Rabbit Pneumothorax:
Feasibility of an Animal Model To Simulate Neonatal Pneumothorax

Steven Don, MD, Mervn D. Cohen, MB,ChB, Robert A. Kruger, PhD, Todd A. Winkler, BS, Barry P. Katz, PhD, Wei Li, MS, Jerry Dreesen, RT, Nuala Kennan, MB, BCh,FRCR, Robert Tarver, MD, Eugene Klatte, MD

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In the neonate, pneumothorax is a common chest radiographic finding. Spontaneous pneumothorax occurs in 1% of infants delivered vaginally(1,2)and in 2% of infants delivered by cesarean section.(1) The highest incidence, 6% to 10%, occurs in mechanically ventilated neonates.(1,3)

The chest radiograph is the reference standard for diagnosing a pneumothorax, and most neonatal pneumothoraces are recognized on the portable, supine radiograph.

Computed radiography (CR) is a new radiographic technique that replaces the x-ray film with photostimulable phosphor plates. This technology is replacing film-screen radiography (FS) in some neonatal intensive care units. However, previous research noted that the neonate is a poor model for testing specific disease because of the multiple radiographic findings in this patient population.(8) Therefore comparison studies between CR and FS in detecting neonatal pneumothorax or other specific disease processes have been performed.

In this study, we attempted to develop an animal model to simulate neonatal pneumothorax and validate the experimental design and methodology. The feasibility of this model depends on the following: 1/accurately controlling the volume of an artificially induced pneumothorax; 2/confirming that the radiographic signs of a supine, neonatal pneumothorax are present in this animal model; and 3/demonstrating that there is no difference in the radiographic appearance of a pneumothorax between CR and FS.

RATIONALE & OBJECTIVES
The feasibility of developing an animal model to simulate radiographic features of neonatal pneumothorax was investigated, and supien computed radiography (CR) and film-screen radiography (FS) images were compared.

METHODS
5Fr pigtail catheters were inserted into the right pleural space of three New Zealand White (NZW) rabbits. Two CR and two FS supine images were obtained using identical technique. After serial 4-mL injections of air, one CR and one FS supine image were obtained. The images were masked and randomized, and four radiologists reviewed the images for typical signs of pneumothorax. Chest computed tomography (CT) was performed before the injection of any air and after completion of the study.

RESULTS
At zero-mL air volume, radiologists did not perceive a pneumthorax. As the air volume increased, the number of signs of a pneumothorax increased; there was no significant difference between CR (Fig 1A/2B) and FS (Fig 2A/2B) in the number of signs of pneumothorax detected at any volume. Chest CT confirmed that there was no unexplained air leak. The volume of air injected correlated with the calculated volume from the CT.

CONCLUSIONS
This induced, volume controlled, animal model simulated the supine radiographic features of neonatal pneumothorax.

KEY WORDS
Computed radiography; film-screen radiography; neonate; pneumothorax.


Figure 1: A/B Computed radiographic images of a rabbit at(A)0ml and (B) 8ml. 8ml. Note mediastinal shift in Figure B

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