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Comparison of propofol and sevoflurane for laryngeal mask airway insertion in elderly patients.

Background: Sevoflurane and propofol have been widely used for anesthesia induction. This study compared the efficacies of sevoflurane and propofol inductions for laryngeal mask airway (LMA) insertion in elderly patients.

Methods: Ninety patients, aged 60 or more, received anesthesia induction with propofol and with sevoflurane 8% using the vital capacity breath (VCB) or tidal volume breath (TVB) techniques. Hemodynamic changes, induction time, complications, and the quality and ease of LMA insertion were observed.

Results: LMA was inserted most, less or least rapidly with propofol (89 [+ or -] 28 s), sevoflurane 8% using the VCB (163 [+ or -] 34 s) or TVB (205 [+ or -] 44 s) techniques, respectively. Anesthesia induction with propofol or sevoflurane 8% using the VCB technique produced either more frequent apnea or greater reduction in mean blood pressure than with sevoflurane 8% using the TVB technique.

Conclusions: Sevoflurane 8% using the TVB technique provides a smoother induction with a stable hemodynamic profile, less apnea and technical demand, but requiring longer time for LMA insertion in unpremedicated elderly patients.

Key Words: laryngeal mask airway, propofol, sevoflurane, elderly patients

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The popular method of anesthetic induction for laryngeal mask airway (LMA) insertion is the use of intravenous (IV) propofol, which has the advantages of rapid onset, short duration of action and depression of upper airway reflex. (1) However, several adverse effects have been associated with propofol, including hypotension, apnea and pain on injection. (2) Sevoflurane seems to be an ideal agent for inhalational anesthesia induction. It improves the conditions of anesthesia induction in comparison with the other volatile agents. (3-5) Recently, sevoflurane inhaled induction with vital capacity breath (VCB) has been used as an alternative to IV induction in adults. (6) This method is featured by little excitatory phenomena, high patient acceptance and good hemodynamic stability. (7) LMA insertion with VCB induction was proved to be effective and less costly as compared with propofol induction. (6) However, fewer relevant studies have focused on the elderly patients who are physiologically characteristic of limited cardiovascular and respiratory reserve. (8,9) These patients are at high risk of perioperative cardiovascular accidents. Maintaining a stable hemodynamic state during induction has therefore become important for minimizing such adverse events in this population. (9)

In this study, we aimed to investigate which of the following commonly used techniques would best provide smooth induction for LMA insertion in the elderly: 1) IV induction with propofol; 2) sevoflurane 8% induction using the VCB technique; and 3) sevoflurane 8% induction using the tidal volume breath (TVB) technique.

Materials and Methods

With approval of the Ethics Committee of Harbin Medical University and written informed consent, a total of 90 patients were involved in this study, who underwent elective urological, orthopedic or general surgery, aged 60 years or more, ASA physical status I-III. Exclusion criteria included heavy smokers (20 cigarettes per day), severe or uncontrolled cardiovascular diseases requiring drug treatment, asthma with an attack within a month and severe respiratory disease with pulse oxygen saturation (Sp[O.sub.2]) of less than 94% while breathing room air, a known and suspected difficult airway or gastroesophageal reflux. Those with hepatic, renal or neuromuscular diseases were also excluded. In addition, patients were excluded if systolic or diastolic blood pressure were above 180 or 110 mm Hg, respectively. Patients were within 15% of ideal body weight [Ideal body weight = 50 or 45.5 kg (for male or female) + 2.3 kg for each inch over 5 feet]. All subjects were allocated randomly by closed envelope technique to one of three groups: 1) Group IVP, n = 30; 2) Group VCB, n = 30; 3) Group TVB, n = 30.

Patients fasted overnight and were kept normothermic. No patients received premedication. At admission to the operation room, peripheral IV cannula was inserted, and a slow infusion of lactated Ringer solution was started. Noninvasive blood pressure, electrocardiogram and pulse oxygen saturation (Sp[O.sub.2]) monitoring were applied (Cardiocap, Datex Instrumentarium, Helsinki, Finland). Patients involved were given a weighted 20 mL syringe to hold. (10) Before anesthesia induction, the patients were preoxygenated for 3 minutes.

