1.     TITLE OF THE TOPIC:   Ultrasound guided Sciatic nerve blockade in the popliteal fossa using the posterior approach- A comparison between pre-bifurcational and post bifurcational nerve blockade by a prospective, randomized control trial.

2.     BRIEF RESUME OF THE INTENDED WORK :

2.1  Introduction:

The popliteal block is the block of the Sciatic nerve at the level of the popliteal fossa. Regional block of the Sciatic nerve is a preferred method of providing analgesia for procedures involving the distal two thirds of the lower limb. Common indications include foot debridement, toe disarticulation, corrective foot surgery, trans-metatarsal amputation and Achilles tendon repair. Popliteal block results in anesthesia of the entire distal two thirds of the lower limb with the exception of the skin over the medial aspect as the cutaneous innervation of the medial leg below the knee is provided by the saphenous nerve, a cutaneous terminal extension of the femoral nerve, which is blocked separately at the level of the tibial tuberosity.

The classical approach to the popliteal block is the posterior approach which involves positioning the patient in either a prone position or a lateral decubitus position.

The use of ultrasound to locate nerve plexus has revolutionized regional blocks, reducing the dose and volume requirement of local anesthetics significantly, thus improving the success rate and safety.  The advantages of using real time ultrasound while performing a nerve block are

A)   Real time visualization of the anatomy of the neurovascular bundle and the surrounding structures hence facilitating precise needle placement and prevention of inadvertent intravascular injection of the drugs.

B)    The sciatic nerve branches into the Tibial and Common Peroneal Nerve. This can occur at varying distances from the popliteal crease and hence visualization under real time ultrasound will ensure that both divisions of the nerve are anesthetized. 

C)    By visualizing the spread of the drug, we can infiltrate smaller volumes of the local anesthetic agent when compared to larger volumes used during blind or nerve stimulator guided techniques.

D)   Increased operator comfort and speed of performing the block, which consequently reduces the time taken for the overall surgical procedure.

For our study, we will be using an standardized anesthetic solution of 15 ml of 0.5% Bupivacaine  containing 5mg/ml of Bupivacaine Hydrochloride and 15 ml of 2% Lignocaine hydrochloride and Adrenaline bitartarate(1:200,000) with each ml of the solution containing 21.3mg of Lignocaine hydrochloride for a total volume of 30ml.

2.2 NEED FOR THE STUDY :

While there are studies that compare the onset of action when the same anesthetic agent has been injected before and after the bifurcation of the sciatic nerve, they have opposing conclusions. A few studies[3,4] have claimed that pre-bifurcational injection of LA has a shorter onset of sensory blockade, others[1,2,5] have concluded that post bifurcational infiltration around the Tibial and Common Peroneal nerve have resulted in a shorter onset of sensory block. Hence there is a need for a comparative prospective randomized control trial to compare the two methods of Popliteal fossa block of Sciatic nerve.

 REVIEW OF LITERATURE :

Review of literature consisting of previous studies done on the same area of work stating potential risks and benefits and outcome measures

In a study done by Buys et al[1] in 2010, 76 patients aged over 18 years, belonging to ASA class 1 and 2  were randomized into two categories- pre-bifurcation and post-bifurcation. In both these groups, the same anesthetic was used- a solution containing 28ml 1.5% Mepivacaine and 1;300,000 Epinephrine along with 1 ml of 100mcg Clonidine and 1ml of 8.4% sodium bicarbonate for a total volume of 30 ml. Using a Sonosite S ultrasound machine and a linear 6- 13 MHz probe, the sciatic nerve was visualized in the popliteal fossa. In the prebifurcation group, 30ml of the anesthetic mixture was injected circumferentially around the nerve at a point proximal to the bifurcation of the sciatic nerve in 5 ml increments with intermittent aspiration. For patients in the post-bifurcation group, the sciatic nerve was identified and traced distally till the Tibial and common peroneal nerves could be identified separately and 15 ml of the anesthetic agent was injected circumferentially around the two nerves . They defined block onset as the time taken for complete loss of pin prick sensation in the region of distribution of the CPN and tibial nerve. They demonstrated that the onset of block was faster in the post bifurcational group rather than in the pre-bifurcational group.

