What is the Pathophysiology of an Asthmatic Attack?  and what are the Consequences?

Initial Response – Respiratory Alkalosis:

• Hyperventilation occurs during an asthma attack.
• Causes blood to become more basic (alkaline), leading to respiratory alkalosis (blood pH rises above 7.45).
• Why?
  • During hyperventilation, excessive CO₂ is expelled from the lungs.
  • CO₂ in blood exists in equilibrium with carbonic acid, hydrogen ions, and bicarbonate.
  • Rapid breathing shifts this equilibrium, decreasing CO₂ and carbonic acid.
  • Less carbonic acid means fewer hydrogen ions (H⁺), raising blood pH.
  • This initial phase is typically alkalotic due to excess breathing out of CO₂.

Progression – Trapped CO₂ and Respiratory Acidosis:

• Due to air trapping from mucus plugs and bronchoconstriction, CO₂ cannot be expelled efficiently.
• CO₂ accumulates in the alveoli and blood, shifting the equilibrium:
  • Increased CO₂ raises carbonic acid levels.
  • More carbonic acid dissociates into hydrogen ions and bicarbonate.
  • Elevated H⁺ ions lower blood pH, resulting in respiratory acidosis.

Impact on Blood Gas Levels:

• Hypoxia: Reduced oxygen levels in blood.
• Hypercapnia: Increased CO₂ (carbonic acid).
• Blood becomes more acidic, impairing cellular function and organ performance.

Severe Respiratory Distress:

• Continued hypoventilation leads to:
  • Critical hypoxemia (arterial oxygen partial pressure <50 mm Hg).
  • Organ dysfunction due to inadequate oxygen supply and acidosis.
  • Cellular and tissue damage, potentially leading to organ failure.

Signs and Symptoms of Low Oxygen:

• Anxiety, confusion, decreased responsiveness.
• Cyanosis (blue lips, fingertips, toes).
• Altered mental state, possible coma.

Status Asthmaticus:

• A persistent severe asthma attack unresponsive to inhalers.
• Requires emergency medical intervention (911).
• Progression includes:
  • Severe hypoxia.
  • Acidosis from CO₂ retention.
  • Enzymatic and cellular dysfunction.
  • Cardiac arrhythmias and neural depression.
  • Loss of responsiveness, potential respiratory and cardiac arrest.

Summary:

During an asthma attack, hyperventilation initially causes respiratory alkalosis, but airway obstruction quickly traps CO₂, leading to respiratory acidosis. If the attack persists and progresses, severe hypoxia, acidosis, and organ failure may occur. In critical cases like status asthmaticus, immediate emergency treatment is vital to prevent death.