The Six Steps of Systematic Acid-Base Evaluation

A patient with chronic bronchitis (COPD): [H+]=44 nmol/l, pCO2=71 mmHg, [HCO3]=39mmol/l

A patinet who has had an acute asthmatic attack: [H+]=24 nmol/l, pCO2=19 mmHg, [HCO3]=20mmol/l

A young man with a history of dyspepsia and excessive alcohol intake who gives a 24-hour history of vomiting: [H+]=28 nmol/l, pCO2=55 mmHg, [HCO3]=48mmol/l

50-year-old man with a 2 week history of vomiting and diarrhoea. On examination he is drhydrated and his breathing is deep and noisy : [H+]=64 nmol/l, pCO2=21 mmHg, [HCO3]=8 mmol/l

Case 1

Mr. Frank is a 60 year-old with pneumonia. He is admitted with dyspnea, fever and chills. His blood gas is below:pH 7.28 CO2 56 PO2 70 HCO3 25 SaO2 89%

Mr. Frank has an partially compensated respiratory acidosis with hypoxemia as a result of his pneumonia.

Oxygen therapy should consist of only the minimal amount necessary to increase his oxygen saturation to normal (95-98%).

hypoxemia 85 – 95 mmHg

Case 2

Ms. Strauss is a 24 year-old college student. She has a history of Crohn's disease and is complaining a four day history of bloody-watery diarrhea. A blood gas is obtained to assess her acid/base balance:pH 7.28 CO2 43 pO2 88 HCO3 20 SaO2 96%

Normally, the respiratory center compensates quickly for metabolic disorders. However, in Ms. Strauss' case she would have to hyperventilate in order to compensate. This may not be possible in her present condition, and should be evaluated further.

Anion gap??

Case 3

Mr. Karl is a 80 year-old nursing home resident admitted with urosepsis. Over the last two hours he has developed shortness of breath and is becoming confused. His ABG shows the following results:pH 7.02 CO2 55 pO2 77 HCO3 14 SaO2 89%

Mr. Karl has a combined metabolic and respiratory acidosis with hypoxemia. The metabolic acidosis is caused by his sepsis. The respiratory acidosis is secondary to respiratory problem. Treatment must be aggressive, because his acidosis is severe. His respiratory status needs to be stabilized, and would probably require mechanical ventilation.Bicarbonate should not be administered until the underlying sepsis and respiratory failure is treated.

hypoxemia 85 – 95 mmHg

Case 4

Mrs. Lauder is a thin, elderly-looking 61 year-old COPD patient. She has an ABG done as part of her routine care in the pulmonary clinic. The results are as follows: pH 7.37 CO2 63 pO2 58 HCO3 35 SaO2 89%

hypoxemia 85 – 95 mmHg

Case 5

Ms. Steele is a 17 year-old with intractable vomiting. She has some electrolyte abnormalities, so a blood gas is obtained to assess her acid/base balance.pH 7.50 CO2 36 pO2 92 HCO3 27 SaO2 97%

Ms. Steele has a partially compensated metabolic alkalosis. This is due to vomiting that results in excessive loss of stomach acid. Treatment consists of fluids, anti-emetics, and management of her electrolyte disorders.

22-26 mmol/l

Case 6

Mr. Casper is a 55 year-old with GERD. He takes about 15 TUMS antacid tablets a day. An ABG is obtained to assess his acid/base balance:pH 7.46 CO2 42 pO2 86 HCO3 29 SaO2 97%

Mr. Casper has overmedicated himself with TUMS, effectively absorbing too much stomach acid. His ABG shows a not-compensated metabolic alkalosis. Treatment consists of better control of his GERD, possibly with H2-blockers (Pepcid®) or proton-pump inhibitors (Prilosec®).

GERD –gastroesophageal reflux disease

Milk-alkali syndrome

Case 7

Mrs. Dobins is found pulseless and not breathing this morning. After a couple minutes of CPR she responds with a pulse and starts breathing on her own. A blood gas is obtained:pH 6.89 CO2 70 pO2 42 HCO3 13 SaO2 50%

Mrs. Dobins has a severe metabolic and respiratory acidosis with hypoxemia. The metabolic component comes from her decreased perfusion, and the respiratory component comes from inadequate ventilation. Treatment would consist of intubation, mechanical ventilation, blood pressure and circulatory support.

hypoxemia 85 – 95 mmHg