Introduction
Background
Pulmonary interstitial emphysema (PIE) is an iatrogenic pulmonary condition of the premature infant with immature lungs. PIE occurs almost exclusively in association with mechanical ventilation. The ventilatory pressure used to keep the alveolar ducts open also may cause the alveolar duct to rupture (usually at the junction of the bronchiole and alveolar duct); this in turn leads to the escape of air into the pulmonary interstitium, lymphatics, and venous circulation.1,2
Close-up examination shows the typical linear pattern of pulmonary interstitial emphysema.
Pathophysiology
The cut section of the lung shows gas dissecting through the interstitium.
Histologic section showing gas within the interstitium, mainly in lymphatic vessels. The pulmonary tissue is atelectatic.
The surface of the lung in pulmonary interstitial emphysema shows subpleural lymphatics distended with air.
Immature lungs are underdeveloped and lack adequate surfactant to keep the alveolar ducts and early alveoli open on inspiration and expiration. As a result of the decrease in surface area, the capacity to transfer gas is reduced; this, in conjunction with widespread atelectasis, leads to inadequate transfer of carbon dioxide and oxygen across the epithelial surfaces to the pulmonary microvascular system. Methods to improve oxygen saturation include administering high concentrations of oxygen and expanding and maintaining the expansion of gas-exchanging surfaces of the lung using high levels of inhaled oxygen and positive pressure ventilation.
Excessive intra-airway pressure may cause gas to leak from the alveolar ducts (primordial acini) into the lung interstitium. Once in the interstitium, the gas is picked up in the rich lymphatic network of the neonate and is carried toward the pleural lymphatics and central bronchopleural lymphatics. PIE usually occurs early during ventilation; most infants with PIE present in the first 72 hours.
PIE occurs less frequently now because immature babies are treated with exogenous surfactant; such treatment increases lung compliance (thus reducing the need for ventilatory pressure) and keeps the alveolar ducts open during both inspiration and expiration.3 It also assists in the recruitment of alveolar ducts to prevent areas of overinflation and underinflation. Currently, PIE is seen more often in infants with bronchopulmonary dysplasia (BPD) who receive long-term ventilator therapy with uneven aeration; in such patients, PIE results from air trapping and airspace rupture.
Frequency
United States
Several decades ago, PIE was a common occurrence in infants with severe respiratory distress on ventilators. Currently, it is an uncommon occurrence because of treatment with surfactant and gentle ventilation, as well as the availability of high-frequency oscillatory ventilation for infants who are difficult to maintain with conventional ventilation.
Mortality/Morbidity
In the past, the mortality associated with PIE was high because the lungs became stiff and gas freely dissected into the interstitium, where oxygen absorption was poor. With rapid measures of prevention and alternative ventilatory improvement, approximately 25% of the infants survived, but all developed severe BPD.
- Complications of PIE include marked loss of pulmonary compliance, eventual epithelialization of the interstitial air pockets, embolus of air into the pulmonary venous circulation, and rupture of subpleural lymphatic blebs into the pleural space with pneumothorax. Infants with PIE inevitably develop BPD. Rupture of bronchiolar connections and release of air into the interstitium promotes edema and oxidant injury in the interstitium.
Sex
PIE is seen with equal frequency in both sexes.
Age
PIE is seen in premature infants usually younger than 32 weeks' gestation and who weigh less than 1200 g. PIE occurs in the first 72 hours of life, although it may be observed as a complication of prolonged positive pressure ventilation in the older premature infant.
Anatomy
PIE may occur diffusely throughout the lung, or it may be unilateral or lobar in occurrence. When PIE is local, the surrounding lung is often compressed as the region with PIE enlarges. The lesion of PIE is mechanical distention (and overdistention) of the alveolar ducts (precursors to alveoli and acini), which causes the ducts to rupture; alternatively, rupture occurs at the relatively weak junction of the alveolar duct and its bronchiole. After rupture, the air leak persists with the pressure of ventilation and motion of respiration. Gas is free to dissect into the interstitium, where it may remain or be taken up by the pulmonary lymphatic system. Cysts and overdistention of the lung reflect the effect of gas within the interstitium.
