Priority in hemorrhage treatment: Restoration of oxygen carrying capacity or microvascular function via targeted plasma

1. Priority in hemorrhage treatment: Restoration of oxygen carrying capacity or microvascular function via targeted plasma expansion? B.Y. Salazar Vázquez, A.G. Tsai, P. Cabrales, M. Intaglietta Department of Bioengineering University of California, San Diego La Jolla, CA

2. Treatment of hemorrhage • Restoration of blood volume & oxygen delivery

3. Five approaches • Blood • Oxygen carrying plasma expanders (blood substitutes) • Crystalloids • Colloids (albumin, starch, dextran) • Super colloids (Dextran 0.5 & 2 mDa, Alginate, PEG-Albumin)

4. Intravascular and tissue O2 tensionHematocrit 11% (extreme hemodilution) Plasma PBH > 3.4 g/dl has no effect on oxygen transport Total hemoglobin g/dl 3.7 rbcs only 5.0 6.3 7.1 †, P<0.05 compared to PBH0; ‡, P<0.05 compared to PBH4; and §, P<0.05 compared to PBH8. Cabrales, P., Tsai, A.G. and M. Intaglietta. Balance between vasoconstriction and enhanced oxygen delivery. Transfusion 48:2087-95, 2008.

5. Alternative blood substitutes • PEG-Hemoglobins: High colloidal osmotic pressure at low concentration, high oxygen affinity. • Hemoglobin polymers: No colloidal osmotic pressure. • Hemoglobin PEG-vesicles: Very high viscosity at clinically significant concentrations.

6. How much Hb can be placed in the circulation? • We do not have evidence that it is safe or possible to exceed 3 g/dl Hb outside of RBCs in blood in a healthy organism. • Equivalent effects can be obtained with non-Hb plasma expanders that enhance microvascular function, with lower toxicity.

7. Blood substitutes:Not designed to be good plasma expanders

8. Summary • FCD (Functional capillary density):The critical parameter in plasma expansion. • Blood/plasma viscosity determines FCD in extreme hemodilution. • FCD and super plasma expanders in shock.

9. Experimental studies in the microcirculation Hamster window chamber model

10. Functional capillary density Hamster Skin Fold Preparation

11. Hemorrhagic shockFunctional capillary density in survivors vs. non survivors Kerger, H., Saltzman, D.J., Menger, M.D., Messmer, K. and M. Intaglietta. Systemic and subcutaneous microvascular pO2 dissociation during 4-h hemorrhagic shock in conscious hamsters. Am. J. Physiol.270(Heart. Circ. Physiol.39):H827-H836, 1996.

12. Is blood a good plasma expander? • 50% hemorrhage for 1 hour • 25% volume resuscitation with normal blood or blood saturated with carbon monoxide

13. Shock resuscitation, CO-RBCs vs. RBCsFunctional capillary density Cabrales, P., Tsai, A.G. and M. Intaglietta.Hemorrhagic shock resuscitation with carbon monoxide saturated blood. Resuscitation72:306-318, 2007.

14. Why going beyond conventional plasma expanders? Functional capillary density in extreme hemodilution Larger molecules

15. Modification Modification Crosslinked Crosslinked Polymerized Polymerized PEG PEG Radius, nm Radius, nm 2.7 2.7 4.9 4.9 14.1 14.1 MW, MW, kDa kDa 68.8 68.8 159.7 159.7 123.4 123.4 Viscosity, cp Viscosity, cp 1.00 1.00 1.36 1.36 3 3 Volume, nm Volume, nm 860 860 4,000 4,000 93,150 93,150 m m - - 1 1 - - 1 1 31 31 ± ± 12 12 31 31 ± ± 14 14 30±10 30±10 NO NO K’ K’ , , M M s s ox ox Albumin vs. polyethylene glycol conjugated albumin Albumin Peg-Albumin Radius, nm 2.5 14.0 MW, kDa 69 124

16. Shock resuscitation, HES vs. PEG-Alb PEG-Alb 12 PEG 5 kDa copies/molecule HES: Pentastarch, MW average 264 kDa, MW number average 63 kDa The “golden” 10 minutes Cabrales, P., Nacharaju, P., Manjula, B.N., Tsai, A.G., Acharya, S.A. and M. Intaglietta. “Early differences in tissue pH and microvascular hemodynamics in hemorrhagic shock resuscitation using polyethylene glycol-albumin and hydroxyethyl starch-based plasma expanders”. Shock 24:66-73, 2005.

