Exogenous surfactant therapy increases static lung compliance, and cannot be assessed by measurements of dynamic compliance alone.
OBJECTIVE
To study the immediate effects of exogenous surfactant therapy on blood gases, lung volumes, and lung mechanics in adult rabbits with experimentally induced respiratory distress syndrome.


METHODS
Prospective randomized, controlled study.


METHODS
Laboratory and animal facility of a large university.


METHODS
Twelve adult New Zealand white rabbits.


METHODS
Respiratory failure was induced by repeated bilateral whole-lung lavage with saline (30 mL/kg body weight). After the last lavage, the animals were randomly assigned to two groups. Group 1 received surfactant (120 mg/kg body weight) that was suspended in a 0.6% sodium chloride solution. Group 2 received comparable volumes of the same hypotonic solution and served as controls.


RESULTS
Before and after endotracheal surfactant instillation, blood gases and functional residual capacity were measured, and lung mechanics from tidal volumes and pressure-volume curves were calculated. Functional residual capacity was measured by a computerized, multiple-breath, washin-washout method using sulfur hexafluoride (SF6) as tracer gas. The pressure-volume curves were obtained by an occlusion technique originally described for measuring static breath-by-breath compliance. The technique was modified for present use and fully computerized. Within 60 mins after surfactant instillation, there were marked improvements in Pao2 (61 +/- 7 torr [8.2 +/- 0.9 kPa] to 470 +/- 47 torr [62.6 +/- 6.2 kPa]) and in functional residual capacity (7.6 +/- 1.4 to 17.7 +/- 1.6 mL/kg body weight) at unchanged ventilatory settings. The pressure-volume curves became steeper over time and the pressure-volume curves for total lung volume were restored to an almost normal state. Maximum compliance calculated from the pressure-volume curves increased by 92% but there was no significant change in dynamic compliance. In the control group, no improvements in any measured or calculated lung parameters were seen.


CONCLUSIONS
The findings indicate that during mechanical ventilation, the effects of surfactant therapy on lung mechanics are best characterized by changes in functional residual capacity and maximum compliance obtained from static pressure-volume curves and not by dynamic compliance.
Gommers
D
D
Department of Anesthesiology, Erasmus University, Rotterdam, The Netherlands.
Vilstrup
C
C
Bos
J A
JA
Larsson
A
A
Werner
O
O
Hannappel
E
E
Lachmann
B
B
D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D005652:Functional Residual Capacity; D008170:Lung Compliance; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D011663:Pulmonary Surfactants / Q000627:therapeutic use*; D011817:Rabbits; D011897:Random Allocation; D012131:Respiratory Insufficiency / Q000188:drug therapy* / Q000503:physiopathology / Q000628:therapy; D014109:Total Lung Capacity
D011663:Pulmonary Surfactants; D002245:Carbon Dioxide; D010100:Oxygen