The Laryngoscope
C 2014 The American Laryngological,
V
Rhinological and Otological Society, Inc.
Stimulation Threshold Greatly Affects the Predictive Value of
Intraoperative Nerve Monitoring
Daniel L. Faden, MD; Lisa A. Orloff, MD; Tokunbo Ayeni, BS; Daniel S. Fink, MD; Katherine Yung, MD
Objectives/Hypothesis: Using a standardized, graded, intraoperative stimulation protocol, we aimed to delineate the
effects of various stimulation levels applied to the recurrent laryngeal nerve on the postoperative predictive value of intraoperative nerve monitoring.
Study Design: A total of 917 nerves at risk were included for analysis. Intraoperatively, patients underwent stimulation
of the recurrent laryngeal nerve at 0.3, 0.5, 0.8, and 1.0 mA followed by postoperative laryngoscopy for correlation with intraoperative findings.
Methods: Sensitivity, specificity, positive predictive value, and negative predictive value were calculated at each stimulation level.
Results: Sensitivity, specificity, positive predictive value, and negative predicative values ranged from 100% to 37%, 6%
to 99%, 2% to 39%, and 100% to 99%, respectively at 0.3 to 1.0 mA. No demographic variables affected sensitivity or specificity. Receiver operating characteristic analysis identified 0.5 mA as the level of stimulation that optimizes sensitivity and
specificity.
Conclusions: The predictive value of intraoperative nerve monitoring varies greatly depending on the stimulation levels
used. At low amplitudes of stimulation, nerve monitoring has high sensitivity and negative predictive value but low specificity
and positive predictive value, related to the high rate of false positives. At high levels of stimulation, specificity and negative
predictive value are high, sensitivity is low, and the positive predictive value rises as the rate of false negatives increase and
the rate of false positives decrease. A stimulation level of 0.5 mA optimizes the predictive value of nerve monitoring; however,
stimulation at multiple levels significantly improves the predictive value of intraoperative nerve monitoring.
Key Words: Recurrent laryngeal nerve, intraoperative nerve monitoring, thyroid surgery.
Level of Evidence: 2b.
Laryngoscope, 125:1265–1270, 2015
INTRODUCTION
Surgery that puts the recurrent laryngeal nerve
(RLN) at risk, including thyroidectomy, parathyroidectomy and central neck dissection, is on the rise in the
United States as the population ages and the incidence
of thyroid cancer increases.1 Although occurring in only
about 3% of patients,2,3 damage to one or both RLNs can
result in significant morbidity including voice changes,
dysphagia, dyspnea, or airway distress, and need for tracheostomy or other interventions. Previously published
Additional Supporting Information may be found in the online
version of this article.
From the Department of Otolaryngology–Head and Neck Surgery
(D.L.F., K.Y.) and School of Medicine (T.A.), University of California, San
Francisco, San Francisco, California; Department of Otolaryngology–
Head and Neck Surgery (L.A.O.), Stanford University, Stanford,
California; and the Department of Otolaryngology–Head and Neck Surgery (D.S.F.), Louisiana State University Health Sciences Center, New
Orleans, Louisiana, U.S.A.
Editor’s Note: This Manuscript was accepted for publication
September 15, 2014.
Presented at the Triological Society 117th Annual Meeting at
COSM, Las Vegas, Nevada, U.S.A., May 15–16, 2014.
The authors have no funding, financial relationships, or conflicts
of interest to disclose.
