The jfish Peripheral Nerve Stimulator

The jfish PNS is simple and easy to use. Familiarity with commercial PNS devices readily translates into using the jPNS. The jPNS also provides an ideal platform for clinicians who have not used a PNS previously to grow comfortable with their use in anaesthesia.

1. PNS leads to clip onto electrodes (red = positive, black = negative)
2. 9 V battery
3. On-off slide switch
4. Current setting knob
5. Pulse pattern selection
6. Indicator LEDs

The choice of which muscle group to use in order to monitor neuromusclular blockade is largely determined by the accessibility of different muscles to the anaesthetist. Usually monitoring via the ulnar nerve or facial nerve branches is the most appropriate. When surgical requirements limit the anaesthetist’s access to the lower limbs only, stimulation of the common peroneal or posterior tibial nerve can be used.

The skin should first be cleaned with an alcohol swab or damp cloth. When the skin is dry, standard ECG electrodes are placed as indicated and the PNS leads clipped on. Care should be taken to always attatch the positive (red) lead proximal to the negative (black) in relation to the normal direction of travel of the action potential. This reduces the magnitude of current required for stimulation.

• Ulnar nerve
  Place the negative electrode 1 cm proximal to the proximal flexion crease of the wrist, immediately lateral to the tendon of flexor carpi ulnaris. The positive electrode is then placed 2 to 5 cm proximal to the negative electrode.
• Facial nerve
  The negative electrode is placed immediately above and immediately lateral to the orbit. The positive electrode is placed immediately below and lateral to the orbit.
• Common peroneal nerve
  Place the negative electrode just behind the head of the fibula and the positive over the patella.
• Posterior tibial nerve
  The negative electrode is placed immediately below and behind the medial malleolus, and the positive immediately above and behind.

The output current is set using the knob on the left side of the device. Current is deliverable from 1 mA to a maximum of 65 mA when the knob is turned maximally anticlockwise.

Ideally the initial threshold of stimulation and supramaximal stimulus current should be determined as described. The supramaximal current will usually be between 40 and 50 mA.

The jfish PNS can deliver the four most commonly used pulse patterns: twitch, TOF, PTC and DBS. After attaching the leads to the electrodes and turning the device on, a pulse pattern can be delivered by pressing the corresponding button. Moving from the bottom to the top of the device, the buttons correspond to twicth, TOF, PTC and DBS respectively.

The green LED when lit indicates the device is powered on. The yellow LED flashes with each current pulse delivered. The red LED lights when the battery is failing and the device can no longer reliably deliver the desired output current.

Further discussion of PNS use can be found in the document ‘The science and use of the peripheral nerve stimulator‘.