Commentary questions two-hour saturation assumption for polymyxin B hemoadsorption

A commentary in Critical Care challenges the assumption that polymyxin B hemoadsorption cartridges reach endotoxin-binding saturation within two hours. Responding to discussion of the Tigris septic shock trial, the authors reinterpret published experiments rather than report new patient data. They argue that plateaus observed in closed-loop experiments may reflect adsorption–desorption equilibrium, not exhausted cartridge capacity.

The authors cite a continuous-loading laboratory study using a neonatal cartridge exposed to lipopolysaccharide at 0.5 µg/hour. Adsorption efficiency declined after two hours, but the adsorption ratio remained approximately 40% thereafter, with cumulative adsorption reaching 4.73 µg at 24 hours without observed saturation. Scaling by fiber mass would imply 66.2 µg for an adult cartridge, although this was not directly measured. A separate clinical study reported a median endotoxin removal rate of 74.4% after 24 hours among septic shock patients whose pre-cartridge concentrations exceeded the assay detection limit.

These findings challenge a fixed two-hour saturation limit but do not demonstrate that longer treatment improves survival or other patient outcomes. Optimal duration and clinical benefits, particularly in patients with endotoxin activity ≥0.90, remain undetermined. Laboratory adsorption measures and extrapolation between cartridge sizes cannot establish clinical effectiveness. One commentary author disclosed lecture fees and research support from Toray Industries, the cartridge manufacturer.