Minimum Effective Volume for Selective Trunk Block

Minimum Effective Local Anaesthetic Volume of a 1:1 Mixture of 2% Lidocaine With 5ug/ml of Epinephrine and 0.5% Levobupivacaine Required for Ultrasound Guided Selective Trunk Block: A Dose Finding Study

The objective of this study is to identify the minimum effective dosage of a mixture of two local anaesthetic drugs called 'levobupivacaine' and 'lignocaine with epinephrine" used to produce an effective ultrasound guided selective trunk block for surgical anaesthesia of the upper limb.

Ultrasound is widely used for brachial plexus block (BPB) and current evidence indicates that it is feasible to accurately identify majority of the main components of the brachial plexus above the clavicle, including the three trunks. Since majority of the innervation to the upper extremity, including the shoulder, arises from the three trunks (superior, middle and inferior) of the brachial plexus, so targeted injections of the individual trunks of the brachial plexus under ultrasound guidance will produce surgical anaesthesia of the entire upper extremity (C5-T1). Principal Investigator refers to this novel technique "selective trunk block" (SeTB) and the preliminary experience with SeTB for surgical anaesthesia of the entire upper extremity has been very encouraging. Currently there are no data describing an optimal dose or volume of local anaesthetic for SeTB. The aim of this study is to identify the minimum dosage of 1:1 mixture of 'levobupivacaine' and "lignocaine with epinephrine" required to produce effective surgical anaesthesia in at least 90% of patients presented for upper limb surgery.

Selective trunk block will be done under ultrasound guidance to patients scheduled for upper extremities surgeries. Local anaesthetic agents (a 1:1 mixture of 2% lidocaine with 5ug/ml of epinephrine and 0.5% levobupivacaine) will be injected at the superior, middle, and inferior trunks of the brachial plexus in order to anaesthetize the whole upper limb.

This study adopts a "Modified Narayana rule (MNR)", a sequential up-and-down pharmacodynamics method (UDM) to estimate the minimum effective local anesthetic volume of 90% (MELAV90) of cases of the aforementioned local anaesthetic (LA) mixture, in order to produce the surgical anaesthesia of the whole upper extremity of the patients scheduled for upper limb surgeries. Based on the principal investigator's clinical experience, the initial volume of 21ml will be used. Depending on the success or failure of the SeTB, which is defined as the readiness for surgery at 30 minutes after the block, the volume for the next patient will be adjusted up or down by 3ml (1ml for each trunk of brachial plexus located above the clavicle). The upper dose limit of the study to minimize the potential for local anaesthetic systemic toxicity will be 30ml and the lower dose limit will be 12ml, which will be of no clinical importance.

Sensation to coldness (ice) will be tested at C5 - Lateral (radial) side of the antecubital fossa (just proximal to elbow crease), C6 - Thumb, dorsal surface, proximal phalanx, C7 - middle finger, dorsal surface, proximal phalanx, C8 - Little finger, dorsal surface, proximal phalanx, and T1 - medial (ulnar) side of the antecubital) fossa, just proximal to the medial epicondyle of the humerus. Sensory block, defined as loss of sensation to cold (ice), will be graded using a numeric rating scale (NRS: 0-100, 100=normal sensation, 0=no sensation). A 3-point qualitative sensory score (0=no block, 1=analgesia/ patient can feel touch but not cold, and 2=anaesthesia / patient cannot feel touch) will be used. Onset of sensory block for each nerve will be defined as the time that it took to achieve a sensory block score of NRS =<30 and Qualitative sensory score =1 .

motor blockade will be graded using a 3-point scale: 0=no block, 1=paresis and 2=paralysis. Motor blockade of each individual nerve in the anaesthetized upper extremity will be evaluated by testing C5 - elbow flexors, C6 - Wrist extensors, C7 - Elbow extensors, C8 - Finger flexors to the middle finger, and T1 - small finger abductors. Onset of Motor block for each nerve will be defined as the time it took to achieve motor score >=1.

Overall sensory score of NRS =<30 (NRS: 0-100; 100=normal sensation, 0=no sensation) and Qualitative sensory score =1 for each nerve; and motor scores >=1 (3 point scale: 0=no block, 1=paresis, 2=paralysis) in all nerves tested. Overall the maximum composite sensory-motor score achievable is 20 points (2 points for each 5 sensory nerves tested and 2 points for each 5 motor nerves tested).

Excursion of the right hemidiaphragm will be measured by ultrasound machine in supine position via the anterior subcostal route. The movement of the diaphragm will be measured in centimetres. The range of diaphragmatic excursion will be recorded from the resting expiratory position to deep inspiration (sigh test) as will be the range of diaphragmatic movement from resting expiratory position when quickly inspiring through the nose (sniff test). The decrease in diaphragmatic excursion will be calculated as the difference (in %) in diaphragmatic excursion measured before and 30 minutes after SeTB. Reduction in diaphragmatic excursion of more than 75%, or no movement, or paradoxical movement will be considered as complete paresis. Reduction in diaphragmatic excursion of both sigh and sniff test between 25% and 75% will be considered as partial paresis and diaphragmatic excursion of less than 25% will be considered as 'no paresis'.

Inclusion Criteria: American Society of Anesthesiologists (ASA) physical status I-III scheduled to undergo elective upper extremity surgery involving the proximal humerus to distal hand or surgery involving any combination of these regions. Exclusion Criteria: Patient refusal pregnancy skin infection at the site of block placement history of allergy to local anaesthetic drugs history of bleeding tendency or with evidence of coagulopathy pre-existing neurological deficit pre-existing neuromuscular disease.