Core Temperature Variations During Midazolam vs Propofol Sedation for Neuraxial Anesthesia

In this study the investigators will select 20 patients scheduled for orthopedic surgery of the knee or foot with neuraxial anesthesia (subarachnoid or sequential blocks). Sedation for these procedures with midazolam or propofol is daily practice in the investigators' department.

So the patients will be randomized, through the envelope method, in 2 groups with 10 patients each: "midazolam group" and "propofol group".

In the "midazolam group" the investigators will administer 0,05mg/kg of midazolam, being 2/3 administered before the neuraxial block and 1/3 after.

In the "propofol group" the investigators will administer 0,033mg/kg of midazolam before the neuraxial block, and immediately after installation of the block the investigators will start a propofol target-controlled infusion (TCI) pump (Schnider model) with an effect concentration set at 1mcg/mL. This pump will be turned off at the end of the surgery.

The neuraxial block will be performed inside the operating room and preferentially in lateral decubitus. The choice of drug and dosage used for the block will be left to the anesthesiologist, to mimetize day-to-day practice. The limit dermatome of sensory block will be noted.

The investigators will administer to every patient: cefazolin 2g iv bolus, ketorolac 30 mg iv bolus, pantoprazole 40 mg iv bolus, paracetamol 1g iv perfusion (initiated 30 minutes before the end of surgery).

Central temperature will be monitored with the SpotOnTM3MTM device from entering till leaving the operating room, through a sensor placed in the patient's forehead. Room temperature will be kept at 17 degrees Celsius (ºC). Patients will be warmed with a underbody forced-air blanket (BairHuggerTM3MTM) set at 38ºC and maximal flow, initiated after performing the neuraxial block and stopped right before leaving the operating room.

Data will be analyzed with the Statistical Package for the Social Sciences (SPSS) program.

Inclusion criteria

• Scheduled for orthopedic surgery of the foot or knee
• Indication to neuraxial anesthesia
• Surgery duration > 30 minutes

Exclusion criteria

• Preference for deep sedation
• Preference for no sedation
• Kidney failure
• Hepatic failure
• No signed informed consent