Inter Scalene Block: Revisiting old technique.

BACKGROUND AND AIMS: The technique of percutaneous brachial plexus block has persisted in many variations since first such block given by Hirsheli in 1911.[1] Both supraclavicular and infraclavicular approaches have been described. Consequent to perivascular technique (Winnie and Collins 1964), Winnie described interscalene block (ISB) in 1970.[23] Winnie's was a single deposit block which relied upon volume for its success. It is nearly 50 years that ISB has stood the test of time and has evolved from single to multiple deposits Block. In mid-90s, ultrasound guidance was first explored by anesthetists for regional anesthesia in University of Vienna.[3] As ultrasound guidance is becoming popular and is increasingly available to budding anesthetist, popularity of old technique has started waning. In this study, old technique of ISB was revisited with a view to assess its success rate with established drugs and examine if in light of ultrasound guidance, this technique has become irrelevant for anesthetist today.
METHODS: A retrospective study, a survey with high response rate, was done on success rate of three variations of old technique of ISB in 100 patients. In variation-1, thirty patients received two deposits of local anesthetic in interscalene groove. In variation-2, thirty patients received four deposits of local anesthetic in interscalene groove. In variation-3, forty patients received six deposits of local anesthetic in interscalene groove along with infiltration of both scalene muscles. In none of the variations, paraesthesia was sought or peripheral nerve stimulator (PNS) or imaging gadget was used. Demographic data in three variations were compared statistically using Chi-square and one-way ANOVA test. Success rate among variations was analyzed by Fisher's exact test.
RESULTS: In variation-1, 17 out of 30, in variation-2, 23 out of 30, and in variation-3, 37 out of 40 blocks were successful.
CONCLUSION: Success of ISB given without PNS or ultrasound guidance is directly proportional to the number of deposits of local anesthetic made in interscalene groove.

INTRODUCTION

Interscalene block (ISB) continues to be popular among anesthetists both in institutional and private practice. Advent of ultrasound guidance has made it possible to see the plexus before you block. Ultrasound-guided blocks are becoming popular day by day. But still, a large number of anesthetists do not have access to imaging facility. Those anesthetists who do not have access to ultrasound imaging have improvised old technique with their own variations. Basically, these variations have made the single deposit technique of ISB described by Winnie into multideposit technique. Many anesthetists feel that through multideposit technique, they are able to administer ISB as successfully as with ultrasound guidance. It was with this in mind that study was conceived to revisit old technique in its variations today. The aim was to find out success rate of different variations with the objective of preserving those with high success rate for training in skill development of budding anesthetists.

METHODS

Retrospective survey of ISB administered without ultrasound guidance or nerve locating gadgets. ISB was administered in three variations based on number of deposits of local anesthetic in interscalene groove. Inclusion criterion was ISB administered without ultrasound imaging or nerve location technique. The only exclusion criterion was single deposit block. Patients in whom ISB was given by leaving two deposits of local anesthetic in interscalene groove were grouped in variation one. Patients administered ISB by leaving four deposits of drug in interscalene groove were grouped as variations two and those who received six deposits of drug along with anterior and middle scalene muscle infiltration were grouped as variation three. Variation-1 and 2 had thirty patients each and variation-3 had forty patients. Patients in all the three variations were matched for gender, age, and weight. Gender match was done using Chi-square-test which showed gender distribution to be homogeneous (P = 0.807). Age and weight were matched using one-way ANOVA test and were found to be matching (P = 0.280 for age) and (P = 0.260 for weight) in all the three variations. Age of patients varied from 10 to 93 years, weight from 25 Kg to 103 Kg, and physical status ASA class from I to III. ASA class, age, and weight distribution of patients are shown in Figures 1–3, respectively.

Figure 1

Variation-wise ASA grade

Figure 3

Variation-wise weight distribution

Variation-wise age distribution

All patients received intravenous pentazocine 0.5 mg/Kg, midazolam 0.04 mg/Kg, and diclofenac 1.25 mg/Kg in premedication. Anesthetic mixture used for block was that of 2% lignocaine with adrenaline and 0.5% bupivacaine, combined dose of two drugs was reduced as follows. In a patient weighing 60 kg, dose of lignocaine 2% with adrenaline at the rate of 7 mg/Kg body weight is 420 mg or 21 mL. Dose of bupivacaine 0.5% at the rate of 2 mg/Kg body weight is 120 mg or 24 mL. Total volume of anesthetic mixture comes to 45 mL (21 + 24) which was reduced to two-third (45 × 2/3), i.e., 30 mL. In 30 mL of calculated volume, both drugs were mixed in 50:50 proportions, i.e.,15 mL of each lignocaine 2% with adrenaline and bupivacaine0.5%. In all patients, block was given with patient lying supine, head resting on a small pillow slightly turned to opposite side. Sternocleidomastoid was made prominent by asking patient to raise head. First three fingers of the right hand were slid laterally over the belly of sternocleidomastoid onto scalene anterior and then into the interscalene groove. Skin over inter scalene groove was infiltrated with 2% Lignocaine with adrenaline. A 24 G short beveled needle was inserted in inter scalene groove at the level of cricoid cartilage. Deposits of local anesthetic mixture were left in the groove from calculated dose of drug in a 20 mL syringe. No attempt was made to elicit paraesthesia. If there was a paraesthesia, needle was pushed no further and deposit was made; otherwise, it was pushed to a depth of not >2 cm. Neither peripheral nerve stimulator (PNS) nor ultrasound guidance was used to locate plexus.

