Improved oxygenation during synchronized intermittent mandatory ventilation in neonates with respiratory distress syndrome: A randomized, crossover study,☆☆,

Presented in part at the annual meeting of the Society for Pediatric Research, Washington, D.C., May 1993.
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Abstract

In a randomized, crossover study, we compared arterial partial pressure of oxygen and of carbon dioxide between consecutive periods of conventional and synchronized intermittent mandatory ventilation (SIMV). We studied spontaneously breathing infants with an endotracheal tube in place. The infants were <12 hours of age, had a diagnosis of respiratory distress syndrome, and had an arterial/alveolar oxygen ratio of <0.25. The infants had a mean birth weight of 1077 gm and gestational age of 28 weeks. The mean rate of asynchrony on intermittent mandatory ventilation (IMV) was 52% (range, 36% to 76%), and on SIMV was <1%. Infants were randomly assigned to IMV or SIMV as their initial ventilator mode and underwent ventilation for four 15-minute periods, and crossed over to the alternate mode after each period. Ventilator settings and the fraction of inspired oxygen were not changed between modes. At the end of each period, arterial blood gas measurements were obtained; 26 paired comparisons were made between modes. The mean arterial partial pressure of oxygen was significantly higher during SIMV than during IMV (mean, 61.5 vs 53.3 mm Hg; p <0.01). The mean arterial partial pressure of carbon dioxide was slightly lower during SIMV than during IMV (mean, 42.7 vs 41.3 mm Hg; p <0.05). The improvement in oxygenation demonstrated with SIMV may allow a reduction in ventilator pressure or oxygen exposure in this group of infants, who are at risk of having complications of ventilation. (J PEDIATR 1995;126:407-11)

Section snippets

Patient population

Infants were eligible for study if their birth weight was less than 1750 gm, gestational age was <32 weeks, and chronologic age was <12 hours. All had radiographic evidence of respiratory distress syndrome, had an arterial line inserted for routine monitoring, were breathing spontaneously on a ventilator, and had an arterial/alveolar oxygen ratio <0.25. The ratio of arterial to alveolar partial pressure of oxygen was calculated with the fraction of inspired oxygen and the arterial oxygen and

RESULTS

Ten infants meeting initial entry criteria were enrolled in the study. The airway flow recording showed one infant to have a rate of asynchrony <10% during IMV, and he was therefore excluded from further study. The rate of synchrony achieved during SIMV was >98%.

Three paired comparisons of PaO2 and PaCO2 between IMV and SIMV were possible for each patient. Twenty-six comparisons were made in the nine infants who completed the study; one comparison was excluded because the ventilator settings

DISCUSSION

We demonstrated an improvement in Pao2 and a small increase in ventilation between IMV and SIMV in low birth weight infants with moderate to severe respiratory distress syndrome. A mean rate of asynchrony of 53% was seen during IMV despite what was thought to be optimal ventilator support based on gas exchange and no visible evidence that the infant was "fighting the ventilator." Asynchrony was essentially eliminated during SIMV.

Asynchrony has been associated with active expiration,2, 3 reduced

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    From the Division of Neonatology, Department of Pediatrics, University of California, San Diego, School of Medicine

    ☆☆

    Reprint requests: John P. Cleary, MD, The Med Center-Memorial, 119 Belmont St., Worcester, MA 01605.

    0022-3476/95/$3.00 + 0 9/23/60904

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