the optimal visualisation of vocal cords during fibreoptic intubation may be utilised for the nares - vocal cord distance ( nvd ) estimation , which is a very useful measurement for blind nasal intubation , positioning of the nasopharyngeal airway ( npa ) or of endotracheal tube as npa and positioning of temperature sensor .
the present study was conducted to measure nvd and to correlate with various external body parameters in indian population .
after approval from hospital ethical committee , this prospective study was conducted on 100 patients ( 50 male and 50 female ) , american society of anesthesiologists physical status i - ii , in the age group of 1860 years who presented for elective surgery under general anaesthesia .
the exclusion criteria were patient 's refusal , body mass index > 35 , reactive airway disease , difficult airway , high risk for aspiration and patient with history of nasal bleed or rhinitis or polyp or snoring or bleeding diathesis .
all patients included in the study were explained the whole procedure and an informed written consent was taken .
the following measurements were taken : height , nares to tragus of ear distance ( ned)-from lateral border of the nares to tragus of ear , nares to angle of mandible distance ( nmd)-lateral border of nares to angle of mandible , sternal length ( sl ) distance - from sternal notch to lower border of xiphisternum , thyro - mental distance ( tmd)-upper margin of thyroid cartilage to chin distance in full extension , sterno - mental distance ( smd)-sternal notch to chin distance in full extension , arm span ( as)-physical measurement of the length from one end of an individual 's arm ( measured at the fingertips ) to the other when raised parallel to the ground at shoulder height at 180 angle to each other , using measuring tape . the age , gender , height and weight of all patients
routine monitors were attached ( electrocardiogram , pulse oximeter , non - invasive blood pressure ) and intravenous access established using 18-gauge intravenous cannula .
nasal decongestant xylometazoline ( otrivin ) 23 drops were instilled in both nostrils 10 min before induction of anaesthesia .
injection glycopyrrolate 0.2 mg , injection midazolam 2 mg and injection pethidine 0.5 mg / kg body weight were given intravenously 2 min prior to induction of anaesthesia .
anaesthesia was induced with intravenous injection propofol 2 mg / kg and vecuronium bromide 0.1 mg / kg body weight was used for neuromuscular blockade .
patient was ventilated with 100% oxygen and 11.5% isoflurane using aladdin 's vapourizer with bain 's circuit for 5 min . a well lubricated fiberoptic bronchoscope ( fob ) ( karl storz , outer diameter 5.2 mm )
continuous insufflation of oxygen at 4 l / min via working channel of fob was given during the procedure .
the fob was marked with tape at the nares when the tip of the fob was positioned precisely between the cords , with head in neutral position .
the length between the mark and tip of fob was measured , corresponding to nvd .
the data according to gender were analysed and compared using two sample unpaired two tailed t - test .
the power analysis was done retrospectively , observing relationship between nvd and external body parameters ( assuming strong positive significant correlation of nvd with external body parameters ( r = 0.001 ) for 100 consecutive patients with  = 0.05 , power 80% ) .
the correlation between nvd and external body parameters was determined by pearson 's correlation coefficient and its statistical significance was determined by two sample unpaired two tailed t - test . a p < 0.05 was taken as cut point for level of statistical significance .
linear regression analysis of the measured data was performed and the relationships between the nvd and following parameters : height , ned , nmd , tmd , smd , sl and as were analysed .
on analysis of the demographic profile , the height and weight were greater in males than in females .
the mean age of males and females ( years ) was 33.98  11.35 , 36.86  11.31 , respectively .
the ned , nmd , smd , tmd , sl , and as were greater in males than females .
the mean nvd of males was 18.50  1.5 cm and females was 15.9  1.1 cm [ table 1 ] .
demographic data and other body parameters of the patients both in males and females the correlation of nvd with height , sl and as was statistically significant ( < 0.001 ) and regression lines were derived which are shown in figures 13 , respectively .
the correlation coefficient for the nvd to sl ( r = 0.759 ) was higher than the nvd to as ( 0.561 ) and least with height ( r = 0.463 ) in males [ table 2 ] .
the correlation coefficient for the nvd to sl ( r = 0.801 ) was higher than the nvd to height ( 0.555 ) and least with as ( r = 0.499 ) in females [ table 2 ] .
the correlation of nvd with ned , nmd , tmd and smd was not statistically significant in both the groups .
after combining the groups ( n = 100 ) the correlation coefficients for the nvd to external body parameters in decreasing order are as follows : sl ( r = 0.887 ) , height ( r = 0.791 ) , as ( r = 0.769 ) , weight ( r = 0.531 ) , smd ( r = 0.466 ) , ned ( r = 0.459 ) , nmd ( r = 0.391 ) , tmd ( r = 0.379 ) [ table 3 ] .
