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The ED₉₅ of end-tidal sevoflurane concentration for the smooth exchange of the tracheal tube for a laryngeal mask airway is 2.97%

[La DE₉₅ de la concentration télé-expiratoire de sévoflurane nécessaire au remplacement sans à-coups du tube endotrachéal par un masque laryngé est de 2,97 %]

From the Department of Anesthesiology Critical Care Medicine Hokkaido University Graduate School of Medicine Sapporo Japan.

Address correspondence to: Dr. Koichi Takita, Department of Anesthesiology and Critical Care Medicine, Hokkaido University Graduate School of Medicine, Kita-15, Nishi-7, Kita-ku, Sapporo 060-8638, Japan. Phone: +81-11-706-7861; Fax: +81-11-706-7861; Email: ktakita{at}med.hokudai.ac.jp

	Abstract

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Purpose: Exchanging the tracheal tube for the laryngeal mask airway (the TT/LMA exchange) while the patient is still anesthetized avoids coughing associated with tracheal extubation. This study was conducted to determine the end-tidal concentration of sevoflurane that prevented response to this exchange in 50% patients (MAC_TT/LMA).

Methods: We studied 21 adult male patients, ASA I, aged 21–54 yr. Anesthesia was induced with thiamylal and sevoflurane, and the trachea was intubated following vecuronium neuromuscular blockade. Anesthesia was maintained with sevoflurane and nitrous oxide in oxygen. After surgery, a predetermined end-tidal sevoflurane concentration was achieved and a steady state was maintained for at least 20 min. The concentration at which the TT/LMA exchange was attempted was determined by a modification of Dixon’s up-and-down method with 0.25% as the step size. At the time of the TT/LMA exchange, no residual nitrous oxide > 3% was detected, and the return to normal neuromuscular function was confirmed. When the TT/LMA exchange was accomplished without coughing, movement, or airway obstruction, it was considered a smooth exchange.

Results: Sevoflurane MAC_TT/LMA determined using the up-and-down method was 2.63% ± 0.14%. The 50% effective dose obtained using a probit analysis was similar [2.53% (95% confidence limits, 2.13–2.82%)].

Conclusion: Sevoflurane MAC_TT/LMA in adult male patients was 2.63% (1.54 MAC) and may be useful for the smooth exchange of the tracheal tube for the LMA in a clinical setting.

	Introduction

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TRACHEAL extubation is often accompanied by coughing. Coughing can cause adverse effects, including an increase in intracranial and intraocular pressures, significant hemodynamic changes, and may threaten the surgical sites. One of the strategies to avoid coughing is tracheal extubation under deep anesthesia, followed by face-mask ventilation. This technique, however, increases the risk of airway obstruction after extubation. Recently, some authors reported that substitution of the laryngeal mask airway (LMA) for the tracheal tube while the patient is still anesthetized prevents the coughing associated with tracheal extubation, and provides a secure airway following tracheal extubation and a smooth recovery period.^1–5 Under light anesthesia, insertion of the LMA and tracheal extubation itself may cause coughing, movement, breath-holding, and/or laryngospasm. Thus, unless the TT/LMA exchange is attempted under adequate anesthesia, this method does not offer any advantage.

In the present study, we attempted to determine the sevoflurane MAC_TT/LMA in adult male patients where sevoflurane MAC_TT/LMA is the end-tidal concentration of sevoflurane at which a smooth exchange of the tracheal tube for the LMA was possible in 50% of patients.

	Methods

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After obtaining Institutional approval and informed consent, we studied 21 adult male patients, ASA physical status I, aged 21–54 yr, scheduled for general anesthesia for elective non-oral surgery. No premedication was used. Anesthesia was induced with thiamylal 5 mg•kg^-1 and sevoflurane, and the trachea was intubated orally with a regular cuffed tracheal tube (internal diameter 8.5-mm) following iv vecuronium 0.12 mg•kg^-1. If a patient presented difficult mask ventilation or difficult intubation, he was excluded from the study. Anesthesia was maintained with sevoflurane and nitrous oxide in oxygen. No other anesthetics were administered before the TT/LMA exchange. The patients were monitored with an electrocardiogram, a non-invasive arterial blood pressure monitor, a pulse oximeter, and a peripheral nerve stimulator applied to the ulnar nerve at the wrist (NS252 peripheral nerve stimulator, Fisher & Paykel Healthcare, Auckland, New Zealand). Breath-by-breath inspired/end-tidal sevoflurane, nitrous oxide and carbon dioxide concentrations were measured with a precalibrated gas monitor (M1026A anesthetic gas module, Philips Medical System Corporation, Best, The Netherlands). Inspired and end-tidal gases were sampled from the proximal end of the tracheal tube at a sampling flow rate of 120 mL•min^-1. Accuracy of end-tidal measurements was confirmed by return of the end-tidal carbon dioxide trace to zero. A semiclosed circle system with a fresh gas flow of 6 L•min^-1 was used. Nitrous oxide was discontinued before the end of surgery. After surgery, a predetermined end-tidal sevoflurane concentration was achieved and a steady state maintained for at least 20 min to allow equilibration between the alveolar and brain concentrations. The concentration a particular patient received was determined by the response of the previous patient to a larger or smaller concentration (with 0.25% as a step size), using a modification of Dixon’s up-and-down sequential method.⁶ At the time of the TT/LMA exchange, no residual nitrous oxide > 3% was detected in the end-tidal sample. Before the exchange, the return to normal neuromuscular function was confirmed with tactile evaluation of the responses of the adductor pollicis muscle to train-of-four stimulation. The airway was suctioned before a predetermined end-tidal sevoflurane concentration was achieved.

