Lung Volume, Gas Mixing, and Mechanics of Breathing in Mechanically Ventilated Very Low Birth Weight Infants with Idiopathic Respiratory Distress Syndrome

Abstract

ABSTRACT. We assessed pulmonary function in 14 mechanically ventilated newborn very low birth weight infants with idiopathic respiratory distress syndrome by means of a face-out, volume displacement body plethysmograph and nitrogen washout analyses. Specially designed computer programs were used for calculations of lung volumes, ventilation, gas mixing efficiency, and mechanical parameters. In addition to very low compliance and moderately elevated resistance of the respiratory system, there were considerably impaired gas mixing efficiency and low functional residual capacity (FRC) For methodologic reasons, lung function studies in newborn infants with IRDS have largely been focused on lung mechanics. Using applied methods makes it possible to obtain a more comprehensive picture of ventilatory conditions, even in very premature, severely affected infants. To further clarify the pathophysiology of IRDS under conditions of mechanical ventilation in this group of infants, we assessed lung volume, alveolar ventilation, gas mixing efficiency, and lung mechanics in mechanically ventilated infants with birth weights below 1500 g. MATERIALS AND METHODSWe studied 14 very low birth weight infants with IRDS during intermittent positive pressure ventilation within 5 d (range 0-5 d) of birth. Six of the infants were boys and eight were girls. Median birth weight was 1.29 kg (range 1.00-1.50 kg) and median gestational age was 29 wk (range 26-33 wk). Informed consent was obtained from the parents of each infant before the procedure was camed out, and the study was approved by the ethics committee of Goteborg University.Maternal history included preeclampsia in six cases and abruption of the placenta in three cases. One infant was a twin. Twelve infants were delivered by cesarean section. Apgar scores were below 5 at 1 min in seven infants and below 7 at 5 min in seven infants. All infants were flushed with oxygen immediately after birth, and nine were also ventilated using a mask. Ten of the infants with adequate spontaneous respiration were treated with continuous positive airway pressure by nasal prongs within 4 h of birth, and the other four were intubated and ventilated within a few minutes of birth. Mechanical ventilation was started within 27 h in all infants. The pulmonary disease was classified as IRDS in all infants (1). All initial radiographs showed a reticulogranular pattern, and no infant had positive blood cultures or hematologic signs of infection.The following guidelines for mechanical ventilation of very low birth weight infants with IRDS were used in the intensive care unit: Nasal intubation with uncuffed endotracheal tubes 2.5-3.0 (Portex LTD, Hythe, Kent, UK) was performed. A Sechrist Infant Ventilator 400 B (Sechrist Industries Inc., Anaheim, CA) was connected to the endotracheal tube. The breathing gas was humidified and heated with a humidifier (Fisher and Paykel, Auckland, New Zealand). Initial ventilator settings were: respiratory rate 60 breathslmin, inspiratory/expiratory ratio 112, PIP 25-30 cm H20,...

The Effects of Nitric Oxide Inhalation on the Pulmonary Circulation of Preterm Lambs

“…The presence of right-to-left shunting of blood in association with neonatal RDS is well documented (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35). Several investigators have suggested that the right-to-left shunting in infants with RDS occurs predominantly within the lungs (29,46,47).…”

“…They suggested that large right-to-left shunts predict an early death of infants with RDS. RDS is also complicated by intrapulmonary shunting of blood (28)(29)(30)(31)(32)(33)(34)(35). Regional atelectasis and hyaline membrane formations probably contribute greatly to the pathophysiology of the intrapulmonary shunting associated with RDS.…”

A Plethysmographic Method for Assessment of Lung Function in Mechanically Ventilated Very Low Birth Weight Infants

“…We also showed, in a lung model, that FRC can be accurately assessed when the Fi02 in the breathing gas is as high as 0. 8. This was also the case in air breathing with a washout FiOz of only 0.…”

“…A nitrogen washout using an Fi02 of 1.0 was performed after ventilation ofthe model with an FiOz of 0. 8 compared with a series of washouts with Fi02 1.0 and a ventilatory Fi02 of 0.2 1. Ten washouts with each gas combination were performed.…”

Lung Function Tests in Neonates and Infants with Chronic Lung Disease of Infancy: Functional Residual Capacity

“…69 Although a wide range of FRCs (from as low as a mean of 7.8 ml/kg to 15.5 ml/kg) was reported in ventilated infants with RDS using clinically determined PEEP ($4 cm H 2 O) and prior to surfactant administration, these values are significantly lower than those predicted from reference data generated in healthy infants breathing without assistance. 2,82,[91][92][93] The effect of varying PEEP level on FRC was assessed systematically. 24,69,70,74,94 Increasing PEEP consistently results in increases in FRC and oxygenation, 74,94 but the correlation between DPEEP and DFRC seems nonlinear.…”