Arterial Blood Gas Analyzer calculator

Clinical inputs

• Arterial pHAccepted range: 6.5 to 7.8
• Arterial carbon dioxide tension (mm Hg)Accepted range: 5 to 150
• Bicarbonate (mmol/L)Accepted range: 1 to 80
• Sodium (mmol/L)Accepted range: 80 to 200
• Chloride (mmol/L)Accepted range: 50 to 160

Primary source

Haber RJ. A practical approach to acid-base disorders. West J Med. PMID: 1877237. The PubMed record year is 1991; the printed discussion is West J Med 1991;155:146-151. Table 1: normal pH is 7.35 through 7.45, acidemia is pH under 7.35, and alkalemia is pH over 7.45; respiratory alkalosis is PCO2 under 35 mm Hg and respiratory acidosis is PCO2 over 45; metabolic acidosis is bicarbonate under 22 mmol/L and metabolic alkalosis is bicarbonate over 26. pH 7.35 and pH 7.45 with PCO2 from 35 through 45, bicarbonate from 22 through 26, and an anion gap under 20 are no disorder. pH under 7.35 with those same gases is acidemia, including pH 7.34 and pH 7.349. pH over 7.45 with those same gases is alkalemia, including pH 7.46 and pH 7.451. pH 7.50 with PCO2 exactly 35 and bicarbonate 22 is alkalemia, not respiratory alkalosis, because carbon dioxide is not under 35. pH 7.25 with PCO2 exactly 45 and bicarbonate 26 is acidemia, not respiratory acidosis, because carbon dioxide is not over 45. A pH from 7.35 through 7.45 whose gases do not match a named process stays an unmatched pattern. Table 2 rule 1: the primary process is the one on the same side of pH 7.40 as the measured pH, because compensation does not return pH fully to 7.40. pH 7.40 itself is not on either side. Rule 2: an anion gap of 20 mmol/L or greater is a primary metabolic acidosis regardless of pH or bicarbonate. That alkali-side class, when carbon dioxide is not under 35 and bicarbonate is not over 26, is anion-gap metabolic acidosis. The anion gap is sodium minus chloride minus bicarbonate, and the normal gap used in rule 3 is 12. A gap above 14 is above the stated 12 plus or minus 2. Rule 3: add the excess gap (gap minus 12) to the measured bicarbonate. A sum above 30 is an added metabolic alkalosis. A sum below 23 is an added nongap metabolic acidosis. A sum from 23 through 30 adds neither. Worked gases in the text: pH 7.50, PCO2 29, bicarbonate 22 is acute respiratory alkalosis; pH 7.25, PCO2 60, bicarbonate 26 is acute respiratory acidosis; pH 7.34, PCO2 60, bicarbonate 31 is chronic respiratory acidosis with metabolic compensation; pH 7.50, PCO2 48, bicarbonate 36 is metabolic alkalosis with respiratory compensation; pH 7.20, PCO2 21, bicarbonate 8 is metabolic acidosis with respiratory compensation; pH 7.50, PCO2 20, bicarbonate 15, sodium 140, chloride 103 is respiratory alkalosis plus an anion-gap metabolic acidosis, and the excess-gap sum of 25 adds no third metabolic process. The class is chosen from these unrounded cutoffs. The result override repeats that comparison so a one-decimal display cannot move pH 7.35, 7.40, or 7.45, PCO2 35 or 45, bicarbonate 22 or 26, an anion gap of 20, or an excess-gap sum of 23 or 30. (1991)