Effects of body positions and anaesthesia on the distribution of ventilation in alpacas (Vicugna pacos).

This study monitored and detected changes in the distribution of ventilation and other electrical impedance tomography (EIT) related ventilation variables across different body positions throughout all peri- and intra-anaesthetic stages in alpacas, while also evaluating intra-individual differences between two anaesthetic procedures. Six healthy adult male alpacas underwent two anaesthetic sessions to assess ventilation using EIT across various body positions, including awake standing (Stand_pre), sternal sedated (sternal_sed), during controlled mechanical ventilation in sternal with different head positions (Sternal_CMVhigh, Sternal_CMVlow), sternal spontaneously breathing with tube (Sternal_spontETT), sternal without tube (Sternal_spont), and post-anaesthesia standing (Stand_post). Sedation and anaesthesia were performed with ketamine, xylazine, and butorphanol, and maintained with isoflurane. EIT data were collected over 2 to 5 min, and six to ten consecutive artefact-free breaths per phase were analysed for EIT-related ventilation variables. Statistical analysis was performed using linear mixed-effects models (significance at p < 0.05). The centre of ventilation along the right-left axis did not differ across phases [F _{(6, 66.08)} = 1.33, p = 0.257], whereas ventral-dorsal values varied significantly [F _{(6, 67.19)} = 3.92, p = 0.002]. Regional ventilation remained stable throughout all phases [F _{(6, 66.06)} = 1.30, p = 0.269]. Tidal rate showed a significant overall effect of phase [F _{(6, 72.00)} = 20.43, p < 0.001], with the highest tidal rate observed during Stand_pre compared with other phases. Tidal impedance variation showed a significant overall difference [F _{(6, 67.08)} = 3.21, p = 0.007], despite no significant post-hoc comparisons. Minute impedance variation (MIV) differed across phases [F _{(6, 67.05)} = 23.58, p < 0.001], and inspiratory time had a significant overall impact on the phases [F _{(6, 67.30)} = 11.37, p < 0.001]. End-expiratory lung impedance remained stable over all phases [F _{(6, 67.05)} = 1.89, p = 0.094]. Alpacas appeared to maintain a relatively stable ventilation distribution with small changes across body positions and anaesthetic phases. This may reflect the influence of their distinctive lung, diaphragm, and gastrointestinal anatomy. Changes from standing to sternal positions minimally affect ventilation parameters, and sedation with xylazine, ketamine, and butorphanol modify some of these variables without compromising overall respiratory performance.