12 Air-Pump-Assisted Endothelial Keratoplasty One of the great challenges faced by surgeons performing corneal endothelial transplantation is ensuring proper positioning and lasting adherence of the transplanted endothelial graft. Accomplishing donor adherence was noted as one of the largest early challenges in the successful development of the technique and remains a critical step of the procedure today.1 The importance of attaining adequate intraoperative placement is underscored by the rate of endothelial graft dislocations, which have been reported as high as 25% in Descemet stripping automated endothelial keratoplasty (DSAEK) and higher still in Descemet membrane endothelial keratoplasty (DMEK) and other more selective forms of endothelial transplantation.2 A number of techniques have been employed to promote graft adhesion, most of which focus on enhancing the dehydration of the donor–recipient interface. Classically, this has been achieved by a combination of air tamponade for 10 to 15 minutes and massage of the corneal surface to facilitate removal of sequestered fluid. The air tamponade is generally achieved via manual injection of air from a syringe. Price and Price described the utility of occasional supplementation of air with an infusion cannula through the paracentesis.1,3 Manual air insufflation presents some limitations. Fluctuations in intraocular pressure (IOP) with manual insufflation occur during the course of the air tamponade, limiting the amount of pressure exerted on the donor graft and decreasing adherence. The anterior chamber can collapse or decompress during attempts at corneal massage, which limits the effectiveness of compressive maneuvers at best and can result in intraoperative graft decentration or dislocation and the need for graft repositioning, associated surgical delays, or occult retention of interface fluid that increases the risk of postoperative nonadherence. To counter these limitations, Meisler et al described a technique for continuous pumping of filtered air into the anterior chamber via a 30-gauge needle passed through a self-sealing corneal tract at the nasal limbus (► Fig. 12.1).4 Citing the use of this principle to provide retinal tamponade and subretinal fluid evacuation in vitreoretinal surgery, it was suggested that a similar technique could be applied to the fluid in the donor–recipient interface. Following graft insertion and manual injection of an initial bubble through a paracentesis, air was continuously pumped into the anterior chamber with a vitreoretinal surgical system (Accurus, Alcon Surgical) to maintain IOP between 30 and 40mm Hg for 10 to 15 minutes, with occasional spikes to 50 or 60 mm Hg as needed, ensuring constant pressure application to the donor–recipient interface. Once this “press” had taken place, air was then partially exchanged for a slow influx of balanced salt solution (BSS) facilitated by gentle manual release of the air through the paracentesis until the residual bubble diameter is achieved at the desired end point pressure. The same-sized corneal entry site of the 30-gauge needle and its long path length into the cornea provided an airtight seal that facilitated chamber stability and limited pressure fluctuations upon needle removal. The use of a continuous and titratable infusion of air during the procedure demonstrated promising early results in the first 12 consecutive eyes, none of which experienced graft dislocation. Recent developments in intraoperative optical coherence tomography (iOCT) have allowed for more objective analysis of the interface fluid dimensions and the impact of surgical interventions on interface fluid and dislocation rates. Xu and colleagues used iOCT to collect spatial and volumetric data of the donor–recipient interface at various points during the DSAEK procedure in 28 eyes, demonstrating a significant decrease in the height of interface fluid after pressure elevation with the continuous air pump technique.5 Although the trend toward reduced interface fluid volume after pressure elevation alone was not statistically significant in this series, the combination of pressure elevation via the air pump technique and manual corneal sweep with a flat irrigation cannula did demonstrate a significant decrease in interface fluid volume. This study provided quantitative data to support the use of continuous air pump for dehydration of the donor–recipient interface and the success of the technique in reducing early graft dislocations. iOCT has also been used to compare the air pump technique (also referred to as the active air infusion technique) to the manual corneal sweep alone.6 While both techniques independently produced a significant decrease in interface fluid, the air pump technique demonstrated a significantly smaller maximum interface fluid area, mean fluid thickness, maximum fluid thickness, and final interface fluid pocket volume compared to the manual corneal sweep, resulting in a trend toward overall less total interface fluid volume. Studies of continuous air infusion with iOCT imaging in the setting of DMEK are under way at our institution.
12.1 Introduction
12.2 Continuous Air Infusion for Graft Adherence
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