The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

PRESSURE ASSIST-CONTROL ON A CONVENTIONAL VENTILATOR ADAPTED FOR NON-INVASIVE MASK VENTILATION.

Robert McConnell, RRT, Jhaymie Cappiello, RRT, Jon Umbdenstock, RRT, Neil MacIntyre, MD, Duke University Medical Center, Durham, NC

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 *
*P<0.05

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.

OF-99-093

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