Mechanisms of hypoxemia episodes in spontaneously breathing preterm infants after mechanical ventilation.

BACKGROUND

Preterm infants often present with recurrent episodes of hypoxemia after mechanical ventilation.

OBJECTIVE

To evaluate the role of abdominal muscle activity and central apnea on the frequency and severity of hypoxemia episodes (HEs) in preterm infants with a history of mechanical ventilation.

METHODS

Continuous recordings of arterial oxygen saturation (SpO(2)), gastric pressure, respiratory inductance plethysmography and abdominal surface electromyography were obtained during 4 h from spontaneously breathing preterm infants who had recently been extubated and presented with frequent HEs.

RESULTS

Ten infants (gestational age 26.4 +/- 1.1 weeks, body weight 816 +/- 128 g, age 44 +/- 21 days, FiO2 0.31 +/- 0.09, mechanically ventilated for 33 +/- 37 days) were studied 12 +/- 7 (mean +/- SD) days after extubation. These infants presented with 10.2 +/- 9.3 HEs/h (SpO2 <88%, > or =10 s). Of these, 8.2 +/- 6.2 HEs/h were associated with abdominal muscle contraction while only 2.0 +/- 4.5 HEs/h were associated with > or =10 s apnea (p < 0.05). Of the more severe HEs (SpO(2) <75%, > or =10 s), 2.7 +/- 3.1 HEs/h were associated with abdominal contraction and only 0.7 +/- 2.1 HEs/h with apnea (p < 0.05). Resting lung volume decreased by 69 +/- 16% of tidal volume in HEs associated with abdominal contraction.

CONCLUSIONS

In this group of premature infants who presented with frequent HEs after mechanical ventilation, most HEs were associated with abdominal muscles contraction and a loss in lung volume. These findings provide an alternate mechanism to explain these episodes in spontaneously breathing preterm infants with a history of mechanical ventilation.