Pulsed Doppler determinations of cardiac output in neonates: normal standards for clinical use.

Noninvasive monitoring of cardiac output can greatly facilitate the clinical assessment and management of neonates with cardiovascular compromise. To assess normal values of cardiac output in neonates, mean blood flow velocity was measured in the ascending aorta from a suprasternal approach using a range-gated, pulsed Doppler velocity meter, and aortic root diameter was determined from an M-mode echocardiogram. These techniques were combined, and cardiac output was evaluated in 59 healthy premature and 62 term newborn infants during the first week of life. Birth weights ranged from 780 g to 4,740 g and gestational age from 27 to 42 weeks. Cardiac output values increased linearly with advancing birth weight (r = +.94, P less than 0.001) and gestational age (r = +.95, P less than .001). Mean cardiac output values (+/- SD) per kilogram of body weight were 249 +/- 34 mL/min/kg and decreased with advancing birth weight: less than 1,500 g = 265 +/- 32 mL/min/kg; 1,500 to 2,500 g = 253 +/- 34 mL/min/kg; and greater than 2,500 g = 241 +/- 33 mL/min/kg. For clinical use, 325 mL/min/kg and 200 mL/min/kg can be used as upper and lower limits of normal, respectively. Doppler cardiac output estimates compared favorably with studies using invasive techniques.

Cardiac output in newborn infants with transient myocardial dysfunction.

Decreased cardiac output is a common presumption in left ventricular myocardial dysfunction in neonates, but because of a lack of reliable noninvasive techniques, data on cardiac output are missing. We measured cardiac output by pulsed Doppler echocardiography in 22 newborn infants with left ventricular myocardial dysfunction diagnosed by M-mode echocardiography. Eleven neonates had severe perinatal asphyxia, seven had tachypnea, two hypoglycemia, and one septic shock; one had no symptoms. Right ventricular function was abnormal in 13 of the 22 infants. Hypotension was found in eight; cardiac output and stroke volume were low in 20. The abnormalities were more pronounced in infants with asphyxia. Six such infants were given dopamine (4 to 10 micrograms/kg/min). Within 1 hour, arterial blood pressure, cardiac output, stroke volume, and heart rate increased sharply, with normalization of the myocardial contractility; the other echocardiographic abnormalities normalized over 24 to 48 hours. Pulsed Doppler echocardiography is an advance in the detection and evaluation of therapy for left ventricular myocardial dysfunction in the neonate.