The TT/LMA exchange was attempted according to the method reported by Dob et al.¹ and Koga et al.² Before tracheal extubation, a deflated LMA was inserted while the tracheal tube was still in place. The lungs were inflated and the tracheal tube removed. The cuff of the LMA was then inflated, the breathing system was connected to the LMA, and adequacy of manual ventilation was confirmed. The size of LMA was determined by the manufacturer’s weight-related recommendations by using size 4 for patients 50–70 kg and size 5 for patients more than 70 kg. The TT/LMA exchange was attempted by a Japanese Board certified anesthesiologist (K.T.) who has considerable experience with this technique. Patients’ responses to the TT/LMA exchange, including coughing, gagging, and gross purposeful muscular movement were observed by an operating nurse and an anesthesiologist who were blinded to the sevoflurane concentration being tested. Airway obstruction immediately after the TT/LMA exchange was also regarded as a negative (adverse) response to the exchange. When the TT/LMA exchange was accomplished without any adverse response, it was considered a smooth exchange. The study protocol ended once it was determined whether the TT/LMA exchange was smooth or not. After completion of the study protocol, narcotics and/or nonsteroidal anti-inflammatory drugs for postoperative analgesia, in addition to antiemetics, were administered if necessary.

Patient demographics (age, body weight, body height, and body mass index), and duration of tracheal intubation are expressed as mean ± standard deviation (SD). We analyzed the value for MAC_TT/LMA obtained by calculating the midpoint concentration of all independent pairs of patients involving a cross-over (i.e., non-smooth exchange to smooth exchange). MAC_TT/LMA was defined as the average of the cross-over midpoints in each pair. MAC_TT/LMA is expressed as mean ± SD. We also analyzed our data using a probit analysis (SPSS; SPSS Inc., Chicago, IL, USA) to obtain the probability of 50% (ED₅₀) and 95% (ED₉₅) smooth TT/LMA exchange vs end-tidal sevoflurane concentration, and 95% confidence limits.

	Results

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The age of the patients was 35.5 ± 12.0 yr; body weight was 59.1 ± 8.6 kg; body height was 166.7 ± 7.3 cm; and body mass index was 21.2 ± 2.0 kg•m^-2. The duration of tracheal intubation was 182.6 ± 80.3 min. None of the patients presented difficult mask ventilation or difficult intubation. In all patients, the LMA was inserted on the first attempt while the tracheal tube was still in place. No patient required repositioning of the LMA after the TT/LMA exchange. Sevoflurane MAC _TT/LMA was 2.63 ± 0.14% (Figure 1). The dose-response curve constructed on the basis of probit analysis data in this patient population (Figure 2) showed that the ED₅₀ and the ED₉₅ of end-tidal sevoflurane concentration were 2.53% (95% confidence limits, 2.13–2.82%) and 2.97% (95% confidence limits, 2.73–6.16%), respectively. Maximum likelihood estimators of the probit model variables in this group showed a P value of 0.660 and a goodness of fit ² of 1.597. Seven patients experienced coughing during insertion of the LMA, and five of them had airway obstruction immediately after the TT/LMA exchange. Three patients had airway obstruction without any other adverse response. These airway obstructions recovered within four minutes. No patient desaturated below 98% by pulse oximetry.

View larger version (11K): [in this window] [in a new window]   FIGURE 1 The responses of the 21 consecutive patients in whom the exchange of the tracheal tube for the laryngeal mask airway was attempted at different end-tidal concentrations of sevoflurane in oxygen. Individual patient data are represented by a circle. Arrows indicate the midpoint concentrations of all independent pairs of patients involving a cross-over; i.e., non-smooth exchange to smooth exchange. The minimum alveolar anesthetic concentration for exchanging the tracheal tube for the laryngeal mask airway at which a smooth exchange is possible in 50% patients was 2.63 ± 0.14% (mean ± SD).

View larger version (11K): [in this window] [in a new window]   FIGURE 2 Dose-response curve for sevoflurane plotted from probit analyses of individual end-tidal concentrations and the respective patient reactions to the exchange of the tracheal tube for the laryngeal mask airway in this patient population. The concentrations at which there was a 50% and 95% probability of smooth exchange of the tracheal tube for the laryngeal mask airway were 2.53% and 2.97%, respectively.

