Department of Anaesthesia, Akita University School of Medicine, Hondo 1-1-1, Akita-city, Akita 010-8543, Japan*Corresponding author. E-mail: mtanaka@med.akita-u.ac.jp
LMA® is the property of Intavent Limited.
Accepted for publication: September 5, 2002
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Abstract |
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Methods. Seventy-five patients undergoing general anaesthesia were randomly assigned to either a COPA (n=38) or LMA (n=37) group for airway management, and each group was further randomized to a saline-propofol or fentanyl-propofol group for anaesthesia induction. The saline-propofol group received i.v. saline and the fentanyl-propofol group received i.v. fentanyl 1 µg kg1 followed 30 s later by i.v. propofol. Insertion of the device was attempted 90 s after propofol administration without the use of neuromuscular blocking agents or other adjuvants, and the responses of movement or no movement were judged by three observers blinded to the drug dose. Each dose of propofol at which insertion was attempted was predetermined by modification of Dixons up-and-down method with 0.5 mg kg1 as the step size, and 2 mg kg1 as an initial dose.
Results. Without fentanyl pretreatment, propofol requirement [mean (SD), 95% CI] for COPA placement [2.17 (0.38), 1.772.56 mg kg1] was significantly less than for LMA insertion [3.42 (0.26), 3.153.69 mg kg1, P<0.001]. In contrast, propofol requirements after fentanyl were comparable between the COPA and LMA groups [1.50 (0.42), 1.061.94 and 1.42 (0.26), 1.151.69 mg kg1, respectively], but were less than for the placebo group with both devices (P<0.05). Haemodynamic changes and duration of apnoea were similar with both devices irrespective of fentanyl pretreatment.
Conclusions. Insertion of the COPA can be accomplished with a smaller bolus dose of propofol compared with the LMA, but propofol requirements are similar with both devices after a small dose of fentanyl.
Br J Anaesth 2003; 90: 1420
Keywords: anaesthetics i.v., propofol; analgesics opioid, fentanyl; equipment, cuffs oropharyngeal; equipment, masks anaesthesia
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Introduction |
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Regarding anaesthetic requirements to insert these devices, studies have shown that the COPA may be inserted under lighter levels of sevoflurane anaesthesia than the LMA,4 5 suggesting that upper airway stimulation is less during COPA than LMA placement. More recently, using the target-controlled infusion system, plasma concentration of propofol required to place the COPA was less than for the LMA.6 However, insertion of these devices is most commonly accomplished by bolus injections of propofol alone or in combination with an opioid.7 8 No clinical trial has compared propofol doses required for successful placement of these devices using a procedure which reflects clinical practice. More importantly, effects of opioid pretreatment on propofol requirements and any haemodynamic changes have not been compared during insertion of the COPA and LMA.
We hypothesized that the COPA would be less stimulating to the upper airway than the LMA during insertion. We also postulated that fentanyl pretreatment would reduce the propofol requirement because of its potent suppressive effect on upper airway reflexes.9 Fentanyl pretreatment should therefore attenuate the adverse haemodynamic effects associated with a bolus of propofol. Accordingly, this prospective, randomized study was designed to determine: (i) propofol requirements for successful placement of the COPA and LMA; (ii) the effect of fentanyl on these propofol requirements; and (iii) any haemodynamic changes from fentanyl pretreatment during propofol induction.
