Tracheal sealing by auto-inflation in tracheal tube cuffs

The purpose of this study was to determine if inspiratory pressure from intermittent positive pressure ventilation may be sufficient to inflate the cuff (thus 'auto-inflation') and thereby seal the trachea.

In a laboratory model we investigated the ability of cuffs of seven 5.0 mm internal diameter (ID) tracheal tubes (Sheridan CF, Mallinckrodt Hi-Contour, Mallinckrodt Sealguard, Mallinckrodt Safety-Flex, Portex Soft Seal, Rueschelit Super-Safety Clear and Microcuff PET) to seal the trachea by auto-inflation, i.e. by using the inspiratory pressure to expand and keep open the cuff within the trachea. A mechanical lung connected to a model trachea made from clear, rigid polyvinylchloride (PVC) (12 mm ID) was used to simulate changes in inspiratory pressures. Respirator settings were: fresh gas flow (air) 6 lxmin(-1); positive end-expiratory pressure 5 cmH(2)O; respiratory rate 20 brxmin(-1); I : E ratio = 1 : 2; inspiratory pressure 5, 10, 15, 20, and 25 cmH(2)O. Percentage of expiratory to inspiratory tidal volume (E : I V(t) volume ratio) was calculated.

Using lubricated Mallinckrodt Seal Guard tube cuffs E : I V(t) volume ratio was almost 100% at a peak inspiratory pressure of 10 cmH(2)o whereas in tube cuffs particularly made of PVC an E : I ratio was achieved only at higher inspiratory pressures, if at all.

Auto-inflation in the Mallinckrodt Seal Guard with high volume-low pressure polyurethane cuff can produce adequate tracheal sealing in the model trachea used. The implication is that such auto-inflation should decrease the risk of tracheal injury from acute or persistent cuff hyperinflation.