CHEST Guidelines-Impact-of-Respiratory-Rate-and-Dead-Space-in-the-C (1)

Impact-of-Respiratory-Rate-and-Dead-Space-in-the-C (1)

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The document, authored by François Lellouche, Mathieu Delorme, and Laurent Brochard, focuses on the impact of respiratory rate and dead space in lung-protective mechanical ventilation. Lung-protective ventilation, beneficial for critically ill patients, often involves reducing tidal volume (VT) and increasing respiratory rate (RR), although exact RR recommendations are unclear. This adjustment has increased the significance of dead space, particularly instrumental dead space (VDinstr), which includes components like heat and moisture exchangers and endotracheal tubes.<br /><br />Protective ventilation, especially with a VT of around 6 mL/kg predicted body weight (PBW), necessitates RRs of at least 25 breaths per minute. In surgical settings, a historical minute ventilation of 100 mL/kg PBW/min is applied, whereas ICU settings often require at least 150 mL/kg PBW/min due to differences in dead space and CO2 production.<br /><br />The reduction of VDinstr, possibly by exchanging an HME for a heated humidifier, can improve CO2 elimination or allow for reduced VT and pressures under constant PaCO2. This adjustment is crucial since dead space/VT rises with decreased VT and increased RR, potentially lowering effective alveolar ventilation (Valv) if VDinstr remains unaddressed.<br /><br />The document emphasizes minimizing VDinstr in protective ventilation, especially at high RRs, to ensure effective CO2 clearance and reduce respiratory drive. The work draws on a review of two decades of literature and suggests that reducing VDinstr can permit reductions in VT, plateau pressure, and respiratory rates, improving outcomes without compromising CO2 management. It underscores the importance of adjusting ventilator settings to accommodate increased RRs within protective ventilation protocols.

Keywords

lung-protective ventilation

respiratory rate

dead space

tidal volume

instrumental dead space

CO2 elimination

alveolar ventilation

ventilator settings

critically ill patients

protective ventilation