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Influence of Minor Ear Surgery on Infrared Tympanic Thermometry
David L. Mandell, MD;
Adam W. Pearl, MD;
Michael A. Rothschild, MD
Arch Otolaryngol Head Neck Surg. 2001;127:547-552.
ABSTRACT
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Background Infrared tympanic thermometry (ITT) is often used for postoperative
recovery room monitoring regardless of recent minor otologic surgery.
Objective To evaluate the use of ITT in pediatric patients who have undergone
bilateral myringotomy with insertion of pressure-equalizing tubes.
Design A prospective cohort study.
Setting Tertiary care academic medical center.
Patients Consecutive patients of a staff pediatric otolaryngologist (M.A.R.):
(1) ear surgery group, children aged 10 years or younger undergoing bilateral
myringotomy with insertion of pressure-equalizing tubes and (2) non–ear
surgery group, children aged 10 years or younger undergoing bilateral tonsillectomy
with or without adenoidectomy.
Interventions Immediate preprocedure temperature measurements included right and left
ear ITT. Immediate postprocedure temperature measurements included right and
left ear ITT and thermistor probe rectal temperature.
Main Outcome Measures The average difference between the preprocedure and postprocedure tympanic
temperature in the ear surgery group was compared with that in the non–ear
surgery group. The average difference between postprocedure rectal and ear
temperature in the ear surgery group was compared with that in the non–ear
surgery group.
Results There were 20 patients (40 ears) in the ear surgery group and 20 patients
(40 ears) in the non–ear surgery group. In the ear surgery group, the
average difference between the preprocedure and postprocedure tympanic temperature
(0.55°C) was not significantly different from that (0.62°C) in the
non–ear surgery group (P = .66, 1-way analysis
of variance). In the ear surgery group, the average difference between postprocedural
rectal and ear temperature (1.94°C) was not significantly different from
that (1.89°C) in the non–ear surgery group (P = .76, 1-way analysis of variance).
Conclusion Recent minor ear surgery (bilateral myringotomy with insertion of pressure-equalizing
tubes) does not have a significant effect on ITT measurements in pediatric
patients.
INTRODUCTION
TEMPERATURE measurement is an integral part of medicine, and is used
routinely in the ambulatory postoperative setting. During the past decade,
noncontact infrared tympanic thermometry (ITT) has been added to the array
of clinical techniques available for temperature measurement of pediatric
patients. The popularity of ITT has been owing to the fact that this technique
provides a temperature reading within seconds, is noninvasive, and is well
accepted by children, parents, and nurses.1
Despite these advantages, the ability of ITT to assess patient temperature
as accurately as other more traditional techniques is still actively debated.2, 3, 4, 5, 6, 7, 8, 9, 10
It has been the practice of the recovery room at our institution to
use ITT routinely in the postoperative evaluation of pediatric patients who
have undergone minor surgical procedures. This prospective cohort study evaluates
the appropriateness of noncontact ITT in pediatric patients who have undergone
bilateral myringotomy with insertion of pressure-equalizing tubes for the
treatment of otitis media related to eustachian tube dysfunction.
PATIENTS AND METHODS
The study population consisted of patients aged 10 years or younger
who were undergoing minor otolaryngologic surgical procedures. All patients
were seen in clinics at Mount Sinai Hospital, New York, NY, under the direction
of a single pediatric otolaryngology attending physician (M.A.R.). No study
exclusions were made based on patient sex or ethnic origin. Standard clinical
indications for surgery were used. Patients with congenital or acquired anatomic
anomalies of the external and/or middle ear that could potentially interfere
with ITT measurements were excluded. Patients with otitis externa were excluded,
as were those who required application of topical otic preparations (which
is not routine at our institution after bilateral myringotomy with ventilation
tube placement).
Approval by the institutional review board at Mount Sinai School of
Medicine was obtained before initiation of the study, and informed consent
by the parent or legal guardian was obtained before each subject's enrollment
in the study.
Two groups of pediatric surgical patients were studied in a prospective
fashion. The first group consisted of 20 consecutive patients with eustachian
tube dysfunction who were undergoing bilateral myringotomy with placement
of pressure-equalizing tubes (the "ear surgery" group). The second group consisted
of 20 consecutive patients with chronic tonsillitis and/or sleep-disordered
breathing who were undergoing bilateral palatine tonsillectomy with or without
adenoidectomy (the "non–ear surgery" group). The following data were
obtained for each patient: age, sex, underlying medical conditions, current
medications, and history of previous myringotomy. Patients undergoing simultaneous
ear surgery and tonsillectomy with or without adenoidectomy were excluded.
