Early changes in lung function and response to surfactant replacement therapy

Lung function in immature baboons with respiratory distress syndrome receiving early caffeine therapy: a pilot study

AIM

The cardiopulmonary effects of early caffeine therapy in surfactant-treated immature baboons were measured.

METHODS

Nine 125-d (term = 185 d) baboons receiving caffeine citrate at 1 and 12 h age as part of a pilot study on the use of nasal CPAP at 24 h were compared to six untreated animals destined for prolonged ventilator support. All received surfactant prior to their first breath and again at 6 h age. Serial physiologic and ventilatory parameters were recorded. Lung mechanics were measured by body plethysmography. Data were compared from 1 through 24 h age.

RESULTS

There were no between-group differences in any study variables prior to caffeine therapy at 1 h age. Airway resistance (RA) was significantly lower in caffeine-treated compared to non-caffeine-treated animals at 12 and 24 h age [median (range)12 h: 47 (35-107) cm H2O/l/s to 135 (120-259) cm H2O/l/s; and 24 h: 93(60-137) cm H2O/l/s to 211 (86-235) cm H2O/l/s; p < 0.05]. Respiratory system compliance (CRS) was higher in caffeine-treated compared to non-caffeine-treated animals at 18 and 24 h age [median (range) 18 h: 0.60 (0.29-1.58) ml/cm H2O/kg to 0.39 (0.33-0.46) ml/cm H2O/kg; and 24 h: 0.68 (0.36-1.20) ml/cm H2O/kg to 0.36 (0.33-0.55) ml/cm H2O/kg; p < 0.05]. Ventilatory efficiency index and arterial/alveolar ratio significantly improved in caffeine-treated animals over the 24-h study period (p < 0.05, repeated measures ANOVA).

CONCLUSIONS

In this pilot study, early caffeine treatment, combined with prophylactic surfactant therapy, was associated with better lung function during the initial 24 h of life. This combined approach may facilitate earlier extubation or prophylactic efforts to support infants on nasal CPAP. Randomized, controlled investigation is warranted.

Changes in lung volume, compliance and oxygenation in the first 48 hours of life in infants given surfactant

Changes in lung volume (functional residual capacity) compliance and oxygenation in the first 48 h of life in infants given surfactant replacement therapy were studied. Fourteen infants, median gestational age 30 weeks (range 26-35), who were given two doses of an artificial surfactant (Exosurf) at approximately 2 h of age and 12 h later, were examined. Compared to baseline, functional residual capacity, compliance of the respiratory system and oxygenation, significantly improved at 24 and 48 hours, but specific compliance (compliance/functional residual capacity) decreased. The greater changes, however, were experienced between baseline and 24 h. These data suggest that the elevation of FRC over the first 48 hours of life may be due to increased distension as well as recruitment of alveoli.

Role of lipid polymorphism in pulmonary surfactant

The development of artificial surfactants for the treatment of respiratory distress syndrome (RDS) requires lipid systems that can spread rapidly from solution to the air-water interface. Because hydration-repulsion forces stabilize liposomal bilayers and oppose spreading, liposome systems that undergo geometric rearrangement from the bilayer (lamellar) phase to the hexagonal II (HII) phase could hasten lipid transfer to the air-water interface through unstable transition intermediates. A liposome system containing dipalmitoylphosphatidylcholine was designed; the system is stable at 23 degrees C but undergoes transformation to the HII phase as the temperature increases to 37 degrees C. The spreading of lipid from this system to the air-water interface was rapid at 37 degrees C but slow at 23 degrees C. When tested in vivo in a neonatal rabbit model, such systems elicited an onset of action equal to that of native human surfactant. These findings suggest that lipid polymorphic phase behavior may have a crucial role in the effective functioning of pulmonary surfactant.