Adjunctive ventilation with tracheal gas insufflation--good vibrations?

Tracheal gas insufflation

Tracheal gas insufflation is a technique in which gas is injected intratracheally during positive pressure ventilation. The fresh gas rinses expired gas from the tracheal tube and anatomical dead space, aiding carbon dioxide elimination. This reduces ventilatory volume and pressure, helping to reduce ventilator-induced lung damage. Complications of tracheal gas insufflation include interference with ventilator function, tracheal damage and barotrauma. Expiratory washout is a variation of tracheal gas insufflation. We designed and constructed an original expiratory washout system and evaluated its safety and performance in lung and animal models. We found that expiratory limb and tracheal tube occlusion tests caused the device to disable itself at acceptable intratracheal pressures. We also demonstrated up to 31% reduction in tidal volume compared with conventional ventilation, supporting the possibility of using this device clinically to lessen volutrauma. We concluded that aspects of this design might alleviate many of the safety concerns of using tracheal gas insufflation.

Aspiration of airway dead space. A new method to enhance CO2 elimination

Alveolar ventilation and CO2 elimination during mechanical ventilation can be enhanced by reducing dead-space ventilation. Aspiration of gas from the dead space (ASPIDS) is a new principle, according to which gas rich in CO2 during late expiration is aspirated through a channel ending at the distal end of the tracheal tube. Simultaneously, fresh gas injected into the inspiratory line fills the airway down to the same site. We hypothesized that ASPIDS would allow a reduction of tidal volume (VT) and airway pressure (Paw). To test our hypothesis we studied six anaesthetized and mechanically ventilated pigs (24 +/- 4 kg). The intention was to decrease VT while keeping PaCO2 constant by using ASPIDS. VT was reduced by decreasing the minute ventilation (V E) in two steps, of 1.8 L/min (VE - 1.8) and 2.2 L/min (VE - 2.2), respectively, and by increasing respiratory rate (RR) from 20 to 46 breaths/min. At ASPIDS, peak Paw was reduced by 35% at VE - 1.8 and at VE - 2.2 (p < 0.001), and by 20% at an RR of 46 (p < 0.01). PaCO2 was maintained or reduced at ASPIDS. No intrinsic positive end-expiratory pressure developed. Arterial blood pressure and heart rate were unaffected. The results show that ASPIDS allows a reduction in VT and Paw while PaCO2 is kept constant. ASPIDS does not lead to problems associated with jet streams of gas or with gas humidification, and can be developed as a safe technique.