The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

FORTY PERCENT HELIOXPROVES BENEFICIAL IN A MECHANICALLY VENTILATED ADULT.

Jodette A. Brewer RCP, RRT,Melissa K. Brown RCP, RRT, Sharp Memorial Hospital, San Diego, CA. Sharp Mary Birch HospitalFor Women, San Diego, CA.

Introduction:Helium-Oxygen (heliox) is a low-density gas mixture. Inhalation of heliox reducesairway resistance and the pressure required to overcome resistance.Thisenables ventilationat lower peak pressures. Heliox can decrease the patient?s work of breathingand may improve ventilation to perfusion matching. Carbon dioxide diffuses fourto five times faster through heliox than nitrox; therefore, a greater amountof CO2 will be eliminated per unit of time. The benefits of helioxhave been documented for the treatment of respiratoryfailure due tostatus asthmaticus. Density of helium-oxygen mixtures is lowest at higher heliumconcentrations. Theoretically, for the patient to receive the greatest benefitfrom heliox therapy, the highest possible concentration of heliox should beutilized. At times, heliox is not initiated, due to the need for a higher fractionof inspired oxygen (FiO2), in the belief that a lower concentrationof heliox will not be effective. This case study documents the outcomeof 40/60 helioxconcentration in an intubated, mechanically ventilated, adult asthmatic.

Case Summary:A 71 year-old female presented to the Emergency Department with acute statusasthmaticus. She was started on methylprednisolone intravenously and continuousalbuterol nebulizer treatments. An arterial blood gas sample (ABG) was drawnwith the patient on an aerosol mask while receiving bronchodilator treatments:pH 7.23, PCO266, PO2311, and HCO327. The patientwas electively intubated and ventilated with a Servo 300A ventilator. The ventilatorsettings were Pressure Regulated Volume Control (PRVC) mode, Tidal Volume (VT)500 ml, peak pressure of 32 cmH2O, PEEPof 0, respiratory rate of 14, I:E ratio of 1:3, and 60% FiO2. Onthose settings, arterial pH was 7.24 mmHg and CO2 was 57mmHg. Immediatelyafter 40/60 heliox was initiated, peak airway pressure dropped from 32 cmH2Oto 20 cmH2O. An ABG drawn 85 minutes after initiation of heliox showedimprovement of arterial pH to 7.40 mmHg and CO2 decreased to 37 mmHg.The 500cc tidal volume and all other initial ventilator settings were maintained.

Discussion:This comparatively low concentration of heliox (40/60) lowered the peak airwaypressures in this patient and improved ventilation. The FiO2 wasweaned, heliox percentage increased, and then the heliox was discontinued twohours prior to successful extubation on hospital day three. When toinitiate helioxand the concentration at which to begin, are key components literature has notyet addressed. Solutions may include looking at individual disease processesand specific delivery devices. Previously, we described an adult asthmatic whoshowed an improvement in ventilation with 60/40 heliox. This case study documentsthat a concentration as low as 40/60 heliox was beneficial in a conventionallyventilated adult asthmatic. More research is required to determine which patientswill respond to heliox and what minimal percentage of heliox is required toachieve any beneficial effect.

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