In Group IVP, anesthesia was induced with constant IV infusion of propofol (10 mg/mL) at a rate of 16 mL/min accompanied by injection of lidocaine 0.3 mg/kg through a three-way stopcock, which was continued until the patient dropped the weighted object. Although lidocaine was administrated as prophylaxis against pain on injection of propofol, it was used in the three groups because of its possible effect on hemodynamic variables. The patients were asked if they felt any pain through induction before loss of consciousness (no response to verbal commands). The procedures of LMA insertion were followed as described by Ti et al (11) Briefly, the ease of mouth opening was assessed (possible and impossible) and, if possible, LMA insertion was attempted by an anesthesiologist. If impossible, repeat attempts were made every 30 seconds up to a maximum of three attempts; each time preceded by propofol boluses of 0.05 mL/kg. Each assessment for mouth opening was considered an attempt at insertion.

For patients in Group VCB, a circle C[O.sub.2] absorber circuit with a 4-L reservoir bag was used. The circuit was primed with sevoflurane 8% (dialed concentration) in a 2:1 ratio of nitrous oxide to oxygen at a fresh gas flow of 6 L/min for 3 minutes. Preoxygenation with 100% oxygen was performed via an additional circuit and oxygen source. Before the start of induction, the patient was instructed to exhale maximally to residual volume. Then, a well-fit mask connected with the primed circuit was placed firmly over the patient's face. The patient was asked to breathe in as deeply as possible and hold it as long as he or she could. If necessary, second and third vital capacity breaths were taken until loss of consciousness. When the patient dropped the weighted object, the ease of mouth opening was evaluated, and LMA insertion was attempted as described above. But between attempts, anesthesia was maintained with sevoflurane at a dialed concentration of 8% and nitrous oxide 67% in oxygen rather than propofol infusion.

In Group TVB, the patients were induced by taking normal breaths of a mixture of sevoflurane 8% (dialed concentration) in a 2:1 ratio of nitrous oxide to oxygen at a fresh gas flow of 6 L/min through a circuit without priming. The procedures for the assessment of mouth opening and LMA insertion were the same as described above.

Anesthesia induction and LMA insertion were performed by the same anesthesiologist familiar with the VCB and TVB induction techniques. Observations were made by an independent, but not blinded, investigator. A size 3 or 4 LMA (LMA Co. Limited, UK) was used for patients weighing <70 kg or >70 kg, respectively, regardless of gender. Any failures of insertion were rescued with succinylcholine 50 mg IV. After the LMA was successfully 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 minutes before decreasing the dialed concentration of sevoflurane to 2% for maintenance. Throughout the study, no controlled or assisted ventilation was given unless the patient had an Sp[O.sub.2] of less than 90%.

Two induction times were recorded as follows: 1) from initial breathing of sevoflurane or starting infusion of propofol (the start of induction) to dropping the object (T1); and 2) to successful LMA insertion (LMA was placed into the right position to maintain a patent airway without patients showing any severe or significant involuntary movements and/or adverse airway events) (T2). The readings of mean blood pressure (MBP), heart rate (HR) and Sp[O.sub.2] were recorded before induction (baseline values) and at 1 minute intervals for 5 minutes from the start of induction. The independent investigator noted the presence of complications related to anesthetic induction and LMA insertion which included involuntary movements (excitatory movement or withdrawal from pain on injection), coughing, gagging, apnea (defined as absence of spontaneous respiration of more than 30 s; in Group VCB, apnea was assessed after the patient became unconscious) and laryngospasm.

Statistical Analysis

Sample size was estimated by using a 2-side [alpha]-level of 0.05 and a power of 0.8. Based on our preliminary trial, the mean maximal decreases of MBP were 11.5 [+ or -] 6.8, 20.6 [+ or -] 8.4, 17.2 [+ or -] 7.1 mm Hg in groups TVB, IVP and VCB, respectively. Using these data to detect a difference among three groups, at least 20 subjects were required in each group. We included a total of 90 patients in the study for a more reliable statistical result.

Statistical calculations were performed using a personal computer statistical software package (Prism version 4.0; GraphPad Software, San Diego, CA). Values were expressed as mean [+ or -] SD (95% CI). Hemodynamics were analyzed using two-way analysis of variance with Bonferroni post hoc test for multiple comparisons if significant F ratios were observed. The other quantitative data were analyzed using analysis of variance with a Student-Newman-Keuls post hoc test for multiple comparisons. Qualitative data were compared using [chi square] test and Fisher exact test as appropriate. P < 0.05 was considered as statistically significant.

