umbilical - vein catheters ( uvcs ) can be used for intravenous administration of parenteral nutrition , hypertonic solutions , blood products , and medication . umbilical - artery catheters ( uacs ) can be used for blood - sampling and continuous monitoring of blood pressure . however , the advantages of umbilical catheters must be carefully balanced against the potential risks . several life - threatening complications have been associated with the use of umbilical catheters including catheter - related infections , intestinal necrosis , thrombosis , cardiac arrhythmias , myocardial perforation , and pleural and pericardial effusion [ 18 ] . accurate prediction of the insertion length of the catheter is therefore paramount , as well as the confirmation of the position after insertion by chest x - ray or with ultrasound [ 9 , 10 ] . several formulas and graphs using various body measurements have been proposed to predict the correct position of umbilical catheters [ 2 , 1116 ] . the dunn - method is based on the measurement of the shoulder - umbilicus length and uses nomograms to determine the insertion length of the catheters . 19 were stillborn and the remaining 31 had died during the first week of life . shukla retrospectively studied 43 neonates ( mean birth weight 2037 [ + /1077 ]  gram ) with uacs and 10 ( mean birth weight 2260 [ + /1144 ]  gram ) with uvcs . in a prospective study , shukla inserted 25 uacs and 16 uvcs in 29 neonates using equations derived from the retrospective study . the accuracy of both methods to estimate the correct insertion length is not well known . both methods have been developed based on a small group of neonates and have not been validated prospectively in larger groups of neonates . we performed a study to compare the accuracy of both methods in determining the correct position of umbilical catheters . in this prospective observational study , we compared the position of umbilical catheters before and after implementation of the shukla - method at our department , in july 2007 . in the first study period , from december 1st 2006 to june 1st 2007 , the policy used to determine the insertion length of umbilical catheters was based on the dunn - method . during this period two members of our group ( gv and el ) observed that the dunn - method was often associated with a too high position and significant inter- and intraobserver variation . to avoid this variation - bias , the method of shukla was implemented in our neonatal nursery and was used in the second study period from october 1st 2007 to april 1st 2008 . during the two 6-month study periods , all neonates admitted to the leiden university medical center who received umbilical catheters were included in the study . parental consent was not necessary , because both the method of dunn and shukla are accepted methods to use for the positioning of umbilical catheters in the netherlands . in accordance with dutch legislation on retrospective observational studies , irb approval was not required . patients with fetal hydrops or major congenital abnormalities were excluded , because of possible interference with the calculated or measured insertion length of the catheters . we also excluded cases in which a uac was mistakenly placed in the umbilical vein instead of an artery or a uvc was placed in an artery . in the first study period , we measured the length from the tip of the neonate 's shoulder to the umbilicus and used the nomograms of dunn to determine the insertion length of the catheters . in the second study period , we calculated the insertion length with the equations of shukla . to calculate the depth for inserting a uac , we multiplied the neonate 's weight in kilograms by 3 and added 9  cm . to calculate the depth for inserting a uvc we used the insertion length of the uac , divided this number by 2 , and added 1  cm [ 2 , 14 , 15 ] . we confirmed the depth of the catheter - tip using antero - posterior chest x - rays . the primary outcome variable was the rate of uvcs and uacs ideally positioned on initial x - ray . ideal position of the uvc was defined as the catheter - tip being visible between the 9th and 10th thoracic vertebrae on a chest x - ray [ 2 , 18 ] . the position of the uvc was considered too high if the tip of the catheter was higher than the 9th thoracic vertebra , and too low if the tip was below the 10th thoracic vertebra . ideal position of the uac was defined as the catheter - tip being visible between the 6th and 10th thoracic vertebrae [ 11 , 16 , 18 , 19 ] . the position of the uac was considered too high if the tip of the catheter was higher than the 6th thoracic vertebra , and too low if the tip was below the 10th thoracic vertebra . secondary outcomes were rates of too high and too low position and rate of complications . the following neonatal data were collected : success of insertion of catheters , gestational age at delivery , birth weight , gender , mortality , respiratory distress syndrome , mechanical ventilation , patent ductus arteriosus requiring medical treatment or surgical closure , necrotizing enterocolitis  bell stage ii , culture - proven sepsis , and catheter - related complications such as thrombosis , cardiac arrhythmias , myocardial perforation , pleural and pericardial effusion . ultrasound examination to rule out catheter - related complications ( such as thrombosis ) was not routinely performed in all neonates . results of categorical variables were compared using fisher 's exact test or chi - square test as appropriate . student 's t - test was used to compare normally distributed values between two groups . during the study period , 220 patients received either a uvc or a uac , or both . four patients were excluded due to fetal hydrops ( n = 2 ) and incorrect insertion of catheters ( uvc in umbilical artery and uac in umbilical vein ) ( n = 2 ) . the remaining 216 patients were included in the study , 97 patients in the dunn - group and 119 patients in the shukla - group . birth weight ranged from 575 to 6430 grams in the total group and gestational age from 25 to 42 weeks . overall , uvcs were successfully introduced in 70% ( 153/220 ) of neonates and uacs were placed successfully in 58% ( 83/144 ) . in the other neonates , the tip of the catheter could not be introduced in the vessel or ( in uvcs ) the tip was in the portal vein . if the tip of the uvc was in the portal vein , a second attempt to introduce a uvc next to the first uvc was made . we found no difference between the rate of successful and correct insertion between residents and experienced neonatologists . figure 1 shows the percentages of uvcs and uacs placed correctly and incorrectly in the dunn - group and shukla - group . positions of the tip of uvcs in the dunn - group and shukla - group ranged from the 4th to the 11th thoracic vertebrae on chest x - rays ( figure 2 ) . in the dunn - group , 41% ( 28/69 ) of uvcs were placed directly in the correct position against 24% ( 20/84 ) in the shukla - group ( p < .05 ) . uvcs placed according to the dunn - method ( 57% , 39/69 ) were less often in a too high position ( above the 9th thoracic vertebra ) compared to uvcs placed according to the shukla - method ( 75% , 63/84 ) ( p < .05 ) . in the dunn - group , 3% ( 2/69 ) of uvcs were placed too low and in the shukla - group 1% ( 1/84 ) ( p = .45 ) . catheter - tips of uvcs placed at two or more vertebrae higher than the 9th thoracic vertebra were found in 32% ( 22/69 ) in the dunn - group and in 55% ( 46/84 ) in the shukla - group ( p < .01 ) ( figure 3 ) . positions of the tip of uacs in the dunn - group and shukla - group ranged from the 1st to the 11th thoracic vertebrae on chest x - rays ( figure 4 ) . uacs in the dunn - group were placed directly in the correct position in 63% ( 24/38 ) compared to   87% ( 39/45 ) of cases in the shukla - group ( p < .05 ) . the tip of uacs was placed too high in 34% ( 13/38 ) of cases in the dunn - group and 13% ( 6/45 ) of cases in the shukla - group ( p < .05 ) . one uac in the dunn - group was in a too low position ( figure 5 ) . one neonate in the shukla - group developed a supraventricular tachycardia directly after umbilical catheterization . the chest x - ray showed malposition of the uvc - tip at the 6th thoracic vertebra . catheter - related thrombosis , diagnosed by ultrasonography , occurred in 5/97 ( 5% ) of patients in the dunn - group and 3/119 ( 3% ) of patients in the shukla - group . in this study , we assessed the accuracy of the two most commonly used methods to predict the appropriate insertion length of uvcs and uacs [ 2 , 14 , 15 ] . we observed that the overall accuracy of both methods is poor and both methods lead to too high positions of umbilical catheters . interestingly , the dunn - method is more accurate than the shukla - method in predicting the appropriate insertion length for uvcs , whereas the shukla - method is more accurate for the placement of uacs . high - positioned venous catheters ( with the tip in the right atrium or deeper ) are associated with cardiac arrhythmias , intracardiac thrombosis , pleural and pericardial effusions , and myocardial perforation and need to be avoided [ 3 , 58 , 20 ] . thrombosis related to the catheter occurred in 8/216 ( 4% ) in the total study group . since ultrasonography to detect or rule out thrombosis was not routinely performed , data on the rate of catheter - related thrombi presented in this study should be interpreted with care as under - reporting can not be ruled out . the high rate of a too high position of uvcs observed in this study can be due to several reasons . both dunn and shukla accepted in their original research a position of the uvc - tip in the right atrium [ 14 , 15 ] , but this position is now considered to