HYALINE MEMBRANE DISEASE RESPIRATORY DISTRESS SYNDROME
ObjectivesTo understand the risk factors, pathogenesis , pathology,and clinical features of respiratory distress syndrome To list the differential diagnosis of respiratory distress in newborn baby To recognise how to to investigate and manage a newborn baby with respiratory distress syndrome To understand the features and management of patent ducutus arteriosus 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
maternal diabetes multiple births cesarean section delivery precipitous delivery asphyxia cold stress history of previously affected infants. The incidence is highest in preterm male or white infants.The risk of RDS is reduced in
pregnancies with chronic or pregnancy-associated hypertension maternal heroin use prolonged rupture of membranes antenatal corticosteroid prophylaxisETIOLOGY &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: -Mixed resp.& metabolic acidosis -Edema,ileus,oliguria In most cases symptoms&signs reach peak within 3 days after which improvement is gradual.
Cyanosis. This critically ill infant exhibits cyanosis and poor skin perfusion.
Flaring. Reflexive widening of the nares may be seen in infants with respiratory distress.Retractions. The inward collapse of the lower anterior chest wall can be seen in this premature infant with RDS.
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
RDS. Note the ground-glass appearance and the presence of air bronchograms
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 hypoplasia8-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
Chest radiograph Arterial blood gas Complete blood count Blood culture Blood glucose Echocardiogram, ECG
Prevention 1-Prevention of prematurity, including : -avoidance of unnecessary or poorly timed c.s -appropriate management of high risk pregnancy& labour. -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 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: 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
Bronchopulmonary dysplasia. Note the alternating areas of hyperinflation and atelectasis.
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, glucomaThe 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.