PLASMA NE CONCENTRATIONS DO NOT ACCURATELY REFLECT SYMPATHETIC NERVOUS-SYSTEM ACTIVITY IN HUMAN SEPSIS

Plasma norepinephrine concentrations ([NE]) when raised in patients wi th sepsis are thought to indicate increased activity of the sympatheti c nervous system (SNS). However, increased SNS activity may occur with out a concomitant rise in plasma [NE]. Measurement of NE kinetics (cle arance and spillover) is a more accurate and direct assessment of SNS activity. In the present study plasma [NE] and NE kinetics were measur ed in six patients with intra-abdominal sepsis (septic) using tritiate d NE infused to achieve a plateau plasma concentration. The measuremen ts were repeated in the same patients after they had recovered (nonsep tic). NE clearance and spillover were both significantly higher (P < 0 .05) in the septic compared with the nonseptic state. However, there w as no statistically significant difference in plasma [NE] between the two conditions. Plasma [NE] indicates no alteration in SNS activity du ring the septic state, whereas NE kinetics indicate increased activity of the SNS during sepsis. The results suggest that plasma [NE] is a p oor indicator of SNS activity during septic illness.