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

The use of lower tidal volume ventilation was shown to improve survival in mechanically ventilated patients with acute lung injury. In some patients this strategy may cause hypercapnic acidosis. A significant body of recent clinical data suggest that hypercapnic acidosis is associated with adverse clinical outcomes including increased hospital mortality. We aimed to review the available treatment options that may be used to manage acute hypercapnic acidosis that may be seen with low tidal volume ventilation. The databases of MEDLINE and EMBASE were searched. Studies including animals or tissues were excluded. We also searched bibliographic references of relevant studies, irrespective of study design with the intention of finding relevant studies to be included in this review. The possible options to treat hypercapnia included optimising the use of low tidal volume mechanical ventilation to enhance carbon dioxide elimination. These include techniques to reduce dead space ventilation, and physiological dead space, use of buffers, airway pressure release ventilation and prone positon ventilation. In patients where hypercapnic acidosis could not be managed with lung protective mechanical ventilation, extracorporeal techniques may be used. Newer, minimally invasive low volume venovenous extracorporeal devices are currently being investigated for managing hypercapnia associated with low and ultra-low volume mechanical ventilation.

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CO2-controlled sampling of alveolar gas in mechanically ventilated patients

Journal of Applied Physiology ◽

10.1152/jappl.2001.90.2.486 ◽

2001 ◽

Vol 90 (2) ◽

pp. 486-492 ◽

Cited By ~ 74

Author(s):

Jochen K. Schubert ◽

Karl-Heinz Spittler ◽

Guenther Braun ◽

Klaus Geiger ◽

Josef Guttmann

Keyword(s):

Dead Space ◽

Coefficient Of Variation ◽

Sampling Technique ◽

Sampling Device ◽

Mechanically Ventilated ◽

Mechanically Ventilated Patients ◽

Selective Enrichment ◽

Gas Sampling ◽

End Tidal ◽

Ventilated Patients

A newly designed gas-sampling device using end-tidal CO2to separate dead space gas from alveolar gas was evaluated in 12 mechanically ventilated patients. For that purpose, CO2-controlled sampling was compared with mixed expiratory sampling. Alveolar sampling valves were easily controlled via CO2concentration. Concentrations of four volatile substances were determined in the expired and inspired gas. Isoflurane and isoprene, which did not occur in the inspired air, had ratios of end-tidal to mixed expired concentrations of 1.75 and 1.81, respectively. Acetone and pentane, found in both the inspired and expired air, showed ratios of 0.96 and 1.0, respectively. Precision of concentration measurements was between 2.4% (isoprene) and 11.2% (isoflurane); reproducibility (as coefficient of variation) was 5%. Because the only possible source of isoflurane and isoprene in this setting was patients' blood, selective enrichment of alveolar gas was demonstrated. By using the new sampling technique, sensitivity of breath analysis was nearly doubled.

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