All operations were performed in their routine manner, by or under the
supervision of the same attending surgeon (M.A.R.). Myringotomy and tube placement
was performed using an operating microscope and a metal ear speculum. Inhalational
halogenated fluorane anesthesia was administered via face mask. Under operative
microscopy, cerumen, if present, was cleared from the right external auditory
canal, and the tympanic membrane was visualized in its entirety. A myringotomy
blade was used to make a radial incision in the anteroinferior quadrant of
the tympanic membrane. Auris media fluid, if present, was aspirated with a
No. 5 otologic suction device. Then, a pressure-equalizing grommet (Shepard
fluoroplastic grommet with wire, 1-mm inner diameter; Smith & Nephew Inc,
Memphis, Tenn) was inserted with an alligator forceps and, if necessary, a
Rosen pick. The same procedure was then performed in the patient's left ear.
In the non–ear surgery group, each patient was orotracheally intubated
and inhalational halogenated fluorane anesthesia was administered by an anesthesiologist.
Under operative microscopy, cerumen, if present, was cleared from the right
and the left external auditory canals, and the right and left tympanic membranes
were visualized in their entirety. The tonsils were then removed in the usual
manner using Bovie electrocautery. The adenoids were examined indirectly with
a dental mirror and, if indicated, were removed using an adenoid curet. Hemostasis
was achieved using suction electrocautery.
Noncontact ITT measurements were taken at the following times: (1) preoperatively
(immediately after induction of general anesthesia [and after intubation in
the non–ear surgery group], but before the start of the otolaryngologic
procedure) and (2) postoperatively (immediately after completion of the otolaryngologic
procedure, but before awakening the patient from general anesthesia). For
preoperative and postoperative ITT, measurements were performed twice in the
right ear and twice in the left ear, such that for every measurement, there
was a first sample and a second sample (repeated measures).
Infrared tympanic thermometry was performed using a noncontact infrared
tympanic thermometer (FirstTemp Genius model 3000A; Intelligent Medical Systems,
Carlsbad, Calif), set to core mode. The tympanic thermometer probe was covered
with a new polyethylene tip for each patient, and was inserted into the external
auditory canal with gentle posterior traction on the pinna. The probe was
aimed in the direction of the tympanic membrane, in the same manner as an
otoscope. The scan button was depressed, and the liquid crystal temperature
display was recorded. The tympanic thermometer was calibrated at the commencement
of the study by the Mount Sinai Hospital Biomedical Engineering Department
using a manufacturer-supplied "black box."11
Immediately after the completion of the surgical procedure, but before
awakening the patient from general anesthesia (while the postoperative ITT
measurements were being recorded), a rigid rectal thermistor probe (Filac
F-1010 Electronic Thermometer; Sherwood Medical, St Louis, Mo) was inserted
into the patient's rectum to a distance of 5 cm. The probe remained in place
long enough for the temperature display to record a final reading (approximately
90 seconds). The rectal thermistor was calibrated at the commencement of the
study by the Mount Sinai Hospital Biomedical Engineering Department.
STATISTICAL ANALYSIS
The statistics program used was Statistical Product and Service Solutions
10.0 for Windows (SPSS Inc, Chicago, Ill).
For all 40 patients enrolled in the study, the mean temperature for
all first-sample measurements was compared with the mean temperature for all
second-sample measurements, and the mean temperature for all right ear measurements
was compared with the mean temperature for all left ear measurements. These
and all subsequent comparisons were performed using a 1-way analysis of variance
(ANOVA) with a 2-sided  level of .05 for statistical significance.
As no difference was found between first- and second-sample measurements (as
reported in the "Right vs Left and First- vs Second-Sample Measurements" subsection
of the "Results" section), only the first ITT measurement in each ear was
used for all subsequent analyses.
Main Outcome Measure 1
The following null hypothesis was tested: the performance of myringotomy
with the insertion of a ventilation tube into the tympanic membrane will have
no effect on the relationship between preoperative and postoperative ITT temperatures.
In the ear surgery group, the mean preoperative tympanic temperature
(40 measurements, 20 each for the right and left ears) was compared with the
mean postoperative tympanic temperature (40 measurements, 20 each for the
right and left ears). An identical analysis was performed to detect any difference
between preoperative and postoperative ITT temperatures in the non–ear
surgery group.