* Send correspondence to Daniel Faden, MD, UCSF Department of
Otolaryngology–Head and Neck Surgery, 2380 Sutter Street, First Floor,
San Francisco, CA, 94115. E-mail: dfaden@ohns.ucsf.edu
DOI: 10.1002/lary.24960
Laryngoscope 125: May 2015
studies have not shown that use of intraoperative nerve
monitoring (IONM) decreases the rate of injury to the
RLN2,3; however, use of IONM has become increasingly
widespread. In recent surveys, approximately 80% of
otolaryngologists and 48% of general surgeons reported
using IONM, and 44% of otolaryngologists and 31% of
general surgeons use IONM routinely.4,5
More recently, interest has focused on the predictive
value of IONM for intraoperative decision making (i.e.,
decision to proceed with contralateral dissection after
loss of IONM signal on the first side) and prognostication.3,6–9 These topics have garnered interest considering
that <15% of injuries to the RLN are predicted intraoperatively.10–13 However, a lack of standardization of how
IONM is used makes interpretation of the literature difficult. Although numerous studies have looked at the
sensitivity and specificity of IONM, many of these studies have significant limitations, including small sample
sizes, different IONM techniques, and lack of standardized and accurate assessment of RLN function postoperatively. To our knowledge no studies have examined
the effects of various stimulation thresholds on the predictive value of IONM using an endotracheal tube surface electrode system. Thus, few practical guidelines
exist as to what level of stimulation to apply to the RLN
intraoperatively. In this study, using a standardized,
graded, intraoperative stimulation protocol, we aimed to
Faden et al: Predictive Value of Nerve Monitoring
1265
TABLE I.
Definitions.
Term
Definition
True positive
Inability to stimulate RLN, abnormal VF function
True negative
False positive
Intact stimulation of RLN, normal VF function
Inability to stimulate RLN, normal VF function
False negative
Intact stimulation of RLN, abnormal VF function
Sensitivity
Specificity
Ability to detect a damaged RLN
Ability to detect a normally functioning RLN
PPV
Likelihood that when an RLN does
not stimulate, VF function is abnormal
NPV
Likelihood that when an RLN stimulates,
VF function is normal
NPV 5 negative predictive value; PPV 5 positive predictive value;
RLN 5 recurrent laryngeal nerve; VF 5 vocal fold.
calculate predictive values of IONM at various stimulation levels to identify thresholds for maximizing postoperative predictive values.
MATERIALS AND METHODS
Patient Selection and Study Protocol
Data were collected from the charts of 732 consecutive
patients who underwent surgery that placed the right and/or
left RLN at risk (thyroid surgery, parathyroid surgery, central
neck dissection) at the University of California, San Francisco
(UCSF) from 2005 to 2013. All patients underwent surgery by a
single surgeon (L.A.O.). This retrospective cohort study was
approved by the institutional review board at UCSF. IONM was
performed using the Medtronic-Xomed (Minneapolis, MN) nerve
integrity monitoring system (NIM version 2.0 or 3.0) in conjunction with the Medtronic-Xomed nerve integrity monitor electromyography endotracheal tube. All patients underwent
preoperative laryngoscopy, and vocal fold (VF) mobility was
documented as normal, paresis, or paralysis
All patients were seen in follow-up 5 to 7 days after surgery and again underwent laryngoscopy and grading. If there
was concern for abnormal VF mobility based on voice changes,
abnormal indirect laryngoscopy, or difficult exam, the patient
underwent laryngovideostroboscopy, and again the VF mobility
was graded. In patients with an abnormal exam, laryngoscopy
was repeated at 4- to 8-week intervals until recovery or until
deemed stable. Patients who had an abnormal preoperative
exam, had the RLN sacrificed or transected during surgery, did
not have the RLN clearly identified during surgery, did not
complete a follow-up appointment within 1 week of surgery, had
incomplete documentation in their chart, or were <18 years old
were excluded from analysis.
Surgical Protocol
Patients were orally intubated with a nerve integrity monitor endotracheal tube by an anesthesiologist. Confirmation of
placement of the electrodes in contact with the VFs was done
with direct visualization. The endotracheal tube was secured,
with care taken not to rotate the tube. A shoulder roll was
placed, and a "tap test" was used to ensure the circuit was
intact. In accordance with the International Standards Guideline Statement,14 impedance values for each electrode were confirmed to be <5 kilohms, and the imbalance between
electrodes<1 kiliohm. If these values were above the threshold,
Laryngoscope 125: May 2015
1266
the tube was repositioned. The evoked potential threshold was
set at 150 mV. This value was chosen based on prior experience
of suboptimal signal-to-noise ratio, as well as occasional evoked
events being triggered by low-level respiratory spontaneous
waveforms, when a threshold of 100 mV was used. This value is
within the range suggested by the International Standards
Guideline Statement of 100 to 200 mV. After surgical dissection
was complete, the most proximal portion of the nerve was identified and stimulated at 0.3 mA. If the nerve did not stimulate
at 0.3 mA, the current was increased in a graded fashion to 0.5,
0.8, and 1.0 mA until stimulation was obtained. The electrodes
were left in place at the end of the procedure until the patient
was extubated so that those patients who exhibited spontaneous
VF mobility could be identified.
