Complications in Equine Surgery. Группа авторов

the lesion (see below).

Besides a correct choice of cryogen and cryosurgical equipment, several measures can be taken to promote fast freezing and limit the duration of the procedure:

       Lesions that exceed the level of the surrounding tissues should be debulked. This decreases the tissue volume to be frozen and helps achieving lower temperatures at a high freezing speed [13, 14].

       For lesions located close to vessels or in a well vascularized area, the efficacy of freezing can be enhanced by the placement of a tourniquet (distal limbs) or a Chalazion clamp (eyelid) to temporarily slow down or stop the circulation in the treated area [8, 16].

       In cases of multiple tumors, time can be gained by freezing a second tumor during the slow thaw phase of a first tumor.

       Similarly, when a large tumor base needs to be frozen in consecutive areas, time can be gained by freezing a second zone during the slow thaw phase of a first zone.

       The slow thawing phase is the most time‐consuming. Nevertheless, it is not advised to speed up that phase of the cycle, for example by heating the probe or using a hair dryer. Indeed, the process of recrystallization resulting in direct cellular damage mainly occurs during the slow thawing phase which is essential for cryosurgical success.

      Finally, temperature should be monitored during the freezing process:

       Use thermocouple needles inside the lesion to make sure –30 to –40°C is reached for ≥1 minute. In larger lesions, multiple thermocouple needles should be placed and it is more important to position them at the periphery of the lesion compared to the center. Placement of the needle close to a blood vessel (heat source) can also influence the temperature measured [18].

       When thermocouple needles are not available or cannot be placed safely, the tissue temperature should be estimated as accurately as possible by:

       Visual inspection of the formed ice‐ball at the level of the cornea [5].

       Inspection and palpation of the formed ice‐ball at the level of the skin [14]. Be aware that the outer edge of the palpable ice‐ball only reaches a tissue temperature of 0°C which is inadequate for cell destruction [20].

       Ultrasonographic monitoring of the ice‐ball. This is used more commonly in human medicine (e.g. for cryotherapy of the prostate and other internal organs). Frozen tissue has a hypoechoic appearance and the boundary between frozen and unfrozen tissue shows as a white hyperechoic rim (HER). At the border between the HER and the hypoechoic frozen tissue, tissue temperature is approximately –15°C. At the outer border of the HER, tissue temperature is approximately 0°C [18].

       Treatment

      If incomplete tumor destruction occurs, treament of the postoperative recurrence may be required.

       Expected outcome

      Incomplete tumor destruction likely results in recurrence postoperatively.

      "Run‐off " of Cryogen

       Definition

      When the cryogen runs down from the site that should be frozen

       Risk factors

       Use of a cryosurgical device that sprays liquid nitrogen

       Fast freezing by pouring liquid nitrogen onto the tissues

       Pathogenesis

      Application of cryogen by spray is less precise than by probes and some technical experience is required to apply cryogen safely [21]. When the sprayed liquid nitrogen comes into contact with the tissue, it evaporates. However, when too much liquid nitrogen is applied at any one time, it does not evaporate immediately and runs off the skin causing inadvertent frost lesions. This complication is more likely to occur when treating large lesions that require the application of more cryogen in order to obtain rapid freezing of the entire lesion.

      When liquid nitrogen is poured onto the tissues without a device to keep it in place, run‐off is unavoidable.

      The size and depth of the frostbite injury that occurs following run‐off depends on the amount that has been spilled. However, full thickness skin lesions are unlikely to occur.

       Diagnosis

      Evident during the procedure as the cryogen runs away from the desired area

       Prevention

For spraying instruments, “cups” can be used to confine the cryogen to the lesion and prevent run‐off. The use of cups is essential when pouring liquid nitrogen directly onto the lesion. Cups are commercially available [20] or can be custom‐made from PVC‐tubing or any other material (Figure 11.1). Different sizes should be used, depending on the lesion to be treated. The use of a contact gel is advised to ensure that the entire cup fits well on the surrounding skin and sticks to the skin as soon as the liquid nitrogen is applied.

An alternative to the use of cups for spraying instruments is to pack the surrounding area with vaseline‐impregnated sponges or styrofoam to prevent run‐off [16]. This is more difficult compared to the use of cups as they often do not seal perfectly to the surrounding normal tissue [14]. Open cell foams and gauze swabs should be avoided as they soak up the cryogen and become themselves a cold sink producing damage which it was intended to prevent [13].

Figure 11.1 A self‐made PVC cup is used to confine the sprayed liquid nitrogen to the lesion. Thermocouple needles (arrowheads) are placed in the tissue to be frozen and the underlying healthy tissue and a gel is used to ensure good sealing between the cup and the surrounding healthy skin.

      Source: Ann Martens.

       Treatment

      When run‐off of cryogen is identified during surgery, the frozen skin should be warmed up as quickly as possible (e.g. with a sponge soaked in warm water). Rubbing is contraindicated as this worsens the skin damage. Topical aloe vera cream or gel (antithromboxane) applied immediately after injury and in the follow‐up period can help prevent local thrombosis and ischemia [22].

       Expected outcome

      Most injuries are superficial and will heal uneventfully. In case of deep injury, hypo‐ or leukotrichia can result.

Early Postoperative Complications

      Bleeding after Cryosurgery

       Definition

      Hemorrhage from the cryoablation site that is evident in the first 2–3 hours after surgery

       Risk factors

       Tumors that require debulking to the level of the surrounding skin before freezing

       Tumors from which a biopsy is taken prior to freezing

       Tumors located over a large superficial vein [14]

       Pathogenesis

      Limited