Abstract
Background:
The use of ventilators without tubing compensation is abundant within the hospital and home care settings. Tidal volume (VT) displayed on these ventilators is often an estimate and does not account for volume lost within the tubing. An external monitoring device can be added to a circuit for accurate volume measurements but this can be cumbersome for infant and pediatric patients. We trialed a simple equation to estimate VT delivered to the patient with the Trilogy 202 non-compensated, single limb circuit.
Methods:
A Philips Trilogy 202 ventilator and Fisher & Paykel 202 circuit with Philips Whisper Swivel was connected to a Michigan Instruments test lung. Test lung setting were at BTPS with the resistance RP50, and compliance 0.005L/cm H2O. The tubing compliance factor (TCF) of the circuit was determined using a Maquet Servo-i pre-use check at 37 degrees C and humidified. The TCF determination was done 3 times and values averaged. We simulated 4 scenarios using the following Trilogy and test lung settings. Ventilator settings were as follows for trial 1; PIP 15, PEEP 5, RR 30 Trial 2; PIP 25, PEEP 5, RR 20 Trial 3; VT 50, RR 30, PEEP 5 Trial 4; VT 200, RR 15, PEEP 10. 10 trials were performed for each setting. Data was collected using the Michigan Instruments PneuView 3.2 software. A novel equation was utilized to estimate delivered VT loss: 1. PIP-PEEP=ΔP 2. ΔP x TCF (1.5) = volume loss 3. Set VT- Volume Loss=Calculated VT The results from the Trilogy displayed VTe, the equation above and from the PneuView software were then compared.
Results:
See table for details. All simulated trials displayed consistency in measured and monitored values. On average, the displayed VT was inaccurate and was 27% more than the measured volumes. The calculated VT was on average more precise, within 5% of the measured volumes.
Conclusions:
Using a novel bedside calculation, providers can better estimate actual tidal volume delivered to the patient that accounts for volume loss in uncompensated circuits. While this equation is specific to the 202 circuit, it can be replicated for virtually any other circuit available. This calculation negates the need for additional equipment and dead space to be used to obtain the same values. Opportunity exists to program EMRs to perform this calculation at the bedside automatically.
This table shows the average VT values form 4 trials, along with their correlating ventilator settings, as well as the percent change from the disaplyed and calculated VT in related to the measured VT. View all access options for this article.Average Diaplayed, Measured and Calculated Tidal Volmes
Trial
Trilogy Settings
Average Displayed VT (A)
Average Measured VT (B)
Average Calculated VT (C)
% Change (A to B)
% Change (B to C)
1
PC 15, PEEP 5, RR 30, Ti 0.5s
55.5 mL
40.5 mL
40.7 mL
27.0%
.5%
2
PC 25/5 RR20 Ti0.8s
125.7 mL
101 mL
112.2 mL
19.6%
9.9%
3
VC VT50 RR30 Ti0.3 PEEP5
48 mL
30.5 mL
33.9 mL
36.5%
10.2%
4
VC VT200 RR15 Ti1.0 PEEP10
181.9 mL
136.5 mL
135.6 mL
24.9%
.6%
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