Background: Many plastic surgeons have promoted the use of hypotonic solutions in conjunction with ultrasound assisted lipectomy. The theoretical advantage of these solutions is that induced adipocyte swelling will increase the stress on the cell membrane, making it more susceptible to disruption by ultrasound energy. However, the optimal tonicity of injectable fluids for increasing adipocyte size is currently unknown. Additionally, potassium has been theorized to increase cell membrane permeability but has not been tested in tumescent fluids. Purpose: Our study determined: 1. The effect of tumescent solution osmolality on diameter of adipocytes isolated from fresh human abdominal subcutaneous tissue; 2. The time course of change in adipocyte size while exposed to hypotonic solution; and 3. The differential effect of adding potassium to the solutions. Methods: Base solutions with three different osmolalities were prepared for the study: Normal saline(NS) (154 mOsm/L), ½ NS(77 mOsm/L), and ¼ NS (38.5 mOsm/L). Each base solution was further modified to contain 0, 5, and 10 mEq/L of potassium, with free water added to adjust to starting osmolality. This resulted in a total of nine different solutions. Adipocytes from abdominal subcutaneous tissue of six patients (mean age = 46) were isolated by collagenase digestion. Adipocytes were suspended in each of the nine solutions, and fat cell diameter determined at 0, 15, 30, and 45 minutes. Digestion was performed by placing 5g samples in 15 mg of collagenase/3.5% BSA for 30 minutes in a 37°C shaking water bath, and centrifuging at 1000 RPM for 10 minutes. The fatty supernatant underwent second centrifugation. Aliquots measuring 100 µl were extracted from the middle adipocyte layer and stabilized in isotonic solution prior to experimentation. Cell sizing was performed using a 100X light microscope. Digital images of a field containing 30-80 adipocytes were taken at a standardized focal length, and diameters of the individual cells measured utilizing image software (Kodak ID 3.6®). Results: Average adipocyte diameter was 79µm ± 8µm at time 0. No significant difference in cell diameter was seen at time 0 in all solutions tested. Cells suspended in NS showed no significant increase in diameter over a period of 45 minutes. Cells suspended in ½ NS achieved an 8% increase in diameter at 45 minutes (p < .05). The ¼ NS group showed the most profound change in cell diameter, increasing by 14%(p < .01) at15 minutes, and 15%(p < .01) at 45 minutes. Potassium, as an independent variable, had no effect on cell diameter. Conclusions: Hypotonic solution can significantly increase human adipocyte cell diameter. The effect of quarter normal saline, a standard commercially available fluid, has a significant effect on cell diameter within fifteen minutes. Therefore, a tumescent solution with an osmolality of 38.8 mOsm/l ¼ NS may be useful to facilitate ultrasonic lipoplasty in a clinical setting.
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