Low-dose Succinylcholine to Facilitate Laryngeal Mask Airway Insertion: A Comparison of Two Doses.

BACKGROUND AND AIMS: Around the world, the use of the laryngeal mask airway (LMA) is becoming more common for different surgeries accounting for it being the dominant choice of airway in numerous surgeries. Although propofol is known to blunt the laryngeal reflexes often patient movement, coughing, and gagging occur on insertion. This study aims to identify the optimum dose of succinylcholine required to facilitate LMA insertion comparing placebo, 0.1 mg/kg and 0.25 mg/kg of succinylcholine. Further objectives were to compare (a) the overall insertion conditions of the LMA, (b) the number of insertion attempts, (c) the amount of propofol consumption, and (d) the hemodynamics in the three groups. SETTING AND
DESIGN: This is a prospective, double-blinded, randomized control trial of 283 patients randomized into three groups-placebo, 0.1 mg/kg and 0.25 mg/kg of succinylcholine. It was done in the day case theatres of a tertiary hospital in Southern India. SUBJECTS AND METHODS: Patients were induced with 2 mg/kg of propofol, after 2 μg/kg of fentanyl. The study drug was given after loss of consciousness. After 60 s, a classic LMA was inserted by the standard method by a single investigator. Jaw relaxation, coughing, gagging, movement, laryngospasm, ease of insertion, number of attempts, propofol usage, and hemodynamics were assessed. STATISTICAL ANALYSIS: Statistical methods used were analysis of variance with Bonferroni's t-test, Chi-square test, and Fisher's test. P < 0.05 was considered statistically significant.
RESULTS: Jaw relaxation was significantly better in the 0.25 mg/kg succinylcholine group. There was no significant difference in coughing and gagging in the groups, but patient movement was more in the placebo group. Two patients in the placebo group experienced partial laryngospasm. Overall insertion conditions were significantly better in the 0.25 mg/kg group compared to the other two groups. Propofol consumption was significantly more in the placebo group.
CONCLUSIONS: The study concludes that 0.25 mg/kg succinylcholine facilitates insertion of the LMA.

INTRODUCTION

In today's fast-paced world where time is of the essence, ambulatory surgery has come up in a major stride. In this setting, general anesthesia through the laryngeal mask airway (LMA) is widely used. LMA insertion is accomplished using propofol as it helps blunt the laryngeal reflexes well, when compared to other induction agents.[1] Often though it has been seen that propofol as a sole agent is not sufficient to prevent patient movement, coughing, and gagging.[2] Additional doses of propofol are required to prevent these undesirable airway reflexes and multiple insertion attempts may be needed. These can be associated with adverse hemodynamic changes and airway trauma.

Succinylcholine is a quick-onset, short-acting depolarizing muscle relaxant. It is a time-tested drug, easily available, and cost-effective. The use of succinylcholine to aid insertion of the LMA is advantageous as it avoids depression of the respiratory center and has no influence on consciousness. Succinylcholine has been proven to facilitate LMA insertion, with and without an additional agent such as fentanyl or midazolam.[3456] Most of these studies used a single arbitrary dose and did not compare two doses to get an optimum dose.[456] Keeping the day case setting in mind, this study compares placebo, 0.1 mg/kg and 0.25 mg/kg of succinylcholine and aims to identify an optimum dose of succinylcholine required to facilitate LMA insertion avoiding its side effects such as myalgia and apnea. Further objectives were to assess (a) the overall insertion conditions of the LMA with the different doses of succinylcholine, (b) the number of insertion attempts, (c) to determine the amount of propofol consumption with the different succinylcholine doses and (d) to compare hemodynamics in the three groups.

