Heparin-induced platelet dysfunction and cardiopulmonary bypass.
BACKGROUND
Cardiopulmonary bypass is associated with impaired platelet macroaggregation. Heparin contributes to platelet dysfunction before extracorporeal circulation. In vitro heparinization of whole blood does not impair macroaggregation. Heparin releases several endothelial proteins; thus heparin may inhibit macroaggregation indirectly.


METHODS
Patients undergoing operations using cardiopulmonary bypass and ABO blood group compatible volunteers were studied. Whole blood impedance aggregometry assessed macroaggregation in response to collagen (0.6 microg ml(-1)) in blood diluted either with normal saline or with platelet poor plasma, obtained from patients at different stages of cardiopulmonary bypass.


RESULTS
Before heparinization, blood diluted with its own platelet poor plasma recorded an impedance change of 13.0 (4.7 to 15.6) Ohms. Platelet poor plasma obtained after heparinization or during extracorporeal circulation reduced this response to 3.7 (1.1 to 8.4) and 2.0 (1.1 to 3.3) Ohms, respectively (both p < 0.0001 versus pre-heparin; n = 13). Macroaggregation in blood from volunteers was similarly inhibited by patients' platelet poor plasma (n = 30). The macroaggregatory response in blood sampled after heparinization for cardiopulmonary bypass, decreased gradually from 11.4 (8.2 to 15.9) Ohms immediately after sampling to 1.7 (1.4 to 4.1) Ohms 2 hours later (p < 0.0001; n = 11).


CONCLUSIONS
In vivo heparinization induces plasma changes that inhibit platelet macroaggregation. This is an indirect, delayed inhibition that is transferable in vitro to normal platelets.
Muriithi
E W
EW
Department of Cardiac Surgery, University of Glasgow, Royal Infirmary, Scotland. e.w.muriithi@clinmed.gla.ac.uk
Belcher
P R
PR
Day
S P
SP
Menys
V C
VC
Wheatley
D J
DJ
D001791:Blood Platelet Disorders / Q000097:blood / Q000139:chemically induced*; D001792:Blood Platelets / Q000187:drug effects*; D002315:Cardiopulmonary Bypass; D004305:Dose-Response Relationship, Drug; D006438:Hemodilution; D006493:Heparin / Q000008:administration & dosage / Q000009:adverse effects*; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects
D006493:Heparin