HELI-OX
Helium is a colorless, tasteless, noncombustible, nonexplosive gas that is seven times lighter than air and is generally considered inert as it relates to the body. Helium is a relatively rare natural gas and the cost to administer it for medical purposes is fairly high. 1) Barach was the first to use helium for the treatment of asthma and upper airway obstructive lesions in the larynx and trachea in 1935. 2) Since then it has been primarily used for diagnostic purposes in the pulmonary function lab and for the treatment of acute upper airway obstruction. 3-5 Over the past 12 years numerous papers have been published noting positive results with helium and Oxygen (Heliox) therapy in patients presenting with acute severe asthma and to a lessor extent decompensated COPD.
Patients presenting with acute severe asthma often experience respiratory acidosis and an increased work of breathing (WOB) due to decreased diameter of the airways. The bronchospastic inflammatory process in asthma decreases the diameter of the airways and results in more turbulent airflow leading to increased airway resistance (Raw). Normally Raw is about 3 cmH2O. During bronchospasm, Raw can increase to 30-50 cmH2O. 9 The therapeutic use of Heliox due to its lower gas density and, therefore, less turbulent flow characteristics, may reduce Raw by 28-49% thus decreasing WOB. 9 Heliox also offers enhanced diffusion of carbon dioxide (CO2) 4 to 5 times faster than nitrogen oxygen mixtures, thus in a time dependent fashion facilitates greater reduction in carbon dioxide.
Numerous studies have noted significant decrease in CO2 and an increase in blood pH in patients treated with Heliox therapy. 5,6,7,11 Manthos et al 8 in a study of patients with severe asthma, pulsus paradoxus >15 mmHg, and Peak Expiratory Flowrate (PEF) of <250 LPM noted a significant improvement in pulsus paradoxous and PEF in 15 of 16 patients treated with Heliox. Kass and Terregino 9 performed a prospective, randomized, controlled study of 23 patients presenting to the ED with acute severe asthma. PEF, dyspnea score, heart rate (HR), respiratory rate (RR) and blood pressure (BP) were measured at baseline and at 20, 120, 240, 360 and 480 minutes after gas delivery. Patients were randomized into two groups. One group received 70/30 heliox while the other received 30% oxygen. At the 20 minute mark, there was a 58.4% improvement in the percent predicted PEF (% PEF), a decrease in dyspnea score and RR in the heliox group. There was only a 10.1% increase in % PEF in the oxygen group and no variables improved significantly until the 360 minute measurement. In a study of 12 acute severe asthmatics with acute severe respiratory acidosis (pH <7.35 and CO2 •45 mm Hg), eight responded to Heliox therapy and four did not. 6 Responders were those patients who had a drop in CO2 of •15% and a rise in pH of •0.05. All of the responders presented within 24 hours of the onset of symptoms while three of the four non-responders with prolonged •96 hours of symptoms.
A noteworthy study of seven ventilated patients treated with a 60/40 Heliox mixture showed a dramatic improvement in peak inspiratory pressures and CO2 and pH. 7 Patients were entered into the Helium treatment protocol if they had a pH <7.20, PaO2 > 60 and a PaCO2 >50 mmHg and a persistently elevated peak inspiratory pressure (PIP) in excess of 75mmH20 and persistent hypercapnia and acidosis after one hour of conventional therapy. These patients had a mean decrease in PIP of 32.86 cmH2O within five minutes of Heliox therapy. The mean elapsed time for reduction of CO2 was 22.2 minutes and the mean reduction in CO2 was 35.7 mmHg with a corresponding improvement in pH. These findings in these studies suggest that in acute severe asthma with acute acidosis, Heliox significantly improved PEF, dyspnea, decreased pulsus paradoxus, RR and CO2 with a fairly rapid onset of action. In a specific group of ventilated patients, significant improvements were noted in PIP, CO2 and pH.
For significant therapeutic benefit, helium concentration percentage must be at least 60% with 40% oxygen or a 60/40 Heliox mixture. Many researchers recommend helium concentrations ranging from 60% to 80%. 6-10 At Jewish Hospital, a 65/35 mixture or 70/30 is used per protocol. Conventional oxygen flowmeters will not accurately reflect heliox gas flows. An 80/20-heliox mixture is 1.8 times less dense when compared to 100% oxygen. A 70/30 concentration is 1.6 times less dense. For example, if you set the oxygen flowmeter at 10 lpm while delivering an 80/20-heliox mixture, you will deliver 18 lpm and for a 70/30 concentration you will deliver 16 lpm of heliox flow.
The most commonly used delivery device is an oxygen non-rebreather mask. The rule for Heliox is to deliver enough flow to the mask to keep the reservoir bag well inflated especially during inspiration. This is particularly important during the first several minutes of mask initiation because the patient is often very air hungry during this period and will have a higher respiratory demand.
Heliox may also be delivered to a patient via a mechanical ventilator both in intubated and non-invasive ventilation. 5,6,7,10,12,14 Both volume and pressure modes of ventilation may be used to deliver Heliox. When volume ventilation is used, take into account the actual tidal volume delivered to the patient will vary during the administration of Heliox on all ventilators. Therefore, during volume ventilation you must perform calculations dependent upon the model of ventilator and gas concentration used. It is beyond the scope of this article to offer a detailed discussion of the appropriateness of ventilation with pressure or volume with Heliox or exactly which parameters to assess when making the judgment for its use. Appropriate selection of an ICU ventilator and volume calculations can be found in the references. 14
The primary goal of our Heliox Protocol is to minimize the number of intubations required for patients presenting to the emergency department (ED) with either acute severe asthma or acute upper airway obstruction. Patients presenting to the ED with ASA should first be placed on the ED Bronchodilator Protocol for a period of one hour. If the patient does not improve or worsens and has the following symptoms, the Heliox protocol should be initiated:
pH of <7.35
Respiratory Rate >25 Breaths per Minute
Peak flow <100 Liters per Minute
Patient that exhibits signs and symptoms of respiratory failure e.g. Anxiety, airtrapping or extreme air hunger.
Heliox has a place in the treatment of patients who present to the emergency department with acute severe asthma, specifically those non-intubated patients with a pH of <7.35, RR >25, PEF <100 LPM that exhibit impending respiratory failure and are non-responsive to conventional bronchodilator therapy but do not need immediate intubation. Heliox has a very limited role in intubated patients. Our recommendation for heliox use in the severe asthmatic ventilated patients is only when high PIP persist >50 cmH20 or static pressures are >35 cmH2O despite sedation, bronchodilator therapy and low tidal volume or low pressure ventilator management.
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