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Arterial Blood Gas

- See:
      - Metabolic Acidosis
      - Resp. Acidosis
      - Metabolic Alkalosis
      - Resp. Alkalosis

- Decreased PaCO2:
    - if PaCOz is less than 35 mmHg and pH more than 7.45, the patient is hyperventilated and the respiratory frequency or IMV rate of the ventilator should be reduced;
    - respiratory alkalosis results in a reduced serum potassium;
         - if digitalis has been prescribed, combination of digitalis and hypokalemia can result in arrhythmias;
    - PaCO2 of < 36 mmHg & pH of < 7.36 constitute hyperventilatory response to metabolic acidosis;
         - if possible, treat underlying cause of metabolic acidosis & remeasure arterial blood gases;
         - continue steps until the PaCOz and pH are within normal limits;

- Increased PaCO2:
    - if PaCO is > 44 mmHg & pH is < 7.35, condition is hypoventilation;
    - increase frequency of IMV, & after 20 minutes remeasure ABG;
    - if response is minimal, incorrect tidal volume may have been selected;
    - increase tidal volume by 100 mL and repeat arterial blood gases

Base deficit stratifies mortality and determines therapy.

Assessing acid-base status in circulatory failure. Differences between arterial and central venous blood.