A supraclavicular approach for blockade of the brachial plexus was first described by Kulenkampf in 1911.¹ The dissemination and use of supraclavicular blockade has        been tempered by the risk of pneumothorax during localization of the nerve trunks with the injection needle and the more frequent incidence of pneumothorax when learning the technique.^2,3 Interest in supraclavicular blockade has been rekindled by the use of two-dimensional ultrasonic images to localize the brachial plexus⁴. The sonographic image can be used in real time to guide the injection needle while minimizing the risk of contact with structures such as the pleural dome and subclavian artery. Ultrasound-guided supraclavicular blockade has been highly successful ⁴, though the success rate of the technique has not been compared in a randomized study to more traditional supraclavicular approaches suction Supraclavicular block provides excellent anesthesia for upper limb surgery.^5,6Recently ultrasound guidance in supraclavicular block has been introduced and gaining popularity. Ultrasound-guided supraclavicular block has many advantages including the higher success rate, faster onset time, and fewer complications7,8 In the previous studies on the ultrasound- guided axillary blocks and interscalene blocks, the possibility of the reduced volume of local anesthetics was demonstrated.9,10

Working on the minimum effective volume for the ultrasound-guided supraclavicular block by Edel Duggan et al11 the Dixon and Massey up and down method (DUDM) and biased coin design up and down method (BUDM) were used to calculate the minimum effective volume (MEV) 50, MEV90, and MEV95, respectively. These effective volumes were speculated by statistical calculation. In our study ultrasonic guidance would increase the proportion of successful blocks, decrease block execution time, and reduce the incidence of complications such as pneumothorax intravascular drug deposition and neuropathy12. Determination of minimal effective volume is important to prevent the unnecessary administration of potentially toxic doses. Furthermore, when multiple blocks are performed in the same patient, knowledge of minimal effective volume ensures success without sacrificing safety and efficacy.13

Orebaugh et al14 pointed out that the results from the DUDM may be different from those of the clinical practice, and the comparison of the varied anesthetic volumes in the clinical practice has not been studied much.

In our study we want to compare different volume of local anesthetics mixture in ultrasound guided supraclavicular block.

AIMS

The aim and objective of this study was to detect the minimal effective volume of local anaesthetic agents in ultrasound guided supraclavicular brachial plexus block for achievement of surgical anaesthesia.

Single blinded observational cohort study in Tertiary Care Superspeciality Hospital. The study is to be completed within a span of 2 years. Subjects assigned to 3 groups as per choice of consultant anaesthesiologist. After approval by the institutional local ethical committee written informed consent was taken from each of the patients. Seventy-five patients of American Society of Anaesthesiologist (ASA) Grade I to III of either sex, aged 18–60 years, scheduled to undergo various bony orthopedic surgeries on the upper limb at or below elbow under supraclavicular brachial plexus block were assigned to three groups, each containing 25 patients.

A: INCLUSION CRITERIA

1. ASA physical status grade I -grade III
2. Age between 18 to 60 years
3. Orthopaedic surgeries of bone and soft tissue of at or below elbow.

B: EXCLUSION CRITERIA: Patients with

1. Coagulation disorders
2. Severe cardiomyopathies
3. Liver and kidney diseases
4. Neurologic disorders
5. associated peripheral neuropathy
6. Skin lesion at the sight of blockade
7.  surgeries anticipated duration more than 3.5 hours
8. Pregnant patients

50:50 Mixture of local anaesthetic agents were Bupivacaine 0.5% (preservative free) and lignocaine 2% with adrenaline (1:200000) injected to following groups with volume

Group A: 25 ml

Group B: 20ml

Group C:15ml

Blinding- Single blinded as observer anaesthesiologist do not knows the volume of injection

On arrival in the operation room, baseline heart rate, blood pressure and oxygen saturation recorded. An intravenous line secured in the unaffected limb with 18G intra venous cannula and Ringer's lactate started. All the patients received brachial plexus block through the ultrasound guided supraclavicular approach by an experienced under mild sedation with midazolam 0.05mg/kg. The anaesthesiologist performing block was different from the one assessing the patient intra and postoperatively. Neural localization achieved by using a nerve locator connected to a 22 G, 100-mm-long insulated stimulating needle B Braun nerve locator. The location end point was a distal motor response with an output at 0.5 mA in the median nerve and radial nerve region. Following negative aspiration, respective volume of a solution containing local anaesthetic agents as mentioned above injected.

Sensory block assessed by the icecold method. Before starting of assessment eyes were closed. Assessment of sensory block was   done at each minute after completion of drug injection in the dermatomal areas corresponding to median nerve, radial nerve, ulnar nerve and musculocutaneous nerve till complete sensory blockade. Sensory onset is to be considered when there is a mild sensation to cold sensation along the distribution of any of the above-mentioned nerves. Complete sensory block considered when there is complete loss of sensation to ice cold.

