Preoperative preparations and anesthesia protocol
The patients were computer-randomized into three groups, SK0.25 group
(0.25 mg.kg−1 esketamine), SK0.5 group (0.5
mg.kg−1 esketamine) and saline control group
(equivalent volume of normal saline). The patients, anesthesiologist,
gastroenterologists and nurses in the recovery room were blinded to the
grouping.
After an overnight fasting, the non-premedicated patients were brought
to the endoscopy room, where a 20-gauge intravenous cannula was
established in the peripheral vein for Ringer Lactate solution infusion
and drugs. Heart rate (HR), noninvasive blood pressure (BP),
electrocardiogram (ECG) and peripheral oxygen saturation
(SpO2) were monitored continuously during endoscopic
procedures (Philips HP Viridia 24/26 M1205A). Oxygen was administered at
a rate of 3 L/min by nasal catheter during the study.
After preoxygenation, propofol (AstraZeneca Company, Italy) was
administered by a computer-controlled infusion TCI (Graseby™ 3500 TCI
Syringe Pump, SIMS Graseby Ltd., Herts, England) using the Marsh
pharmacokinetic parameters at an initial plasma target concentration of
2.5 μg/mL in three groups. We started the first dose of propofol at 2.5
μg/mL based on our pre-test. Once the target concentration of propofol
achieved, esketamine was injected immediately. All esketamine solutions
were diluted into 10 ml and prepared by an anesthesiologist nurse who
was no longer involved in the follow-up. Patients were administered with
different doses of esketamine: 0.25 mg/kg esketamine (SK0.25 group), 0.5
mg/kg esketamine (SK0.5 group) and blank saline solution (Control
group). In our endoscopy center, as a rule, the patients underwent
gastroscopy first followed by colonoscopy. Qualified and experienced
gastroenterologists started gastroscopy 3 min after esketamine injection
and propofol TCI pump was stopped just before the end of the
colonoscopy. Coughing, retch, and purposeful movement of the head or
limbs during endoscopy are defined as “responsive”. If the patient
presented “responsive”, propofol 2-3 mL was given as a rescue
medication immediately, and the target plasma concentration of propofol
for the subsequent patient would be increased by 0.5 μg/mL. If coughing,
or retch, or purposeful movements did not occur, which defined as
“non-responsive”, the subsequent target plasma concentration of
propofol was decreased by 0.5 μg/mL. This method was called up-and-down
method of Dixon, described as early in 1965 [14].
Emergency equipment was available throughout the procedure. A bolus of
6-10 mg ephedrine was given once mean arterial pressure (MBP) decrease
by 30 % over the baseline value, and 0.25mg atropine was injected once
heart rate (HR) fell below 50 bpm. Appropriate nitroglycerin was
injected once MBP rose above 120 mmHg. If spontaneous ventilation was
insufficient (SpO2 < 90%), the
anesthesiologist performed an unarmed airway opening and an artificial
ventilation support as necessary.