Arterial blood gas Dr. Basu MD

(Acid) The Respiratory System ↑ ventilation: "blow off" CO2 (acid) →↓ CO2 (acid) → Alkalosis. ↓ ventilation → retain CO2 (acid) → ↑ CO2 (acid) → Acidosis.

(Base) The Renal System Acidosis: ↑ H+ and low HCO3 (base) Compensation: Kidney: excreting H+ and retaining HCO3 (base). Lung: increasing ventilation to blow off CO2 (acid) and decrease the Acidosis.

(Base) The Renal System Alkalosis: ↓ H+ and excess HCO3 (base). Compensation: Kidney: excrete HCO3 and retain H+ Lung: hypoventilation to retain CO2 (acid) to decrease the Alkalosis.

Normal value pH 7.35-7.45, pCO2 of 35-45 mmHg HCO3 22-26 mmol/L

How to reads the data First, look at pH. (Normal = 7.35-7.45) pH is < 7.35; = ACIDOSIS. pH is > 7.45 = ALKALOSIS.

look at pH again If -- 7.35-7.45 (normal): COMPENSATED. If : pH is <7.35 or >7.45 : UNCOMPENSATED.

Metabolic or respiratory CO2 is <35 or >45= RESPIRATORY. HCO3 is <22 or >26 = METABOLIC.

? pH = 7.55 , CO2 = 40, HCO3 = 30 pH = 7.35, CO2 = 45, HCO3 = 20 If it is 7.35-7.45 (normal): COMPENSATED. If the pH is <7.35 or >7.45 : UNCOMPENSATED. CO2 is <35 or >45= RESPIRATORY. HCO3 is <22 or >26 = METABOLIC

pH = 7.44 PaCO2 = 47 HCO3 = 28 pH = 7.35 PaCO2 = 31 HCO3 = 18.1 CO2 is <35 or >45= RESPIRATORY. HCO3 is <22 or >26 = METABOLIC pH = 7.50 PaCO2 = 45 HCO3 = 33 Uncomp. Met. Alk. pH = 7.44 PaCO2 = 47 HCO3 = 28 Com Met alka. pH = 7.20 PaCO2 = 36 HCO3 = 14 Met acidosis pH = 7.35 PaCO2 = 31 HCO3 = 18.1 Com. Met acidosis

pH = 7.43 PaCO2 = 32 HCO3 = 21 pH = 7.42 PaCO2 = 32 HCO3 = 20 Uncomp Resp. alka pH = 7.43 PaCO2 = 32 HCO3 = 21 pH = 7.42 PaCO2 = 32 HCO3 = 20 Com Resp alka pH = 7.23 PaCO2 = 59 HCO3 = 22 Resp acidosis pH = 7.36 PaCO2 = 56 HCO3 = 31.4 pH = 7.38 PaCO2 = 70 HCO3 = 42 Com Resp acidicosis CO2 is <35 or >45= RESPIRATORY. HCO3 is <22 or >26 = METABOLIC

Respiratory Acidosis ↑ pCO2 . Compensation: ↑ HCO3 Cause: Chronic obstructive pulmonary disease (COPD) Electrolyte deficiencies (K+, P04 - )

Initial value / after Compensation Without Compensation pH (<7.35) PaCO2 (>47 mm Hg) HCO3 20-26 mmol/L WithCompensation pH ( ~ 7.35) PaCO2 (>47 mm Hg) HCO3: 32mmol/L ( acute) HCO3: 44mmol/L ( chronic)

Respiratory alkalosis arterial pCO2 falls Compensation: ↓ bicarbonate slightly. Hyperventilation Pneumonia Shock/decreased cardiac output

Respiratory alkalosis pH (> 7.45) PaCO2 ( 20 mm Hg) HCO3 28 mmol/L pH ( ~ 7.35) PaCO2 ( 20 mm Hg) HCO3 18 mmol/L

Metabolic acidosis ↑ in fixed acids in the blood. Compensation: hyperventilation > ↓ pCO2 Cause: Diarrhea Alcoholism (ethanol) Ketoacidosis

Metabolic acidosis: ketoacidosis Glucose > 250 pH: 7.00 to 7.24 HCO3: 10 to < 15 PaCO2 ( 25 mm Hg) Anion gap: >11 Increased electrolytes

Metabolic alkalosis Plasma bicarbonate increases Compensation: hypoventilation > CO2 retention. Cause: Gastric fluid loss Vomiting

Metabolic alkalosis pH 7.58 pCO2 21 mmHg HCO3 40 mmol/l > 26 pO2  154 mmHg pH ~ 7.50 pCO2 : ~ 60 mmHg HCO3  40 mmol/l pO2  154 mmHg

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