Acid–base disturbances are common occurrence in acute care setting, their rapid assessment and analysis are important, and pH of 6.8–7.8 is compatible with life. The definition of acid and base is different for biochemist, physiologist, cook, and others. Acid–base analysis gives us information about oxygenation, ventilation, acid–base status, electrolytes, lactate level, and clue to etiology and probable diagnosis.