be too high . the optimal position for uvcs is at the junction of the inferior vena cava and the right atrium [ 9 , 21 ] . this will correspond to the catheter - tip being visible between the 9th and 10th thoracic vertebrae on a chest x - ray , although positioning at the level of the 8th thoracic vertebra may also be adequate in some patients . also , both methods were developed based on a small sample size ( n = 50 in the dunn - study and n = 29 in the prospective part of the shukla - study ) and have not been validated prospectively in larger groups of neonates [ 14 , 15 ] . in addition , the dunn - method is limited by interobserver variation . our findings are in agreement with the results from a recent randomized controlled trial reported by wright et al . , in which they report that placement of uacs using the dunn - method leads to a too high position in many neonates . the aim of this trial was to establish the validity of a newly derived formula [ ( 4  birth weight ) + 7  cm ] compared to the dunn - method . wright et al . showed that the use of this formula significantly reduced the rate of uacs placed too high . in 3% ( 1/35 ) of neonates in which the new formula was used the uac was too high , against 49% ( 19/39 ) in the control group in which the dunn - method was used , ( p < .0001 ) . whether this new formula is more accurate than the shukla - method has not been studied and requires further investigation . moreover , only very low - birth weight infants were included ( < 1500  gram ) , limiting the applicability of this new formula to this subgroup . a major disadvantage of wright 's formula is the high rate ( 11% ) of catheters positioned too low , which is of concern given the association with gut ischemia and thrombosis of renal and mesenteric arteries . ideally , uacs should either be placed in a high position ( between the 6th and 10th thoracic vertebrae ) or in a low position ( between the 3rd and 5th lumbal vertebrae ) [ 11 , 19 , 22 , 23 ] . a recent cochrane systematic shukla and ferrara verified their own formulas and found all catheter - tips in acceptable positions , but they only verified 26 uacs and 16 uvcs . weaver and ahlgren based their equation to predict the insertion length of uacs on measurement of the heel - to - crown length of the neonate and reported that in 39 of 40 cases the catheter - tip was at the desired level . heel - to - crown length , however , is difficult to measure and this method is not widely used . although our study is limited by the non - randomized , nonblinded design , the catheters were inserted by almost 20 doctors and most of them were unaware of the advantages or disadvantages of both methods ( in terms of accuracy ) . another limitation is related to the confirmation of catheter position with x - ray . whether radiography is the ideal diagnostic tool to determine the correct position of uvcs and uacs is controversial . some authors advocate bedside real - time ultrasonography as the gold standard in verifying the position of umbilical catheters . although the method of dunn is more accurate than the method of shukla for determining the appropriate insertion length of uvcs , the shukla - method is superior for determining the appropriate insertion length of uacs . however , it would not be practical to combine two different methods for the insertion of umbilical catheters , which may even lead to confusion and mistakes . ideally , new and more reliable formulas should be developed for determining the correct insertion length of uvcs as well as uacs . these formulas should be validated in large studies of neonates including a wide range of gestational age and birth weight .
this study compares the methods of dunn and shukla in determining the appropriate insertion length of umbilical catheters . in july 2007 
 , we changed our policy for umbilical catheter insertions from the method of dunn to the method of shukla . 
 we report our percentage of inaccurate placement of umbilical - vein catheters ( uvcs ) and umbilical - artery catheters ( uacs ) before and after the change of policy . in the dunn - group , 41% ( 28/69 ) of uvcs 
 were placed directly in the correct position against 24% ( 20/84 ) in the shukla - group . 
 the position of the catheter - tip of uvcs in the dunn - group and the shukla - group was too high in 57% ( 39/69 ) and 75% ( 63/84 ) of neonates , respectively . 
 uacs in the dunn - group were placed directly in the correct position in 63% ( 24/38 ) compared to the 87% ( 39/45 ) of cases in shukla - group . 
 the position of the catheter - tip of uacs in the dunn - group and the shukla - group was too high in 34% ( 13/38 ) and 13% ( 6/45 ) of neonates , respectively . 
 in conclusion , 
 the dunn - method is more accurate than the shukla - method in predicting the insertion length for uvcs , whereas the shukla - method is more accurate for uacs .