Statistical Analysis and Definitions
Data analysis was performed in nine cohorts: normal VF
motion versus abnormal (paralysis and paresis), normal VF
motion versus paralysis, and normal VF motion versus paresis,
for left-sided surgeries, right-sided surgeries, and again as a
combined cohort, with the nerves treated as independent observations. Because patients who had bilateral surgery represented
two data points that were treated as independent observations
in the combined cohort, we calculated a kappa statistic. Kappa
was 0.37, indicating fair agreement, and giving an actual percentage agreement of 97.5% compared to a chance level of
agreement of 96.1%. This small difference was deemed acceptable for the purposes of this study.
Calculations of sensitivity, specificity, positive predictive
value (PPV), negative predictive value (NPV), and receiver operator characteristic (ROC) curves were calculated in the standard fashion using SAS statistical software (SAS 9.4; SAS
Institute Inc., Cary, NC). If a nerve stimulated at a given level,
all levels above that were assumed to be functional. Statistical
significance was set at P <.05 using the Fisher exact test.
Paralysis is defined as immobility of the VF due to nerve injury,
paresis as decreased mobility of the VF due to nerve injury, and
abnormal function as either paresis or paralysis. A positive
result in our study was set as inability to stimulate the RLN
intraoperatively. Table I lists the corresponding definitions used
in this study.
Because of the concern for bias in having the operating
surgeon also grading postoperative VF motion, we utilized a
reliability cohort to ensure accuracy. Fifty-two nerves (5% of the
cohort) from patients who underwent laryngovideostroboscopy
by the operating surgeon underwent blinded review and grading by an independent laryngologist (D.S.F.). These results were
then compared with a kappa statistic to existing grading. The
calculated kappa was 0.65. This is considered substantial interrater agreement and was deemed acceptable for this study.
RESULTS
A total of 614 patients met inclusion criteria. Fortynine percent of patients had bilateral surgery, resulting
in a total of 917 nerves at risk. The mean patient age
was 50.2 years (range, 18–96 years). Additional patient
characteristics, and operative and postoperative statistics are described in Table II. Cases of paresis and paralysis were equally distributed between the left and right
sides. In patients who suffered paresis or paralysis,
spontaneous recovery occurred in 49%, on average, 38
days postoperatively. Of the patients with abnormal
postoperative vocal fold motion, including those after
RLN sacrifice, 55% had an intervention, most commonly
Faden et al: Predictive Value of Nerve Monitoring
TABLE II.
Descriptive Statistics.
Category
No.
%
White
Asian
442
89
73.9
14.7
Other
54
9.8
Black
Gender
21
3.5
Race
Female
Male
Previous surgery on the neck
Yes
No
Previous radiation to head and neck
No
Yes
Sternotomy
484
78.8
130
21.2
208
34.0
404
66.0
562
92.0
49
8.0
Yes
4
0.7
No
RLN transected, total
610
6
99.4
0.7
RLN sacrificed, total
7
0.8
Principle diagnoses
Papillary thyroid cancer
236
38.0
Parathyroid adenoma
97
16.0
Follicular adenoma
Thyroiditis
75
42
12.0
7.0
Goiter
42
7.0
Other
Neoplasm
122
20.0
338
55.1
276
4
44.9
0.9
No
Yes
Left VF paresis
Left VF paralysis
7
1.5
Total abnormal function on left
Right VF paresis
11
4
2.4
0.9
Right VF paralysis
9
2.0
Total abnormal function on right
Total paresis
13
8
2.8
0.9
Total paralysis
16
1.7
Total abnormal function
Bilateral paresis
24
1
2.6
0.1
Bilateral paralysis
3
0.3
RLN 5 recurrent laryngeal nerve; VF 5 vocal fold.
injection laryngoplasty, with a median time to intervention of 51 days.
