Ventilation–perfusion relationships in preterm infants after surfactant treatment

Abstract

Arterial-alveolar partial pressure differences for oxygen, carbon dioxide, and nitrogen were measured before and after surfactant replacement therapy on 15 occasions in 14 ventilator-dependent preterm infants with hyaline membrane disease (HMD). Eight treatments resulted in a significant improvement in arterial partial pressure of oxygen (PaO2) 2 hr after treatment; 7 did not. Neither group showed any significant change in arterial-alveolar partial pressure differences for oxygen, nitrogen, and carbon dioxide. This observation suggests that if surfactant replacement therapy produces an improvement in PaO2 it does so by recruitment of atelectatic alveoli with a balanced ventilation/perfusion ratio rather than by redistribution of ventilation within already ventilated alveoli.

Functional Residual Capacity (FRC) Does Not Predict Response to Surfactant in Preterm Infants

“…Variability in the initial response to surfactant treatment has been reported in preterm infants with RDS. [7][8][9][10][11][12]17 This study confirms this variability. Out of 41 surfactant treatments in this study, only 27 resulted in a favorable response at 2 hours with improvement in oxygenation.…”

“…27 A recent study from this laboratory by Bowen et al indicates that improvement in oxygenation after surfactant takes place without major changes in arterial-alveolar differences for CO 2 or N 2 , suggesting that surfactant treatment does not result in the production of alveoli with excessively high or low V/Q ratios. 17 Overdistended alveoli would contribute to an a-A difference for CO 2 , while newly recruited but poorly ventilated atelectatic alveoli would contribute to an a-A difference for nitrogen (V/Q ratio <1.0) during expansion as they went from an atelectatic state (V/Q = 0) to a normal FRC. In conjunction with Bowen's data, 17 the present study suggests that infants who respond favorably to surfactant replacement develop alveoli with V/Q ratios within the normal range, with little over-or underventilation.…”

“…17 Overdistended alveoli would contribute to an a-A difference for CO 2 , while newly recruited but poorly ventilated atelectatic alveoli would contribute to an a-A difference for nitrogen (V/Q ratio <1.0) during expansion as they went from an atelectatic state (V/Q = 0) to a normal FRC. In conjunction with Bowen's data, 17 the present study suggests that infants who respond favorably to surfactant replacement develop alveoli with V/Q ratios within the normal range, with little over-or underventilation.…”

“…Infants in this study were divided into two groups (Table 1) based on the results of a study done in this laboratory. 17 The two groups were: "Responders" to Survanta treatment, those with >10 mmHg rise in PaO 2 120 minutes after surfactant treatment; and "Nonresponders," those with <10 mmHg rise in PaO 2 .…”

Surfactant Therapy Prior to the Interhospital Transport of Preterm Infants

“…Eligibility for surfactant replacement was determined by: (1) clinical and radiographic evidence of hyaline membrane disease in an infant less than 36 weeks' gestational age; (2) requirement for mechanical ventilation; and (3) inability to attain an arterial partial pressure of oxygen greater than 80 torr while inhaling a fractional concentration of oxygen of 0.3 or higher. 15 The charts of 66 consecutive out-born infants that required mechanical ventilation for respiratory distress syndrome and were transferred to Cornell during the time period from January 2, 1992, to December 24, 1992, were reviewed to determine which infants ultimately received surfactant, and if they did, what type and the relation of administration to transport. Our institutional review boards (ethics committees) and the authors felt it would be ethically difficult to completely withhold surfactant prior to transport, and thus this nonrandomized trial was designed.…”