2001 OPEN FORUM Abstracts
HelioxVentilation in a Dog with Induced ARDS
Nisar Ashraf,Meka Brewer, Muhammad R. Khan, Respiratory Therapy Program, Indiana University,Jeff Attwood, RRT, Respiratory Care, Clarian Health, Linda Van Scoder, EdD,RRT, Respiratory Therapy Program, Schools of Allied Health Sciences and Medicine,Indiana University.
BACKGROUND Evidencehas suggested that smaller tidal volumes and higher end-expiratory lung volumesmay protect adult respiratory distress syndrome (ARDS) patients from furtherventilator associated lung injury and may improve outcomes. Heliox (a mixtureof helium and oxygen) has been shown to decrease airway resistance in intubatedpatients, and relieve dyspnea in nonintubated patients. In addition, carbondioxide elimination is enhanced due to its rapid diffusion through heliox. Thepurpose of this study was to evaluate whether the use of reduced tidal volumeventilation with heliox in an ARDS induced lab animal would result in improvedventilation and decreased PCO2 levels compared to ventilation with an O2/N2mixture.
METHODS A trialwas conducted on a hound weighing 25 kilograms. Sodium phenobarbital (30 mg/kg)and pancuronium bromide (0.1 mg /kg) were used to initiate anesthesia and paralysis.ARDS was induced by infusing oleic acid (0.12ml/kg) into the right atrium overfive minutes. A Siemens 300A ventilator was utilized based on previous studiesdemonstrating that the use of 80%He/20%O2 with this machine had no effect ondelivered tidal volume or FIO2 when used in a volume controlled mode. Initialventilator settings were tidal volume 300ml (12cc/kg), f-14, 30% O2 and 3 cmPEEP. O2 and PEEP levels were adjusted to maintain oxygenation as the degreeof lung injury progressed. Stabilization occurred at a mixture of 70% O2/30%N2 with a resultant PaO2/FiO2 ratio of <200confirming ARDS. At this point the dog was alternated between heliox 70%O2/30%He and 70%O2/30%N2 at varying tidal volumes and arterialblood gases were collected and analyzed.
RESULTS Therewas little difference in pH or PaCO2 between heliox and O2/N2at the various ventilator settings. (see Table)Mean pH and PaCO2 at VariousVentilator Settings for Heliox vs O2/N2
|VT(ml) / PEEP (mmHg)||HelioxpH||O2/N2pH||HelioxPaCO2||O2/N2PaCO2|
|300 / 7.5||7.10||7.12||60.9||58.6|
|300 / 10||6.99||6.99||81.0||82.8|
|200 / 15||6.87||6.87||118.3||130.0|
EXPERIENCE Becauseof its physical characteristics, we had expected heliox ventilation to be superior.One possible explanation why this did not occur may be related to the moderatelylow concentration of helium (30%) being delivered. Revisions to our study protocolare being evaluated prior to performing further research.
CONCLUSION Theuse of heliox did not improve ventilation in a dog with induced ARDS.