ALPHA STAT & PH STAT.pptx

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1. PH STAT AND ALPHA STAT

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

8. *Alpha-stat during reperfusion ,rewarming and termination of cardiopulmonary bypass.

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.