[Assessment of pulmonary function of preterm newborn infants with respiratory distress syndrome at different positive end expiratory pressure levels].

OBJECTIVE

To verify the alterations of pulmonary function in preterm newborn infants with respiratory distress syndrome (RDS). The parameters analyzed were Dynamic Compliance (Cdyn), Inspiratory Tidal Volume (TVinsp), partial arterial pressure of carbon dioxide (PaCO2).

METHODS

Eleven preterm newborn infants, with gestational age <35 weeks, and birth weight <2,500 g, were include in a control case study. All infants presented RDS and were treated with 120 mg/Kg of porcine surfactant. The initial positive end expiratory pressure (PEEP) was 3 cm H2O. A pneumotachograph with a graphical monitor was used to assess the pulmonary function. After each increase in the PEEP (4 and 6 cm H2O), there was an interval of 20 minutes before measuring the arterial data of pulmonary function and arterial gases.

RESULTS

There were three males and eight females (1:2.7) among the infants with RDS. The mean gestational age was 30.78. +/- 2.05 weeks, ranging from 26 to 34 weeks. The increase in the PEEP from 3 to 6 cm H2O caused significant decrease in the TVinsp (6.46 +/- 3.43 to 4.20 +/- 2.35, P=0.0262). With the increase in the PEEP from 4 to 6 cm H2O, there was also a decrease in the TVinsp (5.98 +/- 3.33 to 4.20 +/- 2.35), (P=0.0044). Regarding the Cdyn, when there was an increase in the PEEP from 3 to 6 cm H2O, the reduction was statistically significant (0.58 +/- 0.27 to 0.46 +/- 0.25, P=0.0408) and from 4 to 6 cm H2O, the reduction in the Cdyn was also important (0.77 +/- 0.27 to 0.46 +/- 0.25), (P=0.0164). Increases in the PEEP from 4 to 6 cm H2O caused increases in the PaCO2 (52.81 +/- 15.49 to 64.90 +/- 12.69), (P= 0.0141). A more significant increase was observed when the PEEP was elevated from 3 to 6 cm H2O (41.45 +/- 7.87 to 64.90 +/- 12.69, P=0.0033).

CONCLUSIONS

The study showed that the PEEP from 3 to 4 cm H2O produces better results in terms of Cdyn and less collateral effects regarding respiratory acidosis and pulmonary hyperventilation with impairment of the alveolar ventilation, evidenced by the increase in the PaCO2 and the decrease in the TVinsp.