1998 OPEN FORUM Abstracts
THE EFFECTIVENESS OF THE MISTY OX HIGH FIO_{2} - HIGH FLOW NEBULIZER IN DELIVERING HIGH OXYGEN CONCENTRATIONS.
Jason T. Higgins, BS, CRTT; John A. Hernandez, BS, CRTT; Jay I. Peters, MD; and David C. Shelledy, PhD, RRT. The University of Texas Health Science Center at San Antonio.
BACKGROUND: The Misty Ox (MO) high FIO_{2} - high flow nebulizer (MMCA, Cosa Mesa, CA) was developed to overcome shortcomings of conventional air-entrainment devices. The MO is designed to deliver FIO_{2}s from .60 to .96 with total gas flows from 42 to 80 L/min. We sought to determine the actual delivered F_{D}O_{2} when using the MO via aerosol mask in normal subjects. METHOD: Following informed consent, 23 healthy volunteers, ages 22 to 41, were placed on a MO connected to 54" of large bore tubing and a standard aerosol mask (SIMS, Ft. Myers, FL). Prior to initiation of the MO, each subject had a 10 french nasal catheter (NC) inserted through the nares with the tip positioned immediately above and behind the uvula. Oxygen therapy was then initiated at a set FIO_{2} of .60, .75 and .96 at 40 L/min flow using a high-flow flowmeter (Precision Medical, Inc., Northampton, PA) for a period of five minutes at each FIO_{2}. Gas was analyzed at the MO outlet and at the subjects' lip using a previously calibrated oxygen analyzer (Hudson RCI, Temecula, CA). With the subject breathing normally, a 180 ml gas sample was then aspirated from the NC to a "T" piece and oxygen sensor. Three pharyngeal gas samples were obtained at each FIO_{2} setting and the mean values were calculated. Results: The means, standard deviations and ranges for the analyzed oxygen concentrations were:
Misty Ox High FIO_{2} - High Flow Nebulizer via
Aerosol Mask at 40 L/m
Location of Gas Analysis
Nebulizer Outlet Subjects Lip
Set FIO_{2} .60 .75 .96 .60 .75 .96
Analyzed FIO_{2}* .59 .70 .89 .58 .68 .87
(SD) (.02) (.02) (.01) (.02) (.03) (.02)
Range .54- .64- .87- .53- .62- .81-
.62 .74 .93 .60 .72 .91
Oropharynx
Set FIO_{2} .60 .75 .96
Analyzed FIO_{2}* .53 .63 .77
(SD) (.03) (.05) (.09)
Range .46- .50- .56-
.57 .72 .88
* mean (SD) of all subjects
Based on pharyngeal gas analysis, the F_{D}O_{2} averaged 7% less than the set value on .60, 12% less than set on .75 and 19% less than set on .96. Mean FIO_{2} analyzed at the lip averaged 5-10% greater than pharyngeal F_{D}O_{2}. Conclusions: Actual delivered F_{D}O_{2} when using the MO nebulizer can vary considerably from the set value. Care should be taken when interpreting patients clinical response to oxygen therapy when using this device in that patients may be receiving an F_{D}O_{2} much less than anticipated based on the nebulizer setting.
The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.