the partial pressure of carbon dioxide in the arterial blood in mmhg the kidney and the liver are two main organs responsible for the metabolic homeostasis of ph. bicarbonate is a base that helps to accept excess hydrogen ions whenever there is acidaemia. however, this mechanism is slower than the respiratory pathway and may take from a few hours to 3 days to take effect. in acidaemia, the bicarbonate levels rise, so that they can neutralize the excess acid, while the contrary happens when there is alkalaemia. thus when an arterial blood gas test reveals, for example, an elevated bicarbonate, the problem has been present for a couple of days, and metabolic compensation took place over a blood acidaemia problem. in general, it is much easier to correct acute ph derangement by adjusting respiration. metabolic compensations take place at a much later stage. however, in a critical setting, a person with a normal ph, a high co2, and a high bicarbonate means that, although there is a high carbon dioxide level, there is metabolic compensation. as a result, one must be careful as to not artificially adjust breaths to lower the carbon dioxide. in such case, lowering the carbon dioxide abruptly means that the bicarbonate will be in excess and will cause a metabolic alkalosis. in such a case, carbon dioxide levels should be slowly diminished.