Topic 6B - Alpha stat versus pH stat Flashcards
Buffer systems designed to maintain
constant ratio of?
Ratio of [OH-] to [H+] (16:1) despite changes in temperature
Bicarbonate; protein; phosphate
Primary blood buffering system
responsible for this maintaining the constant ratio is?
the imidazole moiety of the amino acid histidine
Found on most blood borne proteins
HIm+ <> H+ + Im
imidazole
In blood, this dissociation accounts
for most of the changes in pH due to
changes in temperature
Alpha stat and pH stat management
ONLY affect control of?
control of the arterial PCO2 and pH
How do you correct arterial pO2?
MUST be temperature corrected
pH of the blood will ______ with changes in temperature
vary inversely
Within body, temperature and pH ____
from organ to organ
will vary
Acid-Base balancing system does? (3)
- 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
pH-stat is what?
- maintain constant pH with change in temperature
- CO2 content has to increase as temperature decreases and has to decrease as temperature increases
pH-stat
— ratio changes ?
ratio of unprotonated histidine imidazole group to H+ (alpha value) changes as CO2 content increases
Alpha stat
- maintain constant CO2 content with change in temperature
- pH will increase as temperature decreases and pH will decrease as temperature increased
Alpha stat
— ratio changes how?
ratio of unprotonated histidine imidazole group to H+ (alpha value) remains constant
Alpha stat pH will increase as ___
pH will increase as temperature decreases
maintain constant CO2 content with change in temperature
Alpha stat
-maintain constant pH with change in temperature
pH stat
ratio of unprotonated histidine imidazole group to H+ (alpha value) remains constant
Alpha stat
ratio of unprotonated histidine imidazole group to H+ (alpha value) changes as CO2 content increases
pH stat
pH stat Consequences during hypothermia (5)
- blood more acidic
- hydrogen ion gradient across the cell membrane changes
- acidity alters metabolic activity
- cells do not maintain electroneutrality
- added CO2 influences blood flow regulation
pH stat – as temp decrease how do you maintain “normal” pH
as temperature decreases, CO2 is added to maintain “normal” pH
pH stat – as temp increases how do you maintain “normal” pH
as temperature increases, CO2 must be removed
Alpha Stat - as temperature decreases, pH _?
as temperature decreases, pH will rise
Alpha Stat - as temperature increases, pH will?
as temperature increases, pH will fall
Alpha Stat - Consequences during hypothermia
- 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
maintain constant total CO2 content in the blood
Alpha stat
total CO2 content in the blood must increase
- active addition of CO2
- alteration of ventilation
pH stat
pH-stat shifts oxy-hemoglobin
dissociation curve to ___ which offsets ____
…right which offsets leftward shift due to hypothermia
Cerebral Blood flow loses autoregulation when temp falls below?
Loses autoregulation when temperature falls
below 20C
When temp falls below 20C - what is the affect on Cerebral Blood Flow ? (2)
- flow becomes pressure dependent
- luxury flow (flow»_space; metabolic rate)
Cerebral Blood Flow
– pH-stat uncouples what?
flow and metabolism
Cerebral Blood Flow
– Alpha-stat maintains?
maintains autoregulation
Cerebral Blood Flow
– pH-stat uncouples flow and metabolism which means greater bld flow is __ dependent
greater blood flow–pressure dependent
Cerebral Blood Flow
– pH-stat Luxury Flow predisposes what? (3)
- predispose to risk of embolic injury
- high intracranial pressure
- edema
Cerebral Blood Flow
- alpha stat lower blood flow–based on?
lower blood flow–based on metabolism
Cerebral Blood Flow
- alpha stat predispose to ?
predispose to adverse distribution of blood flow–risk of ischemic injury
pH or alpha stat?
PROFOUND ARREST w/ADULTS
Combination (cross-over) best approach–use pH stat while cooling to ensure maximal cerebral metabolic suppression–switch to alpha-stat to remove acidosis
pH or alpha stat?
INFANTS
Appears pH-stat may offer better outcomes (major cause of brain injury may relate more to hypoperfusion rather than emboli
pH or alpha stat?
REGULAR BYPASS ADULTS: With little or no hypothermia
With little or no hypothermia might not make any difference.
pH or alpha stat?
REGULAR BYPASS ADULTS: With mild to moderate hypothermia
With mild to moderate hypothermia alpha-stat might be better
keep uncorrected pH and PCO2 values at normal levels (7.4 & 40 mmHg)
Alpha stat
keep corrected PCO2 equal to the patient’s core temperature (i.e. PCO2 will decrease) and corrected pH will increase
Alpha stat
Alpha stat - look at which pH and PCO2 values?
uncorrected pH and PCO2 values at normal levels
keep corrected pH and PCO2 values at normal levels (7.4 & 40 mmHg)
pH stat
pH stat - looks at which pH and PCO2 values?
keep corrected pH and pCO2 values
uncorrected pH will decrease and the uncorrected PCO2 will increase