Sensitivity, specificity, PPV, and NPV were calculated at 0.3-, 0.5-, 0.8-, and 1.0-mA stimulation levels for
normal versus abnormal, normal versus paralysis, and
normal versus paresis, for left, right, and combined
cohorts, giving nine distinct cohorts at each stimulation
level (see Supporting Table I in the online version of this
article). No appreciable differences were observed
between these cohorts; therefore, we focused our analyLaryngoscope 125: May 2015
sis on normal versus abnormal function in the left- and
right-sided combined cohort. Sensitivity and specificity
were inversely related. Sensitivity was 100% at 0.3 mA
and dropped nearly linearly as the stimulation current
increased to 37% at 1.0 mA (Fig. 1). Specificity was 6.0%
at 0.3 mA but increased rapidly from 0.5 mA upward to
99% at 1.0 mA. PPV was poor at all stimulation levels
but increased with increasing stimulation, whereas NPV
was high at all levels (100%–98%). The ROC identified
0.5 mA as the optimal level of stimulation if sensitivity
and specificity are weighted equally (nearest to 0.1 on
Fig. 2).
We examined the effects of selected variables (age,
gender, tumor size, nodal status, previous neck surgery,
previous radiation to the neck, malignant disease vs
benign disease, need for sternotomy) on the sensitivity
and specificity of IONM. There were no statistically significant differences in sensitivity or specificity for any of
the variables.
DISCUSSION
Surgeries that place the RLN at risk are increasing
in frequency in the United States as the average life
expectancy increases and the incidence of thyroid cancer
rises.1 IONM has gained popularity despite a lack of
data showing that its use decreases RLN injury.2,3 More
recently, studies have attempted to assess the value of
IONM for intraoperative decision making, postsurgical
monitoring, and long-term prognosis.3,6–9 However, there
is considerable variability in methodology between these
studies, making comparisons and thus the ability to
draw meaningful, clinically relevant conclusions, challenging. For example, studies assessing the predictive
value of IONM include various techniques for measurement of RLN function including laryngeal palpation,15
placement of intramuscular electrodes with stimulation
of the RLN16 or vagus nerve,17 and more recently, endotracheal tube surface electrodes, as in our study.
We identified five studies in the English literature
that report predictive values for IONM using surface
electrodes on the endotracheal tube, stimulation of the
RLN, sample sizes greater than 100 and pre/postoperative laryngoscopy to confirm VF findings.9,18–21 Rates of
sensitivity and specificity, according to our definitions,
vary considerably in these studies (sensitivity 52%–
100%, mean 73%; and specificity 94%–99%, mean 96%).
Four of these studies calculated PPV and NPV (PPV
29%–72%, mean 43%; and NPV 97%–100%, mean
99%).18–21 One, of many variables that differ between
these studies is the level of stimulation applied to the
RLN intraoperatively, ranging from 0.5 to 2 mA. Four of
the five studies used multiple levels of stimulation, and
one study used a single level.20 None of these studies
examined the predictive value of IONM at various levels
of stimulation within the same patient or between
patients.
