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Flashcards in Topic 7 Deck (35)
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1
Q

Buffer systems designed to maintain constant ratio of

A

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

2
Q

Primary blood buffering system responsible for this is the

A

imidazole moiety of the amino acid histidine

-Found on most blood borne proteins

3
Q

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

A

changes in temperature

4
Q

Alpha stat and pH stat management ONLY affect control of the

A

arterial pCO2 and pH

5
Q

Arterial pO2 MUST be

A

temperature corrected

6
Q

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

A

Total CO2 contend DOES NOT CHANGE!!!!

•This represents alpha stat management of CO2 & pH

7
Q

pH of the blood will vary _____ with changes in temperature

A

inversely

-pH will change from organ to organ

8
Q

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

A

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

9
Q

pH-stat=

A
  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
10
Q

Alpha-stat=

A
  1. 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
11
Q

pH-stat:

as temperature decreases

A

CO2 is added to maintain “normal” pH

12
Q

pH-stat:

as temperature increases

A

CO2 must be removed

13
Q

pH-stat consequences during hypothermia

A
  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***
14
Q

alpha-stat :

as temperature decreases

A

pH will rise

15
Q

alpha-stat :

as temperature increases

A

pH will fall

16
Q

alpha-stat consequences during hypothermia

A
  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***
17
Q

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

A

decrease in temperature

18
Q

Alpha-stat maintain constant

A

total CO2 content in the blood

19
Q

pH-Stat: keep pH normal at all

A

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

20
Q

pH-stat: total CO2 content in the blood must

A

increase

  • active addition of CO2
  • alteration of ventilation
21
Q

Affects on Tissue Oxygenation:

pH-stat shifts oxy-hemoglobin dissociation curve to the

A

right

-which offsets leftward shift due to hypothermia

22
Q

Cerebral blood flow normally autoregulated=

A

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

23
Q

Hypothermia: Affect on Cerebral Blood Flow=

A

Loses autoregulation when temperature falls below 20C

  • flow becomes pressure dependent
  • luxury flow (flow»_space; metabolic rate)
24
Q

Affect on Cerebral Blood Flow:

pH-stat uncouples flow and metabolism=

A
  1. greater blood flow – pressure dependent
  2. improved cooling – more homogeneous
  3. luxury flow – predispose to risk of embolic injury, high intracranial pressure, edema
25
Q

Affect on Cerebral Blood Flow:

Alpha-stat maintains autoregulation=

A
  1. lower blood flow – based on metabolism

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

26
Q

What is BEST Strategy for REGULAR BYPASS ADULTS

A
  • With little or no hypothermia might not make any difference.
  • With mild to moderate alpha-stat might be better
27
Q

What is BEST Strategy for PROFOUND WITH ARREST ADULTS

A

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

28
Q

What is BEST Strategy for INFANTS

A

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

29
Q

To manage pH-stat:

A
  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
30
Q

To manage alpha-stat:

A
  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
31
Q

Which value to use for pO2
Alpha?
pH?

A
Alpha= Corrected
ph= Corrected
32
Q

Which value to use for pCO2
Alpha?
pH?

A
Alpha= Non corrected
ph= Corrected
33
Q

Which value to use for pH
Alpha?
pH?

A
Alpha= Non corrected
ph= Corrected
34
Q
Increased Temp=
pp?
h+?
Solubility?
pH?
A

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

35
Q
Decreased Temp=
pp?
h+?
Solubility?
pH?
A

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