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Background: Three different approaches for assessing the acid-base status of a patient exist, i.e. the Boston, Copenhagen, and Stewart´s approach, and they employ different parameters to assess a given acid-base disturbance. Students, researchers, and clinicians are getting confused by heated debates about which of these performs best and by the fact that during their curricula, they typically get acquainted with one of the approaches only, which prevents them to understand sources employing other approaches and to critically evaluate the advantages and drawbacks of each approach. In this paper, the authors introduce and define the basic parameters characterizing each of the approaches and point out differences and similarities between them. Special attention is devoted to how the different approaches assess the degree of change in the concentration of plasma bicarbonate that occurs during primary respiratory changes; proper understanding of these is necessary to correctly interpret chronic respiratory and metabolic acid-base changes.Conclusion: During acute respiratory acidosis the concentration of bicarbonate rises and during acute respiratory alkalosis it falls, depending on the buffering strength of non-bicarbonate buffers. During acute respiratory acid-base disturbances, buffer base (employed by the Copenhagen approach), apparent and effective strong ion difference, as well as strong ion gap (employed by the Stewart approach) remain unchanged; the anion gap (employed by the Boston and Copenhagen approach) falls during acute respiratory acidosis and rises during acute respiratory alkalosis.