In this study, we examined the predictive value of
IONM at various levels of stimulation, within the same
patient (internal control), in 917 nerves at risk. All
nerves underwent stimulation at 0.3, 0.5, 0.8, and 1 mA,
Faden et al: Predictive Value of Nerve Monitoring
1267
Fig. 1. Relationship of sensitivity,
specificity, positive predicitive value
(PPV), and negative predictive value
(NPV) at 0.3, 0.5, 0.8, 1.0 mA stimulation levels for normal versus
abnormal exam in a left- and rightsided combined cohort. [Color figure
can be viewed in the online issue,
which is available at www.laryngoscope.com.]
or until stimulation was achieved. Sensitivity, specificity,
NPV, and PPV were then calculated at each level. The
starting value was chosen as 0.3 mA because it has been
reported as the level at which the RLN first begins to
stimulate if the nerve is dry and dissected free from fascia.14 0.3 mA is assumed to induce depolarization of only
a subset of RLN fibers and is thus "subphysiologic." Furthermore, 0.8 mA is the level described in the literature
as corresponding to complete depolarization of the RLN,
and thus this was used as the initial level for confirmation of identification of the RLN. 1.0 mA was chosen as
Fig. 2. Receiver operator characteristic curve for normal versus
abnormal exam in a left- and right-sided combined cohort showing 0.5 mA as the optimal level of stimulation. [Color figure can be
viewed in the online issue, which is available at www.laryngoscope.com.]
Laryngoscope 125: May 2015
1268
the upper limit of stimulation as it has been considered
in the literature as a safe "suprathreshold" level of
stimulation.14
The total rate of VF motion impairment in our
study was 2.6%, consistent with previously published
series.2,3 Findings did not differ significantly between
the left and right side or between paresis and paralysis.
The relationships between sensitivity, specificity, PPV,
and NPV are demonstrated graphically in Figure 1 (and
numerically in Supporting Table IA in the online version
of this article). In essence, at low amplitudes of stimulation (0.3 mA), nerve monitoring has high sensitivity and
NPV but low specificity and PPV, meaning it is excellent
at confirming that a nerve that stimulates intraoperatively will have normal function postoperatively, but is
poor at predicting that a nerve that does not stimulate
intraoperatively will not function postoperatively, due to
the high rate of false positives. At high levels of stimulation (1.0 mA), the NPV and specificity are high, the sensitivity is low, and the PPV rises, meaning inability to
stimulate the RLN at this level is a better predictor of
loss of function than at lower levels as the rate of false
positives decreases. Ability to stimulate the RLN
remains a good predictor of normal postoperative function at this level; however, there is an increased rate of
false negatives leading to a lower sensitivity.
Predictive values from this study, despite stringent
surgical protocols and internal control, show considerable
variability between stimulation levels, suggesting the
threshold of stimulation is paramount in the predictive
value of IONM. The ranges in predictive values in this
study parallel the ranges seen in our review of the literature above. When we combine values to estimate the best
possible predictive values at all ranges of stimulation,
our sensitivity, specificity, PPV, and NPV are 100%, 99%,
39%, and 100%, respectively. These values again closely
Faden et al: Predictive Value of Nerve Monitoring
approximate the mean values for similar studies, presented above. This broad data range highlights the
importance of the level of stimulation when using IONM
to guide intra- or postoperative decision making and is
vital information for the operating surgeon.
We used an ROC to identify the single threshold of
stimulation to optimize sensitivity and specificity, which
we found to be 0.5 mA (sensitivity 68% and specificity
84%). However, an ROC assumes that sensitivity and
specificity are equally weighted in the eyes of the test
user. In reality, the most important function of IONM is
to capture all true positives, and thus sensitivity should
be weighted more heavily than specificity. Although it is
tempting to suggest that 0.3 mA would be an excellent
level at which to simulate (100% sensitivity), the number of false positives (849) is unreasonably high. This is
in agreement with the idea that 0.3 mA is subphysiologic. Sensitivity drops off significantly after 0.3 mA.
Low sensitivity exists for numerous reasons in addition
to this low level of stimulation, including malfunction of
the IONM system due to tube malposition, transient
nerve dysfunction due to traction injury, light soft tissue
coverage (most common), or wetness of the nerve,14
among others.
At 1.0 mA, stimulation of the RLN is a supraphysiologic event, implying simply that a portion of the RLNVF circuit is intact.14 As seen in our data, although the
NPV remains high, stimulation at this level increases
the number of false negatives, decreasing the sensitivity.
