Year : 2015 | Volume
| Issue : 1 | Page : 27-32
Effective dose 50 of desflurane for laryngeal mask airway removal in anaesthetized children in cataract surgeries with subtenon block
Sameer Sethi1, Babita Ghai1, Dipika Bansal2, Jagat Ram3
1 Department of Pharmacy, National Institute of Pharmaceutical Education and Research, Pharmacy Practice, Mohali, Punjab, India
2 National Institute of Pharmaceutical Education and Research, Pharmacy Practice, Mohali, Punjab, India
3 Department of Ophthalmology, Post Graduate Institute of Medical Education and Research, Chandigarh, Punjab, India
Dr. Sameer Sethi
Department of Anesthesia, Post Graduate Institute of Medical Education and Research, Sector 12, Chandigarh - 160 012, Punjab
Source of Support: None, Conflict of Interest: None
Clinical trial registration CTRI/2014/06/004650
|Date of Web Publication||5-Dec-2014|
Background: Quantification of the depth of desflurane anesthesia required for laryngeal mask airway (LMA) removal in children has been done with the use of intravenous fentanyl or caudal anesthesia. This study aimed to determine the end-tidal concentration of desflurane required for LMA removal in children without the use of caudal or opioid analgesia in children undergoing elective cataract surgery. Materials and Methods: Our study enrolled 25 American Society of Anesthesiologists I and II children aged 2-10 years, undergoing elective cataract surgery. Anesthesia was induced with sevoflurane and oxygen/nitrous oxide using face mask and a size 2 LMA inserted. A subtenon block was administered in all children before surgical incision. Desflurane was used for maintenance of anesthesia. Predetermined end tidal concentration of desflurane was maintained for 10 min at the end of surgery before LMA removal was attempted. End tidal concentrations were increased/decreased using the Dixon up-down method (with 0.5% as a step size) in the next patient depending on the previous patient's response. Patient responses to LMA removal were classified as "movement" or "no movement." Results: 50% effective dose (ED 50 ) for successful removal of the LMA with desflurane in the presence of subtenon block was 3.6% (3.20-3.97%) and that the 95% ED 95 was 4.648% (4.15-6.47%). Conclusion: Laryngeal mask airway removal can be successfully accomplished in 50% and 95% anesthetized children at 3.6% and 4.65% end-tidal desflurane concentration.
Keywords: Cataract surgeries, desflurane, laryngeal mask airway removal, pediatric, subtenon block
|How to cite this article:|
Sethi S, Ghai B, Bansal D, Ram J. Effective dose 50 of desflurane for laryngeal mask airway removal in anaesthetized children in cataract surgeries with subtenon block. Saudi J Anaesth 2015;9:27-32
|How to cite this URL:|
Sethi S, Ghai B, Bansal D, Ram J. Effective dose 50 of desflurane for laryngeal mask airway removal in anaesthetized children in cataract surgeries with subtenon block. Saudi J Anaesth [serial online] 2015 [cited 2021 Aug 4];9:27-32. Available from: https://www.saudija.org/text.asp?2015/9/1/27/146277
| Introduction|| |
Removal of the laryngeal mask airway (LMA) in children can be performed in deeply anaesthetized or awake state. ,,, In children and some selected conditions such as asthma, removal of the LMA in a deeply anaesthetized state reduces the incidence of airway complications such as coughing, biting, hypersalivation, and desaturation. ,, However, removal of LMA in the deep state carries the disadvantage of maintaining the active laryngeal reflexes suppressed which can lead to delayed recovery, upper-airway obstruction and increased risk of aspiration.  Hence, return of airway reflexes is desirable in such situations. An inhalational agent with low-blood/gas partition coefficient such as desflurane allows a brisk return of airway reflexes after LMA removal during deep anesthesia. ,
Only two studies have quantified the depth of desflurane anesthesia required for LMA removal in children. , However, in these studies intravenous (IV) fentanyl  or caudal anesthesia  was used intraoperatively for analgesia which might have confounded the end-tidal concentration of desflurane for LMA removal. The end-tidal concentration of desflurane for LMA removal in the absence of caudal or opioid analgesia is not studied till date and needs to be determined.
Therefore, the purpose of this study was to determine the end-tidal concentration of desflurane required for LMA removal in children with the supplementation of subtenon analgesia without the use of caudal or opioid analgesia in children undergoing elective cataract surgery using Dixon's up-and-down method.
| Materials and Methods|| |
Ethical approval of this study (NK/611/Res) was provided by Post Graduate Institute of Medical Education and Research, Chandigarh, India (Chairperson Prof. Kartar Singh) on 16 May 2013 and the trial was registered with the Clinical Trial Registry of India (CTRI) with an assigned number of CTRI/2014/06/004650.
