Aspiration of dead space allows normocapnic ventilation at low tidal volumes in man

Aspiration of dead space (ASPIDS) improves carbon dioxide (CO2) elimination by replacing dead space air rich in CO2 with fresh gas during expiration. The hypothesis was that ASPIDS allows normocapnia to be maintained at low tidal volumes (VT).

Prospective study.

Adult intensive care unit in a university hospital.

Seven patients ventilated for neurological reasons were studied. All patients were clinically and haemodynamically stable and monitored according to clinical needs.

ASPIDS implies that, during expiration, gas is aspirated through a catheter inserted in the tracheal tube. Simultaneously, a compensatory flow of fresh gas is injected into the inspiratory line. ASPIDS was achieved with a computer/ventilator system controlling two solenoid valves for aspiration and injection.

At the basal respiratory rate of 12.6 breaths min-1, with ASPIDS VT decreased from 602 to 456 ml, as did the airway pressures to a corresponding degree. PaCO2 and PaO2 remained stable. At a frequency of 20 breaths min-1, with ASPIDS VT was further reduced to 305 ml with preserved normocapnia. ASPIDS did not interfere with the positive end-expiratory pressure (PEEP) level. No intrinsic PEEP developed. All patients remained stable. No haemodynamic or other side effects of ASPIDS were noticed.

The results of this study suggest that ASPIDS may be a useful and safe modality of mechanical ventilation that limits alveolar pressure and minute ventilation requirements while keeping PaCO2 constant.