Restoration of lung pressure-volume characteristics with surfactant: comparison of nebulization versus instillation and natural versus synthetic surfactant.

The pressure-volume (PV) characteristics of 21 adult rat lungs were examined before and after lung washing after which natural or synthetic (dipalmitoyl lecithin (DPL)) surfactant was administered by either an ultrasonic nebulizer or instilled directly into the trachea. Lungs receiving surfactant by nebulization were ventilated at a rate of 40/min at 20 cm H2O peak inspiratory pressure and with 7 cm H2O positive end expiratory pressure (PEEP) for 2 hr. Lungs receiving surfactant by instillation were ventilated for 5 min in a fashion similar to the nebulization study; then a final PV curve was obtained. Results from the deflation limb of the PV curves at 5 and 10 cm H2O were analyzed and expressed as a percentage of the original total lung capacity obtained at 30 cm H2O (percentage of TLC). The control values of percentage of TLC were 52.8 +/- 6.4 at 5 cm H2O and 73.9 +/- 3.9 at 10 cm H2O. Neither nebulization nor instillation of DPL produced a significant increase in percentage of TLC. Nebulization of natural surfactant produced only a slight increase in percentage of TLC from 4.8 +/- 2,4 to 6.7 +/- 2.1 (not significant) at 5 cm H2O and from 21.1 +/- 6.1 to 27.8 +/- 5.4 (P less than 0.05) at 10 cm H2O. Instillation of natural surfactant produced a very striking increase of percentage of TLC from 13.2 +/- 8.0 to 55.6 +/- 4.3 (P less than 0.01) at 5 cm H2O and from 47.9 +/- 6.1 to78.6 +/- 4.2 (P less than 0.01) at 10 cm H2O.