2. INTRODUCTION
• Alpha-stat and ph-stat are the techniques used for acid-base manangement.
• Acid-base interpretation is used to assess the acid-base disorders which
include:
Respiratoty acidosis(acute and chronic), Respiratory alkalosis(acute and
chronic).
• The normal value of
ph = 7.4
pco2 = 40 mmHg
• Most of the sugeries use the strategy of hypothermia. As the degree of
temperature falls, ph value increases and pco2 value decreases i.e.,
temperature is directly proportional to pco2 and indirectly proportional to ph.
• With the ph and alpha stat strategies,ph and pco2 values can be maintained
constant at varying temperature.They have a broad spectrum of advantages
which is to be discussed in the upcoming slides.
3. ALPHA-STAT
• The term “alpha-stat” refers to keeping the
ionized(alpha) imidazole of histidine is an
intracellular protein buffer involved in maintaining
intracellular pH.
• The alpha-stat strategy aims to maintain
intracellular function by maintaining intracellular pH
and enzymatic function. This is an important
consideration with increasing levels of hypothermia.
4. During cooling,exogenous co2 is not added to the
system when following alpha-stat.
• It is the most widely used approach for acid-base
management during cpb in adults.
5. PH-STAT
• pH-stat refers to keeping the blood pH
Constant at the prescribed level of hypothermia.
• This technique simply adjusts the blood gas
Values(PaO2 and PaCO2) using corrective
equations based on the temperature the blood
exists within the patient.
• The addition of CO2 is generally needed to
achieve pH-stat management because of the
increased solubility of gas at hypothermia.
6. pH-stat management,with its low pH at deep
hypothermia,suppresses the cerebral metabolic
rate which may prolong oxygen availability during
period of circulatory arrest.
• pH-stat is most commonly achieved on bypass with
air and oxygen delivered through a gas blender and
graduated flow meter with the addition of low flow
100% CO2.
7. EFFECT OF HYPOTHERMIA ON ACID-BASE
BALANCE:
• pH-stat may be beneficial in infants to increase CBF
and allow more efficient cooling.
• Alpha-stat appears advantageous in adults by limiting
the microemboli load to the brain
• Protection of the brain during deep
hypothermia(temp<20 deg C) may be best accomplished
with a mixed acid-base startegy:
*pH-stat during initial cooling phase
9. CHARACTERISTICS OF pH-STAT
ADVANTAGES
• Increased cerebral blood flow-quick amd
homogeneous brain cooling phase of DHCA.
• Offers protection in neonatal and infant cardiac
surgery.
• Particularly beneficial in cyanotic neonates and
infants.
• Shifts more cerebral flow towards the cerebral
circulation.
10. • Improves cerebral cooling and oxygen supply.
• Inhibit lactate buildup during arrest and early
reperfusion.
DISADVANTAGES
• Loss of cerebral autoregulation.
• “Luxury brain perfusion”: mismatch of CBF &
CMRO2.
• Increased risk of cerbral embolization and cerebral
edema.
• Slightly complex than alpha-stat strategy.
11. CHARACTERISTICS OF ALPHA-STAT STRATEGY
ADVANTAGES
• Preserves cerebral autoregulatiom during
moderate hypothermia.
• Reduced CBF, decreased risk of microemboli.
• Possibly more preferrable in adults.
12. pH-STAT vs. ALPHA-STAT
• Proponents of alpha-stat method suggest that pH-stat
management may put the brain at risk for damage from
microemboli,cerebral edema, or high intracranial
pressure, or may actually predispose to an adverse
redistribution of blood flow(“steal”) away from marginally
perfused areas in patients with cerebrovascular disease.
• On the other hand,proponents of pH-stat strategy
suggested that enhanced CBF may be helpful in
improvong cerebral cooling before the initiation of
circulatory arrest.
