Steven A. Gould

Fluosol-DA as a red-cell substitute in acute anemia.

Abstract We assessed the safety and efficacy of Fluosol-DA as a red-cell substitute in acute anemia. Twenty-three surgical patients with blood loss and religious objections to receiving blood transfusions were evaluated. Fifteen moderately anemic patients with a mean hemoglobin level (±SE) of 7.2±0.5 g per deciliter had no evidence of a physiologic need for increased arterial oxygen content and did not receive Fluosol-DA. Eight severely anemic patients with a mean hemoglobin level of 3.0±0.4 g per deciliter met the criteria of need and received the drug until the physiologic need disappeared or a maximal dose of 40 ml per kilogram of body weight was reached. We observed no adverse reactions to Fluosol-DA. The average peak increment in arterial oxygen content with the drug was only 0.7±0.1 ml per deciliter. There were no appreciable beneficial effects of Fluosol-DA, perhaps because of the small increase in arterial oxygen content, the brief half-life of the drug (24.3±4.3 hours), and the limited total dose...

Clinical utility of human polymerized hemoglobin as a blood substitute after acute trauma and urgent surgery.

We have previously documented the safety of 1 unit (50 gram) of human polymerized hemoglobin (Poly SFH-P) in healthy volunteers. This report describes the first patient trial to assess the therapeutic benefit of Poly SFH-P in acute blood loss. Thirty-nine patients received 1 (n = 14), 2 (n = 2), 3 (n = 15), or 6 (n = 8) units of Poly SFH-P instead of red cells as part of their blood replacement after trauma and urgent surgery. There were no safety issues related to the infusion of Poly SFH-P. The plasma hemoglobin concentration ([Hb]) after the infusion of 6 units (300 gram) of Poly SFH-P was 4.8 +/- 0.8 g/dL (mean +/- SD). Although the red cell [Hb] fell to 2.9 +/- 1.2 g/dL, the total [Hb] was maintained at 7.5 +/- 1.2 g/dL. Poly SFH-P maintained total [Hb], despite the marked fall in red cell [Hb] due to blood loss. The utilization of O2 (extraction ratio) was 27 +/- 16% from the red cells and 37 +/- 13% from the Poly SFH-P. Twenty-three patients (59%) avoided allogeneic transfusions during the first 24 hours after blood loss. Poly SFH-P effectively loads and unloads O2 and maintains total hemoglobin in lieu of red cells after acute blood loss, thereby reducing allogeneic transfusions. Poly SFH-P seems to be a clinically useful blood substitute.

Clinical Development of Human Polymerized Hemoglobin as a Blood Substitute

Abstract. Although the efficacy of hemoglobin-based oxygen carriers was established more than 60 years ago, all prior clinical trials have demonstrated significant toxicity characterized by renal dysfunction, gastrointestinal distress, and systemic vasoconstriction. The mechanisms of these toxicities now appear to be understood. Tetrameric forms of the hemoglobin molecule extravasate from the circulation and interact with endothelium-derived relaxing factor, leading to unopposed vasoconstriction. Although numerous efforts are under way to chemically modify the native tetramer, it is likely that all tetrameric forms of the hemoglobin molecule will continue to extravasate. We have focused on developing a polymerized form of hemoglobin that is virtually free of unreacted tetramer. The development and characterization of this polymerized pyridoxylated hemoglobin solution (Poly SFH-P) is described. Clinical trials have been completed successfully in volunteers and are now under way to assess the safety and efficacy of Poly SFH-P as a clinically useful red blood cell substitute for treatment of acute blood loss in the setting of trauma and surgery.

Preparation and in vitro characteristics of polymerized pyridoxylated hemoglobin

Stroma‐free hemoglobin solutions have been the subject of extensive studies as potential acellular oxygen carriers. Oncotic pressure considerations limit the hemoglobin concentration of the solutions (6–8 g/dl) to one‐half the normal whole blood values. Furthermore, the free hemoglobin has a short plasma half‐life (2–4 hours). In principle, polymerization offers a means of normalizing the oxygen‐carrying capacity as well as extending the plasma half‐life. Pyridoxylation of hemoglobin prior to polymerization provides an acceptable P50. Pyridoxylated hemoglobin (14–16 g/dl) was polymerized with a 12.5 percent glutaraldehyde solution. Since the goal was to obtain a 15 g per dl solution iso‐oncotic with plasma, the polymerization reaction was monitored by the drop in colloid osmotic pressure. The reaction was quenched with 1.3 M lysine when the colloid osmotic pressure reached normal values (20–25 torr). The polymerization yield was 80 percent, with molecular weights ranging from 120,000 to 600,000 Dalton. The polymerized hemoglobin had a binding coefficient of 1.32, a Pso of 16 torr, a Bohr coefficient of –0.12, and a Hill coefficient of 1.7. The viscosity of the solution was 4.5 centipoise. The methemoglobin levels were comparable to that of unpolymerized stroma‐free hemoglobin. Polymerized hemoglobin solutions provide a normal oxygen‐carrying capacity with a P50 comparable to that of unpolymerized stroma‐free hemoglobin solutions.

