INTRODUCTION:In severe asthmatic exacerbations requiring intubation, dynamic hyperinflation not only increases the risk of pneumothorax from high peak airway pressures, but also impedes the clearance of carbon dioxide through ineffective ventilation. Occasionally, the standard therapies of steroids, continuous bronchodilators, aminophylline, paralysis, and manipulation of ventilator settings to achieve the longest expiratory time are not enough to stabilize the patient. One potentially helpful modality which has not been well studied in the literature is the use of a helium-oxygen mixture (Heliox) for mechanical ventilation of asthmatics. There are only a few case reports in the literature which address the use of Heliox in intubated asthmatics, and only with continuous administration. We describe a case of an intubated asthmatic patient in whom we successfully used only intermittent Heliox.
CASE PRESENTATION:A 58-year-old male with a history of severe asthma presented with wheezing and shortness of breath. Due to severe respiratory acidosis and impending fatigue, he was intubated and started on methylprednisolone, bronchodilators, and magnesium sulfate. His initial peak airway pressure in the ICU was 46 cmH20, and pCO2 was 78 mmHg. Sedation was increased, and aminophylline plus vecuronium drips were added. Despite all above measures and optimization of mechanical ventilation to achieve maximal expiratory time, his intrinsic PEEP was still 22 cmH20 after 3 days of therapy. Continuous 70:30 Heliox was started via a special adaptor on the Avea ventilator, but after 6 hours, the decision was made to switch to intermittent use due to a limited hospital supply. Heliox was used one hour before, during, and one hour after each bronchodilator treatment. The initial use of continuous Heliox dramatically reduced peak airway pressure and auto-PEEP to 17 cmH20 and 2 cmH20 within one hour. This benefit was sustained over the next two days despite the use of only intermittent Heliox. Unfortunately, due to severe generalized weakness from steroid/vecuronium-induced myopathy, successful weaning could not be achieved and the patient eventually required a tracheostomy.
DISCUSSIONS:Helium is a light-weight inert gas which decreases airways turbulence and facilitates diffusion due to its kinsematic viscosity. When mixed with oxygen, helium can theoretically decrease airways resistance, reduce hyperinflation, and improve CO2 clearance, all attractive attributes for the treatment of obstructive lung diseases. Several studies have evaluated the physiological effects of Heliox in patients who are mechanically ventilated for severe COPD. They found that Heliox reduced dynamic hyperinflation, peak airway pressure, work of breathing, and ventilator days. In intubated adult asthmatics, however, there are only a few cases series which demonstrate this benefit. The most impressive data was published by Gluck et al, in which the use of Heliox in seven intubated asthmatics reduced pCO2 by an average of 35.7mmHg in 22.2 minutes, and peak airway pressures by an average of 33 cmH20 in 2.5 minutes. However, the Heliox was administered continuously.
CONCLUSION:Our case report demonstrates that we were able to achieve similar endpoints with only intermittent Heliox administration. This may be due to the improved deposition of albuterol in the more distal airways when Heliox is used as the vehicle of nebulization, as was demonstrated by Goode et al with an in vitro lung model of obstructive lung disease. Ultimately, this could be a more cost-effective way of using Heliox as it would require less helium and less respiratory therapy man-power. A randomized controlled trial of continuous versus intermittent Heliox administration should be performed to resolve this question.
DISCLOSURE:Ashish Patel, No Financial Disclosure Information; No Product/Research Disclosure Information