Assessment of motor block carried out by the same observer at each minute till complete motor blockade after drug injection. Onset of motor blockade considered when there is Grade 1 motor blockade. Motor block determined according to a modified Bromage scale for upper one extremity (3-point scale)-

Grade 0: Normal motor function with full flexion and extension of elbow, wrist and fingers

Grade 1: Decreased motor strength with ability to move the fingers only

Grade 2: Complete motor block with inability to move the fingers

The block was considered incomplete when there is no analgesia in any of the segments supplied by median, radial, ulnar and musculocutaneous nerve even after 30 min of drug injection. When more than one nerve remains unaffected, it was considered a failed block. Patients was monitored for haemodynamic variables such as heart rate, blood pressure (mean arterial pressure) and oxygen saturation every 5 min after the block for 1st 30mins preoperatively followed by 30 minutes interval intraoperatively till 3.5 hrs. During the operative procedure, quality of block was assessed according to the following numeric scale:

Grade 4: (Excellent) No complaint from patient Grade3:(Good) Minor complaint with need for the mild supplemental analgesics

Grade 2: (Moderate) Complaint that required moderate supplemental analgesia and   sedation

Grade 1: (Unsuccessful) Patient given general anaesthesia Mild Supplemental analgesia include iv paracetamol 1 gm, iv

Moderate Supplemental analgesia sedation include paracetamol 1 gm, iv +fentanyl(1- 2ugm/kg)+ propofol 2mg /kg ± in infusion with the rate of 1-2 mg /kg/hr

Assessment of blood loss was done and fluid was administered as per the loss. The intra- and post-operative assessment was done by an anaesthesiologist who is unaware of the drug used. All patients observed for any side-effects like nausea, vomiting, dryness of mouth and complications like pneumothorax, haematoma, local anaesthetic toxicity and post-bock neuropathy in the intra- and post-operative periods.

Sample size calculation- In previous pilot studies by R Perlas et al7 the response with in each group was normally distributed with a visual analog scale (1-10) with a a standard deviation of 2  point. To reject the null hypothesis that the pain score means of the experimental and control are equal with a probability (power) of 0.9. The calculated sample size is 20 hence we have taken 25 patients in each group considering drop out. The type I error probability associated with this test of null hypothesis is 0.05, all data recorded and analysed later by statistician. If any untoward event or unanticipated difficulty is encountered during any part of study, then the study abandoned at that very moment to ensure patient safety that considered as a dropout.

Statical analysis- Continuous variables like Age, height, weight, Heart Rate and MAP at different time points, Oxygen Saturation %, Onset of sensory and Motor Block and Quality of Block are expressed as Mean ± Standard Deviation and compared across the groups using ANOVA Test. Further Onset of sensory and Motor Block and Quality of Block compared across 2 groups using repeated unpaired t test. Categorical variables like Gender, Nausea, Vomiting and other adverse effects are expressed as Number of patients and percentage of patients and compared across the groups using Pearson’s Chi Square test for Independence of Attributes. The statistical software SPSS version 20 has been used for the analysis. An alpha level of 5% has been taken, i.e. if any p value is less than 0.05 it has been considered as significant.

There was no statistically significant difference between the two groups in     respect to demographic parameters like age, sex, weight, height as the patients had in each group. (p>0.05).

TABLE 3: Trends In Heart Rate

The baseline hemodynamic parameters were comparable in all groups. Significant higher heart rate was observed at30,60, 90, 120, 150, 180and 210 minutes in group c as compared to group A and B. Table 2[p<0.05].

There is a significant rise in MAP after 25 min in group C. there is no difference between MAP in group A and B

Figure 12: Comparison of oxygen saturation in all groups

Ø  There is no difference in oxygen saturation during surgery in all groups

Ø  There is no difference between onset of sensory block and motor block onset in all groups. Quality of block in group A (4 ± 0), B (3.92 ± 0.28) and C (3.08 ± 0.28) observed. In comparison to group A, group B has no difference in quality of block(p-.155). In compare to group c it has significant difference(p-0.001) with group A. There is a significant difference between group B and group C(p-0.001)

Ø  There is no significant difference between group A, B and C in incidence of nausea

Ø  There is no significant difference between group A, B and C in incidence of vomiting

Local anesthetic systemic toxicity is still frequent and dose dependent. Therefore, reducing the dose of local anesthetic in regional anesthesia can contribute to the safety of patient30.

Some authors demonstrated the possibility of dose reduction in ultrasound-guided axillary blocks and interscalene blocks31-33,41. However, such possibility in ultrasound- guided supraclavicular block is controversial11,34. Duggan et al11 estimated MEV95 and MEV50 to be 42 ml and 23 ml, respectively, using Dixon and Massey up and down method (DUDM). According to the study results, it was concluded that they could not reduce the volume of local anesthetic in ultrasound- guided supraclavicular block.

