COMPARISON OF THE EFFECTS OF 4 IV ANESTHETIC AGENTS ON POLYMORPHONUCLEAR LEUKOCYTE FUNCTION

Initial resistance to bacterial infection is mediated primarily by pol ymorphonuclear leucocytes (PMN). Anaesthetic agents have been reported to impair various aspects of PMN function. It is possible that the us e of these agents to sedate critically ill patients may further compro mise an already depressed host defence mechanism. A flow cytometric te chnique with fresh whole blood from 10 healthy volunteers was used. Ph agocytic and respiratory burst activity of PMN incubated for 1 h with either propofol, thiopentone, midazolam or ketamine at both clinical p lasma concentrations and 100 times this concentration were determined. Thiopentone at the higher concentration reduced both respiratory burs t activity (mean peak channel 50.7 compared with control value of 77.6 (P < 0.0001)) and phagocytosis (mean peak channel 47.5 compared with 79.9 (P < 0.0001)). Ketamine at 100 times the clinical plasma concentr ation also reduced respiratory burst and phagocytosis, but this failed to reach statistical significance (P = 0.10 and P = 0.053, respective ly). No significant depression occurred in the other groups. The resul ts suggest that these i.v. anaesthetic agents, at clinically relevant concentrations, have minimal effects on PMN phagocytosis and oxygen fr ee radical production. At higher concentrations thiopentone and ketami ne may affect phagocytic function and thiopentone may impair intracell ular cytolysis.