Cryogenic Numbing to Reduce Injection Discomfort during Indocyanine Green Lymphography
22 May 2018
18 June 2018
12 August 2018 (online)
Indocyanine green (ICG) lymphography has become a popular imaging examination for diagnostic assessment of lymphedema and presurgical lymphatic mapping for lymphovenous anastomosis (LVA). It involves intradermal or subcutaneous injection of a small amount of ICG solution (∼0.1–0.3 mL) into the hands or feet. The near-infrared camera system enables us to observe the lymphatics in real time. The linear vessels represent normal lymphatics, while dermal backflow indicates lymph fluid reflux to lymphatic capillaries in the skin.
Indocyanine green lymphography has a wide variety of clinical applications for lymphedema management. These applications range from determining eligibility for lymphatic surgical procedures such as LVA or lymph node transfer, use in early detection of lymphedema and prophylactic management, through to longitudinal examinations of at-risk patients, and use as a functional indicator of lymph fluid transport capacity.  Despite the versatility of ICG lymphography, one of the major shortcomings is the discomfort experienced from having multiple injections into the sensitive tissue of the hands and feet.
Mixing ICG with a topical anesthetic agent such as Xylocaine has been proposed as a method to reduce injection discomfort.  However, this will not reduce the needle sting itself and prolonged numbness is not necessary for this imaging procedure. Smooth muscle cells in the lymphatic vessel walls contract and propel lymphatic fluid proximally with peristaltic movement. The possibility that adding an anesthetic agent to the ICG solution may compromise this intrinsic pumping mechanism and reduce lymphatic transport capacity is a genuine concern.
A cryogenic numbing device (CoolSense; CoolSense Medical Ltd., Tel Aviv, Israel) has been developed to temporarily anesthetize the injection site to reduce needle stick pain ([Fig. 1]). CoolSense is a handheld device approved by Food and Drug Administration and the European Commission as a topical skin-numbing applicator. The device is placed in the freezer for 1 hour before use. The cooled metal head is sterilized with alcohol gel and then applied to the patient's skin for 4 to 5 seconds immediately prior to injection. A built-in thermos sensor indicates when the device has reached the appropriate temperature (between −4 and 0°C) and aids in reducing the risk of a cold burn.
We have used this device in our outpatient clinic for more than 250 patients undergoing ICG lymphography. In our protocol, we apply four intradermal injections to each affected limb to assess lymphedema severity and condition. In the upper limb, these injections are made in the first and fourth web spaces and two medial wrist sites, and in the lower limb, they are made in the first web space and three sites around the foot. In our clinic, patients are asked about their immediate needle injection experience and have universally reported minimal pain at the time of the event and no persistent discomfort at the injection sites. The device did not appear to impair the uptake or transport of ICG by the lymphatics. Based on these findings, we propose that cryogenic numbing should be considered as an option to reduce injection discomfort during ICG lymphography.
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