SUBJECTS AND METHODS

This is a double-blinded randomized control trial done on 283 patients. The Institutional Review Board approved the study. This study was done in the daycare theater. Patients were not premedicated. All cases were in the elective setting. Surgeries requiring general anesthesia using the LMA were included in this study. Patients included were of the American Society of Anesthesiologists (ASA) physical status Classes I and II, age between 20 and 65 requiring general anesthesia using the LMA. Obese patients with a body mass index (BMI) >30, patients with a known difficult airway and patients posted for oral surgery were excluded from the study. Informed consent was obtained from all patients. Patients were preoxygenated with 100% oxygen. Anesthesia was induced with 2 μg/kg of fentanyl followed by 2 mg/kg of propofol at a constant rate of 40 mg over 10 s titrated to loss of verbal response. If this dose of propofol was not adequate, further boluses of 0.25 mg/kg were given every 15 s till depth was adequate. A computer block randomization was used to allocate patients into three groups, placebo (Group I), 0.1 mg/kg (Group II), and 0.25 mg/kg (Group III) of Succinylcholine. The method of allocation concealment was using opaque envelopes with serial numbers. The person administering the drug would choose the appropriate syringe out of three which was loaded by the anesthesiologist; according to what was mentioned in the envelope. The classic LMA was inserted 60 s after the study drug was given using the classical method of insertion. Patients were assessed for jaw relaxation, coughing, gagging, laryngospasm, and overall insertion conditions by the same anesthesiologist for all cases as these are subjective end points. Number of attempts at insertion and total propofol consumption were also recorded, as were duration of apnea, hemodynamics, presence of fasciculations, and postoperative myalgia. Preinduction heart rate, systolic blood pressure, diastolic blood pressure, mean arterial blood pressure, and saturation were recorded. The same were recorded post induction and post insertion of the LMA. If insertion was not possible at the first attempt, anesthesia was maintained with 2% of isoflurane, an additional dose of 1 mg/kg of propofol was given, and insertion attempted 30 s later. Patients were monitored using standard methods of monitoring with the electrocardiogram, noninvasive blood pressure, pulse oximetry, and end-tidal CO2. Intraoperative anesthesia was maintained using O2 and N2O 50:50, and isoflurane 1%. Intraoperative use of analgesics was standardized. 1 g of paracetamol intravenous was administered to all patients. If the anesthesiologist felt that the patient required additional analgesia either intraoperatively or postoperatively, it was administered, and noted. Patients were examined for myalgia at 2 and 4 h postoperatively. Myalgia up to 24 h was assessed telephonically. LMA insertion assessment was made using different standard criteria as mentioned in Table 1.[6] Scoring of LMA insertion was performed only for the first attempt at insertion.

Table 1

Assessment of laryngeal mask airway insertion conditions

Statistical analysis

The required sample size to show a difference in the insertion conditions was found to be 92 in each group with an anticipated proportion of insertion conditions as 30%, 15%, and 10%, respectively, with 80% power and 1% level of significance (this is done for three group comparisons). Values were taken from the “overall insertion conditions” table in the study “A comparison of midazolam and mini-dose succinylcholine to aid LMA insertion during propofol anesthesia” by Salem.[6] Statistical analysis was performed using analysis of variance with Bonferroni's t-test and Chi-square test to compare groups and calculate the duration of apnea. Fisher's exact test was used to assess insertion conditions, fasciculations, and myalgia. P < 0.05 was considered statistically significant.

RESULTS

There was equal number of patients in all three groups, group I being placebo, Group II 0.1 mg/kg succinylcholine, and Group III 0.25 mg/kg of succinylcholine. Demographically, all groups were equally distributed in terms of age, weight, height, and BMI. The male to female ratio was equal in all three groups although there were more males than females in each group [Table 2].

Table 2

Demography

Jaw relaxation was significantly better in Group III than Group II and Group I; with P 0.026. It was also seen that jaw relaxation was incomplete in close to 30% of the patients in the 0.1 mg/kg succinylcholine group.

Coughing and gagging had no statistically significant difference between all three groups although clinically there was more in the placebo group.

The patient movement was significantly more in the placebo group, with P = 0.018. Group II and III had similar values.

Partial laryngospasm occurred in only two patients in the placebo group. None of the other patients had laryngospasm.

Overall insertion conditions were evidently better in Group III with P = 0.003. Although excellent insertion conditions were seen in 82% of Group II, this group had a higher number of unacceptable insertion conditions compared to Group I. This helps us conclude that 0.1 mg/kg of succinylcholine is not sufficient to aid smooth insertion of the LMA.

In most patients, the LMA was inserted in the first attempt. Only 18 patients required two attempts and only one patient required three attempts. Out of the 18 patients that required a second attempt, there were 8 each from Group I and Group II, and only 2 from Group III. Thus, statistically, there was no difference in number of insertion attempts. Most often the LMA was inserted, there would be patient reaction, and an additional dose of propofol was be given. Most cases would settle with the LMA well in place, not requiring a second attempt at insertion [Table 3].

Table 3

Jaw relaxation, coughing and gagging, patient movement, laryngospasm, overall insertion conditions

Total dose of propofol was significantly more in the placebo group with P = 0.024. Out of those requiring 3 mg/kg, most were from the placebo and 0.1 mg/kg succinylcholine group. 249 patients of 283 required 2 mg/kg, and 34 needed 3 mg/kg [Table 4].

Table 4

Propofol consumption and fasciculations

There were no statistically significant differences in hemodynamics between the groups. As hemodynamics were not different, the use of vasopressors was not significantly different between the groups.

The average duration of apnea was 5–6 min. There was no clinically significant difference in the duration of apnea between the groups. This could be because the placebo group required significantly more propofol.

Fasciculations were more in Group III. Only one patient in Group II complained of myalgia after 2 h. Two patients in Group I complained of myalgia after 4 h. Intraoperative analgesia was standardized for all patients so that it would not confound results of postoperative myalgia. If the anesthesiologist felt the patient required more analgesia, it was administered and recorded. There was no statistically significant difference in the amount of additional analgesia given. Hence, it was not a confounding factor toward postoperative myalgia.

