various techniques have been formulated to obtain favourable conditions for intubation and one such technique is the priming technique . priming principle refers to administration of a small dose of non - depolarising blocker which when followed by a large intubating dose after 2 - 4 min produces a relatively rapid and profound blockade to ensure a suitable condition for endotracheal intubation . the theory behind this principle is that a small dose of non - depolarizing agent can block large number of acetylcholine receptors at the neuromuscular junctions ( nmj ) before appreciable clinical reduction in neuromuscular transmission . the second larger dose blocks the remaining receptors and effects more rapid onset of intubating conditions . when using the priming principle to accelerate the onset of neuromuscular blockade , the initial dose should not exceed 10% of the drug 's ed95 . the priming technique is considered clinically superior to the bolus method and is preferred in all elective cases and in those patients in whom succinylcholine is contraindicated . the effects of pretreatment of three different non - depolarising muscle relaxants , rocuronium , vecuronium and atracurium on the facilitation of endotracheal intubation with rocuronium are compared as also the haemodynamic changes and adverse effects , if any . a double - blinded , randomised controlled prospective study was conducted at a tertiary health care hospital between september 2010 and august 2012 . after obtaining approval by the institutional ethics committee , 105 patients of american society of anaesthesiologists physical status i and ii aged between 20 and 60 years , both sexes , undergoing surgeries under general anaesthesia , patients with renal diseases , hepatic diseases , neurological disorders and neuropathies , cardiovascular diseases and respiratory problems with anticipated airway difficulties , any known allergy to study drugs were excluded from the study . based on previous studies , it was calculated that a sample size of 28 patients would be required per group to demonstrate a clinically significant difference among the groups for improving intubating conditions , at  = 0.05 with a power ( 1- ) of 80% . in order to improve the weight of the results , of the study , 35 patients were enrolled for each group . patients were randomly allocated into three groups by computer generated randomisation chart to receive the drugs during the study as follows : group a ( n = 35 ) - rocuronium ( 0.06 mg / kg body weight ) , group b ( n = 35 ) - vecuronium ( 0.01 mg / kg body weight ) and group c ( n = 35 ) - atracurium ( 0.05 mg / kg body weight ) . on arrival at the operation theatre , the patients were connected to the monitors for measuring the heart rate ( hr ) , blood pressure ( bp ) , electrocardiogram , peripheral oxygen saturation ( spo2 ) , and the baseline values of these variables were recorded . for neuromuscular monitoring , a peripheral nerve stimulator then , a priming dose of the test drug ( 10% of the ed95 ) , which was prepared and loaded in a syringe by an assistant not involved in the assessment , was administered . this was followed by preoxygenation with 100% oxygen over 2 min and the anaesthesia was induced with injection thiopentone sodium until the loss of eye lash reflex . 90% ( 0.54 mg / kg body weight ) of the calculated intubating dose ( 0.6 mg / kg body weight ) of rocuronium was administered to facilitate endotracheal intubation . the ulnar nerve was stimulated percutaneously at the wrist joint immediately after administering the intubating bolus dose . the electromagnetic response of single twitch contractions ( 0.1 hz ) of adductor pollicis muscle obtained by stimulation of ulnar nerve with supra maximal stimulus of 0.2 ms duration was recorded . oxygenation was continued and endotracheal intubation was attempted at 60s from the end of rocuronium injection . the single twitch height was first recorded immediately after the administration of the intubating dose of rocuronium and at the end of 60s ; another single twitch response was recorded . consisting of a total score of 9 in relation to jaw relaxation , condition of the vocal cords and response to intubation , which are graded as excellent ( if score is 8 - 9 ) , good ( if score is 6 - 7 ) , fair ( if score is 3 - 5 ) and poor ( if score is 0 - 2 ] ) . after successful intubation vital haemodynamic parameters were recorded at 0 , 1 , 2 , 3 , 4 , 5 and 10 min following intubation . 0 minute was defined as the point of time where the remaining 90% of the intubating dose of rocuronium was administered following the priming dose . patients were extubated after the return of airway protective reflexes and monitored in post anaesthetic care unit ( pacu ) before transfer to the pacu . the parameters and patient data were recorded and entered in microsoft excel sheet ( microsoft office 2007 professional ) and compared among the three groups using anova test for categorical variable , student 's t - test for continuous variables , and p  0.05 was deemed significant . statistical package for social sciences ( spss ) for windows version 16.0 software , chicago , spss inc . was used for statistical analysis . the age , weight , and sex distribution of the three groups were uniform and comparable [ table 1 ] . the hr [ figure 1 ] rose from the baseline value reaching its maximum value at 1 min and thereafter receded even though it did not come down near the baseline