Physiologic effects of acute anemia : implications for a reduced transfusion trigger

The risks of transfusion‐associated infectious disease have led to a reassessment of transfusion practice, which in turn has resulted in a trend toward the reduction of homologous transfusion. This reduction is primarily due to the initiation of hemotherapy at more severe levels of anemia. The optimum threshold for the initiation of transfusion therapy, or the transfusion trigger (TT), is unknown. The purpose of this study is to evaluate the effects of withholding transfusion or lowering the TT to a hematocrit (Hct) of 15 percent in unanesthetized animals. Nineteen adult baboons underwent a laparotomy to simulate surgical stress. Upon their recovery from anesthesia, hemodynamic measurements were obtained, and the animals underwent an exchange transfusion (ET) with 6‐percent hetastarch to a final Hct of 15 percent. After ET, hemodynamic measurements were repeated, and the animals were followed for 2 months. There was no morbidity after ET or during the 2‐month observation period. After ET, there was a significant increase in both the cardiac output (3.3 vs. 2.5 L/min, p less than 0.001) and the oxygen extraction ratio (59.9 vs. 38.2%, p less than 0.0001). Oxygen delivery fell after ET (18.9 vs. 11.1 cc/kg/min, p less than 0.001), but there was no significant change in oxygen consumption after ET. The unanesthetized animals adapted well to severe anemia and experienced no adverse effects on their long‐term survival in this setting, which suggests that the reduction of the TT to a Hct of 15 percent in normal animals is safe. Adoption of this TT could result in a significant reduction in the requirements for homologous transfusion with its attendant risks.

Oxygen extraction ratio: a valid indicator of myocardial metabolism in anemia.

We have shown that primates adequately compensate for acute normovolemic anemia to hematocrits (HCT) of 10%. We have described a whole-body extraction ratio (O2 consumption/O2 delivery; ER) of 50% as a reliable physiologic indicator of transfusion need. There is concern that whole-body ER may not accurately reflect impaired myocardial metabolism. The onset of significant lactate production by the left ventricle is an indicator of anaerobic metabolism. Our purpose is to compare left ventricular lactate metabolism (arterial-coronary sinus lactate; delta [L]) to ER in acute normovolemic anemia. Fourteen adult baboons were anesthetized, paralyzed, and ventilated on room air. Left atrial, coronary sinus, aortic, and Swan-Ganz catheters were inserted. Experimental animals (N = 7) were hemodiluted, at constant left atrial pressure (LAP), with 5% human serum albumin (HSA) to a HCT below 4%. Control animals (N = 7) underwent similar volume exchanges, also at constant LAP, with homologous RBCs resuspended in HSA. Whole-body extraction ratio and left ventricular lactate production were measured at baseline and at hematocrits of 20, 10, 6, and 4% in the experimental group. Data were obtained at similar volume exchange points in the control group. Significant lactate production occurred only in the experimental animals (P less than 0.05) when extraction ratio exceeded 50%. Significant lactate production does not occur before the whole-body ER exceeds 50%. ER appears to be a valid indicator of myocardial metabolism in anemia, in this setting.

Acute dilutional anemia and critical left anterior descending coronary artery stenosis impairs end organ oxygen delivery

