Increased Postoperative Opioid Use is a Risk Factor for an Ileus After Laparoscopic Colorectal Surgery---A Case Control Study

2.1 Study design For this case-control study, all elective laparoscopic colorectal procedures performed at a university hospital between Jan 2018 and June 2020 were retrospectively collected by reviewing the institutional colorectal surgery database. The study protocol was approved by the Institutional Review Board of Peking University People's Hospital (2021PHB144-001, May 24, 2021), Beijing, China, and informed consent was waived due to the retrospective design.

The anesthesia medical information system was searched for patients aged 18 years old and above, undergoing elective laparoscopic colorectal procedures who received patient controlled intravenous analgesia postoperatively. Patients were excluded if they had chronic opioid use, converted to open, admitted to intensive care unit(ICU), patient controlled analgesia (PCA) regimens other than sufentanil, PCA used shorter than 48 hours, or incomplete postoperative opioid usage record. Patients were followed up until discharge from the hospital.

2.2 Patient allocation Patients who experienced postoperative ileus were included in ileus group. In accordance with the definition of Vather et al, diagnosis of postoperative ileus required 2 or more of following persistent symptoms on the fourth postoperative day and onward: nausea and vomiting, inability to tolerate solid or semi-liquid diet or failure to pass gas or stool during a 24 hour period, abdominal distension and radiological evidence of ileus. Patient charts, including radiographs were evaluated retrospectively. Diagnosis of an ileus was confirmed clinically and radiographically in all cases. The control group (at a 1:1 ratio) was matched by selecting the same range of age (±5 years of age), the same grade of American Society of Anesthesiology(ASA) classification, and the same types of surgery (colectomy, rectectomy, whole colon resection, or others).

2.3 Perioperative management All patients received standard anesthesia protocol for laparoscopic colorectal procedures within Peking University People's Hospital. Patients might received bilateral transversus abdominis plane(TAP) blocks (0.3% Ropivacaine of 30~40ml under the ultrasound guidance) at the discretion of the anesthesiologist in charge.

General anesthesia was induced using etomidate (0.2-0.6 mg/kg) and sufentanil (0.3 μg/kg) and maintained with continuous infusion of propofol (4-6 mg/kg/h) to target a bispectral index of 40-60. Cisatracurium (0.15 mg/kg) was injected intravenously to facilitate endotracheal intubation. Intravenous sufentanil (0.1 μg/kg) was added before skin incision. During surgery, continuous infusion of remifentanil (0.1-0.2 μg /kg/min) was adjusted to keep heart rate (HR) and mean arterial blood pressure (MAP) within 80-120% of baseline. Hypotension (MAP < 80% of baseline) lasting for 3 min was managed with a bolus of 6 mg of ephedrine or 50 μg of phenylephrine. Bradycardia (HR < 45/min) was treated with atropine (0.25-0.5 mg). At the end of surgery, neostigmine (1 mg) and atropine (0.5 mg) were used to antagonize neuromuscular blockade, and tracheal extubation was performed when the patient was fully awake and breathing adequately. Patients were transferred to the post-anesthesia care unit (PACU) and discharged when the Modified Aldrete Score reached 10.