Elsevier

The Journal of Pediatrics

Volume 127, Issue 5, November 1995, Pages 767-773
The Journal of Pediatrics

Mechanisms for episodes of hypoxemia in preterm infants undergoing mechanical ventilation,☆☆,,★★

https://doi.org/10.1016/S0022-3476(95)70171-0Get rights and content

Abstract

Objective: To ascertain possible mechanisms implicated in the development of transient episodes of hypoxemia (oxygen saturation <85%) frequently observed in preterm infants undergoing mechanical ventilation, even after the acute phase of respiratory failure has passed. Study design: Tidal flow, airway and esophageal pressure, and oxygen saturation were continuously recorded in 10 infants (mean ± SD, birth weight 733 ± 149 gm, gestational age 25.5 ± 2.2 weeks, age 26.3 ± 11.9 days) who had repeated episodes of hypoxemia without any evident cause. Measurements of minute ventilation (v̇E), inspiratory compliance (Ci), and inspiratory resistance (Ri) were compared before and during episodes of hypoxemia. Results: All episodes of hypoxemia were preceded by an active exhalation that produced a mean decrease in end-expiratory lung volume of 6.4 ± 2.8 ml/kg. The reduction in lung volume was immediately followed by a sudden decrease in tidal flow and volume, despite continuation of mechanical ventilation at the same rate and peak pressure. The resulting hypoventilation was associated with a drop in Ci to approximately one half and an increase in Ri to more than double the baseline values. Approximately 30 seconds after the beginning of hypoventilation, the arterial oxygen saturation reached a hypoxemic level (oxygen saturation <85%). Conclusion: Most hypoxemic episodes were triggered by an expiratory effort that produced a large decrease in lung volume. This reduction in lung volume probably leads to closure of small airways and the development of intrapulmonary shunts, which would explain the rapid development of hypoxemia. (J PEDIATR 1995;127:767-73)

Section snippets

Study patients

Ten preterm infants with birth weights between 500 and 100 gm, who were undergoing ventilation and who had frequent unexplained episodes of pulse oximetry saturation (10 or more daily episodes of pulse oximetry saturation <85% lasting for 1 to 2 minutes) were the subjects of this study. These episodes were unexplained because they occurred without any obvious cause, such as a malfunction of the ventilator, a malposition of the endotracheal tube, an obstruction of the endotracheal tube with

Discussion

The results of this study indicate that most unexplained episodes of hypoxemia in preterm infants undergoing ventilation are triggered by a forced expiratory effort. This active exhalation produces a large decrease in lung volume, an increase in pulmonary resistance, and a drop in lung compliance. As a consequence of these changes, minute ventilation decreases. Evidence of an active expiration was provided by the increase in esophageal pressure that preceded every episode, indicating a rise in

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      Citation Excerpt :

      The frequency of these episodes increases over the first weeks after birth, and they are influenced by the severity of their underlying lung disease.3–5 In mechanically ventilated infants episodes of IH are often associated with increased activity and forceful exhalations that lead to loss in lung volume and hypoventilation.6–9 In spontaneously breathing infants, IH is often associated with apneic events,10 but IH episodes triggered by forceful exhalations have also been observed.11

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    From the Division of Neonatology, Department of Pediatrics, University of Miami School of Medicine, Miami, Florida

    ☆☆

    Supported by the University of Miami Project: New Born.

    Reprint requests: Tilo Gerhardt, MD, Professor of Pediatrics, Department of Pediatrics (R-131), University of Miami School of Medicine, PO Box 016960, Miami, FL 33101.

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    0022-3476/95/$5.00 + 0 9/23/67468

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