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Paper text:
thyroidectomy is largely a straightforward , safe and effective surgery for benign and malignant thyroid disease . as such
, thyroidectomy is performed by surgeons with varying levels of expertise . in the past two decades several technological advances
have altered the approach to thyroid surgery including the introduction of intraoperative nerve monitoring ( ionm ) to prevent recurrent laryngeal nerve injury , a shift to ambulatory surgery , and more recently robotic approaches for cosmetic reasons .
the evidence to support ionm of the recurrent laryngeal nerve during thyroidectomy remains controversial and describes only modest   or no benefit .
yet , the adoption of ionm was reportedly as high as 29% among surveyed otolaryngologists in 2007 and 37% among surveyed endocrine surgeons in 2006 .
however , the evidence remains limited and nearly all studies involve a single medical center with high - volume surgeons .
given the breadth of surgeons performing thyroidectomy , national databases can provide further insight into the effect of broad ionm adoption on vcp rates . as complications following thyroidectomy are low , national databases with high volume and case diversity present an opportunity for robust sub - group analysis .
databases such as the nationwide inpatient sample can yield broad generalizable results in a field with substantial variability among surgeons . in this light ,
the objective of this study is to measure the nationwide outcomes of thyroidectomy with and without ionm .
the nationwide inpatient sample is a national database funded by the united states agency for healthcare research and quality ( ahrq ) .
it is the largest all - payer inpatient health care database in the united states and collects data from a 20% stratified sample of the hospitals around the country .
data from admission to discharge are included for each patient in this database including charge and cost data .
cases that were performed in an outpatient or ambulatory setting are not included in the nis .
nationwide inpatient sample data were obtained according to the agency for healthcare research and quality ( ahrq ) guidelines .
the years 2008 to 2011 were selected due to the introduction of the international classification of diseases-9 revision , clinical modification ( icd-9-cm ) code for intraoperative nerve monitoring ( 00.94 ) in 2007 . it should be noted that icd-9-cm does not distinguish between intermittent or continuous ionm .
a listing of icd-9-cm codes utilized for this study can be found in table 1 .
the primary endpoint of this study was a diagnosis of same admission vocal cord paralysis .
while diagnoses of partial and complete vocal cord paralysis were included in our outcome , the distinction between transient and permanent vcp is not captured within the icd-9-cm coding scheme .
it should be noted , however , that the codes used are distinct from dysphonia ( 784.42 ) which was not included in our analysis .
surgeon - level analysis could not be performed because the ahrq removed surgeon - level data from 2009 onward .
propensity - score analysis was performed first by identifying pre - operative variables that significantly differed by a p - value of less than 0.001 between conventional and intraoperative nerve monitoring ( ionm ) groups .
these variables were entered into a binary logistic regression and the logit was stored as the propensity score .
nearest neighbor one - to - one matching then was performed for each thyroidectomy type .
between 2008 to 2011 , 243,527 thyroidectomies were accrued in the nationwide inpatient sample database .
patients who received ionm were younger with more chronic conditions , thyroid malignancy , concurrent neck dissection , and were more frequently treated at hospitals that were smaller , urban , and teaching hospitals .
conventional cases predominated ( 94.7% ) with a yearly increase in intraoperative nerve monitoring ( ionm ) utilization [ figure 1 ] . as ionm utilization increased throughout the study period , overall vcp rates in
the ionm group initially increased year - over - year [ 0.9%(2008 ) , 2.4%(2009 ) , 2.5%(2010 ) ] , but were lower in the last year 1.4%(2011 ) .
overall , conventional vcp rates ( 1.4% ) were significantly lower than ionm vcp rates ( 1.9% , p<0.001 ) .
conventional partial thyroidectomy had fewer vcp events ( 1% ) compared with ionm ( 1.6% , p<0.001 ) .
similarly , conventional total thyroidectomy without neck dissection had a vcp rate of 1.3% versus 1.8% in ionm cases ( p<0.001 ) .
however , ionm did demonstrate a significant benefit within total thyroidectomies with neck dissection ( 2.9% versus conventional 4.2% , p=0.01 ) .
given the preoperative differences between treatment groups , a propensity score was calculated for each patient in order to control for treatment bias .
following one - to - one nearest neighbor matching , ionm continued to be associated with higher vcp rates in partial thyroidectomy and lower vcp rates for total thyroidectomy with neck dissection ( table 3 ) .
interestingly , patients in the lowest propensity score quartile ( e.g. patients least likely to receive ionm ) appeared to contribute most to the differential vcp rates between ionm ( 2.5% ) and conventional cases ( 1.2% , p=0.03 ) .
we examined hospital - level rates of laryngoscopy in order to identify whether the increase in vcp rates was due to an increased surveillance for complications .
overall , 29% of patients diagnosed with vcp also had a documented laryngoscopy . in hospitals
that did not use laryngoscopy in any of their thyroidectomy admissions , vcp rates were the same between conventional and ionm cases ( 0.8% vs 0.9% respectively ) . for hospitals that utilized laryngoscopy in less than 50% of inpatient stays , ionm continued to have increased vcp rates ( 2.2% versus conventional 1.8% , p=0.002 ) .
similarly , within hospitals that utilized laryngoscopy more than 50% of the time , ionm cases continued to have more vcp ( 4.2% versus conventional 1.8% , p=0.009 ) .
to ensure that coding practices did not confound the association of treatment group and vcp rates , we repeated the analysis excluding hospitals that never coded for ionm .
vcp rates in ionm remained significantly higher in all thyroidectomy types except for significantly lower vcp in total thyroidectomy with neck dissection . to examine the effect of government payers that do not reimburse ionm
, we restricted the analysis to patients within medicare , medicaid , and all other insurance types as primary insurance .
