Effects of helium-oxygen on respiratory mechanics, gas exchange, and ventilation-perfusion relationships in a porcine model of stable methacholine-induced bronchospasm

Objective: To explore the consequences of helium/oxygen (He/O2) inhalation on respiratory mechanics, gas exchange, and ventilation-perfusion (VA/Q) relationships in an animal model of severe induced bronchospasm during mechanical ventilation. Design: Prospective, interventional study. Setting: Experimental animal laboratory, university hospital. Interventions: Seven piglets were anesthetized, paralyzed, and mechanically ventilated, with all ventilator settings remaining constant throughout the protocol. Acute stable bronchospasm was obtained through continuous aerosolization of methacholine. Once steady-state was achieved, the animals successively breathed air/O2 and He/O2 (FIO2 0.3), or inversely, in random order. Measurements were taken at baseline, during bronchospasm, and after 30min of He/O2 inhalation. Results: Bronchospasm increased lung peak inspiratory pressure (49±6.9 vs 18±1cmH2O, P<0.001), lung resistance (22.7±1.5 vs 6.8±1.5cmH2O.l−1.s, P<0.001), dynamic elastance (76±11.2 vs 22.8±4.1cmH2O.l−1, P<0.001), and work of breathing (1.51±0.26 vs 0.47±0.08, P<0.001). Arterial pH decreased (7.47±0.06 vs 7.32±0.06, P<0.001), PaCO2 increased, and PaO2 decreased. Multiple inert gas elimination showed an absence of shunt, substantial increases in perfusion to low VA/Q regions, and dispersion of VA/Q distribution. He/O2 reduced lung resistance and work of breathing, and worsened hypercapnia and respiratory acidosis. Conclusions: In this model, while He/O2 improved respiratory mechanics and reduced work of breathing, hypercapnia and respiratory acidosis increased. Close attention should be paid to monitoring arterial blood gases when He/O2 is used in mechanically ventilated acute severe asthm

Comparative effects of helium-oxygen and external positive end-expiratory pressure on respiratory mechanics, gas exchange, and ventilation-perfusion relationships in mechanically ventilated patients with chronic obstructive pulmonary disease

Objective: To compare the effects of He/O2 and external PEEP (PEEPe) on intrinsic PEEP (PEEPi), respiratory mechanics, gas exchange, and ventilation/perfusion (V̇A/Q̇) in mechanically ventilated COPD patients. Design and setting: Prospective, interventional study in the intensive care unit of a university hospital. Interventions: Ten intubated, sedated, paralyzed, mechanically ventilated COPD patients studied in the following conditions: (a) baseline settings made by clinician in charge, air/O2, ZEEP; (b) He/O2, ZEEP; (c) air/O2, ZEEP; (d) air/O2, PEEPe 80% of PEEPi. Measurements at each condition included V̇A/Q̇ by the multiple inert gas elimination technique (MIGET). Results: PEEPi and trapped gas volume were comparably reduced by He/O2 (4.2±4 vs. 7.7±4cmH2O and 98±82 vs. 217±124ml, respectively) and PEEPe (4.4±1.3 vs. 7.8±3.6cmH2O and 120±107 vs. 216±115ml, respectively). He/O2 reduced inspiratory and expiratory respiratory system resistance (15.5±4.4 vs. 20.7±6.9 and 19±9 vs. 28.8±15cmH2Ol−1s−1, respectively) and plateau pressure (13±4 vs. 17±6cmH2O). PEEPe increased airway pressures, including total PEEP, and elastance. PaO2/FIO2 was slightly reduced by He/O2 (225±83 vs. 245±82) without significant V̇A/Q̇ change. Conclusions: He/O2 and PEEPe comparably reduced PEEPi and trapped gas volume. However, He/O2 decreased airway resistance and intrathoracic pressures, at a small cost in arterial oxygenation. He/O2 could offer an attractive option in COPD patients with PEEPi/dynamic hyperinflatio