We measured changes in airway pressure (Paw) caused by microsurgical instruments introduced into a rigid bronchoscope during high frequency jet ventilation (HFJV). With approval of the institutional Ethics Committee, 10 adults undergoing elective tracheobronchial endoscopy and endosonography during general anaesthesia were investigated. Inflation of an endosonography probe balloon in the left main stem bronchus caused airway obstruction. Pressure measurements proximal and distal to the obstruction were compared after three degrees of obstruction (0%, 50% and 90%) and with two different driving pressure settings. Airway obstruction increased the mean (SD) peak inspiratory pressure (PIP) from 7.5 (2.6) to 9.5 (3.5) mm Hg for 2 atm (P = 0.0008) and from 9.7 (3.7) to 13.0 (5.1) mm Hg for 3 atm (P = 0.0001). Airway obstruction did not alter peripheral PIP (7.2 (4.1) to 7.1 (3.7) mm Hg for 2 atm and 8.8 (4.3) to 9.4 (5.2) mm for 3 atm), but resulted in an end-expiratory pressure (EEP) beyond the narrowing being significantly greater than in the unobstructed airway (2.5 (3.4) to 5.5 (3.7) mm Hg for 2 atm; P = 0.0005) and 3.2 (3.6) to 8.0 (4.3) mm for 3 atm; P < 0.0001). Severe airway narrowing increases inspiratory pressure proximal and expiratory pressure distal to the obstruction in relation to the applied driving pressure. Since the distal EEP never exceeded PIP, even near-total airway obstruction should not cause severe lung distension or barotrauma in subjects with normal lungs.
Oxygen saturation and carbon dioxide values should be monitored during high-frequency jet ventilation (HFJV). Modern transcutaneous PCO2 (PtcCO2) measurement allows the estimation of ventilation efficiency. We studied how tests of lung function could predict carbon dioxide elimination during HFJV. Lung function tests from 180 adult patients undergoing rigid bronchoscopy were analysed as factors affecting carbon dioxide elimination. The lung function test results showed a significant relationship with the efficiency of carbon dioxide elimination; the greatest impairment of carbon dioxide elimination was found in patients with combined abnormalities of lung function. Further factors associated with difficult carbon dioxide elimination were male gender and elevated body weight. Of the patients investigated, 72% had normal carbon dioxide elimination, whereas in 23% hypercapnia could be avoided only by increasing the driving pressure. The prevalence of abnormal preoperative lung function test results predicts (sensitivity 76%, positive predictive value 27%) impaired carbon dioxide elimination during jet ventilation and rigid bronchoscopy.
The application of low FiO (2) with CPAP provided a better oxygenation and a lower pulmonary shunt during the OLV compared to high FiO (2) without CPAP.
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