Initial link of pathogenesis
The key triggering factor of the disease is a pulmonary surfactant deficiency or a critical decrease in its physiological effects. There are four main causes of this condition:
- Immaturity of the lung tissue, which leads to an absolute insufficiency of surfactant production, up to the complete cessation of its synthesis.
- Anomalies of physicochemical characteristics — a situation where surfactant is produced in optimal amounts, but its structure is impaired.
- Insufficient effects of surfactant with normal composition and volume.
- Accelerated destruction of surfactant under the influence of pathological factors.
The main consequence of this deficiency is the progressive process of alveolar collapse, known as atelectasis. As a result, there is a progressive decrease in total lung capacity, which makes adequate gas exchange impossible.
Formation of hyaline membranes
The further development of the pathology is associated with morphological changes in the airways. A pathological exudate begins to actively form and accumulate within them, characterized by a high content of protein and leukocytes.
In parallel with this process, there is an accumulation of debris — a breakdown product of damaged pulmonary epithelial cells. During microscopic examination, this stained cellular and protein debris visually resembles dense membranes. It was precisely this specific pathomorphological picture that once provided the basis for the term "hyaline membrane disease", which is used today as a fully valid synonym for the primary diagnosis.
Cascade of systemic disorders
The pathogenesis of the syndrome is not limited to alveolar collapse alone. It triggers a complex cascade of reactions affecting the entire body:
- Inflammatory reaction. The content of formed blood elements (neutrophils, platelets, and erythrocytes) sharply increases in the pulmonary microvessels. An imbalance of biologically active substances occurs: cytokines, hormones, and reactive oxygen species are released in excess. All of this potentiates potent local and systemic inflammation.
- Vascular and hemostatic disorders. Damage to the microvascular endothelium occurs, leading to endothelial dysfunction. The logical outcome is hemostasis disorders and the development of thrombohemorrhagic syndrome. Microcirculation disorders affect the intravascular, transmural, and extravascular bed in both the lungs and other organs.
- Gas exchange and hemodynamic disorders. Pathological blood shunting (right-to-left shunt) is formed. This causes acute respiratory failure and general respiratory-type hypoxia. Subsequently, systemic circulatory failure, secondary pulmonary hypertension, heart failure, and arterial hypotension join in.
Principles of therapy
Therapeutic tactics for NRDS are based on two fundamental principles: etiotropic and pathogenetic.
Etiotropic principle is aimed at eliminating the root cause and emergency care. It addresses the following tasks:
- Emergency airway support: within the first 2–3 minutes after birth, physicians are required to provide the newborn with an adequate ventilation volume.
- Surfactant therapy: simultaneous administration of a surfactant preparation directly into the airways.
- Oxygen therapy: administration of strictly dosed oxygen therapy according to indications.
Pathogenetic principle aims to block the key links in the development of the disease described above (combating inflammation, vascular catastrophes, and hemodynamic shifts).
Briefly: answers to topical questions
What specific pathogenic factors cause accelerated surfactant destruction in a newborn?
According to the sources, the explicitly indicated factors are: 1) hypoxia (pre- and postnatal) — the triggering factor of the cascade in which surfactant production is impaired: insufficient synthesis or rapid destruction; 2) meconium aspiration — a consequence of intrauterine hypoxia leading to airway obstruction, inflammatory changes, and surfactant inactivation.
Which lung tissue cells directly synthesize surfactant?
Surfactant is synthesized by specialized epithelial cells of the airways and alveoli. The producing cells include:
- Type 2 alveolar cells — secretory (large) pneumocytes located on the basement membrane and serving as the primary "factory" for surfactant.
- Non-ciliated bronchiolar epithelial cells — cells localized in the epithelium of respiratory bronchioles.
Additionally, lipofibroblasts supply pneumocytes with a lipid substrate for the synthesis of the phospholipid fraction.
What chemical compounds make up normal pulmonary surfactant?
Normal pulmonary surfactant is a surface-active substance. Its composition includes: 1) lipids — 90% of mass: predominantly phospholipids, as well as cholesterol; phosphatidylcholines, sphingomyelins, and dipalmitoylphosphatidylcholine are specifically indicated as the main component of surfactant; 2) proteins — 10% of mass, divided into 4 groups.
Class and exam questions
Why is NRDS more common in premature infants?
The main cause lies in the immaturity of the lung tissue, which is unable to synthesize surfactant in the required volume. The risk of developing the syndrome at 28 weeks of gestation reaches 60%.
What are hyaline membranes?
This is an accumulation of protein exudate, leukocytes, and epithelial debris in the airways. Under microscopy, they look like characteristic dense membranes lining the alveoli.
What hemodynamic disorders does NRDS lead to?
Right-to-left blood shunting occurs, secondary pulmonary hypertension develops, along with systemic circulatory failure, heart failure, and arterial hypotension.
What is the essence of etiotropic therapy for the syndrome?
It includes emergency provision of an adequate breathing volume in the first 2–3 minutes of life, administration of surfactant directly into the airways, and metered oxygen supply.
What else to study on this topic
- Mechanisms of development of multiple organ dysfunction syndrome in NRDS.
- The role of reactive oxygen species and cytokines in pulmonary inflammation.
- Pathogenesis of thrombohemorrhagic syndrome against the background of endothelial dysfunction.
- Types of microcirculation disorders: intravascular, transmural, and extravascular.
Master the entire topic in the "Pathophysiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Neonatal respiratory distress syndrome" and another 4,913 pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 135 video lessons on the subject
Other topics of section "Chapter 23. Typical Forms of Pathology of the External Respiration System"
Free video lessons: pathophysiologyShort lessons with lecture notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.