Infant Respiratory Distress Syndrome

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Summary1)First Aid: USMLE Step 1 by Tao Le

Infant Respiratory Distress Syndrome or also known as hyaline membrane disease is a disorder in which the infant’s lungs produce inadequate surfactant, a protein normally secreted by type II pneumocytes in mature lungs.

Pathophysiology2)Infant Respiratory Distress Syndrome (Wikipedia)

The lungs of infants with respiratory distress syndrome are developmentally deficient in a material called surfactant, which helps prevent collapse of the terminal air-spaces (the future site of alveolar development) throughout the normal cycle of inhalation and exhalation.

Pulmonary surfactant is a complex system of lipids, proteins and glycoproteins that are produced in specialized lung cells called Type II cells or Type II pneumocytes. The surfactant is packaged by the cell in structures called lamellar bodies, and extruded into the air-spaces. The lamellar bodies then unfold into a complex lining of the air-space. This layer reduces the surface tension of the fluid that lines the alveolar air-space. Surface tension is responsible for approximately 2/3 of the inward elastic recoil forces.

In the same way that a bubble will contract to give the smallest surface area for a given volume, so the air/water interface means that the liquid surface will tend toward being as small as possible, thereby causing the air-space to contract. By reducing surface tension, surfactant prevents the air-spaces from completely collapsing on exhalation. In addition, the decreased surface tension allows re-opening of the air-space with a lower amount of force. Therefore, without adequate amounts of surfactant, the air-spaces collapse and are very difficult to expand.

Causes

  • Lack of surfactant

Symptoms 3)MedlinePlus

  • Lung involvement – brief stop in breathing (apnea), decreased urine output, grunting, nasal flaring, rapid breathing, shallow breathing, shortness of breath, unusual breathing movement (such as drawing back of the chest muscles with breathing)
  • Skin changes – bluish color of the skin and mucus membranes (cyanosis)

Diagnosis 4)medEssentials for the USMLE Step 1 by Michael Manley 5)MedlinePlus

  • Amniotic fluid lecithin ratio – sphingomyelin ratio (a ratio of 2:1 implies adequate surfactant is present
  • Blood gas analysis – shows low oxygen and excess acid in the body fluids
  • Chest x-ray – shows a “ground glass” appearance to the lungs that is typical of the disease. This often develops 6 to 12 hours after birth

Treatment 6)medEssentials for the USMLE Step 1 by Michael Manley 7)Infant Respiratory Distress Syndrome (Wikipedia)

  • Glucocorticoids – given to the mother to accelerate fetal lung maturation
  • Extracorporeal membrane oxygenation (ECMO) –  imitates the gas exchange process of the lungs

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