In a study done by Prasad et al[2] in 2010, 62 patients aged 18- 85 years of age, and belonging to ASA grade 1, 2 and 3 were randomized into two groups- a pre-bifurcational and a post- bifurcational group. In both groups, 30ml of a standardized local anesthetic solution consisting of equal volumes of 2% lidocaine and 0.5% bupivacaine with 1:200,000 adrenaline was used. They used a  Philips HD11XE ultrasound unit or SonoSite MTurbo ultrasound unit and a high-frequency (6-12 MHz) linear array transducer. In group P (Proximal), 30ml of the anesthetic solution was injected under USG guidance around the sciatic nerve 5 cm proximal to its bifurcation in a circumferential manner. For patients in group D (Distal), 15 mL of the same solution was injected around the tibial nerve and 15 mL around the common peroneal nerve, 3cms distal to the site of bifurcation, in a circumferential manner under USG guidance. They demonstrated that the onset of sensory and motor blockade was 30% shorter when the anesthetic agent was injected distal to the sciatic nerve bifurcation.

Whereas in a study done by Tran et al[3] in 2011, 50 patients aged 18- 70 years of age and belonging to ASA class 1,2 and 3 were randomized into two groups of 25 each- group SUB (sub-epineural) and SEPI (Separate) group. All patients were premedicated with 0.03mg/kg Midazolam and 0.6 mcg/kg of Fentanyl and standard anesthesia monitors were connected. Patients were placed in prone position and a standardized anesthetic solution containing 15 ml of 2% Lignocaine and 15 ml of 0.5% Bupivacaine for a total volume of 30ml with Adrenaline 5mcg/ml was used to block the sciatic nerve in the popliteal fossa under ultrasound guidance using a Sonosite Mturbo machine. In group SUB, the exact site of sciatic nerve bifurcation was identified and using a 17G Tuohy needle with its tip positioned between the tibial and common peroneal nerves, 30 ml of the anesthetic solution was deposited. In the SEPI group, at a point 2-3cms distal to the sciatic nerve bifurcation, the Tibial and Common peroneal nerves were separately identified and 15 ml of the anesthetic solution were injected circumferentially around the two nerves. Sensory blockade of the tibial and common peroneal was assessed on the plantar and dorsolateral aspect of the foot respectively. Motor blockade of the tibial and common peroneal nerve was assessed by noting plantar and dorsiflexion of the foot respectively. They demonstrated that the onset of the sensory and motor block was faster in the Subepineural group and that this method provided higher success rate and required lesser time to be carried out.         .       

Similarly in a study done by Perlas Et al[4] in 2013, 89 patients aged between 18 to 85 years, and belonging to ASA class 1, 2 and 3 were randomized into two groups- a pre-bifurcation and post bifurcation group. In both groups the same anesthetic agent was used- solution of equal parts of lidocaine 2% plain and bupivacaine 0.5% with 1:200,000 epinephrine for a total volume of 30 mL and for both groups a Philips CD50 ultrasound unit or SonoSite M-Turbo ultrasound unit with a high-frequency (5-12 or 6-13 MHz) linear array transducer was used. In group A, block was performed at the site of sciatic nerve bifurcation. The needle end point was to lie between the TN and CPN within the common paraneural sheath and external to the epineurium of each individual nerve. After negative aspiration, the standard anesthetic solution was injected as a single injection within the sheath compartment in 5-mL increments for a total volume of 30mL, ensuring local anesthetic spread between and around the two nerves. In group B, The TN and CPN were followed distally along their course until they clearly become 2 separate entities no longer sharing a common paraneural sheath.15 mL of standardized local anesthetic solution was injected circumferentially around each TN and CPN separately after negative aspiration. They observed that patients in group A had a 30% shorter time of onset of both sensory and motor blockade when compared to patients in group B. They also observed that the nerve diameter and cross sectional area remained the same indicating no neural distortion.

