Saturday, November 1, 2014

For the severe asthmatic patient who is not responsive to aggressive beta-agonist and steroid therapy, there may be an indication for using Heliox (helium–oxygen mixture):

For the severe asthmatic patient who is not responsive to aggressive beta-agonist and steroid therapy, there may be an indication for using Heliox (helium–oxygen mixture):

a. This will make arterial blood gas measurements useless, since the Heliox displaces oxygen on the hemoglobin molecule and causes falsely low Po2 readings.

b. Originally used as a gas mixture for deep dives, Heliox triggers the mammalian diving reflex, which protects the brain from hypox
ia.
c. The addition of helium to the breathing mixture lowers alveolar Pco2, thereby reducing the work of respiration.
d. The Heliox mixture directly causes bronchial smooth muscle relaxation.
e. The Heliox mixture is less dense than air, allowing increased flow and less work of respiration.


The answer is e. Heliox (a mixture of 60–80% helium and 20–40% oxygen) improves PEFR and ABG results in nonintubated asthmatics and decreases peak airway pressures in ventilated asthmatics. Helium is an inert gas with one-eighth the density of nitrogen. When helium is blended with oxygen, the resulting gas mixture has a threefold reduction in density compared to air. Heliox reduces the resistance associated with gas flow through airways with nonlaminar flow (the upper and more proximal airways). This reduces respiratory muscle work and possibly improves gas exchange by improving ventilation–perfusion relationships or distal gas mixing and diffusion.
Constant monitoring of oxygen saturation and frequent blood gas monitoring are recommended for patients receiving Heliox.

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