Xiao et al.: ENFLURANE AND LMA REMOVAL
195
are awake than when they are deeply anesthetized.1,2
Neuraxial anesthesia has been shown to markedly
increase the sedative effects of midazolam in
humans,3–5 which suggests that neural block may itself
have sedative properties. We hypothesized that caudal
anesthesia would reduce general anesthetic require-
ments for other, nonsurgical purposes, such as
removal of the LMA. Minimum alveolar concentra-
tion for LMA extubation (MACex) is defined as ade-
quate general anesthesia to provide satisfactory LMA
extubation in 50% of patients.
group, using a short B bevel, 22- gauge needle by the
attending anesthesiologist. No caudal anesthesia was
administered in the LMA without caudal anesthesia
group. Noninvasive mean arterial pressure, heart rate,
and oxygen saturation was recorded five minutes
before induction of anesthesia, followed by measure-
ment at five-minute intervals during anesthesia. End-
tidal carbon dioxide (ETco2) and concentration of
enflurane were measured continuously at the elbow of
the breathing circuit using a gas monitor (AS/3™;
Detex, Helsinki, Finland). The concentration of enflu-
rane was adjusted in response to clinical signs. No
other analgesic or local anesthetic was used during the
operation. All children breathed spontaneously with
manual assistance to maintain an ETco2 ranging from
35 to 50 mmHg during the procedure. Nitrous oxide
was discontinued before the end of surgery. At the end
of surgery, a predetermined end-tidal enflurane con-
centration was achieved and a steady state maintained
for at least ten minutes to allow equilibration between
the alveolar and brain concentrations. Immediately at
the end of surgery, oropharyngeal secretions were suc-
tioned gently. The target enflurane concentration
received by a particular patient in each group was
determined by the response of the previous patient to
a higher or lower concentration (with 0.1% as the step
size) using Dixon’s up-and-down sequential method.6
The first patient in each group was tested at 1.0% end-
tidal enflurane, based on results of our previous study.7
At the time of LMA extubation, no residual nitrous
oxide >3% was detected in the end-tidal sample. The
LMA was removed and a face mask with jaw lift was
applied with 100% oxygen for five minutes for all chil-
dren. Patients who developed coughing, teeth clench-
ing, or gross purposeful muscle movements during or
within one minute after removal, or patients who
developed breath holding, laryngospasm or desatura-
tion to Spo2 <90% during or immediately after LMA
removal were regarded as not having had successful
removal. A result defined as unsuccessful extubation
directed an increase by 0.1% of enflurane for the next
patient, whereas if a given patient had a successful
extubation, the enflurane concentration was decreased
by 0.1% in the subsequent patient. The anesthesiolo-
gist performing the LMA extubation procedure and
subsequent assessment was blinded to the concentra-
tion used and group allocation. Postoperative pain was
assessed and iv morphine or oral tramadol was offered
at the discretion of the anesthesiologist.
We tested whether ropivacaine caudal anesthesia
reduces general anesthetic requirements as measured
by the MACex of enflurane.
Methods
After obtaining Institutional Human Investigation
Committee approval and written, informed consent of
the parents, 50 boys, aged three to ten years, ASA phys-
ical status I, undergoing elective hypospadias repair
were included in this prospective, randomized study.
Children were randomized, using a systematic random-
sample technique, to one of two treatment groups to
receive LMA with or without caudal anesthesia after
induction of general anesthesia. Children with an
abnormal airway, gastroesophageal reflux, a history of
respiratory tract infection in the preceding four weeks,
or skin infection of the caudal area were excluded.
Patients were fasted and no premedication was
given. After applying standard monitors, general anes-
thesia was induced via face mask by using sevoflurane
in oxygen and 60% nitrous oxide. Scopolamine 0.01
mg·kg–1 was administrated iv after iv access was
obtained for infusion of Lactated Ringer’s solution.
When the depth of anesthesia was considered satisfac-
tory, the LMA was inserted with the opening of the
LMA facing posteriorly, followed by rotation through
180. The LMA size was determined by the manufac-
turer’s (previous) guidelines using a size 2 for children
6.5–20 kg and a size 2.5 for children 20–30 kg. The
LMA was deflated and K-Y™ brand sterile lubricating
jelly (plain lubricant; Johnson & Johnson, New
Brunswick, NJ, USA) was applied to the back of the
mask prior to placement. Sevoflurane was discontin-
ued after induction, and anesthesia was maintained in
all patients with enflurane in approximately 60%
nitrous oxide in oxygen with a total inflow of 5
L·min–1. We used a modified Jackson Rees system for
children weighing <20 kg and a pediatric circle system
for those weighing 20 kg. After successful LMA inser-
tion the child was turned in the left lateral position
and a caudal injection of ropivacaine 0.2%, 1 mL·kg– 1
was administered in the LMA with caudal anesthesia
Demographic data were collected and are present-
ed as mean (SD), median (interquartile range) as
appropriate. SD were analyzed using one-way analysis
of variance, medians (interquartile ranges) were ana-