Tran et al34 calculated MEV90 to be 32 ml, using biased coin design up and down method for ultrasound-guided supraclavicular block in their study. This volume (32 ml) for 90% success rate was lower compared with the conventional technique using 40 ml of local anesthetics. However, their results were derived from the estimated values using BUDM. The limitations of Duggan et al.’s study were the wide confidence interval and no comparison with the conventional supraclavicular block 11. The limitations of Tran et al34 were that the operators were trainees and 16-point scale including motor block was used for definition of successful block.34 Therefore, we think that their estimated MEV90 (32 ml) may be larger than the local anesthetic volume for surgical anesthesia. Orebaugh et al14 indicated that the results from DUDM do not seem to be easily translated to the clinical practice of peripheral nerve blockade. Therefore, we decided to perform a clinical comparison of the success rates with varied volumes of local anesthetics in ultrasound-guided supraclavicular block. In our study we have compared in between   25 ml ,20ml and 15 ml of local anesthetic based on the results (MEV 95 = 42 ml, MEV90 = 32 ml, and MEV 50 = 23 ml) from the previous studies.11,34

In general, the volume of local anesthetic for conventional supraclavicular block is known to be 40 ml. A 90.3% success rate was achieved with the traditional technique using 40 ml local anesthetics.35 Ultrasound-guided techniques allowed for the reduction of the volume of local anaesthetics with an equivalent success rate. In our study quality of block in 25ml in group A was (4 ± 0) (mean ±sd), in group B (3.92 ± 0.28) and group C (3.08 ± 0.28) observed. By this data we can conclude that quality of block in group B and group A are better as compare to group C. There is no significant difference between group A and B in quality of blocks. There was statistically significant difference between the two groups with respect to increase in heart rate trend after 25 minutes, with more rise in heart rate was noticed in group C. There was significant rise in mean arterial pressure in group C whereas rise in mean arterial pressure in group A and B patients was not significant. This increase in heart rate and mean arterial reassure is because of low quality of block in group c. In group C we have taken lowest volume i.e 15 ml and in group A and group B 25ml,20ml respectively.

By enabling anesthesiologists to visualize LA spread and to reposition the needle tip in real time, ultrasound is purported to decrease the amount of LA required. Compared with neuro stimulation. In our study also we have used ultrasound to  reduce the dose of local anesthetcs. Casati et al36 and Danelli et al37 have reported 42% and 37% reductions in MEV50 for the femoral and (subgluteal) sciatic nerve, respectively, with US. Furthermore, dose-finding studies for the mid femoral sciatic nerve and axillary brachial plexus have concluded that volumes as low as 5.7 and 1.0 mL can reliably anesthetize the sciatic nerve38 and terminal branches of the brachial plexus19. In stark contrast, Fredrickson et al39 and Duggan et al11 have calculated the MEV95 of the interscalene and supraclavicular brachial plexus block to be 20.5 and 42 mL, respectively. Their results seem more in keeping with our own findings. However, because of differences in study subjects (patient vs volunteer), body mass indices, nerve blocks, techniques (in-plane vs out-of-plane; bolus through needle vs catheter), LA, concentrations, definitions of success, and statistical methods, caution must be exercised when comparing these studies. In our study there was no statistically significant difference between the two groups in respect to demographic parameters like age, sex, weight, height as well as type of surgeries the patients had undergone in each group.

However, in studies that used a single-injection technique, a larger volume was invariably required.11,39 We suggest a possible explanation as to why we could not reduce the volume of local anesthetic to be 15 ml as we expected in spite of using ultrasound. In our study we divided the local anaesthetic dose and infiltrated near to subclavian artery and around the plexus. Cornish et al40,36 injected contrast dye into the tunnel that surrounded brachial plexus and observed various patterns of flow within the tunnel. The dye did not spread homogeneously. With this observation, they asserted that the brachial plexus was surrounded within the rigid- walled tunnel as differently from the simple tubular structure, such as a sheath. In simple tubular structure, the local anesthetic injected at one point can spread throughout the tunnel. However, compartmentalization is present in the rigid tunnel, because the layers of connective tissue are not homogeneous. Therefore, the Injection at one point in this rigid-walled tunnel may not spread to other nerves in the tunnel. With this theory, presumed that the lower volume of local anesthetic was not able to spread to all nerves in this study. At this point, we wondered why the reduction of local anesthetic in ultrasound-guided axillary block could be possible.41,42. In the supraclavicular region, each nerve could not be distinguished, it is located in the form of a cluster therefore, the local anesthetics should be filled in the tunnel. By the use of  ultrasound and nerve stimulator. Permitting unmarked reduction in the volume from that used traditionally.  With this finding, we compared the differences under the condition with same local anesthetic volume (Group A, (25ml) Group B (20, and          Group 15).  This can be explained by the brachial plexus anatomy and the approach technique used in this study.

From above finding we conclude that minimal effective volume of local anesthetic agents in ultrasound guided supraclavicular brachial plexus block for achievement of surgical anaesthesia using would be 20 ml of local anesthetics 50:50 mixture of Bupivacaine 0.5% (preservative free) and lignocaine 2% with adrenaline (1:200000).

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