DISCUSSION

In most tertiary and secondary hospitals, there is a growing need for time efficient and safe surgeries such as those in the ambulatory setting. Most of these are under general anesthesia using the LMA, as regional or neuraxial anesthesia is associated with slower recovery and later discharge.[7] In fact around the world, the use of the LMA is becoming more common for different surgeries accounting for it being the dominant choice of airway in around 50% of cases in the UK.[8] We wanted to determine means of improving provider ease and patient safety in improving this process. Hence, the relevance of this study.

Propofol is the induction agent of choice in LMA placement as it blunts the laryngeal reflexes. The disadvantage of using propofol alone is excessive patient movement, coughing, and gagging. This leads to additional propofol usage, ensuing hypotension, and prolonged duration of apnea. Salem found that failed insertion attempts of LMA placement were due to coughing and gagging in 75% of patients when only propofol was used.[6] Successful insertion at first attempt was only 60%.

Numerous agents have been studied and are still being studied to aid propofol in LMA insertion. These include drugs such as midazolam,[69] opioids such as fentanyl,[10] alfentanil,[1112] remifentanil,[213] and butorphanol,[14] muscle relaxants such as mivacurium,[15] atracurium,[16] and rocuronium,[17] and drugs such as clonidine,[18] dexmedetomidine,[1920] ketamine,[92122] and lignocaine.[21] Side effects such as sedation, postoperative nausea, and vomiting, residual neuromuscular blockade, and cost remains a concern with these drugs, especially in the day care setting.

Succinylcholine is a quick-onset, short-acting depolarizing muscle relaxant. It is a time-tested drug, easily available, and cost-effective. The use of succinycholine to aid insertion of the LMA is advantageous as it avoids depression of the respiratory center and has no influence on consciousness, unlike opiods, α2 agonists, and benzodiazepines. Regarding side effects of succinylcholine such as malignant hyperthermia (MH), we justify the use of succinylcholine as the genetic susceptibility to MH is low in Asia compared to the Caucasian population.[23] The overall incidence of MH during general anesthesia has been quoted as 1:40,000–1:50,000 anesthetics in adults with only a handful of case reports from Asia.[24]

The use of succinylcholine to facilitate LMA insertion has been studied in the past. Succinylcholine has been proven to facilitate LMA insertion though most of these studies used a single arbitrary dose and did not compare two doses to get an ideal dose or used larger doses that resulted in significant postoperative myalgia. Monem compared succinylcholine 0.35 mg/kg with atracurium 0.06 mg/kg under thiopentone induction with no preinduction narcotic and found no failure in the succinylcholine group compared with 17% failure rate with atracurium. Postoperative myalgia was 3.3% in each group.[25] Yoshino et al. comparing 0.25 with 0.5 mg/kg of succinylcholine found that 0.5 mg/kg of succinylcholine was required to blunt adverse airway reflexes associated with LMA insertion. The induction agent he used was thiopentone without an opioid. Unfortunately, this dose was also coupled with more myalgia and a longer duration of apnea.[3] Liou et al. compared insertion conditions in three arms with etomidate alone (0.3 mg/kg), etomidate along with fentanyl (2 μg/kg), and etomidate along with succinylcholine (1 mg/kg) and found that succinylcholine provided significantly better jaw relaxation, shortened the time to insert the LMA, and increased the success rate of LMA insertion. They did not comment on myalgia.[5]

Minidose of succinylcholine (0.1 mg/kg) is known to break laryngospasm and has been studied to facilitate LMA insertion.[26] Ho and Chui compared 0.1 mg/kg succinylcholine and placebo, using 2.5 mg/kg of propofol without an opioid at induction and found it to be better, with lesser insertion attempts and smoother insertion. Propofol requirement was less, thus there was less hypotension. The duration of apnea was not found to be different. Myalgia though was more with succinylcholine.[4] Similarly, Aghamohammadi also compared 0.1 mg/kg succinylcholine with placebo using midazolam 0.01 mg/kg, fentanyl 1 μg/kg, and propofol 2 mg/kg at induction and found smoother insertion conditions with this mini dose of succinylcholine.[27] Salem compared 0.1 mg/kg of succinylcholine and midazolam 0.04 mg/kg using 2.5 mg/kg of propofol for induction, without fentanyl and concluded that midazolam had the advantages of better insertion conditions, less change in hemodynamics, shorter duration of apnea, less fasciculations, and myalgia.[6]

From the previous studies, we know that 0.5 mg/kg of succinylcholine may not be needed and can be associated with myalgia and apnea. In addition, we infer that 0.1 mg/kg of succinylcholine is adequate but with higher doses of propofol or in combination with fentanyl and midazolam.[427] We wanted to compare 0.1 mg/kg and 0.25 mg/kg of succinylcholine to determine the optimal dose with minimal side effects using 2.0 mg/kg of propofol and 2 μg/kg of fentanyl at induction.

