Reflection of differential pulmonary perfusion in polytrauma patients on differential lung ventilation (DLV). A comparison of two CO2-derived methods.

Seventeen polytrauma patients with asymmetric pulmonary contusion were treated with differential lung ventilation (DLV). The ratios of differential values of end-tidal CO2 concentration (ETCO2) and CO2 excretion ml/min (VCO2) were compared as indirect parameters for differential pulmonary perfusion. Both CO2-derived methods indicated asymmetry after starting DLV suggesting asymmetric pulmonary perfusion as a consequence of contusion. Prior to stopping DLV a significant improvement in asymmetry was indicated by the differential ratios of ETCO2 and VCO2 values. The ETCO2 ratio increased from 0.74 +/- 0.17 to 0.88 +/- 0.10, the VCO2 ratio from 0.57 +/- 0.23 to 0.86 +/- 0.11. In two patients with very severe contusion who underwent bilobectomies a marked difference between the ratios of ETCO2 and VCO2 was observed. It is concluded that differential measurement of CO2-derived variables may be useful in indicating differential perfusion in clinical practice on DLV. In very severe asymmetric contusion ETCO2 ratios may underestimate the differential perfusion ratio.