The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

FUNCTIONAL RESIDUAL CAPACITY (FRC) DURING CONTINUOUS AND EXPIRATORY TRACHEAL GAS INSUFFLATION (TGI).

Yuji Fujino MD, Masaji Nishimura MD, Nobuyuki Tacnaka MD, Ikuto Yoshiya MD. Intensive Care Unit, Osaka University Hospital, and Hyogo College of Medicine

TGI is a method to facilitate carbon dioxide elimination. It may increase expiratory resistance and cause intrinsic PEEP. It is impossible to measure intrinsic PEEP with the existence of TGI, and we evaluated gas trapping by measuring FRC.

Methods: We chose argon washout method to measure FRC of a lung model during both continuous and expiratory TGI. Ten percent argon in oxygen (Ar) and 100% oxygen (O_{2}) cylinders were connected to a crossover solenoid valve in parallel. The outlet of the valve was connected to a ventilator oxygen inlet and a flowmeter for TGI via a Y shape hose. To perform expiratory TGI, the second solenoid valve was placed into the hose between the Y and TGI flowmeter. The valve was controlled by a signal from the ventilator to synchronize with the expiratory valve of the ventilator. Flow and Ar concentration were measured at downstream of the expiratory valve with a hot-wire flowmeter (Minato Medical, Japan) and a mass-spectrometer (Marquette 1100), respectively. Those signals were fed to a microcomputer. The settings of the ventilator were as follows: PCV mode, PIP 15cmH_{2}O, RR 15/min, and T_{1} 1 and 2 sec. with continuous and expiratory TGI of 4, 8, and 12 L/min flow. After Ar concentration in the lung model became constant, the gas was changed to O_{2}. The computer controlled the first solenoid valve to change Ar to O_{2} according to a signal from the ventilator at an end-expiration, and started integration of the signals of flow and Ar concentration, simultaneously.

Results: Table shows FRC in each setting of the ventilator and TGI flow. At T_{1} 1 sec, FRC did not differ significantly during continuous and expiratory TGI. At T_{1} 2 sec, FRC in continuous TGI was significantly greater with all TGI flow. Conclusion: FRC measurement is the alternative method of intrinsic PEEP measurement to evaluate air trapping during TGI. Expiratory TGI caused less dynamic hyperinflation than continuous TGI, and expiratory TGI may be safer.

TGI flow T_{1} 1.0 sec T_{1} 2.0 sec

(L/min) cont. exp. cont. exp.

4 216±21 250±15 496±23 436±6*

8 533±36 573±52 770±12 606±15*

12 550±21 660±31 903±10 713±17*

(ml) (^{*}p < 0.05)

Reference: OF-96-179

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