Oxygen-carrying fluids

One of the most important functions of blood is the binding of oxygen by haemoglobin and its transport to the tissues. Administration of blood and blood products, however, carries with it a number of risks (Table 20.3) and are not always the initial choice to replace blood or plasma loss. Blood and blood products are also expensive, have a limited availability, and a very limited shelf life. A number of alternative oxygen-carrying fluids have been developed, and some are close to release for clinical use. 

Therapeutic intravenous (TV) fluids include crystalloid solutions, colloidal solutions, and oxygen-carrying resuscitation solutions. Crystalloids are composed of water and electrolytes, all of which pass freely through semipermeable membranes and remain in the intravascular space for shorter periods of time. As such, these solutions are very useful for correcting electrolyte imbalances but result in smaller hemodynamic changes for a given unit of volume. 

Rudolph AS, Cliff RO, Klipper R, et al. Circulation persistence and biodistribution of lyophilized liposome-encapsulated hemoglobin an oxygen-carrying resuscitative fluid. Crit Care Med 1994 22 142. 

The oxygen-carrying capacity of the hemoglobin in your hlood and the activity of the enzymes in your cells are very sensitive to the pH of your hody fluids. Our bodies use a combination of compounds known as a bujfer system to keep the pH within a narrow range. 

In patients with significant blood loss, blood transfusion may be indicated. This is generally in the form of packed red blood cells. The criteria for blood transfusion are controversial, but a hematocrit of 25% generally is accepted. In the individual patient, the decision is often determined by the overall chnical status and the ability of the patient to compensate for the reduction in oxygen-carrying capacity associated with an acute anemia. Additional blood component therapy with fresh frozen plasma or platelets is also based on the needs of the individual patient. Aggressive fluid therapy often must be continued in the postoperative period because fluid will continue to sequester in the peritoneal cavity, bowel wall, and lumen. 

The interior of a red cell is a concentrated solution of hemoglobin, the oxygen-carrying protein, and it behaves as a Newtonian fluid [Cokelet and Meiselman, 1968]. In a normal population of cells there is a distribution of hemoglobin concentrations in the range 29 to 39 g/dl. The viscosity of the cytosol depends... 

In laboratory reactions, in industrial processes, and in the bodies of plants and animals, it is often necessary to keep the pH nearly constant despite the addition of acids or bases. The oxygen-carrying capacity of the hemoglobin in your blood and the activity of the enzymes in your cells are very sensitive to the pH of your body fluids. A change in blood pH of 0.5 units (a change in [H3O+] by a factor of about 3) can be fatal. Our bodies use a combination of compounds known as a buffer system to keep the pH within a narrow range. 

---