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

Introduction

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 (Vd_aw) 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 Vd_aw 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, Paw_peak, VCO₂, blood gases.

Results

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

Conclusions

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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