ISOVOLAEMIC HEMODILUTION WITH HYDROXYETHYLSTARCH HAS NO EFFECT ON SOMATOSENSORY-EVOKED POTENTIALS IN HEALTHY-VOLUNTEERS

Background: An animal study in anaesthetized baboons demonstrated that somatosensory evoked potentials (SSEP) can be affected by extreme hae modilution. This might lead to misinterpretation and reduce the value of intraoperative SSEP monitoring when colloids are administered. In t he present study, the effect of haemodilution (HD) and subsequent retr ansfusion of autologous blood on SSEP was determined in healthy non-pr emedicated volunteers. Method: Acute isovolaemic HD served as a model for blood loss immediately replaced with colloids. In 12 volunteers, 2 0 ml/kg . bw blood was withdrawn within 30 minutes and simultaneously replaced with 6% hydroxyethylstarch (HES). 30 minutes later, the autol ogous blood was retransfused within 30 minutes. Recording sites and pa rameters were: 1. Median nerve SSEP: cortical, cervical (C2), Erb's po int; 2. Posterior tibial nerve SSEP: cortical, cervical (C2), lumbar ( L1). In addition to SSEP latency and amplitude, median and tibial nerv e central conduction times, spinal conduction time and nerve conductio n velocity were determined. Serial SSEP measurements were made before, during and after HD and retransfusion every 15 minutes. Results: HD c onsisting of a withdrawal Volume of 1550+/-155 mi (mean+/-SD) induced a decrease in haematocrit from 42.0+/-3.1% to 29.6+/-1.6% (P<0.001). F ollowing retransfusion, haematocrit increased to 35.0+/-2.1% (P<0.001) . Neither HD nor retransfusion influenced SSEP parameters. Conclusion: We conclude from our data that the therapy of blood loss up to 30% of estimated blood volume with HES does not affect SSEP monitoring as lo ng as normovolaemia is maintained.