Evaluation of Expiratory CO2 waveform at a lobar level by fibrobronchocapnography

To evaluate regional pulmonary blood flow, the authors employed fibrobronchocapnography (FBC) which consisted of a flexible bronchoscope (FFB) and a compact infrared CO2 meter (250 mm × 250 mm, 200 mm). A CO2 sampling tube made of teflon and measuring 1.8 m in length, 0.5 mm inner diameter, and 1.0 mm outer diameter, was introduced into a lobar bronchial orifice through the working channel of a FFB. The air from the lobe was constantly aspirated at a rate of 20 ml/min. The CO2 waveform was continuously monitored. This method was used in 13 patients with lung cancer and one with pulmonary embolism. In patients with lung cancer, group A (cases with blood flow disturbances) exhibited decreases in the end-tidal PCO2 (PETCO2) and mean alveolar PCO2 (PMACO2), and the CO2 waveform showed a flat form with a high PCO2 peak at the early inspiratory phase. Group B (cases without blood flow disturbances) demonstrated no differences in PETCO2, PMACO2, and CO2 wave form. In the case of pulmonary embolism, lung scan revealed impaired blood flow through the artery to right lower lobe. Gas sampling from this lobe showed decreased PETCO2 and PMACO2 and the CO2 wave form was flattened but without a peak. Anticoagulant therapy in this patient reversed these abnormalities. As the expired CO2 concentration in the lobe with disturbed blood flow is very low, PETCO2 and PMACO2 will also be low and CO2 wave form is flat. In lobes without disturbances in the blood flow, the end-expiratory gas in the central bronchi and trachea had higher CO2 concentration. During the next inspiration, the sampling tube aspirates the gas with higher CO2 concentration, giving rise to high PCO2 peak in the wave form. The authors conclude that FBC may be a useful method for the diagnosis and localization of blood flow disturbances and in evaluating the efficacy of therapy in pulmonary diseases that are associated with blood flow disturbances.