In this randomized, double-blind, placebo-controlled trial, intravenous lidocaine administered as a bolus of 1.5 mg/kg and then as a continuous infusion of 2 mg/kg/h during operative hysteroscopy reduced the severity of earlier postoperative hypogastric pain as well as the incidence of throat pain. Moreover, lidocaine administration reduced the remifentanil requirement during operative hysteroscopy.
Lidocaine infused intravenously has shown effectiveness in controlling postoperative pain[5]. The analgesic mechanisms of intravenous lidocaine are multifactorial, including a sodium channel blockade, a reduction in spinal cord sensitivity and a synergic effect with the general anesthetic agents[6]. The analgesic efficacy of intravenous lidocaine has been observed mostly in abdominal surgeries, including colectomy[7], gastrectomy[8], and cholecystectomy[9]. Moreover, Kim et al. confirmed the postoperative analgesic effects of intravenous lidocaine after ESD[4], a kind of endoscopic surgical procedure of natural lumens, which is similar to operative hysteroscopy. In this same study, it was speculated the analgesic effects of lidocaine were mainly for visceral pain[4]. Therefore, we hypothesized that intravenous lidocaine would be beneficial for controlling visceral pain from operative hysteroscopy. In our study, administration of intravenous lidocaine resulted in reduction of earlier postoperative hypogastric pain intensity and less remifentanil consumption during operative hysteroscopy, which was consistent with a previous report that lidocaine infused intravenously had an impact on pain scores in the early postoperative phase[10]. It was confirmed that the half-life of lidocaine was only 1.5-2 hours after bolus injection or infusion lasting less than 12 hours[11]. This may contribute to the reason why analgesic effect was noted at earlier postoperative but not at 24 hours in our results.
The NTI determined by the Narcotrend monitoring system is a dimensionless continuous variable scored from 0 to 100 that reflects the depth of anaesthesia. Based on the NTI, the depth of anaesthesia is from stage A (awake) to stage F (very deep anesthesia), with stage D (37-64) indicating the routine depth of anaesthesia for surgery. Previous studies reported that intravenous lidocaine had a propofol sparing effect during GA [12-13]. In this study we ensured that each patient was at a consistent anesthetic depth by Narcotrend monitor. The results of this study indicated that intravenous use of lidocaine could reduce the amount of propofol, but there was no significant difference. The reason may be short hysteroscopic procedure time, resulting in insufficient observation time.
Remifentanil is the drug of choice for endoscopy because of its rapid onset and offset of action, and minimal adverse effects on cardiovascular and respiratory parameters[14]. To observe postoperative earlier analgesic effect of intravenous lidocaine, another advantage of remifentanil is the ability to avoid interference of using other opioid drugs. Administration of intravenous lidocaine was shown to have an opioid sparing effect during GA, including fentanyl[15], sufentanil[16] and morphine[17]. Recent studies showed that a remifentanil sparing effect of intravenous lidocaine in the intraoperative period was found[18], which was consistent with our findings. However, another study reported that perioperative intravenous lidocaine infusion had no significant effect on remifentanil requirement during hypotensive anesthesia for elective transsphenoidal endoscopic hypophyseal adenoma excision procedure [19]. This difference was likely due to the distinct types of surgery performed and different anesthesia management regime.
We used the laryngeal mask for mechanical ventilation to assure the respiratory safety of patients in this study. On the other hand, the placement of the laryngeal mask also provided another way for us to observe the analgesic effect of lidocaine. Administration of intravenous lidocaine reduced the incidence of throat pain caused by placing the laryngeal mask from 47.5% to 22.5% in this study. Our observations were in line with several studies that administration of IV lidocaine was effective in reducing throat pain after endoscopic submucosal dissection[4] and postoperative sore throat caused by tracheal intubation[20]. As sore throat was the source of discomfort after minor surgery, efforts to reduce throat pain with drugs should be taken. We did not observe any significant difference in the incidence of postoperative nausea or vomiting, which is consistent with previous report[21-22].
There are some limitations in our study. We have not measured the plasma levels of lidocaine in our patients because this service is not available in our institution. However, the protocol of administering a loading dose followed by a continuous IV infusion of lidocaine during GA has been used in several previous investigations. This dose was reported to be well below the toxic level[23-24]. Another limitation is the small number of patients. Hence, a larger-scale trial is needed to further validate our results.
In conclusion, Intravenous lidocaine infusion for operative hysteroscopy alleviated earlier postoperative hypogastric pain and throat pain, and decreased remifentanil consumption.