Comparison of the perfusion index as an index of noxious stimulation in monitored anesthesia care of propofol/remifentanil and propofol/dexmedetomidine: a prospective, randomized, case-control, observational study

Ethics approval and consent to participate

This prospective, randomized, case-control, observational study was approved by the Samsung Medical Center Institutional Review Board, Samsung Medical Center, Seoul, Republic of Korea (Chairperson: Prof. Young Keun On) on 6th, December 2018 (no. SMC 2018-11-111). Prior to the recruitment of the first participants, we registered them in the Clinical Trial Registry of Korea (https://cris.nih.go.kr; registration no. KCT0003501, principal investigator: Ji Seon Jeong; date of first registration:13/02/2019). Written informed consent was obtained from all participants before enrolment in the study. All methods were performed in accordance with the Declaration of Helsinki and its revisions.

Patients and protocols

Adult patients aged 19–70 years with American Society of Anesthesiologists physical status I and II scheduled for elective chemoport insertion under monitored anesthesia care were assessed for eligibility and were included between February 2019 and December 2019. Exclusion criteria were allergy to certain anesthetic agents; body mass index ≥ 30 kg/m2; diabetes mellitus; cardiovascular disease (e.g., myocardial infarction, heart failure, or arrhythmia including bradycardia ≤ 50 bpm); use of α/β blocking agents; pre-existing chronic pain; use of analgesics; peripheral occlusive artery disease; severe liver or kidney disease; or pregnancy.

Randomization and group allocation

One statistician who was not involved in this trial generated a random allocation sequence using permuted-block randomization with a block size of 4. Randomization and group allocation were performed in a 1:1 ratio using the sealed opaque envelope technique. The study drugs were prepared in a 20 ml syringe depending on the group assigned:

Remifentanil group

remifentanil 1 mg (Remiva Inj., Remifentanil Hydrochloride, Hana Pharm Co., Ltd.) + 0.9% saline 20 ml.

Dexmedetomidine group

dexmedetomidine 80 μg (premixed solution of 4 mcg/ml) (Precedex Inj. Dexmedetomidine Hydrochloride, Pfizer Ltd.)

Protocol

Premedication was not permitted for all participants. The prepared study drug was delivered to a clinical anesthesiologist (unrelated to this study) just before the start of anesthesia induction. On arrival in the operating room, standard monitors, including electrocardiograms, pulse oximetry, and noninvasive blood pressure (NIBP), were applied. A PI sensor (Radical-7®; Masimo Corporation, Irvine, CA, USA) was attached to the index finger and the finger was covered with a black opaque pouch to minimize light interference. The body temperature of all patients in our institute was maintained above 36.5 °C in the operating room using circulating-water blanket. The temperature of the operating room and PACU was maintained as 21 and 23 °C to prevent the influence of environmental temperature. In addition, to prevent the influence on blood flow, the NIBP was measured on the opposite side of the attachment site of the PI sensor.

The degree of sedation was evaluated using the modified observer’s assessment of alertness/sedation (OAA/S) scale. To maintain OAA/S scale of 3–4, the study drugs were administered at the following doses: remifentanil 0.05–0.1 μg/kg/min and dexmedetomidine 0.2–0.7 μg/kg/h. The propofol infusion rate was adjusted to within the range of 25–75 μg/kg/min. If the patient or surgeon requested more sedation, 1–2 mg midazolam was additionally injected during the procedure. Before the surgical incision, all participants were administered 80 mg of 2% lidocaine as a local anesthetic on the skin. Depending on the surgical procedure, PI values, mean blood pressure (MBP), and heart rate (HR) were recorded at baseline, skin incision, dilator insertion, and skin suture. Intraoperative airway management was performed, including head tilting, chin lifting, jaw-thrust manipulation, and nasopharyngeal and laryngeal airway insertion. If airway management was required, the anesthetic dose was adjusted.

After finishing the surgery, all anesthetics including the study drugs were discontinued in the operating room. Then, the patient was transferred to the post anesthesia care unit (PACU). PI values, pain severity, OAA/S scale, and additional analgesic requirements were recorded. Pain severity was investigated using numerical rating scale (NRS) scores on a 10-point scale and patient satisfaction was recorded using 5-point Likert scale [8]. All variables began to measured approximately 5 min after study drugs were discontinued and were collected at 10-minute intervals from the admission to discharge from the PACU. Paracetamol 1 g (Kabi Paracetamol Injection, acetaminophen 10 mg/mL, Fresenius Kabi, Bad Homburg v.d.H. Germany) was additionally administered when the patient expressed surgical site pain with an NRS score ≥ 4 and the patient requested. Researcher who recorded the study variables in the PACU was blinded to the assigned group until all recordings were completed.

Outcomes

The primary outcome was the comparison of PI values 30 min after admission to the PACU. To evaluate the lasting effect of the anesthetic used during sedation, PI measurement time of the primary outcome was set to 30 min after entering the PACU. The secondary outcomes were the comparison of NRS scores and PI values according to the time intervals in the PACU and the correlation of the PI and NRS scores in the PACU. In addition, the incidence of airway management during surgery and additional analgesic requirements in the PACU were investigated.

Statistical analysis

The sample size was calculated based on unpublished clinical data. The mean (standard deviation) of PI value at 30 min after entering PACU was 2.81 (1.88) in dexmedetomidine group and 1.5 (1.38) in remifentanil group. To evaluate this at a significance level of 5% and power of 90%, we needed 35 patients in each group. Considering an expected dropout rate of 10%, 78 participants were required.

Continuous variables were expressed as mean (standard deviation) or median (interquartile range), as appropriate, and normality was assessed using the Shapiro-Wilk test. Categorical variables were presented as numbers (percentages). Intraoperative and postoperative continuous variables were compared using the t-test or Mann-Whitney U test as appropriate. Bonferroni corrections were applied for post-hoc analyses. Categorical variables were analyzed using Pearson’s chi-square test or Fisher’s exact test, as appropriate. Changes in PI in the PACU were analyzed using the Wilcoxon signed-rank test. The correlation between NRS scores and PI values in the PACU was analyzed using Pearson’s correlation coefficient. Statistical analysis was performed using SPSS 25.0 (SPSS Inc., Chicago, IL, USA). P < 0.05 was considered as statistically significant.

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