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Methods |
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All patients received famotidine 20 mg orally 90 min before induction of general anaesthesia. No other opioid or sedative premedication was given. Anaesthetic management and insertion of both extratracheal devices were performed by a single anaesthetist (M. T.), who had experience of more than 100 and 300 insertions of the COPA and the LMA, respectively. The anaesthetic induction technique was standardized: monitors were applied before induction, including electrocardiogram, pulse oximeter, and non-invasive arterial pressure monitor. After preoxygenation for 5 min, saline 10 ml or fentanyl 1 µg kg1 diluted in 10 ml of saline was given i.v. to the saline-propofol and fentanyl-propofol groups, respectively. Thirty seconds later, each patient received a predetermined dose of i.v. propofol, beginning with 2 mg kg1 for the first patient in each group, given over 30 s through a peripheral i.v. catheter. Then, 60 s after the completion of the propofol injection, the COPA or LMA insertion was attempted by the investigator, who was blinded to both the dose of propofol and the group (saline vs fentanyl) assignment. If the patient response was described as movement, additional bolus dose of propofol 0.5 mg kg1 was given and insertion was reattempted at 30-s intervals until it was successful.
The dose of propofol for each patient was predetermined by a modification of Dixons up-and-down method.11 For the next patient, the predetermined dose of propofol was increased by 0.5 mg kg1 if the preceding patients response was judged as movement, or decreased by 0.5 mg kg1 if a response was described as no movement during insertion of either airway device. Both devices were inserted and fixed according to the manufacturers instructions and the literature.12 The size of the COPA was determined by placing the distal end of the upright COPA at the angle of the mandible. When viewed from the side, the tooth/lip guard of the COPA would be 1 cm ventral to the lip in a device of the appropriate size. After insertion, the COPA was first fastened by the rubber strap, its cuff was inflated with the maximum recommended inflation volume, and then it was connected to the anaesthetic breathing system. A size 3 LMA was selected for women who weighed <65 kg, and a size 4 was used for all other patients. After insertion of the LMA, the cuff was inflated first with the maximum recommended volume of air, and then it was connected to the anaesthetic system.12 Both airway devices were coated with a water-soluble lubricant immediately before use. Manual inflation with an adequate tidal volume was used to confirm a plateau of the end-tidal carbon dioxide waveform on capnography and to assess the patency of the airway. Airway leak was excluded as part of successful insertion. After insertion of either device, the patients were allowed to breathe spontaneously a mixture of inspired sevoflurane 1% in oxygen for 5 min before surgery commenced. Duration of apnoea, defined as the time from propofol administration until spontaneous respiration resumed, as documented on a gas analyser (Capnomac Ultima SV; Datex, Helsinki, Finland) was noted. In addition, non-invasive systolic (SAP) and diastolic arterial pressure (DAP), and heart rate (HR) were recorded at 1-min intervals after the end of propofol administration.
Patients responses to the COPA or LMA were described as no movement or movement. No movement was defined as the absence of bucking or gross purposeful movement after insertion and inflation of the cuff of the COPA or LMA until an effective airway was established. This was confirmed from the square waveform of the capnometer, synchronous thoracoabdominal movements, and the absence of stridor. Movement refers to resistance to mouth opening, gross purposeful movement during instrumentation, coughing, straining or laryngospasm occurring before or after inflation of the device, or when any of the above occurred during airway manipulation before an effective airway was established. The presence or absence of movement was documented by three operating room personnel; the investigator in charge of the anaesthetic, the surgeon and the nurse in charge of the case. When at least two of the observers documented any movement, the case was described as movement, except that difficulty in mouth opening was judged solely by the investigator. Each patient was given a single dose of propofol before the first insertion attempt. The three observers were blinded to the dose of propofol and the group assignment, but not to the airway device.
Propofol requirement was determined by calculating the midpoint dose of all independent pairs of patients using a crossover technique, that is movement to no movement. The ED50 for the COPA and LMA groups were defined as the average of the crossover midpoints in each group. We studied consecutive patients until at least six crossover midpoints were obtained in each group. We analysed our data using a probit test (proprietary software, SAS Version 8.02, Cary, NC, USA) to obtain 95% confidence intervals (CI), and a logistic regression test to obtain the probability of no movement vs dose of propofol, the maximum likelihood estimators of the model variables, and a goodness of fit. Other statistical analyses used were the 2 test and unpaired Students t-test with Bonferronis correction to compare physical characteristics and other variables among groups. Temporal haemodynamic data were first analysed using repeated-measures analysis of variance (ANOVA), and if a significant difference was detected, it was followed by paired Students t-test with Bonferronis correction. All data are expressed as mean (SD). A P-value <0.05 was considered significant.