we chose parameters for regression lines which had significant correlation with nvd in male , female and combined group .
the formulae for the regression lines in the combined group were : nvd ( cm ) = 0.627 + 0.962  sl ( cm ) , nvd ( cm ) = 0.135  height ( cm ) 4.471 or nvd ( cm ) = 0.119  as ( cm ) 2.946 .
relationship between the nares - vocal cord ( y - axis ) and the height ( x - axis ) relationship between nares - vocal cord ( y - axis ) and sterna length ( x - axis ) relationship between nares - vocal cord ( y - axis ) and arm span ( x - axis ) correlation of nvd with various external body parameters in males and females correlation of nvd with various parameters in total patients ( n=100 )
in our study , the correlation of nvd to the sl , as and body height was significant in all the groups .
the pearson 's correlation coefficient for the nvd to other body parameters was in decreasing order of sl , as , height in males and sl , height , as in females .
this suggests that sl can be a better predictor for nvd estimation in both males and females . in individual groups ,
. however , on combining the groups , significant correlation between nvd and other external body parameters was found [ table 3 ] . a similar study in the past found a significant correlation of nvd with both height and ned but not with nmd . in our study ,
relationship of nvd with ned did not show significant correlation in both males and females groups .
however , it had strong correlation with nvd when we combined male and female data ( n = 100 ) which was similar to above study , where male and female data were combined to correlate with nvd .
in contrast to that study , our study showed a significant correlation of nvd with nmd in the combined group ; however , nmd had insignificant correlation with nvd in both males and females group .
this type of study has not been carried out / published in indian population and the difference in the results might be attributed to the racial differences in skeletal makeup .
were , nv length ( cm ) = 0.113  height ( cm ) 1.245 or nv length ( cm ) = 1.158  ne distance ( cm ) + 1.498 .
as height of the nose may be individualised or show ethnic variations , we took the lateral border of the nares for measurement . in 2008 , a study was conducted in which nasotracheal intubation was performed and while inserting the tube as 
the give was felt suggesting passage into pharynx the position of the tube was marked black at the external nares . at the time of extubation when the patient was spontaneously ventilating under deep anaesthesia , the nasal tube was withdrawn until the black line became visible .
the tube was then left in situ as a nasal airway while the patient emerged from anaesthesia .
the distance from the drawn line to the tube tip was measured ( lt distance ) .
the mean lt distance was 14  1.4 cm in males and 12.4  1.4 in females .
there was a correlation between lt distance and patient height ( r = 0.4 , p = 0.02 ) .
in addition , knowing the nvd can be useful for a blind naso - tracheal intubation .
blind conscious nasal intubation is useful for an urgent intubation outside the operating room when mouth opening or neck movement is limited or prohibited .
the correlation coefficients for the nvd to external body parameters in decreasing order were as follows : sl , height , as , weight , smd , ned , nmd , and tmd in the combined group ; whereas when gender was taken into consideration nvd correlated significantly with sl , height , and as and not with the other parameters .
 background and aims : the optimal visualisation of vocal cords during fibreoptic intubation may be utilised for the nares - vocal cord distance ( nvd ) estimation . 
 the present study was conducted to measure nvd and to correlate with various external body parameters.methods:this study was conducted on 50 males and 50 females . 
 we measured nvd and analysed its relationship with height , nares to tragus of ear distance ( ned ) , nares to angle of mandible distance ( nmd ) , sternal length ( sl ) , thyro - mental distance ( tmd ) , sterno - mental distance ( smd ) and arm span ( as).results : the mean nvd of the males was 18.5  1.5 cm , and that of the females was 15.9  1.1 cm . 
 the relationship between the nvd and body height ( males p = 0.001 , r = 0.463 , females p = 0.000 , r = 0.555 ) , sl ( males p = 0.000 , r = 0.463 , females p < 0.000 , r = 0.801 ) or as ( males p = 0.000 , r = 0.561 , 
 females p = 0.000 , r = 0.499 ) showed a significant correlation but ned , nmd , tmd , smd did not . after combining male and female groups , 
 ( n = 100 ) , the correlation of nvd with external body parameters is as follows sl ( r = 0.887 ) , height ( r = 0.791 ) , as ( r = 0.769 ) , weight ( r = 0.531 ) , smd ( r = 0.466 ) , ned ( r = 0.459 ) , nmd ( r = 0.391 ) , tmd ( r = 0.379).conclusion : the relationship of nvd to external body parameters had strong correlation in all parameters in the combined group ; whereas when gender was taken into consideration nvd correlated significantly only with sl , height and as . 
INTRODUCTION
METHODS
RESULTS
DISCUSSION
CONCLUSION