Because of the dichotomous relationship of sensitivity
and specificity at low- and high-stimulation levels, a
graded stimulation protocol, as was done in this study, is
advocated with use of the current IONM system. If a
single value of stimulation is to be used, 0.5 mA optimizes predictive value.
When we examined the effects of selected variables
on sensitivity and specificity, no differences were seen.
This implies the predictive value of IONM is not dependent on any intrinsic patient factors or on previous exposure of the RLN, despite revision surgery itself being
riskier. This is in contrast to recent studies that report
differences in predictive values based on pathology,
among other factors.9,19 However, small samples sizes
within these subgroups and lack of statistical analysis
make interpretation of their data difficult.
We acknowledge a number of limitations of this
study. First, this is a retrospective cohort study, and
thus analysis is confined to the information that exists
in the medical chart. As is true for similar studies of
IONM, low rates of nerve injury make the event being
studied infrequent. Thus, our sample size may not have
been adequate to analyze certain variables. The true
rate of VF motion abnormality may have been underestimated in this study as laryngovideostroboscopy, the gold
standard to identify abnormalities of VF motion, was not
performed in all patients. Last, this study used a single
evoked potential amplitude threshold of 150 mV. Several
recent articles have focused on the potential importance
of the evoked response in the predictive value of
IONM.20,22 This variable was not examined in our study.
The relationship between stimulation levels applied to
Laryngoscope 125: May 2015
the RLN, the evoked response, and predictive measures
of IONM remains a topic for further investigation.
CONCLUSION
Existing studies of IONM have not examined how
stimulation levels applied to the RLN affect predictive
values. Our data support the hypothesis that the predictive value of IONM varies greatly depending on the
stimulation threshold. At low levels of stimulation,
IONM has high sensitivity and NPV but low specificity
and PPV. This means that IONM, at this level, is excellent at confirming that a nerve that stimulates intraoperatively will have normal function postoperatively, but
is poor at predicting that a nerve that does not stimulate
intraoperatively will not function postoperatively, related
to the high rate of false positives. At high levels of stimulation, the NPV and specificity are high, the sensitivity
is low, and the PPV rises, meaning the inability to stimulate the RLN at this level is a better predictor of loss of
function than at lower levels, as the rate of false positive
decreases. Ability to stimulate the RLN remains a good
predictor of normal postoperative function at this level;
however, the rate of false negatives increases leading to
a lower sensitivity. A 0.5 mA stimulation level optimizes
the sensitivity and specificity of nerve monitoring; however, stimulation at multiple levels increases the predictive value of IONM.
BIBLIOGRAPHY
1. Howlader N, Noone AM, Krapcho M, et al. SEER cancer statistics review,
1975–2008. Available at: http://seer.cancer.gov/csr/1975_2008. Accessed
March 1, 2014.
2. Higgins TS, Gupta R, Ketcham AS, Sataloff RT, Wadsworth JT, Sinacori
JT. Recurrent laryngeal nerve monitoring versus identification alone on
post-thyroidectomy true vocal fold palsy: a meta-analysis. Laryngoscope
2011;121:1009–1017.
3. Dralle H, Sekulla C, Lorenz K, Brauckhoff M, Machens A. Intraoperative
monitoring of the recurrent laryngeal nerve in thyroid surgery. World J
Surg 2008;32:1358–1366.
4. Sturgeon C, Sturgeon T, Angelos P. Neuromonitoring in thyroid surgery:
attitudes, usage patterns, and predictors of use among endocrine surgeons. World J Surg 2009;33:417–425.
5. Ho Y, Carr MM, Goldenberg D. Trends in intraoperative neural monitoring
for thyroid and parathyroid surgery amongst otolaryngologists and general surgeons. Eur Arch Otorhinolaryngol 2013;270:2525–2530.
6. Melin M, Schwarz K, Lammers BJ, Goretzki PE. IONM-guided goiter surgery leading to two-stage thyroidectomy—indication and results. Langenbecks Arch Surg 2013;398:411–418.
