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In extremely premature infants, pulmonary interstitial
emphysema can occur at low mean airway pressure and probably reflects
the underdeveloped lung’s increased sensitivity to stretch. Pulmonary
interstitial emphysema has been rarely reported in the absence of
mechanical ventilation or continuous positive airway pressure. Infants
with RDS have an initial increase in interstitial and perivascular
fluid that rapidly declines over the first few days of life. This fluid
may obstruct the movement of gas from ruptured alveoli or airways to the
mediastinum, causing an increase of pulmonary interstitial emphysema.
Another possible mechanism for entrapment of air in the interstitium is the increased amount of pulmonary connective tissue in the immature lung. The entrapment of air in the interstitium may initiate a vicious cycle in which compression atelectasis of the adjacent lung then necessitates a further increase in ventilatory pressure with still more escape of air into the interstitial tissues.
Pulmonary interstitial emphysema is more common in infants of lower gestational age. Pulmonary interstitial emphysema usually occurs within the first weeks of life. Development of pulmonary interstitial emphysema within the first 24-48 hours after birth is often associated with extreme prematurity, very low birth weight, perinatal asphyxia, and/or neonatal sepsis and frequently indicates a grave prognosis.
Lateral Decubitus Positioning
In different case studies of lateral decubitus positioning as a treatment of unilateral pulmonary interstitial emphysema in infants, pulmonary interstitial emphysema resolved in 48 hours to 6 days with minimal recurrence and a low failure rate. Lateral decubitus positioning should be considered as an early first-line therapy in the management of unilateral pulmonary interstitial emphysema. Lateral decubitus positioning has been used successfully for patients with bilateral pulmonary interstitial emphysema when one side is more significantly affected.
Selective Main Bronchial Intubation and Occlusion
This procedure uses an endotracheal tube of the same diameter as for a regular intubation. However, the tube is inserted 2-4 cm beyond its usual position. It is introduced with the bevel on the end of the tube positioned so that the long part of the tube is toward the bronchus to be intubated. This increases the chance of entering the correct bronchus as the tube is advanced into the airway. Turning the infant's head to the left or right moves the tip of the endotracheal tube to the contralateral side of the trachea and may help in selective tube placement.
Weintraub et al have described a method for left selective bronchus intubation using a regular Portex endotracheal tube in which an elliptical hole 1 cm in length has been cut through half the circumference 0.5 cm above the tip of the oblique distal end.With the side with the elliptical hole directed to the left lung, left selective bronchus intubation can be easily and repeatedly accomplished.
Another method of selective intubation is the use of a small fiberoptic bronchoscope to direct the endotracheal tube tip into the desired bronchus. Selective intubation under fluoroscopy can also be considered.
Potential complications of the selective intubation/ventilation include the following:
- Atelectasis in the affected lung
- Injury to bronchial mucosa with subsequent scarring and stenosis
- Acute hypoventilation or hypoxemia if ventilating one lung is inadequate
- Excessive secretions
- Hyperinflation of the intubated (non-occluded) lung
- Upper lobe collapse when intubating the right lung
Similar effects can be achieved by use of high-frequency oscillatory ventilation (HFOV). A study by Clark et al demonstrated the efficacy of HFOV in 27 low-birth-weight infants who developed pulmonary interstitial emphysema and respiratory failure while on conventional ventilation.
Overall survival in nonseptic patients was 80%. Surviving patients showed continued improvement in oxygenation and ventilation at an increasingly lower fraction of inspired oxygen (FiO2) and proximal airway pressure with resolution of pulmonary interstitial emphysema, whereas nonsurvivors progressively developed chronic respiratory insufficiency with continued pulmonary interstitial emphysema from which recovery was not possible.
Clark et al hypothesized that interstitial air leak is decreased during HFOV because adequate ventilation is provided at lower peak distal airway pressures. Although this mode of ventilation has inherent risks, it can be a very effective tool in experienced hands for the treatment of severe diffuse pulmonary interstitial emphysema. Care must be taken in smaller infants who require a high amplitude to ventilate because the active exhalation during HFOV may cause small airway collapse and exacerbate gas trapping.