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Effect of haemodilution, acidosis, and hypothermia on the activity of recombinant factor VIIa
- Hadi Meeran Hussain (5 September 2008)
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Hadi Meeran Hussain Department Of Internal Medicine,combined military hospital,lahore,Pakistan
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This study by Viuff et al,investigates two areas of increasing interest in anaesthesia and critical care: the use of recombinant factor VIIa and the effects of plasma volume expanders on coagulation.(1) The effects of recombinant factor VIIa upon clot formation was measured in vitro by thromboelastography (TEG) in the presence of acidosis (pH 6.8), hypothermia (32°C) and different plasma expanders: 0.9% NaCl, lactated Ringer's solution, 5% albumin, and hydroxyethyl starches (HES) of varying moelcular weights.The recombinant factor VIIa improved TEG R values in the presence of 20% haemodilution with all of the fluids used. At 40% haemodilution, the improvements were similar for albumin, NaCl and Ringer's solution, but HES130 and HES200 required higher recombinant factor VIIa doses and HES600 and HES670 showed no improvement at any dose. Recombinant VIIa improved TEG values in the presence of acidosis and hypothermia. The effect of the higher molecular HES was further investigated in vivo using rabbits. Haemodilution with HES 200 and HES600 prolonged the bleeding time significantly. This prolongation could be improved with the use of recombinant factor VIIa in those animals in the HES200 group but not in the HES600 group. These results need to be interpreted cautiously, as majority of the work is purely in vivo and cannot be readily translated to human subjects. The authors only used a single test (TEG) to investigate the effects of recombinant factor VIIa upon coagulation. This was disappointing, as previous work has shown that some fluids (for example, gelofusine) can markedly lower fibrinogen levels, whilst others have no effect. Without measuring platelet function, thrombin and fibrinogen levels, it is impossible to extrapolate these results into clinical practice and to make suggestions for changes in clinical practice. That said, the fact the the higher molecular weight HES's appeared to lessen the effectiveness of recombinant VIIa is of interest and may be of great clinical significance. Further work is warranted into the effects of the HES's upon coagulation, so the risk- benefit ratio of their use can be more accurately assessed. In the interim, as HES's have not been shown to offer clinically important benefits when compared to other plasma expanders, their use should be limited in those patients receiving recombinant factor VIIa therapy. References: 1.D. Viuff, B. Lauritzen, A. E. Pusateri, S. Andersen, R. Rojkjaer, and P. I. Johansson.Effect of haemodilution, acidosis, and hypothermia on the activity of recombinant factor VIIa (NovoSevenŽ). Br J Anaest 2008; 101: 324-331 Conflict of Interest:None declared |
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