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Lytes Disorders

Acid-Base Disturbances           See also   Hemodynamic Data

The Henderson-Hasselbalch Equation:   pH = 6.1 + log [HCO3] / [0.0301 x pCO2]                                                                 [H+] = 24 x [pCO2/ HCO3]

pH  =  6.90   7.00   7.10   7.20   7.30   7.40   7.50   7.60
[H+]=  125    100    80      64      51      40      32       25

                              Primary change           pH          Compensatory response
Metab. acidosis     decreased HCO3      decreased     decreased pCO2
Metab. alkalosis     increased HCO3       increased      increased pCO2
Resp. acidosis        increased pCO2       decreased      increased HCO3
Resp. alkalosis       decreased pCO2       increased      decreased HCO3

Rules of thumb  for bedside interpretation of acid-base disorders:
For metabolic acidosis

For metabolic alkalosis

For acute respiratory acidosis

For chronic respiratory acidosis

For acute respiratory alkalosis

For chronic respiratory alkalosis

Anion gap = Na - [CL + HCO3]    (Normally =  12 +/- 4 mEq/L)

Normal ABG (arterial blood gases):  
pH 7. 36-7.44, pCO2  35-45 mmHg, HCO3  24-32 mEq/L, paO2 75-100 mmHg, arterial O2 sat SaO2 95-100%,
mixed venous pvO2 38-42 mmHg,

Alveolar-arterial O2 tension difference/gradient  (Normally 10-15 mmHg with room air):
       P(A-a) O2 =  (713 x FiO2  -  1.25 x pCO2)  -  PaO2

REF:
Washington Manual 28th ed. 1995