The Dose of Succinylcholine Required for ExcellentEndotracheal Intubating ConditionsMohamed Naguib, MB, BCh, MSc, MD, Abdulhamid H. Samarkandi, MB, BS, KSUF, FFARCSI,Mansour Emad El-Din, MD, Khaled Abdullah, MB, BCh, MSc, AB, MD, Mazen Khaled, MD, andSaleh W. Alharby, MB, BS, FRCS (Glas)

Department of Anesthesiology and Pain Medicine, The University of Texas M. D. Anderson Cancer Center, Houston,Texas; Departments of Anesthesia and Surgery, King Saud University, Riyadh, Saudi Arabia

In this prospective, randomized, double-blind,placebo-controlled study, we attempted to define thedose of succinylcholine that provides excellent intuba-tion conditions in patients within 60 s during simulatedrapid-sequence induction of anesthesia. Anesthesiawas induced in 180 patients with 2 �g/kg fentanyl and2 mg/kg propofol. After loss of consciousness, patientswere randomly allocated to receive 0.3, 0.5, 1.0, 1.5, or2.0 mg/kg succinylcholine or saline solution (controlgroup). Tracheal intubation was performed 60 s later. Ablinded investigator performed all laryngoscopies andgraded intubating conditions. Intubating conditionswere excellent in 0.0%, 43.3%, 60.0%, 63.3%, 80.0%, and86.7% of patients after 0.0, 0.3, 0.5, 1.0, 1.5, and

2.0 mg/kg succinylcholine, respectively. The incidenceof excellent intubating conditions was significantlymore frequent (P � 0.001) in patients receiving succi-nylcholine than in the controls and in patients who re-ceived 2.0 mg/kg succinylcholine (P � 0.05) than inthose who received 0.3 mg/kg succinylcholine. The cal-culated doses of succinylcholine (and their 95% confi-dence intervals) that are required to achieve excellentintubating conditions in 50% and 80% of patients at 60 sare 0.39 (0.29–0.51) mg/kg and 1.6 (1.2–2.0) mg/kg, re-spectively. It appears that there are no advantages tousing doses of succinylcholine larger than 1.5 mg/kg.

(Anesth Analg 2006;102:151–5)

S uccinylcholine remains the drug of choice forrapid sequence induction of anesthesia. Themost commonly used dose of succinylcholine is

1.0 mg/kg. The reported incidence of acceptable intu-bating conditions (excellent plus good grades com-bined) after administration of 1.0 mg/kg succinylcho-line varies from 91.8% to 98% (1–5). The dose ofsuccinylcholine needs to be individualized, however,depending on the clinical situation. In some situations“acceptable” conditions for tracheal intubation are notideal. In the patient with increased intracranial pres-sure or the patient with a full stomach, for example,any intubating conditions short of excellent may notbe suitable. The reported incidence of excellent intu-bating conditions after administration of 1.0 mg/kg

succinylcholine in simulated rapid sequence inductionvaries from 63% to 80% (1,3–5). The reported incidenceof excellent intubating conditions after administrationof larger doses (1.5 mg/kg) of succinylcholine rangesfrom 55% to 85% (6,7).

In this prospective, randomized, double-blind,placebo-controlled study, we attempted to define thedose of succinylcholine that provides excellent intuba-tion conditions in 90% of patients within 60 s during asimulated rapid sequence induction of anesthesia.

MethodsAfter obtaining institutional approval (King KhalidUniversity Hospital, Riyadh, Saudi Arabia) and in-formed patient consent, we enrolled 180 adult patientsof both sexes who were ASA physical status I, aged30.9 � 10.2 yr (mean � sd), and weighed 69.6 �12.3 kg. All patients underwent elective procedures;had no neuromuscular, renal, or hepatic disease; andno patient was taking any drug known to interferewith neuromuscular function. Exclusion criteria in-cluded a history of drug or alcohol abuse, gastro-esophageal reflux or hiatal hernia, cardiovascular dis-ease, reactive airway disease, allergies to any of the

The results of this study were presented at the American Societyof Anesthesiologists Annual Meeting, October 22–26, 2005, Atlanta,GA.

