Respiratory alkalosis - causes, symptoms, diagnosis, treatment, pathology

Summary

Respiratory alkalosis occurs when the lungs expel too much carbon dioxide, raising blood pH above 7.45. Normally, the respiratory system balances pH by managing CO2 levels. In alkalosis, increased breathing can result from hypoxia, anxiety, or medical interventions. This causes a drop in CO2 levels and a rise in pH. The body responds initially by releasing hydrogen ions, and over time, the kidneys reduce bicarbonate reabsorption to restore pH balance. The condition has acute and chronic phases, depending on whether the kidneys have begun compensating for the pH imbalance.

Takeaways

• 🌬️ Respiratory alkalosis refers to a condition where the lungs remove too much carbon dioxide, causing a rise in blood pH above 7.45.
• 🫁 Normally, the lungs balance pH by pulling in oxygen and releasing carbon dioxide, which regulates carbonic acid and hydrogen ions in the blood.
• 🧠 Chemoreceptors in the carotid arteries and aortic arch detect CO2 levels and signal the brainstem to adjust the breathing rate.
• ⬇️ When CO2 levels drop, the pH rises, and respiratory centers decrease the breathing rate to restore balance.
• 💨 In respiratory alkalosis, the breathing rate increases excessively, leading to a loss of too much CO2 and an increase in blood pH.
• ⛰️ Increased ventilation can occur due to hypoxia from conditions like pneumonia, pulmonary embolism, or even high altitudes.
• 😨 Abnormal increases in ventilation can result from anxiety, panic attacks, sepsis, or salicylate overdose, and sometimes due to brainstem disorders.
• 🩺 Ventilator settings can also cause respiratory alkalosis if not properly adjusted, leading to CO2 depletion.
• ⏳ In the acute phase, cellular mechanisms release hydrogen ions to bind with bicarbonate, but this is usually insufficient to significantly lower the pH.
• 🗓️ Over 3-5 days, the kidneys help by excreting more bicarbonate, lowering its concentration, and bringing the pH closer to normal in the chronic phase.

Q & A

What is respiratory alkalosis?

Respiratory alkalosis is a condition where the lungs remove too much carbon dioxide from the body, causing the blood's pH to rise above 7.45.

What is the role of carbon dioxide in maintaining pH balance in the body?

Carbon dioxide binds with water in the blood to form carbonic acid, which dissociates into hydrogen and bicarbonate ions. This process helps maintain pH balance by regulating the concentration of hydrogen ions in the blood.

How do the lungs normally maintain pH balance?

The lungs regulate pH balance by adjusting the ventilation rate to match the body’s carbon dioxide production. If too much carbon dioxide is removed, pH rises, and if too little is removed, pH falls.

What triggers an increase in ventilation during respiratory alkalosis?

Increased ventilation during respiratory alkalosis can be triggered by low oxygen levels (hypoxia), anxiety, panic attacks, sepsis, or brain stem disorders. It can also occur due to medical interventions, like improper ventilator settings.

How do chemoreceptors respond to changes in pH and carbon dioxide levels?

Peripheral chemoreceptors in the carotid arteries and aortic arch detect changes in pH and carbon dioxide. When carbon dioxide levels drop and pH rises, they fire less, signaling the brainstem to reduce the respiratory rate.

What are the body's initial compensatory mechanisms during respiratory alkalosis?

Initially, acidic molecules within cells, particularly red blood cells, release hydrogen ions that bind with bicarbonate to form carbonic acid. This helps reduce the blood's bicarbonate concentration slightly, but not enough to significantly lower pH.

How do the kidneys contribute to compensation during chronic respiratory alkalosis?

After 3-5 days, the kidneys begin to compensate by reducing bicarbonate reabsorption in the proximal convoluted tubule, increasing its excretion in urine. This helps lower the blood's bicarbonate levels and bring pH closer to normal.

What is the difference between acute and chronic respiratory alkalosis?

Acute respiratory alkalosis occurs shortly after the onset of hyperventilation and lacks significant renal compensation, while chronic respiratory alkalosis develops over days with the kidneys actively lowering bicarbonate levels to correct the pH imbalance.

What happens to pCO2 and bicarbonate levels during respiratory alkalosis?

In respiratory alkalosis, pCO2 levels drop below the normal range (typically below 35 mmHg), leading to a reduction in plasma bicarbonate concentration. In acute cases, the decrease is minimal, but in chronic cases, the kidneys can significantly lower bicarbonate levels.

Why can improper ventilator settings cause respiratory alkalosis?

If a ventilator is set to provide too much ventilation, it can cause excessive removal of carbon dioxide from the blood, leading to respiratory alkalosis by raising the blood pH beyond its normal range.