The Optimal Dose of Succinylcholine for Rapid Sequence Induction

A Systematic Review and Meta-analysis of Randomized Trials

Alessandro Putzu; Martin R. Tramèr; Maxim Giffa; Christoph Czarnetzki

Disclosures

BMC Anesthesiol. 2020;20(54) 

In This Article

Results

Study Selection

Our searches yielded 722 potentially relevant reports (Figure 1). After exclusion of 690 inappropriate studies, 12 studies were retrieved as complete articles. Of these, six were excluded as they did not meet the inclusion criteria. Two of those tested different doses of succinylcholine without comparison with the gold standard regimen (1 mg kg− 1),[17,18] two included obese patients only (body mass index ≥40 kg m− 2),[13,14] and two did not report on intubating conditions.[19,20] We finally included six RCTs with relevant data on 864 patients (Figure 1).[21–26]

Figure 1.

Flow diagram of the study selection process

Study Characteristics

Eligible studies were published between 2003 and 2014 (Table 1). They were performed in four countries (China, India, Saudi Arabia, USA) and included between 69 and 200 patients. Patients were ASA 1 or 2, 18 to 65 years old, with a body mass index < 30 kg m− 2. All patients were eligible for elective surgery under general anaesthesia with tracheal intubation, were fasting preoperatively, had no criteria of difficult airway, no contraindication for succinylcholine, and no family history of an abnormal response to succinylcholine.

All trials included a group with a standard succinylcholine regimen (1.0 mg kg− 1). Experimental regimens were 0.3 mg kg− 1,[21–23,26] 0.4 mg kg− 1,[22,24,25] 0.5 mg kg− 1,[21–23] 0.6 mg kg− 1,[22,24–26] 0.8 mg kg− 1,[25] 1.5 mg kg− 1,[23] and 2.0 mg kg− 1.[23] Five trials were double blinded. The modified Oxford quality score ranged from 2 to 6. One trial was not blinded and therefore judged to be at high risk of bias (Figure S1 and S2).[23] Two trials reported sources of authors' funding and conflicts of interest.[24,26]

Induction Techniques

In three studies, patients were premedicated (Table 1).[21,23,25] Three studies used a true RSI,[21,23,24] and two a modified RSI.[22,25] All five used intravenous propofol 2 mg kg− 1 with a concomitant intravenous opioid for induction. The sixth study used an induction technique with sevoflurane without intravenous opioids; there was no delay between loss of consciousness and the administration of succinylcholine.[26] One study specified the use of a cricoid pressure.[24] In all studies, intubating conditions were evaluated 50 to 60 s after the administration of succinylcholine. Four studies specified that intubations were performed by an experienced anaesthetist.[21–24]

Quality of Intubating Conditions

Excellent Intubating Conditions. With the standard succinylcholine regimen (1.0 mg kg− 1), the incidence of excellent intubating conditions ranged from 58%[26] to 100%[24,25] (cumulative number of patients, 185 of 233 [79%]) (Figure 2).

Figure 2.

Excellent intubating conditions with the standard regimen of succinylcholine (1.0 mg kg− 1) compared with different experimental regimens. Comparisons are listed according to increasing experimental doses. ARD = absolute risk difference; NNT = number needed to treat; CI = confidence interval; ∞ = infinity (i.e. ARD = 0). A positive ARD suggested that an outcome was improved with an experimental regimen compared with the standard regimen and was consequently translated into a positive NNT. A negative ARD suggested that an outcome was worsened with an experimental regimen compared with the standard regimen and was consequently translated into a negative NNT (which may be interpreted as a "number needed to harm"). An ARD of 0, indicating no difference between the experimental and the standard regimen, was translated into an NNT of infinity (∞)

With four experimental regimens that were tested in at least three trials each (0.3, 0.4, and 0.5 mg kg− 1),[21–26] excellent intubating conditions were significantly less frequent compared with 1.0 mg kg− 1 (ARD ranging from − 9% to − 67%) (Figure 2). With 0.8 mg kg− 1, tested in one trial only,[25] excellent intubating conditions were also significantly less frequent compared with 1.0 mg kg− 1 (ARD − 12%) (Figure 2). With 0.6 and 1.5 mg kg− 1, no difference was found. With 2.0 mg kg− 1, excellent intubating conditions were significantly more frequent compared with 1.0 mg kg− 1 (ARD + 23%) (Figure 2). Both 1.5 and 2 mg kg− 1 were tested in one trial only.[23] The I2 ranged from 54% to 95% (Figure S3).

Unacceptable Intubating Conditions. With the standard succinylcholine regimen (1.0 mg kg− 1), the incidence of unacceptable intubating conditions ranged from 0%[22,24,25] to 6.7%[26] (cumulative number of patients, 6 of 233 [2.6%]) (Figure 3). With 0.3 and 0.4 mg kg− 1, tested in at least three trials each,[21–25] unacceptable intubating conditions were significantly more frequent compared with 1.0 mg kg− 1 (ARD + 22% and + 32%) (Figure 3). With 0.5 and 0.6 mg kg− 1, also tested in at least three trials each,[21–25] and with 0.8, 1.5 and 2.0 mg kg− 1, tested in one trial each,[23,25] the likelihood of unacceptable intubating conditions was no different from 1.0 mg kg− 1 (Figure 3). The I2 ranged from 0% to 93% (Figure S4).

Figure 3.

Unacceptable intubating conditions with the standard regimen of succinylcholine (1.0 mg kg− 1) compared with different experimental regimens. Comparisons are listed according to increasing experimental doses. ARD = absolute risk difference; NNT = number needed to treat; CI = confidence interval; ∞ = infinity (i.e. ARD = 0). A positive ARD suggested that an outcome was improved with an experimental regimen compared with the standard regimen and was consequently translated into a positive NNT. A negative ARD suggested that an outcome was worsened with an experimental regimen compared with the standard regimen and was consequently translated into a negative NNT (which may be interpreted as a "number needed to harm"). An ARD of 0, indicating no difference between the experimental and the standard regimen, was translated into an NNT of infinity (∞)

Apnoea Times. With the standard succinylcholine regimen (1.0 mg kg− 1), average apnoea times, reported in four trials,[22,24–26] ranged from 4.0 min[26] to 8.2 min[24] (Figure 4). Two experimental regimens, 0.4 and 0.6 mg kg− 1, were tested in at least three trials,[22,24–26] and in both, apnoea times were significantly shortened compared with the gold standard regimen (MD, − 3.4 and − 1.9 min, respectively). Three regimens (0.3, 0.5, 0.8 mg kg− 1) were tested in one or two trials each[22,25,26] and were associated with shorter apnoea times compared with 1 mg kg− 1 (Figure 4). With 1.5 and 2.0 mg kg− 1, no apnoea times were reported. The I2 ranged from 74% to 97% (Figure S5).

Figure 4.

Apnoea times (in min) with the standard regimen of succinylcholine (1.0 mg kg− 1) compared with different experimental regimens. The time from injection of succinylcholine until first diaphragmatic movement or until obvious recognizable end-tidal CO2 waveforms appearing on the monitor was used as a surrogate of apnoea time. MD = mean difference; CI = confidence interval; n/a = not applicable (no data reported)

Sensitivity Analyses. Computing risk ratios did not change the magnitude of the results (Figure S6), as did the use of a fixed effect model (Figure S7). The exclusion of one trial[22] decreased the degree of heterogeneity in some analyses but aggregated results remained similar (Figure S8).

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