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Departments of *Anesthesiology and
Vascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio;
Department of Anesthesiology, University of Kansas Medical Center, Kansas City, Kansas;
Department of Anesthesiology, University of Michigan Medical Center, Ann Arbor, Michigan; ||Department of Anesthesiology, Emory University Hospital, Atlanta, Georgia; ¶Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri; and #Department of Surgery, Morristown Memorial Hospital, Morristown, and University of Medicine and Dentistry of New Jersey, Newark, New Jersey
Address correspondence and reprint requests to Juraj Sprung, MD, PhD, Department of Anesthesiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905.
| Abstract |
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IMPLICATIONS: The intraoperative use of hemoglobin glutamer-250 (bovine) (HBOC-201, Hemopure®) was generally well tolerated. The administration of HBOC-201 was associated with a delayed increase in the plasma methemoglobin concentrations.
| Introduction |
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Hemoglobin glutamer-250 (bovine) (hemoglobin-based oxygen carrier-201 [HBOC-201], Hemopure®; Biopure Corporation, Cambridge, MA) is an ultrapurified, glutaraldehyde-polymerized, bovine hemoglobin in a balanced electrolyte solution. The bovine hemoglobin in HBOC-201 has a molecular structure similar to that of human hemoglobin. The oxygen affinity is independent of 2,3-diphosphoglycerate, is not affected by storage, and is regulated by chloride ion (11,12). The P50 of HBOC-201 is between 36 and 38 mm Hg. Finally, HBOC-201 transports oxygen in the plasma phase of blood more efficiently than intracellular hemoglobin in erythrocytes, on the basis of enhanced oxygen on-loading and off-loading (13). These properties suggest a great potential of HBOC-201 as an oxygen carrier in surgical procedures that conventionally require blood transfusion.
In the present randomized, placebo-controlled trial, we evaluated the tolerability of HBOC-201 administered to surgical patients.
| Materials and Methods |
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Of the 81 patients enrolled in the study, 26 were randomly assigned to the LR group and 55 to the HBOC-201 group (the study protocol was to enroll the patients in an approximately 2:1 ratio between HBOC-201 and LR). All patients in the HBOC-201 group received the 5-mL test dose. However, 1 patient had an adverse reaction to the test dose and 12 patients had insufficient intraoperative blood loss; therefore, they were excluded from further analysis, and 42 patients received the entire planned single-dose infusion of HBOC-201. One patient was reported previously (14).
Measurements and observations were made at 5 time points: 1) screening was done before or immediately after hospital admission, 2) the baseline period extended from screening until immediately before administration of the test dose of HBOC-201 or LR, 3) the perioperative treatment period began with the administration of the test dose and continued until 24 h after the start of the infusion of HBOC-201 or LR, 4) the postinfusion period extended from 24 h after the start of infusion through Day 7 or until hospital discharge, whichever occurred first, and 5) outpatient follow-up took place approximately 3 to 4 wk after surgery.
All adverse events were recorded. Each occurrence was analyzed with respect to association with clinical trial material. Throughout the study, we recorded the number of blood units given (autologous and allogeneic); total and plasma-free hemoglobin concentrations; methemoglobin concentrations; hematocrit (direct, spun method); reticulocyte count; erythropoietin and plasma iron levels; hemodynamic variables (blood pressure, heart rate); platelet count; fibrinogen levels; activated partial thromboplastin time, prothrombin time, alanine aminotransferase, aspartate aminotransferase, lipase, bilirubin (total, direct, and indirect), creatinine, blood urea nitrogen, and alkaline phosphatase values; serum electrolytes and glucose concentrations; and urinalysis findings. The length of hospitalization was calculated from the end of surgery to the day of discharge from the hospital.
Fifty-nine patients in this study were evaluated for immunoglobulin (Ig)G and IgE antibodies to HBOC-201 (IgG-aHBOC-201 and IgE-aHBOC-201, respectively); 19 were in the LR group and 40 in the HBOC-201 group. For each patient, a serum sample was collected at baseline and a second sample at least 2 wk after infusion of either LR or HBOC-201.
All of the randomized patients who received the full dose of HBOC-201 and all of the patients in the LR group were included in the analyses. The Mann-Whitney test or unpaired two-tail t-test was used for comparisons between the two means, as appropriate, and repeated analysis of variance with the Bonferroni test was used for multiple comparisons. The Fishers exact test was used to test for differences in the distribution of categorical outcomes between groups. Values were expressed as means plus or minus standard deviation (±SD) or as medians and range, as appropriate. Statistical tests were two-sided, with the null hypothesis rejected at P
0.05.
| Results |
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Minor Dermatologic Adverse Events
Six patients (11%) in the HBOC-201 group had dermatologic manifestations: 4 patients had skin (whole body) yellow discoloration (jaundice without an increase in serum bilirubin concentrations), and 2 had ecchymotic rash involving the areas underlying removed adhesives and sites of preoperative shaving. All dermatologic manifestations occurred in patients who received HBOC-201 in a dose of either 2.0 or 2.5 g/kg. No dermatologic adverse events occurred in the LR group.
Antibody Analysis
In the LR group, no patients were positive for IgG-aHBOC-201 or IgE-aHBOC-201 at baseline, and 2 patients (10.5%) had equivocal IgG-aHBOC-201 findings at follow-up (slight signal at the limit of detection of the assay). One patient with a history of mastocytosis was entered into the study. Just before the administration of the HBOC-201 test dose, the patient was given morphine. This patient then experienced immediate hypotension and diaphoresis, which resolved with fluids, ephedrine, phenylephrine, and diphenhydramine. After the event, the patients serum tryptase concentration was 6.3 ng/mL (normal, <1.0 ng/mL), a confirmation of mast cell degranulation.
