Evaluation of impedance cardiography in the canine pup

This study evaluated the use of the noninvasive technique of impedance cardiography to assess central hemodynamics in an animal model similar in size to the neonate. Seven canine pups 5-6 wk of age, with an average weight of 2.2 kg, were studied. To alter cardiac output (Q), the pups were given 12 and 8% O2 to breathe, which produced an arterial PO2 of 30 and 21 Torr, respectively. Q was obtained simultaneously by impedance and thermal dilution under both normoxic and hypoxic conditions. The average Q measured by impedance and thermal dilution were within 10% agreement and moderately correlated (r = 0.76). Impedance Q and stroke volume (SV) averaged 201 ml X min-1 X kg-1 and 2.8 ml, respectively. Thermal dilution Q and SV averaged 212 ml X min-1 X kg-1 and 2.9 ml, respectively. Individual responses to the hyoxemia were variable, but the impedance technique appeared to measure these individual responses as well as the thermal-dilution technique. These findings demonstrate that impedance cardiography may be suitable to assess either the absolute or relative changes in central hemodynamics. The use of this technique in critical care neonatal and pediatric medicine seems justified.