Effect of Crystalloids With Different SID on pH, and Urinary Electrolytes During General Anesthesia

The present study will investigate variations in acid base equilibrium caused by the administration of four different crystalloids with increasing strong ion difference (0.9% saline, Ringer's lactate, Ringer's acetate, plasmalyte-like solution) in patients during general anesthesia. The same crystalloid will be administered throughout the surgery. In order to assess the effect of hemodilution, every patient will receive two fluid boli with different volumes of the same solution. pH and strong ion variations, togher with the renal response to acid base disturbances, will be analysed.