Results

The three groups were comparable with respect to patient characteristics (Table 1). Failures of LMA insertion occurred in three patients in Group IVP and one patient in Group TVB because of an impossible mouth opening after three attempts. LMA insertions in these four patients were rescued successfully with succinylcholine. These patients were included in the analysis of the variables of patient characteristics, anesthesia induction, and overall success rate, but excluded from the analysis pertaining to speed and quality of LMA insertion and hemodynamic changes. Fewer attempts were required in Group IVP than in Groups TVB and VCB (1.2 vs. 1.9 vs. 1.7 attempts, respectively, P < 0.05) (Fig. 1). The three groups did not differ significantly in the successful rates of LMA insertion. The average consumption of propofol was 161 [+ or -] 35 mg.

Induction Times

The time to dropping the weighted object was significantly shorter in Group IVP than in the other groups and shorter in Group VCB as compared with Group TVB (IVP versus TVB P < 0.001; IVP versus VCB P < 0.001; VCB vs. TVB P < 0.001). The fast, intermediate and slow successful LMA insertions were achieved with propofol induction, VCB and TVB techniques, respectively (IVP versus TVB P < 0.001; IVP versus VCB P < 0.001; VCB versus TVB P < 0.001) (Table 2).

[FIGURE 1 OMITTED]

Complications Related to Induction and LMA Insertion

Throughout the study period, the most frequent untoward event was apnea, the incidences of which were higher in Group IVP than in Groups TVB and VCB during both anesthesia induction (IVP versus TVB P = 0.0002; IVP versus VCB P = 0.0379) and LMA insertion (IVP versus TVB P < 0.0001; IVP versus VCB P < 0.0001) but were comparable in the two latter groups (Table 3). In no patient did the apnea continue for longer than 1 minute, and none required assistant ventilation. There were no significant differences in the incidences of the other complications among the three groups. Although laryngospasm occurred in five patients of Groups TVB and VCB, it resolved spontaneously and did not disrupt the induction process. None of the patients with apnea and laryngospasm developed hypoxemia (Sp[O.sub.2] <90%). In Group VCB, two patients had minimum oxygen saturations of 89% and 88%, respectively; in each case, the low saturation was corrected by manual ventilation. About 30% of patients complained of pain during propofol induction despite the use of lidocaine in Group IVP.

Cardiovascular Stability

MBP showed significant decreases after anesthetic induction in Groups IVP and VCB. It was lower at 3, 4, and 5 minutes from the start of induction in Group IVP (87 [+ or -] 17, 85 [+ or -] 13 and 84 [+ or -] 15 mm Hg, respectively) as compared with Group TVB (99 [+ or -] 18, 101 [+ or -] 15 and 105 [+ or -] 16 mm Hg, respectively) (P < 0.05, P < 0.001 and P < 0.001, respectively) and lower at 4 and 5 minutes in Group IVP as compared with Group VCB (96 [+ or -] 13 and 98 [+ or -] 17 mm Hg, respectively) (P < 0.05 and P < 0.01, respectively). Although only at 2 minutes, MBP was significantly decreased in Group VCB than in Group TVB (87 [+ or -] 13 versus 9 [+ or -] 15, P < 0.05); compared with the baseline values, the mean maximal reduction of MBP was much smaller in Group TVB (10.6 [+ or -] 4.5 mm Hg) than in Groups VCB (16.8 [+ or -] 6.4 mm Hg) and IVP (20.9 [+ or -] 7.3 mm Hg) (IVP versus TVB P < 0.001; IVP versus VCB P < 0.05; VCB versus TVB P < 0.001). HR remained relatively stable during the whole study period in the three groups.

