Managing IOP Increases in Small-gauge Surgery

A simple and controlled technique for fluid-PFCL exchange in small-gauge vitreous surgery using 23-to-25-gauge mismatch

PRADEEP VENKATESH, MD • VARUN GOGIA, MD • BHAVIN SHAH, MD • YOG RAJ SHARMA, MD

Perfluorocarbon liquids (PFCLs) serve as useful intraoperative tools during vitreoretinal surgery, particularly in the management of giant retinal tears, in which they help in unfolding the flap. However, injecting PFCL into the vitreous cavity in a fluid-filled eye requires simultaneous egress of the infusion fluid.

When the intraocular fluid does not exit the eye as PFCL is being injected, a dangerous increase occurs in intraocular pressure, as well as anterior ballooning of the peripheral retina due the subretinal fluid shifting anteriorly.

While the former can lead to compromise of optic disc perfusion, the latter increases the risk of iatrogenic tear formation. The most widely recommended means to enable safe injection of PFCL into a fluid-filled eye is to use a double-bored cannula, first described by Stanley Chang, MD. However, this instrument is not widely and freely available to all retina surgeons.

Therefore, in the absence of a double-bore cannula, surgeons achieve PFCL injection by intermittently leaving one of the pars plana ports open to allow some fluid to flow out of the vitreous cavity. This approach, however, is fraught with risks because there is significant fluctuation in the IOP.

Microincisional vitreous surgery (MIVS) has rapidly become the standard procedure of choice for vitreous surgery over the past decade. One of key advantages of MIVS is that it allows the IOP to be maintained at all times due to the tight fit between the cannula and the vitreous instruments. For this reason, during MIVS, the risks of PFCL injection mentioned above are significantly enhanced if no double-bore cannula is available.

We describe this new technique of 23-gauge-to-25-gauge cannula mismatch, which allows for PFCL injection with simultaneous and spontaneous egress of the intraocular fluid, without the need for any specialized instrumentation.

SURGICAL TECHNIQUE

In cases such as giant retinal tears and complex retinal detachments, in which PFCL is often required, we make the infusion port and endoilluminator port using 25-gauge trocar and cannula. For the third (active) port, however, we make the sclerotomy using a 23-gauge trocar and cannula.

After completing vitrectomy, PFCL injection is performed using a syringe on which is mounted a 25-gauge soft-tip cannula. Before the start of the PFCL injection, the infusion pressure is lowered to 15 mm Hg.

Then, as PFCL is injected into the vitreous cavity, IOP rises, and the vitreous fluid spontaneously and passively egresses from the active port due to the mismatch in diameter of the cannula and soft tip (Figure). This mismatch enables better control of the IOP and eliminates the need for having to intermittently keep one of the ports open or stopping the infusion.

Figure 1. Completion of vitrectomy.

Figure 2. Initiation of PFCL injection.

Figure 3. Completion of PFCL injection.

DISCUSSION

We have used MIVS with this technique in nine cases of giant retinal tears and have found it to be very useful in performing more controlled surgery. PFCL is most critical in the management of giant retinal tears with free and rolled-over flaps.

In these situations, PFCL injection is required in larger quantities because it must be injected up to the brim of tear to prevent slippage. This technique helps in keeping the IOP gradients constant, thereby adding safety to the surgery by reducing the risk of anterior ballooning of the peripheral retina and by maintaining optic disc perfusion.

The rationale behind this added safety is that the 23-gauge cannula has a diameter of 0.69 mm while 25-gauge has a diameter of 0.53 mm. The resulting small difference between the port and injection cannula creates an adequate space for simultaneous and equivalent egress of the infusion fluid out of the vitreous cavity with no increase or decrease in IOP.

In conclusion, this novel technique using 23-gauge-to-25-gauge mismatch can improve the safety of surgical procedures in which direct PFCL-fluid exchange is necessary. This is the approach that we now use. RP