For each patient, the difference between preoperative and postoperative
ITT measurements ( pre-post) was calculated by subtracting
the postoperative from the preoperative ITT temperature. (There were 2 pre-post values for each patient, 1 each for the right and left
ears.) Then, to detect differences between the ear surgery and the non–ear
surgery groups, the mean pre-post in the ear surgery
group was compared with the mean pre-post in the non–ear
surgery group.
Main Outcome Measure 2
The following null hypothesis was tested: the performance of myringotomy
with the insertion of a ventilation tube into the tympanic membrane will have
no effect on the relationship between postoperative ITT and rectal temperature
measurements.
For each patient, the difference between postoperative ITT and rectal
temperature measurements (rectal-ear) was calculated
by subtracting the ITT measurement from the rectal temperature. (There were
2 rectal-ear values for each patient, 1 each for the
right and left ears.) Then, to detect differences between the ear surgery
and the non–ear surgery groups, the mean rectal-ear in the ear surgery group was compared with the mean rectal-ear in the non–ear surgery group.
STATISTICAL POWER
For each of the 2 main outcome measures previously described, the total
number of subjects required for a 2-tailed test with a .05 significance level
and a power of 80% was calculated using the following formula: n1 = n2  16 2/ , where n1 is the number
of measurements in the ear surgery group; n2, the number of measurements in the control group; 2, an estimate of the SD, which equals [(SDear surgery group)2 + (SDcontrol group)2]/2; and , the maximal
acceptable temperature difference between the ear surgery group and the non–ear
surgery group, which was chosen to be 0.5°C for both main outcome measures.
The value of 0.5°C for significant temperature change was chosen based
on the fact that the same value was used in a similar statistical power analysis
by Tomkinson et al12 in another published study
that has investigated the effect of myringotomy tubes on ITT.
Main Outcome Measure 1
Using the SDs for the mean pre-post in the ear
surgery and non–ear surgery groups, it was determined that 31 measurements
in each group (ie, a minimum of 16 subjects in each group) would be necessary
to achieve a 5% significance level for a 2-tailed test with a power of 80%.
Main Outcome Measure 2
Using the SDs for the mean rectal-ear in the
ear surgery and non–ear surgery groups, it was determined that 38 measurements
in each group (ie, 19 subjects in each group) would be necessary to achieve
a 5% significance level for a 2-tailed test with a power of 80%.
RESULTS
DEMOGRAPHIC DATA
Twenty consecutive patients (40 ears) were enrolled in the ear surgery
group, and 20 consecutive patients (40 ears) were enrolled in the non–ear
surgery group. The mean patient age was 46.3 months (range, 8-109 months)
for the ear surgery group and 73.8 months (range, 24-121 months) for the non–ear
surgery group. The difference in mean age between the groups was statistically
significant (P = .008, independent-sample t test). The male-female ratio was 18:2 in the ear surgery group and
9:11 in the non–ear surgery group.
In the non–ear surgery group, the preoperative diagnosis was sleep-disordered
breathing in 14 patients and chronic tonsillitis in 6 patients. Tonsillectomy
and adenoidectomy were performed in 17 patients in the non–ear surgery
group, while the remaining 3 patients in this group underwent tonsillectomy
only.
Significant medical history in the ear surgery group included 2 patients
with asthma and 1 with bronchiolitis. In the non–ear surgery group,
significant medical history included 1 patient with -thalassemia and
3 with asthma. Only 4 patients in the ear surgery group were taking medications
at the time of surgery. These included albuterol sulfate home nebulizers for
asthma (1 patient) and oral antibiotics for recent acute otitis media (3 patients).
In the non–ear surgery group, only 2 patients were taking medications
at the time of surgery. These included albuterol, cromolyn sodium, and fluticasone
propionate inhalers for asthma (1 patient) and oral antibiotics for recent
pharyngitis (1 patient). No patient was febrile at the time of surgery.
In the ear surgery group, 4 patients had undergone a single bilateral
myringotomy and tube placement operation in the past. At the time of the present
study, the original ventilation tubes in these 4 patients were no longer in
place, and the tympanic membranes had healed without perforations. No patients
in the non–ear surgery group had undergone prior myringotomy procedures.
