The Science Journal of the American Association for Respiratory Care
Introduction: The low density property of helium makes it a valuable tool for the treatment of airway obstruction by improving gas mobility around obstructions. This increased mobility has a two fold effect. Gas more readily reaches the alveoli thus allowing for greater gas diffusion. Additionally, the patient work of breathing can be significantly reduced by using a less dense gas. Successful use of helium has been well documented in spontaneously breathing patients; however, its use in conjunction with mechanical ventilation is unclear at present. We would like to present the following case as an illustration of how heliox might be used in conjunction with mechanical ventilation both effectively and safely.
Case Presentation: K.H. is a 13 year old white female with a history of reactive airway disease with no prior history of intubation. She was admitted to our PICU from an outside hospital where she was intubated for respiratory failure. The patient was receiving therapeutic doses of aminophylline, methylprednisolone, ipratropium and continuous albuterol (40 mg/hr). She was sedated and paralyzed. Ventilator management was optimized with the aid of continuous airway graphic monitoring and capnography (CO2SMO Plus; Novametrix Medical Systems, Inc.). The pt was acidotic and hypercarbic (pH 7.16; PaCO2 79 mmHg) on admission. The PaCO2 continued to increase. After eight hours the PaCO2 was 89 mmHg. Capnography showed an ETCO2 of 98. A decision was made at that time to initiate heliox therapy (70% helium / 30% FIO2) in conjunction with mechanical ventilation. The ETCO2 showed an immediate decrease from 98 to 71 mmHg. Arterial blood gas analysis showed a PCO2 of 67 mmHg, a decrease of 22mmHg, in less than an hour. The patient extubated 30.5 hours later. Heliox and continuous albuterol were continued via face mask for another 96 hours. The patient was discharged from the PICU after seven days and discharged home two days later.
Discussion: Mechanical ventilation of patients with status asthmaticus is challenging at best. Care must taken to assure adequate tidal volume delivery without further overdistention of the alveoli. Additionally, when gas densities are altered, the ventilator may be unable to discern the true tidal volume since many ventilators use pressure gradients to determine volumes. We were able to carefully monitor the delivered tidal volumes using the CO2SMO Plus, which is configured to compensate flow measurements for specific gas densities. With appropriately monitored delivery, heliox can be a valuable therapeutic modality for the mechanically ventilated patient with airway obstruction.