Hyaline Membrane Disease Li wei-zhong

Introduction HMD, frequently referred to as neonatal respiratory distress syndrome (NRDS), occurs primarily in premature infant. There is rapid or labored breathing, beginning at or immediately after birth. Surfactant deficiency is the primary cause of HMD.

Epidemiology HMD occurs primarily in Premature infant Infants less than 28 wk of GA: 60-80% Infants between 28 and 32 wk: 60% Infants between 32 and 36wk of GA: 15-30% Infants beyond 37 wk of GA: 5%

Epidemiology The incidence of HMD is highest among premature male or white infants. The incidence is higher for cesarean section without labor than vaginal delivery. HMD is more common in gestational diabetes and in insulin-dependent mother. Second-born twin is at greater risk.

Etiology Surfactant Deficiency Prematurity predisposes Cesarean section Male > female White > nonwhite Second- born twin

Etiology Maternal diabetes Maternal hemorrhage Maternal stress Intrauterine growth retardation Prolonged rupture of membranes (>16 hr) Asphyxia

Etiology Hypoxemia Pulmonary Ischemia Hypovolemia and Hypotension Cold Stress High Oxygen concentration

Pathophysiology Surfactant deficiency increases surface tension in Alveolus Surfactant decreases surface tension in the alveolus during expiration, allowing the alveolus to remain partly expanded and in that way maintaining a functional residual capacity.

Pathophysiology The surface tension in the alveolus results in poor lung compliance and atelectasis. decreased tidal volumes increased physiologic dead space Poor lung distensibility Poor alveolar stability

Pathophysiology increased work of breathing perfused but not ventilated alveoli Ventilated but not perfused alveoli Respiratory failure

Pathophysiology The combination of hypercarbia, hypoxia and acidosis produces pulmonary arterial vasoconstriction with increased right-to-left shunting through the foramen ovale and ductus arteriosus and within the lung itself. Reduced effective pulmonary blood flow

Pathology Lung extensive atelectasis Injury to epithelial calls Lung congestion and edema Lung hemorrhage Hyaline membranes contains fibrin and cellular products

Clinical Findings Onset near the time of birth or within 4-6 hr after birth Rapid, shallow respirations ≥ 60/ min Intercostal and subcostal retractions and progressive respiratory distress Expiratory grunt Cyanosis or pallor

Clinical Findings Hypothermia hypotension Fine inspiratory rales Pulmonary or intraventricular hemorrhage Course to death or improvement 3-5d

Clinical Findings Laboratory diagnosis Arterial blood gases Hypoxemia Hypercapnia Mixed respiratory-metabolic Acidemia

Clinical Findings Lecithin/sphingomyelin ratio (L/S)<2:1 Low phosphatidylglycerol(PG) Low saturated phosphatidylcholine (PC) Low surfactant protein A/saturated PC (SP-A/SPC) ratio

Clinical Findings Chest x-ray Typical pattern at 24 hr after birth Ground-glass appearance Air bronchograms Doming of diaphragm and underexpansion (white out)

Diagnosis Tachypnea, cyanosios, and expiratory grunting Poor air movement despite increased work of breathing Blood gases, pH values, and other laboratory finding Chest x-ray showing hypoexpansion and air bronchograms

Differential Diagnosis Wet lung of the newborn (Transient dyspnea) Amniotic fluid and meconium aspiration syndrome Group B streptococcal pneumonia Diaphragmatic hernia

Treatment The basic defect requiring treatment is inadequate pulmonary exchange of oxygen and carbon dioxide. Metabolic acidosis and circulatory insufficiency are secondary manifes-tations.

Treatment Supportive care of LBW infant Surfactant replacement therapy Oxygen therapy Continuous positive airway pressure (CPAP) Assisted mechanical ventilation Blood pressure support Alkali therapy

Prevention Prenatal glucocorticoids for >24 hr Prophylactic administration of exogenous surfactant at birth