Patients on mechanical ventilation may receive medications delivered via aerosol in-line with the patient-ventilator circuit. Some ventilators are not outfitted with a nebulizer port which propels the aerosolized medication and compensates for the additional added
flow. Consequently, an external flow source must be used to drive the nebulizer. Hypothesis- Utilizing an external flow source to deliver aerosolized medications will affect patient-ventilator trigger synchrony.
Methods
A simulated spontaneous breathing model was utilized consisting of a dual chamber, double TTL test lung (Michigan Instruments). One test lung (driver) was powered by a Puritan Bennett 840 (PB840) ventilator (Tyco HealthCare, LLC.) using two “models” to generate spontaneous breathing of a second test lung connected to another PB840 with the following settings: Spontaneous Mode, Pressure Support 5 cmH20, PEEP 5 and baseline trigger 2lpm (flow trigger testing) and 2 cmH2O (pressure trigger testing).
Driver Model 1: “Decreased Respiratory Drive” ACPC, PC 5cmH2O, RR 12, I-time of 1.0 second, Rise time 1%, and PEEP of zero.
Driver Model 2: “Vigorous Respiratory Drive” ACPC, PC 25cmH2O, RR 12, I-time of 1.0 second, Rise time 60%, and PEEP 5.
A Hand Held Nebulizer device was placed 18 inches proximal to the “Y” on the inspiratory limb and was connected to a flow-meter.
Test conditions consisted of allowing the spontaneous model, set on the baseline trigger setting to capture all 12 breaths with no trigger asynchronies. Once this was established the external flow-meter was turned on at 8 lpm, and the ventilator was observed for failure to trigger and/or inspiratory delay time asynchrony.
Results
Model 1: Out of 38 trigger titrations (19 Flow, 19 pressure, 2.0-to-0.2, 0.1 increments) there was 38 trigger asynchronies. There was no statistical difference when comparing a flow or pressure trigger in regards to failure to trigger (p 0.17) and inspiratory delay time asynchronies (p 0.17).
Model 2: The ventilator was able to capture all breaths without any failure to trigger or inspiratory time delay asynchronies.
Conclusion
The results of this study validate that introducing an external flow source into the inspiratory limb of the patient ventilator circuit; the additional flow can generate trigger asynchronies in patients wi
th a decreased respiratory drive.
