Purpose
To determine thermal characteristics of Signature Ellips (Abbott Medical Optics) and Infiniti OZil (Alcon, Inc.) transverse ultrasound and compare both with longitudinal ultrasound in clinically relevant scenarios.
Design
Laboratory investigation.
Methods
Temperature increase over baseline after 60 seconds was measured in water at positions in 90-degree increments around the sleeve near the proximal needle shaft in an artificial chamber for Ellips and OZil on continuous ultrasound with aspiration blocked and unblocked. This was also done with Signature using longitudinal ultrasound, with and without micropulse (6 ms on, 12 ms off), with aspiration blocked and unblocked, and at the OZil sleeve tip on continuous transverse mode with aspiration unblocked.
Results
OZil (8.1 ± 0.3 C) had greater temperature increase than Ellips (5.2 ± 0.3 C; P < .0001) with aspiration unblocked and blocked (29.3 ± 1.0 C vs 12.2 ± 0.7 C; P < .0001). OZil had uneven distribution of heat around the shaft (30.1 ± 0.5 C vs 28.5 ± 0.6 C; P < .0001), whereas Ellips did not ( P = .57). OZil was cooler at the tip (6.6 ± 0.2 C; P < .0001). Friction in a cadaver eye incision only increased these numbers by 10% (OZil, irrigation blocked).
Conclusions
Metal stress probably creates heat at the proximal needle junction for both transverse methods. Heat generation differences between OZil and Ellips result from the manner in which they create needle motion. Incision burns may occur, especially for OZil, under nonpulsed settings during fragment removal with occlusion when reaching across the anterior chamber such that the proximal needle shaft came near the wound.
Incision burn, a serious complication of phacoemulsification, is caused by heat generated from friction created by ultrasonic movement of the phacoemulsification tip. Several studies have examined the conditions necessary for this complication to occur. These studies have implicated needle position (pressure on the wound), low-flow or no-flow conditions, and the use of high levels of continuous ultrasound. This complication has persisted despite advances in technology. Transverse ultrasound power modulation is a new variation that minimizes chatter from the nuclear fragments that are being emulsified. The 2 transverse power designs available today are the Infiniti OZil (Alcon, Inc, Fort Worth, Texas, USA) and the Signature Ellips (Abbott Medical Optics, Santa Ana, California, USA) systems. The transverse motion is somewhat different in each system. OZil creates torsional rotation that subtends an arc and requires a Kelman tip (arc motion is 90 degrees from the bend in the needle). Ellips creates both lateral and some longitudinal motion that subtends an ellipse with the long axis the transverse motion, and the short axis the longitudinal motion. It can be used with a straight tip.
A phacoemulsification needle shaft that rotates, rather than sliding back and forth in the wound, would seem to be very protective of ultrasound-induced incision burns. Previous studies have compared the thermal characteristics of Infiniti (Alcon, Inc.) and Sovereign (Abbott Medical Optics) with conventional longitudinal ultrasound ; however, little is known about the thermal properties of these new transverse ultrasound systems. Han and associates did show that there is approximately half the heat generated with OZil under an elastic band suspending a weight when compared with continuous longitudinal ultrasound. We surmise that the transverse motion creates metal stress, with resultant heat buildup greatest in the proximal phacoemulsification needle shaft, and very little resulting from friction with the wound, as in longitudinal ultrasound. This study was undertaken to test this hypothesis and to compare these 2 transverse ultrasound methods with longitudinal ultrasound thermal generation.
Methods
The Infiniti phacoemulsification unit was used with an OZil handpiece, and the Signature phacoemulsification unit was used with an Ellips handpiece. Kelman needles measuring 0.9 mm 45 degrees were ordered from Microsurgical Technology (MST, Redmond, Washington, USA) with the same physical dimensions except for the thread size to control for differences attributable to needle shape or size. The same phacoemulsification needles were used throughout all testing to eliminate differences resulting from minor phacoemulsification needle dimensional irregularity. Each handpiece was fitted with a similar sleeve, which also was supplied by MST. The Alcon test chamber was used for both devices so as to have a similar chamber size in all tests. Test runs were conducted with the test chamber in place, as described in previous studies. One experiment was in a human cadaver eye to determine the additive thermal effect of incision friction. Because leakage was a variable for which we could not control, there was no leakage from any of the artificial chamber experiments, and we purposely made a tight incision to eliminate leakage from the human cadaver eye experiment. If leakage occurred from the human cadaver eye, it was not apparent.
