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Anesth Analg 1999;88:908
© 1999 International Anesthesia Research Society

GENERAL ARTICLES

Comparison of Sevoflurane with Propofol for Laryngeal Mask Airway Insertion in Adults

Lian Kah Ti, MMED*, Mark Y. H. Chow, MMED{dagger}, and Tat Leang Lee, MMED, FFARACS*

*Department of Anaesthesia, National University Hospital; and {dagger}Department of Anaesthesia and Surgical Intensive Care, Singapore General Hospital, Singapore

Address correspondence and reprints requests to Lian Kah Ti, MMed, Department of Anaesthesia, National University Hospital, 5 Lower Kent Ridge Rd., Singapore 119074, Republic of Singapore. Address e-mail to anatilk{at}nus.edu.sg


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
We performed a prospective, randomized, controlled trial to compare the quality and ease of laryngeal mask airway (LMA) insertion after either rapid inhaled sevoflurane or IV propofol induction of anesthesia. Seventy-six unpremedicated ASA physical status I or II patients were anesthetized with either a single vital capacity breath of sevoflurane 8% or IV propofol 3 mg/kg, which produced equally rapid loss of consciousness (40.5 ± 13.9 vs 37.7 ± 9.9 s; P > 0.05). The LMA was inserted more rapidly in patients in the propofol group (74 ± 29 vs 127 ± 35 s; P < 0.01) and required fewer attempts (1.2 vs 1.6; P < 0.05) than the sevoflurane group. There was a greater incidence of initially impossible mouth opening in the sevoflurane group (45% vs 21%; P < 0.05). Once mouth opening was possible, the degree of attenuation of laryngeal reflexes was similar. The overall incidence of complications related to LMA insertion, especially apnea (32% vs 0%; P < 0.01), was more frequent in the propofol group (82% vs 26%; P < 0.01). There were four failures of LMA insertion in the propofol group and none in the sevoflurane group. Both groups had stable hemodynamic profiles and good patient satisfaction. We conclude that sevoflurane vital capacity breath induction compares favorably with IV propofol induction for LMA insertion in adults. However, prolonged jaw tightness after the sevoflurane induction of anesthesia may delay LMA insertion.

Implications: In this randomized, controlled trial, we compared the ease of insertion of the laryngeal mask airway in adults after induction of anesthesia with either a sevoflurane vital capacity breath technique or propofol IV. We conclude that sevoflurane compares favorably with propofol, although prolonged jaw tightness may delay laryngeal mask airway insertion.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Insertion of the laryngeal mask airway (LMA) under deep inhaled anesthesia alone is not commonly performed in adult patients. A popular method of providing anesthesia for LMA insertion is with the use of IV propofol, which has the advantages of inducing anesthesia rapidly and depressing upper airway reflexes (1). However, propofol is by no means ideal, as it has been associated with several adverse effects including hypotension, apnea, and pain on injection (2).

Recently, single vital capacity breath (VCB) inhaled induction of anesthesia with sevoflurane has been used as an alternative to IV induction in adults. This method is rapid, with little excitatory phenomena, high patient acceptance, and good hemodynamic stability (3). Rapid insertion of the LMA after VCB induction may allow the use of sevoflurane as a single drug for the induction and maintenance of anesthesia, which would ease the transition period and lead to cost-savings (4). Therefore, in this study, we compared the reliability, quality, and speed of LMA insertion in adult patients after sevoflurane VCB inhaled induction and propofol IV induction of anesthesia.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
Institutional ethical approval and written informed consent were obtained from all patients. Seventy-six adult ASA physical status I or II patients aged 18–52 yr undergoing minor surgical procedures were recruited. Patients with an allergy or sensitivity to volatile anesthetics or to propofol, known or suspected genetic susceptibility to malignant hyperthermia, heavy smokers (>=20 cigarettes per day), and with impaired ability to communicate (e.g., confusion, poor hearing or language barrier) were excluded from the study. The patients were randomized by computer-generated numbers into two groups. Patients allocated to the sevoflurane group were taught the VCB technique. No patients were premedicated.