17. Alginate Brown seaweeds (Phaeophyceae, mainly Laminaria) Linear unbranched polymers Guluronic acid (G) / Mannuronic acid (M) Molecular weights (500 – 10000 kDa)

18. Functional capillary densityHyperviscous vs. hypertonic resuscitation H+alginate, 0.8% H+alginate, 0.7% Shock Resuscitation H+HES 200, 5% H = NaCl, 7.5% NR-SHAM Time, min Cabrales, P., Tsai, A.G., and M. Intaglietta. Hyperosmotic-hyperoncotic vs. hyperosmotic-hyperviscous small volume resuscitation in hemorrhagic shock. Shock22:431-437, 2004. †, A0.7% vs HES 5%; ‡, A0.8% vs. HES 5% (P<0.05).

19. What is happening?

20. Hemodilution with Dextran 70 kDa & 500 kDa High viscosity plasma 2.2 cP (Final hematocrit: 11%) Low viscosity plasma 1.4 cP Tsai, A.G., Friesenecker, B., McCarthy, M., Sakai, H. and M. Intaglietta. Plasma viscosity regulates capillary perfusion during during extreme hemodilution in hamster skin fold model. Am. J. Physiol. 275:(Heart. Circ. Physiol. 44):H2170-H2180, 1998.

21. Capillary pressure and FCD in extreme hemodilution Cabrales, P., Tsai, A.G., Winslow, R.M. and M. Intaglietta. Effects of extreme hemodilution with hemoglobin-based O2 carriers on microvascular pressure. Am. J. Physiol. Heart Circ. Physiol. 288:H2146-H2153, 2005.

22. Extreme shock modelComparison of PEG-Alb (4%) and Voluven • 50% (blood volume) exchange transfusion to simulate preoperative hemodilution. • 60% (blood volume) hemorrhage to reproduce a severe surgical bleed over a one hr period.

23. Extreme shock modelComparison of PEG-Alb (4%) and Voluven

24. Extreme shock modelComparison of PEG-Alb (4%) and Voluven Martini, J., Cabrales, P., K, A., Acharya, S.A., Intaglietta, M. and A.G. Tsai. Survival time in severe hemorrhagic shock after perioperiative hemodilution scenario with polyethylene glycol conjugated human serum albumin is longer than with HES 130/0.4: a microvascular perspective. Crit. Care12:R54, 2008.

25. Plasma expansion: The initial limiting factor • Plasma expanders directly affect microvascular function (FCD) & outcome. • Blood is a good plasma expander due its viscogenic properties. • Large, viscous semi-colloids are microvascular function enhancers, compensating for lowered oxygen carrying capacity.

26. Conclusions • Plasma expanders directly affect microvascular function & outcome. • Blood is a good plasma expander due its viscogenic properties. • Large, viscous semi-colloids are microvascular function enhancers, compensating for lowered oxygen carrying capacity.

27. NO measurements

28. Perivascular nitric oxideExtreme hemodilution, Hct 11% Tsai, A.G., Acero, C., Nance, P.R., Cabrales, P., Frangos, J.A., Buerk, D.G. and M.Intaglietta. Elevated plasma viscosity in extreme hemodilution increases perivascular nitric oxide concentration and microvascular perfusion. Am. J. Physiol. Heart Circ. Physiol. 288:H1730-H1739, 2005.

29. Shock resuscitation: effect of plasma viscosity

30. Conclusions • Optimal plasma expansion improves FCD reducing the need for O2 carrying capacity • Oxygen is not the only gas to be transported • We do not know the lower limit of O2 carrying capacity in the light of optimal plasma expansion. • A few red cells may do everything with optimal plasma expansion. A little extra O2 may help

31. Why functional capillary density (FCD)?

32. Mechanism?

33. Extreme hemodilution (Hct = 11%) Colloidal plasma expanders of different viscosityDex 70 (6%) = 2.7 cP; Dex 500 (6%) = 5.9 cp; Alginate (0.7%) + Dex 70 (4%) = 8.8 cP Plasma viscosity, cP 1.4 2.1 2.7 Blood viscosity, cP 2.1 2.9 3.9 Cabrales, P., Tsai, A.G. and M. Intaglietta. Alginate plasma expander maintains perfusion and plasma viscosity during extreme hemodilution. Am. J. Physiol. Heart Circ. Physiol.288: H1708-H1716, 2005.

34. Does increasing oxygen carrying capacity with hemoglobin based blood substitutes help?

35. Shock resuscitation: effect of plasma viscosity Salazar Vázquez, B.Y., Wettstein, R., Cabrales, P., Tsai, A.G. and M. Intaglietta. Microvascular experimental evidence on the relative significance of restoring oxygen carrying capacity vs.blood viscosity in shock resuscitation”. Biochim. Biophys. Acta 1784:1421-1427, 2008.