The arterial blood gas analysis (PaO2, PaCO2, pH, HCO3p, BE(Ecf),....) are changed during cardiopulmonary bypass depends on patient condition and perfusion management. is there any reference values upon which we can say that the patient has metabolic/respiratory acidosis or alkalosis?
Thank you in advance
Determining acid-base status of a patient under cardiopulmonary bypass
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Blood gases are measured at 37 degree C. correction may be done according to body temperature. 1 degree down increase pH 0.015. Accordingly if in vitro temperature is 37 C and pH is 7.4 , the in vivo pH in 27 C will be 7.55. In lower temperature the pH increases. In vivo PaO2 decreases .
There are 2 strategies to handle the ABG: pH stat and alpha- stat. pH stat (temperature corrected) time keeping constant arterial pH at 7.4and PaCO2 at 40 at any given temperature. The alpha stat (temperature uncorrected) aims keeping constant ratio of [OH-] : [H+] at 16:1.
Thank you Sherif Sultan, you are right, alpha-stat and pH-stat management should be considered first. I attend many open-heart surgeries where nearly all patient outcomes are good (after 3 days) and I asked about how did they know that the acid-base balance and oxygenation is adequate. Actually, they depend on blood pH and lactate, all based on their own experience.
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