Ventilation modes and factors influencing tidal volume in nonventilated lung during one-lung ventilation in patients undergoing thorascopic surgery: monitoring using electrical impedance tomography

Abstract

Objective To evaluate the ventilation modes and factors influencing the tidal volume(VT)in the nonventilated lung during one-lung ventilation(OLV)in patients undergoing thorascopic surgery using electrical impedance tomography. Methods Thirteen American Society of Anesthesiologists physical statusⅠ or Ⅱ patients of both sexes, aged 45-64 yr, weighing 45-80 kg, undergoing elective pulmonary surgery performed via video-assisted thoracoscope, were enrolled in the study.After anesthesia induction, a double lumen tube was placed, and correct tube placement was confirmed with a fiberoptic bronchoscope.Two-lung ventilation and OLV were performed sequentially when in supine position with a fixed VT of 8 ml/kg and respiratory rate(RR)of 12 breaths/min.When the patients were turned to lateral position(with the operated lung on the upper side), correct placement of the tube was reconfirmed with a fiberoptic bronchoscope.Bilateral lungs were ventilated with VT of 8 ml/kg and RR of 12 breaths/min, and unilateral lungs were then ventilated in the following modes in sequence: VT 8 ml/kg and RR 12 breaths/min for the lung on the upper side; VT 8 ml/kg and RR 12 breaths/min for the lung on the lower side; VT 8 ml/kg, RR 12 breaths/min and positive end-expiratory pressure(PEEP)4 cmH2O for the lung on the lower side; VT 6 ml/kg and RR 16 breaths/min for the lung on the lower side; VT 4 ml/kg and RR 24 breaths/min for the lung on the lower side.Each ventilation mode stabilized for 2 min.At 2 min of OLV in each mode, electrical impedance tomography was used to record the ventilation mode in the nonventilated lung, anesthesia machine was used to record VT in the nonventilated lung, and the percentage of VT on nonventilated side in VT on ventilated side(VT-non/VT-ven%)was calculated.When the unilateral lung on the lower side was ventilated in lateral position, logistic regression analysis was used to analyze the correlation between VT on ventilated side(no PEEP)and that on nonventilated side. Results Opposite ventilation was found in the nonventilated lung during OLV.VT-non/VT-ven% was significantly higher in lateral position than in supine position(P<0.05). VT-non/VT-ven% was significantly higher when the lung on the lower side was ventilated than that when the lung on the upper side was ventilated(P<0.05). Four cmH2O PEEP exerted no effect on VT-non/VT-ven%.When the lung on the lower side was ventilated in lateral position, there was a linear positive correlation between VT on ventilated side(no PEEP)and that on nonventilated side(r=0.899, P<0.05). Conclusion During OLV in patients undergoing thorascopic surgery, there is opposite ventilation in the nonventilated lung, and VT is influenced by body positions and VT in contralateral lungs. Key words: Respiration, artificial; Pulmonary ventilation; Thoracoscopy