selected group of patients with hearing loss at high frequency and still preserved hearing at low frequencies do not benefit from the classic hearing aid .
parallelly , due to residual hearing they do not meet the qualification criteria for classic cochlear implant . nevertheless , ongoing development indicated that the hybrid system  concept of electro - acoustic stimulation   i.e. , combination of hearing aid , that amplifies the residual hearing and cochlear implant , that stimulates cut off frequencies at the level of the basal turn of the cochlea will work best for that group of patients .
preliminary observations that proceeded research and development on the hybrid system were combined with observations on conservation of residual hearing in cochlear implants recipients .
results showed that 50  % of operated patients retained sufficient hearing for effective use of ipsilateral ite hearing aid .
number of studies indicates that bimodal stimulation is not just a simple additive effect of both devices , but they show the synergistic action , that is especially appreciated by patients experiencing so called  cocktail party effect  in difficult listening environments [ 36 ] .
new , less traumatic electrodes were introduced as well as the surgery improved from 11.2  mm cochleostomy to the round window approach .
atraumaticity i.e. , preservation both hearing and vestibular function   become the key element in the hybrid surgery .
recent advances in that field brought the hybrid - l electrode attached to nucleus freedom implant .
straight , thinner and shorter ( 16  mm ) comparing with contour advanced electrode , but with 22 active contacts hybrid - l electrode was developed to facilitate the less traumatic insertion through the round window to preserve residual hearing .
new nucleus freedom hybrid - l system was introduced into the clinical practice in 2009 .
first experiences with new electrode were presented by lenarz et al .   confirming the safety on both histological and clinical level [ 1 , 9 ] . with
that perspective authors would like to share their own observations on hearing preservation with hybrid - l system .
study was designed as the retrospective analysis conducted at the department of otolaryngology and oncological laryngology , poznan university of medical science .
twenty - one patients with high frequency hearing loss ( n  =  21 ) were included to the study .
there were 12 females and 9 males , ranging in age from 16 to 77  years of age , with a mean of 49.5  years and median 52.5  years of age .
nucleus freedom hybrid - l device ( cochlear , australia ) was implanted in every patient by the same surgeon ( ws ) with the standardized surgical technique described previously [ 8 , 10 ] .
patients were qualified for the surgery according to the audiometric indications ( pta ) , minimum 5  years of stable hearing loss , insufficient gain form hearing aid ( 30  % of speech understanding ) .
speech processor switch - on was done in 58  weeks , depending on acoustic component delivery . up to date
, all the patients use electric as well as acoustic stimulation  none of the patient use only electric stimulation .
first one with classic indication for hybrid - l implant ( group a , n  =  13 ) and second with extended criteria according to lenarz et al .
the mean value for three lower frequencies ( 250 , 500 and 1,000  hz ) were calculated .
acoustic thresholds > 110  db or without recordings were considered as hearing loss and for statistic evaluation marked as 120  db .
the difference between mean values before and after surgery was studied and defined as follows : hearing preservation  mean value up to 10  db ; hearing impairment 
mean value between 10 and 30  db ; hearing loss for patients with no thresholds recorded postoperatively .
in the group of 21 implanted patients in 17 cases we have observed preservation of hearing ( 12 patients from group a , 5 patients from group b ) . in 4 out of 21 patients deafness on the implanted ear was noted ( group a1 patient , group b3 patients ) , although all these 4 patients reported significant difference in hearing after acoustic component activation . in 17 patients with preservation of hearing analysis of audiometric results revealed that within the a group ( 13pts . ) in 9 cases average hearing thresholds were calculated for 3 evaluated frequencies . in 3 cases hearing threshold for 1,000  hz was not detectable , comparing to preoperative values : 80 , 110 and 100  db .
post difference of mean hearing threshold was 010  db in 6 cases , 1120  db in 3 cases , and 2130  db in 3 cases . within the b group ( 8pts . ) in 4 cases hearing threshold for three examined frequencies was established .
post difference of mean hearing threshold was 010  db in 3 cases and 2130  db in 2 cases .
