Korean J Anesthesiol 2010 June; 58(6): 527-531
Clinical Research Article
Copyright ⓒ Korean Society of Anesthesiologists, 2010
Background: An anesthetic state can reduce adverse airway reaction during laryngeal mask airway (LMA) removal
in children. However, the anesthetic state has risks of upper airway obstruction or delayed emergence; so possibly
less anesthetic depth is advisable. Caudal analgesia reduces the requirement of anesthetic agents for sedation or
anesthesia; it is expected to reduce the sevoflurane requirement for LMA removal. Therefore, we determined the
EC50 of sevoflurane for LMA removal with caudal analgesia and compared that to the EC50 without caudal analgesia.
Methods: Forty-three unpremedicated children aged 1 to 6 yr were enrolled. They were allocated to receive or not
to receive caudal block according to their parents’ consent. General anesthesia were induced and maintained with
sevoflurane and oxygen in air. EC50 of sevoflurane for a smooth LMA removal with and without caudal analgesia were
estimated by the Dixon up-and-down method. The LMA was removed when predetermined end-tidal sevoflurane
concentration was achieved, and the sevoflurane concentration of a subsequent patient was determined by the
success or failure of the previous patient with 0.2% as the step size; success was defined by the absence of an adverse
airway reaction during and after LMA removal. EC50 of sevoflurane with caudal block, and that without caudal block,
were compared by a rank-sum test.
Results: The EC50 of sevoflurane to achieve successful LMA removal in children with caudal block was 1.47%; 1.81%
without caudal block. The EC50 were significantly different between the two groups (P < 0.001).
Conclusions: Caudal analgesia significantly reduced the sevoflurane concentration for a smooth LMA removal in
anesthetized children. (Korean J Anesthesiol 2010; 58: 527-531)
Key Words: Caudal analgesia, Laryngeal mask airway, Sevoflurane.
Caudal analgesia reduces the sevoflurane requirement for
LMA removal in anesthetized children
Joon-Sik Kim1, Wyun Kon Park1, Min-Huiy Lee1, Kyu-Hyun Hwang1, Hee-Soo Kim2, and Jeong Rim Lee1
1Department of Anesthesiology and Pain Medicine, and Anesthesia and Pain Research Institute, Yonsei University College of
Medicine, 2Department of Anesthesiology and Pain Medicine, Seoul National University College of Medicinie, Seoul, Korea
Received: February 8, 2010. Revised: March 8, 2010. Accepted: March 29, 2010.
Corresponding author: Jeong Rim Lee, M.D., Ph.D., Department of Anesthesiology and Pain Medicine, and Anesthesia and Pain Research
Institute, Yonsei University College of Medicine, 250, Seongsan-no, Sinchon-dong, Seodaemun-gu, Seoul 120-752, Korea. Tel: 82-2-2227-3840,
Fax: 82-2-2227-7897, E-mail: firstname.lastname@example.org
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://
creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium,
provided the original work is properly cited.
Caudal analgesia with sevoflurane for LMA removal
Vol. 58, No. 6, June 2010
The laryngeal mask airway (LMA) is recommended to be
removed when patients are fully awake because of the possi-
bility of complications . However, characteristics of children
are different from those of adults, and some children respond
poorly to verbal commands; so it is difficult to judge whether
the child is awake or lightly anesthetized. Therefore, several
reports suggest an anesthetized state for the safe LMA removal
in children [2,3].
However, the question is how deep the anesthesia should be,
because if the LMA is removed at too deep a level of anesthesia,
the patient’s airway is at risk of being left unprotected for
a relatively long time. So it might be ideal to preserve the
advantage of extubation under the anesthetic state while
reducing the recovery time after the LMA removal. Though
a previous study quantified the sevoflurane concentration
required for LMA removal without an airway complication in
children , it should be useful if any other method can further
reduce the sevoflurane requirement.
Neuraxial anesthesia exhibits sedative properties that may
reduce requirements for general anesthesia [5-9], and caudal
epidural block is one of the most commonly performed regional
techniques with a reliable perioperative analgesia in pediatric
patients. So it is expected that the caudal analgesia would
reduce the sevoflurane requirement for a smooth LMA removal
The purpose of this study was to evaluate how much caudal
block reduces the sevoflurane requirement for LMA removal
without an airway complication in children. So we determined
the EC50 of sevoflurane for a smooth LMA removal in children
with and without caudal block and compared the EC50 of
sevoflurane of each group.