For patients in the sevoflurane group, a circle CO2 absorber circuit with a 5-L reservoir bag was used. The circuit was primed with sevoflurane 8% in a 2:1 ratio of nitrous oxide to oxygen at a fresh gas flow of 6 L/min for 1 min. The patients were asked to take a deep breath then exhale to residual volume. The mask with the primed circuit was placed firmly over the patient’s face. The patients were then instructed to inhale a VCB and hold it as long as they could. The start of induction was taken as the point at which the patients completed their VCB. While holding their breath, the patients were asked to open their eyes every 10 s. Failure to do so was taken as loss of consciousness (LOC). This was confirmed by testing for the loss of eyelash reflex. Duration of vital capacity breath-hold was noted. Ninety seconds after the start of induction, the ease of mouth opening was assessed (possible or impossible). Ninety seconds was chosen because it represents the time at which all patients would have completed their VCB. If mouth opening was impossible, another attempt was made every 30 s up, to a maximum of four tries. An attempt to open the mouth was considered an attempt at insertion. During this time, anesthesia was maintained with sevoflurane at a dial concentration of 8% and nitrous oxide 67% in oxygen.

Once mouth opening was possible, insertion of the LMA was attempted, and the degree of attenuation of laryngeal reflexes was assessed. This was classified as full when the LMA was inserted smoothly; partial when insertion was accompanied by gagging, coughing or involuntary movement; or poor when LMA insertion was impossible. A size 3 or 4 LMA was used for patients weighing <70 kg or >70 kg, respectively, regardless of gender.

Patients in the propofol group breathed oxygen for 3 min and were anesthetized with propofol 3 mg/kg IV mixed with lidocaine 0.3 mg/kg, given over 30 s. Midway through induction (at 15 s), the patients were asked if they felt any pain from the injection. Time to LOC was determined as it had been for the sevoflurane group. Thirty seconds after the completion of propofol induction (i.e., 60 s after the start of the propofol injection), ease of mouth opening was assessed and, if possible, LMA insertion was attempted. If impossible, repeat attempts were made every 30 s up to a maximum of four attempts, each time preceded by propofol boluses of 0.5 mg/kg IV

LMA insertions were performed by the same investigator (LKT) using the technique recommended in the Intavent® LMA manual (Berkshire, UK). Once the LMA was inserted, all patients were given sevoflurane 4.0% in 67% nitrous oxide in oxygen at a fresh gas flow rate of 3 L/min for 3 min, before decreasing the dial concentration of sevoflurane to 2% for maintenance. Noninvasive blood pressure, electrocardiogram lead II, pulse oximeter, ETCO2, and end-tidal sevoflurane readings were recorded every minute for 5 min. Any failures of insertion, defined as failure to insert the laryngeal mask after four tries, were rescued with succinylcholine 25 mg IV. No controlled or assisted breaths were given unless the patient suffered oxygen desaturation to a pulse oximetry reading of <90%. The decision not to manually ventilate our patients between LMA insertion attempts was intended to avoid abolishing their hypercarbic drive, which would prolong the period of apnea.

An independent but nonblinded observer noted the presence of complications related to anesthetic induction and insertion of the LMA. These included involuntary movement (excitatory movement or withdrawal from pain of injection), coughing, gagging, apnea (when time to onset of spontaneous respiration after insertion of the laryngeal mask was >30 s) and laryngospasm. At the end of the operation, the LMAs were removed with the patients still anesthetized. The presence of blood on the mask, signifying trauma on insertion, was noted. Once fully awake, the patients were interviewed by a blinded investigator who asked whether they found the induction of anesthesia pleasant and whether they had a sore throat.

