The Science Journal of the American Association for Respiratory Care

2001 OPEN FORUM Abstracts

Effect of Internaland External Nebulizer Flow on Tidal Volume (Vt) Delivery During MechanicalVentilation (MV)

Robert S. CampbellRRT, FAARC, Paul N. Austin PhD CRNA (Lt Col USAF), Richard D. Branson, RRTFAARC, Jay A. Johannigman MD, Fred A. Luchette MD, Sandra L. Miller MD, KennethDavis Jr. Md. University of Cincinnati, Cincinnati, OH 45267-0558

BACKGROUND:Delivery of inhaled medication is common during MV. Manu new vents provide aninternal net (INT NEB) that provides preset neb flow during inspiration. A continuousexternally prodvided gas flow is used to power a neb (EXT NEB) on vents thatdo not have an INT NEB. We designed a bench study to evaluate the volume andpressure delivery to the lung during use of both INT NEB and EXT NEB use andto determine the effect of ventilator mode

Methods: Fivevents were evaluated: 300 (Siemens), 849 and 720 (Puritan-Bennett), Evita 4(Drager), and Galileo (Hamilton Medical). Each vent was set to ventilate oneside of a two chamber test lung (TTL, Michigan Instruments) at a compliance9C) of 50 ml/cmH2O and resistance (R) of 20 cmH2O/L/sec. Vents were set to aCMV rate of 15, PEEP of 10 cmH2O, FiO2 of 0.60, and inspiratory times (Ti) of1.0 and 2.0 sec. Three modes were tested: VCV st to 450, PCV set to ÆP of 20cmH2O, and dual control (DC) with Vt targetde of 450. A pneumotach and pressuretransducer were placed between the circuit and TTL to measure flow, volume,and pressure delivered to the lung. Peak inspiratory pressure and VT measuredby each vent was also recorded. FiO2 entering the TTL was measured using a ZirconiumO2 analyzer. Data was recorded at baseline (no neb), with INT NEB on, and withEXT NEB lfow of 8 lpm (O2). All neb flow was injected into the inspiratory limb,10" prox to the wye, via a Mini-neb (Salter LAbs). Five breaths at eachcondition were recorded.

Results: Only7200, Evita 4, and Galileo have INT NEBs. Vt delivery to the lungh increasdby 27±1% and 52±1% during VCV with Galileo with Ti of 1 and 2sec, respectively with INT NEB. INT NEB use did not change lung Vt by more than8% with any other vent or mode use. INT NEB use did not result in large changesinFiO2 (>3%) with any vent or mode tested. USe of EXT NEB with VCV increasedlung Vt by 36±4% with Ti of 1 and by 64 ±8% with Ti of 2 (allvents). EXT NEB used with PCV increased lung Vt by 14 ±2% at Tiof 1 (7200) and by 13 ±2% at ti of 2 (300, 7200, Evita 4). EXT NEB usedwith DC increased Lug Vt by 35%±3 at Ti of 1 and by 62% ±4 atTi of 2 (300, 840, E4). EXT NEB cased an average increase in FiO2 of 14 ±4%(300, 840, 7200, Galileo), Ext NEB caused FiO2 to increase by 22 ±3%with Evita 4. Vent measured Vt was within 10% of delivered Vt for all ventswith NO NEB or with INT NEB use. Galileo measured Vt was within 10% o fdeliveredat all settings. Measured Vt exceeded delivery Vt by >50% when EXT NEB wasused with the 300, 840, 7200 and E4 with all modes and Tis.

DISCUSSION/CONCLUSION: TheINT NEB on the Galileo is not “volume compensated”, resultin gin additionalVt delivery during VCV. EXT NEB increases delivered Vt in all cases, exceptPCV with Ti of 1 (all vents), PCV with Ti of 2 (840, Galileo), and DC with T1of 1 and 2 (Galileo). Clinicians should be aware that delivery of inhaled medicatinby nebulization may affect the measurement and delivery of Vt and FiO2 differently,depending o the vent used, mode employed, Ti, and NEB delivery technique.


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