1
Fifth stage
Pediatric
Lec-3
.د
فارس
1/1/2014
HYALINE MEMBRANE DISEASE
RESPIRATORY DISTRESS SYNDROME
Objectives
1. To understand the risk factors, pathogenesis , pathology,and clinical features of
respiratory distress syndrome
2. To list the differential diagnosis of respiratory distress in newborn baby
3. To recognise how to to investigate and manage a newborn baby with respiratory
distress syndrome
4. To understand the features and management of patent ducutus arteriosus
5. To recognise the pathogenesis and clinical features of bronchopulmonary dysplasia
and retinopathy of prematurity
Respiratory distress in the newborn is defined by the presence of one or more of the
following:
tachypnea, retractions, nasal flaring, grunting, and cyanosis .
INCIDENCE
HMD occurs primarily in premature infants, and its incidence inversely proportional to the
gestational age and birth weight.
60-80% of infants less than 28wk of gestation
15-30% of infants between 32&36 wk
in about 5% beyond 37 wk, and rarely at term
The risk of developing RDS increases with
1. maternal diabetes
2. multiple births
3. cesarean section delivery
4. precipitous delivery
5. asphyxia
6. cold stress
7. history of previously affected infants.
The incidence is highest in preterm male or white infants .
The risk of RDS is reduced in
1. pregnancies with chronic or pregnancy-associated hypertension
2. maternal heroin use
3. prolonged rupture of membranes
4. antenatal corticosteroid prophylaxis
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ETIOLOGY &PATHOPHISOLOGY
Surfactant deficiency [decreased production&secretion] is the primary cause of HMD.
Surfactant Is phospholipid protein ,its major constituents:
1-Dipalmitoyl phostidylcholine [Lecithine]
2-Phosphatidyle glycerol
3-Apoproteins
4-Cholesterol
Surfactants are synthesized and stored in type2 alveolar cells.
Deficiency of surfactant leads to:
-alveolar collapse
-decreased lung volume &compliance
-ventilation-perfusion abnormalities
-right to left shunt
-persistent hypoxemia[<30mm Hg]causes metabolic acidosis
-respiratory acidosis also present because alveolar hypoventilation
Decreased myocardial contractility, decreased cardiac out put&arterial blood pressure
-Perfusion of kidneys,GIT,muscle,&skin is reduced leading to edema & electrolytes
disorders.
PATHOLOGY
The lungs appear deep purplish red,&liver like in consistency.
Microscopically:
A number of alveolar ducts, alveoli,& resp. bronchiole are lined with acidophilic
homogenous, or granular membrane.
Clinical manifestations
Signs of HMD usually appear within minutes of birth, but may be delayed for several hours
in large premature infants.
Early clinical signs of HMD:
1-Tachypnea[>60/min]
2-Expiratory grunting
3-Sternal&intercostal recession
4-Cyanosis in room air
5-Delayed onset of respiration in very immature babies
Late clinical signs in severe HMD
1-Decrease blood pressure
2-Fatigue
3-Cyanosis
4-Pallor increase
5-Grunting decrease or disappears
6-Apnea& irregular respiration[ominous sign]
Other signs:
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-Mixed resp.& metabolic acidosis
-Edema,ileus,oliguria
In most cases symptoms&signs reach peak within 3 days after which improvement is
gradual.
INVESTIGATIONS
Chest x.ray
-Grade-1-fine reticular granular mottling, good lung expansion
-Grade-2-mottling with air bronchogram
-Grade-3-diffuse mottling,heart border just discernable,prominent air bronchogram
-Grade-4-bilateral confluent opacification of lungs[white out]
BD gas analysis
1-Initially hypoxemia
2-Later progressive hypoxemia ,hypercapnia, &metabolic acidosis
Differential diagnosis of RDS
1-congenital pneumonia
2-aspiration pneumonia
3-meconium aspiration syndrome
4-air leak [pneumothorax, pulmonary interstitial emphesema, pneumomediastinum]
5-transient tachypnea of newborn
6-lobar emphesema
7-pulmonary hypoplasia
8-diaphragmatic hernia
9-heart failure
10-persistent pulmonary hypertension
11-asphyxia&increased intracranial pressure
12-metabolic acidosis
13-congenital neuromuscular disorder
14-anemia&hypovolemia
Initial Laboratory Evaluation of Respiratory Distress
1. Chest radiograph
2. Arterial blood gas
3. Complete blood count
4. Blood culture
5. Blood glucose
6. Echocardiogram, ECG
Prevention
1-Prevention of prematurity, including :
-avoidance of unnecessary or poorly timed c.s
-appropriate management of high risk pregnancy& labour.
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-Estimation of fetal head circumferance by ultrasound& determination of lecithin
concentration in the amniotic fluid by [L/S]ratio decrease likehood of delivering premature
infants
2-Adminstration of betamethasone to women 48hr before delivery of fetuses between 24-
34wk of gestation significantly reduce the incidence&mortality&morbidity of HMD.One
course of corticosteroid required.
