Flow cytometry evaluation of the in vitro influence of four i.v. anaesthetics on respiratory burst of neutrophils

Exposure of neutrophils to anaesthetic agents may alter their functional characteristics and in patients undergoing long-term sedation this may be clinically relevant. We have investigated the in vitro influence of propofol, thiopentone, methohexitone and midazolam on phorbol 12-myristate 13-acetate (PMA)-induced respiratory burst of neutrophils by the intracellular oxidative transformation of dihydrorhodamine-123 to the fluorescent dye rhodamine-123 via flow cytometry. We tested in vitro concentrations similar to sedating, anaesthetic, 10-fold sedating and 10-fold anaesthetic plasma concentrations. All drugs showed similar inhibition of respiratory burst at sedating concentrations (1-6%). At anaesthetic concentrations, propofol produced significantly higher mean inhibition (7.3%) compared with thiopentone (4.5%) and methohexitone (0.9%). At 10-fold anaesthetic concentrations inhibition of respiratory burst by propofol was almost complete (90.8%) and significantly higher than that by thiopentone (29.2%) and methohexitone (1.8%). Methohexitone and midazolam had only minimal effects at all concentrations. The effect of the solvent of propofol (10% Intralipid) was similar to that of propofol. Thus suppression of respiratory burst of neutrophils by propofol may be caused by this lipid carrier.