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Laboratory and Animal Investigations |

Effects of Fiberoptic Bronchoscopy During Mechanical Ventilation in a Lung Model*

R. Wayne Lawson, MS, RRT; Jay I. Peters, MD, FCCP; David C. Shelledy, PhD, RRT
Author and Funding Information

*From the Department of Respiratory Care (Mr. Lawson and Dr. Shelledy), and Department of Medicine, Division of Pulmonary and Critical Care Medicine (Dr. Peters), University of Texas Health Science Center at San Antonio, San Antonio, TX.

Correspondence to: R. Wayne Lawson, MS, RRT, Department of Respiratory Care, MSC-6248, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78229-3900; e-mail: LAWSON@uthscsa.edu



Chest. 2000;118(3):824-831. doi:10.1378/chest.118.3.824
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Study objectives: To evaluate the effects of fiberoptic bronchoscopy (FOB) on delivered volumes and pressures during mechanical ventilation, utilizing a lung model.

Design: Bench study.

Setting: Laboratory.

Materials and methods: Using varying-sized endotracheal tubes (ETTs), we ventilated a lung model at two levels of compliance utilizing different modes and parameters of ventilation. After establishing baseline measurements, the bronchoscope was inserted and measurements repeated.

Measurements and results: During controlled mechanical ventilation (CMV) with a preset high-pressure limit (HPL), tidal volumes (Vts) were reduced from 700 mL to 0 to 500 mL following insertion of the bronchoscope. Increasing the HPL to 120 cm H2O resulted in a Vt of 40 to 680 mL. Changing from square to decelerating flow waveform resulted in no consistent difference in Vt. Auto-positive end-expiratory pressure (auto-PEEP) of 0 to 41 cm H2O was present under most conditions. Higher rates and lower peak inspiratory flows were associated with higher levels of auto-PEEP. In the pressure-control (PC) mode, using a preset inspiratory pressure level (IP), Vt was reduced from 700 mL to 40 to 280 mL following insertion of the bronchoscope. Maximum IP (100 cm H2O) increased Vt to 260 to 700 mL. Auto-PEEP was less in the PC mode.

Conclusions: Extreme care must be taken when bronchoscopy is performed on a patient receiving mechanical ventilation. Extremely low Vt and significant auto-PEEP may develop unless flow, respiratory rate, mode, and ETT size are carefully selected. The PC mode delivered more volume than did the CMV mode. When performing FOB during mechanical ventilation, the inside diameter of the ETT should be ≥ 2.0-mm larger than the outside diameter of the bronchoscope to maintain volume delivery and minimize the development of auto-PEEP.

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