Inhalant Anesthesia Essay

Inhalant anaesthesia in dorsal recumbency can result in hypoventilation and in the development of intrapulmonary shunts (Oura et al. 2012). The respiratory dysfunction is associated with formation of atelectasis in dependent lung areas, which can impair pulmonary compliance, gas exchange and oxygenation (Staffieri et al. 2007; De Monte et al. 2013). Such alterations may be prevented by using mechanical ventilation, which can be adjusted in terms of fraction of inspired oxygen (FiO2), positive end-expiratory pressure (PEEP), mode of ventilation and tidal volume (VT) aiming to prevent further respiratory impairments and cardiovascular adverse effects (Guldner et al. 2015).
In protective mechanical ventilation strategies, a high FiO2 of near 100%
2012). Despite the use of a high VT during anesthesia may be associated with alveolar hyperdistension or rupture (Guldner et al. 2015), an exact threshold value has not been established in healthy dogs. The use of VT of 12-15 mL kg-1 in healthy dogs have been described with no association with respiratory clinical adverse effects (Staffieri et al. 2007; De Monte et al. 2013). The VT plays a role in the development of intrapulmonary shunts (Oura et al. 2012) but the mechanisms are unclear. This lack of information has been inevitable since techniques, such as electrical impedance tomography (EIT), capable of imaging lung aeration has not long been introduced to veterinary practices. Other imaging techniques, such as the computed tomography (CT), have shown that lung atelectasis during anesthesia are formed within dependent lung regions, and that the efficacy of alveolar recruitment maneuvers (ARM) is associated with the ability to open closed alveoli into these areas (Staffieri et al. 2007; De Monte et al. 2013). As high peak inspiratory pressures (PIP) from ARM, and high VT from mechanical ventilation are effective to improve lung compliance and shunting (Canfran et al. 2012; Oura et al. 2012; De Monte et al. 2013), we suspect that different VT during mechanical ventilation may have different impact over ventilation distribution within the lungs. Since volume distribution to dependent lung areas has a great impact over the pulmonary mechanics and function, the aim of this study was to monitor the ventilation distribution to dependent and non-dependent lung areas when using low and high VT. Additionally, we aimed to assess whether an ARM and 5 cmH2O PEEP can improve ventilation in dependent lung areas. The hypothesis is that the differences in respiratory mechanics, gas exchange and oxygenation resulting