Effects of Heat-Moisture Exchangers and Dead Space Compensation on CO 2 Clearance and Mechanical Power in Critically Ill Intubated Subjects

Abstract

Background:

Heat and moisture exchangers (HMEs) preserve airway humidification in mechanically ventilated subjects. However, the additional instrumental dead-space (V_D) may impair carbon dioxide (CO₂) elimination and require an increase mechanical power (MP), both associated with higher risk of ventilator-induced lung injury. The physiological effects (P_aCO₂ and MP) of HME use and instrumental V_D compensation strategies have not been comprehensively evaluated. We sought to evaluate the impact of HMEs on arterial CO₂ and MP in intubated subjects undergoing controlled mechanical ventilation, and to compare the effect of compensation strategies—tidal volume (V_T) or breathing frequency (f)—on CO₂ and MP.

Methods:

Prospective crossover study including intubated adults receiving controlled mechanical ventilation. We evaluated 4 conditions. (1) HME, (2) no HME, (3) HME + high V_T, (4) HME + high f. Main outcomes were P_aCO₂ and MP.

Results:

Adding the HME increased P_aCO₂ and ventilatory ratio and reduced arterial pH (P < .001). When V_T or f was increased to compensate for the HME-associated V_D, the P_aCO₂ decreased (P < .001) but the MP increased (P < .001), mainly because of its resistive component. A compensation strategy based on higher V_T was more effective in restoring P_aCO₂ to baseline levels than increasing f (P = .035); however, increasing V_T augmented the global and elastic MP (P < .001 and P = .002, respectively).

Conclusions:

The HME impaired CO₂ elimination. Increasing V_T or f to compensate for the HME-associated V_D increased MP. At an equivalent minute ventilation, increasing V_T was more effective for CO₂ clearance but may compromise lung protection. Under iso-CO₂ conditions, the strategies did not differ.

Keywords

heat and moisture exchanger mechanical power ventilator-induced lung injury mechanical ventilation lung protective ventilation

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