Phase 4, Single Centre, Single Blinded,Prospective Randomised Cross Over Comparison on the Physiological Response of Post Extubation Intensive Care Patients to Non-invasive Ventilation Using Either Air O2 or Heliox21

Failure to wean from mechanical ventilatory support occurs when the magnitude of respiratory system loading exceeds its capacity to respond. Extubation success depends on the condition being resolved or improved. Gas exchange capacity, respiratory muscle strength, laryngeal function and cough strength, nutritional status and psychological state can all lead to extubation failure. However, efforts to reduce the work of breathing might offer an alternative strategy.

Studies recently carried out in both paediatric and adult populations disclose the serious consequences of failed extubation, namely prolonged intensive care and hospital stays, greater mortality rates and increased care costs.

Gas flow in an airway can be either laminar or turbulent. There needs to be a greater pressure differential to drive a turbulent flow than a laminar one. Helium is an inert gas with no systemic biological effects (at standard temperature and pressure).

The low density and viscosity of Helium means that its substitution for nitrogen in air allows laminar flow to be maintained at much higher flow rates, and flow rates to be maintained at much lower working pressures (5). As a result, the use of helium-oxygen mixtures (Heliox21) has potential to reduce work of breathing, and also to limit dynamic gas trapping through increased cavity emptying, and altered lung mechanics/ forced expiratory pressures. As a result, Heliox21 has been used as a respiratory therapeutic bridge for over 30 years, with demonstrable advantage in the management of conditions including tracheal obstruction and chronic obstructive pulmonary disease (COPD).

In theory, the use of Heliox21 should reduce work of breathing by improving the balance between work demand and capacity during the process of weaning patients from mechanical ventilation. In general studies of the use of Heliox21 after extubation have been limited. Thus, we aim to extend our knowledge of the potential role for Heliox21 in the post-extubation environment of the Intensive Care Unit. Whilst Heliox21 has generally been administered through a simple face-mask (+/- rebreathing bag), the development of the HAMILTON G5 AVEA ventilator now allows the accurate administration of Heliox21 (21% helium/79% oxygen) with defined inspired fractional oxygen concentrations. This advent offers the means to safely administer helium as an adjunct to non-invasive ventilatory support.