Analgesic Efficacy of Free-opioid Anesthesia for Colorectal Surgery

Objectives: To compare free-opioid anesthesia (the combination of epidural anesthesia, intravenous lidocaine, ketamine, propofol, and sevoflurane) and opioid anesthesia (fentanyl, propofol and sevoflurane) regarding intraoperative analgesic efficacy in colectomies and rectal resections at Viet Tiep Friendship Hospital.

Methods: A prospective, randomized controlled clinical trial was performed on 98 patients who were anesthetized for colorectal surgery from December 2019 to November 2021. Patients were randomized into 2 groups: Group OA - Opioid anesthesia (n = 49): Intraoperative pain control by fentanyl; FOA group - Free-opioid anesthesia (n = 49): Intraoperative pain control by continuous infusion of lidocaine, bolus doses of ketamine combined with epidural levobupivacaine.

After being placed an epidural catheter and given a bolus dose of dexamethasone 0.1 mg/kg, patients was endotracheal anesthetized with propofol 1% 2-2.5 mg/kg, rocuronium 0.6 mg/kg. Intubation was implemented when TOF (Train Of Four)=0 and RE (Response Entropy), SE (State Entropy) ≤ 60. Patients in OA group received a bolus dose of fentanyl 2 µg/kg before induction of anesthesia while those in FOA group received bolus doses of lidocaine 1 mg/kg and ketamine 0.5 mg/kg. In FOA group, lidocaine 10% was sprayed on the patients glottis to facilitate intubation.

For anesthesia maintenance, in group OA, a bolus dose of fentanyl 3 µg/kg was given 5 minutes before skin incision, and then a continuous infusion of fentanyl 2 µg/kg/h was maintained for intraoperative pain management; fentanyl 0.5 μg/kg was bolused when SPI (Surgical Pleth Index) \> 50, 40 \< SE \< 60, TOF = 0 and the patient was hemodynamically stable. Propofol and fentanyl were discontinued at the start of skin closure. In FOA group, patients received intraoperative multimodal analgesia, in which an epidural bolus of 3 - 5 ml of levobupivacaine 0.1% was followed by a continuous infusion of 3 - 5 ml/h epidurally; in addition, intravenous infusion of lidocaine 1 mg/kg/hour and ketamine 0.25 mg/kg/h were maintained until the end of surgery. Patients were given a bolus of 3-5 ml levobupivacaine 0.1% epidurally and ketamine 0.25 mg/kg intravenously if SPI \> 50, 40 \< SE \< 60, TOF = 0 and hemodynamics was stable.

For all patients, anesthesia was maintained by volatile anesthetics (Sevoflurane or Desflurane) to ensure 40 \< SE \< 60, and rocuronium 0.2 mg/kg was repeated when TOF = 2 (the last injection of neuromuscular blockade was not given when the estimated duration from the point of injection to the point of abdominal closure is shorter than 20 minutes). Mechanical ventilation was provided with a tidal volume 6-8 ml/kg in the volume-controlled mode and respiratory rate at 10-12 breath/minute, FiO2 (Fraction of inspired oxygen)=50%. Peak airway pressure was maintained within the range of 12-16 cmH2O and EtCO2 (End-tidal Carbon dioxide) was kept from 35 to 40 mmHg with a fresh gas flow of 1.2 - 2 liters/minute. At the end of surgery, reversal of neuromuscular blockade was performed with neostigmine combined with atropine, and extubation was carried out when patients met the criteria. Postoperative pain management was implemented with patient-controlled epidural levobupivacaine 0.1% for 72 hours, and pain rescue with fentanyl 0.5 μg/kg.

Eligibility Criteria:
Inclusion Criteria:

* Patients agreed to participate in the study.
* Patients aged ≥ 18 years old,
* Those who underwent elective colectomies or rectal resections,
* Those who were ASA (American Society of Anesthesiologists) classified as I - III,
* Those who were indicated for general endotracheal anesthesia from December 2019 to November 2021 at Viet Tiep Friendship Hospital

Exclusion Criteria:

* Patients refused to participate in the study,
* Patients had BMI (Body Mass Index) ≥ 35;
* Pregnant or lactating or menstruating women;
* Those who had liver failure, renal failure, heart failure, history of chronic pain, alcohol or drug abuse, mental illnesses, allergies or contraindications to any studied medications.
* Those who were unable to assess pain or use of patient-controlled analgesia devices (PCA).