Materials and Methods
After the approval by the institutional review board (IRB),
forty-three children (1-6 years) of ASA 1, scheduled for elective
inguinal hernia repair, were enrolled in this study. Written
informed consent was obtained from the parents of each
participant. Patients with an abnormal airway, reactive airway
disease, chronic respiratory disease, or a history of an upper
respiratory tract infection in the preceding 6-week period were
The patients were assigned to two groups: to receive caudal
analgesia (caudal group) or not (control group), based on
parents’ consent of caudal analgesia. All children were not
premedicated. Upon arrival at the operating room, patients
were monitored with pulse oximetry, capnography, inhaled and
exhaled sevoflurane concentrations, electrocardiography, and
noninvasive arterial blood pressure. Anesthesia was induced
using an inhaled technique with 8 vol% of sevoflurane in
oxygen via a pediatric circle system. After loss of consciousness,
the sevoflurane was adjusted to 3-3.5% according to the vital
signs of the patient, and the same concentration of sevoflurane
was maintained for several minutes until an adequate jaw
relaxation was attained for a LMA (LMATM , The laryngeal mask
company Ltd, UK) insertion. The LMA size was determined
by the manufacturer’s guidelines, which suggests size 1.5 for
5-10 kg, size 2 for 10-20 kg, and size 2.5 for 20-30 kg. After
the LMA insertion and before the operation, patients enrolled
in the caudal group received caudal block with 1 ml/kg of 0.2%
ropivacaine by the attending anesthesiologist. Caudal block was
not performed for the patients in the control group. Anesthesia
was maintained with sevoflurane in 50% oxygen in air with a
total inflow of 2 L/min, and the sevoflurane concentration was
adjusted in response to clinical signs. Spontaneous ventilation
was maintained throughout the anesthetic maintenance of all
patients, and the end-tidal CO2 ranged from 35 to 50 mmHg
during the procedure.
At the end of the surgery, the inhaled sevoflurane concent-
ration was adjusted to the ‘predetermined’ concentration in
approximately 50% oxygen in air with a total inflow of 6 L/
min and maintained until the exhaled end-tidal sevoflurane
concentration was the same as the inhaled concentration; this
steady state was kept for at least 10 min. The ‘predetermined’
concentration of sevoflurane for a particular patient was
determined by the response of the previous patient to a larger
or smaller concentration (with 0.2% as a step size) using
Dixon’s up-and-down sequential method , starting at 1.8%.
Because the patients were not randomly allocated, another
anesthesiologist, who didn’t know whether the caudal block was
performed or not, performed a LMA removal for the blinded
study being blinded to the predetermined concentration of
sevoflurane. This anesthesiologist removed a LMA with the cuff
inflated and recorded whether the LMA removal was successful
or not. A successful LMA removal was defined as the absence
of any coughing, clenching, breath holding, laryngospasm,
desaturation to SpO2 < 90%, and gross movement during
or within 1min of the LMA removal [4,11-13]. If a LMA was
removed successfully, the sevoflurane concentration for the
LMA removal of the next patient was decreased by 0.2%.
Conversely, if any of the above complications developed, a LMA
removal was regarded as unsuccessful, and the sevoflurane
concentration was increased by 0.2% in the next patient. After
a LMA removal, a facemask of 100% oxygen was routinely
applied for 5 min. If a laryngospasm was suspicious, breath
holding persisted for more than 30 s, or tidal volumes were less
than 6 ml/kg, positive pressure ventilation was applied. When
any complication was settled and adequate ventilation without
Korean J Anesthesiol
Kim, et al.
any assistance was confirmed, the patient was transferred to
the recovery room. In the recovery room, pain or emergence
delirium was controlled by a 1 mcg/kg intravenous fentanyl
injection, with close observation.
Demographic data were collected and presented as a median
and range, or mean ± SD, and were analyzed using the Mann-
Whitney test or Fisher’s exact test. Dixon’s up-and-down method
needs at least six pairs of failure-success for a statistical analysis
of EC50, and the number of enrolled patients came from the
basis of Dixon’s method. In this study, EC50 was calculated
from the mean of seven pairs of failure-success. To evaluate the
effect of caudal analgesia on the sevoflurane requirement for a
successful LMA removal, we compared EC50 of sevoflurane with
caudal block to that without caudal block by a rank-sum test. P
< 0.05 was considered statistically significant.
The demographic data and the anesthetic duration are
presented in Table 1.
The sequences of successful and unsuccessful LMA removal
in each group are shown in Fig. 1. In the control group, EC50 of
sevoflurane for LMA removal without airway complication was
1.81 ± 0.11%. However, in the caudal group, EC50 of sevoflurane
was 1.47 ± 0.08%; these EC50 were significantly different between
two groups (P < 0.001).
In the caudal group, 5 of the 13 children with a successful
LMA removal required a chin lift for upper airway support.
