1995 OPEN FORUM Abstracts
EXPIRATORY TRACHEAL GAS INSUFLATION (E-TGI): A PROTOTYPE DEVICE FOR USE WITH THE PB 7200AE VENTILATOR.
V.Riggi, RRT. CBET; H.Imanaka, MD; R.Ritz, BA, RRT; D.Hess, PhD, RRT; R.M.Kacmarek, PhD, RRT. Respiratory Care and Anesthesia, Massachusetts General Hospital and Harvard Medical School, Boston, MA.
TGI has been suggested as a possible method to reduce PaCO_2 and improve PaO_2 in mechanically ventilated patients with acute respiratory failure. TGI may be continuous or phasic (during exhalation only). The consequences of continuous TGI are increased V_T and PIP. Phase specific or E-TGI was explored as a possible solution to this problem.
Methods: An external 3 way solenoid was wired to the exhalation valve solenoid of the PB7200AE ventilator (PB sol-4) which provided the phasic electric signal needed to energize and de-energize the TGI solenoid. During inspiration the TGI solenoid was energized and the gas supply in the Common (COM) port flowed out the Normally Closed (N.C.) port. During exhalation the solenoid was de-energized and the flow was diverted to the Normally Open (N.O.) port. The source flow to the COM port was supplied by a blender to a flowmeter through a humidifier (Cascade 1A). A #5 French catheter inserted into an ETT was connected to the N.O. outlet. The N.C. outlet provided a path to atmosphere to which we attached an identical #5 French catheter. Delivered flow pattern and system pressure in the TGI design were determined. Appropriate location of the humidifier was explored.
Results: With the solenoid placed downstream to the humidifier, the flow pattern resembled a square wave with a rise time of 120 ms and a fall time of 210 ms. When placed upstream the wave form was severely dampened and did not return to zero. As flow increased, catheter resistance created a rising back-pressure in the TGI system. PIP and V_T were significantly smaller in E-TGI than in continuous TGI (top table). Delivered flow was nearly the same as the set value (bottom table). The ventilator's diagnostic software did not generate any error codes after more than 72 hours of testing.
ER E R
C-TGI E-TGI noTGI C-TGI E-TGI noTGI C-TGIE-TGI noTGI
TGI (L/min) 12 12 012 12 01212 0
PIP (cmH_2O) 39.829.328.241.429.229 31.2 28 28
V_T(L)0.51.36 .39 .61 .38 .42 .58 .50 .59
ER: C=02 L/cm H_2O, R=20 cm H_2O/L/s; E: C=.02 L/cm H_2O, R=5/cm H_2O/L/s;
R: C=05 L/cm H_2O, R=20 cm H_2O/L/s
TTL lung model. PB7200AE ventilator, PCV 20 cm H_2O, Rate 15/min, +10 peep, FiO_2 21%, Tinsp 2 seconds, ETT ID 8mm.
TGI flow (L/min) 4 8 10 12
TGI system pressure (psi) 6.3 14.5 19.3 24.2
TGI catheter (L/min) 4.4 8.19.511.7
Conclusion: Our system provided a consistent phasic square wave of expiratory TGI with minimal manufacturing. Further evaluation of the humidifying system as well as any possible consequences from attaching to the exhalation valve signal must be studied.