Re-expansion pulmonary edema in a boy with spontaneous pneumothorax during an influenza B virus infection *

Re-expansion Pulmonary Edema (RPE) is an uncommon complication following rapid re-expansion of the lungs, and the most common disorder associated with RPE is spontaneous pneumothorax. The majority of patients with RPE associated with pneumothorax have been adults; only 4 cases have been reported in children. We present a patient who developed RPE after treatment of spontaneous pneumothorax that occurred during an influenza B virus infection. His condition improved only with oxygen supplementation and intravenous corticosteroids. Infection with influenza B virus leads to increased production of lung epithelial oxidants, which might have contributed to the development of RPE in our patient.


INTRODUCTION
Re-expansion Pulmonary Edema (RPE) is an uncommon complication that occurs when a collapsed lung is rapidly re-expanded after evacuation of air or fluid from the pleural space [1].Although it is possible for RPE to occur in every type of chronically collapsed lung that can be re-expanded, the most common disorder associated with RPE is spontaneous pneumothorax [2].The majority of patients with RPE associated with pneumothorax have been adults [1]; only 4 cases have been reported in children [3][4][5].We report a patient who developed RPE after treatment of spontaneous pneumothorax that occurred during an influenza B virus infection.

PATIENT REPORT
A previously healthy, 6-year-old boy was admitted to our hospital after 2 days of cough, dyspnea and high-grade fever.On admission, the patient was febrile with a body temperature of 39.6˚C, and his oxygen saturation was 94% while breathing ambient air.
Physical examination showed tachypnea and diminished breath sounds over the left hemi-thorax.A nasopharyngeal swab tested positive for influenza B on a rapid influenza antigen detection test.Routine laboratory tests were normal except for a slightly elevated C-reactive protein concentration.Chest radiography revealed a left-sided pneumothorax (Figure 1(a)).His symptoms improved immediately after placement of a chest tube with application of a negative pressure of 10 cm H 2 O.However, after 30 minutes, the patient again exhibited tachypnea and his oxygen saturation decreased to 88%.Chest auscultation revealed left-sided inspiratory crackles.Repeat chest radiography showed a fully expanded left lung, but also left-sided pulmonary edema (Figure 1(b)).
The patient was diagnosed with RPE occurring after treatment of pneumothorax.He was administered oxygen supplementation (5 L/min via face mask) and intravenous corticosteroids.His condition gradually improved over the next 2 days, and after an additional 3 days, his pneumothorax and RPE completely resolved.The patient was discharged after the chest tube was removed, without further sequelae.The patient remained well over a 6 months follow-up period.

DISCUSSION
RPE has been reported after rapid evacuation of large pneumothorax or large pleural effusion [4].The clinical features of RPE include the following: a collapsed lung over period of 3 days or more; an evacuation volume of 2000 ml or more; a period of less than 1 hour from re-expansion to the onset of RPE; and the pulmonary edema is classified as permeability pulmonary edema [2].Risk factors for RPE include the degree of lung collapse and a rapid re-expansion [1].The symptoms of RPE range from asymptomatic presentation to cardiopulmonary insufficiency [4] and the reported mortality rate has ranged from 0% to 20% [1].Despite the fact that the rate of occurrence of RPE after drainage of a pneumothorax varies from 14.4% to 27%, there have only been 4 reports from the pediatric population [3][4][5].Pediatric cases of RPE with diseases other than pneumothorax are also rare; RPE has been reported in children with pleural effusion due to nephrotic syndrome [6] or non-Hodgkin's lymphoma [7,8], with reinflation of a retracted lung following patent ductus arterious ligation [9] or following general anesthesia [10], and with pleural empyema [11].
Treatment for RPE remains supportive, using oxygenation, positive-pressure mechanical ventilation and utilization of positive end-respiratory pressure, diuresis and hemodynamic support.In addition, the use of prostaglandin analogs or corticosteroids has been also reported [1,2,12].However, the best treatment is to avoid rapid lung re-expansion [2].
Although the precise pathogenic mechanism for the development of RPE remains unclear, the common end-point in the pathological process is probably enhanced endothelial permeability caused by a combination of alveolar-capillary membrane disruption and ischemia-reperfusion-mediated injury [1,2].Oxygen radicals and interleukin 8 (IL-8) have also been reported to be contributing factors in the development of RPE [1,2].
In our patient, RPE occurred following treatment of pneumothorax associated with influenza B virus infection.Infection with influenza virus leads to increased production of lung epithelial oxidants, which directly and/or via IL-8 expression results in injury to the lung epithelial cells [13].Influenza virus induction of these mediators might have contributed to the development of RPE in our patient.

Figure 1 .
Figure 1.(a) Chest radiograph on admission showing spontaneous pneumothorax of the left lung; (b) Chest radiograph after insertion of the chest tube showing reexpansion pulmonary edema of the left lung.