in one patient from the b group hearing threshold for 1,000  hz was not recorded pre- and postoperatively ( table  1).table  1summary of the audiometric results in patients implanted with nucleus hybrid - l electrode recorded pre- and postoperativelypatient numbergroupimplanted earagegenderpre - op ptapost - op ptamean pre - op ( db)mean post - op ( db)hl ( db)preservation of hearing250  hz500  hz1,000  hz250  hz500  hz1,000  hz1al16.5f30459025759055.063.38.3 + 3ar64f55606070809558.381.723.3 + 6ar18.5f20202035403020.035.015.0 + 7al77m55606012012012058.3120.061.7x9al18f6565808010012070.0100.030.0 + 10al66m45457050558553.363.310.0 + 12al53.5f305070303510050.055.05.0 + 14ar47m30508530558555.056.71.7 + 15al37f5055100558011068.381.713.3 + 16ar50f607095657010075.078.33.3 + 17ar69f25506030556545.050.05.0 + 19ar52.5f45601108510012071.7101.730.0 + 21al30.5m204090305512050.068.318.3+mean value for the group a 
 13.62br34.5m70708075709073.378.35.0 + 4br75.5m70909012012012083.3120.036.7x5bl49.5f45707545757563.365.01.7 + 8br54.5f55657560658065.068.33.3 + 11br75m65655590858061.785.023.3 + 13bl64m70659512012012076.7120.043.3x18br77.5m4555x7090x50.080.030.0 + 20bl20.5f80909012012012086.7120.033.3xmean value for the group b 
 12.7mean value for both groups ( a  +  b ) 
 13.1mean value for all patients in the study19.1 in all cases where threshold could not be recorded the value of 120  db was used for statistic calculation 
 patient(s ) with hearing loss excluded from the calculation summary of the audiometric results in patients implanted with nucleus hybrid - l electrode recorded pre- and postoperatively in all cases where threshold could not be recorded the value of 120  db was used for statistic calculation 
 patient(s ) with hearing loss excluded from the calculation
general overviews indicated that conservation of residual hearing in ci patient can be achieved in approximately 50  % [ 2 , 11 ] .
years after first publication on the topic , carlson et al .   interestingly pointed out that hearing preservation after standard cochlear electrode implantation remains unpredictable , but should be considered as the realistic goal . to improve the safety and increase the atraumaticity of the surgery various strategies
were proposed , among which the technique called  soft surgery  proposed by lehnhardt , become the gold standard in all ci surgeries .
other options , such as lubricants ( i.e. , hialuronic acid ) added during the surgery are in the routine use , whereas , round window approach , as the alternative to the cochleostomy in classic ci remains under discussion .
hybrid cochlear implants , unlikely the conventional ones , requires the residual hearing to give the recipient the best feedback .
therefore , hearing preservation is not an option , but the key point element to be achieved .
first experiences with hybrid s electrode ( cochlear , australia ) implanted in patients with residual hearing in low frequencies were very successful [ 1619 ] .
although the design of the electrode ( 10  mm in length , six active contacts ) was addressed to minimize trauma of the basilar turn of the cochlea , to reduce the risk of hearing loss , this could not be avoided . in patients with loss of residual hearing ,
the only electrical stimulation based on six contacts on the electrode was not sufficient , resulting in necessity of re - implantation with longer electrode .
this 16  mm with 22 contacts electrode covers approximately 270 of the basal turn of the cochlea , which is an equivalent of the former nucleus 24 straight electrode .
the stopper and the wing ascertains the comparable electrode position in the cochlea of the operated patients . thus ,
variable such as insertion depth is not an issue in cochlear nucleus freedom hybrid - l implant .
that is parallel with our experience , although , the position of the round window , caused minor technical problem during the insertion ( the angle ) and it was not the primary goal of investigation .
the overall hearing preservation rate in the current study was 80.95  % ( 17/21 ) . within the classic indication group ( group a ) it was 92.3  % ( 12/13 ) , but unfortunately , for patients with extended indications ( group b ) hearing preservation rate was lower62.5  % ( 5/8 ) . nevertheless , it is still over 50  % above the level indicated in the literature .
looking at the potential cause of hearing loss in patients from our study , surgery variations was not an issue , because all cases were operated by the same surgeon .
thus , other reasons for the failure such as age of the patients ( two were over 70  years ) , diabetes , vascular problems or inflammatory responses should be taken under consideration .
our results clearly indicate that with standard procedure hearing preservation can be obtained in majority of patients .
hearing preservation was not achieved in 19.05  % , but owing to design of the electrode of the cochlear nucleus hybrid - l that enables to work as ci platform alone , in patients who lost their hearing after surgery re - implantations were not required .
this proves that eas is a safe and reliable method to help patients with specific type of hearing loss .
 the objective of the paper is to evaluate the hearing preservation rate in patients with high frequency hearing loss , treated with cochlear nucleus freedom hybrid - l implant in the otolaryngology department , poznan university of medical sciences in poland . 
 study was designed as the retrospective analysis . 
 twenty - one patients were operated and implanted with nucleus freedom hybrid - l implant . 
 pure tone thresholds were recorded prior to the surgery and at the time of speech processor switch - on . 
 patients were subdivided into two groups with respect to their pta thresholds : group a  
 classic indications and group b  extended indications . 
 average pta for three frequencies ( 250 , 500 , 1,000  hz ) were calculated for each patient pre- and postoperatively . in the group of 21 implanted patients in 17 cases 
 we have observed preservation of hearing ( 12 patients from group a , 5 patients from group b ) with a mean value of 13.1  db . in 4 out of 21 patients deafness on the implanted ear was noted . 
 our results clearly indicate that with standard procedure hearing preservation can be obtained in majority of patients . 
 hearing preservation was not achieved in 19  % , but owing to design of the electrode of the cochlear nucleus hybrid - l that enables to work as ci platform alone , in patients who lost their hearing after surgery re - implantations were not required . 
 this proves that eas is a safe and reliable method to help patients with specific type of hearing loss . 
Introduction
Materials and methods
Results
Discussion
Conclusions