The Study of Regional Hemodynamic Changes After Specific Brachial Plexus Block by Ultrasound Guidance

Phase 1 Brachial plexus block (BPB) is a widely used regional anesthetic technique for upper limb surgery. The effect of sympathetic block of BPB can leads to vasodilatation and increase blood flow and skin temperature in the ipsilateral upper limb. At the level of the axillary region, the sympathetic nerves innervating the radial and ulnar artery travel with the brachial plexus, but it is unclear which specific nerve: musculocutaneous, radial, ulnar, and median innervates radial or ulnar artery. Radial and ulnar artery and their branches are common donor or recipient vessels in the vascular reconstruction surgery and their hemodynamic changes may affect the blood flow of vascular anastomoses in vascular reconstruction. Sometimes, brachial plexus could be partially blocked intentionally or unintentionally, with the resultant regional hemodynamic changes unclear.

As the use of ultrasound guided peripheral nerve block getting increasingly popular, peripheral nerve can be blocked visually, with good accuracy and ease. It has made specific nerve block in the axillary region possible. Can specific nerve block increase the blood flow of target artery (radial or ulnar artery) and benefit microvascular surgery, or will it decrease the blood flow in other arteries and have a negative impact on microvascular surgery? In this study, the investigators will measure the hemodynamic changes of radial and ulnar artery after performing specific nerve blocks of the musculocutaneous, radial, ulnar, or median nerves respectively in patients without vascular disease. The aim is to assess the effect of specific nerve block on hemodynamics of upper extremity, and provided evidence for further research in patients undergoing microvascular surgery.

The subjects of study are patients undergoing upper extremity operation. All patients will be randomized into 4 groups according to the specific nerve block (SNB) of brachial plexus: group MC (musculocutaneous), group UL (ulnar), group RA (radial) and group ME (median). Patients are randomised to the four groups by random number(generated by computer) in sealed envelopes. Sample randomization will be done in four groups by random-number using sealed envelopes. Each patient will receive allocated SNB of brachial plexus (musculocutaneous, radial, ulnar, or median) followed by Axillary brachial plexus block successively using ultrasound guidance combined neurostimulation. All nerve blocks will be performed by a single dedicated anesthetist. A second investigator, who is blinded to the protocol and patient allocation, will perform the measurements.

Sensory blockade will be assessed by pinprick sensation (22 G needle) and compare with the opposite forearm/hand for normal, hypoesthesia or no sensation. Success of SNB is defined as only loss of sensation in the cutaneous distribution of the specific nerve (musculocutaneous, ulnar, radial, or median nerves) at 30min after SNB. If hypoesthesia or no sensation is detected in the innervation areas of any other nerve, the patient will be excluded. Success of BPB is defined as the absence of sensation to in all innervation areas of above four nerves 30min after the BPB.

Measurement of hemodynamic parameters The ulnar artery and radial artery is located at 1 cm proximal to the ulnar or radial styloid process. Specific points will be located with skin marker to provide consistency with all measurements taken. Hemodynamic parameters will is measured by Pulsed-wave Doppler (PWD) ultrasound. The probe will be placed on the ventral wrist parallel to the long axis of the forearm without undue pressure on the artery during the PWD measurements. The volume gate will be positioned in the center of the arterial lumen, and the size of the gate will be 1/3 lumen of the artery. The angle of insonation is adjusted and maintained at 50-60 degrees. Once a desired PWD spectral waveform is achieved, the arterial hemodynamic parameters will be recorded.

Phase 2 The subjects of study are patients undergoing upper extremity operation under supraclavicular brachial plexus block. All patients will be randomly assigned to receive 30ml ropivacaine in concentrations of 0.125%, 0.2%, 0.25%, 0.375%, 0.5%, or 0.75%. Patients are randomised to the four groups by random number(generated by computer) in sealed envelopes. All nerve blocks were performed by a single dedicated anaesthetist who remains blinded to the concentration of ropivacaine.

A second investigator, who is blinded to the protocol and patient allocation, will perform the measurements. Another investigator, who is not present during the conduct of the BPB and blinded to the concentration of ropivacaine used will assess each blockade. Patient are also blinded.

The brachial plexus will be visualized using a high-frequency linear ultrasound transducer in the supraclavicular fossa. After skin disinfection and infiltrating with 1% lidocaine, nerve stimulation needle will be inserted using in-line technique,and advanced among the divisions of brachial plexus with electric impulses (2 Hz, 0.3mA, 0.1 ms) of nerve stimulator. If visible contraction of the innervated muscle is elicited, the needle will be withdrawn slowly until the corresponding muscle contraction disappears to avoid intrafascicular puncture. The local anesthetic will be injected at three locations: adjacent to the superficial divisions of the plexus, adjacent to the middle divisions and inferior divisions. The proportion of the volume injected in each area is at the discretion of the expert operator according to the spread of local anesthetic.

The efficacy of the block will be assessed by pinprick sensation (22 G needle) and compared with the opposite arm/hand for normal, hypoesthesia or no sensation. For patients with an ineffective block, supplementary local anesthesia will be administered according to the distribution of the block and site of surgery after measurement. If the patient experienced any pain during surgery, supplementary analgesia, sedation, or general anesthesia will be administered as required.

Patient's arm is in supination. The brachial artery will be located in 2 cm proximal to the antecubital fossa. Hemodynamic Parameters will be measured by Pulsed-wave Doppler(PWD) ultrasound. The probe will be parallel the long axis of the arm without undue pressure on the artery during the PWD measurements. The volume gate will be positioned in the center of the arterial lumen, and the size of the gate will be 1/3 lumen of the artery. The angle of insonation will be adjusted and maintained at 50-60 degrees. Once a desired PWD spectral waveform is achieved, the arterial hemodynamic parameters will be recorded. The cross-sectional area (CSA) of the artery will be assessed with B-mode imaging. Probe should be as perpendicular as possible to the long axis of the artery to obtain as round an arterial section as possible. The image at end diastole will be chosen and measured with the cine loop.