Respiratory Distress Syndrome (RDS)

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http://www.adhb.govt.nz/newborn/TeachingResources/Radiology/LungParenchy...

Introduction and Etiology

Respiratory Distress Syndrome (RDS) is a life threatening pulmonary disease primarily of the premature infant caused by surfactant deficiency 

Pulmonary surfactant is a complex lipoprotein composed of phospholipids and apoproteins synthesized by alveolar type 2 epithelial cells and airway Clara cells. These lipoproteins function to decrease surface tension at the air-liquid interface of the lung and also play a role in host defense against infection and inflammation [1-3].

Impairment in the synthesis and/or secretion of surfactant leads to an increase in dead space due to atelectasis and a decrease in lung compliance. Consequences include ventilation-perfusion mismatch, hypoxemia and hypercarbia that in turn lead to respiratory acidosis.

Acidosis causes vasoconstriction that impairs the endothelial and epithelial integrity in the lungs, thus leaking an exudate that forms the hyaline membrane from which the name of the disease is derived.

 

Epidemiology

About 1 in 20,000-30,000 newborn US infants will have RDS. Approximately half of neonates born at gestation age of 26-28 weeks will develop RDS, while about 30% of 30-31 gestation week neonates will develop it [4]. Although prematurity is the primary risk factor, there are several other risk factors including maternal diabetes, cesarean section, asphyxia, rapid labor, and complications that reduce blood flow to the fetus [5, 6].

Internationally, RDS occurs less frequently than in the US but overall, it is more common in white premature infants.

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Clinical presentation

Symptoms observed in infants with RDS are indicative of difficulty with breathing. They typically present shortly after birth, at times hours afterwards, and include:

  • Cyanosis
  • Tachypnea
  • Nasal flaring
  • Subcostal and intercostal retractions
  • Expiratory grunting
  • Apnea

 

Potential complications

Several of the complications of RDS are reduced with adequate treatment. In certain cases, a combination of the disease and its treatment result in the complications of:

  • Patent ductus arteriosus (PDA)
  • Pulmonary hemorrhage
  • Pneumothorax
  • Bronchopulmonary dysplasia (BPD)
  • Septicemia
  • Hypertension
  • Failure to thrive
  • Apnea
  • Intraventricular hemorrhage (IVH)

 

Differential diagnosis

With hyaline membrane disease causing respiratory distress syndrome, there are quite a few other diseases or conditions that can present similarly. Some of which are:

  • Transient tachypnea of the newborn
  • Pneumonia
  • Sepsis
  • Pneumothorax
  • Persistent pulmonary hypertension
  • Congenital lung malformations
  • Aspiration syndromes

 

Treatment

Urgent delivery of care to infants with hyaline membrane disease is very important. With prematurity being the most common risk factor responsible for RDS, neonatologists are on hand for the delivery and can administer immediate treatment required.

Resuscitation is the primary treatment required so as to minimize sequelae of the disease. It entails administration of warm, moist oxygen and assisted ventilation. The oxygen is critically important but can also cause damage to the lungs via generation of radical ions [7]. As such, great care is taken to ensure that the patients are receiving the smallest possible amount of oxygen required.

Continuous positive airway pressure (CPAP) is often used to promote ventilation, by keeping the alveoli open at the end of expiration thereby reducing the chances of atelectasis [8]. Using CPAP reduces the associated side effect of lung damage due to mechanical ventilation.

Surfactant replacement therapy is also being used to treat HMD and has reduced the mortality rate from respiratory distress syndrome by about half. The surfactant protects the immature lung from inflammation and also partially restores the surface tension that helps keep alveoli from collapsing. It is typically administered shortly after birth [9]. Interestingly, the ideal type of surfactant that will be most beneficial to these patients is yet to be ascertained [10].

Corticosteroids are another group of medications used in the management of infants at risk for HMD. In this case, mothers at an increased risk of having children with hyaline membrane disease are given a single dose of corticosteroid. Several doses have been shown to have no additional benefit but a repeat dose can be considered in the event that the woman does not deliver within a week of prior corticosteroid administration [11, 12].

Other forms of management include supportive therapy to promote circulation and aid in respiration such as fluid and metabolic support. In addition, antibiotics may be administered if there also risk factors for infection.

 

Prognosis

Typically, the symptoms worsen a few days after birth but slowly improve afterwards. The goal is to support the infant while the lungs begin producing surfactant.  Providing adequate nutritional requirements is also important for recovery and growth.

Many infants with RDS suffer the complications of oxygen and ventilation therapy but recover within the first couple of years of life as the lung tissue is replaced with new and functional tissue.

Damage to other organs such as the brain may also occur which is due to a combination of factors including hypoxia and intraventricular hemorrhage, so it is imperative to begin therapy early and monitor organ damage.

 

References:

  1. Goerke, J., Pulmonary surfactant: functions and molecular composition. Biochim Biophys Acta, 1998. 1408(2-3): p. 79-89.
  2. Whitsett, J.A., et al., Human surfactant protein B: structure, function, regulation, and genetic disease. Physiological reviews, 1995. 75(4): p. 749-57.
  3. Wright, J.R., Immunomodulatory functions of surfactant. Physiological reviews, 1997. 77(4): p. 931-62.
  4. Hintz, S.R., et al., Neurodevelopmental outcomes of premature infants with severe respiratory failure enrolled in a randomized controlled trial of inhaled nitric oxide. The Journal of pediatrics, 2007. 151(1): p. 16-22, 22 e1-3.
  5. Gerten, K.A., et al., Cesarean delivery and respiratory distress syndrome: does labor make a difference? American journal of obstetrics and gynecology, 2005. 193(3 Pt 2): p. 1061-4.
  6. Qiu, X., et al., Comparison of singleton and multiple-birth outcomes of infants born at or before 32 weeks of gestation. Obstetrics and gynecology, 2008. 111(2 Pt 1): p. 365-71.
  7. Wells, D.A., D. Gillies, and D.A. Fitzgerald, Positioning for acute respiratory distress in hospitalised infants and children. Cochrane database of systematic reviews, 2005(2): p. CD003645.
  8. Murray, P.G. and M.J. Stewart, Use of nasal continuous positive airway pressure during retrieval of neonates with acute respiratory distress. Pediatrics, 2008. 121(4): p. e754-8.
  9. Engle, W.A., Surfactant-replacement therapy for respiratory distress in the preterm and term neonate. Pediatrics, 2008. 121(2): p. 419-32.
  10. Pfister, R.H., R.F. Soll, and T. Wiswell, Protein containing synthetic surfactant versus animal derived surfactant extract for the prevention and treatment of respiratory distress syndrome. Cochrane database of systematic reviews, 2007(4): p. CD006069.
  11. Doyle, L.W., et al., Outcome at 2 years of age of infants from the DART study: a multicenter, international, randomized, controlled trial of low-dose dexamethasone. Pediatrics, 2007. 119(4): p. 716-21.
  12. Wapner, R.J., et al., Long-term outcomes after repeat doses of antenatal corticosteroids. The New England journal of medicine, 2007. 357(12): p. 1190-8.