OBJECTIVE Limited cardiac reserve, secondary to coronary disease, may be associated with end organ morbidity. In this study, we investigate the significance of anemia in the pathogenesis of this phenomenon. DESIGN Nonrandomized controlled animal trial. SETTINGS Animal laboratory in a university hospital. SUBJECT Anesthetized dogs. INTERVENTIONS/MEASUREMENTS: Fourteen anesthetized dogs underwent isovolemic hemodilution with 6% hetastarch from a baseline hematocrit of 40 to 20%. Radioactive microspheres were used to evaluate regional blood flow and cardiac index. Systemic oxygen delivery, consumption, serum lactate, and systemic vascular resistance were recorded during each experiment. Arterial venous oxygen difference was determined from arterial and mixed venous blood. Seven dogs had an iatrogenic critical stenosis of their left anterior descending coronary artery (experimental group); seven dogs did not (control). MAIN RESULTS Only in the control animals, the cardiac index increased by 35% with hemodilution to 20%. Systemic oxygen delivery decreased in both the control and the experimental animals. Systemic oxygen consumption and lactate levels were unchanged in both groups. In the renal cortex, spleen, distal colon, ileum, gallbladder, and stomach body, regional O2 delivery was significantly decreased with hemodilution to 20% in both groups. This finding was also observed in the left ventricle and cervical spinal cord in the experimental group. In addition, regional O2 delivery was reduced in the spleen, distal colon, and gallbladder with hemodilution to only 30%. Regional blood flow in the stomach body, gallbladder, ileum, renal cortex, and distal colon, in both groups, and the spleen in the control group was unchanged from baseline with hemodilution to 20%. However, regional blood flow under all other circumstances (control or experimental) was significantly increased with hemodilution to 20% with the exception of the spleen, which showed significant regional blood flow decrease in the experimental group only. CONCLUSIONS These data suggest that with limited cardiac reserve, anemia may compromise aerobic splanchnic circulation. These observations may further our understanding of the pathogenesis of cholecystitis, gastric stress ulcers, ileal endotoxin translocation, and ischemic colitis in critically ill patients with coronary artery disease.

Large-volume preparation of pyridoxylated hemoglobin with high P50☆☆☆

A technique is described for the preparation of a stroma-free pyridoxylated hemoglobin solution in volumes of up to 20 liters and hemoglobin concentrations of 18–20 g%. The methemoglobin concentration is 3–7%; the phospholipid content is 5–10% of lysate; and normal values for prothrombin time and activated partial thromboplastin time are obtained. Electrophoresis on cellulose acetate strips shows that 70% of the hemoglobin is covalently linked to pyridoxal-5′-phosphate. This proportion can be raised to greater than 85% (PLP fraction) by batch purification with DEAE-Sephadex. The final solution has an in vitroP50 of 22–26 mm Hg (pH = 7.40, pCO2 = 40 mm Hg, temperature = 37°C). Both the proportion of pyridoxylated to unmodified hemoglobin and the P50 remain unchanged throughout the course of total exchange transfusion in the baboon.

Plasma expanders: An update

This review of the literature has revealed that isotonic fluids, such as 0.9 percent sodium chloride and Ringers lactate, are effective plasma volume expanders. Despite the continued use of a variety of colloid solutions in resuscitation, there is no good evidence to document a benefit of these solutions over the crystalloid solutions. The additional cost of colloid compared with crystalloid is another argument against colloid use. The most interesting solution currently being assessed is hypertonic saline solution. Its major benefit is that a small volume of fluid can achieve effective resuscitation. The smaller weight gain and lower incidence of peripheral edema may also prove to be significant benefits. Further evaluations are needed to verify the efficacy of this therapy. Finally, a recent National Institute of Health consensus panel identified the appropriate indications for fresh frozen plasma. They concluded that there is no indication for the use of fresh frozen plasma as a volume expander.

Treatment of Acute Postoperative Anemia with Recombinant Human Erythropoietin

Risks inherent in the administration of blood products have increased efforts to avoid homologous transfusion. Although this has increased interest in autologous transfusion and intraoperative salvage, little attention has been focused on efforts to enhance endogenous erythropoiesis as a method of minimizing exposure to homologous blood. Recombinant human erythropoietin (rHuEPO) has been shown to enhance erythropoiesis. The purpose of this study is to evaluate the effect of rHuEPO, administered postoperatively, on a model of acute blood loss. Eleven adult male baboons were randomized into two groups. All animals underwent a laparotomy and an exchange transfusion, with 6% hetastarch, to a final hematocrit of 15%. Group I (N = 6) received 1,000 units/kg of recombinant human erythropoietin daily for the first 14 postoperative days. Group II (N = 5) received an equivalent volume of placebo. All animals were given supplemental vitamin B12, folate and 200% of shed iron, as iron dextran IV, after exchange transfusion. Response was observed for a period of 35 days. All animals survived the protocol. There were no adverse reactions to rHuEPO or surgical complications. The hematocrits were similar between groups at baseline and after exchange transfusion. The maximal rate of erythropoiesis was significantly faster in the rHuEPO group (2.1 vs. 1.3%/day; p less than 0.01). The time required to return to hematocrits of 30% (9.9 vs. 17.4 days, p less than 0.001) and to baseline hematocrits (11.9 vs. 32.1 days, p less than 0.01) were both significantly shorter in the rHuEPO group. The data show that rHuEPO accelerates the recovery from anemia in the postoperative setting. Acceleration of erythropoiesis represents another alternative to homologous transfusion.(ABSTRACT TRUNCATED AT 250 WORDS)