Spontaneous breathing through an inspiratory impedance threshold device augments cardiac index and stroke volume index in a pediatric porcine model of hemorrhagic hypovolemia.

BACKGROUND: Hemorrhagic shock secondary to trauma is associated with poor survival. The impedance threshold device (ITD) has been shown to improve blood pressure and survival rates in an adult porcine model of hemorrhagic hypovolemia. Pediatric hemodynamics, anatomy, and physiology differ from adults. Evaluation of the ITD has not been previously assessed in a pediatric porcine model of hypovolemia induced by hemorrhage.
OBJECTIVE: To determine whether ITD-assisted breathing, with and without positive end-expiratory pressure, will improve key hemodynamic parameters following hypovolemia induced by hemorrhage in a pediatric porcine model.
METHODS: Intubated, anesthetized, hemodynamically stable, spontaneously breathing piglets were rapidly bled 40% of their calculated blood volume. Piglets' hemodynamic and intrathoracic pressures were continuously monitored during 10-min normovolemic baseline, bleed to hypotensive baseline, 10-min ITD-assisted breathing, 10 mins without ITD, 10-min ITD-assisted breathing randomized with or without positive end-expiratory pressure (3 cm H2O), 10 mins without ITD, reinfusion of shed blood, 10-min baseline following return to normovolemia. The ITD had an inspiratory cracking pressure of -7 cm H2O. Transthoracic echocardiographic parameters were measured at the end of each 10-min period.
RESULTS: There was no significant difference in baseline assessments between groups. Systolic blood pressure, cardiac index, and stroke volume index were significantly greater during ITD-assisted breathing. There was a trend toward increased left ventricular end-diastolic dimension during ITD use. Heart rate, systemic vascular resistance index, left ventricular end-systolic dimension, and shortening fraction did not change significantly during ITD-assisted breathing. There was equivalent improvement in systolic blood pressure, cardiac index, and stroke volume index, when the ITD alone and ITD plus positive end-expiratory pressure were used.
CONCLUSIONS: ITD-assisted breathing significantly augmented systolic blood pressure, cardiac index, and stroke volume index in this pediatric porcine model of hemorrhagic hypovolemia. These effects appear related to increased left ventricular preload and not by increased systemic vascular resistance or heart rate. These beneficial effects of ITD-assisted breathing are not changed by the addition of positive end-expiratory pressures of 3 cm H2O.