1

Buffer systems designed to maintain constant ratio of

Answer 1

[OH-] to [H+] (16:1) despite changes in temperature
Bicarbonate
protein
phosphate

Question 2

Primary blood buffering system responsible for this is the

Answer 2

imidazole moiety of the amino acid histidine

-Found on most blood borne proteins

Question 3

Imidazole
HIm+(Protonated) H+ + Im (Nonprotonated)
In blood, this dissociation accounts for most of the changes in pH due to

Answer 3

changes in temperature

Question 4

Alpha stat and pH stat management ONLY affect control of the

Answer 4

arterial pCO2 and pH

Question 5

Arterial pO2 MUST be

Answer 5

temperature corrected

Question 6

Allowing CO2 and pH to change “naturally” based on solubility changes and changes in Imidazole dissociation=

Answer 6

Total CO2 contend DOES NOT CHANGE!!!!

•This represents alpha stat management of CO2 & pH

Question 7

pH of the blood will vary _____ with changes in temperature

Answer 7

inversely

-pH will change from organ to organ

Question 8

Forcing CO2 and pH to remain at “normal” values=

Answer 8

Total CO2 contend HAS TO INCREASE!!!
•CO2 has to be added to the system
•This represent pH stat management of pCO2 & pH

Question 9

pH-stat=

Answer 9

1. maintain constant pH with change in temperature
   - CO2 content has to increase as temperature decreases and has to decrease as temperature increases
   - ratio of unprotonated histidine imidazole group to H+ (alpha value) changes as CO2 content increases

Question 10

Alpha-stat=

Answer 10

2. maintain constant CO2 content with change in temperature
   - pH will increase as temperature decreases and will decrease as temperature increased
   - ratio of unprotonated histidine imidazole group to H+ (alpha value) remains constant

Question 11

pH-stat:

as temperature decreases

Answer 11

CO2 is added to maintain “normal” pH

Question 12

pH-stat:

as temperature increases

Answer 12

CO2 must be removed

Question 13

pH-stat consequences during hypothermia

Answer 13

1. blood more acidic
2. hydrogen ion gradient across the cell membrane changes
3. acidity alters metabolic activity
4. cells do not maintain electroneutrality
5. added CO2 influences blood flow regulation***

Question 14

alpha-stat :

as temperature decreases

Answer 14

pH will rise

Question 15

alpha-stat :

as temperature increases

Answer 15

pH will fall

Question 16

alpha-stat consequences during hypothermia

Answer 16

1. maintain constant charge on alpha-imidazole side chain
2. hydrogen ion gradient across cell does not change
3. cellular enzyme functions are maintained
4. cells maintain electroneutrality
5. auto-regulation of blood flow maintained***

Question 17

Alpha-Stat: allow an increase in pH (decrease in pCO2) with a

Answer 17

decrease in temperature

Question 18

Alpha-stat maintain constant

Answer 18

total CO2 content in the blood

Question 19

pH-Stat: keep pH normal at all

Answer 19

temperatures (when compared to alpha stat at each temperature, allowed a decrease in pH with a decrease in temperature)

Question 20

pH-stat: total CO2 content in the blood must

Answer 20

increase

• active addition of CO2
• alteration of ventilation

Question 21

Affects on Tissue Oxygenation:

pH-stat shifts oxy-hemoglobin dissociation curve to the

Answer 21

right

-which offsets leftward shift due to hypothermia

Question 22

Cerebral blood flow normally autoregulated=

Answer 22

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

Question 23

Hypothermia: Affect on Cerebral Blood Flow=

Answer 23

Loses autoregulation when temperature falls below 20C

• flow becomes pressure dependent
• luxury flow (flow&raquo_space; metabolic rate)

Question 24

Affect on Cerebral Blood Flow:

pH-stat uncouples flow and metabolism=

Answer 24

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

Question 25

Affect on Cerebral Blood Flow:

Alpha-stat maintains autoregulation=

Answer 25

1. lower blood flow – based on metabolism

2. predispose to adverse distribution of blood flow – risk of ischemic injury

Question 26

What is BEST Strategy for REGULAR BYPASS ADULTS

Answer 26

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

Question 27

What is BEST Strategy for PROFOUND WITH ARREST ADULTS

Answer 27

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

Question 28

What is BEST Strategy for INFANTS

Answer 28

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

Question 29

To manage pH-stat:

Answer 29

1. Keep temperature corrected pCO2 at 40 mmHg
2. Keep temperature corrected pH at 7.40
   - uncorrected pH will decrease and the uncorrected PCO2 will increase

Question 30

To manage alpha-stat:

Answer 30

1. keep uncorrected pH and pCO2 values at normal levels (7.4 & 40 mmHg)
2. OR keep corrected PCO2 equal to the patient’s core temperature (i.e. PCO2 will decrease) and corrected pH will increase

Question 31

Which value to use for pO2
Alpha?
pH?

Answer 31

Alpha= Corrected
ph= Corrected

Question 32

Which value to use for pCO2
Alpha?
pH?

Answer 32

Alpha= Non corrected
ph= Corrected

Question 33

Which value to use for pH
Alpha?
pH?

Answer 33

Alpha= Non corrected
ph= Corrected

Question 34

Increased Temp=
pp?
h+?
Solubility?
pH?

Answer 34

pp= increase
h+= increase
Solubility=decrease
pH= decrease

Question 35

Decreased Temp=
pp?
h+?
Solubility?
pH?

Answer 35

pp= decrease
h+= decrease
Solubility=increase
pH= increase