Study design: Randomized prospective experimental trial. Sixteen young, healthy, specific pathogen-free Giant Flemish cross Chinchilla rabbits (10 females and 6 males) weighing 4.1 ± 0.8 kg were included.
Rabbits were assigned randomly to one of three treatment groups: facemask with spontaneous ventilation (FM-SV; n = 5), LMA with spontaneous ventilation (LMA-SV; n = 5), and LMA with controlled ventilation (LMA-CV; n = 6). In dorsal recumbency, and at 2.3% end-tidal isoflurane concentration, Fé isoflurane, Fi isoflurane, partial pressure of expired isoflurane (PéCO2), partial pressure of inspired carbon dioxide (PiCO2), heart rate, respiratory rate, minute volume, arterial oxygen tensions (PaO2), arterial carbon dioxide tensions (PaCO2), arterial pH (pHa), arterial standard base excess (SBEa) values were measured for 120 minutes.
Results: Two individuals in the FM-SV group had PaCO2 > 100 mm Hg. One rabbit in the FM-SV had PaO2 < 80 mm Hg. All FM-SV rabbits showed signs of airway obstruction, and two were withdrawn from the study at 45 and 90 minutes, respectively, because cyanosis was observed.
No signs of airway obstruction were observed in either LMA group. Four rabbits in the LMA-CV group developed gastric tympanism, one of which refluxed gastric contents after 110 minutes. There were no differences between FM-SV and LMA-SV in any variable tested. PaCO2 and PéCO2 were decreased, while PaO2 and minute volume were increased in the LMA-CV group compared to the LMA-SV group.
Conclusions: An LMA provided a better airway than a facemask during spontaneous breathing in rabbits, as the use of a facemask was associated with hypercapnia and low partial pressures of oxygen. Although an LMA can be used for intermittent positive pressure ventilation (IPPV), gastric tympanism may develop, especially at a peak inspiratory pressure of 14 cm H2O.
Thus, the LMA can be used in rabbits but further work is needed before it is applied routinely.
Source: Bateman, Leigh, Ludders, John W, Gleed, Robin D & Erb, Hollis N (2005): Comparison between facemask and laryngeal mask airway in rabbits during isoflurane anesthesia. In: Veterinary Anaesthesia and Analgesia 32 (5), 280-288.
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