Whereas in a study done by Eldegwy et al [5] in 2015, 40 patients aged over 18 years and belonging to ASA category 1, 2 and 3 were randomized into two groups containing 20 each. In both groups 20 ml of 0.5% Levobupivacaine was used as the anesthetic agent. In Group 1 the patients received the sciatic nerve block at a point 2cms cephalad to its bifurcation. In Group 2 the patients received a popliteal sciatic nerve block caudate to the bifurcation
with separate circumferential injection around TN and CPN. The block performance time, block efficacy, success rate, complications and patient’s satisfaction were evaluated. They observed that the onset of sensory blockade was shorter in the post bifurcation group when compared to the pre-bifurcation group. However, the complete motor block, block time performance, success rate and patient’s satisfaction were not significantly different between the groups.

2.3      OBJECTIVES OF THE STUDY :

 Primary

1.     To compare the onset of sensory and motor blockade in patients undergoing foot surgeries when ultrasound guided sciatic nerve blockade is performed in the popliteal fossa when the anesthetic agent is injected proximal to the bifurcation of sciatic nerve versus when the drug is injected distal to the sciatic nerve bifurcation.

Secondary

1.     To compare the time taken for the block procedure between the two groups .

2.     To compare the quality of block between the two patient groups.

7. MATERIALS AND METHODS:

7.1   SOURCE OF DATA:

         Place of Study:  St. John’s Medical College Hospital, Bangalore                     Study period     : Two years

State inclusion criteria

1.    Consenting Adults aged 18-60 years, undergoing elective & emergency lower limb procedures which can be performed under Popliteal nerve block

2.    Weight range 40-80 kgs.

3.    Adults belonging to either sex of ASA Grade 1,2 or 3.

State exclusion criteria

1.     Patients with pre existing neurological disorders (peripheral neuropathy or motor weakness)

2.     Known history of hypersensitivity to drugs used.

3.     History of significant cardiac, respiratory, renal, hepatic or central nervous system diseases.

4.     Infection at the site of the block.

5.     History of coagulopathy or anticoagulant medication intake.

6.     Pregnant or lactating women

7.     If the area to be operated upon is higher than the distal two thirds of the leg.

ALLOCATION OF GROUPS 

Patients will be randomly assigned to one of the two groups

GROUP A: In this group, under ultrasound guidance, 30 ml of a standardized anesthetic solution of 15 ml of 0.5% Bupivacaine containing 5mg/ml of Bupivacaine Hydrochloride and 15 ml of 2% Lignocaine hydrochloride and Adrenaline bitartarate (1:200,000) with each ml of the solution containing 21.3mg of Lignocaine hydrochloride will be injected at a point 2 centimeters proximal to Sciatic nerve bifurcation.
    

GROUP B:  In this group, under ultrasound guidance 15 ml of a standard anesthetic solution of 15 ml of 0.5% Bupivacaine  containing 5mg/ml of Bupivacaine Hydrochloride and 15 ml of 2% Lignocaine hydrochloride and Adrenaline bitartarate(1:200,000) with each ml of the solution containing 21.3mg of Lignocaine hydrochloride will be injected around the tibial nerve and Common Peroneal nerve separately after the bifurcation of sciatic nerve.

 7.2 METHODOLOGY 

Type of study- Randomized Control trial. 

Required sample size was calculated based on Mean ± SD, onset of motor and sensory block across two groups obtained from the study-Ultrasound Guided Popliteal Block Distal to Sciatic Nerve Bifurcation Shortens Onset Time- A prospective, randomized, double blind study by Prasad et al. Assuming a 10% drop out rate, an additional 6 patients will be added to the calculated sample size for a total of 54 patients divided into two groups of 27 each with 5% level of significance and 80% power 

After obtaining clearance from the institutional ethical committee, 54 patients aged between 18-70 years posted for distal lower limb surgeries will be included in the study. They will be divided into two groups of each into group A and B.  Written informed consent will be taken from all the patients. The patients will be kept nil per orally for 6 hours for solids and 2 hours for water, prior to surgery. Standard anaesthesia monitors ECG, HR, NIBP, SPO2 will be connected. Intravenous access will be secured. All patients will be supplemented with intravenous midazolam (0.05 mg/kg). 

