CHANGES IN LEFT-VENTRICULAR FUNCTION IN SHOCKED NEWBORNS

Objective: To assess whether the change in cardiac output after volume replacement is due to elevation of stroke volume or heart rate and to determine the effect of mechanical ventilation on the hemodynamic sit uation. Design: Prospective study. Setting: A ten-bed neonatal intensi ve care unit (level III) at a university hospital. Patients: 15 consec utive newborns with blood pressure below the 10(th) percentile related to age and weight. Interventions: Volume replacement with Ringer's la ctate 20 ml/kg body weight. Measurements and results. Before and after volume replacement, arterial pressure recordings, blood gas analysis, and an echocardiographic study were carried out. Left ventricular and aortic diameters were measured by the two-dimensional M-mode techniqu e and velocity time integral of aortic now by the pulsed color Doppler technique. From these data, stroke volume and cardiac output were cal culated. Cardiac output (703 +/- 204 vs 826 +/- 166 ml/min, p < 0.005) and cardiac index (267 +/- 69 vs 302 +/- 55 ml/min per kg body weight , p < 0.01) changed significantly due to an appreciable elevation in s troke volume (5.2 +/- 1.7 vs 5.8 +/- 1.7 ml, p < 0.05), whereas heart rate was unaltered (140 +/- 12 vs 142 +/- 20 beats/min; NS). The chang e in blood pressure (32 +/- 5 vs 38 +/- 8 mm Hg, p < 0.01) was also si gnificant. Cardiac index before and after volume replacement showed a significant inverse correlation with the severity of respiratory disea se expressed as alveolar-arterial oxygen difference (A-aDO(2)) (A-aDO( 2) vs cardiac index before volume replacement: r = -0.77, p < 0.001; a fter volume replacement: r = -0.73, p < 0.005) or oxygenation index (o xygenation index vs cardiac index before volume replacement: r = -0.73 , p < 0.005: after volume replacement: r = -0.73, p < 0.005). Changes in left ventricular diastolic diameter, left ventricular systolic diam eter, and fractional shortening were not significant. Conclusions: The se results indicate that the major regulator of left ventricular outpu t in newborns with hypovolemic or cardiogenic shock is stroke volume a nd not heart rate and that cardiac output depends on the severity of t he respiratory disease.