RIGHT VS LEFT AND FIRST- VS SECOND-SAMPLE MEASUREMENTS
The mean temperature for all right ITT measurements (35.46°C; SD,
0.65°C) was compared with the mean temperature for all left ITT measurements
(35.41°C; SD, 0.73°C), and no difference was found (P = .52, 1-way ANOVA). In addition, when the mean temperature for all
first-sample ITT measurements (35.49°C; SD, 0.66°C) was compared with
the mean temperature for all second-sample ITT measurements (35.38°C;
SD, 0.71°C), no difference was found (P = .14,
1-way ANOVA). For all further analyses, only the first ITT measurement in
each ear was used.
MAIN OUTCOME MEASURE 1
For the 20 subjects (40 ears) in the ear surgery group, the mean preoperative
ITT temperature (35.73°C; SD, 0.56°C) was significantly higher than
the mean postoperative ITT temperature (35.18°C; SD, 0.69°C) (P<.001, 1-way ANOVA). Overall, the postoperative ITT
temperature was lower than the preoperative ITT temperature in 29 of 40 paired
measurements (Figure 1).
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Figure 1. Preoperative and postoperative
infrared tympanic thermometry measurements in the ear surgery group.
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For the 20 subjects (40 ears) in the non–ear surgery group, the
mean preoperative ITT temperature (35.84°C; SD, 0.52°C) was significantly
higher than the mean postoperative ITT temperature (35.22°C; SD, 0.61°C)
(P<.001, 1-way ANOVA). Overall, the postoperative
ITT temperature was lower than the preoperative ITT temperature in 36 of 40
paired measurements (Figure 2).
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Figure 2. Preoperative and postoperative
infrared tympanic thermometry measurements in the non–ear surgery group.
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The pre-post was then calculated for each ear
in each patient, and the mean pre-post in the ear
surgery group (0.55°C; SD, 0.71°C) was compared with the mean pre-post in the non–ear surgery group (0.62°C; SD, 0.68°C)
(Figure 3); no difference was found
(P = .66, 1-way ANOVA).
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Figure 3. The difference between preoperative
and postoperative infrared tympanic thermometry measurements (pre-post) in the ear surgery group and the non–ear surgery
group (box-and-whisker plot). The dotted line indicates the median; the box,
the 25th to the 75th percentile; bars, the largest and smallest nonoutlier
values; O, minor outlier; and E, major outlier.
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MAIN OUTCOME MEASURE 2
The rectal-ear was calculated for each patient
(2 rectal-ear values for each patient, 1 each for
the right and left ears). The mean rectal-ear in the
ear surgery group (1.94°C; SD, 0.78°C) was then compared with the
mean rectal-ear in the non–ear surgery group
(1.89°C; SD, 0.77°C) (Figure 4), and no significant difference was found (P = .76,
1-way ANOVA).
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Figure 4. The postoperative difference between
infrared tympanic thermometry and rectal temperature measurements (rectal-ear) in the ear surgery group and the non–ear surgery
group (box-and-whisker plot). The dotted line indicates the median; the box,
the 25th to the 75th percentile; and bars, the largest and smallest nonoutlier
values. There were no outlier values present.
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Postoperative rectal temperatures were invariably higher than postoperative
ITT temperatures in all subjects. For patients in the ear surgery group, postoperative
rectal temperatures were between 0.1°C and 3.3°C (mean, 1.94°C)
higher than postoperative ITT temperatures. For patients in the non–ear
surgery group, postoperative rectal temperatures were between 0.5°C and
3.7°C (mean, 1.89°C) higher than postoperative ITT temperatures.
COMMENT
In the present study, noncontact ITT readings were shown to be unaffected
by the performance of bilateral myringotomy with ventilation tube placement
in pediatric patients. The placement of a ventilation tube in the tympanic
membrane had no significant effect on (1) the relationship between preoperative
and postoperative ITT measurements and (2) the relationship between simultaneous
postoperative ITT and rectal temperature measurements. The fact that the null
hypotheses of the study were proved supports continued use of ITT as a routine
method of postoperative temperature assessment in children undergoing myringotomy
tube placement.