Phacoemulsification handpieces were placed in a horizontal position on a table. Measuring tapes were fastened to each bottle so that bottle height or vertical distance from the level of the fluid in each bottle to the level of the phacoemulsification needle could be measured. Bottle height was readjusted to 70 cm for each run. Both machines were run at 100% power. OZil was set to 100% amplitude, as was Ellips at full amplitude, and actual vacuum was adjusted to 200 mm Hg, according to parameters established by Georgescu and associates. Aspiration was set to 20 mL/minute. The lower aspiration rate was used to capture more easily the thermal differences between the different ultrasound methods. Higher flow would eliminate thermal energy creation more efficiently. Both OZil and Ellips were set to the maximum possible amplitude and power, and neither was tested with any simultaneous longitudinal ultrasound component.
Temperature was measured continuously using a microthermistor sensor (T164A Thermocouple; Physitemp Instruments, Inc, Clifton, New Jersey, USA), which was connected by a Type T Copper-Constantan miniconnector wire to an isothermal block (Physitemp Instruments, Inc) with an accuracy of ± 0.1 C. The microthermistor wire was glued to the phacoemulsification sleeve with the tip of the thermocoupled sensor at the proximal needle junction. Each thermistor was positioned in the exact same way on the sleeve for every test run. The standard irrigation and aspiration cycle and tuning cycle were run on each machine at the beginning of the day. Normal saline was flushed through the test chamber, needle, and sleeve with the foot pedal held in position 2 until temperature leveled out at a constant 23.0 C ± 0.4 C, for long enough to ensure that any residual heat had been dissipated from the handle (usually 20 to 30 seconds).
In the first experiment, OZil and Ellips both were run on continuous mode. The temperature was recorded at each 90 degrees, with the Kelman bend considered to be at 270 degrees. Twenty test runs were completed for each position. During those trials, the pedal was in fully depressed position 3, with the machine set at 100% ultrasound power.
The second experiment followed the same protocol, with OZil and Ellips both on continuous mode but with aspiration blocked by clamping the aspiration line. Because of the increased heat associated with blocking aspiration, only the positions of 0 and 90 degrees (one in the plane of the Kelman tip and one perpendicular to the plane) were tested to preserve the function of the handpiece. The temperature was recorded at 15, 30, 45, and 60 seconds so that if the handpiece exceeded a temperature of 70 C, the trial could be stopped to save the handpiece.
In a third experiment, the Signature handpiece was tested with longitudinal ultrasound in continuous mode (100% power), and the same 2 positions (0 and 90 degrees) were tested with the same protocol as was followed in the second experiment. The same handpiece was tested using micropulsed longitudinal ultrasound (6 ms on and 12 ms off; 100% power), in all 4 positions (because much less heat was generated, preserving the handpiece was not a concern), with aspiration unblocked. Then, 2 positions were run with aspiration blocked.
In a fourth experiment, instead of placing the microthermistor at the proximal needle junction, temperature was recorded 1 mm from the tip of the sleeve, as in previous studies, with OZil on continuous mode, with aspiration unblocked, for 20 trials.
In a fifth experiment with 100% OZil, the same parameters, and with aspiration blocked, the temperature was recorded mid shaft in the artificial chamber and in the 2.8-mm incision of a human cadaver eye with the thermistor positioned superiorly in the incision at the point of greatest friction with the limbal tissue.
In a sixth experiment, the manufacturer’s Kelman 20-gauge tip was tested in the direction of OZil motion on the proximal needle with aspiration unblocked, with the same parameters as with the test needle otherwise used.