Discussion

Our results showed that the three induction methods involved in this study were all effective for LMA insertion in elderly patients. Although anesthesia induction with propofol allowed a more rapid speed of LMA insertion, it was associated with more complications with apnea and pain on injection being the prominent drawbacks. Furthermore, compared with sevoflurane inhalation techniques, MBP exhibited a larger change with propofol induction, although propofol was given at a constant infusion rate instead of a single bolus administration. This result corresponds to others. (11-13) Ti et al (11) found in the investigation on LMA insertion in adults that propofol induction was associated with a greater drop in mean arterial pressure (MAP) than 8% sevoflurane-VCB technique. Thwaites et al (12) also reported that anesthesia induction with propofol infused at 16 to 18 mL/min produced a decrease of 20 mm Hg in MAP which persisted for at least the first 5 minutes of anesthesia. In contrast, the reduction in MAP was only 10 mm Hg with sevoflurane-TVB technique. In the Yamaguchi et al (13) study, decreases of 30 mm Hg or more from baseline values in MAP were observed with propofol 2 mg/kg induction in the elderly patients. In the other previous studies, (7,14,15) propofol and sevoflurane-VCB inductions produced comparable hemodynamic effects; however, these studies were carried out in healthy adults (ASA I-III, 18-65 yr) rather than elderly patients aged 60 or more. Elderly patients are particularly sensitive to hypotension after propofol induction. (16)

The transition from induction to maintenance in Groups TVB and VCB was significantly smoother, which was demonstrated by no apnea associated with LMA insertion, than in Group IVP. This difference can be attributed to the fact that during inhalational anesthetic induction, the inspired and alveolar concentrations of the volatile agent are almost equilibrated so that subsequent small changes in the depth of anesthesia are readily achieved. In contrast, after IV drug induction, rapid distribution of the drug may lead to a decrease in the depth of anesthesia. (12)

In young adults, the combining use of sevoflurane 8% in nitrous oxide and the VCB technique provided rapid induction and low complications, but also was associated with a reduction of approximately 20% of the preinduction value in systolic arterial pressure. (7,12) The myocardial depression occurs with high concentrations of sevoflurane, as a result of an effect on calcium channels. (17) Elderly patients are more subject to cardiovascular depression with volatile agents. (8,9,13) In the Yamaguchi et al (13) study on sevoflurane induction, compared with the traditional VCB technique, a new technique using a gradual reduction of concentration largely prevented the decrease in MAP. In our study, the mean maximal reduction in MBP was smaller with the TVB technique than with the VCB technique. The cause may be that the VCB led to an instant increase to a high alveolar sevoflurane concentration, whereas the TVB made sevoflurane reach a maximum more slowly, thereby minimizing the hemodynamic effect of sevoflurane. Such differences may not be of great clinical significance for healthy patients, but for the elderly who usually suffer from cardiovascular diseases, the relative hypotension appears to be dangerous. In addition, the VCB technique required the cooperation of patients. Elderly patients are usually unable to hold a vital capacity breath for a sufficient length of time because of inadequate cardiovascular and respiratory reserve. Walpole and Logan (8) indicated that elderly patients might have difficulty in holding a breath for 30 seconds or more and reported a modified vital capacity inhalation induction. In this study, most patients required second and third vital capacity breaths.

Another problem with the VCB technique is related to preoxygenation. Although it had been proven that even in elderly patients, oxygen saturation was well maintained throughout induction with sevoflurane in 50% nitrous oxide because of the presence of a vital capacity volume of 50% oxygen in the lungs as induction began, (8) theoretically, the main oxygen store exists in the functional residual capacity of lung (FRC), and thus all techniques of preoxygenation should be based on denitrogenation of FRC, using 100% oxygen. (18) On the consideration that many elderly patients may suffer from pulmonary dysfunction, the traditional technique of preoxygenation is preferred. Indeed, several studies have shown that the time to desaturation after preoxygenation via a few vital capacity breaths was significantly shorter compared with a longer period of tidal volume breathing of 100% oxygen. (19) In our study, two patients had minimum oxygen saturations of 89% and 88% in Group VCB, although the slow breathing frequency may be the main cause; inadequate preoxygenation also seemed to be a contributing factor.

