30.18 : Disorders of Acid-Base Balance

The human body maintains a precise pH range of arterial blood between 7.35 and 7.45. Deviations result in either acidosis (pH < 7.35) or alkalosis (pH > 7.45). These conditions are further classified as respiratory or metabolic disorders based on their underlying cause.

Respiratory Acidosis and Alkalosis
Respiratory acidosis occurs due to an increase in the partial pressure of carbon dioxide PCO₂ in the blood. It often arises from shallow breathing or impaired gas exchange caused by pneumonia, cystic fibrosis, or emphysema. These conditions lead to CO₂accumulation, resulting in a decrease in blood pH.

Respiratory alkalosis, by contrast, is caused by a decrease in blood PCO₂ ​​ below 35 mmHg, typically due to hyperventilation. Common triggers include oxygen deficiency, stroke, or severe anxiety. This reduction in PCO₂ causes an increase in blood pH, shifting the body into an alkalotic state.

Metabolic Acidosis and Alkalosis
Unlike respiratory disorders, which originate from changes in CO₂ levels, metabolic disorders arise due to fluctuations in bicarbonate levels or non-carbonic acids. Metabolic acidosis is characterized by decreased blood bicarbonate ion (HCO₃⁻) levels below 22 mEq/L. This condition may result from:

1. Loss of HCO₃⁻ through diarrhea or renal dysfunction
2. Accumulation of non-carbonic acids such as lactic acid or ketones
3. Impaired kidney function leading to reduced excretion of hydrogen ions (H⁺)

These factors contribute to a drop in blood pH.

Metabolic alkalosis occurs when blood HCO₃⁻ levels rise above 26 mEq/L, causing a corresponding increase in blood pH above 7.45. This condition often results from:

1. Non-respiratory acid loss due to excessive vomiting or gastric suctioning
2. Overconsumption of antacids or alkaline drugs
3. Endocrine disorders, diuretics, or severe dehydration

Respiratory and metabolic acid-base disorders can disrupt homeostasis and require prompt intervention to restore pH balance. If left untreated, these disorders may lead to severe physiological complications. Prompt intervention is critical to restoring pH balance.