Effect of body position and time on quantitative computed tomographic measurements of lung volume and attenuation in healthy anesthetized cats

Abstract

OBJECTIVE To quantify the effect of time and recumbency on CT measurements of lung volume and attenuation in healthy cats under general anesthesia. ANIMALS 8 healthy research cats. PROCEDURES Anesthetized cats were positioned in sternal recumbency for 20 minutes and then in left, right, and left lateral recumbency (40 minutes/position). Expiratory helical CT scan of the thorax was performed at 0 and 20 minutes in sternal recumbency and at 0, 5, 10, 20, 30, and 40 minutes in each lateral recumbent position. For each lung, CT measurements of lung volume and attenuation and the extent of lung areas that were hyperaerated (-1,000 to -901 Hounsfield units [HU]), normoaerated (-900 to -501 HU), poorly aerated (-500 to -101 HU), or nonaerated (-100 to +100 HU [indicative of atelectasis]) were determined with a semiautomatic threshold-based technique. A restricted maximum likelihood analysis was performed. RESULTS In lateral recumbency, the dependent lung had significantly greater attenuation and a lower volume than the nondependent lung. Within the dependent lung, there was a significantly higher percentage of poorly aerated lung tissue, compared with that in the nondependent lung. These changes were detected immediately after positioning the cats in lateral recumbency and remained static with no further significant time-related change. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that once anesthetized healthy cats were positioned in lateral recumbency, the dependent lung lobes underwent a rapid reduction in lung volume and increase in lung attenuation that did not progress over time, predominantly attributable to an increase in poorly aerated lung tissue.

Prevalence of lung atelectasis in sedated dogs examined with computed tomography

“…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].…”

“…Although successful CT studies of awake animals have been done using positioning devices in cats where little or no development of lung atelectasis was seen, [3,10], this is not applicable in every day practice, especially not in dogs with high stress levels. Previous CT´studies have evaluated how lung attenuation alters with different anesthesia protocols and recumbencies [6][7][8][11][12][13]. Results point towards the fact that animals positioned in a lateral recumbency tend to be at a higher risk of developing atelectasis or increase in lung attenuation than animals positioned in a sternal recumbency [7,13,14].…”

“…Previous CT´studies have evaluated how lung attenuation alters with different anesthesia protocols and recumbencies [6][7][8][11][12][13]. Results point towards the fact that animals positioned in a lateral recumbency tend to be at a higher risk of developing atelectasis or increase in lung attenuation than animals positioned in a sternal recumbency [7,13,14]. 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].…”

>b<Avaliação da manobra de recrutamento alveolar por escalonamento da PEEP por meio da técnica de tomografia computadorizada em cães submetidos a anestesia intravenosa total>/b<

“…A tomografia computadorizada é considerada a melhor ferramenta para mensurar o recrutamento alveolar, pois permite quantificar exatamente o tecido recrutado após a insuflação do parênquima (Gattinoni et al, 2017). Baseado nas diferenças de atenuação expressas em unidades Housnfield (HU) é possível distinguir áreas pulmonares que possam estar hiperaeradas (-1000 a -901), normoaeradas (-900 a -501), pouco aeradas (-500 a -101) e não aeradas (-100 a + 100indicativo de atelectasia) (Gattinoni et al, (1995); FOO et al, (2018)).…”

“…A TC fornece imagens em tempo real do desempenho dinâmico do pulmão no fim da inspiração e expiração, a fim de quantificar as alterações de atenuação e volume pulmonar durante a MRA. A diminuição do volume e aumento da atenuação estão relacionados a atelectasia (anestesia e decúbito), sendo definida em imagens de TC como HU entre -100 a +100 (FOO et al, 2018). O recrutamento alveolar por meio da TC é descrito como um aumento na aeração do tecido pulmonar antes não aerado, podendo facilmente detectar e mensurar a recrutabilidade do pulmão, mas na prática diária é raramente empregada para quantificar o recrutamento (GATTINONI et al, 2010).…”