Fergus M. B. Moylan

Percutaneous catheterization of the radial artery in the critically ill neonate.

Percutaneous catheterization of the radial artery appears to be a simple and safe alternative to catheterization of the umbilical artery for monitoring critically ill neonates. This avoids the serious and potentially fatal complications associated with use of the umbilical arterial catheter, and it is also applicable to monitoring of neonates in whom the umbilical artery is no longer patent. We observed no serious sequelae in cannulation of the radial artery and think that the technique should be used more widely.

The relationship of bronchopulmonary dysplasia to the occurrence of alveolar rupture during positive pressure ventilation.

The effect of altered mechanical ventilation on the incidence of alveolar rupture and bronchopulmonary dysplasia (BPD) was reviewed in infants who had neonatal respiratory distress syndrome (RDS) (N = 99). From 1971 to 1974 we attempted to minimize pulmonary oxygen exposure. Accordingly, during the resolution of respiratory distress syndrome, the ventilator pressures were not reduced until the FIO2 had been lowered to 0.4 (N = 61). In 1974 to 1975 earlier reduction of pressures was instituted as the FIO2 was lowered to 0.6 or less (N = 38). Birth weight and gestational age were comparable in the two groups. With earlier reduction of ventilator pressures, there was a significant decrease in the duration of exposure to peak inspiratory pressures ≥40 cm H2O (p < 0.004) and ≥50 cm H2O (p < 0.02). The incidence of alveolar rupture during positive pressure ventilation fell from 51 to 24% (p < 0.015) and bronchopulmonary dysplasia from 41 to 13% (p < 0.003). In addition, there was a decrease in the duration of mechanical ventilation (p < 0.02) and exposure to an FIO2 ≥ 0.6 (p = 0.07). The results confirm the intimate relationship of pulmonary barotrauma, as reflected by the occurrence of alveolar rupture during positive pressure inflation of the lungs, to the subsequent development of bronchopulmonary dysplasia and that prevention of the former is associated with a concomitant fall in the incidence of the latter.

Alveolar rupture as an independent predictor of bronchopulmonary dysplasia.

The chest radiographs and charts of 99 surviving neonates treated with positive pressure ventilation for respiratory distress syndrome were reviewed. Forty infants developed alveolar rupture during mechanical ventilation. Of these, 27 (67.5%) developed bronchopulmonary dysplasia (BPD). Only 3 (5.4%) of the remaining 59 infants developed BPD. The relative odds of developing BPD if alveolar rupture occurred increased by a factor of 39 (p < 0.001). Significant associations between BPD and the duration of ventilation with high peak inspiratory pressures (IP) ≥ 40 cm H2O, low peak IP ≤ 39 cm H2O, continuous distending pressure ≥ 5 cm H2O and fractional inspired oxygen concentration (Fio2) ≥ 0.6 were examined. Since these ventilatory parameters had a significant association (p ≤ 0.02) with both BPD and alveolar rupture, an attempt was made to identify the independent contributions of these factors to the development of BPD by a stepwise discriminant analysis. Controlling for the most significant associations, FIO2 ≥ 0.6 and peak IP ≤ 39 cm H2O, subsequent analysis showed no added discriminant power of predicting BPD in the duration of exposure to high peak IP ≥ 40 cm H2O and continuous distending pressure ≥ 5 cm H2O. Alveolar rupture remained overwhelmingly significant (p < 0.001), but it did not account entirely for the development of BPD. Duration of exposure to peak IP ≤ 39 cm H2O and FIO2 ≥ 0.6 remained significant. These results suggest that pulmonary barotrauma as reflected by the occurrence of alveolar rupture during positive pressure ventilation is intimately related with the subsequent development of BPD.

PERCUTANEOUS CATHETERIZATION OF THE RADIAL ARTERY IN THE CRITICALLY ILL NEONATE

Percutaneous catheterization of the radial artery appears to be a simple and safe alternative to catheterization of the umbilical artery for monitoring critically ill neonates. This avoids the serious and potentially fatal complications associated with use of the umbilical arterial catheter, and it is also applicable to monitoring of neonates in whom the umbilical artery is no longer patent. We observed no serious sequelae in cannulation of the radial artery and think that the technique should be used more widely.

Regional lung function in infants.

Measurement of regional ventilation and blood flow in infants with the use of an intravenous bolus of 133Xenon reliably estimates the ventilation-perfusion abnormalities responsible for hypoxemia and eventually hypercapnea.A composite ventilation-perfusion index (&OV0312;ci/&OV0422;) of >0.85 was found in well infants with Pao2 >90 torr, and < 0.55 in sick infants with Pao2 < 50 torr. Indices of < 0.6 were associated with CO2 retention; indices of < 0.55 were found in patients requiring mechanical ventilation.Redistribution of blood flow away from a poorly ventilated region during air breathing but not during oxygen breathing suggests that alveolar hypoxia is an effective stimulus to increase regional vascular resistance. It is predictable that the lack of redistribution during oxygen breathing contributes to CO2 retention.The findings of this study substantiate the use of 133Xenon bolus technique for a better understanding of the regional contribution to the pathophysiology in the infants lung.