Serum Chloride Levels in Severe Vomiting Without Dehydration
In a patient with severe vomiting who is not yet dehydrated, the serum chloride level would be lower than normal (option D).
Pathophysiology of Chloride Loss in Vomiting
Vomiting leads to significant loss of gastric contents, which contain hydrochloric acid. This process has several important electrolyte consequences:
- Loss of hydrogen and chloride ions: Gastric secretions are rich in HCl, resulting in direct loss of chloride from the body 1
- Metabolic alkalosis development: The loss of acid from the stomach creates a metabolic alkalosis 2
- Compensatory mechanisms: Even before dehydration occurs, the body begins compensatory mechanisms to maintain acid-base balance
Electrolyte Changes in Early Vomiting
When severe vomiting occurs but the patient is not yet dehydrated, the following changes occur:
- Hypochloremia: Chloride levels decrease due to direct loss in gastric contents 2
- Metabolic alkalosis: The loss of acid leads to increased bicarbonate 2
- Normal volume status: Since the patient is not yet dehydrated, volume-related compensatory mechanisms haven't fully activated
Clinical Evidence Supporting Hypochloremia
The evidence clearly demonstrates that chloride levels decrease with vomiting:
- Studies of patients with self-induced vomiting show hypochloremic metabolic alkalosis as a consistent finding 2
- Chloride levels typically fall below normal reference ranges even before significant dehydration occurs 2
- Urine chloride levels are typically very low (<10 mEq/L) in patients with vomiting, reflecting the body's attempt to conserve chloride 2
Distinguishing Features from Other Conditions
It's important to note that hypochloremia from vomiting can be distinguished from other causes:
- In Bartter's syndrome, hypochloremia occurs with high urinary chloride (>20 mEq/L), whereas vomiting causes low urinary chloride (<10 mEq/L) 2
- Once dehydration develops, additional electrolyte abnormalities may occur, but hypochloremia is an early finding 1
Treatment Implications
Understanding the chloride status has important treatment implications:
- Isotonic fluid replacement is recommended for patients with volume depletion following vomiting 3
- Electrolyte replacement should include chloride to correct the deficiency 3
- Monitoring serum osmolality is important, with values >300 mOsm/kg indicating definitive dehydration 1
Common Pitfalls
- Assuming electrolyte abnormalities only occur with dehydration
- Failing to check chloride levels in patients with vomiting
- Misattributing hypochloremic alkalosis to other conditions when vomiting is the cause
In summary, severe vomiting leads to loss of gastric acid, resulting in hypochloremia (low serum chloride) even before clinical dehydration develops.