Intravenous Lidocaine as Adjuvant to Sevoflurane Anesthesia for Endotracheal Intubation in Children

Tracheal intubation without muscle relaxant (TIWMR) has gained great popularity among pediatric anesthesiologists. A survey of the Society of Pediatric Anesthesia members, published in 1999, showed a considerable use of TIWMR (1). The use of additional drugs, such as lidocaine, for TIWMR to supplement an inhaled induction of anesthesia may potentiate depression of the laryngeal reflexes and thus may improve the intubating conditions (2,3). The present study reports the intubating conditions in children, as well as the changes of blood pressure and heart rate (HR), after a sevoflurane induction of anesthesia as compared with that achieved after the induction of anesthesia with sevoflurane supplemented with IV lidocaine. Methods The ethics committee of the hospital approved the study protocol, and informed parental consent was obtained. In a prospective, double-blinded design, 90 children, aged 1–8 yr and ASA physical status I or II, were randomized into two groups: Group S = sevoflurane (n = 46) and Group SL = sevoflurane supplemented with lidocaine (n = 44). Children with a history or signs predictive of difficult tracheal intubation or at risk for pulmonary aspiration were excluded from the study. All children were scheduled for tonsillectomy or adenoidectomy. Children were premedicated 30 min before the induction of anesthesia with 0.5 mg/kg of oral midazolam. Children were randomly assigned to one of the two study groups. The study drug (lidocaine) or the placebo (saline) were prepared by the pharmacy, and their identity was unknown to the anesthesiologist. An electrocardiogram, pulse oximeter, noninvasive arterial blood pressure monitor, and a rectal temperature probe were attached. A side-stream connector for measurement of end-tidal (ET) sevoflurane concentration and carbon dioxide was introduced between the face mask and the anesthesia circle system (Anesthesia monitor, airway module, Datex-Engstrom AS/3, Finland). Anesthesia was induced by a circle system using a vaporizer concentration of 8% sevoflurane in an oxygen flow of 6 L/min. After loss of consciousness, an IV cannula was inserted in all children. When the ET sevoflurane concentration reached 5%, 2 mg/kg of lidocaine was injected IV in Group SL and a similar volume of saline in Group S. Two minutes after saline or lidocaine, direct laryngoscopy and tracheal intubation were attempted. A cuffed tube having an internal diameter of 4 mm was used for children aged 1 yr. For children 2–8 yr of age, the cuffed tracheal tube size was calculated according to the following formula: Internal diameter = (age/4 + 4) − 0.5 mm (4). All tracheal intubations were attempted and scored by the same anesthesiologist. Intubating conditions were assessed on the basis of the scoring system devised by Helbo-Hansen et al (5). Laryngoscopy, vocal cord position, and coughing were evaluated using a four-point scale (Table 1). Coughing was considered slight if no more than two coughs in sequence occurred, moderate if three to five coughs in sequence occurred, and severe if more than five coughs in sequence occurred. Intubating conditions were judged acceptable when each individual category score was two or less.Table 1: Tracheal Intubating ConditionsHR and systolic blood pressure (SBP) were recorded after midazolam premedication and immediately before the inhaled induction as well as after the induction at ET sevoflurane 5%, 2 min after injection of lidocaine or placebo, or just before laryngoscopy. HR and SBP were also monitored immediately after tracheal intubation and 1 min and 3 min after intubation. The incidence of acceptable intubating conditions after the induction with sevoflurane without adjuvants is close to 80%(6). To detect a difference of 0.15 between the proportions of acceptable intubating conditions with 80% power and 0.05 level of significance, 42 patients are required in each group. Data are expressed as mean ± sd. Statistical analyses are performed with Student’s t-test, χ2, or Fisher’s exact test as appropriate. P < 0.05 is considered as statistically significant. Results Patients in Group S and Group SL had comparable age and weight (53 ± 22 mo versus 52 ± 20 mo and 18.2 ± 5.2 kg versus 18.1 ± 4.8 kg, respectively). The time to endotracheal intubation was comparable between Group S and Group SL (5.4 ± 1.4 min and 5.2 ± 1.2 min, respectively). The mean ET sevoflurane concentration measured immediately before placement of the endotracheal tube was comparable in both groups (5.8 ± 0.7 in Group S and 5.7 ± 0.7 in Group SL). As shown in Table 1, 42 of 44 (95%) patients in Group SL showed acceptable intubating conditions compared with 35 of 46 (76%) patients in Group S (P = 0.006). No movement during laryngoscopy was noted in any patient. In Group S, two patients received propofol after tracheal intubation because of severe coughing, and one patient received succinylcholine because of vocal cord closure. Baseline values of HR and SBP were not significantly different between the two groups. After tracheal intubation, an 18%–20% increase in HR occurred in both groups as compared with baseline values. Also, SBP increased in both groups; however, the percentage increase was significantly larger in Group S compared with Group SL (P < 0.05) (Fig. 1).Figure 1: Systolic blood pressure (SBP) in Group S and Group SL (mean ± sd). 1 = baseline values, 2 = after the induction of anesthesia at end-tidal (ET) sevoflurane 5%, 3 = 2 min after the administration of lidocaine or placebo before intubation, 4 = immediately after intubation, 5 = 1 min after intubation, and 6 = 3 min after intubation. Within groups, statistically significant changes compared with baseline values: *P < 0.05, **P < 0.01, ***P < 0.001. Between groups, statistically significant percentage changes from baseline values: †P < 0.05.Discussion After a sevoflurane induction of anesthesia and TIWMR in children, the incidence of acceptable intubating conditions ranges between 35% and 87%(6,7). Previous pediatric studies have shown that lidocaine improves intubating conditions when combined with halothane-nitrous-oxide sequence (2,8); it suppresses reflex responses after endotracheal intubation such as coughing, increases in intraocular pressure, HR, and mean arterial blood pressure (2). In the present study, we found a more frequent incidence (95%) of acceptable intubating conditions in children in the sevoflurane-lidocaine group as compared with the sevoflurane group (76%) at similar ET sevoflurane concentrations and similar times to intubation. The beneficial effect of IV lidocaine on intubating conditions was mainly related to cough suppression. SBP increased to a lesser extent after tracheal intubation in the sevoflurane-lidocaine group than in the sevoflurane group, confirming the beneficial effects of IV lidocaine in attenuating the hemodynamic response to laryngoscopy and intubation (2). However, the increase of blood pressure after tracheal intubation was not clinically significant because the gradient was only 10–15 mm Hg. Yukioka et al. (9) have shown that coughing was suppressed completely when 2 mg/kg was injected between one and five minutes before attempting tracheal intubation compared with partial suppression of cough with 1 and 1.5 mg/kg; in addition, the authors did not report any side effects related to the use of lidocaine at these doses. The combination of lidocaine and sevoflurane seems to decrease laryngeal reflexes more reliably than sevoflurane anesthesia alone. Although a peripheral effect of IV lidocaine has not been excluded (10), several observations indicate that lidocaine acts primarily as a central nervous system depressant (11–13). In conclusion, the present report shows that the administration of IV lidocaine 2 mg/kg after a sevoflurane induction of anesthesia without muscle relaxants decreases the amount of moderate or severe coughing and attenuates the blood pressure increase after tracheal intubation in children.