The effects of thoracic epidural blockade on ventilation-perfusion matching during one-lung ventilation: An exploratory study.

Objective: Electrical impedance tomography (EIT) enables continuous image acquisition, facilitating real-time measurements of ventilation and perfusion at the clinical bedside. Experimental and clinical studies on controversial effects of thoracic epidural blockade (TEB) with local anesthetics on ventilation-perfusion(V/Q) matching and hypoxia during one lung ventilation (OLV) are rare. The aim of this study was to use EIT to investigate the effects of TEB combined with general anesthesia on pulmonary perfusion distribution and V/Q matching during one-lung ventilation.

Design: Single-centered, prospective, unblinded, randomized, parallel-group clinical trial.

Setting: Surgical suite of a university-affiliated teaching hospital.

Patients: Thirty patients prepared for thoracic surgery were randomly assigned to either the control group or the TEB group, which received a combination of thoracic epidural blockade and general anesthesia.

Measurements: EIT measurements and blood gas analysis were conducted in the lateral position during two-lung ventilation(T), 15 min after OLV(T), and 15 min after administration of 0.25 % ropivacaine or 0.9 % saline via epidural delivery during OLV(T). Hemodynamic and respiratory parameters were recorded, and Dead Space%, Shunt%, and V/Q Match% were calculated based on blood gas analysis and EIT images.

Results: Mean arterial pressure (p < 0.05) significantly decreased 15 min after TEB, while there were no significant changes in heart rate among the 30 patients (p = 0.547). OLV resulted in a significant decrease in arterial oxygen partial pressure/inspired oxygen fraction (PaO/FiO) from T to T in both groups. The PaO/FiO in the TEB group was significantly lower after epidural administration of the local anesthetic (p < 0.05). Shunt- ABG (%) was significantly higher in the TEB group compared to the control group at T (p < 0.05). TEB increased non-ventilated perfusion distribution(p < 0.05), and Shunt-EIT % (p < 0.05) and reduced Matched Region % (p < 0.05), while Dead Space-EIT % remained (p = 0.499).

Conclusions: Based on the contrast-enhanced EIT evaluation of pulmonary perfusion and ventilation, TEB appears to induce a V/Q mismatch in patients undergoing OLV in the lateral position for thoracic surgery.

Trial Registration: ClinicalTrials.gov, NCT04730089. Registration on January 25th, 2021.