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From the Department of Anesthesia, Akita University School of Medicine, Hondo 1-1-1, Akita-shi, Akita-ken 010-8543, Japan.
Address correspondence to: Dr. Makoto Tanaka, Phone: 81-18-884-6448; Fax: 81-18-884-6448; E-mail: mtanaka{at}med.akita-u.ac.jp
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Abstract |
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Methods: After ethics committee approval and informed consent, 41 patients were randomly assigned to receive 5 µg•kg–1 clonidine po premedication 90 min before entering the operating room (n = 22), or no clonidine (n = 19). To alleviate pain associated with iv propofol, 3 ml lidocaine 2%iv were administered. General anesthesia was induced, 30 sec later, with propofol at a rate of 100 mg•min–1 (600 ml•hr–1) iv. The dose of propofol at which insertion of the LMA was attempted was predetermined by modification of Dixon's up-and-down method with an initial dose of 2.5 mg•kg–1 and 0.25 mg•kg–1 as the step size. An LMA was inserted, without muscle relaxants or other adjuvants 90 sec after completion of the propofol injection, by an anesthesiologist blinded to the treatment of the patient.
Results: The ED50 of propofol for LMA insertion in clonidine-treated patients (2.0 ± 0.2 mg•kg–1, 1.8–2.3 mg•kg–1 [95% confidence interval]), was less than that in patients without clonidine (2.5 ± 0.1 mg•kg–1, 2.4–2.6 mg•kg–1, P < 0.01).
Conclusion: Oral clonidine premedication reduces propofol requirement for LMA insertion.
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Introduction |
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Method |
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Standard monitoring including electrocardiography, noninvasive blood pressure and pulse oximetry were applied. Oxygen, 6 l•min–1, was delivered via a face mask for three minutes before general anesthesia induction and was continued until an effective airway was established. To alleviate pain from iv propofol, 3 ml lidocaine 2% was first administered. Then, general anesthesia was induced in the supine position 30 sec later with propofol at a rate of 100 mg•min–1 iv. A laryngeal mask airway (size #3) was inserted without other adjuvants 90 sec after completion of the propofol injection. The dose of propofol at which insertion of the LMA was attempted was predetermined by the response of the previous patient, using modification of Dixon's up-and-down method.6 The first patient in each group received 2.5 mg•kg–1,4 and the step size was 0.25 mg•kg–1. All anesthetic management and insertions of the LMA were performed by a single anesthesiologist (TG) blinded to the patients treatment and propofol doses.
Patients response to the insertion of the LMA was described as "no movement" or "movement". "No movement" refers to the absence of bucking or gross purposeful muscular movements until an effective airway was established by confirming the square waveform of the capnograph, synchronous thoracoabdominal movement, and the absence of stridor. "Movement" refers to difficult mouth opening, gross purposeful movement, coughing, straining or laryngospasm before or after inflation of the LMA.7 If the patient "moved", the maneuver was stopped, and a further attempt was not made until 30 sec after an additional injection of 0.5 mg•kg–1 propofol. The presence or absence of movement was documented by the anesthesiologist (TG) and the nurse in charge of the case, who also remained blinded to the patients treatment and the propofol dose. When both observers documented any movement, the case was described as "movement". Each patient was tested for a single propofol dose.
The ED50 was estimated from calculating the midpoint dose of all independent pairs of patients involving a cross-over, i.e. "movement" to "no movement". The ED50 was defined as the average of the cross-over midpoints in each group. We have studied consecutive patients until six cross-over midpoints were obtained. Statistical analyses were performed using unpaired Student's t test, the probit test (SAS proprietary software, Chicago, IL), and a logistic regression test as appropriate. All values are expressed as mean ± SD, and a P value < 0.05 was considered statistically significant.
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Results |
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) P = 0.0013). Logistic regression curves of the probability of no movement upon the LMA insertion in the clonidine and control groups are shown in Figure 2. Maximum likelihood estimators of the logistic regression model parameters and assessment of goodness of fit are presented in the Table. There were no differences between the observed and the predicted values in both groups. At LMA insertion, no patient developed SpO2 < 97%.
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Discussion |
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One may argue that we used lidocaine before propofol injection to reduce pain from iv propofol. Lidocaine, 1.5 mg•kg–1, reduces coughing, airway obstruction and incidence of failure in LMA insertion.9 Thus, the use of lidocaine before propofol may have resulted in underestimation of the ED50 of both groups. Second, although no patient developed hypotension or bradycardia at induction, clonidine alone or in combination with propofol may produce hemodynamic perturbations in the elderly. Finally, there was a wide range in patient age in our study. However, MAC required for LMA insertion in the elderly (65–90 yr) is similar to that of young adults (18–50 yr),10 suggesting that sensitivity of pharynx to mechanical stimulation may not be age-related.
In conclusion, oral clonidine reduces propofol requirement for smooth insertion of the LMA in healthy surgical patients.
Accepted for publication March 10, 2000.
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References |
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2 Goyagi T, Tanaka M, Nishikawa T. Oral clonidine premedication reduces the awakening concentration of isoflurane. Anesth Analg 1998; 86: 410–3.[Abstract]
3 Nishina K, Mikawa K, Shiga M, Maekawa N, Obara H. Oral clonidine premedication reduces minimum alveolar concentration of sevoflurane for tracheal intubation in children. Anesthesiology 1997; 87: 1324–7.[Medline]
4 Blake DW, Dawson P, Donnan G, Bjorksten A. Propofol induction for laryngeal mask airway insertion: dose requirement and cardiorespiratory effects. Anaesth Intensive Care 1992; 20: 479–83.[Medline]
5 McKeating K, Bali IM, Dundee JW. The effects of thiopentone and propofol on upper airway integrity. Anaesthesia 1988; 43: 638–40.[Medline]
6 Dixon WJ. Quantal response to valuable experimentation: the up-and-down method. In: McArthur JW, Colton T (Eds.). Statistics in Endocrinology. Cambridge: MIT Press, 1967: 251–64.
7 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.[Medline]
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Goyagi T, Tanaka M, Nishikawa T. Oral clonidine premedication reduces induction dose and prolongs awakening time from propofol-nitrous oxide anesthesia. Can J Anesth 1999; 46: 894–6.
9 Stoneham MD, Bree SE. Facilitation of laryngeal mask insertion. Effects of lignocaine given intravenously before induction with propofol. Anaesthesia 1995; 50: 464–6.[Medline]
10 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]
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