value in all three groups . the three groups when compared showed no significant difference in hr at different time intervals ( p > 0.05 ) . the distribution of patient 's demographic profile in three groups the distribution of pulse rate ( rate per minute ) in the three groups at different time intervals the systolic blood pressure ( sbp ) in all the three groups rose from the baseline value reaching its maximum in the  0 min even though the rise was highly significant throughout all the time intervals [ figure 2 ] . the changes in sbp when the three groups were compared by f test at different time intervals showed no significant difference ( p > 0.05 ) . the variation in sbp from the baseline value till the first 5 min was significant within all three groups . the distribution of systolic blood pressure ( in mmhg ) in the three groups at different time intervals the changes in the mean arterial bp [ figure 3 ] followed the same trend as that of sbp . the three groups when compared together at different time intervals showed no significant differences ( not statistically significant ) among the groups . the distribution of mean arterial pressure ( in mmhg ) in the three groups at different time intervals single twitch height measured just before the intubation ( t2 ) showed significant change when compared with baseline ( t1 ) , noted immediately after administration of intubating dose of rocuronium in all the three groups as shown in table 2 . when the twitch heights were compared in between the groups , significant difference was noted only between the twitch heights at intubation , of groups b and c. the distribution of single twitch height in the three groups grading of the quality of intubating conditions is shown in table 3 . maximum number of  excellent intubating conditions was observed in group c. intubating conditions were excellent in 85.71% , 88.57% , and 97.14% in groups a , b , and c respectively . fair intubating conditions were seen in only 1 patient from group a. the distribution of intubating condition level - wise in the three groups since the first report of the priming principle as a method to accelerate the onset of neuromuscular block as well as to provide excellent intubation conditions , many investigations directed to optimise the priming technique have been performed . several workers used small doses of vecuronium ( 0.015 mg / kg ) and proved that administration of vecuronium in divided doses gave satisfactory intubating conditions in majority of patients . recently rao et al . proved that priming with rocuronium provides excellent intubating conditions in < 60s with no adverse effects . the synergistic effect of rocuronium when combined with itself or with various other non - depolarizing muscle relaxants have been observed in priming studies . in a retrospective study by patanwala et al . , first attempt successful intubation with rocuronium ( 72.6% ) and succinylcholine ( 72.9% ) were similar . in this study , surprisingly , 100% first attempt successful intubations were seen 60s after administering the bolus dose . the least possible dose of rocuronium ( 0.6 mg / kg ) was used as bolus for intubation as against higher doses used by some studies and excellent intubating conditions were achieved . were of the opinion that , when using the priming principle to accelerate the onset of neuromuscular blockade , the initial dose should nt exceed 10% of the drug 's ed95 . respectively used 0.015 mg / kg vecuronium , 0.015 mg / kg vecuronium , ( 0.01 mg / kg ) vecuronium and 0.05 mg / kg atracurium as priming doses . accordingly , the priming dose used in this study was guided by the above mentioned studies . though the onset time was not studied , the priming interval of 3 min was adopted as done by yavascaoglu et al . and endotracheal intubation performed 60s after the bolus dose . this is a shorter priming interval when compared with that of tripathi and pandey et al . who advocated a priming interval of not < 5 min . several workers explained the entropy suppression and haemodynamic stability respectively provided by rocuronium at optimum doses and was hailed as the drug of choice with optimum dose and a preferable drug for intubation for avoiding the side effects of succinylcholine . observed limited increase in hr without change in map and attributed this effect to the weak vagolytic activity of rocuronium . in the present study , there was statistically insignificant change in map in the three groups at all - time intervals . however , statistically significant but clinically insignificant increase in map at 0 and 1 min was observed . this increase in map at 0 min could be due to the haemodynamic responses induced by rocuronium injection pain , and the increase at 1 min could be due to the sympathetic stimulation produced due to laryngoscopy and intubation . simultaneously , there were no statistically significant differences in the hr , even though it increased from the baseline value in all the groups till the 3 min . this rise in hr following intubation as found in all the groups may be the result of the usual responses to laryngoscopy and intubation . even though the study of haemodynamic changes was not the primary aim , it was studied as a secondary outcome of the study , and we observed an increase in haemodynamic parameters at various time intervals in all the three study groups after the bolus dose of rocuronium . no significant differences were observed between the quantitative