Variation 1

Two deposits of anesthetic mixture were made in interscalene groove through the same prick. First deposit was made at the level of cricoid cartilage; needle was withdrawn to subcutaneous plane and reinserted again into the groove to make second deposit little caudal to first.

Variation 2

Block was administered exactly like in variation-1 except that two pricks were made, second prick caudal to first, and total four deposits of local anesthetic mixture, two from each prick, were made in interscalene groove.

Variation 3

Block was administered exactly like in variations 1 and 2 except that three pricks were made in interscalene groove first at the level of cricoid cartilage, second few mm caudal to first, and third few mm caudal to second; two deposits of local anesthetic were made through each prick. In all six, deposits were made in interscalene groove, and as needle was withdrawn, both anterior and middle scalene muscles were infiltrated with anesthetic mixture. In this variation, third prick actually became closer to clavicle where needle was allowed to explore deeper than 2 cm to a maximum of about 4 cm keeping it lateral to pulsation of artery.

Evaluation of block was done under two criteria; both had to be met for a block to be counted successful. The first criterion was necessity for rescue anesthesia in any form. The second was painful response to pinch with toothed forceps 30 min after block at any of the four places, namely base of little finger, dorsum of the base of thumb, base of index finger on palmar aspect, and lateral side of forearm.

RESULTS

As per evaluation criteria of successful blocks, variation-1 had seventeen (17) successful blocks out of thirty (30) [Figure 4]. Variation-2 had twenty-three (23) successful blocks out of 30 [Figure 5]. Variation-3 had thirty-seven (37) successful blocks out of forty (40) blocks given [Figure 6]. The success rate of block compared using Fisher's exact test was found to be highly significant in variation-3 (P = 0.002).

Figure 4

Success rate variation-1

Figure 5

Success rate variation-2

Figure 6

Success rate variation-3

No major complications related to blocks were reported. Variation-wise distribution of minor complications is given in Table 1. One patient each in variation-1 and variation-3 developed Horner's syndrome which resolved by next day. Three patients, two in variation-2 and one in variation-3, developed hoarseness of voice, managed with reassurance and voice rest. Four patients complained of shortness of breath. They were managed with oxygen inhalation through nasal prongs kept under observation till the symptoms resolved. The chest X-ray was done after 6 h, pneumothorax excluded. In one patient in variation-3, block persisted till the next day and resolved. Transient hypotension, bradycardia was observed in few patients, it was managed with crystalloid infusion and atropine 0.3mg intravenously. Out of 100 patients surveyed, only 69 could be followed up after 1 week, and none had any postoperative neurologic symptoms.

Table 1

Variation wise minor complications

When failed blocks were analyzed [Table 2] out of 13 failures that variation-1 had, all showed ulnar sparing; in three patients, ulnar sparing was also associated with radial sparing. Variation-2 had 7 failures and 6 showed ulnar sparing out of which one had radial sparing as well. One patient did not have any sparing yet needed rescue anesthesia. Variation-3 had just 3 failures; two had breakthrough pain at tourniquet site and one had musculocutaneous sparing.

Table 2

Analysis of failed blocks

DISCUSSION

Results clearly show that success rate of blind approach to ISB is directly proportional to number of local anesthetic deposits made in interscalene groove. In variation-1, with two deposits of local anesthetic, successful blocks are 56.6% (17 out of 30). In variation-2, with four deposits, successful blocks are 76.6% (23 out of 30). In variation-3, with six deposits and infiltration of both scalene muscles, success rate rose to 92.5% (37 out of 40).

Animal experiments have shown that a nerve length of 3 cm,[4] a volume as little as 1.6% of what is usually administered in a block, and a concentration as little as 0.02% in the neural tissue is sufficient to produce block.[56] With the volume and concentration commonly used, 1.6% of volume and 0.02% concentration should be easily obtainable around point of injection. What appears crucial determinant in block is the 3 cm stretch of nerve length. Multideposit technique making multiple deposits of local anesthetic mixture in interscalene groove is more likely to ensure soaking greater plexus length. Longitudinal spread of local anesthetic is more than circumferential spread because of a potential space existing between epineurium and surrounding connective tissue.[789] If the longitudinal spread is fast, circumferential and full thickness soaking of plexus can become crucial determinant of block. Multiple deposits are likely to enhance both longitudinal as well as circumferential spread for a given volume of local anesthetic in a given chunk of tissue. This could be one reason as to why multideposit technique is more effective. Brachial plexus roots form trunks which converge between two scalene muscles before dividing into divisions over lateral border of first rib. Any approach depositing multiple deposits of drug in a chunk of tissue which is compact with converging plexus is likely to soak more plexus. This could be another reason why multiple deposits ISB are more successful.

