Simple steps for surgeons to optimize phaco fluidics

Adjusting bottle height, aspiration flow rate and vacuum level can improve efficiency and increase patient safety during cataract surgery.

Uday Devgan

One of the principle challenges of cataract surgery is that we are working in a very confined space in close proximity to delicate ocular structures.

For a typical eye with an anterior chamber depth of 3 mm, the volume of the anterior chamber is about 0.2 mL, and the posterior chamber volume is even less. This yields a total working volume of just six to eight drops (using the metric definition of one drop equaling 0.05 mL) in which to remove the cataract and insert the IOL without damage to ocular structures. By optimizing the settings of our phaco machines, we can make cataract surgery more efficient for the surgeon and safer for the patient.

Ophthalmologists recognize that when the fluidics are balanced, the anterior chamber is stable and formed, the cataract pieces flow toward the phaco tip, and aspiration of the lens fragments is efficient. For a peristaltic pump system, the primary fluidic parameters are bottle height (cm), flow rate (cc/minute) and vacuum level (mm Hg).

Effect of bottle height

There is only one source of fluid inflow during cataract surgery: the balanced salt solution that is hanging on the pole. In retinal surgery, there is forced infusion and a closed system so that surgeons can set a desired IOP. But the typical cataract surgery is done with an open system with a small amount of fluid leak at the main phaco incision to provide cooling. Tight non-leaking incisions coupled with ultrasonic phaco energy can result in a phaco wound burn (Figure 1).

Figure 1. A very tight phaco incision and excessive ultrasonic energy can result in a phaco wound burn, causing a fish-mouth appearance to the corneal incision. Images: Devgan U

In cataract surgery, by raising the bottle, we increase the infusion pressure by way of gravity, similar to having a high water tower to create inflow of water into your home. The higher the bottle is, the higher the level of infusion pressure and the greater the volume of inflow fluid. Remember that it is the level of the bottle relative to the level of the eye that is important. Surgeons who raise the operating room table for comfort or raise the head of breathing-impaired patients will need to raise the bottle height correspondingly. Finally, the size of the inflow tubing and phaco tip can also limit the amount of inflow.

Ophthalmologists can measure their specific inflow at their desired bottle heights to know the exact amount of fluid inflow. Using an empty 60-cc syringe as a measuring device, see how much fluid will flow in 1 minute with a given bottle height (Figure 2). This is the maximum amount of inflow in cc/min.

Figure 2. Measure the actual amount of fluidic inflow at a specific bottle height by filling an empty syringe using the phaco handpiece for 1 minute.

Adjusting the flow rate

The flow rate is the amount of fluid per minute that the peristaltic pump will aspirate from the eye. There is also some leakage from the phaco and paracentesis incisions, typically 5 cc/min to 10 cc/min. Thus, there are two sources of fluid outflow: the fluid that is being aspirated via the phaco tip and the leakage of fluid from the incisions. The ideal situation is one in which the inflow of fluid from the infusion bottle balances the outflow of fluid via the peristaltic pump and leakage from the incisions.

The flow rate will determine how quickly the cataract pieces are brought to the phaco tip, and this makes for more efficient surgery. If the measured maximum inflow at your selected bottle height is 60 cc/min, then assume 10 cc/min of fluid leakage from the incisions, and set your maximum aspiration outflow rate as 45 cc/min to allow an additional buffer of 5 cc/min. During surgery, if you notice an excessive amount of chamber bounce or instability, drop the aspiration flow rate further or increase the bottle height in order to improve the inflow-to-outflow balance. Mismatched fluidic inflow and outflow rates can lead to surge and a rupture of the posterior capsule during surgery.

Setting vacuum level

Adjusting the vacuum level determines the highest level that will be reached using the peristaltic pump upon occlusion of the phaco or irrigation and aspiration tip. The level of vacuum that you require will also depend on the size of the phaco needle. If you are using a larger-bore needle, you can achieve good flow with lower vacuum; however, with the smaller-gauge phaco needles, a higher level of vacuum will be needed to achieve the same level of flow.

If your technique involves sculpting a nuclear groove, such as with divide-and-conquer or stop-and-chop, a lower vacuum setting (50 mm Hg to 60 mm Hg with large-bore needles, 80 mm Hg to 100 mm Hg for smaller-bore needles) is sufficient to remove the emulsified material. If you require purchasing power to hold or manipulate the nuclear pieces, such as with a chop technique, then a higher vacuum level is needed (200 mm Hg to 250 mm Hg for large-bore needles, 350 mm Hg to 450 mm Hg for small-bore needles). Because our goal is phaco-assisted aspiration of the cataract, in which the primary modality is fluidics with the ultrasound energy used to prevent blockage of the tip, a high vacuum level should be used to remove nuclear fragments.

Simple adjustments to your bottle height, aspiration flow rate and vacuum level can improve your efficiency and increase patient safety during cataract surgery. No matter your technique of phacoemulsification, we can optimize each of these parameters to improve surgery.

Reference:

• Rabsilber TM, Khoramnia R, Auffarth GU. Anterior chamber measurements using Pentacam rotating Scheimpflug camera. J Cataract Refract Surg. 2006;32(3):456-459.

• Uday Devgan, MD, FACS, FRCS, is in private practice at Devgan Eye Surgery in Los Angeles and Beverly Hills. He can be reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; email: devgan@gmail.com; website: www.DevganEye.com.
• Disclosure: No products or companies are mentioned that would require financial disclosure.