Pediatric subjects of either sex aged 2-10 years, weighing 10-20 kg, of American Society of Anesthesiologists (ASA) I and II children undergoing elective cataract surgery and requiring LMA size 2 were recruited for the study. Any child with reactive airway disease, airway abnormalities which precluded the use of the LMA, or, or a history of an upper respiratory tract infection in the preceding 3 weeks, children with tumors or infections of the orbit, with raised intraocular pressure, eye injury, who were blind in the eye other than that which was to be operated, were excluded. Children with a history of allergy to local anesthetics, a full stomach and compromised sclera were also excluded from the study. After written had informed consent from parents or legal guardians, 25 children were enrolled in this up and down sequential allocation trial [Figure 1].
All children underwent a detailed preanesthetic evaluation. No premedication was given. Anesthesia was induced with inspired sevoflurane 8% in a 40:60% mixture of oxygen/nitrous oxide using face mask. Intravenous access was established after induction of anesthesia. A size 2 LMA was inserted for maintenance of airway after achieving sufficient depth of anesthesia. Anesthesia was maintained with 4-6% desflurane in oxygen and nitrous oxide (50:50) with a total inflow of 2 L/min keeping a cumulative minimum alveolar concentration (MAC) of 1-1.3. A subtenon block was administered in all children with 0.08-0.10 mL/kg of 0.5% bupivacaine before surgical incision. Surgery was started 10 min after the block. Spontaneous ventilation was maintained in all patients. Ventilation was assisted if end-tidal CO 2 became >50 mm Hg. At the sign of inadequate analgesia (increase of more than 20% of preincision baseline heart rate (HR) or mean arterial pressure), rescue analgesia with IV. bolus of 0.5 μg/kg fentanyl was administered. HR, noninvasive blood pressure, pulse oximetry, capnography, end-tidal desflurane, inspired desflurane concentration and respiratory rate were monitored intraoperatively. With the use of the circle system end-tidal gas concentrations were measured by Datex-Ohmeda M CAiOV gas analyser software version 3.2 with automatic agent identification with Datex-Ohmeda S/5 monitor (Datex-Ohmeda, Finland) placed between the LMA and the breathing circuit. Before the start of each case, the gas analyzer was calibrated using Datex-Ohmeda Airway module calibration gas stock number 755583.
Nitrous oxide was stopped at the end of surgery, and end tidal concentration was set at 5% in the first child. On attaining the same concentration of exhaled end tidal desflurane concentration, it was maintained for at least 10 min to allow equilibrium between alveolar and brain concentrations and the LMA was then removed with cuff inflated, and 100% oxygen was administered. The desflurane target concentration for the next child was determined by increasing or decreasing the end tidal concentration by 0.5% in response to the previous child using Dixon's up-and-down sequential method.  The patients were observed for 1-min after LMA removal and evaluated as "movement" or "no movement". It was recorded as "movement" if which there was coughing, clenching, development of breath holding, laryngospasm, or desaturation to SpO 2 <90% or gross purposeful movement during or within 1-min of LMA removal. "Movement" occurring within 1-min of LMA removal was considered as unsuccessful, and 0.5% end tidal concentration was increased in the next patient. On the other hand, if no such above mentioned problems occurred, it was termed as "no movement" and LMA removal was considered as successful, and the desflurane concentration was decreased by 0.5% in the next child. The results of failure-success were recorded. Obstruction of the airway was relieved by head extension, and the jaw was lifted only if the obstruction persisted.
Primary outcome of the study was effective dose (ED 50 ) of desflurane for successful LMA. Secondary outcome measures studied were success rate of LMA, incidence of coughing, clenching of teeth, complications, and maneuvers used to relive airway obstruction.
Demographic data were presented as mean ± standard deviation (SD). The Dixon's up-and-down method was used to calculate ED 50, and it requires six pairs of failure-successes for statistical analysis which formed the basis of our sample size.
ED 50 was calculated with averaging the midpoint concentration of all independent pairs of patients involving a crossover. The ED 50 and ED 95 were estimated using a probit analysis.
Logistic regression analysis was used to obtain the probability of smooth removal of LMA versus end tidal desflurane concentration.
| Results|| |
Parents of 28 children consented to participate in this study. Three children were excluded because of the inability to follow the study methodology [Figure 1]. All the exclusions were performed before the inclusion of the next patient.
Demographic data are presented in [Table 1]. The mean ± SD end-tidal concentration of desflurane for successful LMA removal with subtenon analgesia was 3.64 ± 0.59 by Dixon's method. The sequences of successful and unsuccessful removal of LMA are shown in [Figure 2]. The logistic regression curve of probability of successful removal [Figure 3] showed that 50% ED 50 for successful removal of a LMA with desflurane in the presence of subtenon block was 3.595% (95% confidence limits, 3.205-3.973%), and that the 95% ED 95 was 4.648% (95% confidence limits, 4.149-6.475%) [Table 2]. The LMA was removed successfully in 14 out of 25 patients. Movement occurred in 6 patients (2 each at 4.0%, 3.5% and 3.0%), clenching in 3 patients at 2.5%, 3.0% and 3.5% and both in 2 at 2.5% and 3%. Coughing occurred in 3 patients (1 at 2.5% and 2 at 3%) and did not require treatment. None of the patients developed laryngospasm, breath holding or desaturation. No patient required intraoperative fentanyl.
