The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

THE EFFECTS OF HELIUM-OXYGEN MIXTURES IN PEDIATRIC PATIENTS IN STATUS ASTHMA TICUS REQUIRING MECHANICAL VENTILATION.

Mark Rogers BS RRT RCP Tom Malinowski BS RRT RCP Shamel Abd-Allah MD Loma Linda University Children's Hospital, Loma Linda, California 92354.

Introduction: Patients in severe status asthmaticus (SA) may require continuous mechanical ventilation (CMV) for life threatening ventilatory failure. Mechanically ventilated patients in SA are at risk of air-trapping, elevated peak inspiratory pressures (PIP), prolonged expiratory phase, auto-PEEP, and barotrauma. Low density helium-oxygen (HO) gas mixtures have been advocated to aid ventilation in patients with airway obstruction. Little has been published on the use of HO in mechanically ventilated patients in SA. Study Objective: This study was designed to examine the effects of HO on ventilatory parameters and blood gas indices in CMV patients in SA. Methodology: Fifteen patients in SA requiring CMV admitted to our pediatric intensive care unit between September 1994 and May 1997 were enrolled in this study. Patients were stabilized on CMV, bronchodilators, corticosteroids and antibiotics as indicated. Hypercapnea was permitted, keeping the arterial blood pH >= 7.30. Arterial blood gas and PIP measurements were taken prior to being placed on HO and immediately after. Helium and oxygen were connected via a wye and attached to the low pressure inlet of the Servo 900C. Helium and oxygen flows were titrated to maintain the desired FIO_{2}. The group's FIO_{2} ranged from .30 to .50, FIHe ranged from .50 to .70. Ventilator settings were not changed between pre and post measurements. Clinically, mechanical tidal volumes were not corrected for the decreased density of the gas. A correction factor for tidal volume (Kirmse et. al, Respir Care 1996;41(10): 954.) was utilized to compare minute ventilation (VE) retrospectively. Results: HO resulted in a statistically and clinically significant improvement in ventilation indices (PCO_{2}, pH) (p < 0.05). PIP was reduced by a statistically significant amount (p < 0.05). Despite no mechanical rate changes, VE increased by 20% when corrected for the lower density HO; but this was not considered statistically significant (p=0.07).

Parameter PCO_{2} - mm Hg pH PIP - cm H_{2}O VE - liters

Pre HO 65.1 ± 24.3 7.26 ± 0.14 39.2 ± 6.8 3.77 ± 1.1

Post HO 52.1 ± 20.1 7.36 ± 0.13 33.4 ± 5.1 4.58 ± 1.4

± Standard deviation

Conclusions: 1) HO mixtures increase ventilation. 2) HO mixtures may reduce the elevated PIP typically associated with SA.

OF-97-164

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