Answer:
(From Grabb and Smith CD-ROM:)
Aspirating cannulas come in a variety of tip configurations and sizes. Multiple openings at the distal end of the cannula increase the speed and efficiency of extraction. Most surgeons use a blunt-tip instrument with aspiration apertures set back a few millimeters from the end of the cannula. Setting the apertures back from the tip and along the sides of the cannula prevents excessive resection if the tip is inadvertently pressed up against the undersurface of the dermis. Use of small-diameter cannulas (2–5 mm) permits small access incisions and inconspicuous scars. Small-diameter cannulas also produce fewer surface irregularities and a smoother final result.
The cannula is usually attached by flexible tubing to an aspirating pump off the surgical field. The pump should be powerful enough to achieve vapor pressure, because vaporization of the water in aspirated tissues significantly increases flow rate and compensates for the reduction in flow rate secondary to the use of small-diameter cannulas.
Cannulas also can be attached to syringes that create a vacuum when the plunger is withdrawn. The fat is collected in the syringe (syringe liposuction). This technique is useful for harvesting fat under sterile conditions and reinjecting the fat as grafts. In most instances, however, an electric-powered vacuum pump is more efficient for large-volume fat extraction.