RESPIRATORY MECHANICS AND DIFFUSION CAPACITY IN AWAKE, ADULT LLAMAS: CLINICAL APPLICATIONS IN CRITICAL CARE MEDICINE

The purpose of this study was to establish reference values of respiratory mechanics and diffusion capacity in awake llamas for the interpretation and diagnosis of respiratory disease in critically ill camelids. The following procedures were performed in 10 healthy adult llamas (2–9 years; 100–204 kg): Respiratory Inductive Plethysmography and Pneumotachography (RIP) for the assessment of thoraco‐abdominal synchrony and airflow obstruction (Hoffman, J Appl Physiol 2001;91: 2767–75), diffusion capacity of carbon monoxide (DLCO) and functional residual capacity (FRC) via helium dilution, esophageal balloon‐pneumotachography to determine pulmonary resistance (RL) and dynamic compliance (Cdyn), as well as Monofrequency Forced Oscillatory Mechanics (FOM) (Young, J Appl Physiol 1994;76:2467–72) to establish respiratory system resistance (Rrs) and reactance (Xrs) at the oscillatory frequencies of 1,2,3,5 and 7 Hz. RIP was further performed in 3 camelid patients to determine the cause of respiratory failure. The results of conventional lung mechanics, FOM (1 Hz), DLCO and FRC in healthy llamas are listed in the table below. Rrs at 1 Hz (closest to breathing frequency) was positively correlated with RL (P=.05). The calculated mean resonant frequency was 3.37 (+/−0.68) Hz. RIP results showed a peak difference between plethysmographic flow (V'sum) and nasal flow (V'n) of 2.61 (+/−1.02) during expiration (PEsf), and 2.48 (+/−1.04) during inspiration (PIsf). The area difference between V'sum and V'n was 0.05 (+/−0.14) and 0.05 (+/−.04) during the first 25% of expiration (SFEx) and inspiration (SFIx), respectively. Noninvasive evaluation of respiratory mechanics in clinical patients was essential to establish severity, type and progression of respiratory disease, especially in camelids presenting for upper airway obstruction, pulmonary disease or thoraco‐abdominal asynchrony. TV [L] PIF [L/s] PEF [L/s] FRC/ kg [ml/kg] DLCO [ml/min/ mmHg] Cdyn [L/ cmH2O] RL [cmH2O/ L/s] Rrs(1 Hz) [cmH2O/ L/s] Xrs(1 Hz) [cmH2O/ L/s] Mean 0.98 2.13 2.00 39.18 10.70 1.44 1.48 2.40 −1.17 SD 0.28 0.61 0.75 11.45 3.37 0.75 0.57 0.93 0.46