Research

In vitro norepinephrine significantly activates isolated platelets from healthy volunteers and critically ill patients following severe traumatic brain injury

Christoph Tschuor¹ , Lars M Asmis² , Philipp M Lenzlinger³ , Martina Tanner¹ , Luc Härter³ , Marius Keel³ , Reto Stocker¹ and John F Stover¹

¹Surgical Intensive Care Medicine, University Hospital Zuerich, Raemistrasse 100, CH 8091 Zuerich, Switzerland

²Institute for Clinical Hematology, University Hospital Zuerich, Raemistrasse 100, CH 8091 Zuerich, Switzerland

³Division of Trauma Surgery, Department of Surgery, University Hospital Zuerich, Raemistrasse 100, CH 8091 Zuerich, Switzerland

author email corresponding author email

Critical Care 2008, 12:R80doi:10.1186/cc6931

Published:	18 June 2008

Abstract

Introduction

Norepinephrine, regularly used to increase systemic arterial blood pressure and thus improve cerebral perfusion following severe traumatic brain injury (TBI), may activate platelets. This, in turn, could promote microthrombosis formation and induce additional brain damage.

Methods

The objective of this study was to investigate the influence of norepinephrine on platelets isolated from healthy volunteers and TBI patients during the first two post-traumatic weeks. A total of 18 female and 18 male healthy volunteers of different age groups were recruited, while 11 critically ill TBI patients admitted consecutively to our intensive care unit were studied. Arterial and jugular venous platelets were isolated from norepinephrine-receiving TBI patients; peripheral venous platelets were studied in healthy volunteers. Concentration-dependent functional alterations of isolated platelets were analyzed by flow cytometry, assessing changes in surface P-selectin expression and platelet-derived microparticles before and after in vitro stimulation with norepinephrine ranging from 10 nM to 100 μM. The thrombin receptor-activating peptide (TRAP) served as a positive control.

Results

During the first week following TBI, norepinephrine-mediated stimulation of isolated platelets was significantly reduced compared with volunteers (control). In the second week, the number of P-selectin- and microparticle-positive platelets was significantly decreased by 60% compared with the first week and compared with volunteers. This, however, was associated with a significantly increased susceptibility to norepinephrine-mediated stimulation, exceeding changes observed in volunteers and TBI patients during the first week. This pronounced norepinephrine-induced responsiveness coincided with increased arterio-jugular venous difference in platelets, reflecting intracerebral adherence and signs of cerebral deterioration reflected by elevated intracranial pressure and reduced jugular venous oxygen saturation.

Conclusion

Clinically infused norepinephrine might influence platelets, possibly promoting microthrombosis formation. In vitro stimulation revealed a concentration- and time-dependent differential level of norepinephrine-mediated platelet activation, possibly reflecting changes in receptor expression and function. Whether norepinephrine should be avoided in the second post-traumatic week and whether norepinephrine-stimulated platelets might induce additional brain damage warrant further investigations.