Discrepancies in CDE and Measured Phaco Tip Energy: Comparison of Energy Produced in Longitudinal and Torsional Ultrasound Using Calorimetry

Abstract

Reiker G Ricks,1,2 Ivan A Cardenas,1,2 Jenna L Jensen,1,2 Tanner K Nelson,1,2 Randall J Olson,1 Jeff H Pettey1 1Department of Ophthalmology and Visual Sciences, John A Moran Eye Center, University of Utah, Salt Lake City, UT, 84132, USA; 2University of Utah School of Medicine, Salt Lake City, UT, 84132, USACorrespondence: Jeff H Pettey, John A Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT, 84132, USA, Tel [phone], Fax [phone], Email [email protected]: This study aims to investigate the differences between the heat energy produced during cataract surgery and Cumulative dissipated energy (CDE). CDE is often used as a medium for understanding the energy delivered to the eye during cataract surgery. However, the actual energy produced at the tip level of the tip is not well understood. We propose that a discrepancy may exist between the CDE reported by the surgical machine and the actual energy delivered to the eye.Methods: About 50 mL of distilled water were degassed and placed in an isobaric calorimeter. Using the Alcon Centurion and Ozil handpiece fitted with the balanced tip, an investigator immersed the phaco tip into the water and pressed the foot pedal to position 3. The device was set to 100% continuous power, vacuum to 0 mmHg, with aspiration 12 mL/min aspiration. To prevent system changes in the system within the calorimeter, the aspiration tubing was occluded. Temperature change recorded by another investigator was observed from 0 to 60 seconds. After 60 seconds the first researcher immediately released the pedal and removed the phaco tip from the water. Trials were performed 10 times using solely torsional or longitudinal settings and averaged. CDE also was recorded and averaged.Results: No significant difference was seen in the temperature change or energy calculated in Joules between ultrasound modalities, with torsional producing a magnitude of 163 J and longitudinal producing 172 J (P = 0.2). However, the CDE generated in the 60 seconds period was significantly different, with a magnitude of 61 for longitudinal compared to 24 for torsional (P < 0.001).਌onclusion: Significantly more energy was generated using torsional ultrasound than longitudinal at the tip level of the tip. CDE did not appear to accurately reflect these differences. This suggests that other factors should be considered when evaluating CDE and surgical outcomes.Plain Language Summary: This study looked at possible differences between the energy generated during cataract surgery that is reported by the surgical device and the actual energy measured as thermal heat using different machine settings, namely longitudinal and torsional ultrasound. A common metric used for energy delivery to the eye is cumulative dissipated energy. The problem is that this measure accounts for the energy delivered to the eye where the surgical instrument passes through the cornea. Energy that is produced by the rest of the instrument that is inside the eye is less understood, although others have studied postoperative outcomes. We used a method called calorimetry to measure the thermal heat produced by the entire tip and compared this to what the machine reported as cumulative dissipated energy. Calorimetry calculates energy by measuring the change in temperature of liquids. The surgical instrument generated heat in a chamber containing water, and we used the change in temperature to calculate the energy produced by the surgical instrument. We found that longitudinal and torsional ultrasound produced similar heat energy, but the machine reported very different energy. Our results suggest that the machine may not be reporting all of the energy which the surgical instrument produces, and that surgeons may not be able to rely on cumulative dissipated energy to predict operative outcomes.Keywords: Cumulative dissipated energy, phacoemulsification, calorimetry, torsional ultrasound, longitudinal ultrasound

Keywords

• cumulative dissipated energy
• phacoemulsification
• calorimetry
• torsional ultrasound
• longitudinal ultrasound.