values of each component of intubating score in the present study . all the patients could be intubated at 1 min after the bolus dose of rocuronium was given . this is in agreement with the study by cooper et al . who explained the rapid onset of neuromuscular block to be due to the low potency of rocuronium , which results in a high molecular load being present at the nmj , producing an initial high concentration gradient and transfer of molecules of the drug to the biophase . similar findings were observed by different workers and this could be because of the fact that when rocuronium is combined in equipotent doses with other non - depolarizing agent , it acts synergistically in the early part of blockade . though statistically insignificant , establishment of excellent intubating conditions in 97.14% of patients in atracurium primed group as against 88.57% vecuronium and 85.71% rocuronium primed group may suggest a greater synergism between two drugs belonging to structurally different groups - atracurium being a non - steroidal benzylisoquinolone compound and rocuronium a mono quaternary steroid . though single twitch response was recorded just before intubation , it was not used as the guiding parameter . the baseline twitch height was 98.74% ( recorded after administering bolus dose ) and 34.80% just before intubation . intergroup comparison showed significant difference only between the single twitch response recorded in vecuronium and atracurium groups just before intubation . however , when the intubating grades were compared , more number of patients in the atracurium primed group had excellent intubating conditions . withdrawal response was seen in 3 , 2 and 1 patient in rocuronium , vecuronium and atracurium groups respectively . a study by borgeat and kwiatkowski has shown that injection of rocuronium is associated with severe , burning pain of short duration responsible for spontaneous movements in the arm observed after induction of anaesthesia . however , intubating conditions were excellent in all these patients . priming technique alleviated the withdrawal responses associated with intravenous administration of rocuronium as only 6 patients ( 0.05% ) showed withdrawal response to rocuronium injection . this is in agreement with the study by lee et al . who found similar results . no symptoms of muscle weakness were observed which may be compared with the findings of abdulatif et al . there were a few limitations in this study which included the following : the priming effect of the various agents could have been assessed at a shorter point of time than the predetermined time of 60s . the pharmacokinetics of the agents along with the economical aspect of the study could have been assessed . the confounding effects of rocuronium injection and laryngoscopy and intubation on haemodynamic responses could have been further addressed . there is a strong possibility that endotracheal intubation could have been successfully performed earlier than 60s as it is possible to do so when the intubating conditions were only good , a presumptive event which might have happened before the establishment of excellent conditions in almost 90% of cases at 60s . however , we were guided by the recommendation that intubation should be performed at 60s with rocuronium ( 0.6 mg / kg ) . though the study did not prove a significant difference in intubating conditions among the three groups , it explains the efficacy of using priming principle for attaining excellent intubating conditions proved by numerous studies .
background and aims : priming principle refers to administration of a small dose of non - depolarising blocker , which when followed by a large intubating dose produces a relatively rapid and profound blockade to ensure suitable conditions for endotracheal intubation . 
 we aimed to compare the effects of rocuronium , vecuronium , and atracurium as  pretreatment  drugs on intubating conditions with 
 rocuronium facilitated endotracheal intubation.methods:this double - blinded , randomised controlled prospective study was carried out at a tertiary health care hospital on patients undergoing surgical procedures under general anaesthesia . 
 they were randomly allocated into three groups ( n = 35 ) by computer generated randomisation chart to receive either rocuronium ( 0.06 mg / kg body weight ) ( group a ) ; vecuronium ( 0.01 mg / kg body weight ) ( group b ) or , atracurium ( 0.05 mg / kg body weight ) ( group c ) , followed by intubating dose ( 0.6 mg / kg body weight ) of rocuronium . 
 the haemodynamic parameters and intubating conditions were studied and statistically analysed by anova test and student 's t - test as applicable using statistical package for the social sciences 16.0 for windows ( spss inc . , chicago , il , usa).results : excellent intubating conditions were noted in maximum number of patients in group c ( 97.41% ) . 
 no significant differences were observed in the systolic blood pressure in all the three groups at all - time intervals . 
 the mean arterial pressure rose significantly from baseline value to maximum , at  0 min in all the groups ; however , no significant difference was observed amongst the groups ( p > 0.05).conclusion : pretreatment with rocuronium bromide can facilitate endotracheal intubation in 60 s irrespective of non - depolarising muscle relaxants used for priming ; however , it can not attenuate haemodynamic changes associated with laryngoscopy and intubation .