The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

A COMPARISON OF TOTAL PATIENT INSPIRATORY WORK OF BREATHING (TPiWOB) BETWEEN HELIOX MIXTURES AND AIR DURING PRESSURE SUPPORT VENTILATION (PSV) IN AN OBSTRUCTIVE SPONTANEOUS BREATHING LUNG MODEL.



Vines DL, MHS, RRT; Ditsch KA, BS, 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 determine if TPiWOB is significantly lowered by 80/20, 70/30, or 60/40 heliox mixtures when combined with PSV using a new heliox delivery system in a spontaneously breathing lung model with normal and elevated airway resistance.

METHODS:
WOB was first measured on lung B at tidal volumes of 300, 400, 500, and 600 mL with peak flows varying from 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 these 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 contains mean values and standard deviations for TPiWOB (J/L) and exhaled VT during PSV at various gas mixtures and demanded peak flows.

Gas Source PSV 5 cmH2O PSV 10 cmH2O PSV 15 cmH2O PSV 20 cmH2O
  TPiWOB (J/L) Mean Exhaled VT (mL) TPiWOB (J/L) Mean Exhaled VT (mL) TPiWOB (J/L) Mean Exhaled VT (mL) TPiWOB (J/L) Mean Exhaled VT (mL)
80/20 Heliox 0.55+ .29 a,b 411+ 95 0.24+ 0.23 a,b 498+ 59 0.10+ 0.12 a, b 710+ 40 c 0.05+ 0.07 a, b 984+ 94d
70/30 Heliox 0.63+ .34 a,b 407+ 96 0.33+ 0.30 a,b 485+ 77 0.17+ 0.23 a,b 668+ 114 .07+ .09 a, b 958+ 175d
60/40 Heliox 0.72+ .37 a,b 409+ 98 0.41+ 0.35 a,b 481+ 86 0.22+ 0.28 a,b 681+ 152 0.11+ 0.17a, b 969+ 146d
Air Aptaer 1.03+ .53 402+ 104 0.73+ 0.49 465+ 87 0.53+ 0.49 616+ 159 0.27+ 0.30 956+ 132d
Air Servo i 1.03+ .52 403+ 100 0.71+ 0.49 469+ 80 0.42+ 0.39 646+ 70 0.25+ 0.26 878+ 86

a. Significantly less than air Aptaer b. Significantly less than air Servo i

c. Significantly greater than air Aptaer d. Significantly greater than air Servo i

CONCLUSION: The use of heliox with the heliox deliver system significantly lowered TPiWOB compared to air delivered via heliox delivery system or conventional ventilator at PSV of 5, 10, 15, or 20 cmH2O. The use of heliox mixtures and low levels of PSV via the heliox delivery system may significantly reduce WOB in patients with increased airway resistance.

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