7. Perie S, Ait-Mansour A, Devos M, Sonji G, Baujat B, St Guily JL. Value of
recurrent laryngeal nerve monitoring in the operative strategy during
total thyroidectomy and parathyroidectomy. Eur Ann Otorhinolaryngol
Head Neck Dis 2013;130:131–136.
8. Sadowski SM, Soardo P, Leuchter I, Robert JH, Triponez F. Systematic use
of recurrent laryngeal nerve neuromonitoring changes the operative
strategy in planned bilateral thyroidectomy. Thyroid 2013;23:329–333.
9. Eid I, Miller FR, Rowan S, Otto RA. The role of nerve monitoring to predict postoperative recurrent laryngeal nerve function in thyroid and
parathyroid surgery. Laryngoscope 2013;123:2583–2586.
10. Poveda MD, G. Sitges-Serra A, Barczynski M, et al. Intraoperative monitoring of the recurrent laryngeal nerve during thyroidectomy: a standardized approach (part 1). World J Endocr Surg 2011;3:144–150.
11. Bergenfelz A, Jansson S, Kristoffersson A, et al. Complications to thyroid
surgery: results as reported in a database from a multicenter audit comprising 3,660 patients. Langenbecks Arch Surg 2008;393:667–673.
12. Lo CY, Kwok KF, Yuen PW. A prospective evaluation of recurrent laryngeal nerve paralysis during thyroidectomy. Arch Surg 2000;135:204–207.
13. Patow CA, Norton JA, Brennan MF. Vocal cord paralysis and reoperative
parathyroidectomy. A prospective study. Ann Surg 1986;203:282–285.
14. Otto RA, Cochran CS. Sensitivity and specificity of intraoperative recurrent laryngeal nerve stimulation in predicting postoperative nerve
paralysis. Ann Otol Rhinol Laryngol 2002;111:1005–1007.
15. Hermann M, Hellebart C, Freissmuth M. Neuromonitoring in thyroid surgery: prospective evaluation of intraoperative electrophysiological
Faden et al: Predictive Value of Nerve Monitoring
1269
16.
17.
18.
19.
responses for the prediction of recurrent laryngeal nerve injury. Ann
Surg 2004;240:9–17.
Hamelmann WH, Meyer T, Timm S, Timmermann W. A critical estimation
of intraoperative neuromonitoring (IONM) in thyroid surgery [in German]. Zentralbl Chir 2002;127:409–413.
Chan WF, Lang BH, Lo CY. The role of intraoperative neuromonitoring of
recurrent laryngeal nerve during thyroidectomy: a comparative study on
1000 nerves at risk. Surgery 2006;140:866–872; discussion 872–863.
Chan WF, Lo CY. Pitfalls of intraoperative neuromonitoring for predicting
postoperative recurrent laryngeal nerve function during thyroidectomy.
World J Surg 2006;30:806–812.
Genther DJ, Kandil EH, Noureldine SI, Tufano RP. Correlation of final
evoked potential amplitudes on intraoperative electromyography of the
recurrent laryngeal nerve with immediate postoperative vocal fold func-
Laryngoscope 125: May 2015
1270
tion after thyroid and parathyroid surgery. JAMA Otolaryngol Head
Neck Surg 2014;140:124–128.
20. Koulouris C, Papavramidis TS, Pliakos I, et al. Intraoperative stimulation
neuromonitoring versus intraoperative continuous electromyographic
neuromonitoring in total thyroidectomy: identifying laryngeal complications. Am J Surg 2012;204:49–53.
21. Randolph GW, Dralle H, Abdullah H, et al. Electrophysiologic recurrent
laryngeal nerve monitoring during thyroid and parathyroid surgery:
international standards guideline statement. Laryngoscope 2011;
121(suppl 1):S1–S16.
22. Caragacianu D, Kamani D, Randolph GW. Intraoperative monitoring: normative range associated with normal postoperative glottic function.
Laryngoscope 2013;123:3026–3031.
Faden et al: Predictive Value of Nerve Monitoring