|Figure 2: Successful - Unsuccessful sequence ● Successful ○ Unsuccessful|
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|Figure 3: Dose-response curve for desflurane plotted from the probit analyses of individual end tidal concentrations and the respective patient reactions to the removal of the laryngeal mask airway. The concentrations at which there were 50% probabilities of successful laryngeal mask airway removal were 3.59%|
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| Discussion|| |
The results of our study showed that the ED 50 and ED 95 of the end-tidal desflurane with subtenon block for successful LMA removal are 3.595% (3.60%) and 4.648% (4.65%) respectively. All children could preserve their airway patency with slight support, such as extension of the head at these concentrations. No child suffered any major airway-related complication.
Recently, ED 50 and ED 95 of the end-tidal desflurane for successful LMA removal in children was studied in only two studies , and they have used either IV fentanyl or caudal analgesia which might have affected the MAC of desflurane.
[Additional file 1]
Makkar et al.  showed that the ED 50 and ED 95 of end tidal desflurane with IV fentanyl for successful LMA removal are 3.56% and 4.29%, respectively without any serious airway-related complications such as breath holding, laryngospasm, or desaturation in 36 children of ASA status I between 1 and 10 years of age undergoing ophthalmological lid surgery.
In another study by the same author,  ED 50 and ED 95 of end tidal desflurane with caudal analgesia for successful LMA was 3.39% and 4.13%, respectively with 20% children developing laryngospasm during emergence from anesthesia and no other airway-related complication in any of the 22 children of ASA status I between the age group of 2 and 10 years who underwent infraumbilical surgery.
In both these studies, general anesthesia was induced with sevoflurane and oxygen followed by insertion of LMA. The target concentration each time at the time of removal was predetermined by the Dixon up-down method (with 0.5% as a step size) starting at 5% end tidal concentration and was maintained for 10 min at the end of surgery before LMA removal.
In these two studies , mentioned above either IV fentanyl or caudal analgesia was used which might have confounded the MAC of desflurane. Hence we planned to conduct a study without the use of caudal and IV fentanyl to calculate ED 50 of desflurane for LMA removal. We have used subtenon block in our study for analgesia assuming that it being a peripheral nerve block will only provide anesthesia and analgesia for required surgery and would not have any systemic effect or effect on reticular activating system. Hence, it will not confound the ED 50 of desflurane for LMA removal. Also, peripheral nerve block affecting the MAC of inhalational agent has not been reported.
However, our ED 50 of desflurane with subtenon block for successful LMA removal is similar to that with fentanyl or caudal analgesia.
The similar ED 50 to that with fentanyl or caudal analgesia is probably because pain was not a confounding factor as we chose subtenon block to provide an optimal dose of analgesic by an adequate route to achieve timely and efficient analgesia in these children with no effect on the MAC. We hypothesize that the physiological effect of subtenon analgesia is to de-afferent the input from that part of the eye so that the pain and affect input is removed with no systemic general anesthetic effect of the absorbed drug. This provides an unaltered MAC for LMA removal. The reason for similar results to that with IV fentanyl used by Jeetinder et al. was that it was used in dose of 1 μg/kg around 45 min before the LMA removal and by this time the effect of this dose might have worn off and would not have affected the MAC of desflurane. The reason for similar results to that with caudal analgesia could be as hypothesised by authors in their study that the only physiologic effect of caudal analgesia is to de-afferent the lower extremities, so that pain and affect input is removed and probably provided undisturbed MAC.
Ours is the first study of determination of ED 50 of desflurane for LMA removal which is performed in the absence of opioid or caudal analgesia.
One of the limitations is the calculation of ED 95 by application of the probit regression. This could be an inaccurate prediction since it is well accepted that the Dixon up-and-down method is not reliable for calculating small or large percentage points such as the ED 95 . Although it may not be the best method, probit analysis is a technique generally used by researchers for calculating the ED 95 when the up-and-down method is used. ,, Moreover, it is definitely clinically important as illustrated by the fact that there was no failure in LMA removal in patients maintained on at least 4.65%.
Use of nitrous oxide could have attributed in the inaccurate measurement. We used nitrous oxide due to nonavailability of medical air. However, we assured that no end-tidal nitrous oxide was present at the time of removal of LMA and, therefore, the use of nitrous oxide is unlikely to alter the value of ED 50 of desflurane.
We have not given any premedication as it may have a systemic effect and could have confounded the results. Moreover, subtenon block itself have been reported to improve the emergence agitation in ocular surgery. 
Another limitation of the current study is the absence of a control group without a subtenon anesthesia, but we have administered subtenon block to provide analgesia and thereby avoiding opioids which might have their systemic effects.
| Conclusion|| |
We found that in the presence of subtenon block LMA removal can be successfully accomplished in 50% and 95% anaesthetized children aged 2-10 years at 3.595% (3.20-3.97%) and 4.65% (4.15-6.47%) end-tidal desflurane concentration.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]