Abstract
The main objective of fluid resuscitation in hemorrhage induced hypovolemia is to increase oxygen delivery to vital organs and to restore other hemodynamic variables to acceptable physiological range. Since replacement of blood with fluid causes both increase in cardiac output and decrease in the plasma oxygen carrying unit concentration, there is an overall opposing effect on total oxygen delivery rate to tissue. Thus, optimal fluid infusion rate and volume may be expected. The purpose of this study was to study the temporal dynamics of oxygen delivery rate during fluid replacement in a controlled hemorrhage scenario and seek these optimal values. A hemodynamic model of the human adult cardiovascular system was developed to simulate and evaluate arterial oxygen delivery at normal and at hemorrhagic conditions in different fluid resuscitation regimes. The results demonstrated the existence of a unique optimal fluid replacement regimen for maximal oxygen delivery rate at different controlled bleeding scenarios. The maintenance of high oxygen delivery rate was better with lower fluid infusion rates. The model results indicate that hematocrit and mean arterial pressure can be used to determine the optimal infusion rate and fluid infusion endpoint in fluid resuscitation.
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No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Jamal Siam, Yossi Mandel and Ofer Barnea declare that they have no conflict of interest.
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Associate Editor Ajit P. Yoganathan oversaw the review of this article.
Jamal Siam and Yossi Mandel share equal contribution to the paper.
Appendix
Appendix
Fluid Exchange
The fluid exchange model assumes that the concentration of colloids in the interstitial space is constant (2%,2) and there is no escape of colloids from the intravascular compartment to the interstitial space; the model also ignores the lymph return. The plasma and RBCs volumes are computed separately. The plasma volume during hemorrhage is computed using Eq. (10) which takes into account the combined effect of the fluid loss through bleeding and the fluid exchange with interstitial space. In this equation Q bleed(t) is the volume bleeding rate which includes both the plasma and red blood cells losses. While the loss of RBCs is assumed to occur only during hemorrhage, HCT levels are affected both during hemorrhage and fluid resuscitation. The volume loss of red blood cells is computed using Eq. (11).
The blood oncotic pressure is assumed to change with the concentration of colloids according to Eq. (5). The change of blood proteins concentration during both hemorrhage and fluid resuscitation is assumed to be proportional to the value of HCT, it is computed by: \( C_{{{\text{col\_B}}}} (t) = C_{{{\text{col\_B\_norm}}}} .\frac{HCT\left( t \right)}{{HCT_{\text{norm}} }} \) (Eq. (12),1), where C col_B_norm = 7.3% and HCT norm = 44%. The total weight of blood proteins is computed by W prot_B(t) = C col_B(t)·V plasma(t).
During treatment with colloid fluids, the plasma colloids concentration is increased according to the fluid infusion rate. The weight of infused colloids is W col_B_inf(t) = C inf·V inf(t). The concentration of blood colloids, in the case of controlled hemorrhage and treatment with colloid fluids, is computed by: \( C_{{{\text{col}}\_{\text{B}}}} \left( t \right) = \frac{{W_{{{\text{prot}}\_{\text{B}}}} \left( t \right) + W_{{{\text{col}}\_{\text{B}}\_{ \inf }}} \left( t \right) }}{{V_{\text{plasma}} \left( t \right)}} \). In this expression V plasma(t) was computed by the integration of Eq. (12) which takes into account the combined effect of fluid infusion and exchange with the interstitial space.
Fluid exchange between the intravascular and interstitial compartments is computed as the net filtration of fluid at the arterial and venous ends of the capillary (Eq. (8)). The fluid is assumed to flow between the two compartments through a fluid exchange resistance \( R_{\text{exch}} = 25\;{\text{mmHg}}\;\text{s} /{\text{mL}} \).13 Which is taken as constant and equal for both capillary sides. The flow of fluid at each capillary side is composed of two components, the first component is proportional to the hydrostatic pressure difference, while the second component is proportional to the oncotic pressure difference between the intravascular and interstitial compartments (Eqs. (6) and (7)).
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Siam, J., Mandel, Y. & Barnea, O. Optimization of Oxygen Delivery in Fluid Resuscitation for Hemorrhagic Shock: A Computer Simulation Study. Cardiovasc Eng Tech 5, 82–95 (2014). https://doi.org/10.1007/s13239-013-0169-z
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DOI: https://doi.org/10.1007/s13239-013-0169-z