3-Adminstration of first dose of surfactant in to the trachea of symptomatic premature
infants immediately after birth[prophylactic] reduce air leak&mortality from HMD
Treatment
Maintenance of temperature:
Preterm infants should be nursed in incubator or under radiant heat warmer [maintain core
temp 36.5-37° c].
Calories &fluid:
Provided by intravenous fluid.
Excessive fluid contribute to development of PDA,NEC&BPD.
Maintenance of normoxemia:
The aim is to keep arterial oxygen tension in range of[55-75mm Hg].
For babies with spontaneous respiration humidified oxygen should be given.
Too little oxygen will cause hypoxemia, metabolic acidosis,&tissue damage.
Too much oxygen associated with development of retinopathy of prematurity.
Assisted ventilation
1-CPAP: is distending pressure which prevent alveolar collapse during expiration& thus
improving oxygenation.
2-Mechanical ventilation:
indication for I.P.P.V
1-failure to establish respiration at birth
2-intractable apneic attacks
3-respiratory failure [ph<7.2,paco2>66mm Hg ,pao2<53mm Hg in 90%O2
3-High frequency ventilation
Surfactant therapy:
Synthetic &natural surfactants[from calf,pig,&cow lungs].Multidose endotracheal
instillation of surfactant
Metabolic acidosis:
in RDS may be a result from perinatal asphyxia &hypotension.
The aim to keep pH above 7.25.
It is treated by sodium bicarbonate 1-2meq/kg administered over 15-20min through
peripheral or umbilical vein.
Complications of HMD
1-Patent ductus arteroisus
2-Interventricular hemorrhage
3-pulmonary:
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A-air leak:
pneumothorax,pneumomediastinum, P.I.E,pneumopericardium,pneumoperitonium,air
embolism, subcutanous emphesema.
B-bronchopulmonary dysplasia.
C-pneumonia: aspiration,bacterial.
4-Complication of mechanical ventilation.
5-Long term neurological sequele.
Patent Ductus Arteriosus
The ductus arteriosus constrict after birth in normal term infants in response to elevated
PaO2 level.
The ductus in preterm infant is less responsive to vasoconstrictive stimuli due to persistant
vasodilator effect of PGE2 in addition to hypoxemia during RDS leads to persistent PDA that
creat shunt between the pulmonary&systemic circulation.
Clinical features:
When RDS improves&pulmonary vascular resistance declines &flow through ductus
increases in a left to right direction.
It may produce no symptoms or it may cause apnoea and bradycardia, increased oxygen
requirement and difficulty in weaning the infant from artificial ventilation.
Pulse pressure widens,active precordial impulse. Active&bounding peripheral pulse. The
murmur of PDA may be continous or usually systolic. Heart failure&pulmonary edema
result in rales & hepatomegally.
Chest x-ray: cardiomegally &pulmonary edema.
Treatment: during RDS involves an initial period of fluid restriction& diuretics.If no
improvement after 24-48 hr indomethacin {prostaglandin synthetase inhibitor} 0.2mg/kg
I.V every 12 hr, 3 doses. If the patient not respond to repeated courses of indomethacine &
in heart failure surgical ligation is required.
BRNCHOPULMONARY DYSPLASIA
Oxygen concentration above 40% are toxic to the neonatal lung.
Oxygen mediated lung injury results from generation of super oxides, hydrogen
peroxides[H2O2],&Oxygen free radicals which disrupt membrane lipids. Mechanical
ventilation with high peak pressure produces barotroma.
Definition: Failure of RDS to improve after 2 weeks& need for prolonged mechanical
ventilation,&oxygen therapy required at 36 weeks post conception age.
Clinical feature:
Oxygen dependence, hypercapnia , compensatory metabolic alkalosis,pulmonary
hypertension, poor growth,& development of right sided heart failure.Increase air way
resistance with reactive air way constriction.
Treatment:
1-Bronchodilator
2-Fluid restriction& diuretics
3-Mechanical ventilation
4-Dexamethazone
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Retinopathy of prematurity [ROP] Retrolental fibroplasia
It is caused by acute and chronic effects of oxygen toxicity on the developing blood vessels
of premature retina.
The completely vascularized retina of term infant is not susceptible to ROP.
ROP is a leading cause of blindness for VLBW infant[<15oogm].
Excessive arterial oxygen tensions produce vasoconstriction of retinal vessels this followed
by vaso obliteration,then proliferative stages[extraretinal fibrovascular proliferation].
Severe cases leads to retinal detachment, leukokoria, glaucoma
The incidence of ROP may be reduced by careful monitoring of arterial blood gases& to
keep arterial PaO250-70mm Hg.
Infant <1500gm, or born before 28 weeks gestation should be screened when they are
older than 7 weeks old.
Laser therapy &less often cryotherapy may be used for viterous hemorrhage& for severe
progressive proliferation.
Surgery indicated for retinal detachment.