Apparatus deadspace

Intubation of the airway is commonly said to reduce anatomical dead-space by half, i.e. from 100-150 ml to 50-75 ml, or approximately 125 ml to 60 ml. However, the tube needs to be connected to the ventilatory circuit, and the volume of additional tubing and Y-piece, as well as a possible heat-moisture exchanger, will result in an apparatus dead-space that is greater than the bypassed anatomical dead-space. Even the use of a small exchanger will result in a total apparatus dead-space of 120 to 140 ml. Although the increased dead-space volume may seem modest, it easily increases the ventilatory demand by another liter per minute, depending on the ventilatory pattern of the patient. This has implications for both mechanical ventilation and spontaneous breathing. During mechanical ventilation the increased ventilatory demand raises mean airway pressure and may promote volutrauma/barotrauma. During spontaneous breathing the increased ventilatory demand may cause or contribute to respiratory fatigue. The additional dead-space volume has often been neglected but, more recently, there has been increased interest in reducing its effect on gas exchange and ventilation. The technique of tracheal gas insufflation has been developed, based on introducing a catheter through the tracheal tube to its distal end and using it to flush end-expiratory gas out of the tube towards the expiratory port of the ventilatory circuit. This decreases rebreathing, so that the minute ventilation needed to maintain Paco2 is reduced.

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Sleep Apnea

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