Accepted for publication July 22, 2005.Address correspondence and reprint requests to Mohamed

Naguib, MB, BCh, MSc, MD, Department of Anesthesiology andPain Medicine, The University of Texas M. D. Anderson CancerCenter, 1400 Holcombe Boulevard, Unit 409, Houston, TX 77030–4009. Address e-mail to naguib@mdanderson.org.

DOI: 10.1213/01.ANE.0000181320.88283.BE

©2006 by the International Anesthesia Research Society0003-2999/06 Anesth Analg 2006;102:151–5 151

study drugs, administration of sedative or narcoticdrugs in the previous 24 h, renal or hepatic impair-ment, or anticipated difficult intubation. No premed-ication was administered. An IV infusion of lactatedRinger’s solution was started before induction of an-esthesia. Standard monitoring was used.

The ability to ventilate the lungs was tested beforeinduction of anesthesia by applying positive airwaypressure via a tightly fitting mask. Thereafter, all pa-tients inhaled 100% oxygen from the anesthesia circuitvia a facemask, and 2 �g/kg fentanyl was adminis-tered IV. Administration of oxygen was continued for3 min and then 2 mg/kg propofol was administeredIV. When the patient lost consciousness, one of thefollowing was administered through a rapidly flowingIV line: 0.3, 0.5, 1.0, 1.5, or 2.0 mg/kg succinylcholineor saline solution (control group). Succinylcholine andplacebo (saline) were prepared in coded syringes toachieve double blinding. The coded syringes wereprepared by a pharmacist using a randomizationschedule provided in sealed envelopes according to acomputer-generated list. All other personnel wereblinded as to the patient’s treatment group. Each pa-tient was randomly assigned to a particular dosagegroup or to the control group (n � 30 in each group).

Because observation of fasciculations would iden-tify the drug administered as succinylcholine, the an-esthesiologist performing and grading the intubationwas positioned with his back to the patient until justbefore beginning the intubation sequence. The tra-cheal intubation sequence was begun between 40 and45 s after administration of succinylcholine. The headwas positioned, laryngoscopy was started at 50 s usinga size 3 Macintosh blade, and tracheal intubation wassubsequently performed 60 s after succinylcholine ad-ministration. Cuffed endotracheal tubes of 7-mm and8-mm sizes were used in female and male patients,respectively. The scheme for grading conditions fortracheal intubation was based on accepted criteria forgood clinical research practice (Table 1) (8). Intubatingconditions were graded as excellent if all variableswere excellent. If all the variables were not excellent,

intubating conditions were graded as good unless anyvariable was graded poor. If any variable was poor,the intubating conditions were graded as poor. Theinvestigator performing the intubation and gradingintubation conditions was an experienced anesthesiol-ogist and was blinded as to which group the patienthad been assigned.

Before induction of anesthesia, surface electrodeswere placed over the ulnar nerve at the wrist. Afterloss of consciousness, the ulnar nerve was stimulatedat the wrist with square wave stimulus set at a currentof 60 mA and a duration of 0.2 ms. Each stimulus wasdelivered in a train-of-four (TOF) sequence and re-peated every 12 s using a Myotest peripheral nervestimulator (Biometer International, Odense, Den-mark). An investigator counted the number of tactileTOF responses immediately after administration ofthe study drug. Onset time was defined as the timefrom the end of injection of the study drug untilmaximum block of the TOF response. The duration ofaction was the time from injection until return of thetactile TOF response. Thereafter, the investigatory in-tervention was terminated, and anesthesia continuedas appropriate for surgery. Each patient was moni-tored for any adverse effects.