All results are expressed as mean ± SD or as group percentages. Student’s t-tests, with Bonferroni correction where appropriate, were used for the patients’ variables and hemodynamic changes. {chi}2 tests, incorporating Fisher’s exact test where appropriate, were used for the variables of induction, quality of LMA insertion, complications, and postoperative assessment. A P value <0.05 was taken as statistically significant. Statistical calculations were performed using SPSS 8.0 (SPSS Inc., Chicago, IL).


   Results
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 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
The patients in both groups were comparable (Table 1). The patients in the sevoflurane group held their VCB for 45.2 ± 16.9 s, resulting in an end-tidal sevoflurane concentration of 4.4% ± 0.7% on release. Sevoflurane and propofol produced equally rapid LOC (40.5 ± 13.9 vs 37.7 ± 9.9 s; P > 0.05). Twelve patients (31%) complained of pain during the injection of propofol (Table 2). Two patients in the sevoflurane group developed laryngospasm after release of their VCB. However, this was self-limiting and did not require intervention. Neither patient suffered oxygen desaturation.


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  		Table 1. Demographic Data
 

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  		Table 2. Incidence of Complications During the Induction of Anesthesia and Laryngeal Mask Airway Insertion
 
The LMA was inserted more rapidly in patients in the propofol group versus those in the sevoflurane group (74 [60–150] vs 127 [90–210] s; P < 0.01). However, there were four insertion failures in the propofol group, whereas all insertions of the LMA were successful in the sevoflurane group (Table 3). The failures were due to the inability to open the patients’ mouths within the four tries allowed. All four patients were rescued with succinylcholine (as required by protocol) 150–210 s after the induction of anesthesia. The data from these patients were included in the analysis of demographic, induction of anesthesia, and overall success of insertion variables, but they were excluded from analysis of the data pertaining to speed and quality of LMA insertion, hemodynamic changes, and postoperative interviews.


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  		Table 3. Quality of Laryngeal Mask Airway Insertion and Postoperative Interview Results
 
More attempts at insertion of the LMA were required in patients in the sevoflurane group versus those in the propofol group (1.6 vs 1.2 attempts; P < 0.05) (Figure 1). This was primarily because of a greater incidence of initially impossible mouth openings in the sevoflurane group (45% vs 21%; P < 0.05). However, once mouth opening was possible, the degree of attenuation of laryngeal reflexes was similar in both groups (Table 3).



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  		Figure 1. Comparison of the number of attempts at laryngeal mask airway (LMA) insertion required for successful placement after the induction of anesthesia with propofol ({blacksquare}) or sevoflurane ({square}). Fewer attempts were required with propofol (1.2 vs 1.6 attempts; P < 0.05).

 
The overall incidence of complications related to the LMA insertion was higher in the propofol group (82% vs 26%; P < 0.01). Although more patients had involuntary movement, coughing and gagging in the propofol group, this did not reach significance. There was a more frequent incidence of apnea (32% vs 0%; P < 0.01) in the propofol group. In these patients, apnea lasted an average of 69 s. However, none of the patients suffered oxygen desaturation. Both groups exhibited stable hemodynamic profiles, although propofol produced a larger decrease in mean blood pressure compared with sevoflurane (Table 4). Compared with baseline, the average decrease in mean blood pressure during the study period was 18.7% (0%–41%) and 17.0% (2%–43%) in the propofol and sevoflurane groups respectively. Our patients found both techniques satisfactory, and the incidence of traumatic insertion was similar (Table 3).


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  		Table 4. Hemodynamic Data
 

   Discussion
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 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
In this study, we demonstrate that sevoflurane single VCB induction compares favorably with propofol for the insertion of LMA in adults. Both sevoflurane and propofol successfully induced anesthesia in all patients in approximately 40 s. The hemodynamic responses were stable for both groups. Insertion of LMA after sevoflurane induction was achieved in all patients in that group, compared with four failures in the propofol group. Despite some complications during the induction of anesthesia, there were fewer complications during LMA insertion in the sevoflurane group. There was good acceptability for both induction techniques. However, more attempts at insertion were required in the sevoflurane group, and the time to successful LMA insertion was 53 s longer.

