SGD: Compensation in Metabolic Acidosis

Questions asked by a student at SGD:

1. Why in Metabolic Acidosis, the compensation has no acute phase? 
2. Why is Respiratory Alkalosis single phase?
3. Is the compensation acute or chronic?
4. How long is the compensation in Metabolic Acidosis?

In Metabolic Acidosis, there is a marked drop in bicarbonate concentration, and pH falls considerably. The compensation is a steady (smooth hyperbolic) increase in PCO2. In the acute phase response or compensation, the blood buffers try to correct the change first and breathing slows down (becomes slower, hypoventilate). The slowed breathing continues past the 10-minute critical timeline and for up to 12 to 24 hours (approx. 1 day) whereby the body is able to retain sufficient CO2 to increase the PCO2 and the pH steadies to a higher level but never reaching 7.40. A rising pH and PCO2 are sufficient to tell us that compensation is taking place. When the PCO2 is high and pH near normal, then that is considered as complete compensation, and the patient should be breathing normally by 24 hours (one day observation).