The objective was to assess the contribution of left ventricular output (LVO) in determining low mean arterial blood pressure (MABP) in preterm infants admitted to the neonatal intensive care unit. Doppler echocardiography was prospectively performed on a cohort of 17 consecutive infants with low MABP (<30 mmHg) and on 17 consecutive control subjects (range: 600-1520 g; 27-30.7 weeks gestation). The median haematocrit was 42.5% in the low MABP group versus 49.4% in the control group (P < 0.01). The index of resistance to the LVO (RILV = MABP:LVO ratio) was lower in the low MABP group (98 vs 156 mmHg x l(-1) x kg(-1) x min(-1); P < 0.05). An analysis of the low MABP group regarding LVO revealed that a subgroup of four infants had LVO <10th percentile (185 ml x kg(-1) x min(-1)) with a high RILV (>90th percentile: 226 mmHg x l(-1) x kg(-1) x min(-1)) for three of the infants. The remaining 13 infants had LVO >10th percentile and a shortening fraction >25th percentile. In this subgroup, a high proportion of infants (9/13 vs 2/17, P < 0.01) had low RILV (<10th percentile: 96 mmHg x l(-1) x kg(-1) x min(-1) and the incidence of haemodynamically significant patent ductus arteriosus was higher than in the control group (10/13 vs 4/17, P < 0.01).
Conclusion: Left ventricular output, index of resistance to left ventricular output and patent ductus arteriosus status are important to consider in evaluating mean arterial blood pressure during early postnatal life in preterm infants. Low mean arterial blood pressure is frequently associated with normal or high left ventricular output, low index of resistance to left ventricular output and significant patent ductus arteriosus.