	Discussion

TOP Abstract Introduction Methods Results Discussion References

Use of the LMA after tracheal extubation under anesthesia provides suitable conditions for neurosurgical patients in terms of hemodynamic stability, avoidance of coughing, and airway maintenance.^3–5 Dob et al. and Koga et al. also showed that substitution of the LMA for the tracheal tube decreases the incidence of respiratory complications, including coughing and peripheral arterial oxygen desaturation during recovery from anesthesia, when compared with the use of a Guedel airway after extubation under deep anesthesia.^1,2 Although TT/LMA exchange must be attempted under adequate anesthesia to suppress airway reflexes, the depth of anesthesia required for smooth TT/LMA exchange remains unclear. In previous reports, exchanges were performed while patients were still anesthetized and effectively paralyzed.^1–5 These studies did not provide detailed information on the adequate depth of anesthesia for smooth TT/LMA exchange. MAC_TT/LMA and ED₉₅ values of sevoflurane determined in the present study may provide useful information for smooth TT/LMA exchange in the clinical setting. However, when the MAC_TT/LMA and ED₉₅ determined in the present study are applied to normal clinical practice, it should be taken into account that several factors, including the patient’s age and the use of narcotics, affect the sevoflurane concentration required to ensure smooth TT/LMA exchange.

In the present study, anesthesia was induced with thiamylal 5 mg•kg^-1 and vecuronium 0.12 mg•kg^-1 was used to facilitate tracheal intubation. However, it is likely that these agents had little influence on the determination of sevoflurane MAC_TT/LMA. This is because the TT/LMA exchange was attempted more than 70 min after the administration of thiamylal, an induction dose of which has an effective duration of about five to eight minutes,⁸ and the return to normal neuromuscular function was confirmed before the exchange.

The technique of TT/LMA exchange is composed of insertion of the LMA and tracheal extubation. Previous investigations have shown that the end-tidal concentrations of sevoflurane to prevent response to insertion of the LMA in 50% of patients (MAC_LMA) and to prevent response to tracheal extubation (MAC_EX) are 2.00% and 1.07%, respectively.^9,10 It is unclear why the TT/LMA exchange requires a higher end-tidal concentration of sevoflurane than do the individual procedures taken separately. In the present study, insertion of the LMA was attempted before tracheal extubation. This method can avoid the risk of compromising the airway if insertion of the LMA were impossible, though this technique does not always guarantee maintenance of the airway after tracheal extubation. Using this sequence, insertion of the LMA stimulates the trachea and the vocal cords via the movement of the tracheal tube, in addition to the stimulation of the upper airway caused by the LMA itself. This may explain why a TT/LMA exchange requires higher end-tidal concentration of sevoflurane.

In conclusion, sevoflurane MAC_TT/LMA and ED₉₅ values of end-tidal sevoflurane concentration for smooth TT/LMA exchange are 2.63% and 2.97%, respectively. The MAC_TT/LMA and ED₉₅ values of sevoflurane determined in the present study may be useful for smooth TT/LMA exchange in the clinical setting.

Revision received November 6, 2002. Accepted for publication July 29, 2002.

	References

TOP Abstract Introduction Methods Results Discussion References

 
1 Dob DP, Shannon CN, Bailey PM. Efficacy and safety of the laryngeal mask airway vs Guedel airway following tracheal extubation. Can J Anesth 1999; 46: 179–81.[Abstract/Free Full Text]

2 Koga K, Asai T, Vaughan RS, Latto IP. Respiratory complications associated with tracheal extubation. Anaesthesia 1998; 53: 540–4.[Medline]

3 Nair I, Bailey PM. Use of the laryngeal mask for airway maintenance following tracheal extubation (Letter). Anaesthesia 1995; 50: 174–5.[Medline]

4 Silva LCE, Brimacombe JR. Tracheal tube/laryngeal mask exchange for emergence (Letter). Anesthesiology 1996; 85: 218.[Medline]

5 Silva LCE, Brimacombe JR. The laryngeal mask for carotid endarterectomy (Letter). J Cardiothor Vasc Anesth 1996; 10: 972–3.[Medline]

6 Dixon WJ. Quantal-response variable experimentation: the up-and-down method. In: McArthur JW, Colton T (Eds.). Statistics in Endocrinology. Cambridge, MA: MIT Press; 1970: 251–67.

7 Katoh T, Ikeda K. The minimum alveolar concentration (MAC) of sevoflurane in humans. Anesthesiology 1987; 66: 301–3.[Medline]

8 Fragen RJ, Avram MJ. Barbiturates. In: Miller RD (Ed.) Anesthesia, 5th ed. Philadelphia: Churchill Livingstone Inc.; 2000: 209–27.

9 Tanaka M, Watanabe S, Nishikawa T. Minimum alveolar sevoflurane concentrations required for insertion of the cuffed oropharyngeal airway and the laryngeal mask airway: a comparative study. Anaesthesia 1999; 54: 1155–60.[Medline]

10 Inomata S, Yaguchi Y, Taguchi M, Toyooka H. End-tidal sevoflurane concentration for tracheal extubation (MAC_EX) in adults: comparison with isoflurane. Br J Anaesth 1999; 82: 852–6.[Abstract/Free Full Text]

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