Most studies only had serum bicarbonate concentrations available and defined metabolic acidosis using the bicarbonate levels as standard. At time no meaningful contribution of respiratory system was considered in metabolic acidosis. Most epidemiologic studies have measured serum bicarbonate using an autoanalyzer using either an electrode-based or enzymatic method. The specimens are often shipped to a central laboratory by air to minimize assay variability. Scientists found that there was a difference in the bicarbonate levels between measurement of blood at a local laboratory and those shipped to a central laboratory. Bicarbonate measured at a central laboratory was always lower than that measured at a local laboratory. Then it was hypothesized that it is due to potential gas leak from a different atmospheric pressure during air travel. The time that samples were exposed to air in commercial laboratories also contributed to the variability in bicarbonate values. There are few studies that measured arterialized venous blood gas. For sampling, The patient’s hand or wrist have been placed in a warmer set to 42°C for a minimum of 15 minutes for Arterialized venous blood gas samples. As it provides a full assessment of acid-base status and is usually measured at the point of care, thus eliminating the errors that might have occurred during specimen transport. Due to cumbersome method of obtaining arterial blood gas sample, arterialized venous blood gas is often used for research purpose.^[1][2][3]