Minimal atelectasis and poorly aerated lung on thoracic CT images of normal dogs acquired under sedation

Abstract

General anesthesia optimizes image quality of thoracic CT in dogs by providing patient immobilization and respiratory control. However, it also comes with disadvantages that may serve as a detractor to the use of CT in veterinary practice. With the use of multidetector helical CT combined with injectable sedation for restraint, parameters such as atelectasis and poorly aerated lung should not be appreciably different from what has been observed in dogs under general anesthesia. This prospective pilot study aimed to evaluate the mean lung attenuation and the amount of atelectasis and poorly aerated lung on thoracic CT images acquired under injectable sedation in normal dogs.The entire thorax of 10 client-owned dogs was scanned. Attenuation measurements were generated by three-dimensional reconstruction software. Mean ± SD lung attenuation was -707.0 ± 60.0. Atelectasis was not identified on any of the scans. Hypoinflated lung, the percentage of lung parenchyma with attenuation greater than -500 and -250 Hounsfield units (HU), was 10.7 ± 4.7% and 2.4 ± 1.2% (mean ± SD), respectively.There was no significant change in these percentages over time. Compared to previously published data, thoracic CT images obtained under sedation had mean attenuation comparable to normal expiratory lung and a lower percentage of poorly aerated lung compared to that of anesthetized dogs. Using sedation to complete canine thoracic CT does not itself lead to alterations of lung attenuation and may confer less hypoinflation and atelectasis than general anesthesia.

Prevalence of lung atelectasis in sedated dogs examined with computed tomography

“…The findings show that neither atelectasis nor areas with poorly aerated lung tissue could be detected. These findings strengthens the results from a recent study done on sedated animals examined with CT [9], indicating that sedation alone is not a risk factor for lung atelectasis in healthy dogs. Also, compared to previous studies done on anesthetized animals, these results show lower frequency of alterations in lung attenuation [3,8,11,14].…”

“…These changes developed rapidly between Scan 1 and Scan 2. These findings support previous studies in which alterations in lung attenuation developed rapidly, often within 3 to 8 min after anesthesia, and then remained relatively static over time [7][8][9]. The findings indicate that it is beneficial to initiate the patient's CT scanning as soon as possible after sedation or anesthesia is induced to avoid an increased lung attenuation.…”

“…Computed tomography (CT) scanning is known as a valuable tool when examining thoracic and pulmonary disease in dogs and cats and is considered gold standard for diagnosing several conditions [1][2][3][4]. Animals undergoing CT-scans generally need to be sedated or anesthetized in order to perform the exam, but this may increase the risk of developing an increase in lung attenuation and even lung atelectasis [5][6][7][8][9]. Lung atelectasis is defined as an value between − 100 to 100 Hounsfield units (HU) while increase in lung attenuation ranges between − 500 to − 101 HU [15].…”

“…These changes tend to develop rapidly after anesthesia is induced, and that once it occurs, it might not resolve although the animal is repositioned [7]. In one recent study [9], ten dogs receiving intravenous sedation were examined with CT scanning showing no atelectatic lung changes. This study also showed that approximately 13,1% of the dogs developed hypoinflated lung parenchyma of which 2,4 ± 1,2% had a lung attenuation greater than − 250 HU.…”

Thoracic computed tomography in dogs with neoplasia

“…Furthermore, in several studies, the performances of radiography and CT in the it is advised to maintain them in sternal recumbency as lung atelectasis develops rapidly and may affect image quality (Bertolini et al, 2011). In a recent study by Hunt et al (2021), CT images obtained in dogs under sedation showed a lower percentage of poorly aerated lung than CT images obtained in anesthetized dogs; in the same study, the use of sedation protocols has been described. Nevertheless, the use of general anesthesia allows the acquisition of the images during a phase of apnea, limiting the motion artifacts related to the respiration, and therefore increasing the quality and the clinical usefulness of the CT study.…”