This study demonstrated that intravenous infusions of lidocaine and dexmedetomidine were effective in attenuating cough, hypertension and tachycardia during the tracheal extubation period in patients undergoing thyroid surgery, when compared with patients who were treated with normal saline. Additionally, both of these treatments were able to reduce postoperative drainage when compared with patients who were treated with normal saline.
Lidocaine has several beneficial effects, such as analgesia, anti-hyperalgesia and anti-inflammation [14,15]. Moreover, lidocaine can depress spike activity, amplitude and conduction time in both myelinated A and unmyelinated C nerve fibers [16]. Several studies have shown that lidocaine can reduce the incidence and severity of cough during anesthetic emergence through different methods, including intracuff, tube lubrication, intratracheal instillation and intravenous bolus infusions before an induction [17-20]. Shabnum et al [12]. found that both IV and intratracheal lidocaine are effective in the attenuation of cough. In our study, the incidence and severity of cough was 28.3% in the LIDO group, and the rate of cough was significantly lower than the rate in a previous study (72.1%) [8]. We speculate that the methods of intravenous infusion of lidocaine might contribute to the difference. The effective serum concentration of lidocaine for the attenuation of cough is between 2.3 μg/ml and 3.0 μg/ml [21], and it is difficult to achieve this concentration in a timely manner via bolus infusion administration; however, the target concentration can likely be obtained by extending the intravenous infusion time. The present study demonstrated that the intravenous infusion of lidocaine can effectively suppress cough during the tracheal extubation period.
Several studies have shown that dexmedetomidine can effectively reduce cough during anesthetic emergence [8,10], but the exact mechanism is unclear. A previous study has shown that a peripheral alpha-2 receptor may be involved in cough inhibition [22]. In addition, a previous study showed that the sedative characteristics of dexmedetomidine can suppress the sensitivity of tracheal stimulation, which then results in cough inhibition [23]. However, several studies have shown that a dexmedetomidine infusion, at a rate of 0.4 μg/kg/h during the operation period, did not inhibit cough [24,25]. Park et al [26]. compared the effect of a single dose of 0.5μg/kg dexmedetomidine with remifentanil by the use of a target-controlled infusion in reducing cough during anesthetic emergence. The results of this study showed that the effect of dexmedetomidine was lower than that of remifentanil. In addition to the administration of a loading dose of infusion before the induction of anesthesia, a continuous infusion administration was also given until 30 minutes before the end of surgery in the DEX group. In our study, the incidence of cough decreased by 35% in the DEX group, which thus contributed to the sedative effect of dexmedetomidine.
Cough during the tracheal extubation period in patients undergoing thyroid surgery may increase the incidence of postoperative bleeding, which can lead to cervical hematoma and reoperation [5]. Furthermore, severe cervical hematoma is a fatal complication after thyroid surgery [6]. Additionally, coughing can be accompanied by increased venous pressure, which may then cause a ligature to slip or cause nonligated small vessels to bleed profusely [27]. A recent study showed that incision drainage is closely correlated with inflammation, while dexmedetomidine and lidocaine both have anti-inflammation effects [28-30]. Postoperative hematomas usually occur within 12 hours, and especially occur within 6 hours after surgery [31]. In our study, the volume of drainage within 24 hours after surgery was lower in the two treatment groups than in the control group. The authors attribute these results to the reduction of cough, as well as the anti-inflammatory effects of dexmedetomidine and lidocaine.
The stimulation of the respiratory tract by an endotracheal tube during an endotracheal extubation causes transient sympathetic activity, which can lead to hypertension and tachycardia [32]. Various attempts have been made to attenuate the pressor response via intravenous administrations of lidocaine and dexmedetomidine. A previous study reported that intravenous lidocaine can blunt increases in HR and MAP during the tracheal extubation period [33]. Luthra et al [34]. demonstrated that intravenous dexmedetomidine can alleviate stress responses to tracheal extubation. In our study, both MAP and HR were decreased in the LIDO group and the DEX group at the time of immediate extubation and 5 minutes after extubation, compared to the CON group. These findings may be explained by the analgesic properties of both lidocaine and dexmedetomidine.
Although the abovementioned drugs, including both lidocaine and dexmedetomidine, can reduce the incidence of cough, some unexpected side effects, such as sinus bradycardia, hypotension, hypertension, and lidocaine-induced neurotoxicity, may occur during drug administration [34,35]. However, there were no adverse effects observed in our study.
There were several limitations in this study. First, the consumption of anesthetic agents and the incidence of postoperative pain were not evaluated; however, both lidocaine and dexmedetomidine have analgesic properties [9,36]. Second, this study was a single-center clinical study, and the conclusions still need to be further supported by large sample and multicenter studies.