In contrast, our results suggested that in unpremedicated elderly patients, anesthetic induction with sevoflurane 8% using the TVB technique was more likely to be an appropriate choice for LMA insertion. It offered better hemodynamic profiles with less apnea, smoother transition to the maintenance phase and no special requirements for patients, as also abolishing the breathing circuit priming and painful injection. When especially taking the cost and priming time into account, it was obviously superior to the VCB technique. The main disadvantage of it was a long period of time taken to establish the adequate anesthesia induction. The possible reason accounting for this is that for a similar depth of anesthesia, propofol produced greater jaw relaxation than sevoflurane. (11)

Notwithstanding our results, it is noteworthy that the depth of anesthesia among the three groups in this study is not compared. The use of electroencephalographic-related technology is likely to be helpful in resolving this problem, but the correlation between sevoflurane anesthesia and adequate anesthesia to prevent movement using electroencephalographic derivatives has not been clearly defined. In many situations, LMA placement is preceded by opioid administration, which helps reduce the excitatory phenomena but probably exerts a synergistic cardiac depressant effect when sevoflurane is combined. (15) We did not use opioids to keep a clear comparison between propofol and sevoflurane induction techniques. One limitation of our study regards a possible observer bias. But the incidence of successful LMA insertion and apnea are all related to such a bias or various time definitions.

Conclusion

Our results demonstrate that although anesthetic induction with sevoflurane 8% using the TVB or VCB techniques take longer time and more attempts to complete LMA insertion in unpremedicated elderly patients as compared with propofol induction, they are associated with less frequent apnea and hypotension. The TVB technique is more likely to maintain cardiovascular stability, as it also might be less costly and technically demanding because of no need for circuit priming and patient cooperation; however, it seems to be more time consuming for LMA insertion than the VCB technique.

Acknowledgments

We would like to acknowledge Professor FuShan Xue for reviewing the manuscript and providing valuable advice.

References

1. Kati I, Demirel CB, Huseyinoglu UA, et al. Comparison of propofol and sevoflurane for laryngeal mask airway insertion. Tohoku J Exp Med 2003;200:111-118.

2. Gupta A, Stierer T, Zuckerman R, et al. Comparison of recovery profile after ambulatory anesthesia with propofol, isoflurane, sevoflurane and desflurane: a systematic review. Anesth Analg 2004;98:632-641.

3. Conzen PF, Kharasch ED, Czerner SF, et al. Low-flow sevoflurane compared with low-flow isoflurane anesthesia in patients with stable renal insufficiency. Anesthesiology 2002;97:578-584.

4. Nieminen K, Westeren-Punnonen S, Kokki H, et al. Sevoflurane anaesthesia in children after induction of anaesthesia with midazolam and thiopental does not cause epileptiform EEG. Br J Anaesth 2002;89:853-856.

5. Dhdhia KN, Kudalkar A. Comparison of sevoflurane and halothane for induction of anaesthesia and laryngeal mask airway insertion in paediatric patients. I J Anaesth 2004;48:465-468.

6. Hall JE, Stewart JI, 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;52:410-415.

7. Chawathe M, Zatman T, Hall JE, et al. Sevoflurane (12% and 8%) inhalational induction in children. Paediatr Anaesth 2005;15:470-475.

8. Walpole R, Logan M. Effect of sevoflurane concentration on inhalation induction of anaesthesia in the elderly. Br J Anaesth 1999;82:20-24.

9. Jin F, Chung F. Minimizing perioperative adverse events in the elderly. Br J Anaesth 2001;87:608-624.

10. Baker CE, Smith I. Sevoflurane: a comparison between vital capacity and tidal breathing techniques for the induction of anaesthesia and laryngeal mask airway placement. Anaesthesia 1999;54:841-844.

11. Ti LK, Chow MY, Lee TL. Comparison of sevoflurane with propofol for laryngeal mask airway insertion in adults. Anesth Analg 1999;88:908-912.

12. Thwaites A, Edmends S, Smith I. Inhalation induction with sevoflurane: a double-blind comparison with propofol. Br J Anaesth 1997;78:356-361.

13. Yamaguchi S, Ikeda T, Wake K, et al. A sevoflurane induction of anesthesia with gradual reduction of concentration is well tolerated in elderly patients. Can J Anesth 2003;50:26-31.

14. Siddik-Sayyid SM, Aouad MT, Taha SK, et al. A comparison of sevoflurane-propofol versus sevoflurane or propofol for laryngeal mask airway insertion in adults. Anesth Analg 2005;100:1204-1209.

15. Sivalingam P, Kandasamy R, Madhavan G, et al. Conditions for laryngeal mask insertion: a comparison of propofol versus sevoflurane with or without alfentanil. Anaesthesia 1999;54:271-276.

