The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts


Jodette A. Brewer RRT, Melissa K. Brown RRT, Sharp Memorial Hospital, San Diego, California; Children's Hospital and Health Center, San Diego, California.

Introduction: Asthma is the cause of more than three million physician visits and 200,000 hospitalizations a year. During an asthma attack the lining of the airways become swollen and the airways produce a thick mucus. The muscles around the airways tighten and make the airways narrower causing bronchoconstriction. This bronchoconstriction leads to ventilation to perfusion (V/Q) mismatch. Heliox is a blend of helium and oxygen. Heliox, being a low-density gas, can allow for additional alveolar ventilation, resulting in improved gas exchange. Frequently this mixture has been used at a high helium percentage to oxygen percentage (79/21 or 70/30) suggesting the best possible results in ventilation. However, many patients are not offered heliox therapy, secondary to the widely held belief that lower concentrations of helium cannot produce sufficient beneficial effects. Using high concentrations of helium limits the FiO2 and many asthmatic patients require more than 30% oxygen. This case study examines the benefit of 60/40 heliox in an intubated adult asthmatic. Case Summary: The patient is a 25-year-old, 59-kg. female, with a history of asthma and a previous intubation. She had been feeling ill for a couple of days, which developed into a sudden onset of shortness of breath. She called 911 and went into respiratory arrest while in route to the hospital. The patient was intubated and placed on mechanical ventilation. Due to extreme bronchial constriction, high peak pressures and low tidal volumes, the patient was placed immediately on Pressure Control Ventilation (PCV) on a Servo 900C. For 19 hours the patient was ventilated and had four arterial blood gases drawn with unresponsive respiratory acidosis. Without any ventilator changes, the patient was placed on a heliox concentration of 60% helium and 40% oxygen (60/40). Arterial Blood Gas results 45 minutes later showed an improved respiratory acidosis, as well as tidal volumes (VT) increasing from 440mL to 670mL. The patients PO2 improved slightly. The following chart summarizes the arterial blood gases pre and post heliox therapy:

Arterial Blood Gas pH PC02 P02 HC03 Sa02
PCV46/0, 1:4 I:E, r.16, 7.22 72 78 28.5 95.6
VT=440, 40% Fi02
PCV46/0, 1:4 I:E, r.16, 7.31 45 81 22.1 97.9
VT=670, heliox (60/40)

Discussion: 60/40 heliox normalized the blood gas values of this intubated asthmatic patient. The benefits of elevated heliox mixtures for patients with asthma are being documented with increasing frequency. This case study documents that a 60% helium and 40% oxygen can provide beneficial effects while maintaining therapeutic oxygen concentrations. More research is required to determine what the lowest effective heliox mixture is required to improve ventilation and respiratory acidosis in an asthmatic patient.