Anesthetic induction and LMA insertion using sevoflurane have several advantages. Sevoflurane allows a smoother transition to the maintenance phase without a period of apnea. Apnea (defined as failure to start spontaneous ventilation within 30 s of LMA insertion) occurred in 32% of the patients in the propofol group but did not occur in the sevoflurane group. The presence of apnea often requires the anesthesiologist to ventilate the patient manually while awaiting the return of spontaneous ventilation, therefore nullifying the benefit of freeing the anesthesiologist’s hands afforded by the LMA. Sevoflurane prevents the pain on injection associated with propofol. In this study, 31% of patients complained of pain during propofol induction despite the use of lidocaine. There was less hypotension with sevoflurane, although transient hypotension >20% of baseline was seen in individual patients from both groups.

In a related study, Muzi et al. (5) achieved insertion of LMA after sevoflurane induction after 1.7 min, compared with the time taken for LMA insertion in our sevoflurane group (127 s). The shorter time may be related to their use of the less reported triple breath technique, which is associated with a shorter time of induction (6). However, no comparison was made with other techniques. Hall et al. (7) compared LMA insertion using the single breath technique with sevoflurane 8% with that using IV propofol 3 mg/kg. They showed that the addition of nitrous oxide enhances the safety and speed of sevoflurane induction, but they did not compare the ease and quality of LMA insertion at the earliest opportunity. This resulted in relatively slow times for LMA insertion (109 and 146 s for the propofol and sevoflurane groups, respectively).

Our main difficulty regarding the quality of LMA insertion when using sevoflurane was initial difficulty in mouth opening. Interestingly, Muzi et al. (5) also reported jaw tightness after sevoflurane anesthetic induction, which resulted in failure to insert the LMA in several patients. Similarly, Hall et al. (7) reported longer time to jaw relaxation with sevoflurane compared with propofol, although they did not postulate any reasons for it. The likely explanation for the poor mouth opening in our patients is the lag time during which the alveolar concentration of sevoflurane equilibrates with the brain, which results in inadequate anesthesia during the initial attempt at insertion. This is supported by the fact that the LMA was eventually inserted in all patients. Furthermore, relaxation of the jaw muscles sufficient for a jaw thrust may be a reflection of adequate depth of anesthesia (8). However, Inomata and Nishikawa (9) dispute the importance of this lag time. They argue that this is unlikely to be important with sevoflurane because of its low blood-gas partition coefficient. In our patients, the end-tidal concentration of sevoflurane was 4.4% on release of the VCB, which translates into 2.45 minimum alveolar anesthetic concentration (MAC). This is adequate for LMA insertion because, although a MAC value for insertion of the LMA in adults is not known, it is likely to approximate 2.00%, the MAC value of sevoflurane for LMA insertion in children (10).

Another possible explanation for the difference in jaw relaxation between propofol and sevoflurane may be that the propofol group received more anesthetic, as equipotent doses of both drugs could not be determined. This may account for the greater number of patients with apnea in the propofol group. However, the dose of 3 mg/kg was not excessively large for the young unpremedicated patients we studied. A third possibility is related to the anesthetics themselves. Propofol is known to have a relaxant effect on jaw muscles (11), whereas inhaled anesthetics may cause increased muscle tone and spasticity (12). Therefore, for a similar depth of anesthesia, there may be greater jaw relaxation with propofol.

In contrast to the jaw tightness, there was excellent attenuation of laryngeal reflexes with both sevoflurane and propofol. This resulted in a low incidence of traumatic LMA insertions in our patients. Although LMA placement is more closely associated with deglutition and may only require suppression of the less sensitive hypopharynx for successful placement (13), stimulation of the anterior laryngeal structures may occur during insertion. Therefore, successful attenuation of the laryngeal reflexes was essential to reduce the incidence of respiratory complications during LMA insertions. This is not surprising for propofol, as it is known to depress laryngeal reflexes and facilitate LMA insertion (14). However, sevoflurane preserves laryngeal reflexes at values up to 1.8 MAC (15). Its effect on laryngeal reflexes above this value is unknown, but this study suggests that sevoflurane may depress laryngeal reflexes at the higher MAC values achieved in our patients.

