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Aspiration of airway dead space (ASPIDS) in mechanically ventilated patients


Alveolar ventilation can be improved and CO2 clearance enhanced by reducing dead space. We studied a system for the aspiration of gas from the airway dead space (Vdaw) denoted ASPIDS. During ASPIDS, in the late expiration, CO2 rich gas is aspirated from the distal end of the tracheal tube; simultaneously fresh gas is injected in the inspiratory line. Our hypothesis was that CO2-laden gas in the Vdaw could be eliminated and, keeping alveolar ventilation constant, a reduction in minute ventilation (MV) and airway pressure (Paw) achieved.

Materials and Methods

Six patients (4m/2f, mean age 56 ± 23 years) mechanically ventilated for cerebral pathologies (Crs: 78 ± 20 ml/cmH2O) with a computer controlled Servo Ventilator 900C (basal ventilation: MV: 7.7 l/min; RR: 12.7; Ti: 33%; Tpaus: 5%; PEEP: 5 cmH2O), were studied. The computer controls 2 solenoid valves for aspiration and injection. The aim was to keep PaCO2 constant during ASPIDS while decreasing MV. ASPIDS was expected to clear from CO2 the volume of connecting tubings (ie 150 ml). Consequently, MV was decreased, during ASPIDS, of 150 × RR (ie 1900 ml). Data collected after 20 min of ASPIDS were compared with baseline ventilation using a T test. The following parameters were recorded: HR, mABP, MV, Pawpeak, VCO2, blood gases.


Patients were stable during ASPIDS. PEEP level was maintained and no PEEPi developed. No side effects were observed.


From our preliminary results, ASPIDS appears to be a new safe and promising method that improves the efficiency of ventilation, decreases the pressure required, and reduces the potential for lung injury during mechanical ventilation.



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Robertis, E.D., Servillo, G., Rossano, F. et al. Aspiration of airway dead space (ASPIDS) in mechanically ventilated patients. Crit Care 2 (Suppl 1), P083 (1998).

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