What is the ultimate goal in acid-base regulation?

1 Department of Physiology, Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry, India 2 School of Medicine, Faculty of Medical and Health Sciences, Asian Institute of Medicine, Science, and Technology, Sungai Petani, Kedah Darul Aman, Malaysia Address for reprint requests and other correspondence: E. S. Prakash, School of Medicine, Faculty of Medical and Health Sciences, Asian Institute of Medicine, Science and Technology, 2 Persiaran Cempaka, Amanjaya Campus, 08000 Sungai Petani, Kedah Darul Aman, Malaysia (e-mail: dresprakash{at}gmail.com ) Abstract It is common to see chapters on acid-base physiology state that the goal of acid-base regulatory mechanisms is to maintain the pH of arterial plasma and not arterial P CO 2 (Pa CO 2 ) or plasma HCO 3 . A hypothetical situation in which the Pa CO 2 of arterial plasma is 80 mmHg and the plasma HCO 3 concentration is 48 mM is presented and analyzed to get over this misconception. As per the modified Henderson equation, the pH of arterial plasma would be 7.4; however, we explain that this may be associated with intracellular acidosis due to intracellular hypercapnia and that derangement of homeostasis is evident from the occurrence of respiratory depression and, eventually, coma in the patient described. This suggests that the ultimate goal of acid-base regulatory mechanisms is not just the maintenance of the pH of arterial plasma but the maintenance of the steady-state pH of intracellular fluid as well. Key words: acidosis; intracellular pH; homeostasis