BACKGROUND: The effects of Trendelenburg positions used to expose the surgical field may induce intraoperative hemodynamic and respiratory changes that complicate anesthetic management. This study was performed to evaluate the effects of the lithotomy-Trendelenburg position on respiratory and hemodynamic changes with time passage during general anesthesia. METHODS: Twenty patients undergoing anorectal surgery with general anesthesia were studied. Hemodynamic and respiratory parameters were measured before the lithotomy-Trendelenburg position (L) and 3 min (LT3), 6 min (LT6), 12 min (LT12), 30 min (LT30) and 60 min (LT60) after the 30 degree Trendelenburg position. The cardiac index (CI), stroke volume (SV), systemic vascular resistance (SVR), airway resistance (Raw) and dynamic compliance (Cdyn) were measured by a non-invasive cardiac output monitor. RESULTS: Central venous pressure and peak inspiratory pressure were markedly increased from the lithotomy to the lithotomy-Trendelenburg position. Heart rate was slightly increased while SV, CI, SVR and MAP were decreased. No significant changes of the SV or CI were observed during surgery. The Cdyn was significantly decreased. CONCLUSIONS: The steep lithotomy-Trendelenburg position induces moderate adverse hemodynamic and respiratory effects in healthy patients. These findings indicate the need for more active hemodynamic and respiratory monitoring in patients with a compromised cardiopulmonary function.