ARDS and HMD - MedPath

Hyaline Membrane Disease (HMD)

Neonatal disease due to surfactant deficiency, leading to alveolar collapse

Adult respiratory distress syndrome

Acute onset, inflammatory lung injury with increased permeability

What affects gas exchange and lead to hypoxemia

ARDS and HMD

What does this refer to

• Tendency of water molecules to contract to the smallest possible surface area (bead) with exposure to air

• Increased ______ = increased work of breathing

Surface tension

What does this refer to

• : The smaller a sphere’s radius (alveoli) the greater the surface tension and the more difficult (work) to expand the alveoli

• Surfactant reduces fluid surface tension lining the alveoli and decreases tendency to collapse, preventing atelectasis

Laplace’s Law

What does this refer to

• Fulminant form of respiratory failure characterized by acute lung inflammation and diffuse alveolocapillary injury

• Injury to the pulmonary capillary endothelium

• Inflammation

• Surfactant inactivation

• Atelectasis

• Is a restrictive lung disorder

Acute respiratory distress syndrome (ARDS)

What does this refer to

• Direct: pneumonia, aspiration, inhalation injury

• Indirect: sepsis, trauma, pancreatitis, transfusions

• Systemic inflammation is key

Causes of ARDS

What does this refer to

• Initial injury increases capillary permeability

• Fluid and proteins leak into alveoli, impairing gas exchange

• Inflammatory mediators recruit neutrophils, worsening injury

Pathophysiology of ARDS

What phase of ARDS is the following

• : damage and fluid leakage

Exudative

What phase of ARDS is the following

• : repair and recovery

Proliferative

What phase of ARDS is the following

• : scarring and chronic changes

Fibrotic

What phase of ARDS is the following

• Occurs within 0–7 days post-injury

• Alveolar edema with protein-rich fluid

• Formation of hyaline membranes from fibrin and cell debris

Exudative Phase

What phase of ARDS is the following

• Occurs around day 7–21

• Resolution of edema, proliferation of fibroblasts and type II pneumocytes

• Beginning of tissue repair

Proliferative Phase

What phase of ARDS is the following

• Occurs after 3 weeks

• Fibrosis and remodeling of lung tissue

• May result in permanent reduction in lung compliance

Fibrotic Phase

What does this refer to

• Rapidly progressive dyspnea, tachypnea, hypoxemia

• Inspiratory rales, cyanosis, accessory muscle use

• 24-48 hours- infiltrates on CXR

• Become refractory to oxygen therapy —> increase PaCO2 —> organ dysfunction —> CO and BP decreases —> DEATH

Manifestations of Acute Respiratory Distress Syndrome (ARDS)

What does this refer to

• Refractory hypoxemia, CXR with B infiltrates, and pulmonary edema (exclude cardiogenic pulmonary edema)

• Based on Berlin Criteria:

  • Timing – 1 week

  • Origin of edema – noncardiac

  • Imaging – bilateral opacities

  • Oxygenation - PaO2/FIO2 with PEEP

• Exclude cardiac failure with echocardiogram or BNP

Diagnosis of ARDS

What does this refer to

• Chest X-ray: bilateral infiltrates, not explained by effusion/collapse

• CT: more sensitive, shows ground-glass opacities and consolidation

Imaging in ARDS

What does this refer to

• Early: hyaline (transparent or glassy) membranes lining alveoli

• Later: type II pneumocyte hyperplasia, interstitial fibrosis

• Neutrophil infiltration and alveolar damage

Histology in ARDS

What does this refer to

• Treat underlying cause (e.g., antibiotics for sepsis)

• Supportive care with oxygen and mechanical ventilation

• Fluid management to avoid pulmonary edema

Management of ARDS

What does this refer to

• Low tidal volume (6 mL/kg IBW) to prevent barotrauma

• PEEP to prevent alveolar collapse

• Prone positioning improves oxygenation

Ventilation Strategies

What does this refer to

• Barotrauma from mechanical ventilation

• Ventilator-associated pneumonia (VAP)

• Long-term lung dysfunction and neuromuscular weakness

Complications of ARDS

What does this refer to

• Mortality varies by severity: up to 40%

• Many survivors have long-term physical and psychological effects

• Better outcomes with early recognition and lung-protective ventilation

Prognosis of ARDS

What does this refer to

• Occurs in premature infants due to immature lungs

• Surfactant deficiency is central cause

• Results in atelectasis, decreased lung compliance, hypoxemia

Hyaline Membrane Disease

What does this refer to

• Secreted by type II pneumocytes around 24–28 weeks gestation

• Reduces surface tension, stabilizes alveoli

• Deficiency causes alveolar collapse and impaired gas exchange

Surfactant Function

What does this refer to

• Inadequate surfactant → alveolar collapse

• Leads to hypoxemia, increased work of breathing

• Proteinaceous exudate and necrotic cells form hyaline membranes

Pathogenesis of HMD

What does this refer to

• Prematurity (<34 weeks), male sex

• Maternal diabetes: delayed surfactant production

• Cesarean delivery without labor: less stress-induced surfactant release

Risk Factors for HMD

What does this refer to

• Tachypnea, nasal flaring, grunting, cyanosis within hours after birth

• Progressive respiratory failure if untreated

• Findings correlate with gestational age and severity

Clinical Features of HMD

What does this refer to

• Chest X-ray: reticulogranular (ground-glass) pattern, air bronchograms

• Blood gases: hypoxemia, respiratory acidosis

• Confirmatory: lecithin-sphingomyelin ratio <2.0 in amniotic fluid

Diagnosis of HMD

What does this refer to

• Collapsed alveoli with eosinophilic hyaline membranes

• Similar histology to ARDS

• Inflammatory infiltrates are minimal compared to ARDS

Histology in HMD

What does this refer to

• Antenatal corticosteroids (betamethasone) accelerate surfactant production

• Avoid elective delivery before 39 weeks unless indicated

• Amniocentesis to assess fetal lung maturity if needed

Prevention of HMD

What does this refer to

• Surfactant replacement via endotracheal tube

• CPAP for mild-moderate disease

• Mechanical ventilation for severe cases

Treatment of HMD

What does this refer to

• Bronchopulmonary dysplasia (chronic lung disease)

• Air leak syndromes (pneumothorax)

• Intraventricular hemorrhage in very premature infants

Complications of HMD

What does this refer to

• Greatly improved with surfactant and modern neonatal care

• Mild cases often recover completely

• Severe or recurrent cases may have long-term respiratory issues

Prognosis of HMD

What does this refer to

• : acute, inflammatory, adult disease

• Impairs gas exchange and respiratory failure

ARDs

What does this refer to

• : neonatal surfactant deficiency

• Impairs gas exchange and respiratory

HMD