(Gr. helios, the sun). Helium is a light inert gas and the second most abundant element in the universe, after hydrogen. It was detected during the 1868 solar eclipse by Janssen, as a new line in the solar spectrum. Lockyer and Frankland suggest the name helium for the new element. In 1895 Ramsay discovered helium in the uranium crystal cleveite while it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet at about the same time. Rutherford and Royds demonstrated that alpha particles are helium nuclei in 1907.
Helium is present in air and in natural gas from which it is extracted. It is supplied at 137 bar as either Heliox (79% He, 21% O2) in white cylinders with white/brown shoulders or as 100% helium in brown cylinders.
Helium has a lower density (and hence specific gravity) than oxygen, nitrogen and air. Therefore, during turbulent flow the velocity will be higher when Heliox is used. This will reduce the work of breathing in patients with an upper airway obstruction such as a tumour. It use in severe asthma and other lower airway disease has also been suggested.
It has also been used to investigate small airway resistance to flow, by comparing flow-volume loops breathing air and helium/O2. The two curves are more similar in small airway obstruction than in normal lungs.
Helium is used in the measurement of lung volumes because of its very low solubility.
The lower density of helium/oxygen mixture produces the typical squeaky voice due to the higher frequency vocal sounds.
Helium/oxygen mixtures are also used for deep water diving to avoid nitrogen narcosis.
i] Heliox for asthma in the emergency department: a review of the literature. Review. A D Reuben and A R Harris. Emerg Med J 2004; 21:131-135
ii] Heliox and high-frequency oscillatory ventilation: Has helium finally found its niche? Creery D, Smith H. Pediatr Crit Care Med. 2000 Jul;1(1):91-2
iii] New anesthesia techniques. Tung A. Thorac Surg Clin. 2005 Feb;15(1):27-38
iv] The output of two sevoflurane vaporizers in the presence of helium. Carvalho B, Sanders D. Br J Anaesth. 2002 May;88(5):711-3.
v] Beneficial effects of albuterol therapy driven by heliox versus by oxygen in severe asthma exacerbation. Lee DL, Hsu CW, Lee H, Chang HW, Huang YC. Acad Emerg Med. 2005 Sep;12(9):820-7.
OBJECTIVES: To determine and define the beneficial effects of heliox-driven albuterol therapy on severe asthma exacerbation and clinical factors that affect greater response.
METHODS: The authors conducted two randomized, double-blinded, controlled trials in patients with severe asthma exacerbation. The first trial recruited 80 patients in the emergency department (ED). They received three consecutive doses of albuterol delivered by a nebulizer powered by either O(2) (O(2) group) or heliox (He/O(2) = 80:20; heliox group). Changes in peak expiratory flow rate (PEF) were compared, and factors influencing the response to heliox-driven albuterol therapy were identified. The second trial of 80 patients was conducted in older patients, a subpopulation associated with greater response in the first trial.
RESULTS: In the first trial, the heliox group had more rapid and greater improvement in PEF compared with the O(2) group. There tended to be more patients in the heliox group reaching the predetermined dischargeable PEF (>60% predicted) after three albuterol treatments (odds ratio, 2.58; 95% confidence interval = 1.03 to 6.46; p = 0.069). For patients eventually discharged from the ED, the ED stay was shorter by 10 minutes per patient in the heliox group compared with the O(2) group (p = 0.007). Logistic regression showed older age and lower pretreatment PEF to be associated with favorable heliox responses. The second trial, which recruited older patients (older than 40 years), showed greater improvement in PEF and dyspnea score with heliox-driven albuterol therapy in patients with lower pretreatment PEF.
CONCLUSIONS: Heliox-driven albuterol may be a useful adjunct therapy for older asthmatic patients with severe asthma exacerbation.
vi] Effects of helium on high frequency jet ventilation in model of airway stenosis.
Buczkowski PW, Fombon FN, Russell WC, Thompson JP. Br J Anaesth. 2005 Sep 2.
BACKGROUND: The addition of helium to the inspired gas may facilitate ventilation in the presence of clinically evident upper airway obstruction. However, there are no data on the effects of using a helium-oxygen mixture during high frequency jet ventilation (HFJV) in upper airway obstruction.
METHODS: HFJV at a frequency of 150 min(-1) (driving pressure 2 bar, inspiratory time 30%) was applied to a trachea-lung model to simulate ventilation through varying degrees of fixed laryngotracheal stenosis (2.5-8.5 mm). HFJV was delivered from above, through and below the level of stenosis to simulate supraglottic, transglottic and infraglottic administration. Measurements of distal tracheal pressures were repeated for each route at steady state for each stenosis diameter using both 100% oxygen and helium-oxygen (50% oxygen, 50% helium). The output of the ventilator was measured during operation on oxygen and helium-oxygen.
RESULTS: Peak, mean and end-expiratory pressures were greater during simulated supraglottic HFJV than during transglottic and infraglottic HFJV, and pressures increased markedly as the diameter of the stenosis decreased for all routes of ventilation (P<0.001). Generated pressures during HFJV using helium-oxygen and 100% oxygen were very similar overall, although reductions in pressures were observed during ventilation with helium-oxygen via the transglottic and transtracheal routes at stenosis diameters <4 mm (P<0.05). However, HFJV with the helium-oxygen mixture increased the delivered gas volumes by approximately 18%.
CONCLUSIONS: Using 50% helium-oxygen during HFJV in the presence of airway stenosis allows an 18% increase in minute volume at generated airway pressures which are the same as or lower than those when using 100% oxygen.
vii] Usefulness of helium-oxygen mixtures in the treatment of mechanically ventilated patients. Jolliet P, Tassaux D. Curr Opin Crit Care. 2003 Feb;9(1):45-50