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

Effect of Crystalloids With Different SID on Hemodilution, Plasmatic Acid Base Equilibrium and Urinary Electrolytes in Patients 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.

Inclusion Criteria:

• Adult patients (between 18 and 75 years old);
• ASA (American Society of Anesthesiologists) physical status classification system 1 or 2;
• Patients undergoing spinal surgery under general anesthesia, intubated and mechanically ventilated;
• Normal preoperative albumin;
• Surgery with an estimated duration of at least 3 hours.

Exclusion Criteria:

• Patients who are pregnant;
• Patients with obesity (BMI > 35);
• Patients with a chronic obstructive pulmonary disease (COPD);
• Patients with obstructive sleep apnea (OSA) treated with CPAP;
• Patients with chronic heart failure (CHF) with a NYHA (New York Heart Association) class ≥2;
• Patients receiving diuretics in the pre-operative period;
• Patients with a chronic kidney disease (CKD), defined as a GFR < 60 ml/min/1.73 m2;
• Patients with diabetes mellitus treated with insulin;
• Patients with myopathies; Patients undergoing a surgery with likely fluid losses or with unexpected bleeding during surgery.