From the Research
Vomiting can significantly affect your arterial blood gas (ABG) results by causing metabolic alkalosis, which is characterized by increased blood pH and bicarbonate levels. When you vomit, you lose gastric acid (hydrochloric acid) from your stomach, which decreases the acid content in your body. This loss of acid shifts your body's pH balance toward the alkaline side. Severe or prolonged vomiting can lead to significant metabolic alkalosis, characterized by pH > 7.45 and HCO3- > 26 mEq/L on ABG testing. Additionally, vomiting can cause dehydration and electrolyte imbalances, particularly potassium, chloride, and sodium depletion, which may further impact acid-base balance. The body tries to compensate for this alkalosis through respiratory mechanisms by decreasing breathing rate to retain more carbon dioxide, which can appear as a compensatory respiratory acidosis on ABG results. In clinical settings, understanding these changes is important when interpreting ABG results in patients with recent or ongoing vomiting episodes, as the underlying cause of the alkalosis needs to be addressed alongside symptomatic treatment, as noted in studies such as 1. Key points to consider include:
- Metabolic alkalosis can lead to respiratory inhibition and increased need for ventilatory support or prolongation of weaning from ventilation for patients with chronic respiratory disease.
- Acetazolamide can reduce alkalaemia and may reduce respiratory depression, but its effectiveness in patients with chronic obstructive pulmonary disease or obesity hypoventilation syndrome is still being researched, with some studies suggesting little impact on respiratory failure with metabolic alkalosis in these patients 1.
- The certainty of evidence for the use of acetazolamide in these cases is generally low, and larger trials are required to fully understand its benefits and harms. Given the potential for vomiting to cause significant metabolic alkalosis and impact ABG results, it is crucial to consider the effects of vomiting when interpreting ABG results and to address the underlying cause of the alkalosis in addition to providing symptomatic treatment.