Objective: To evaluate the effectiveness of reduction of inspired oxygen fraction (Fio2) or application of positive end-expiratory pressure (PEEP) after an alveolar recruitment maneuver (ARM) in minimizing anesthesia-induced atelectasis in dogs. Animals: 30 healthy female dogs. Procedures: During anesthesia and neuromuscular blockade, dogs were mechanically ventilated under baseline conditions (tidal volume, 12 mL/kg; inspiratory-to-expiratory ratio, 1:2; Fio2, 1; and zero end-expiratory pressure [ZEEP]). After 40 minutes, lungs were inflated (airway pressure, 40 cm H2O) for 20 seconds. Dogs were then exposed to baseline conditions (ZEEP100 group), baseline conditions with Fio2 reduced to 0.4 (ZEEP40 group), or baseline conditions with PEEP at 5 cm H2O (PEEP100 group; 10 dogs/group). For each dog, arterial blood gas variables and respiratory system mechanics were evaluated and CT scans of the thorax were obtained before and at 5 (T5) and 30 (T30) minutes after the ARM. Results: Compared with pre-ARM findings, atelectasis decreased and Pao2:Fio2 ratio increased at T5 in all groups. At T30, atelectasis and oxygenation returned to pre-ARM findings in the ZEEP100 group but remained similar to T5 findings in the other groups. At T5 and T30, lung static compliance in the PEEP100 group was higher than values in the other groups. Conclusions and Clinical Relevance: Application of airway pressure of 40 cm H2O for 20 seconds followed by Fio2 reduction to 0.4 or ventilation with PEEP (5 cm H2O) was effective in diminishing anesthesia-induced atelectasis and maintaining lung function in dogs, compared with the effects of mechanical ventilation providing an Fio2 of 1.

Objective-To qualitatively describe lung CT images obtained from sedated healthy equine neonates (≤ 14 days of age), use quantitative analysis of CT images to characterize attenuation and distribution of gas and tissue volumes within the lungs, and identify differences between lung characteristics of foals ≤ 7 days of age and foals > 7 days of age. Animals-10 Standardbred foals between 2.5 and 13 days of age. Procedures-Foals were sedated with butorphanol, midazolam, and propofol and positioned in sternal recumbency for thoracic CT. Image analysis software was used to exclude lung from nonlung structures. Lung attenuation was measured in Hounsfield units (HU) for analysis of whole lung and regional changes in attenuation and lung gas and tissue components. Degree of lung attenuation was classified as follows: hyperinflated or emphysema, −1,000 to −901 HU; well aerated, −900 to −501 HU; poorly aerated, −500 to −101 HU; and nonaerated, > −100 HU. Results-Qualitative evidence of an increase in lung attenuation and patchy alveolar patterns in the ventral lung region were more pronounced in foals ≤ 7 days of age than in older foals. Quantitative analysis revealed that mean +/- SD lung attenuation was greater in foals ≤ 7 days of age (−442 +/- 28 HU) than in foals > 7 days of age (−521 +/- 24 HU). Lung aeration and gas volumes were lower than in other regions ventrally and in the mid lung region caudal to the heart. Conclusions and Clinical Relevance-Identified radiographic patterns and changes in attenuation were most consistent with atelectasis and appeared more severe in foals ≤ 7 days of age than in older neonatal foals. Recognition of these changes may have implications for accurate CT interpretation in sedated neonatal foals with pulmonary disease.