Helium/Oxygen Mixture Reduces the Work of Breathing
Objective: To test the hypothesis that helium/oxygen mixture can reduce the work of breathing at the end of the weaning process in patients with chronic obstructive pulmonary disease.
Design: Prospective, randomized, crossover study.
Setting: Two medical intensive care units at two university tertiary care centers.
Patients: Thirteen patients with chronic obstructive pulmonary disease evaluated just before and after extubation.
Interventions: Helium/oxygen and air/oxygen mixtures were administered sequentially, for 20 mins each, in a randomized order, just before extubation. It was possible to repeat the study after extubation in five patients.
Measurements and Main Results: Before extubation, the helium/oxygen mixture induced no significant variation in the breathing pattern. By contrast, it reduced the work of breathing from 1.442 ± 0.718 J/L (mean ± sd) to 1.133 ± 0.500 J/L (p < .05). This reduction was explained mainly by a reduction in the resistive component of the work of breathing from 0.662 ± 0.376 to 0.459 ± 0.256 J/L (p < .01). We also observed a slight reduction in the intrinsic positive end-expiratory pressure from 2.9 ± 2.1 cm H₂O to 2.1 ± 1.8 cm H₂O (p < .05). Similar results were also observed after extubation in five patients in whom the repetition of the study was possible.
Conclusions: In spontaneously breathing intubated patients with chronic obstructive pulmonary disease recovering from an acute exacerbation, helium/oxygen mixture reduces the work of breathing as well as intrinsic positive end-expiratory pressure without modifying the breathing pattern.

Weaning failure frequently results from an imbalance between the loads imposed on the respiratory system and its capacity. In this way, patients with chronic obstructive pulmonary disease (COPD) frequently exhibit increased resistive loads (favored by bronchospasm and airway secretions) as well as increased elastic loads (especially in relation to pulmonary hyperinflation). Moreover, pulmonary inflation also decreases the inspiratory contractile capacity by putting the respiratory muscles at an unfavorable position on their tension-length curves.

The low density of helium, compared with air, can decrease resistances to gas flow. A helium/oxygen mixture therefore could be beneficial during the weaning process of COPD patients. Limited encouraging data are available on the effects of the helium/oxygen mixture in COPD patients. All studies focused either on stable patients or on decompensated patients during the acute phase of an exacerbation. We have chosen to study the effects of the mixture in spontaneously breathing COPD patients recovering from an acute exacerbation. The study was performed when patients were in a stable condition, just before and after extubation. It was designed to test the main hypothesis that, in these conditions, the helium/oxygen mixture could reduce the work of breathing (WOB) and the dynamic intrinsic positive end-expiratory pressure (PEEPi), which are known to be key variables of the weaning process in COPD patients.