The pH scale measures how acidic or alkaline a substance is, with 7.0 being neutral. The human body maintains a narrow, slightly alkaline blood pH range between 7.35 and 7.45. This tight control is necessary because even minor fluctuations can severely disrupt biological function. The condition where the blood pH rises above this normal range is known as alkalosis.
Understanding Alkalosis
Alkalosis is defined as a blood pH greater than 7.45, representing a decreased concentration of hydrogen ions in the bloodstream. This condition is termed alkalemia, indicating that the blood itself is too alkaline.
An elevated pH is dangerous because it affects the body’s proteins and enzymes. Proteins rely on a specific three-dimensional structure maintained by chemical bonds. An alkaline environment alters the electrical charge of amino acids, causing the protein to change shape, a process called denaturation. This structural change prevents enzymes from performing their catalytic functions, halting chemical reactions essential for life.
The Body’s pH Control Systems
The body employs three lines of defense to maintain acid-base balance, starting with rapid chemical buffers. The most important is the bicarbonate buffer system, consisting of carbonic acid and bicarbonate ions circulating in the blood. If a base is introduced, carbonic acid neutralizes it; if an acid is introduced, bicarbonate ions neutralize it, preventing dramatic pH shifts. This system provides immediate protection against pH changes throughout the body.
The second line of defense is the respiratory control system, which acts within minutes to regulate carbon dioxide (CO2) levels. CO2 is produced by cellular metabolism and combines with water to form carbonic acid, affecting the blood’s acidity. Specialized chemoreceptors monitor blood acidity and signal the respiratory centers.
If blood becomes too alkaline, the respiratory center slows the breathing rate and depth. This hypoventilation causes CO2 to build up in the blood, increasing the concentration of carbonic acid and hydrogen ions, lowering the pH toward the normal range. Conversely, if the blood becomes too acidic, the body increases ventilation to expel CO2, raising the pH.
The third and most powerful line of defense is the renal control system, though its effects take hours to days to manifest. The kidneys regulate pH by selectively reabsorbing or excreting hydrogen and bicarbonate ions. In alkalosis, specialized cells in the kidney tubules (Type B intercalated cells) excrete excess bicarbonate into the urine.
Simultaneously, the kidneys decrease the secretion of hydrogen ions, conserving acid to counteract the blood’s high alkalinity. This slow but powerful mechanism ensures the long-term adjustment of the body’s base load. The kidneys also generate new bicarbonate to replace any lost during buffering of metabolic acids.
Primary Causes of Elevated pH
Alkalosis is categorized into two types: respiratory and metabolic. Respiratory alkalosis occurs when a person exhales too much carbon dioxide too quickly. This hyperventilation rapidly lowers the amount of CO2 in the blood, reducing the concentration of carbonic acid and raising the pH.
Common triggers for respiratory alkalosis include panic attacks or extreme anxiety, where rapid breathing is a physiological response. It can also be caused by conditions that stimulate the respiratory center, such as high altitude, where lower oxygen pressure forces an increased breathing rate. Fever and certain lung diseases can also lead to hyperventilation.
Metabolic alkalosis is caused by excessive acid loss or bicarbonate accumulation. The most common cause is sustained loss of stomach acid, often due to severe vomiting or gastric suctioning. The stomach contains concentrated hydrochloric acid, and losing it directly removes acid from the body fluids.
Another mechanism is the use of certain diuretics, such as furosemide, which leads to a loss of hydrogen ions and potassium in the urine, indirectly increasing blood bicarbonate concentration. In rare cases, ingesting large amounts of alkali-containing substances, like excessive antacids, can overwhelm the body’s buffering capacity and contribute to metabolic alkalosis.
Symptoms and Medical Intervention
Symptoms of alkalosis often relate to altered nerve and muscle function, a direct consequence of the elevated pH affecting calcium levels. High alkalinity causes more calcium to bind to proteins like albumin, decreasing the amount of free, active calcium in the blood (hypocalcemia). This can lead to muscle twitching, spasms, and tetany in severe cases.
Patients may experience numbness or tingling sensations, particularly around the mouth, hands, and feet, along with lightheadedness or confusion. Diagnosing alkalosis requires an arterial blood gas (ABG) analysis, which measures the blood’s pH, carbon dioxide, and bicarbonate levels. Electrolyte panels are also performed to check for imbalances in minerals like potassium and chloride, which often accompany metabolic alkalosis.
Treatment focuses on correcting the underlying cause, as alkalosis is usually a symptom of another condition. For respiratory alkalosis, the immediate goal is to slow the breathing rate, often achieved by calming the patient or having them rebreathe into a paper bag to restore CO2 levels. For metabolic alkalosis, intervention may involve intravenous fluids and electrolytes, such as saline solution and potassium chloride, to replace what was lost during vomiting or diuretic use.