The difference between baseline temperature and temperature at 60 seconds was recorded for all trials; 70 C was not exceeded. Results were compared by independent sample t tests. Statistical significance was set at P < .003 (17 comparisons) by a Bonferroni power adjustment. Because the machine sound characterized what was being tested, there was no masking of the experimental runs; however, all data analysis was masked.
Results
In the first experiment, with aspiration unblocked, OZil on continuous mode had a significantly greater increase in temperature in the axis perpendicular to the Kelman tip (0 and 180 degrees), compared with the positions in the same axis as the tip (90 and 270 degrees; P < .0001). Although the actual difference was small (0.37 C with aspiration not blocked and 1.61 C with aspiration blocked), because of the small variations in testing, the differences were statistically significant. Although probably not of clinical importance, this finding is consistent with and supportive of our hypothesis ( Table 1 ).
| Machine | Position (Degrees) | Aspiration Unblocked | Aspiration Blocked |
|---|---|---|---|
| OZil continuous | 0, 180 | 8.25 ± 0.21 3 | 30.15 ± 0.49 |
| 90, 270 | 7.88 ± 0.17 | 28.54 ± 0.58 | |
| All positions combined | 8.07 ± 0.27 | 29.34 ± 0.97 | |
| Ellips continuous | 0, 180 | 5.24 ± 0.33 1 | 12.12 ± 0.62 2 |
| 90, 270 | 5.18 ± 0.24 1 | 12.25 ± 0.70 2 | |
| All positions combined | 5.21 ± 0.29 | 12.18 ± 0.66 | |
| Signature longitudinal continuous | 0, 90 | 21.63 ± 0.76 | — |
| Signature longitudinal micropulse (6 ms on/12 ms off) | All positions combined | 6.14 ± 0.29 | 21.63 ± 0.57 |
| OZil tip continuous b | 0 | 6.64 ± 0.19 | — |
| OZil mid-shaft continuous | 28.63 ± 1.01 | ||
| OZil mid-shaft continuous in cadaver eye incision | 31.93 ± 1.49 | ||
| OZil continuous, manufacturer’s needle | 0, 180 | 8.61 ± 0.34 3 |
a Results are at 60 seconds with increase over baseline (room temperature) recorded. Temperature recorded on the phaco sleeve near the proximal needle junction at 4 positions indicated by degrees, with Kelman tip being 270 degrees. All comparisons P < .0001 except for: P = .41, P = .57, P = .001.
Ellips did not have any significant difference in temperature change between any axis (aspiration blocked and unblocked), so the needle must move equally, or almost so, in all transverse meridians ( Table 1 ). OZil had 1.5 times greater maximal increase in temperature when compared with Ellips (aspiration unblocked, continuous mode for both; P < .0001; Table 2 ).
| Category | Position (Degrees) | Ultrasound Setting | Aspiration | Ratios |
|---|---|---|---|---|
| OZil/Ellips | 0 | Continuous | Unblocked | 1.57 |
| OZil/Ellips | 90 | Continuous | Unblocked | 1.53 |
| OZil/Ellips | 180 | Continuous | Unblocked | 1.55 |
| OZil/Ellips | 270 | Continuous | Unblocked | 1.50 |
| OZil/Ellips | 0 | Continuous | Blocked | 2.49 |
| OZil/Ellips | 90 | Continuous | Blocked | 2.33 |
| Ellips/Signature | 0 | Cont/Micropulse | Unblocked | 0.87 |
| Ellips/Signature | 90 | Cont/Micropulse | Unblocked | 0.83 |
| Ellips/Signature | 0 | Cont/Micropulse | Blocked | 0.56 |
| Ellips/Signature | 90 | Cont/Micropulse | Blocked | 0.56 |
| OZil/Signature | 0 | Cont/Micropulse | Unblocked | 1.36 |
| OZil/Signature | 90 | Cont/Micropulse | Unblocked | 1.26 |
| OZil/Signature | 0 | Cont/Micropulse | Blocked | 1.39 |
| OZil/Signature | 90 | Cont/Micropulse | Blocked | 1.31 |
| Signature/OZil | 0 | Continuous | Unblocked | 2.57 |
| Signature/Ellips | 0 | Continuous | Unblocked | 4.03 |
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