Abstract

Visualization of avian thoracic and abdominal structures can be achieved using plain or contrast radiographs. The use of positive pressure radiography in an anesthetized, intubated avian patient increases the volume of air in the respiratory system to provide more contrast and organ separation, allowing enhanced visualization of structures. The main purpose of this study was to investigate the safety and diagnostic utility of contrast radiography using positive pressure insufflation in an avian species.

Six adult male Northern pintails (Anas acuta) were divided without bias into two groups of three birds each and scheduled for either two (Group 1) or three (Group 2) procedures, 1 wk apart. Two groups were created in order to determine if multiple procedures induced any detectable clinicopathologic signs of barotrauma. Ducks were induced with 2.5% isoflurane (Abbott Laboratories, North Chicago, IL 60064 USA) by facemask, intubated (2.5 mm i.d., all-silicone endotracheal tube) without inflating the cuff, and maintained at 1.5%-3% isoflurane via anesthetic rebreathing circuit, for an average of 20 min.

Both survey and positive pressure insufflation contrast radiographs were obtained from anesthetized ducks. These consisted of preliminary whole body lateral and ventrodorsal films, followed by radiographs taken during brief positive pressure insufflation, achieved by maintaining 20 cm of water pressure during x-ray exposure. Thus, each duck had four radiographs (two survey and two contrast films) taken per procedure. Following recovery, ducks were returned to their normal enclosures and routines for 1 wk. After recovering from their second (Group 1) or third (Group 2) procedure, ducks were euthanatized by i.m. and i.v. overdoses of anesthetic drugs, and complete postmortem examinations were performed immediately. Representative tissues from the upper and lower respiratory tract (including trachea, syrinx, bronchi, lung, and air sacs) were preserved in buffered 10% formalin and prepared routinely for histologic examination (hematoxylin and eosin stain).

Survey and positive pressure insufflation contrast radiographs for each bird were placed on a light table and digitized individually by the same investigator using a hand held digital camera (Nikon Coolpix 950, Nikon Inc., Melville, NY 11747 USA) to capture high quality images. Digitized images of thoracic and abdominal air sacs and lung regions were traced (by one person) manually via touch-pad using PC software capable of measuring multiple polygonal areas (Scion Image, Scion Corporation, Frederick, MD 21703 USA). A marker of known length was included in each radiograph to standardize area measurements (in mm²). Total air sac and lung areas traced from survey lateral and ventrodorsal radiographs of each bird for each procedure were compared to contrast films of the same view. The difference between survey and contrast total areas was calculated as an individual percent change for each lateral and ventrodorsal film set per duck. Percent change values for both study groups were combined and averaged separately for lateral and ventrodorsal views.

Birds recovered quickly with no signs of respiratory distress. Complications observed were the occurrence of 4-5 mm mucohemorrhagic plugs at the tip of the endotracheal tubes in certain cases, mild leakage of anesthetic gases around the endotracheal tube during positive pressure insufflation, and intermittent apnea. No gross or histologic lesions attributable to barotrauma (e.g., bullae, ruptures, diathesis, or hemorrhage) were observed in either group. Microscopic respiratory tract findings were considered unrelated to the procedures and included mild to moderate anthrasilicosis of lung and air sacs, with associated mild to moderate lymphocytic infiltration.

Average increases in percentage area resulting from positive pressure insufflation on lateral and ventrodorsal radiographs compared with survey films were 79% and 90%, respectively. For each bird, there were minor variations in manual tracings of lungs and abdominal and thoracic air sacs on the radiographs between weeks, resulting in slightly different values of total mm² measured from procedure to procedure. These variations were due to the partially subjective nature of manual tracing, as well as technical differences in radiographic positioning, organ location, presence of ingesta, and/or digitization processes, but were deemed insignificant for the purposes of this study.

There was improved visualization of thoracic and abdominal structures on contrast films compared to survey films, as judged by attending veterinarians. Boundaries of lungs and air sacs became more distinct with positive pressure insufflation. Cardiohepatic, lung, renal, gastrointestinal, vertebral, and testicular silhouettes and margins were more easily distinguished and assessed for potential abnormalities on contrast films than on survey films. For example, changes in testicular size and shape were better visualized from week to week on contrast radiographs. We postulate that this technique can provide a minimally invasive method of detecting lesions in internal organs caused by a variety of conditions, including granulomatous infections of lungs and air sacs, hepatic neoplasia, and anatomic reproductive changes.

In this study, we demonstrated that positive pressure insufflation using 20 cm of water is a clinically safe and effective method of filling the air sacs of anesthetized Northern pintails and does not result in detectable immediate or long-term barotrauma. Radiographs obtained during air sac insufflation provided improved visualization of thoracic and abdominal avian structures on both lateral and ventrodorsal radiographs as a result of increasing average air sac and lung region areas by greater than 75%. This simple technique utilizes the principle that positive pressure insufflation introduces air as a safe and useful contrast medium, increasing the diagnostic capability of radiographs for avian patients.

Acknowledgments

The authors wish to thank the keepers and curator of the Department of Ornithology at the Conservation Research Center for their assistance in this project. Special gratitude is extended toward the talented members of the Department of Pathology at the Smithsonian National Zoological Park, especially Anne Bratthauer, Donna Fischer, Vera Bonshock, Jim Raymond, Don Nichols, and Nancy Spangler for technical support. This work was supported in part by the Friends of the National Zoo (FONZ).