Dear Editor,

Suction devices are used to produce blisters for epidermal grafting over the vitiliginous patch and achieve a good cosmetic result, but the process takes 1 to 3 hrs ^{1 - 3} . To hasten the suction process, heat and normal saline intralesional injection can be given over the site; the blister formation takes about 1 hour using a modified disposable syringe with a small disposable syringe cup and a three-way cannula ^{4 , 5} . However, the cup suction device is small and more stable than the syringe device, and it is easier to create negative pressure in the suction cup. Considering the advantages of the small three-way cannula-cup device over longer suction devices, a set of small cups of various radii can be used to produce suction blisters.

There is a relation between the height (h), radius (r), and volume (v) of the suction cup and the blister. The syringe suction cup is a small cylinder, and its produced blister is a small hemispherical structure. If the suction cup is cut at the height/length of its radius, then the cup's height will equal its radius (h=r). This means that the volume of the cup (cylinder), given by πr2h, can be considered as πr³, and the volume of the blister (half of a sphere/hemisphere), given by 1/2 x 4/3 πr³, can be considered as 2/3 x πr³. So, the ratio of the volume of the cup to the volume of the blister is equal to (πr³)÷(2/3πr³), simplified to 3/2 or 1.5. This shows that the volume of the suction cup, even at its radial height (h=r), is about 1.5 times the volume of the blister. Thus, even at its radius height, the cup has an adequate volume for producing an intact and complete blister.

Syringes of 5, 10, 20, and 50 ml capacity with radii of 6, 8, 10, and 15 mm, respectively, were selected. Then, the syringes were smoothly cut from their needle hub side at suction heights equal to their radii, and the volume of the cups (πr³) was calculated as 0.67, 1.6, 3.14, and 10.6 ml, respectively. After this, vaseline was applied to the rim of the cups on its needle hub and over the aseptic suction site to improve its air-sealed property. Following this, each of the four three-way cannula-cup devices was applied airtight over the lateral side of the thigh. A vacuum was created inside the cup by sucking out 1.7, 4.0, 7.6, and 26 ml of air, respectively, equal to about 2 to 2.25 times the volume of the cups, including the airspace in the needle hub of the cup and in the outlet of the three-way cannula, with an appropriate syringe size. In another practical way, the air can be sucked out with a syringe from the cup till a well-formed hemispherical shape of skin tissue is formed inside the cup. Following this, the air connection of the cannula was blocked, and the syringe was detached from the suction device. The suction process was continued for 1 hour, and the changes inside the cups were noted at intervals of 15 minutes. During the suction process, the patient was advised to immobilize the part as far as possible.

Upon observation, vesicles were produced at 15 to 20 minutes, started to coalesce at 30 to 40 minutes, and formed different shapes of blisters and vesicles at 50 to 60 minutes. The suction process was well tolerated. Complete bullae were produced in 5 ml and 10 ml cups without hemorrhage. In 20 ml and 50 ml cups, various sizes of hemorrhagic vesicles were produced, which coalesced to form large blisters by applying painless lateral pressure with the finger and thumb (Figure 1 a-f).

Figure 1. Changes observed at 15-minute intervals during the suction process using the three-way cannula-suction cup device

Therefore, a small three-way cannula-cup device of its radial height is an effective, fast, and stable suction device for producing suction blisters. Intralesional hemorrhage and incomplete blisters were observed with bigger cups, which is why their negative pressure should be titrated with a barometer, and the air suction volume should not be more than two times the cup volume in larger cups to achieve a flawless blister. In case of a vesicle is not seen after 15 to 20 minutes, then a few ml of air can be sucked out to enhance the suction process but with care about hemorrhage or rupture of the blister. To remain on the safe side, it is best to suck out air about two times the cup volume. Heat can be applied over the site to enhance the suction process. Less mobile, plain sites are better for a successful suction procedure.

Conflict of Interest

None declared.

References

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2. Laxmisha C, Thappa DM. Reliable site for suction blister induction and harvesting. Ind J Dermatol Venereol Leprol. 2005; 71(5):321-324.
3. Anbar TS, Moftah NH, El-Khayayat MAM, et al. Syringes versus Chinese cups in harvesting suction induced blister graft: a randomized split-body study. Int J Dermatol. 2018; 57(10):1249-1252.
4. Mukhtar M, Singh S, Shukla VK, et al. Surgical pearl: Suction syringe for epidermal grafting. J Am Acad Dermatol. 1997; 37(4):638-639.
5. Mukhtar M. Disposable syringe cup for 3-way cannula –syringe suction. J Am Acad Dermatol. 2020; 86(1):E3-E4.