The drawback of this study is that the depth of anesthesia between the two groups was not compared. However, it is difficult to compare the depth of anesthesia between inhaled and IV anesthetics. Although adequate depth of anesthesia may be correlated to plasma concentration for propofol (16), the correlation between MAC values and depth of anesthesia for sevoflurane is not clearly defined. This is because MAC refers to a state of equilibrium, which is not achieved during single VCB induction. Furthermore, the presence of a lag time between alveolar and brain concentrations may confound any attempted correlation. The use of electroencephalographic-related technology may provide some answers, as it has been shown to correlate with propofol-induced sedation (17). However, there is no correlation between sevoflurane anesthesia and adequate anesthesia to prevent movement using electroencephalographic derivatives (18). In addition, its reliability during single VCB induction has not been evaluated.

The cost of LMA insertion with sevoflurane was marginally less than with propofol. Using Dion’s equation (19), the cost of sevoflurane induction and the transition to maintenance as performed in this study, including the cost of priming the circuit, amounted to $12.17. The cost for the propofol group, including a 20-mL vial of propofol and the cost of sevoflurane during the transition to the maintenance phase, was $13.04.

We showed that the quality, safety, and reliability of sevoflurane single VCB induction of anesthesia makes it an alternative to IV propofol for the insertion of the LMA in adults. No adjuvant drugs were required. Sevoflurane VCB induction resulted in comparable complication rates and stable hemodynamic profile during the induction of anesthesia but a lower complication rate during LMA insertion. It produced a lower incidence of apnea and allowed a smoother transition to the maintenance phase. However, it may result in a longer time to LMA insertion due to prolonged jaw tightness.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

  1. Scanlon P, Carey M, Power M. Patient response to laryngeal mask insertion after induction of anaesthesia with propofol or thiopentone. Can J Anaesth 1993;40:816–8.[Web of Science][Medline]
  2. Sebel PS, Lowdon JD. Propofol: a new intravenous anesthetic. Anesthesiology 1989;71:260–77.[Web of Science][Medline]
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  4. Thwaites A, Edmends S, Smith I. Inhalation induction with sevoflurane: a double-blind comparison with propofol. Br J Anaesth 1997;78:356–61.[Abstract/Free Full Text]
  5. Muzi M, Robinson BJ, Ebert TJ, O’Brien TJ. Induction of anesthesia and tracheal intubation with sevoflurane in adults. Anesthesiology 1996;85:536–43.[Web of Science][Medline]
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  7. Hall JE, Stewart JIM, Harmer M. Single-breath inhalation induction of sevoflurane anaesthesia with and without nitrous oxide: a feasibility study in adults and comparison with an intravenous bolus of propofol. Anaesthesia 1997;52:410–5.[Web of Science][Medline]
  8. Drage MP, Nunez J, Vaughan RS, Asai T. Jaw thrusting as a clinical test to assess the adequate depth of anaesthesia for insertion of the laryngeal mask. Anaesthesia 1996;51:1167–70.[Web of Science][Medline]
  9. Inomata S, Nishikawa T. Determination of end-tidal sevoflurane concentration for tracheal intubation in children with the rapid method. Can J Anaesth 1996;43:806–11.[Web of Science][Medline]
  10. Taguchi M, Watanabe S, Asakura N, Inomata S. End-tidal sevoflurane concentrations for laryngeal mask airway insertion and for tracheal intubation in children. Anesthesiology 1994;81:628–31.[Web of Science][Medline]
  11. Ummenhofer WC, Kindler C, Tschalèr G, et al. Propofol reduces succinylcholine induced increase of masseter muscle tone. Can J Anaesth 1998;45:417–23.[Web of Science][Medline]
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Accepted for publication December 28, 1998.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press