Comparison of gravimetric and a double-indicator dilution technique for assessment of extra-vascular lung water in endotoxaemia

Abstract

Objective: To compare a molecular double-indicator dilution technique with the gravimetrical reference method for measurement of extra-vascular lung water in porcine endotoxin shock. Design: Open comparative experimental study. Setting: Animal research laboratory. Measurements and results: In fourteen anaesthetised, mechanically ventilated landrace pigs, central and pulmonary haemodynamics as well as pulmonary gas exchange were measured. Extra-vascular lung water was quantitated gravimetrically as well as with a molecular double indicator dilution technique. Eight of these animals were subjected to endotoxaemia, the rest serving as sham controls. No difference in extra-vascular lung water was observed between the two methods in sham animals. Furthermore, extra-vascular lung water assessed with the molecular double-indicator dilution technique at the initiation of endotoxin infusion did not differ significantly from the corresponding values for sham animals. Endotoxaemia induced a hypodynamic shock with concurrent pulmonary hypertension and a pronounced deterioration in gas exchange. No increase in extravascular lung water was detected with the molecular double-indicator dilution technique in response to endotoxin, whereas this parameter was significantly higher when assessed with the gravimetric method. Conclusion: The molecular double-indicator dilution technique showed similar results as the gravimetrical method for assessment of extra-vascular lung water in non-endotoxaemic conditions. However, during endotoxin-induced lung injury the molecular double indicator dilution technique failed to detect the significant increase in extra-vascular lung water as measured by the gravimetric method. These data suggest that the molecular double indicator dilution technique may be of limited value during sepsis-induced lung injury.