Neonatal Handbook

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Respiratory Distress Syndrome (RDS)

Summary
Introduction
Differential Diagnosis
Investigations
Management
Sudden deterioration
Areas of Uncertainty in Clinical Practice

Summary

attention to thermoregulation and oxygenation can decrease the severity of RDS
antibiotics are usually indicated for infants with respiratory distress
level of experience and expertise dictate what technical procedures (IV and ETT insertion) are indicated prior to arrival of the transport team
surfactant administration should follow as soon after endotracheal intubation as possible
infants requiring more than 60% oxygen should be managed in a tertiary centre

Introduction

Respiratory distress syndrome (RDS), also known as Hyaline Membrane Disease (HMD), is the dominant clinical problem faced by preterm infants.

The greatest risk factor is low gestational age and the development of the disease begins with the impaired synthesis of pulmonary surfactant associated with prematurity.

The disease is exacerbated by treatable/preventable factors including

cold stress
hypoxia
acidosis

The diagnosis is made on the basis of the combination of clinical (grunting respirations, intercostals recession, nasal flaring, cyanosis and increased oxygen requirement) and radiological (diffuse reticulogranular pattern with air bronchograms) features.

The natural history is for the clinical signs to develop within 6 hours of life, with progressive worsening over the first 48 to 72 hours of life followed by recovery.

The condition can be prevented or the severity diminished by antenatal administration of betamethasone. The course of the disease is altered by exogenous surfactant therapy and assisted ventilation.

Differential Diagnosis

Signs and radiolological appearance of RDS are not specific and other causes of respiratory distress should be considered. In particular it is difficult to exclude sepsis as a possible diagnosis initially and antibiotic therapy should be given until blood cultures prove negative.

"Wet lung" and lung malformations as well as non-pulmonary causes of respiratory distress are uncommon in the preterm infant but should be excluded using the appropriate tests.

Investigation

A chest xray is useful and should be performed in all cases of respiratory distress once the oxygen requirement exceeds 30%. The X-ray may need to be repeated if the illness runs a course that is unusual or protracted or the infant’s status suddenly worsens when air leak complications must be considered.

A full blood count and blood culture should be performed prior to starting antibiotics but antibiotics should not be withheld if blood sampling proves technically difficult. Antibiotics may be given intramuscularly in these circumstances.

Management

Nonrespiratory

temperature control is an important facet of the care of the infant with respiratory distress and both hypo and hyperthermia should be avoided. The temperature should be maintained in the neutral thermal range

enteral feeding should generally be avoided in infants with significant respiratory distress (oxygen requirements greater than 35%). During the initial stabilisation intravenous fluid therapy is useful if it can be started easily but premature infants do not necessarily require an IV immediately. Exposure to manipulation and cold stress may do more harm than good in this situation. Attention to prevention of hypoglycemia is, however, an important part of on-going care

minimal handling is important. This can be facilitated by the use of monitors to help assess infant status (cardiorespiratory, temperature and oxygen saturation monitiors should be used whenever possible)

antibiotics — commence penicillin and gentamicin therapy after initial investigations

Respiratory

Airway

Placing the infant in the lateral or prone posture rather than supine provides a clear airway. Repeated suctioning of the pharynx is not required and may cause apnoea and hypoxia.

Oxygen

Although both too much and too little oxygen are bad for preterm infants, hypoxia is much more dangerous over the short period of time while awaiting transport.

Monitoring

Arterial blood gases — accurate assessments can be made from samples taken from indwelling arterial lines which are usually performed in an intensive care setting, aiming to keep pO₂ between 50 and 80 mm Hg. Assessment of oxygen requirements from arterial ‘stabs’ is not reliable.

Non-invasive monitoring — oxygen saturation monitors may be attached to the infant’s hand or foot. The desired range for infants less than 34 weeks gestation is 88 to 95% and for more mature infants 88 to 100%.

Cyanotic threshold — keep the ambient oxygen concentration 5 to 10% above the level at which the infant is noted to be cyanosed.

Administration

Oxygen concentrations up to 40% may be achieved through the oxygen port into an incubator. Above 40% is best achieved using warmed, humidified gas delivered via a headbox. Flow rates of at least 6-8 l/min are required to avoid rebreathing.

Intubation and intermittent positive pressure ventilation (IPPV)

Indications

cyanosis that persists in spite of maximal oxygen therapy
severe recurrent apnoea
respiratory failure (pCO₂ > 70 and pH < 7.2)

See Intubation Procedure section for further details.

Stabilization ventilator settings

For an infant with RDS reasonable settings are: ventilator rate 60 breaths per minute, inspiratory time 0.3 sec (expiratory time 0.7 sec), PEEP 5 cm and oxygen set to maintain saturations of 88 to 95%. Peak inspiratory pressure (PIP) should be set to achieve "reasonable" chest movement — usual intial settings in RDS will lie between 20 and 30 cm water.

Surfactant administration should be considered in any intubated infant with a presumed diagnosis of RDS.

Sudden deterioration

In a spontaneously ventilating infant sudden deterioration may be caused by

pneumothorax
failure of oxygen supply
increase in severity of the underlying disease

Infants may be able to sustain the protracted tachypnoea associated with RDS for hours or days before developing respiratory failure. This may be signalled by onset of apnoea, sudden increase in oxygen requirements or very laboured respiratory efforts. Continued close monitoring throughout the infan's entire illness is mandatory.

In a ventilated infant sudden deterioration is most likely to be caused by

pneumothorax (easily overlooked clinically so transillumination or a further chest X-Ray are essential.)
endotracheal tube blockage or displacement
mechanical failure with the ventilator
increase in the severity of the underlying lung disease
massive intraventricular haemorrhage
necrotizing enterocolitis, especially if perforation has occurred
patent ductus arterious

Areas of Uncertainty in Clinical Practice

NCPAP vs endotracheal intubation and surfactant for infants with RDS.

References

Stabilization and transport of newborn infants and at-risk pregnancies 4^th Edition 1998 NETS Publication
Neonatal-perinatal medicine: Diseases of the fetus and infant 6^th ed 1997. Fanaroff AA and Martin RJ (eds). Mosby-Year Book.