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 Respiratory Distress Syndrome
INTRODUCTION
Background: Respiratory distress syndrome (RDS), also known as hyaline membrane disease (HMD), occurs almost exclusively in premature infants. The incidence and severity of RDS are related inversely to the gestational age of the infant. The outcome of RDS has improved in recent years with the increased use of antenatal steroids to improve pulmonary maturity, early postnatal surfactant therapy to replace surfactant deficiency, and gentler techniques of ventilation to minimize damage to the immature lungs.
Notes:
- RDS is the leading cause of mortality and morbidity in premature infants.
- RDS is a developmental disorder not a disease process.
- Occurrence and severity is proportional to gestational age. (Lower, the higher +sever).
- In USA 20,000 — 40,000 case yearly.
- In France 4000 cases yearly.
Pathophysiology:
A relative deficiency of surfactant, which leads to decrease in lung compliance and functional residual capacity with increased dead space, causes RDS., the lungs appear airless and ruddy (i.e. liver like)
- Surfactant is a complex lipoprotein which lowers the surface tension at the alveolar.
- Hypoxia, acidosis, hypothermia, and hypotension may impair surfactant production and/or secretion of surfactant.
History
RDS frequently occurs in the following individuals:
- Male infants.
- Infants born to mothers with diabetes.
- Infants delivered via cesarean without maternal labor.
- Second-born twins.
- Infants with a family history of RDS.
In contrast, the incidence of RDS decreases with the following:
- Use of antenatal steroids.
- Pregnancy-induced or chronic maternal hypertension.
- Prolonged rupture of membranes.
- Maternal narcotic addiction.
Secondary surfactant deficiency may occur in
infants with the following:
- Intrapartum asphyxia.
- Pulmonary infections.
- Pulmonary hemorrhage.
- Meconium aspiration pneumonia.
- Oxygen toxicity along with barotrauma or volutrauma to the lungs.
Secondary Surfactant Deficiency in Neonates
- A recent report in the Journal of Perinatology described 3 neonates with acute respiratory failure at age 1 to 3 weeks who demonstrated improvement following surfactant therapy.[17] It was hypothesized that these infants suffered from "secondary surfactant deficiency" as a result of surfactant inactivation. In other words, although their primary diagnoses were not RDS, their primary respiratory pathologies produced injury to the lungs and a functional surfactant deficiency that responded to the administration of surfactant.
- Pulmonary hemorrhage, pulmonary edema, pneumonia, and atelectasis are among the neonatal respiratory conditions that might lead to and then be exacerbated by surfactant deficiency. Pneumonia is accompanied by the leakage of plasma proteins into the airways, release of cytokines, and a corresponding inflammatory response that can be the source of significant surfactant inhibition and damage to type II pneumocytes.[18] Pulmonary hemorrhage, thought to be primarily a complication of surfactant administration, can further impair the surfactant system because hemoglobin and cell membrane lipids are potent inhibitors of endogenous surfactant.
Meconium Aspiration
Searches were made using Medline (1985 to January 2000) (MeSH terms: pulmonary surfactant and meconium aspiration; limits: age groups, newborns; publication type, clinical trials), previous reviews including cross-references, abstracts, conference and symposia proceedings, expert informants, and journal hand searching in the English language. Authors were directly contacted to provide additional data.
Reviewers' conclusions
In infants with meconium aspiration syndrome, surfactant administration may reduce the severity of respiratory illness and decrease the number of infants with progressive respiratory failure requiring support with ECMO. The relative efficacy of surfactant therapy compared to, or in conjunction with, other approaches to treatment including inhaled nitric oxide, liquid ventilation, and high frequency ventilation remains to be tested.
Internationally, RDS has been reported in all races worldwide, occurring more often in premature infants of Caucasian ancestry.
Manifestations
- Tachypnea.
- Expiratory grunting.
- Subcostal intercostal retractions.
- Cyanosis.
- Nasal flaring.
- Hypothermia.
- Infant apnea.
- Other problems may co-exist (pneumonia, Pulmonary hemorrhage, congenital anomalies of the lungs, hematological problems.
