The human body maintains a delicate equilibrium of acids and bases, a process known as pH regulation. This balance is remarkably precise, allowing for proper cellular function throughout all organ systems. While vomiting is a common experience, its effect on blood chemistry is significant and specific. The mechanical loss of stomach contents fundamentally disrupts this balance, moving the body not toward a state of excessive acidity, but rather toward a state of excessive alkalinity. Vomiting typically causes a condition called metabolic alkalosis.
Understanding Acidosis and Alkalosis
The acidity or alkalinity of the body’s fluids is measured using the pH scale, which runs from 0 to 14. A neutral pH is 7.0; values below this point are acidic, and values above it are alkaline, or basic. Blood is naturally slightly alkaline, and a healthy pH range is tightly controlled between 7.35 and 7.45.
Acidosis occurs when the blood pH falls below 7.35, indicating an excess of acid or a deficit of base. Conversely, alkalosis is defined by a blood pH that rises above 7.45, reflecting a deficiency of acid or an overabundance of base. These conditions are classified as metabolic when they result from changes in the level of bicarbonate (a base), which is regulated by the kidneys.
The Mechanism of Gastric Acid Loss
The stomach produces gastric juice, a highly acidic fluid rich in hydrochloric acid (HCl). Specialized cells generate this acid by secreting hydrogen ions (H+), the primary component of acid, into the stomach cavity. For every hydrogen ion secreted, a bicarbonate ion (HCO3-), which is a base, is simultaneously released into the bloodstream.
This process normally results in a temporary, mild rise in blood bicarbonate known as the post-prandial alkaline tide. When a person vomits, the highly acidic contents of the stomach, including the H+ ions, are forcefully expelled. This physical removal of acid means the bicarbonate released into the blood is left behind, unopposed by the acid it was meant to neutralize. The net effect is an increase in the proportion of bicarbonate relative to acid, directly generating metabolic alkalosis.
Systemic Compensation and Restoration of Balance
The body activates feedback loops involving the lungs and kidneys to correct the rising pH. The respiratory system provides the fastest response by slowing breathing (hypoventilation). Slower breaths retain more carbon dioxide (CO2), which combines with water to form carbonic acid. This retention of acid helps buffer the excess bicarbonate and drives the blood pH back toward the normal range.
The renal system attempts to restore balance by adjusting the excretion of bicarbonate and hydrogen ions, though this process is slower. Kidneys normally excrete excess bicarbonate in the urine to correct alkalosis. However, severe vomiting often causes fluid loss and dehydration, triggering the body to prioritize retaining sodium and water to maintain blood volume. This volume-conserving mechanism inadvertently causes the kidneys to also retain bicarbonate, preventing correction. Furthermore, the loss of potassium (hypokalemia) and chloride (hypochloremia) exacerbates the problem, making it difficult for the kidneys to eliminate the excess base.
Recognizing Severe Electrolyte Imbalances
Prolonged or severe metabolic alkalosis is accompanied by disturbances in key electrolytes. Gastric fluid loss depletes the body’s chloride store, causing hypochloremia, which sustains the alkalosis. Concurrent loss of potassium from the stomach and increased renal excretion results in hypokalemia (low potassium levels).
These electrolyte abnormalities can profoundly affect muscle and nerve function. Symptoms include severe muscle weakness, cramps, or spasms, and sensations of numbness or tingling in the extremities. Concerning signs involve the cardiovascular and central nervous systems, such as confusion, agitation, or, in severe cases, an irregular heart rhythm or seizures. Correction of the imbalance focuses on addressing the underlying fluid depletion and replacing the lost electrolytes, particularly chloride, often through an intravenous saline solution.