Effect of tidal volume on extravascular lung water content during one-lung ventilation for video-assisted thoracoscopic surgery: A randomised, controlled trial

BACKGROUND: The use of low tidal volume during one-lung ventilation (OLV) has been shown to attenuate the incidence of acute lung injury after thoracic surgery. OBJECTIVE To test the effect of tidal volume during OLV for video-assisted thoracoscopic surgery on the extravascular lung water content index (EVLWI). DESIGN: A randomised, double-blind, controlled study. SETTING: Single university hospital. PARTICIPANTS Thirty-nine patients scheduled for elective video-assisted thoracoscopic surgery. INTERVENTIONS Patients were randomly assigned to one of three groups (n=13 per group) to ventilate the dependent lung with a tidal volume of 4, 6 or 8 ml kg^-1 predicted body weight with I:E ratio of 1:2.5 and PEEP of 5cmH2O. MAIN OUTCOME MEASURES: The primary outcomes were perioperative changes in EVLWI and EVLWI to intrathoracic blood volume index (ITBVI) ratio. Secondary outcomes included haemodynamics, oxygenation indices, incidences of postoperative acute lung injury, atelectasis, pneumonia, morbidity and 30-day mortality. RESULTS: A tidal volume of 4 compared with 6 and 8 ml kg^-1 after 45 min of OLV resulted in an EVLWI of 4.1 [95% confidence interval (CI) 3.5 to 4.7] compared with 7.7 (95% CI 6.7 to 8.6) and 8.6 (95% CI 7.5 to 9.7) ml kg^-1, respectively (P<0.003). EVLWI/ITBVI ratios were 0.57 (95% CI 0.46 to 0.68) compared with 0.90 (95% CI 0.75 to 1.05) and 1.00 (95% CI 0.80 to 1.21), respectively (P<0.05). The incidences of postoperative acute lung injury, atelectasis, pneumonia, morbidity, hospitalisation and 30-day mortality were similar in the three groups. CONCLUSION: The use of a tidal volume of 4 ml kg^-1 during OLV was associated with less lung water content than with larger tidal volumes of 6 to 8 ml kg^-1, although no patient developed acute lung injury. Further studies are required to address the usefulness of EVLWI as a marker for the development of postoperative acute lung injury after the use of a low tidal volume during OLV in patients undergoing pulmonary resection.