ISB is given fairly proximally where nerves are compact and ratio of connective tissue to neural tissue in the nerve is 1:1 as against distally where this ratio is about 2:1.[10] In such a situation, precise location of nerve to inject local anesthetic is fraught with the danger of damage to neural tissue. An injection without eliciting paraesthesia would appear a safer bid in such a proximal block.

It was seen that in variation-3 third prick was fairly inferior and quite close to clavicle, in fact it is akin to supraclavicular perivascular approach which is known to produce complete anesthesia of upper extremity. This could be the reason for high success rate seen in this variation. It also proves that if given by this technique, an interscalene block that is used mainly for shoulder surgery is as good for any surgery of upper extremity. Limitation of study lies in small sample size of 40 patients; a larger series would be appropriate to prove the point.

Ultrasound-guided block is also not a precision block without failure. An important point of contention is that ultrasound-guided blocks are also multiple injection blocks.[111213] It is claimed that lower trunk of brachial plexus is commonly missed in paraesthesia or PNS technique but not in ultrasound-guided supraclavicular block.[1415] It may well be due to multiple injections rather than precision.

In latest review on the subject, American Society of Regional Anesthesia and Pain (ASRA) compared ultrasound-guided approach with that of PNS. They reported that although there were less number of needle passes with ultrasound-guided approach, it did not translate into greater patient satisfaction and reduced complication rate.[16] In a blind approach, multiple needle passes are handled better because one has to only manipulate a 20 ml syringe. In ultrasound-guided/PNS approach, one has to see image/contraction as well as anatomy. Hand-eye coordination in such a situation is poor which could account for poor patient satisfaction. Attempts have been made to foolproof ultrasound-guided blocks with concomitant use of PNS without success.[1617]

Ultrasound-guided blocks use considerable volume to ensure spread of local anesthetic around plexus. In one study, it was noticed that minimum volume of 23 ml was required to produce block in 50% of patients.[18] In this survey, volume of the drug was based on body weight of patient. There were ten patients in whom blocks were successful with volume 23 ml or less. Volume as little as 13 ml produced the block in a child weighing 25 kg with just two deposits and 52 ml was required to produce block in a patient weighing 103 kg with six deposits and scalene infiltration.

Fear of pleural puncture persists even in ultrasound-guided supraclavicular block. In a recent study, they have tried to correlate plexus depth in supraclavicular fossa with body mass index of Indian patients so as to avoid pleural puncture.[19] Brachial plexus is quite superficial superiorly in interscalene groove,[20] as it courses downward behind clavicle, it is deep. In a magnetic resonance image-based study, skin to nerve distance was reported to vary from 1.8 to 4.5 cm.[21] It is here that chances of piercing pleura are more because needle has to go deeper. Old approach is based only on surface anatomy. Practitioner of this approach will never discount knowledge of anatomy which one using ultrasound may because he thinks he is giving block under direct vision. It is important to note that ultrasound vision is not direct vision; there is lot of parallax due to refraction, hand movement, angle of eye, probe placement, tissue edema, artifacts, and subcutaneous air.[22] Learning curve is longer for ultrasound-guided technique than for old surface anatomy-based technique. Training in age-old skill will facilitate ultrasound-guided approach and help augment safety and standard of care.

Although it is argued that anatomical variations can be seen through ultrasound-guided brachial plexus blocks to ensure that block is made foolproof, actually, even under ultrasound by giving multiple deposits, you are infiltrating full chunk of tissue that contains brachial plexus no matter of what anatomical variation. It is like an automatic weapon covering area with shower of bullets instead of repeatedly aiming at individual target. In our opinion, success of the ultrasound-guided block is also attributable, at least partly, to multiple deposits rather than precision.

There are recent case reports that show complications such as nerve injury and intravascular injection do occur despite the use of ultrasound.[2324] If ISB given without ultrasound and nerve locating gadgets is as safe and foolproof as with them, then it can be said that such a technique is still relevant in training and skill development.

CONCLUSION

Technology invasion has its side effects. It stimulates shortcut approach to success. Use of technology is also a skill to be developed the right way. As has been brought out in variation-3, blind multideposit technique of ISB with scalene infiltration is better than other techniques. It is simple, safe, and effective. Skills like this, if learnt, before trying to learn skill of ultrasound-guided block, will help improve expertise and shorten learning curve. Neglect of surface anatomy-based blind skills will lead to compromise on versatility of anesthesiologist.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.