The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

PRESSURE-VOLUME CHARACTERISTICS OF THE 3100B HIGH FREQUENCY OSCILLATOR USING TWO DIFFERENT BENCH MODELS TO MIMIC AIRWAY RESISTANCE

Tom J. Blackson1, Joseph A. Ciarlo1, Tim Cox2, Thomas H. Shaffer3; 1Allied Health Education, Christiana Care Health Services/DT&CC, Newark, DE; 2Respiratory Care, duPont Hospital for Children, Wilmington, DE; 3Nemours Research Lung Center, Nemours Biomedical Research, Wilmington, DE

Background: One ventilation strategy that is espoused for use with the 3100B high frequency oscillator (HFO), is to adjust the pressure amplitude (ΔP) based upon “wiggle factor”. The assumption is that ventilation increases with increasing ΔP. We have previously reported a sigmoidal shaped pressure-volume response from the 3100B during ΔP adjustment using a Michigan test lung model with parabolic resistors (PR) to mimic airway resistance. One critique focused on the potential for the PR to cause the artifactual “flat” volume response at high ΔP. Purpose: To evaluate the pressure-volume characteristics of the 3100B HFO using two different bench models of airway resistance (RAW) in a simulated ARDS patient. Materials & Methods: A bench model of ARDS was created with a Michigan test lung, (Michigan Instruments, Grand Rapids, MI) set with a compliance of 0.02 L/cm H2O. All trials were conducted with a mean airway pressure: 30 cm H2O, bias flow: 30 L/min., and inspiratory time: 33%. We evaluated frequencies of 3 through 6 HZ in combination with ΔPs between 30 and 120 cm H2O adjusted in 10 cm H2O pressure increments. Raw was varied using PR #5 and #20 for one lung model and endotracheal tubes (Mallinckrodt, St. Louis, MO) with an ID of 6.0, 7.0, and 8.0 mm for the second model. A hot-wire anemometer flow sensor, (Florian, Acutronics), was placed between the ventilator “Y” and the airway resistor for volume measurements during each trial. Twelve consecutive volume measurements at each test condition were recorded and used for analysis. Results: Incremental changes in VT were inconsistent across the ΔP ranges under all test conditions. VT changes for a 10 cm H2O ΔP change ranged from a minimum of -0.08 mL to a maximum of 58.75 mL with a PR #5 and from -3.92 mL to 65.17 mL with a #8 ET. Consistent with our previous bench model, VT reaches a plateau prior to achieving maximum ΔP under certain combinations of frequency and Raw. Conclusions: Fixed increases in ΔP produce inconsistent changes in VT delivered from the 3100B in both test lung models. Exhaled VT reaches a plateau despite further increases in ΔP under certain combinations of f and Raw. In the absence of bedside VT monitoring, VT plateau can not be identified via ΔP monitoring feedback provided by the 3100B HFO. Clinical management of ventilation and acid/base balance may be delayed if effective increases in VT delivery are presumed to result from increased ΔP adjustments. Clinical study is warranted. Sponsored Research - None

Representative P-V relationship comparing parabolic resistor #5 to #8.0 mm ID OET

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