SQUELEA
- Progressive worsening of symptoms, complications appearing.
- Most cases peak up within 3 days, as progression decreases.
- Mortality is rare within first day, but increases between 2—7 days.
Complications
- There are 2 groups of RDS complications:
- Acute complications: Pneumothorax, PIE, PDA, IVH, PUL-HEMO. NEC, Air leaks, ROP, Infections.
- Chronic complications: ROP, PDA, BPD, Neurological impairment, CHF, Familial psychopathology.
Lab Studies
Blood gases exhibit respiratory and metabolic acidosis.
Imaging Studies
- Chest radiographs of an infant with RDS exhibit bilateral diffuse reticular granular or ground glass appearance, air bronchograms, and poor lung expansion. The cardiac silhouette may be normal or enlarged.
- Echocardiographic evaluation is performed in selected infants to assist the clinician in diagnosing PDA and determine the direction and degree of shunting. It is also useful in making the diagnosis of pulmonary hypertension and excluding structural heart disease.
Treatment
- Procedures: sedation, arterial puncture, vascular access, tracheal intubation, gastric tubes, etc…
- Medical: prenatal prevention and prediction of RDS. Delivery and resuscitation, surfactant replacement therapy, care of ventilation.
- Supportive: temperature regulation, metabolism, fluids, and nutrition care, etc…
Medical Care
- Prenatal prevention and prediction of RDS: Fetal lung maturity can be predicted by estimating the lecithin-to-sphingomyelin ratio and the presence of phosphatidylglycerol in the amniotic fluid obtained via amniocentesis.
- Delivery and resuscitation.
- Surfactant replacement therapy: The mortality rate of RDS has decreased 50% during the last decade with the advent of surfactant therapy.
- Infants diagnosed with RDS who require assisted ventilation with more than 0.40 fraction of inspiratory oxygen (FIO2 should receive intratracheal surfactant as soon as possible, preferably within 2 hours after birth.
- Because surfactant is protective of delicate lungs, several investigators have recommended prophylactic use following resuscitation in extremely premature infants (<27 weeks' gestation).
- The recommended dose of the clinically available surfactant preparations has a range of 50-200 mg/kg,. Rapid bolus administration of surfactant after adequate lung recruitment using 2-4 cm positive end-expiratory pressure (PEEP) and adequate positive pressure. Most infants require 2 doses; however, as many as 4 doses at 6- to 12-hour intervals have been used in several clinical trials.
Supportive therapy includes the following:
- Temperature regulation.
- Fluids, metabolism, and nutrition.
- Circulation and anemia. Antibiotic administration.
- Support of parents and family.
Surfactant System
Definition: Surface active material at the respiratory epithelium interface in the alveoli provides surface tension lowering activity that contributes to the remarkable pressure
- Volume association of the lungs.
- Lowers surface tension.
- Stabilize small airways& small alveoli.
Secretion
Surfactant is stored within TYPE 2 cells in lipid rich organelles (LAMELLAR bodies). Secretion occurs by a process of EXOCYTOSIS which initiated by a number of PHYSICAL and HORMONAL factors.
Preparations
SURFACTANTS
- Synthetic and natural presentations are being used for the treatment of RDS reducing MORTALITY and MORBIDITY.
- Natural surfactants are faster, more effective in terms of reducing pulmonary air leaks and mortality.
- Prophylactic surfactant at birth may be more effective than later treatment.
- Surfactant treatment may be indicated for other neonatal and adult lung diseases.
- It is generally accepted that the dose of surfactant should be at least 100mg /kg/BW.
Clinical Success Prevention
- Reduced the incidence of death due to RDS by up to 87 %.
- Reduced the incidence of RDS up to 70 %.
- Reduced the incidence of air leaks and PIE.
- Improved measures of oxygenation and ventilation at 72 hours of age.
- Was very well tolerated.
Conclusion
In the US although premature birth rate (7%) still the same since decades but incidence of RDS or its complications decreased due to the large advances that had been made in the field of medicine. (Antenatal steroids, ventilation tech., exogenous surfactant therapy, better NICU’S, etc).
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