Verifying Delivered Versus Set Tidal Volumes With Pediatric Acute Care Ventilators

Abstract

Background:

With a previously accepted abstract, our institution has continued to use a novel calculation to estimate tidal volume (V_T) loss within the circuit during mechanical ventilation on a non-compensated circuit with active humidification. While the Trilogy 202 was most widely used in our pediatric patient population, an active recall resulted in many patients switching to the LTV 1200 ventilator. We aimed to replicate the prior study with the LTV 1200 dual limb non-compensated circuit with active humidity to validate our estimated V_T calculation in the Trilogy 202.

Methods:

In an IRB-exempt bench study, two models were used: model 1 with a Vyaire 15 mm patient circuit without PEEP and model 2 with a Vyaire 22 mm patient circuit without PEEP, both with a FandP MR850 heater interfaced with a Michigan Test Lung (MTL). A tubing compliance factor (TCF) was determined by using a Getinge Servo U pre-use check (heated and humidified to 37°C) to get a compliance factor of 0.55 mL/cm H₂O for the 15 mm circuit and 0.99 mL/cm H₂O for the 22 mm circuit (performed 3 times and averaged). Four trials were simulated using the following LTV and MTL settings. The MTL was set with resistance RP50, and compliance 0.005L/cm H₂O and ventilator settings were Setting 1: PIP 15, PEEP 5, RR 30. Setting 2: PIP 25, PEEP 5, RR 20. Setting 3: V_T 50, RR 30, PEEP 5. Setting 4: V_T 200, RR 15, PEEP 10. Ten trials were performed for each setting. Data was collected using the Michigan Instruments PneuView 3.2 software and LTV 1200 display. Equation utilized to estimate delivered V_T loss: 1. PIP-PEEP = Delta P. 2. Delta P x TCF (0.99 or 0.55) = Volume Loss. 3. Set V_T - Volume Loss = Calculated V_T. The results from the LTV displayed VTe, the calculated V_T and data from the MTL software were compared.

Results:

On average, the displayed VTe was inaccurate, < 10% more than the measured volumes (Table 1). The calculated V_T was on average less precise, 15-20% difference from the measured volumes.

Conclusions:

While using a novel bedside calculation has been extremely successful with a non-compensated single limb circuit, it did not prove accurate with a dual limb circuit. Further studies should be done to test other ventilators and circuits that do not have tubing compensation.

MODEL 1 TRIAL	LTV SETTINGS	MEAN Displayed VT (A)	MEAN Measured VT-PneuView (B)	MEAN Calculated VT-TCF 0.55 (C)	% Change (A to B)	% Change (A to C)	MEAN Volume Loss
1	PC 15, PEEP 5, RR 30, Ti 0.5	36mL	32.8mL	30.5mL	8.90%	15.28%	5.5mL
2	VC VT 50, RR 30, PEEP 5, Ti 0.3	49.2mL	46.2mL	40.4mL	6.10%	17.89%	8.8mL
MODEL 2 TRIAL	LTV SETTINGS	MEAN Displayed VT (A)	MEAN Measured VT-PneuView (B)	MEAN Calculated VT-TCF 0.99 (C)	% Change (A to B)	% Change (A to C)	MEAN Volume Loss
3	PC 25, PEEP 5, RR 20, Ti 0.3	112.6mL	105.2mL	92.8mL	6.70%	17.58%	19.8mL
4	VC VT 200, RR 20, PEEP 5, Ti 1.0	166.6mL	149.6mL	133.93mL	10.20%	19.61%	32.67mL