Distribution and elimination of the solute and water components of urological irrigating fluids

Irrigating fluids are used to dilate mucosal spaces and to remove blood and cut tissue from the operating field during endoscopic procedures. We have studied their disposition, since irrigating solutions are sometimes absorbed and may therefore be regarded as intravenous drugs.

The distribution and the rate of elimination of four irrigating fluids containing glycine, mannitol and sorbitol were studied after infusing 0.75 ml/kg/min of them over a period of 20 min in 10 male volunteers. Kinetic calculations were based on 12 blood samples collected over 120 min using traditional pharmacokinetics for the solutes and volume kinetics for the water component.

The solutes had distribution half-lives of between 3 and 7 min; the elimination half-lives were 39 min (glycine), 97 min (mannitol) and 33 min (sorbitol). The volume of distribution during steady state was between 20 and 36 litres, while the volume of the body fluid space expanded by the water component of the irrigating fluids varied between 6 and 9 litres. Although the solutes became distributed over a much larger space than the infused fluid volume, the intersubject variation was smaller for the solute concentrations than for the dilution of the plasma fraction of the blood.

The kinetics of the solute and water components of urological irrigating fluids can be analysed and compared using computer-based mathematical models.