2005 OPEN FORUM Abstracts
DESCRIPTION OF A DEVICE TO SIMULATE PRESSURE VOLUME CURVE INFLECTION POINTS USING A MICHIGAN TTL TEST LUNG
Mark Siobal BS RRT, Respiratory Care Services, San Francisco General Hospital, UCSF Department of Anesthesia, William Wagner BS RRT, Draeger Medical
Background: Automated pressure volume curve (PVC) maneuvers are available on several ventilator platforms. Low inspiratory flow maneuvers are can be performed by manipulating settings on some ventilators. Simulation of a PVC with lower and upper inflection points on a Michigan TTL is not possible because the set compliance is linear through the respiratory cycle. We describe a simple device that alters the compliance curve on a Michigan TTL during a low flow PVC maneuver that allows simulation of a lower and upper inflection point.
Method: A unidirectional flow circuit utilizing a threshold resistor 15 cm H2O PEEP valve (Vital Signs Inc., Totowa, NJ) and two one-way valves (Hudson RCI, Temecula, CA) are assembled in a closed loop such that flow into the device is diverted through the PEEP valve and into the test lung. An Evita XL ventilator automated PCV procedure with Starting Pressure of 5 cm H20, Pressure Limit of 60 cm H20, Flow of 4 L/min, and Volume Limit of 800 mL is used. The ventilator is connected in series to the device and then to a single chamber of the test lung (compliance set at 20 mL/cm H2O) via a 8.0 mm ETT. Following the start of the maneuver, as ventilator circuit pressure exceeds the PEEP valve threshold, the PEEP valve opens to the test lung chamber, increases the slope of the compliance curve, and simulates the lower inflection point. As the test lung chamber fills, a clamp positioned on the test lung volume indicator scale impedes the rise of the chamber plate, decreases the slope of the compliance curve, and simulates the upper inflection point. The simulated PVC morphology can be altered by changing the threshold of the PEEP valve.
Results: This simple device allows repetitive PVC simulation with a lower and upper inflection point and can be used for demonstrating PVC maneuvers, developing user competency in performing the technique, and training users in interpretation of the results.