Respiratory distress syndrome: Pathology Review

What is respiratory distress syndrome? Acute respiratory distress syndrome happens when inflammation causes diffuse alveolar injury and pulmonary edema. Neonatal respiratory distress syndrome is caused by a deficiency of surfactant.

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Respiratory Distress Syndrome – ARDS and NRDS
Respiratory distress syndromes, including Acute Respiratory Distress Syndrome (ARDS) and Neonatal Respiratory Distress Syndrome (NRDS), are critical conditions that affect the lungs' capacity to facilitate gas exchange. This article provides a comprehensive overview of these syndromes, their causes, pathophysiology, diagnosis, and treatment approaches.

Understanding ARDS and NRDS
Acute Respiratory Distress Syndrome (ARDS)
ARDS is characterized by a rapid onset of widespread inflammation in the lungs, typically triggered by conditions such as sepsis, aspiration, trauma, or pancreatitis. It is not a primary disease but a complication that arises when the lungs are affected by another severe condition.

Pathophysiology:
In ARDS, damage to the alveoli, the tiny air sacs in the lungs, initiates an inflammatory response. Type II pneumocytes, responsible for producing surfactant, are damaged, leading to a reduction in surfactant levels. Surfactant is a vital substance that reduces surface tension, preventing the collapse of alveoli. When surfactant is insufficient, alveoli collapse, leading to decreased gas exchange. Inflammatory cytokines like TNF-α and interleukin-1 are released, attracting neutrophils, which further exacerbate lung damage through the release of toxic mediators like reactive oxygen species. This sequence results in alveolar edema, hyaline membrane formation, and impaired oxygen exchange.

Diagnosis:
The diagnosis of ARDS involves four essential criteria:

Acute Onset: The condition must have developed within one week.
Bilateral Lung Opacities: Evidenced on imaging, indicating the presence of pulmonary edema that is not explained by other causes.
PF Ratio Below 300: The PF ratio (partial pressure of arterial oxygen to the fraction of inspired oxygen) should be below 300 mmHg, with lower values indicating more severe ARDS.
Exclusion of Cardiac Causes: ARDS must not be attributed to heart failure, which is usually evaluated using echocardiography and pulmonary capillary wedge pressure measurements.
Symptoms:
Patients with ARDS experience significant respiratory distress, including shortness of breath, rapid breathing (tachypnea), and hypoxemia. They often present with hypotension and cyanosis, and crackling sounds (rales) can be heard during auscultation due to alveolar collapse.

Treatment:
The treatment of ARDS primarily focuses on managing the underlying cause, alongside providing supportive care:

Oxygen Therapy: To improve blood oxygen levels.
Mechanical Ventilation: Positive end-expiratory pressure (PEEP) is often used to keep alveoli open during exhalation, which prevents collapse.
Low Tidal Volume Ventilation: Reducing the tidal volume helps to minimize further alveolar damage caused by over-inflation.
Neonatal Respiratory Distress Syndrome (NRDS)
NRDS is a condition seen in newborns, predominantly affecting preterm infants, and is caused by insufficient production of surfactant, a substance critical for keeping the alveoli open.

Pathophysiology:
Surfactant deficiency is the root cause of NRDS. Normally, type II pneumocytes produce surfactant around the later stages of fetal development, allowing the alveoli to remain stable and functional after birth. In premature infants, this process may be incomplete, leading to alveolar collapse (atelectasis). As a result, the newborns exhibit increased work of breathing, which can rapidly progress to respiratory failure if not managed effectively.

Risk Factors:
Several factors contribute to the likelihood of NRDS:

Prematurity: The most significant risk, as surfactant production increases late in gestation.
Maternal Diabetes: High insulin levels in infants of diabetic mothers can interfere with surfactant production.
Cesarean Delivery: Unlike vaginal delivery, a C-section does not stimulate the surge in glucocorticoids that promote surfactant release.
Diagnosis:
The diagnosis of NRDS is based on clinical findings and imaging:

Chest X-ray: Characteristic "ground-glass" appearance due to diffuse atelectasis, along with air bronchograms, indicates the presence of NRDS.
Blood Gases: Hypoxemia and hypercapnia (increased carbon dioxide) are often observed in arterial blood gas measurements.
Symptoms:
Infants with NRDS typically show signs within hours of birth. These include rapid breathing, nasal flaring, grunting during exhalation, and chest wall retractions. As the condition worsens, cyanosis (a bluish tint to the skin due to low oxygen levels) may develop.

Treatment:

Antenatal Corticosteroids: Administered to mothers at risk of preterm labor to enhance fetal lung maturity.
Nasal Continuous Positive Airway Pressure (CPAP): Used in newborns to keep their airways open.
Surfactant Replacement Therapy: If non-invasive ventilation is insufficient, intratracheal surfactant is administered to support alveolar function.
Comparative Overview: ARDS vs. NRDS
While both ARDS and NRDS involve respiratory failure and impaired gas exchange, their causes and affected populations are distinct. ARDS often results from underlying inflammatory triggers in adults or children, whereas NRDS is primarily related to immature lungs in preterm infants. Treatment for both syndromes involves supportive care, with a particular emphasis on improving lung function and managing the underlying causes.

Conclusion
Respiratory distress syndromes such as ARDS and NRDS represent significant medical emergencies that require prompt diagnosis and management to prevent severe complications. Understanding the differences in their causes, pathophysiology, and treatment approaches helps clinicians manage these conditions effectively. Maintaining alveolar stability through appropriate oxygenation, surfactant supplementation, and careful ventilation strategies remains at the core of successful treatment for both ARDS and NRDS.

[aspirant]

Osmosis is best .. u made this so easy

[miranmuslem]

Thank you! Great video and well explained!

[ridaallauddin]

how patient is developing hypotension. please explain

[aineedadadi]

Can BALF (high counts of inflammatory cells like macrophages/eosonophiles) be also a diagnosis for ARDS?

[suhanishukla]

this video helped me a lot in my exams, Thank you Much😀😀😀😀

[jeyaprakash]

In last summery why did you mentioed heart failure rouled out but ards was you said

[hpwr-gjlc]

What occurs in ARDS .... respiratory alkalosis or metabolic-respiratory acidosis ?

[SeemaSharma-owwh]

well it's not exactly a pathology video is it? it has all components of internal medicine.

edit: can you add Physical therapy school shirts?