Objective: To report the range of normal values for impedance-derived cardiac output, stroke volume, and the baseline transthoracic impedance in the healthy preterm and term neonate over the weight range generally found in the intensive care nursery.
Design: Prospective, case-referent study.
Setting: University medical center special care and term nurseries.
Patients: Twenty-seven preterm and 25 term newborns with no evidence of cardiovascular problems.
Interventions: We determined the values for impedance cardiac output and stroke volume to be used as reference values. Also measured was the baseline transthoracic impedance, a number that reflects the air/fluid ratio of the thorax.
Measurements and main results: Stroke volume and stroke volume index were, respectively, 2.0 +/- 0.8 (SD) mL and 1.4 +/- 0.5 mL/kg for preterm infants, and 5.0 +/- 2.0 mL and 1.6 +/- 0.7 mL/kg for term neonates. Cardiac output and cardiac index were, respectively, 304 +/- 114 mL/min and 214 +/- 68 mL/min.kg for preterm newborns, and 648 +/- 244 mL/min and 205 +/- 78 mL/min.kg in term newborns. These values compared favorably with published values utilizing other techniques for these populations. Both cardiac output and stroke volume were linearly correlated to body weight, being largest in the heavier neonates. Transthoracic impedance values were 42.7 +/- 9.0 ohms and 6.7 +/- 1.7 ohms/cm for preterm infants and 32.3 +/- 4.3 ohms and 3.9 +/- 0.6 ohms/cm for term infants. Transthoracic impedance and transthoracic impedance/cm values were correlated negatively to body weight and were curvilinearly related to body weight.
Conclusions: These values for transthoracic impedance and transthoracic impedance/cm are the first reported using the standard electrode lead configuration in neonates.