Ours is one of the largest study with 283 patients. They were equally distributed in all three groups, and the baseline characteristics were comparable. Overall, there were more males than females. This is probably because patients coming for urological procedures were mainly male. Anorectal disorders are more in males than females in this age group.[28] Many of these day case surgeries were anorectal procedures. This is also one of the reasons for more males than females.

Jaw relaxation was clearly better in Group III. Group II had quite a high incidence of incomplete and poor jaw relaxation. This helps us infer that 0.1 mg/kg of succinylcholine is probably not sufficient, and 0.25 mg/kg is better for adequate jaw relaxation.

There was no significant difference in the incidence of coughing and gagging between all three groups. Clinically, there were more numbers in the placebo group though not statistically significant.

Patient movement was significantly more in the placebo group. This was the most common reason for additional propofol requirement.

Laryngospasm was not experienced by any patient; there was partial laryngospasm in only two patients in the placebo group.

Overall, insertion conditions were clearly better in the Group III, both clinically and statistically. Group II had similar values to Group III in the “excellent” insertion conditions group, but 6.3% had “good” and 4.2% patients had “poor” insertion conditions. Surprisingly, Group II had 7.4% patients with unacceptable’ insertion conditions, due to inadequate jaw relaxation, and patient movement; compared to the placebo group, which had only 4.2%. One explanation could be that there was more patient movement in the placebo group during attempts to open the jaw; hence, an additional dose of propofol was given before attempting insertion itself. In the Group II, the first signs of inadequate dose were during insertion of the LMA itself and that is probably why this group had a higher number of unacceptable insertion conditions. We infer again that 0.1 mg/kg of succinylcholine is not sufficient to facilitate smooth insertion of the LMA.

Number of insertion attempts was not statistically significant, most requiring one attempt. The number of patients requiring >1 insertion attempt was 19, of which 18 needed two attempts. Of these, there were eight each from Group I and II, showing us that number of insertion attempts was clinically more in these groups though not statistically significant.

Total propofol consumption was significantly more in the placebo group. Most patients in the study required 2 mg/kg of propofol, but 12% required 3 mg/kg, of which 60% were from the placebo group and 32% from the 0.1 mg/kg group. This again shows us that clinically more patients in these groups required more propofol though statistically not significant.

Hemodynamic stability was similar in all groups. Although a large drop in blood pressure was expected in the placebo group because they required more propofol, they were found to be stable. Only 26 in the entire 283 patients required a vasopressor, ephedrine 6 mg to restore the blood pressure, most often after insertion of the LMA. Duration of apnea was the same in all groups. The placebo group though expected to have a shorter duration of apnea had duration similar to the succinylcholine groups. This is probably because of the increased propofol consumption.

Fasciculations were more in the Group III. Some patients in the 0.1 mg/kg group did not have fasciculations. There were two patients in the placebo group who had “fasciculations,” these were probably involuntary movements that can occur with propofol and were interpreted as fasciculations.

The incidence of myalgia was very low. Lately, it has been observed that myalgia is common after ambulatory surgery, and the causes are multifactorial. The incidence of myalgia is highest in the first 24 h, but does occur even afterward.[29] In this study, patients were checked for myalgia for up to 24 h postoperatively. Myalgia was seen in one patient in Group II after 2 h and two patients in the placebo group after 4 h. This too may advocate the multifactorial cause of myalgia.

Other side effects of succinylcholine are bradycardia, masseter rigidity, and hyperkalemia. Out of 293 patients, none experienced bradycardia or masseter rigidity. Although we did not look for hyperkalemia, as our patient population was of the physical status ASA classes 1 and 2, a rise of potassium by 0.5 mEq/L was not clinically significant. Side effects such as raised intragastric, intraoccular, and intracranial pressure too were insignificant in these patients. Prolonged paralysis too did not occur in any patient.

Limitations

Although the primary investigator was blinded, fasciculations were sometimes a confounding factor. Myalgia was assessed only up to 24 h postoperatively. There may have been more myalgia later than this period. Other side effects of Succinylcholine such as hyperkalemia were not looked into. The incidence of post op sore throat was not analyzed.

CONCLUSIONS

This study concludes that a low dose of succinylcholine does facilitate the insertion of the LMA. 0.25 mg/kg of succinylcholine seems to be the optimum dose as it provides significantly better intubating conditions compared to 0.1 mg/kg succinylcholine and placebo without significant adverse effects. We suggest that succinylcholine is a useful and cost-effective adjunct in the Asian population where mivacurium, rapacuronium, and remifentanil are not yet available, especially for short cases.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.