16. Dundee JW, Robinson FP, McCollom JS, et al. Sensitivity to propofol in the elderly. Anaesthesia 1986;41:482-485.

17. Hatakeyama N, Ito Y, Momose Y. Effects of sevoflurane, isoflurane and halothane on mechanical and electrophysiologic properties of canine myocardium. Anesth Analg 1993;76:1327-1332.

18. Schlack W, Heck Z. Is a single vital capacity breath a suitable method for preoxygenation? Can J Anesth 2001;48:423-424.

19. Campbell IT, Beatty PCW. Monitoring preoxygenation. Br J Anaesth 1994;72:3-4.
The moment one gives close attention to anything, even a blade of grass,
it becomes a mysterious, awesome, indescribably magnificent world in
itself.
--Henry Miller


GuiQian Shao, MD, and GuoHua Zhang, MD

From the Department of Anesthesiology, the First Affiliated Hospital of Harbin Medical University, Harbin, China; and the Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.

Reprint requests to Dr. GuoHua Zhang, Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Ba-Da-Chu Road, Shi-Jing-Shan District, Beijing, People's Republic of China 100041. Email: d1974@163.com

Accepted October 18, 2006.

RELATED ARTICLE: Key Points

* Anesthesia inductions with propofol and with sevoflurane 8% using the vital capacity breath (VCB) or tidal volume breath (TVB) techniques can all provide clinically accepted conditions for laryngeal mask airway (LMA) insertion in elderly patients.

* Propofol induction offered more rapid LMA insertion with fewer attempts, but also greater reduction in mean blood pressure and more frequent apnea, compared with the two sevoflurane induction methods.

* Although sevoflurane 8% plus VCB technique took less time for insertion of LMA, it resulted in more pronounced hemodynamic changes and required extra patient cooperation and anesthesia circuit priming as compared to sevoflurane 8% plus TVB technique.

* Sevoflurane 8% plus TVB technique was able to provide smoother anesthesia induction for LMA insertion in elderly patients with fewer untoward events at the cost of longer induction time.
Table 1. Patient characteristics in the three groups

 Group IVP Group TVB Group VCB

Number (n) 30 30 30
Age (yr) 71 [+ or -] 6 70 [+ or -] 5 68 [+ or -] 7
Gender (M/F) 16/14 20/10 13/17
Weight (kg) 62.5 [+ or -] 11.9 68.8 [+ or -] 13.4 64.2 [+ or -] 10.7
ASA 7/22/1 5/24/1 3/25/2
 (I/II/III)
Smoker 6/24 9/21 5/25
 (yes/no)
Sp[O.sub.2] 97.0 [+ or -] 0.5 96.8 [+ or -] 0.6 97.1 [+ or -] 0.4
 (%)

Values are mean [+ or -] SD or number of patients.

Table 2. Induction times in the three groups

Groups T1(s) T2(s) (a)

IVP 58 [+ or -] 15 [53-62] 89 [+ or -] 28 [78-99]
TVB 145 [+ or -] 23 [136-152]* (#) 205 [+ or -] 44 [189-220]* (#)
VCB 113 [+ or -] 19 [105-117]* 163 [+ or -] 34 [151-174]*

(a) Three patients in Group IVP and one patient in Group TVB were
excluded from analysis because of failures in LMA insertion within three
attempts; Values are mean [+ or -] SD [95% CI].
*P < 0.05, compared with Group IVP; (#) P < 0.05, compared with Group
VCB.

Table 3. Events related to anesthesia induction and laryngeal mask
airway (LMA) insertion

 Induction (No. of patients)
Groups Apnea Coughing Laryngospasm Movements

IVP 20 1 0 11
TVB 4* 4 2 4
VCB 11* 1 3 9

 LMA insertion (a) (No. of patients)
Groups Apnea Coughing Gagging Movements

IVP 11 5 6 16
TVB 0* 1 4 12
VCB 0* 1 3 10

(a) Three patients in Group IVP and one patient in Group TVB were
excluded from analysis because of failures in LMA insertion within three
attempts. Values are numbers of patients.
*P < 0.05, compared with Group IVP.
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Title Annotation:Original Article
Author:Zhang, GuoHua
Publication:Southern Medical Journal
Date:Apr 1, 2007
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