Fluid, Electrolyte, and Acid-Base Imbalances

Buffer Systems

The body utilizes several buffering systems to neutralize sudden changes in acidity. The most important is the sodium bicarbonate–carbonic acid system, which serves as the major extracellular fluid (ECF) buffer and is regulated by both the respiratory and renal systems. Other vital buffering systems include:

• Phosphate buffers
• Hemoglobin
• Protein buffers

Compensation Mechanisms

When an imbalance occurs, the body initiates compensation mechanisms to attempt to restore the relative proportion of hydrogen ions ($H^+$) and bicarbonate ions ($HCO_3^-$) in the circulation. These mechanisms include the activation of buffers, changes in respiration (breathing patterns), and changes in renal function.

Clinical Note: Compensation is typically a short-term response. It helps stabilize the pH, but it does not remove the underlying cause of the imbalance. If the causative problem becomes more severe or the compensation mechanisms fail, the patient enters a state of decompensation, which is a life-threatening emergency requiring immediate medical intervention.

Acidosis

Acidosis is defined by an excess of hydrogen ions ($H^+$) and a subsequent decrease in serum pH. This state can be categorized by its origin:

Respiratory Acidosis

This occurs when the lungs cannot effectively remove enough $CO_2$, leading to an accumulation of carbonic acid.

• Acute causes: Pneumonia, airway obstruction, chest injuries, or drugs that depress the respiratory control center.
• Chronic causes: Most commonly associated with Chronic Obstructive Pulmonary Disease (COPD).

Metabolic Acidosis

This involves a deficit of bicarbonate ions or an accumulation of metabolic acids.

• Causes: Excessive loss of bicarbonate (such as through diarrhea), renal disease, or renal failure (where the kidneys fail to excrete acids or produce enough bicarbonate).

Effects and Compensation of Acidosis: Acidosis often impairs nervous system function, leading to symptoms such as headache, lethargy, confusion, and potentially coma or death. To compensate, the body will attempt deep, rapid breathing to blow off $CO_2$ and will secrete urine with a low pH to rid the body of excess acid.

Alkalosis

Alkalosis is characterized by a deficit of hydrogen ions and an increase in serum pH.

Respiratory Alkalosis

This is caused by hyperventilation, which results in the excessive loss of $CO_2$.

• Causes: Anxiety, high fever, head injuries, or brainstem tumors.

Metabolic Alkalosis

This is caused by an increase in serum bicarbonate or a loss of acid.

• Causes: Loss of hydrochloric acid from the stomach (e.g., through vomiting), hypokalemia, or the excessive ingestion of antacids.

Effects and Treatment of Alkalosis: Alkalosis tends to increase the irritability of the nervous system. Patients may experience restlessness, muscle twitching, tingling/numbness in the fingers, tetany, seizures, or even coma.

Treatment Strategy: The primary goal of treatment is to address the underlying cause. Immediate corrective measures may include fluid and electrolyte replacement or, in the case of acidosis, the addition of bicarbonate to the blood to reverse the pH drop.