Pulmonary blood flow and tissue volume. Assessment of a non-invasive technique of measurement

Lung volume and pulmonary blood flow measurements following exogenous surfactant

Lung function in eight infants with clinical and radiological features of surfactant deficiency treated with exogenous porcine surfactant was studied before and at 15 min, 2h and 6h after the intratracheal administration of porcine surfactant. We measured alveolar-arterial oxygen tension difference, dynamic lung compliance, lung volume and effective pulmonary blood flow in all infants. The alveolar-arterial oxygen tension difference fell from a mean (SD) 43.3 (14.5) kPa before treatment to 8.8 (8.8) kPa at 1 h and 12.2 (6.8) kPa 6h after treatment (P < 0.001). There was no change in mean (SD) dynamic compliance (0.39 [0.10] ml/cmH2O/kg pre dose; 0.36 [0.13] ml/cmH2O/kg 6h post treatment). Accessible functional residual capacity and effective pulmonary blood flow were measured using an adaptation of the argon/freon rebreathing method and showed an increase in mean (SD) functional residual capacity from 7.5 (1.4) ml/kg predose to 10.8 (3.3) ml/kg within 15 min of treatment, 11.4 (3.4) ml/kg 2h later and 12.7 (3.1) ml/kg 6h after treatment (P = 0.009). Mean (SD) effective pulmonary blood flow values did not differ significantly, changing from 78.2 (20.9) ml/kg per min predose to 88.7 (24.1) ml/kg per min 15 min post dose, 87.6 (21.7) ml/kg per min 2h post dose and 90.0 (22.7) ml/kg per min 6h post dose (P = 0.711).

CONCLUSION

The improvement in oxygenation after surfactant treatment is associated with an increase in lung volume but is not related to an improvement in dynamic lung compliance or effective pulmonary blood flow. The change in lung volume is detectable within 15 min of administration of the surfactant.