Excessive Nasogastric (NG) drainage and acid base status

Case details

A postoperative surgical patient had a nasogastric tube (figure) in for three days.

Nasogastric tube

 

Figure- Nasogastric tube

 

The nurse caring for the patient stated that there was much drainage from the tube that is why she felt so sick. What could be the reason?

A. Metabolic Acidosis

B. Metabolic Alkalosis

C. Respiratory Acidosis

D. Respiratory Alkalosis

E. None of the above.

The correct answer is- B-Metabolic alkalosis.

Metabolic alkalosis is primary increase in HCO3 − with or without compensatory increase in PCO2; pH may be high or nearly normal.

Whenever a hydrogen ion is excreted, a bicarbonate ion is gained into the extracellular space. Hydrogen ions may be lost through the kidneys or the GI tract. Vomiting or nasogastric (NG) suction generates metabolic alkalosis by the loss of gastric secretions, which are rich in hydrochloric acid (HCl).

Causes of metabolic alkalosis can be divided into chloride-responsive alkalosis (urine chloride <20 mEq/L), chloride-resistant alkalosis (urine chloride >20 mEq/L), and other causes, including alkali-loading alkalosis.

  • Chloride-responsive alkalosis (urine chloride <20 mEq/L)
    • Loss of gastric secretions – Vomiting, NG suction
    • Loss of colonic secretions
    • Thiazides and loop diuretics (after discontinuation)
    • Cystic fibrosis( Due to loss of chloride in the sweat)
    • Ingestion of large doses of non absorbable antacids
  • Chloride-resistant alkalosis (urine chloride >20 mEq/L)
      • Primary hyperaldosteronism
      • Current use of diuretics in hypertension
      • Cushing syndrome
      • Exogenous mineralocorticoids or glucocorticoids
      • Severe potassium depletion
  • Other causes(Alkali loading alkalosis)
    • Exogenous alkali administration – Sodium bicarbonate therapy in the presence of renal failure.
    • Milk-alkali syndrome (Hypercalcemia increases renal bicarbonate reabsorption)
    • Massive blood transfusion (citrate in the transfused blood is converted to bicarbonate).
    • End-stage renal disease

Hypoventilation and hypokalemia are diagnostic of metabolic alkalosis. The arterial blood pH and bicarbonate are elevated. The arterial pCO2 is increased.

Mild alkalosis is generally well tolerated. Severe or symptomatic alkalosis (pH > 7.60) requires urgent treatment.

Severe metabolic alkalosis (i.e., blood pH >7.55) is a serious medical problem. Mortality rates have been reported as 45% in patients with an arterial blood pH of 7.55 and 80% when the pH was greater than 7.65.

 

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