The Science Journal of the American Association for Respiratory Care
BACKGROUND/HYPOTHESIS: Non-invasive mask ventilation commonly uses specially designed bi-level pressure targeted ventilators. Adaptation of a conventional ventilator for this purpose offers the advantages of a double limb circuit (ie less CO2 rebreathing), more precise FiO2 delivery, and the immediate availability of a conventional ventilator should intubation be required. We hypothesized that a conventional ventilator (TBird AVS System - Thermo Respiratory Group, Palm Springs, CA) set in the pressure assist/control mode (ie pressure targeted - time cycled) could function effectively as a non-invasive positive pressure ventilator (NPPV) in patients with acute exacerbation of COPD. PATIENT POPULATION: Consecutive patients that presented to the Emergency Department with acute exacerbation of COPD were studied. Entry criteria included dyspnea, respiratory rate >25, use of accessory muscles or abdominal paradox, and moderate hypercarbia (pH < 7.35 with PaCO2 > 45mmHg). Patients were excluded if they were hypoxemic secondary to pneumonia, if they exhibited signs and symptoms of congestive heart failure, or if they were either uncooperative or incoherent.
Methods: The ventilator was equipped with a conventional double limb circuit with the addition of a full-face mask and supportive headgear attached to the wye (patient connection adapter) of the circuit. Pressure assist/control ventilation was attempted for at least 90 minutes with the range of ventilator settings as follows: FiO2(0.30 - 0.40), Inspiratory Pressure (10-14 cmH2O), PEEP (3-5 cmH2O). In three patients, no backup rate was provided; in the other two, a rate of 14 was set. Pre and post treatment blood gas and vital sign data were analyzed by paired t tests.
Results: A total of 5 patients were enrolled and successfully ventilated by NPPV with the conventional ventilator. Following treatment, there were significant reductions in PaCO2, blood pressure (BP) and respiratory rate (Table):
|Mean Values (±SD)|
|Pre Therapy||Post Therapy||Change|
|pH||7.27 (±0.06)||7.32 (±.05)||0.05 *|
|PaCO2||82.4 (±17)||70.8 (±19)||-11.6 *|
|FiO2||0.63 (±.3)||0.32 (±.07)||-0.30|
|P/F Ratio||180 (±47)||249 (±53)||69|
|HR||117 (±25)||119 (±27)||2|
|BP||156 (±18)||140 (±19)||-12 *|
|RR||38 (±10)||23 (±3)||-15 *|
None of the 5 patients required intubation. Only 2 were admitted to the ICU (3 days or less duration) and all were discharged from the hospital within 5-9 days after admission. CONCLUSION: A conventional ventilator in the pressure assist/control mode can be a safe and effective non-invasive mask ventilator, often avoiding the need for an artificial airway and the resultant risks involved.