However, in the control group, all 10 children with a successful
LMA removal required a chin lift and/or jaw thrust against
upper airway obstruction. In unsuccessful LMA removal cases,
most of the airway complications that occurred were treated
without any problem; mild laryngospasm, which was defined as
an inspiratory stridor without complete obstruction, occurred
in 5 patients in the caudal group and in 4 patients in the control
group. They were treated with continuous positive airway
pressure with 100% oxygen. Desaturation (SaO2 < 90%) was not
noticed in any of the patients.
From our results, EC50 of sevoflurane for a smooth LMA
removal was reduced from 1.81% to 1.47% when caudal block
was accompanied in pediatric patients aged 1-6 years.
In children, several studies suggest that the anesthetic
state is a better condition for LMA removal in the aspect of
reducing airway complication, such as coughing, biting, hyper-
salivation, and hypoxia [2,3]. However, when an airway device
is removed during too deep of an anesthetized state, the risk
of prolonged upper airway obstruction or a delayed return
of protective reflexes is of main concern [14,15]. In the study
about the laryngeal tube, which is a supraglottic airway device
similar as the LMA, its removal under an anesthetic state of
2% sevoflurane significantly reduced airway complication but
Table 1. Patients’ Characteristics and Duration of Laryngeal Mask
Caudal group Control group
Number of patients
Age (yr) (median/range)
Weight (kg) (mean/SD)
Duration of LMA insertion (min)
Caudal group received caudal injection of 0.2% ropivacaine 1 ml/kg
before operation, control group did not. Duration of LMA insertion
refers to the elapsed time the patient was maintained in the laryn-
geal mask airway insertion state. Statistical significance accepted
when P < 0.05. No significant differences were found between the
Fig. 1. Responses of consecutive patients in whom LMA removal was attempted at predetermined sevoflurane concentration. Caudal group
received caudal injection of 0.2% ropivacaine 1 ml/kg before operation, control group did not. A circle represents each patient’s data. Success or
failure for LMA removal is defined in the text.
Caudal analgesia with sevoflurane for LMA removal
Vol. 58, No. 6, June 2010
was related to a double incidence of upper airway obstruction
compared to its removal in the awake state . In addition,
LMA removal in the anesthetic state carries a disadvantage of
active pharyngeal reflexes remaining suppressed, resulting in
a delayed return of the airway reflex, which causes a potential
risk of the patient’s airway being left unprotected. Therefore,
when a LMA would be removed under the anesthetic state, it is
important to apply the least amount of anesthesia, if possible.
Several previous studies quantified the adequate depth of
anesthesia for LMA removal [4,11,13]; but if caudal block could
reduce the sevoflurane requirement more, it would be useful
because caudal block is a commonly performed procedure
without any direct effect on the airway reflex. Our study showed
the expected result-that caudal block reduced about 20% of the
sevoflurane concentration for LMA removal without an airway
Xiao et al. studied the effect of caudal anesthesia on the
enflurane concentration for LMA removal , and the
neuraxial anesthesia is known to potentiate sedative drug
effects or decrease the minimum alveolar concentration (MAC)
of inhalational anesthetics [5-9]. This phenomenon has been
explained by several mechanisms. First, pain is considered to
play the most important role in the arousal from an anesthesia
; caudal analgesia blocks pain from the surgical site, and it
decreases the general anesthetic demand. The local anesthetic
volume used in this study, 1 ml/kg of 0.2% ropivacaine, is
expected to block about T 12 dermatome . Therefore the
considerable decrease in the sevoflurane requirement for a
smooth LMA removal would be induced by the blockade of
nociceptive stimuli throughout caudal analgesia. Secondly,
neuraxial block reduces the anesthetic requirement to suppress
movement in response to a noxious stimulus above the level
of sensory block. The afferentation theory proposes that tonic
sensory and muscle-spindle activity modulate cerebral activity
and maintain a state of wakefulness, and decreased afferent
input to the brain could lessen the excitatory descending
modulation of the spinal cord motoneurons and suppress
motor function [19-21]. Through these mechanisms, caudal
block could reduce the sevoflurane requirement for LMA
removal despite the fact that caudal block does not have a direct
analgesic effect on the upper airway.
The limitation of our study is that there were no data of time
intervals between LMA removal and the return of airway reflex
in each group. This study was focused on the effect of caudal
block on reducing the sevoflurane requirement for a smooth
LMA removal, and so was designed to compare sevoflurane
concentrations. We thought the interval in the caudal group
might be shorter than that in the no-caudal group owing to the
difference in the sevoflurane concentration for LMA removal
between the two groups; if the time intervals between the two
groups were significant, this study would have been weightier.
In conclusion, caudal analgesia can reduce the sevoflurane
requirement for a smooth LMA removal-0.6 MAC is sufficient
for LMA removal without any airwayz-related complication
in 50% of children while 0.8 MAC is required when caudal
analgesia is not performed. Less anesthetic requirements for
LMA removal by caudal block would be beneficial for a faster
recovery after the LMA removal.
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