A Comparison Between Conventional and Waveform-Confirmed Loss-of-Resistance for Thoracic Epidural Blocks

Inclusion Criteria: * the patients undergoing thoracic epidural catheter insertion for thoracic and abdominal surgery or rib fractures with American Society of Anesthesiologists (ASA) classification 1-3 and body mass index between 18 and 35 Exclusion Criteria: * adults who are unable to give their own consent * coagulopathy (assessed by history and physical examination and, if deemed clinically necessary, by blood work up ie platelets ≤ 100, or International Normalized Ratio ≥ 1.4) * renal failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up ie creatinine ≥ 100) * hepatic failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up ie transaminases ≥ 100) * allergy to local anesthetic (LA) * pregnancy * prior surgery in the thoracic spine