A nurse cares for a patient who has a nasogastric tube attached to low suction because of a suspected bowel obstruction. Which of the following arterial blood gas results might be expected in this patient?
A. pH 7.52, PCO2 54 mmHg.
B. pH 7.42, PCO2 40 mmHg.
C. pH 7.25, PCO2 25 mmHg.
D. pH 7.38, PCO2 36 mmHg.
Correct Answer: A. pH 7.52, PCO2 54 mmHg.
A patient on nasogastric suction is at risk of metabolic alkalosis as a result of loss of hydrochloric acid in gastric fluid. Of the answers given, only answer A (pH 7.52, PCO2 54 mm Hg) represents alkalosis. Normal range for pH range from 7.35-7.45. CO2 level has a normal range of 35 to 45 mmHg. Normal range for HCO3 is 22-26 mmol/L. The lower the number, the more acidotic the patient is. The higher the pH, the more base is in the blood sample.
Option B: This result is a normal blood gas value. Arterial blood gas analysis assesses a patient’s partial pressure of oxygen (PaO2), providing information on the oxygenation status; the partial pressure of carbon dioxide (PaCO2), providing information on the ventilation status (chronic or acute respiratory failure, and is changed by hyperventilation (rapid or deep breathing) and hypoventilation (slow or shallow breathing); and acid-base status.
Option C: This result represents respiratory acidosis. Arterial blood gas interpretation is best approached systematically. Interpretation leads to an understanding of the degree or severity of abnormalities, whether the abnormalities are acute or chronic, and if the primary disorder is metabolic or respiratory in origin. Several articles have described simplistic ways to interpret ABG results. However, the Romanski method of analysis is most simplistic for all levels of providers. This method assists with determining the presence of an acid-base disorder, its primary cause, and whether compensation is present.
Option D: This result is borderline normal with slightly low PCO2. The PaCO2 indicates whether the acidosis or alkalemia is primarily from a respiratory or metabolic acidosis/alkalosis. Paco2>40 with a pH<7.4, indicates a respiratory acidosis, and <40 and pH<7.4 indicates a respiratory alkalosis (but is often from hyperventilation from anxiety or compensation for a metabolic acidosis).