10-12 mm Hg is what you want during breath hold CT....

Which Airway Pressure Should Be Applied During Breath-Hold in Dogs Undergoing Thoracic Computed Tomography?

Alessandro Guarracino, Luca Lacitignola, Edoardo Auriemma, Valentina De Monte, Salvatore Grasso, Antonio Crovace, Francesco Staffieri

Background
Computed tomography (CT) is widely used for thoracic imaging in dogs, but general anesthesia, necessary for image acquisition, can cause pulmonary atelectasis, leading to reduced image quality. The application of positive pressure (PP) during breath-hold may reduce atelectasis, but the optimal PP level remains unclear. This study aimed to determine the optimal PP that minimizes atelectasis while avoiding pulmonary hyperinflation in dogs undergoing thoracic CT.

Methods
This randomized controlled trial included 60 dogs undergoing thoracic CT for pulmonary metastasis screening. Dogs were assigned to six groups with different PP levels during breath-hold: 0 (control), 5, 8, 10, 12, and 15 cmH₂O. Lung aeration was assessed by analyzing CT images, classifying lung regions as atelectatic, poorly aerated, normally aerated, or hyperinflated. Statistical analyses were performed to compare lung aeration across groups and determine the optimal PP level.

Results
PP levels of 10 and 12 cmH₂O significantly reduced atelectatic and poorly aerated lung regions compared to the control group while increasing normally aerated lung regions. A PP of 15 cmH₂O resulted in mild hyperinflation. No significant differences in heart rate, oxygen saturation, or mean arterial pressure were observed across groups, suggesting that PP levels up to 12 cmH₂O did not cause adverse hemodynamic effects.

Limitations
The study was limited to healthy dogs without pre-existing lung disease, and results may not apply to patients with compromised pulmonary function. Hemodynamic effects were not comprehensively assessed beyond heart rate and blood pressure. Additionally, the CPAP ventilation mode used in this study may not be available in all veterinary settings.

Conclusions
A PP of 10–12 cmH₂O during breath-hold was optimal for improving lung aeration and minimizing atelectasis in anesthetized dogs undergoing thoracic CT. PP levels above 12 cmH₂O may lead to hyperinflation and should be used cautiously. This study provides guidance for optimizing CT image quality while minimizing anesthesia-related pulmonary changes.

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