Redução da reinalação de dióxido de carbono com adição de vazamentos expiratórios intencionais em ventilação mecânica com o capacete ELMO®: um estudo cruzado com ventiladores de circuito único e duplo

Abstract

Helmet ventilatory support (HVS) can be delivered using continuous gas flow CPAP systems (H-CPAP Flow) or mechanical ventilators (H-NIV). A common limitation of this interface is the rebreathing of carbon dioxide (CO₂), which may impair the effectiveness of ventilatory support. We hypothesized that the addition of high intentional air leaks positioned at the expiratory port of the HVS would reduce CO₂ rebreathing in both H-CPAP and H-NIV, without causing significant airway depressurization. This study aimed to evaluate the effects of introducing high expiratory leaks on CO₂ rebreathing, airway pressurization, patient comfort, and patient–ventilator asynchronies across four HVS configurations. This was a randomized, crossover physiological study involving ten healthy volunteers exposed to four HVS strategies: H-CPAP Flow; H-CPAP and H-NIV with a portable single-limb ventilator; and H-NIV with an intensive care unit (ICU) dual-limb ventilator. The interface used was the ELMO® helmet, and each configuration was tested with minimal leakage, followed by the addition of intentional high leakage at the expiratory port up to the highest level that did not significantly impair patient–ventilator interaction. The primary outcome was inspired CO₂ pressure (PiCO₂), and secondary outcomes included transcutaneous CO₂ pressure (PtcCO₂), breathing pattern, intra-helmet pressure, overall, acoustic, thermal, and respiratory discomfort scores, as well as patient–ventilator asynchrony. The addition of high intentional leakage, averaging 58 L/min with the portable ventilator and 84.68% with the ICU ventilator, resulted in a significant reduction in PiCO₂ across all configurations (p < 0.001), with the greatest reduction observed in the H-NIV dual-limb configuration (5.70 ± 0.59 vs. 0.38 ± 0.14 mmHg; p < 0.001). PtcCO₂ remained within normal limits. H-NIV with a dual-limb circuit also reduced respiratory rate and increased expiratory time when compared to H-CPAP Flow and H-CPAP with a single-limb circuit, respectively, without increasing discomfort. Even under high leak conditions, expiratory pressure was preserved without a significant drop. However, a reduction in inspiratory pressure of at least 2 cmH₂O was observed in the H-NIV configurations. Discomfort scores remained low in all configurations. Although the asynchrony index was higher in the H-NIV dual-limb configuration (10.3 ± 3.6%) under high leak, the difference was not statistically significant. The introduction of high expiratory leaks in the ELMO® helmet significantly reduced CO₂ rebreathing in both H-CPAP and H-NIV configurations using mechanical ventilators, without compromising ventilation, comfort, or patient–ventilator synchrony.