Comparison between direct humidification and nebulization of the respiratory tract at mechanical ventilation: distribution of saline solution studied by gamma camera

Aim. To study the effectiveness of this procedure, an intra‐individual pilot study comparing the distribution of an instilled radiolabelled saline solution and an inhaled nebulized radiolabelled saline solution was performed using a scintigraphic technique. Background. In patients treated with mechanical ventilation, we have routinely used instillation of saline solution in the endotracheal tube before suctioning with the aim of softening mucus and facilitating removal of secretions. In our experience, the effectiveness of this procedure is doubtful. It may also have adverse effects. Methods. Nine patients on mechanical ventilation were examined with Single Photon Emission Computed Tomography on the same occasion using both humidification methods. The entire examination was carried out with the patient kept in a constant position in relation to the gamma camera, thereby allowing subtraction of the first registration from the second registration and subsequent evaluation and digital comparison of the two humidification methods. Results. Most of the instilled fluid goes to the posterior portion of the right lower pulmonary lobe. Compared with direct instillation, nebulized solution is more uniformly distributed between and within the lungs. With nebulization, distribution is less influenced by gravitation than with instillation. The aerosol reaches the periphery of the lung to a larger extent. Conclusions. Through the use of an aerosol with specific size characteristics, it may be possible to optimize the distribution of a fluid in the respiratory tract and achieve a more homogenous humidification. It is recommended to replicate the study using 25 subjects. Relevance to clinical practice. Direct instillation of saline should not be used with mechanical ventilation.