Demographic data were analyzed with analysis ofvariance or �2 test as appropriate. If analyses of vari-ance results were significant, the Dunnett post hoc testwas used to compare the study groups and the controlgroup. The Duncan multiple range test was used tocompare the onset time and duration of block amongthe different succinylcholine dosage groups. Intubat-ing conditions and TOF counts were analyzed with aKruskal-Wallis test for multiple comparisons usingthe Bonferroni adjustments. Statistical analyses wereperformed using the BMDP statistical software pack-age (release 7.01; University of California Press, Berke-ley, CA; 1994) and StatXaxt for Windows (version4.0.1; CYTEL Software Corporation, Cambridge, MA;1999). The doses of succinylcholine that were requiredto achieve excellent intubation conditions in 50% and80% of patients at 60 s were calculated by probit

Table 1. Criteria for Grading Tracheal Intubation Conditions

Variables

Intubating conditions

Excellent Good Poor

Laryngoscopy Easy Fair DifficultVocal cords

Position Abducted Intermediate ClosedMovements None Moving Closing

Reaction to intubationMovement of limbs None Slight VigorousCoughing None Diaphragm Sustained (�10 s)

Intubation conditions: Excellent � all variables are excellent; Good � all variables are either excellent or good; Poor � the presence of one or more variablesgraded as poor.

Laryngoscopy: Easy � jaw relaxed, no resistance to blade during laryngoscopy; Fair � jaw not fully relaxed, slight resistance to blade; Difficult � poor jawrelaxation, active resistance by the patient.

152 ANESTHETIC PHARMACOLOGY NAGUIB ET AL. ANESTH ANALGSUCCINYLCHOLINE AND TRACHEAL INTUBATION 2006;102:151–5

analysis using the pharmacologic software programsof Tallarida and Murray (9). Logistic regression anal-ysis was performed to test the influence of body massindex (BMI), age, and dose as predictors for excellentintubating conditions. Unless otherwise specified, re-sults are expressed as means and sd or medians andinterquartile ranges (25%–75%) and are consideredsignificant at P � 0.05.

ResultsThere were no significant differences among the sixgroups regarding baseline demographics (Table 2). Allpatients underwent successful tracheal intubation ex-cept for seven patients in the control group. Intubatingconditions were excellent in 0.0%, 43.3%, 60.0%, 63.3%,80.0%, and 86.7% of patients after 0.0, 0.3, 0.5, 1.0, 1.5,and 2.0 mg/kg succinylcholine, respectively (Fig. 1and Table 2). The incidence of excellent intubatingconditions was significantly more frequent (P � 0.001)in patients receiving succinylcholine than in those inthe control group and in the 2.0 mg/kg succinylcho-line group (P � 0.05) than in the 0.3 mg/kg succinyl-choline group. Probit analysis yielded calculateddoses of succinylcholine (and their 95% confidenceintervals) that are required to achieve excellent intu-bating conditions in 50% and 80% of patients at 60 s of0.39 (0.29–0.51) mg/kg and 1.6 (1.2–2.0) mg/kg, re-spectively (Fig. 2). Logistic regression model adjustedfor age and BMI predicted that the dose was a signif-icant predictor for excellent intubating conditions.

TOF response was abolished at �60 s in 6, 18, 25, 24,and 26 patients after administration of succinylcholinedoses of 0.3, 0.5, 1.0, 1.5, and 2.0 mg/kg, respectively(Table 2). There were no significant differences in the

onset times among the different doses of succinylcho-line studied (Table 3). The duration of action of succi-nylcholine was dose dependent and was significantlylonger after doses of 1.5 and 2.0 mg/kg than afterdoses of 0.3, 0.5, and 1.0 mg/kg (Table 3).