Presentation
PIE develops in infants who have established pulmonary disease of prematurity with respiratory distress syndrome who are being treated with supplemental oxygen, endotracheal intubation, and positive pressure mechanical ventilation. Most premature infants at risk for respiratory distress syndrome are treated with endotracheal surfactant, which improves pulmonary expansion, lung compliance, and oxygen exchange. PIE often occurs rapidly, arising in one region of the lung and quickly involving multiple lobes with fixed hyperexpansion, causing the clinical condition to worsen. Oxygen saturation of the blood falls, and ventilatory requirements increase.4
Emergent management takes several forms: initiation of high-frequency oscillatory ventilation with the rapid exchange of low volumes of gas at low pressure and, if PIE is localized, selective intubation of the airway bypassing the bronchus to the involved lobe.5,6
Studies have demonstrated the presence of free elastase and alpha 1 -proteinase inhibitor, as well as elastase-alpha 1 -proteinase inhibitor, in tracheal aspirate fluid of neonates with severe respiratory distress syndrome. Infants who develop PIE appear to have free elastase activity in tracheal aspirate fluid. Elastolytic damage and barotrauma may contribute to acute pulmonary injury and PIE in the early stages of respiratory distress syndrome.7
Preferred Examination
Clinical examination involves the evaluation of pH and arterial oxygen saturation in proportion to the fraction of inspired oxygen.
PIE may be identified with a frontal chest radiograph. Disease progression is assessed with sequential studies.8
Limitations of Techniques
In an ill infant, it may be difficult to differentiate PIE from lucent overdistention of the bronchioles, though overdistended distal airways tend to be round and of uniform diameter, whereas PIE tends to be ovoid in the direction of the bronchovascular bundles; in addition, the lesions of PIE tend to be of different sizes. It is also difficult to differentiate PIE from early BPD with uneven patterns of aeration.
Differential Diagnoses
More on Pulmonary Interstitial Emphysema |
 Overview: Pulmonary Interstitial Emphysema |
| Imaging: Pulmonary Interstitial Emphysema |
| Follow-up: Pulmonary Interstitial Emphysema |
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| References |
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References
Cochran DP, Pilling DW, Shaw NJ. The relationship of pulmonary interstitial emphysema to subsequent type of chronic lung disease. Br J Radiol. Dec 1994;67(804):1155-7. [Medline].
Roll C, Hanssler L, Voit T. Case 30-1997: pulmonary interstitial emphysema in infancy [letter; comment]. N Engl J Med. Mar 5 1998;338(10):689-90. [Medline].
Soll, RF, Morley, CJ. Cochrane Database Syst Rev 2001;2:CD000510Prophylactic versus selective use of surfactant in preventing morbidity and mortality in preterm infants. Cochrane Review. 2001;2:CD000510.
Stevens TP, Harrington EW, Blennow M, Soll RF. Early surfactant administration with brief ventilation vs. selective surfactant and continued mechanical ventilation for preterm infants with or at risk for respiratory distress syndrome. Cochrane Database Syst Rev. Oct 17 2007;CD003063. [Medline].
Nelle M, Zilow EP, Linderkamp O. Effects of high-frequency oscillatory ventilation on circulation in neonates with pulmonary interstitial emphysema or RDS [see comments]. Intensive Care Med. Jun 1997;23(6):671-6. [Medline].
Plavka R, Kopecky P, Sebron V. A prospective randomized comparison of conventional mechanical ventilation and very early high frequency oscillatory ventilation in extremely premature newborns with respiratory distress syndrome. Intensive Care Med. Jan 1999;25(1):68-75. [Medline].
Speer CP, Ruess D, Harms K. Neutrophil elastase and acute pulmonary damage in neonates with severe respiratory distress syndrome. Pediatrics. Apr 1993;91(4):794-9. [Medline].
Jabra AA, Fishman EK, Shehata BM. Localized persistent pulmonary interstitial emphysema: CT findings with radiographic-pathologic correlation. AJR Am J Roentgenol. Nov 1997;169(5):1381-4. [Medline].
Ahluwalia JS, Rennie JM, Wells FC. Successful outcome of severe unilateral pulmonary interstitial emphysema after bi-lobectomy in a very low birth weight infant. Journal of the Royal Society of Medicine. March, 1996;89:167-168.
[Best Evidence] Greenough A, Dimitriou G, Prendergast M, Milner AD. Synchronized mechanical ventilation for respiratory support in newborn infants. Cochrane Database Syst Rev. Jan 23 2008;CD000456. [Medline].
Chalak LF, Kaiser JR, Arrington RW. Resolution of pulmonary interstitial emphysema following selective left main stem intubation in a premature newborn: an old procedure revisited. Paediatr Anaesth. Feb 2007;17(2):183-6. [Medline].
Thayyil S, Nagakumar P, Gowers H, Sinha A. Optimal endotracheal tube tip position in extremely premature infants. Am J Perinatol. Jan 2008;25(1):13-6. [Medline].
Further Reading
Keywords
acquired cystic lung disease of the premature infant, barotrauma of the premature lung interstitium, PIE