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Results |
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Discussion |
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The dose of propofol required for the placement of the LMA in our study was considerably greater than in previous reports.13 14 Our results suggest that, without fentanyl, propofol 3.7 mg kg1 is required to achieve a satisfactory level of anaesthesia in most patients, while Blake and colleagues,13 recommended propofol 2 mg kg1 for LMA insertion. The difference is partly because our patients received no sedative premedication, while in the study by Blake and colleagues, patients received oral temazepam before induction. Propofol 2.5 mg kg1 alone administered in unpremedicated patients can lead to undesirable effects, such as swallowing, gagging, coughing, vigorous movement of the extremities, and laryngospasm.8 Another possibility would be that our criterion of smooth insertion (i.e. the definition of no movement) may have been relatively strict compared with previous reports.
Our study also demonstrated that fentanyl pretreatment significantly reduced propofol requirements for both COPA and LMA placement. To avoid airway complications, inhibition of the upper airway reflexes, such as the cough reflex, is indispensable for smooth insertion of these devices. Tagaito and colleagues9 studied the effects of fentanyl on upper airway reflexes in humans during propofol anaesthesia, and found dose-dependent suppression. Indeed, a previous study showed that fentanyl 1 µg kg1 given before propofol induction significantly improved the conditions for LMA insertion compared with placebo.14 Similarly, fentanyl has been reported to reduce minimum alveolar sevoflurane concentration required for tracheal intubation in a dose-dependent manner in humans.15 In contrast to our assumption, however, reducing the dose of propofol by fentanyl pretreatment did not result in less haemodynamic change compared with propofol alone, and the degree of arterial pressure decrease was clinically acceptable in all groups. In addition, duration of apnoea was similar with or without fentanyl for both devices. Although a larger study involving more patients may be warranted, our results indicate that there is no clinical benefit of adding fentanyl to a smaller dose of propofol compared with using a larger dose of propofol alone for insertion of the COPA or LMA.
It is not clear from our results why propofol requirements were similar for both airway devices after fentanyl pretreatment, and no previous study has compared the anaesthetic requirement for COPA and LMA insertion after opioid premedication or pretreatment. Considerably different propofol requirements for COPA and LMA insertion without fentanyl, but not when a small dose of fentanyl pretreatment is used, suggest that study design may have affected the results found with these devices in terms of upper airway stimulation. We cannot exclude the possibility that a potent inhibitory effect of fentanyl on upper airway reflexes may have masked the differential stimulatory effects of the COPA and LMA on the upper airway.
Our results must be interpreted with some caution. First, we should have enrolled some patients of Mallampati class 4, as these airway devices may be especially useful when intubation fails or a difficult airway is anticipated.1618 Secondly, there was a chance that the responses of one observer might have biased the judgment of another. Making video recordings of the procedure and subsequent analysis by independent observers would have eliminated such a possibility. Lastly, primary outcome measures, such as the bispectral index, were not monitored, nor was the effect-site concentration of propofol estimated using a target-controlled infusion system. However, a recent report showed that time to the peak effect of propofol after bolus injection was 1.6 min using Marsh kinetics.19 20 Indeed, the lowest bispectral index occurred within 2 min after bolus injection of propofol delivered at a speed similar to our procedure in healthy adult patients.21
In conclusion, our study demonstrated that the propofol requirement for smooth insertion of the COPA was less compared with the LMA when propofol was used alone, but was similar to the LMA when fentanyl 1 µg kg1 was given immediately before the propofol. Even though fentanyl pretreatment reduced the propofol requirements for both devices, our data did not support the routine use of fentanyl in combination with propofol for the placement of the COPA or LMA.
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References |
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