DiscussionIn rapid sequence induction of anesthesia, 0.39 (0.29–0.51) mg/kg and 1.6 (1.2–2.0) mg/kg succinylcholinewould be required to achieve excellent intubating con-ditions in 50% and 80 of patients with normal airway

Figure 1. Intubating conditions with different doses of succinylcho-line (n � 30 in. each group). The incidence of excellent intubatingconditions was significantly more frequent (*P � 0.001) in patientsreceiving succinylcholine than in those of the control group and inthe 2.0 mg/kg succinylcholine group (#P � 0.05) than in the0.3 mg/kg succinylcholine group (Kruskal-Wallis test for multiplecomparisons).

Table 2. Demographic Characteristics, Intubating Conditions, and Train-of-Four Count

Succinylcholine dose

Control(n � 30)

0.3 mg/kg(n � 30)

0.5 mg/kg(n � 30)

1.0 mg/kg(n � 30)

1.5 mg/kg(n � 30)

2.0 mg/kg(n � 30)

Age (yr) 33.5 � 8.7 29.7 � 8.8 28.3 � 7.9 31.5 � 9.6 33.8 � 14.8 20.1 � 8.8Weight (kg) 67.8 � 10.3 67.3 � 10.8 71.1 � 14.2 72.9 � 12.5 70.9 � 14.5 67.4 � 10.7Sex (male/female) 13/17 11/19 17/13 16/14 12/18 11/19Height (cm) 162 � 8 162 � 10 165 � 10 166 � 9 165 � 9 162 � 9Body mass index

(kg/m2)25.6 � 2.8 25.6 � 3.2 25.9 � 3.9 26.2 � 3.2 25.7 � 3.9 25.7 � 3.4

Intubating ConditionsExcellent (%) 13 (43.3%)* 18 (60%)* 19 (63.3%)* 24 (80%)* 26 (86.7%)*† –Good (%) 15 (50%) 10 (33.3%) 10 (33.3%) 5 (16.7%) 4 (13.3%) 9 (30%)Poor (%) 2 (6.7%) 2 (6.7%) 1 (3.3%) 1 (3.3%) – 14 (46.7%)Failed (%) – – – – – 7 (23.3%)

TOF Count 3 (0.8–4) 0 (0–2.3)* 0 (0–0)*† 0 (0–0)*† 0 (0–0)*† 4 (4–4)

Data are means � SD, number (%), or medians and interquartile ranges (25%–75%).TOF count � the number of tactile train-of-four responses immediately after tracheal intubation.*P � 0.001 versus the control group (Kruskal-Wallis test for multiple comparisons); †P � 0.05 versus the 0.3 mg/kg succinylcholine group (Kruskal-Wallis test

for multiple comparisons).

ANESTH ANALG ANESTHETIC PHARMACOLOGY NAGUIB ET AL. 1532006;102:151–5 SUCCINYLCHOLINE AND TRACHEAL INTUBATION

anatomy anesthetized with 2 �g/kg fentanyl and2 mg/kg propofol%, respectively.

Consistent with our results, Stewart et al. (7) re-ported that, after induction of anesthesia with5 mg/kg thiopental, 23 (85%) of 27 patients receiving1.5 mg/kg succinylcholine, and 18 (56%) of 32 patientsreceiving 0.5 mg/kg succinylcholine had excellent in-tubating conditions at 60 s. Iamaroon et al. (6) reportedthat, in patients anesthetized with 5 mg/kg thiopental,the incidence of excellent intubating conditions at 60 s

after 1.5 mg/kg succinylcholine was 55% as assessedby the intubationist. In the present study, increasingthe succinylcholine dose from 1.5 to 2.0 mg/kg re-sulted in only 6.7% improvement in the incidence ofexcellent intubating conditions (from 80% to 86.7%).There is probably no advantage to exceeding a dose ofsuccinylcholine of 1.5 mg/kg, as the results in thisgroup were not significantly different from those ofthe 2.0 mg/kg group. Our data also suggest that thedose required to achieve excellent intubating condi-tions in 90% of patients is larger than 2.0 mg/kgsuccinylcholine. It is possible that increasing succinyl-choline dosage to 3 mg/kg, for instance, would haveincreased the incidence of excellent intubating condi-tions to 90%. The question remains, is there any justi-fication to using doses of this magnitude? In fact, nodose of succinylcholine would guarantee excellent in-tubating conditions within 60 s in 100% of patientsbecause of the limiting effects of the circulation timeand muscle blood flow (10–12). In patients anesthe-tized with 2.0–2.5 mg/kg propofol, a succinylcholinedose of 3.0 mg/kg failed to produce uniform excellentintubating conditions within 60 s (13).