During the past decade, ITT has been added to the array of techniques
available for clinical temperature measurement. The goal of any method of
clinical temperature assessment is to determine core body temperature as accurately
as possible. True core body temperature is found at the hypothalamus, a clinically
inaccessible site. The pulmonary artery is considered to be the most accurate
measurable site for assessing core temperature, but this type of measurement
is only practical in specialized critical care situations.13
In young children in ambulatory care and home settings, it has been argued
that rectal temperature is the most reliable technique for clinical temperature
assessment.14 However, this technique may upset
young children, requires clothing removal, and carries with it the remote
risk of rectal perforation.15 Axillary temperature,
while easily accessible, provides less accurate readings than rectal temperature
measurements,16 and has low sensitivity for
the detection of fever.7, 14 Oral
temperature measurements, while convenient and less invasive than rectal temperature
measurements, are not practical in infants and many young children, and may
demonstrate poor reliability in patients who have recently ingested hot or
cold liquids.17
Infrared tympanic thermometry has become increasingly popular since
its commercial introduction. This technique provides a temperature reading
within seconds, is easy to use, requires no clothing removal and no direct
mucous membrane contact, and is well accepted by children, parents, and nurses.1
The tympanic thermometer works by identifying infrared emissions generated
by the tympanic membrane as a function of temperature.11
It has been hypothesized that the temperature of the tympanic membrane, due
to its proximity to the blood supply of the hypothalamus, may reflect true
core body temperature.18 In critical care and
intraoperative settings, ITT has performed well when compared with other more
invasive techniques of core body temperature measurement in children, including
direct-contact tympanic membrane thermometry.13, 16, 19, 20
The ability of noncontact ITT to accurately measure core body temperature
in the pediatric outpatient setting has been debated in the literature. Infrared
tympanic thermometry measurements have been described as reliable for clinical
use in various pediatric age groups,2, 3, 4, 5
with a sensitivity for fever detection as high as 100% in a pediatric emergency
department.5 However, several studies6, 7, 8, 9, 10
have found ITT to be inaccurate, with unacceptably low levels of sensitivity
for fever detection, and have recommended against its routine use in a pediatric
outpatient setting. The present study was not designed to assess the sensitivity
of ITT for the detection of fever.
The presence of otitis media does not appear to have any significant
effect on the agreement between ITT and standard rectal measurements in pediatric
patients.2, 6 In addition, several
investigators2, 6 have found no
difference between ITT temperature readings of infected ears when compared
with uninfected ears in the same patient. No differences have been found for
mean ITT temperatures between right and left ears in pediatric patients in
general,2, 3, 4 and
this finding is also supported by the present study. In addition, the presence
of cerumen in the external auditory canal does not appear to affect ITT readings.4, 21
In the present study, for most subjects in the ear surgery and the non–ear
surgery groups, postoperative ITT measurements were significantly lower than
preoperative ITT measurements. This cooling effect was most likely due to
the routine use of the inhalational general anesthetic agents isoflurane and
sevoflurane in the study patients. These agents are well known to decrease
core body temperature during an operation due to anesthetic-induced impairment
of physiologic thermoregulatory control.22
The effect of minor pediatric ear surgery on ITT measurements has been
infrequently studied. In a 1991 report by Pransky,21
ITT and standard electronic oral thermometry were performed on 100 pediatric
outpatients undergoing routine otolaryngologic office assessments for various
conditions. Myringotomy tubes, which were present in some of the patients,
reportedly did not affect ITT accuracy. In a 1996 study by Tomkinson et al,12 21 children with otitis media (mean age, 5.3 years)
underwent bilateral ITT preoperatively and postoperatively, and these readings
were shown to be unaffected by the removal of middle ear fluid and the placement
of a pressure-equalizing grommet. This study failed to include a distant temperature
reference site for comparison with ITT measurements.
In the present study, ear surgery patients were younger when compared
with non–ear surgery patients (see the "Demographic Data" subsection
of the "Results" section). Since the average age for pressure-equalizing tube
placement is often lower than that for adenotonsillectomy, the decision was
made not to use age-matched cohorts, as this would skew the population away
from the typical patient profile.
The sex imbalance in the ear surgery group that was noted in the present
study was believed to be an anomaly resulting from the relatively small sample
size, since this male preponderance is not replicated in large studies of
eustachian tube dysfunction and standard surgical criteria were used in the
present study for patient selection.
AUTHOR INFORMATION
Accepted for publication September 22, 2000.
Presented at the 15th Annual Meeting American Society of Pediatric Otolaryngology,
Orlando, Fla, May 18, 2000.
From the Departments of Otolaryngology (Drs Mandell, Pearl, and Rothschild)
and Pediatrics (Dr Rothschild), Mount Sinai School of Medicine, New York,
NY.
Corresponding author: Michael A. Rothschild, MD, Department of Otolaryngology,
Box 1189, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York,
NY 10029 (e-mail: michaelr{at}idt.net).
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