Background: Fiber bronchoscopy is a routine operation in intensive care unit (ICU), but it may cause local collapse of the lung. Recruitment maneuver (RM) after fiber bronchoscopy may have the potential to restore functional residual air volume and increase lung volume. However, there is still a lack of quantitative indicators to evaluate the effect of recruitment maneuver. With electrical impedance tomography (EIT), we can monitor lung ventilation in real time to understand the situation of lung ventilation.

Objective: To evaluate whether recruitment maneuver after fiber bronchoscopy can improve lung volume and improve lung ventilation, and which people are most likely to benefit from it, by monitoring the end expiratory pulmonary impedance of critically ill patients undergoing bedside fiber bronchoscopy to monitor the lung ventilation before and after the operation and before and after recruitment maneuver.

Study Design: A prospective observational study was conducted to monitor the end expiratory lung impedance (EELI), tidal impedance variable (TIV), global inhomogeneity (GI) index and Center of Ventilation (CoV) before and after bronchoscopy and recruitment maneuver, and then to understand the changes of lung volume and ventilation.

At present, people pay more and more attention to the atelectasis caused by the sputum suction operation of fiberoptic bronchoscope. A recent observational study confirmed that more than 80% of patients will have atelectasis in at least one lung segment after the completion of the bronchoscope operation using the imaging method of cluster computed tomography (CT). The production of atelectasis will affect the patient's subsequent ventilation function, causing hypoxemia. Pulmonary atelectasis is a commonly used procedure for patients with acute respiratory distress syndrome (ARDS) to restore lung volume and improve atelectasis. Therefore, it is worth exploring whether adopting recruitment maneuver after bronchoscopy can avoid or reduce the problems of subsequent lung collapse and atelectasis in patients, and how to quantify it.

electrical impedance tomography, referred to as EIT, is a new imaging technology that can be implemented at the bedside in real-time, non-invasive and radiation free. The basic principle is to apply a weak current through local electrodes to sense the changes in the chest bioelectrical impedance during breathing, and then use the corresponding imaging algorithm to monitor the status of ventilation function in different areas of the lung, which is presented in real-time dynamic lung tomography ventilation images. Previous studies have found that through EIT, the end expiratory lung impedance (EELI) of the lungs can be monitored, indirectly reflecting the end expiratory volume of the lungs, thereby achieving the goal of monitoring local lung collapse caused by fiberoptic bronchoscope.

After being included in the patient, the EIT chest strap was worn to measure the end expiratory lung impedance and tidal impedance variable before bronchoscopy, and recorded as EELI before and TIV before, global inhomogeneity (GI) index ,Center of Ventilation (CoV), the vital signs of patients, including heart rate, blood pressure, respiratory rate, SpO2, ventilator parameters, including mode, PC/Vt, FiO2, PEEP, and lung compliance before bronchoscopy were recorded. Prepare fiber bronchoscopy and perform fiber bronchoscopy according to routine procedures in ICU. Record the duration of fiberoptic bronchoscopy examination and the condition of secretions.

After the fiber bronchoscopy examination, the end expiratory lung impedance and tidal impedance variables were recorded as EELI after operation and TIV after operation. The GI index, CoV, vital signs of patients, including heart rate, blood pressure, respiratory rate, SpO2, ventilator parameters, including mode, PC/Vt, FiO2, PEEP, and compliance were recorded. Perform recruitment maneuver using PCV mode, PEEP 20 cmH2O, PC 20 cmH2O, for 1 minute, then gradually reduce the ventilator pressure and restore the mode and parameters before bronchoscopy. If complications occur during the process of recruitment maneuver, timely record them. End expiratory lung impedance and tidal impedance variables were recorded as EELI after recruitment and TIV after recruitment. The GI index, CoV, vital signs of patients, including heart rate, blood pressure, respiratory rate, SpO2, ventilator parameters, including mode, PC/Vt, FiO2, PEEP, and compliance were recorded.

Inclusion Criteria:

• Patients with invasive mechanical ventilation undergoing fiberoptic bronchoscopy in ICU

Exclusion Criteria:

• Age<18 years old or>85 years old
• Pregnant women
• Patients undergoing emergency bronchoscopy examination
• Patients who undergo bronchoscopy only to confirm the position of the artificial airway
• Patients who are unable to wear EIT chest straps due to surgical incisions or closed drainage tubes in the chest
• Patients who refuse to participate in this trial

Invasive mechanical ventilation patients admitted to the ICU who plan to undergo bedside fiberoptic bronchoscopy