Introduction
Oxygen is essential for the survival and functioning of living organisms. The respiratory system plays an important role in providing oxygen and removing carbon dioxide. The inability to perform this function of gas exchange results in respiratory failure. There are two types of respiratory failure, and hypoxemic respiratory failure is one type of respiratory failure. Hypoxemic respiratory failure occurs when the body cannot receive an adequate oxygen supply.
What Is Hypoxemia?
Hypoxemia refers to a condition in which the oxygen level in the blood is low. It refers to low oxygen levels in the arterial blood. It occurs due to abnormal delivery of oxygen to the body. Hypoxia is different from hypoxemia and refers to a reduced level of oxygen in the tissues or defective utilization of oxygen by the tissues. Hypoxemia occurs if enough oxygen cannot be breathed in or if the oxygen that is breathed in cannot enter the blood. Hypoxemia can cause mild symptoms or result in death. It causes mild symptoms like headache and shortness of breath. In severe cases, it interferes with heart and brain function and results in hypoxemic respiratory failure.
What Is Hypoxemic Respiratory Failure?
Respiratory failure is a condition in which there is insufficient oxygen in the blood. This occurs due to inadequate gas exchange causing low levels of oxygen or high level of carbon dioxide. Respiratory failure is divided into two types:
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Type I Respiratory Failure - Hypoxemic respiratory failure occurs when the respiratory system loses its ability to provide sufficient oxygen to the body. This occurs due to alveolar hypoventilation, diffusion defect, low atmospheric pressure or fraction of inspired oxygen, ventilation-perfusion mismatch, and right-to-left shunt.
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Type II Respiratory Failure - Hypercapnic respiratory failure occurs when the respiratory system loses its ability to remove carbon dioxide. This occurs due to increased carbon dioxide production and respiratory pump failure.
Respiratory failure can be further divided into acute, chronic, and acute chronic based on chronicity.
What Are the Causes of Hypoxemic Respiratory Failure?
Respiratory failure is caused by an abnormality with any component of the respiratory system. Components of the respiratory system are the upper and lower respiratory tracts, the central and peripheral nervous system, the chest wall, and the muscles of respiration.
How Does Hypoxemic Respiratory Failure Occur?
Hypoxemic respiratory failure is caused by a decrease in the partial pressure of oxygen which is less than 60 mmHg, with a normal or decreased partial pressure of carbon dioxide. Hypoxemic respiratory failure occurs due to the following mechanisms:
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Alveolar Hypoventilation - Alveolar hypoventilation causes the arterial partial pressure of carbon dioxide to increase. An increase in the partial pressure of carbon dioxide decreases the alveolar partial pressure of oxygen. In severe cases, alveolar hypoventilation may progress to hypercapnic respiratory failure. Alveolar hypoventilation may be caused by central nervous system depression (coma, central sleep apnea, hypothyroidism, obesity hypoventilation syndrome, and toxic metabolic encephalopathy), decreased chest wall compliance (flail chest and kyphoscoliosis), and neuromuscular diseases (amyotrophic lateral sclerosis, Guillain-Barre syndrome, and myasthenia gravis).
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Low Atmospheric Pressure or Fraction of Inspired Oxygen - The partial pressure of oxygen decreases at low atmospheric pressures and with low levels of inspired oxygen. This type of respiratory failure occurs at high altitudes.
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Diffusion Defect - Exchange of gases occurs at the alveolar-capillary interface. Diffusion defect occurs across the membrane if there are structural changes in the components of the alveolar-capillary interface, like decreased surface area or increased thickness. A reduction in pulmonary capillary transit time through the alveolar-capillary interface causes diffusion defects across the membrane. The diffusion defect is caused by exercise, emphysema, and interstitial lung disease.
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Ventilation-perfusion Mismatch - The alveolar gas composition is based on the homeostasis between alveolar ventilation and pulmonary capillary blood flow that occurs at the alveolar-capillary interface. The value of the ventilation-perfusion ratio is one if a perfect match occurs between alveolar ventilation and pulmonary capillary blood flow. If ventilation is excessive to perfusion, the ratio is greater than one. Dead space ventilation is seen if the ratio reaches infinity. If perfusion is excessive to ventilation, the ratio is less than one. Shunt occurs if the ratio reaches zero. The ratio is approximately 0.8 in healthy individuals. Ventilation-perfusion mismatch is the major cause of hypoxemic respiratory failure. Ventilation-perfusion mismatch is caused by acute respiratory distress syndrome, atelectasis, chronic obstructive pulmonary disease, congestive heart failure, pneumonia, and pulmonary embolism.
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Right-to-Left Shunt - Shunt occurs when the ventilation-perfusion ratio reaches zero. True shunt occurs when gas exchange at the alveolar-capillary interface is absent. The right-to-left intracardiac shunt observed in atrial septal defect and patent foramen ovale is analogous to the true shunt. The right-to-left shunt is caused by arteriovenous malformations, severe pneumonia, complete atelectasis, and severe pulmonary edema.
What Are the Symptoms of Hypoxemic Respiratory Failure?
The symptoms associated with hypoxemic respiratory failure are:
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Cough.
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Hemoptysis.
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Sputum production.
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Wheezing.
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Chest pain.
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Decreased appetite.
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Heartburn.
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Weight loss.
What Are the Complications of Hypoxemic Respiratory Failure?
Hypoxemic respiratory failure may result in fatal complications. It causes pulmonary complications like pulmonary emboli, bronchopleural fistula, pneumothorax, barotrauma, fibrosis, nosocomial pneumonia, and pneumonia. The extrapulmonary complications include gastrointestinal hemorrhage, acid-base disturbances, decreased cardiac output, hepatic failure, ileus, increased intracranial pressure, malnutrition, pneumoperitoneum, infection, renal failure, and thrombocytopenia.
How Is Hypoxemic Respiratory Failure Diagnosed?
The diagnosis is based on the following tests:
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Arterial Blood Gas Test - Arterial blood gas test is performed to obtain pH (potential of hydrogen, partial pressure of oxygen, partial pressure of carbon dioxide, and serum bicarbonate. The partial pressure of oxygen is used to assess oxygenation.
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Radiography - Computed tomography, magnetic resonance imaging, nuclear medicine, angiography, or ultrasonography is performed to evaluate respiratory failure.
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Pulse Oximetry - Pulse oximeter is a device that is used to measure the oxygen saturation in the pulsatile blood.
How Is Hypoxemic Respiratory Failure Treated?
Hypoxemic respiratory failure requires supplemental oxygen and ventilation. Hypoxemic respiratory failure is managed with oxygen administration, noninvasive ventilation, and mechanical ventilation.
Conclusion
Hypoxemia is a condition in which the oxygen level is low in the blood. Hypoxemic respiratory failure is a type of respiratory failure that is caused by low oxygen levels in the blood. It can cause potentially fatal complications. Early diagnosis and treatment are essential to prevent pulmonary and extrapulmonary complications. It is important to consult the doctor on experiencing symptoms like shortness of breath.