Our data confirm our previous findings that a suc-cinylcholine dose of �0.5 mg/kg is adequate forachieving clinically acceptable (excellent or good) con-ditions for routine tracheal intubation within 60 s (5).Intubating conditions depend on several factors, in-cluding the depth of anesthesia, the interval betweendrug administration and laryngoscopy, the dose of theneuromuscular blocking drug given, the anatomy ofthe airway, and the experience of the intubationist.

There were few differences in onset times for thedoses of succinylcholine (0.3 to 2.0 mg/kg) used in thisstudy (Table 3). The mean onset times were 72 s with0.3 mg/kg and 52 s with 2.0 mg/kg succinylcholine.Koscielniak-Nielsen et al. (14) reported that the meanonset times during fentanyl-thiopental-oxygen anes-thesia, measured by mechanomyography, were 79.5 sand 71 s after administration of 0.3 mg/kg and1 mg/kg succinylcholine, respectively. Kopman et al.(15) reported that the mean onset times, measured byacceleromyographic monitor, were 105 s and 71 s afteradministration of 0.4 mg/kg and 1.0 mg/kg succinyl-choline, respectively, in patients anesthetized withdesflurane-oxygen-opioid anesthesia.

In the present study, the duration of succinylcholine-induced block was dose dependent and ranged from4.4 min for the 0.3 mg/kg dose to 7.5 min for the2.0 mg/kg dose. These results are consistent with previ-ously published results of other investigators (15–18).Katz and Ryan (17), using mechanomyographic moni-toring, found in patients who were anesthetized with150–500 mg thiamylal and whose anesthesia was main-tained with nitrous oxide supplemented by thiamylal,meperidine, trichloroethylene, or halothane, that themean times to 10% recovery of the twitch tension after

Figure 2. Percentage of patients with excellent intubating conditionsin each succinylcholine dosage group is represented by filled circles.The calculated doses giving 50% and 80% excellent intubation con-ditions at 60 s are the open circles, and the error bars are the 95%confidence intervals.

Table 3. Onset Times and Durations of NeuromuscularBlock

Succinylcholinedose (mg/kg)

Onsettime(s)

Duration ofblock (min) n

0.3 72 � 30 4.4 � 1.4 130.5 68 � 44 5.2 � 1.8 271.0 53 � 23 5.9 � 1.9† 301.5 56 � 31 7.2 � 2* 302.0 52 � 21 7.5 � 1.7* 30

Values are means � SD.*P � 0.01 versus succinylcholine 0.3, 0.5, and 1.0 mg/kg groups; †P � 0.05

versus succinylcholine 0.3 mg/kg group.

154 ANESTHETIC PHARMACOLOGY NAGUIB ET AL. ANESTH ANALGSUCCINYLCHOLINE AND TRACHEAL INTUBATION 2006;102:151–5

succinylcholine doses of 0.5, 1.0, and 2.0 mg/kg were 5.5,10.2, and 13.1 min, respectively. Corresponding timesreported by Walts and Dillon (16) and Vanlinthout et al.(18) were 4.6, 8.1, and 10.7 min, and 4.8, 8.5, and 13.0 min,respectively. Kopman et al. (15) reported that, duringdesflurane-oxygen-opioid anesthesia, times to 10% re-covery of twitch height after administration of succinyl-choline doses of 0.6 mg/kg and 1.0 mg/kg were, onaverage, 5.1 and 6.2 min, respectively.

