Anaesthesia-induced atelectasis in the rat animal model (Rattus norvegicus)

Anna Piskovská^1,2*Katarzyna Kraszewska³Michal Gajewski³Miša Škorič¹Vladimír Jekl^1,2

• ¹Veterinarni univerzita Brno, Brno, Czechia
• ²Jekl and Hauptman veterinary clinic, Brno, Czechia
• ³Vetcardia Veterinary Clinic, Warsaw, Poland

Introduction Anaesthesia-induced atelectasis has been described in many animal species, developing during intravenous or inhalational anaesthesia with or without mechanical ventilation. Ultrasonography of the lungs is a rapid and non-invasive method that has been shown to be effective in detecting atelectasis. The aim of this article is to describe anaesthesia-induced atelectasis diagnosed by lung ultrasound in a rat model under isoflurane anaesthesia. Methods Twelve clinically healthy 6-month-old rats (Rattus norvegicus, Wistar rat 509.4 ± 109.6 g; mean ±SOD) were used in this study. Lung ultrasound was performed at 3 time points: (i) - 5 min before anaesthesia; (ii) during induction of anaesthesia, when the animal was already wearing the face mask – immediately after the loss of the righting reflex; and (iii) 2 min after the loss of the righting reflex; 5-second video loops were recorded at each time point. At the end of the experiment, the animals were euthanised and subjected to histopathological examination. A modified version of the Oricco´s Lung Ultrasound Score (LUSS) was adapted for use in rats. The video loops were anonymised by the operator and re-scored by two independent scorers to obtain the interobserver agreement score. Results The LUSS of all conscious animals showed no pathological changes in the lungs. The adapted LUSS proved to be easy to understand and was followed by all observers. The analysis showed moderate agreement between experts in the assessment of recordings before anaesthesia (0.40 < Kendall's tau < 0.59) and very high agreement in the assessment of recordings during induction of anaesthesia and 2 minutes after the onset of anaesthesia, as well as in the overall assessment of recordings before, during and after anaesthesia (0.80 < Kendall's tau < 1.00). Histopathological examination revealed no abnormal findings in any of the animals. Conclusion In conclusion, anaesthesia-induced atelectasis can lead to severe ultrasonographic changes in gravity-dependent areas in a rat model anaesthetised with isoflurane. The modified Oricco´s LUSS showed significant interobserver agreement, indicating its potential reliability for thoracic ultrasound examinations in laboratory and pet rats.