DXM (1 µg kg -1) was loaded intravenously for 10 min before anaesthesia induction.During DXM loading, the depth of anaesthesia was monitored using a bispectral index (BIS) monitor. Electrocardiogram, heart rate, pulse oximetry, and non-invasive arterial blood pressure were monitored at 2-min intervals.

Anaesthesia was induced with propofol 3.5 μg mL 1 and remifentanil 5 ng mL 1 at an effect site concentration using a target-controlled infusion (TCI) device. Anaesthesia was maintained with propofol and remifentanil continuous infusions.

During surgery except the study period, propofol and remifentanil doses were adjusted to maintain BIS value of 40-60 and systolic blood pressure (SBP) within ±20% from baseline respectively.

Saline (1 µg kg -1) was loaded intravenously for 10 min before anaesthesia induction.During saline loading, the depth of anaesthesia was monitored using a bispectral index (BIS) monitor. Electrocardiogram, heart rate, pulse oximetry, and non-invasive arterial blood pressure were monitored at 2-min intervals.

Anaesthesia was induced with propofol 3.5 μg mL 1 and remifentanil 5 ng mL 1 at an effect site concentration using a target-controlled infusion (TCI) device. Anaesthesia was maintained with propofol and remifentanil continuous infusions.

During surgery except the study period, propofol and remifentanil doses were adjusted to maintain BIS value of 40-60 and systolic blood pressure (SBP) within ±20% from baseline respectively.

After induction as mentioned at 'arm description', the effect-site propofol concentration was fixed at 5.0 μg mL-1 at the time of diluted epinephrine injection and was unchanged during the entire hydrodissection period in all patients.

The first patients received effect-site concentrations of remifentanil of 4 ng mL -1, respectively. The EC50 of remifentanil for stable hydrodissection was determined by a modification of Dixon's up-and-down method.If the response was "success (SBP during the entire hydrodissection period being ±20% from baseline)," the next target concentration of remifentanil was decreased by a step of 0.5 ng mL -1. If the response was "fail(SBP > ±20% from baseline)," the target concentration was increased by 0.5 ng mL-1.

Compare remifentanil EC50 for maintaining haemodynamic stability during hydrodissection between 2 groups.

The EC50 of remifentanil for maintaining haemodynamic stability was determined by a modification of Dixon's up-and-down method.If the response was "success (SBP during the entire hydrodissection period being ±20% from baseline)," the next target concentration of remifentanil was decreased by a step of 0.5 ng mL -1. If the response was "fail(SBP > ±20% from baseline)," the target concentration was increased by 0.5 ng mL-1.

Compare total doses of remifentanil and propofol administered intraoperatively between 2 groups.