In conclusion, it appears that there are no advan-tages to using succinylcholine doses larger than1.5 mg/kg in a rapid sequence induction of anesthesia.Succinylcholine doses as large as 2.0 mg/kg do notguarantee excellent intubating conditions within 60 sin 90% of patients.

References1. Blobner M, Mirakhur RK, Wierda JM, et al. Rapacuronium 2.0 or

2.5 mg · kg�1 for rapid-sequence induction: comparison withsuccinylcholine 1.0 mg · kg�1. Br J Anaesth 2000;85:724–31.

2. McCourt KC, Salmela L, Mirakhur RK, et al. Comparison ofrocuronium and suxamethonium for use during rapid sequenceinduction of anaesthesia. Anaesthesia 1998;53:867–71.

3. Andrews JI, Kumar N, van den Brom RH, et al. A large simplerandomized trial of rocuronium versus succinylcholine in rapid-sequence induction of anaesthesia along with propofol. ActaAnaesthesiol Scand 1999;43:4–8.

4. Sparr HJ, Mellinghoff H, Blobner M, Noldge-Schomburg G.Comparison of intubating conditions after rapacuronium (Org9487) and succinylcholine following rapid sequence inductionin adult patients. Br J Anaesth 1999;82:537–41.

5. Naguib M, Samarkandi A, Riad W, Alharby SW. Optimal doseof succinylcholine revisited. Anesthesiology 2003;99:1045–9.

6. Iamaroon A, Pitimana-aree S, Prechawai C, et al. Endotrachealintubation with thiopental/succinylcholine or sevoflurane-nitrous oxide anesthesia in adults: a comparative study. AnesthAnalg 2001;92:523–8.

7. Stewart KG, Hopkins PM, Dean SG. Comparison of high andlow doses of suxamethonium. Anaesthesia 1991;46:833–6.

8. Viby-Mogensen J, Englbaek J, Eriksson LI, et al. Good clinicalresearch practice (GCRP) in pharmacodynamic studies of neuro-muscular blocking agents. Acta Anaesthesiol Scand 1996;40:59–74.

9. Tallarida RJ, Murray RB. Manual of pharmacologic calculationswith computer programs, 2nd ed. New York: Springer-Verlag,1987.

10. Harrison GA, Junius F. The effect of circulation time on theneuromuscular action of suxamethonium. Anaesth IntensiveCare 1972;1:33–40.

11. Goat VA, Yeung ML, Blakeney C, Feldman SA. The effect ofblood flow upon the activity of gallamine triethiodide. Br JAnaesth 1976;48:69–73.

12. Donati F. Onset of action of relaxants. Can J Anaesth 1988;35:S52–8.

13. McLoughlin C, Leslie K, Caldwell JE. Influence of dose onsuxamethonium-induced muscle damage. Br J Anaesth 1994;73:194–8.

14. Koscielniak-Nielsen ZJ, Bevan JC, Popovic V, et al. Onset ofmaximum neuromuscular block following succinylcholine orvecuronium in four age groups. Anesthesiology 1993;79:229 –34.

15. Kopman AF, Zhaku B, Lai KS. The “intubating dose” ofsuccinylcholine: the effect of decreasing doses on recovery time.Anesthesiology 2003;99:1050–4.

16. Walts LF, Dillon JB. Clinical studies on succinylcholine chloride.Anesthesiology 1967;28:372–6.

17. Katz RL, Ryan JF. The neuromuscular effects of suxamethoniumin man. Br J Anaesth 1969;41:381–90.

18. Vanlinthout LE, van Egmond J, de Boo T, et al. Factors affectingmagnitude and time course of neuromuscular block producedby suxamethonium. Br J Anaesth 1992;69:29–35.

ANESTH ANALG ANESTHETIC PHARMACOLOGY NAGUIB ET AL. 1552006;102:151–5 SUCCINYLCHOLINE AND TRACHEAL INTUBATION