Physiologic Effects of Assisted Ventilation with Preserved Spontaneous Breathing Versus Controlled Ventilation in Anesthetized Dogs

Pressure support ventilation (PSV) is an assisted ventilation mode that supports spontaneous inspiratory efforts, whereas pressure-controlled ventilation (PCV) delivers mechanically controlled breaths. This randomized crossover study compared the cardiopulmonary effects of PSV and PCV in five clinically healthy adult Beagle dogs undergoing general anesthesia. Each dog underwent two anesthetic sessions separated by a minimum 2-week washout period. Hemodynamic variables, respiratory mechanics, and gas exchange were assessed during ventilation, and thoracic computed tomography was performed before and after each intervention to quantify lung aeration. PSV was associated with higher tidal volumes overall compared with PCV, while mean airway pressure was significantly lower at two time points. Peak inspiratory pressure did not differ significantly between ventilation modes. No statistically significant differences between ventilation modes were detected in hemodynamic variables, gas exchange, relative lung volume, or the proportions of hypoinflated and collapsed lung regions. Although differences in tidal volume and mean airway pressure were observed between ventilation modes, their physiological and clinical significance remains uncertain. Given the small sample size, these findings should be interpreted cautiously, and further studies are needed to establish their clinical significance.