ionm remained associated with higher vcp rates . to investigate the effect of selective versus routine use of ionm
, we compared hospitals that used ionm in less than and greater than 50% of cases .
hospitals where ionm was applied to > 50% of thyroidectomies had lower vcp rates ( 1.1% ) compared to hospitals where ionm was applied to < 50% ( 1.6%,p=0.016 ) . subgroup analysis by thyroidectomy type revealed that vcp rates for partial thyroidectomy were lowest in hospitals using only conventional surgery , while vcp rates after total thyroidectomy favored hospitals routinely using ionm ( table 4 ) .
higher hospital volume correlated with lower vcp rates in both treatment groups ( table 5 ) . in the conventional group , vcp rates decreased as hospital case volume increased .
this relationship was largely true in the ionm group with the exception of partial thyroidectomy , which demonstrated an increased vcp rate as volume increased .
our results demonstrate that ionm was associated with higher vcp even after controlling for treatment , ascertainment and reimbursement biases . furthermore ,
utilization of ionm and complications both increased from 2008 to 2010 , then complications decreased in 2011 .
sub - analysis demonstrated that less frequent institutional ionm use or use in partial thyroidectomy is associated with higher vcp rates .
these findings suggest that there may be a learning curve to realize the benefits of ionm .
recent international guidelines for ionm use highlight the complexity in optimizing ionm   including proper endotracheal tube and electrode placement , collaboration with anesthesiologist and monitor settings .
any anomaly within the ionm circuit could lead to misrecognition of the recurrent laryngeal nerve .
perhaps another plausible explanation is that ionm may be used as a substitute for , rather than an adjunct to , recurrent laryngeal nerve visualization thereby increasing vcp rates .
this benefit may be due to the increased likelihood for aberrant anatomy , whether from the disease process itself or from prior neck intervention .
indeed , this coincides with studies that demonstrate a more pronounced benefit with ionm in cases with more extensive surgery and in cases of thyroid malignancy . taken together , the evidence does support the ongoing use of ionm in total thyroidectomy with neck dissection .
the finding that partial thyroidectomy with ionm has higher vcp with increasing hospital volume is counterintuitive .
one possible contributor to this sub - cohort is planned total thyroidectomies that are aborted due to a loss of continuous ionm signal , as has been recommended by recent studies . in these instances
, these cases will result in a partial thyroidectomy despite carrying the pre - operative risks of a total thyroidectomy .
however , our results do not fully corroborate this hypothesis as complete unilateral vcp represents only 6% of all vcp cases .
given that this database can not distinguish between intermittent recurrent laryngeal nerve monitoring or continuous ionm , further subanalysis is not possible at this time .
estimations of ionm adoption have been restricted to surveys sent through professional society mailing lists , possibly biasing utilization rates .
it is not clear whether this number is underestimated or prior estimates overestimate utilization due to selection bias of surveys .
it is possible that cases involving government - funded insurance that do not reimburse ionm may lead to under - coded ionm cases .
this relationship appears to extend to the routine use of ionm . for surgeons who are able to reliably achieve improved results with ionm
in addition , a relevant proportion of thyroidectomies occur in ambulatory settings and therefore are not captured in this series .
furthermore , important confounders such as prior neck surgery or prior neck irradiation are not reliably captured in the nis .
these risk factors would affect the complexity of the case , the clinical value of ionm and ultimately the expected rate of vcp .
however , given the increased patient volume and the control of treatment , ascertainment , and coding biases , these results do not support broad adoption of ionm .
further study remains the best option in identifying a causal relationship between ionm and increased vcp .
overall , ionm was associated with a higher rate of vcp even after correction for numerous confounders . in particular ,
less frequent ionm utilization and use in partial thyroidectomies were associated with higher rates of vcp .
backgroundprevious ionm studies have demonstrated modest - to - no benefit and did not include a nationwide sample of hospitals representative of broad thyroidectomy practices . 
 this national study was designed to compare vocal cord paralysis ( vcp ) rates between thyroidectomy with ionm and without monitoring ( conventional).study designwe performed a retrospective analysis of 243,527 thyroidectomies during 2008 - 2011 using the nationwide inpatient sample.resultsionm utilization increased throughout the study period ( 2.6% , 5.6% , 6.1% , 6.9% ) and during this time , vcp rates in the ionm group initially increased year - over - year [ 0.9%(2008 ) , 2.4%(2009 ) , 2.5%(2010 ) , 1.4%(2011 ) ] . in unadjusted analyses , 
 ionm was associated with significantly higher vcp rates ( conventional 1.4% vs ionm 1.9% , p<0.001 ) . 
 after propensity score matching , ionm remained associated with higher vcp rates in partial thyroidectomy and lower vcp rates for total thyroidectomy with neck dissection . 
 hospital - level analysis revealed that vcp rates were not explained by differential laryngoscopy rates , decreasing the likelihood of ascertainment bias . 
 additionally , for hospitals where ionm was applied to > 50% of thyroidectomies , lower vcp rates were observed ( 1.1% ) compared to hospitals that applied ionm to < 50% ( 1.6%,p=0.016 ) . higher hospital volume correlated with lower vcp rates in both groups ( < 75 , 75 - 299 , > 300 thyroidectomies / year : ionm-2.1% , 1.7% , 1.7% , conventional-1.5% , 1.3% , 1.0%).conclusionsaccording to this study 
 , ionm has not been broadly adopted into practice . 
 overall , ionm was associated with a higher rate of vcp even after correction for numerous confounders . in particular , 
 low institutional utilization of ionm and use in partial thyroidectomies is associated with higher rates of vcp . 
 further studies are warranted to support the broader application of ionm in patients where benefit can be reliably achieved .