Cardiopulmonary effects of a new inspiratory impedance threshold device in acute hemorrhagic shock in dogs

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To compare cardiovascular and respiratory effects of an inspiratory impedance threshold device (ITD) in dogs before and after induction of acute hemorrhagic shock.

Study Design

Prospective experimental randomized study.


Eight healthy adult dogs.


Dogs were anesthetized and maintained on spontaneous ventilation. Tidal volume (VT), systolic, mean and diastolic arterial blood pressure (SAP, MAP, DAP), central venous pressure (CVP), gastric PCO2 (GBF) as an indicator of gastric perfusion, cardiac index (CI), systemic vascular resistance (SVR), oxygen delivery (DO2), and plasma lactate were monitored. To monitor respiratory compliance (RC) and respiratory resistance (ResR), animals were briefly placed on mechanical ventilation. Dogs were studied under 4 different conditions: (1) baseline (euvolemic state) (MAP > 60 mm Hg) with and without the ITD and (2) acute hemorrhagic shock (hypovolemic state) (target MAP of 40 mm Hg) with and without ITD. These 4 conditions were performed during one anesthetic period, allowing time for stabilization of parameters for each condition. Data were analyzed by ANOVA for repeated measure mixed models.


No cardiovascular changes were detected between groups with and without use of ITD during euvolemic states. During acute hemorrhagic hypovolemic state, CI and DO2 were higher with the ITD (2.9 ± 0.6 L/min/m2) and (326.5 ± 86.8 mL/min) compared with no ITD (1.8 ± 0.6 L/min/m2) and (191.3 ± 58.1 mL/min), respectively. The use of ITD during hypovolemia also increased SAP and MAP. There was an increase in ResR and decreased RC with the ITD in both euvolemic and hypovolemic states.

Conclusion and clinical relevance

The use of an ITD in dogs during acute hemorrhagic hypovolemic shock improved cardiovascular parameters but had negative effects on RC and ResR.

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