The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

MECHANICAL VENTILATION DURING BRONCHOSCOPY: THE IMPACT OF MODE VENTILATION

Mauro R Tucci, MD; Guilherme PP Schettino, MD; Rogerio Souza, MD; Marcelo BP Amato, MD; Carlos RR Carvalho, MD. Experimental Ventilation Lab, Division of Respiratory Diseases, HC/InCor-University of Sao Paulo Medical School, Brazil

Background: bronchoscopy is a useful diagnostic and therapeutic procedure for critically ill mechanically ventilated patients. However, the presence of a flexible bronchoscope (FB) in the ETT decreases the tube inner diameter and increases airway resistance, altering respiratory mechanics. Both volume (VC) and pressure control (PC) modes may be used to ventilate intubated patients during broncoscopy, but limitation related to control of peak airway pressure (PIP) and tidal volume (VT) occurs. Pressure regulated volume control (PRVC, Servo300A) is a new mode that assure a preset VT with a demand flow pattern that, theoretically, may be advantageously used in this situation. Objective: to compare the performance of different ventilatory modes during broncoscopy in a lung model. Method: Two endotracheal tubes (#7.5 and 8.5) were individually connected to the airway of a low compliance (50ml/cmH2O) mechanical lung. The ventilator was set to assure an alveolar ventilation (VEalv) of 5L/min [VEalv= VE -- (150mL x RR)] with respiratory rates (RR) of 12 and 20/min in all tested modes. Square inspiratory flow rate of 45L/min and I:E ratio of 1:2 were used for VC and PC respectively. The measurements were repeated before (control) and after the FB (Pentax15P, 4.9mm of external diameter) was inserted. A VEalv >4.5L/min, proximal peak inspiratory pressure (PIP) <45cmH2O and positive end expiratory pressure (PEEPi) <5cmH2O were defined as optimal targets during control and broncoscopy trials.

Results: all tested modes settings achieved the target parameters during control measurements. Table presents results recorded during broncoscopy simulation.

Mode RR VEalv (l/min) PIP (cmH2O) PEEPi (cmH2O)
# 7.5 #8.5 # 7.5 #8.5 #7.5 #8.5
VC 12 4.5±0.2 4.6±0.2 50.6*±4.7 23.6±3.0 - -
20 4.4±0.2 4.7±0.2 50.2*±5.2 22.0±1.8 2.0±0.1 -
PC 12 1.9*±0.1 3.8*±0.2 11.9±0.4 11.8±0.8 - -
20 0.4*±0.1 2.6*±0.2 9.7 ±0.3 9.7±0.7 - -
PRVC 12 4.7±0.2 4.9±0.3 28.1±2.2 14.6±0.9 1.6±00 -
20 4.7±0.2 5.0±0.2 34.8±2.8 14.8±0.8 4.0±0.1 -
Mean±SD of 12 consecutive breaths; * represents parameters outside of the defined target levels.

Conclusion: the presence of the FB resulted in low VEalv and high PIP during the use of PC and VC respectively, PRVC was able to maintain target ventilatory levels during all simulated conditions.
Funded by: FAPESP, Pronex and LIM-FMUSP

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