Ultrasound guided Popliteal fossa sciatic nerve block will be done under strict aseptic precautions using lateral approach. After identifying the sciatic nerve, in group A, it will be traced cephalad and at a point 2cms proximal to the bifurcation, 30 ml of anesthetic equimixture will be injected circumferentially around the sciatic nerve. In group B, the Tibial and Common Peroneal nerves will be identified separately and 15 ml of the anesthetic mixture will be injected circumferentially around each nerve for a total volume of 30ml. In each group equal doses of the analgesic agent will be administered after confirming needle placement near the nerve and noting the spread of the drug using real time ultrasound.

Saphenous nerve block will be given at the level of tibial tuberosity to provide anesthesia of medial aspect of leg and foot. The block will be considered a success if complete sensory block (score of 2 for both tibial and peroneal nerves)will be achieved within 30 minutes. Onset time is defined as the time needed to obtain a successful block. Thus, the total anesthesia-related time is equal to the sum of performance and onset times.

The patients will be asked at the end of the procedure to rate their satisfaction with the technique (0=poor, 1=fair, 2=good, 3=excellent). 

ASSESSMENT OF SENSORY BLOCK:

 After the drug has been given, sensory block will be tested by pin prick method once in every 5 minutes in the dermatomal areas corresponding to tibial and common peroneal nerves. Sensory block onset is defined as the time taken for complete loss of pin prick sensation in the region of distribution of the CPN and tibial nerve

Sensory block will be graded as

Grade 0: Pain sensation upon pin prick

Grade 1: Dull sensation/ Touch sensation on pin prick (Analgesia)

Grade 2: No sensation (Anesthesia)

ASSESSMENT OF MOTOR BLOCK:

Grade 0:  Motor power of 5/5 on dorsiflexion or plantar flexion of foot.

Grade 1:  Motor power of â…– or â…— on plantar flexion or dorsiflexion of foot

Grade 2:  Complete motor block with inability to move foot.

The block will be considered incomplete when any of the segments supplied by Tibial nerve and Common Peroneal Nerve still have sensory grade 0 after 45 minutes.

Patients with incomplete block will be supplemented with general anesthesia.

Patients hemodynamic variables such as heart rate, BP, and oxygen saturation will be recorded every 5 min intraoperatively.

All patients will be supplemented with intravenous midazolam(0.05 mg/kg).

ASSESSMENT OF QUALITY:

GRADE 1:  (Excellent) No complaint from patient.

GRADE 2:   (Good) Minor complaint with no need for the supplemental analgesics

GRADE 3:   (Moderate) Complaint that required supplemental analgesia

GRADE 4:   (Unsuccessful) Patient given general anesthesia

Duration of surgery will be noted.

The intra and post operative assessment will be done.

The rescue analgesia will be given in the form of Inj. Pethidine 50mg IV preceded by Inj. Ondansetron 4mg IV 

Side effects like nausea, vomiting, inadvertent intravascular injection, dryness of mouth and complications such as hematoma, local anesthetic toxicity and post block neuropathy in the intra and post-operative periods will be noted.

STATISTICAL ANALYSIS

 Required sample size was calculated based on Mean ± SD, onset of motor and sensory block across two groups obtained from the study-Ultrasound Guided Popliteal Block Distal to Sciatic Nerve Bifurcation Shortens Onset Time- A prospective, randomized, double blind study by Prasad et al. Assuming a 10% drop out rate, an additional 6 patients will be added to the calculated sample size for a total of 54 patients divided into two groups of 27 each with 5% level of significance and 80% power.

  Descriptive and inferential statistical analysis will be carried out in the present study. Results on continuous measurements are presented as Mean ± SD(Min-Max)and results on categorical measurements will be presented as number(%).Significance will be assessed at 5% level of significance.

Analysis of variance (ANOVA) will be used to find  to find the significance of study parameters between the two groups of patients, Student “t” test will be used to find the significance of study parameters on continuous scale within each group. Chi square/ Fisher Exact test will be used to find the significance of study parameters on categorical scale between 2 groups.