The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

THE EFFECTS OF PEAK FLOW AND AIRWAY RESISTANCE ON TOTAL PATIENT INSPIRATORY WORK OF BREATHING (TPiWOB) DURING PRESSURE SUPPORT VENTILATION (PSV) WITH VARIOUS HELIOX MIXTURES AND AIR IN A SPONTANEOUS BREATHING LUNG MODEL.

Ditsch KA, BS, RRT; Vines DL, MHS, RRT; Sorenson HM, MS, RRT; and Peters JI, MD. The University of Texas Health Science Center at San Antonio. San Antonio, Texas.

BACKGROUND:
The objective of this study was to assess the benefits of various heliox concentrations at different demand peak flows and increased airway resistances.

METHODS:
WOB was first measured on lung B at tidal volumes of 300, 400, 500, and 600 mL and peak flows at 40, 60, and 80 L/min with a sine wave flow pattern, using the Ventrak 1550 Respiratory Mechanics Monitoring System (Novametrix Medical Systems, Inc., Wallingford, CT). Then, WOB, exhaled tidal volume (exhaled VT), and peak inspiratory pressure (PIP) were measured at the same tidal volumes and peak flows for lung B to drive lung A at normal resistance (5cmH2O/L/sec), increased resistance (20 cm H2O/L/sec) and severe resistance (40 cm H2O/L/sec) while lung A received assistance from PSV of 5,10,15, or 20 cm H20. These measurements were made using 80/20 heliox, 70/30 heliox, 60/40 heliox, and air through the Aptaer Heliox delivery system (GE Healthcare, Madison, Wisconsin), and air on the SERVOi (Maquet Inc., Bridgewater, NJ). The respiratory mechanics monitor was set for the various gas concentrations. All equipment was calibrated and checked for leaks before use. TPiWOB was then calculated using this formula: [TPiWOB=WOB(B+A) - WOBB]. TPiWOB was converted from joules to joules per liter (J/L) based on the delivered tidal volume to lung A. An ANOVA with a post hoc follow up test (Newman-Keuls) was used to determine significant differences.

RESULTS:
The following table
Gas Airway Resistance 5 Airway Resistance 20 Airway Resistance 40
  40 L/min 60 L/min 80 L/min 40 L/min 60 L/min 80 L/min 40 L/min 60 L/min 80 L/min
80/20 Heliox .10+ .11 .11+ .12 a .20+ .17 a,b .10+ .13 .18 + .20 a,b .35+ .28 a,b .16+ .20 b .32 + .30 a,b .63+ .38 a,b
70/30 Heliox .10+ .10 .13 + .13 a .25 + .20 a,b .11 + .14 .22 + .23 a, b .48 + .30 a,b .18+ .22 b .42 + .34 a,b .84+ .40 a,b
60/40 Heliox .10+ .12 .13 + .15 a .33 + .21 a .13 + .17 .28 + .27 a,b .61 + .32 a,b .22+ .24 b .52 + .35 a,b .99+ .39 a,b
Air Aptaer .10+ .13 .31+ .19 .73 + .30 .22 + .24 .59 + .30 1.01+ .43 .41+ .34 .95 + .40 1.45+ .59
Air Servo i .13+ .14 .25+ .21 .45+ .28 a .26 + .25 .60 + .33 .94 + .44 .50+ .32 .95 + .43 1.36+ .58

displays mean values and standard deviations for TPiWOB (J/L) during PSV at various gas mixtures and demanded peak flows. There were no significant differences in mean exhaled VT or mean PIP.

a. Significantly less than air Aptaer

b. Significantly less than air Servo i

CONCLUSION: At higher peak flows (60 & 80 L/min) and normal and increased airway resistances, the Heliox delivery system using 80/20, 70/30, and 60/40 Heliox significantly reduced TPiWOB compared to using air with the Heliox delivery system or conventional ventilator. At severe airway resistance benefits in TPiWOB were also seen at peak flows of 40 L/min. TPiWOB may be reduced by using this heliox delivery system at 80/20, 70/30, or 60/40 heliox mixtures in a clinical setting where patients' peak flows and/or airway resistance is increased.

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