Functional residual capacity in beagle dogs with and without acute respiratory distress syndrome

Tidal volume in mechanically ventilated dogs: can human strategies be extrapolated to veterinary patients?

This paper compares and describes the tidal volume (Vt) used in mechanically ventilated dogs under a range of clinical conditions. Twenty-eight dogs requiring mechanical ventilation (MV) were classified into 3 groups: healthy dogs mechanically ventilated during surgery (group I, n = 10), dogs requiring MV due to extra-pulmonary reasons (group II, n = 7), and dogs that required MV due to pulmonary pathologies (group III, n = 11). The median Vt used in each group was 16 mL/kg (interquartile range [IQR], 15.14-21) for group I, 12.59 mL/kg (IQR, 9-14.25) for group II, and 12.59 mL/kg (IQR, 10.15-14.96) for group III. The Vt used was significantly lower in group III than in group I (p = 0.016). The thoraco-pulmonary compliance was significantly higher in group I than in groups II and III (p = 0.011 and p = 0.006, respectively). The median driving pressure was similar among the groups with a median of 9, 11, and 10 cmH₂O in groups I, II, and III, respectively (p = 0.260). Critically-ill dogs requiring MV due to the primary pulmonary pathology received a significantly lower Vt than healthy dogs but with a range of values that were markedly higher than those recommended by human guidelines.

Sizing the lung in dogs: the inspiratory capacity defines the tidal volume

Objective

To evaluate a novel physiological approach for setting the tidal volume in mechanical ventilation according to inspiratory capacity, and to determine if it results in an appropriate mechanical and gas exchange measurements in healthy and critically ill dogs.

Methods

Twenty healthy animals were included in the study to assess the tidal volume expressed as a percentage of inspiratory capacity. For inspiratory capacity measurement, the mechanical ventilator was set as follows: pressure control mode with 35cmH₂O of inspired pressure and zero end-expiratory pressure for 5 seconds. Subsequently, the animals were randomized into four groups and ventilated with a tidal volume corresponding to the different percentages of inspiratory capacity. Subsequently, ten critically ill dogs were studied.

Results

Healthy dogs ventilated with a tidal volume of 17% of the inspiratory capacity showed normal respiratory mechanics and presented expected PaCO₂ values more frequently than the other groups. The respiratory system and transpulmonary driving pressure were significantly higher among the critically ill dogs but below 15 cmH₂O in all cases.

Conclusions

The tidal volume based on the inspiratory capacity of each animal has proven to be a useful and simple tool when setting ventilator parameters. A similar approach should also be evaluated in other species, including human beings, if we consider the potential limitations of tidal volume titration based on the calculated ideal body weight.