Objective: To compare the hemodynamic and respiratory effects of an inspiratory impedance threshold device (ITD) in anesthetized normotensive and hypotensive dogs.
Study design: Prospective randomized study.
Animals: Ten adult dogs.
Methods: Dogs were anesthetized with propofol followed by isoflurane. During spontaneous ventilation, tidal volume (.VT), systolic (SAP), mean (MAP) and diastolic arterial blood pressure, central venous pressure, gastric PCO(2) as an indicator of gastric perfusion, subcutaneous oxygen tension, subcutaneous blood flow, cardiac index (CI), systemic vascular resistance and blood lactate were monitored. To monitor respiratory compliance (RC) and resistance (ResR), animals were briefly placed on mechanical ventilation. Dogs were studied under four different conditions: 1) normotension (MAP > 60 mmHg) with and without the ITD and 2) hypotension (target MAP = 40 mmHg) with and without ITD. These four conditions were performed during one anesthetic period, allowing for stabilization of parameters for each condition. Data were analyzed by anova repeated measure mixed models.
Results: No cardiovascular changes were detected between no ITD and ITD in the normotensive state. During hypotension, CI was higher with the ITD (5 +/- 1.0 L minute(-1) m(-2)) compared with no ITD (4 +/- 1.3 L minute(-1) m(-2)). During hypotension, SAP was increased with ITD (80 +/- 14 mmHg) versus without ITD (67 +/- 13 mmHg). There was an increase in ResR and decreased RC with the ITD in both normotensive and hypotensive state.
Conclusion and clinical relevance: Impedance threshold device in dogs during isoflurane-induced hypotension improved CI and SAP but had negative effects on RC and ResR.