The patients in the HBOC-201 group who received the full HBOC-201 treatment were either negative (38 patients) or slightly positive (2 patients) for IgG-aHBOC-201 at baseline, and all patients were negative at both baseline and follow-up for IgE-aHBOC-201. At follow-up, 23 patients in this group (57.5%) had specific IgG-aHBOC-201 responses that were not associated with rash, itching, or flushing. Of these patients, 4 (17%) had maximal antibody concentrations of <1.5 kilo arbitrary units (kAU)/mL, which is close to the limit of detection of the assay; 12 had peak titers between 1.2 and 10 kAU/mL; and 7 had IgG-aHBOC-201 concentrations of >10 kAU/mL. The highest measured IgG-aHBOC-201 titer was 92 kAU/mL, and no hypersensitivity manifestations were recorded in this patient.
Hemoglobin and Other Blood-Related Measurements
Total hemoglobin concentration comprises the red blood cell hemoglobin content and the plasma hemoglobin, which in this study reflects the presence of HBOC-201. In both groups, hemoglobin concentrations decreased postoperatively and returned toward baseline values by the day of outpatient follow-up. There was no difference between the two groups in the total hemoglobin concentrations measured at any time (Fig. 1A).
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As expected, plasma hemoglobin levels were negligible in patients in both groups at baseline and at all measured times for patients in the LR group (Table 3). In the HBOC-201 group, plasma hemoglobin levels increased in a dose-dependent manner after the administration of HBOC-201 and decreased postoperatively but were still more than baseline values at POD 2 and POD 3 (both, P < 0.001) (Fig. 2). By POD 7 or discharge, plasma hemoglobin concentrations in the HBOC-201 subgroups were at baseline levels in the patients who received HBOC-201 in a dose
1.5 g/kg (baseline versus POD 7, P > 0.67) and more than baseline in those who received
2.0 g/kg (P < 0.001). Postoperatively, the percent of plasma methemoglobin increased in the HBOC-201 group and remained low in the patients who received LR. Although the percent of methemoglobin increased only slightly immediately after HBOC-201 infusion, the percent continued to increase during the postoperative period and peaked at POD 3 (mean maximum for all HBOC-201 patients was 3.7%) (Table 3). Figure 2 shows plasma hemoglobin (panel A) and methemoglobin (panel B) in 6 HBOC-201 treatment subgroups. It is evident that methemoglobin concentrations were larger in subgroups who received larger doses of HBOC-201.
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Platelet Counts and Other Coagulation Measurements
Platelet counts, fibrinogen, activated partial thromboplastin time, and prothrombin time values were not different in the two groups before and after the treatment.
Clinical Blood Chemistry and Urinalysis
No statistically significant differences between the two groups were reported for alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, lipase, bilirubin (total, direct, indirect), or creatinine (Table 4). Blood urea nitrogen concentration was mildly increased in the HBOC-201 group on POD 2 and POD 3 (P < 0.05), but because these increases were within normal limits, this finding had no clinical significance. Serum sodium, potassium, chloride, calcium, and glucose values were not different between the two groups at any measured time. There were isolated transient increases in some blood chemistry values, but they were not considered related to exposure to either HBOC-201 or LR. In one patient who received HBOC-201 in a dose of 2 g/kg and underwent reconstruction of an abdominal aortic aneurysm (and superior mesenteric artery), the following enzyme levels were increased: alanine aminotransferase 2382 U/L (POD 2) and 3802 U/L (POD 3); aspartate aminotransferase 3049 U/L (POD 2) and 6979 U/L (POD 3); lipase 1368 U/L (POD 2) and 576 U/L (POD 3); and lactate dehydrogenase
21,500 U/L (both days). All values returned to normal levels before discharge from the hospital, and the patient experienced no other complications. Another patient (who received HBOC-201 in a dose of 0.9 g/kg) had a history of congestive heart failure and underwent hip replacement; his serum lipase concentration increased on POD 2 (406 U/L) and returned to normal on POD 3. Hemoglobin was not detected in the urine of patients who received HBOC-201.
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| Discussion |
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Our study, limited to 42 patients, demonstrated that HBOC-201 was well tolerated even when administered in doses up to 245 g. However, it needs to be stressed that only 6 patients received this large (2.5 g/kg) HBOC-201 dose. Preclinical and clinical pharmacologic data indicated that positive effects on oxygen transport physiology could be achieved with HBOC-201 doses that result in plasma hemoglobin concentrations >0.7 g/dL (22,23). The doses selected for this trial were capable of exceeding such levels for approximately 48 to 72 hours (Fig. 2).
No patient deaths occurred during the study. Most of the adverse reactions were not associated with exposure to HBOC-201 or LR but instead represented possible complications of surgical procedures or underlying disease. Several patients had transient dermatologic changes, and 1 patient with a history of mastocytosis experienced mast cell degranulation after the administration of morphine, a known mast cell degranulator, as well as a test dose of HBOC-201. The complex immune status of mastocytosis patients complicates interpretation of this event. However, we do not know whether IgG-aHBOC-201, which developed in 57.5% of the patients who received HBOC-201, has any potential clinical implications for later repeated use of HBOC-201.
One patient who underwent reconstruction of the aortic and mesenteric arteries and received HBOC-201 (2.0 g/kg) had a large and transient increase in serum transaminases. This clinical picture may represent "acute ischemic hepatitis," which has been described in conjunction with aortic surgery and attributed to splanchnic ischemia (24). It is difficult to associate HBOC-201 administration and this previously described condition. All other blood chemistry values were not statistically significantly different between the two treatment groups. Lee et al. (17) demonstrated that the administration of an early, partially polymerized formulation of bovine hemoglobin (stored frozen) in large doses to rats may induce mild, reversible renal toxicity. The postulated nephrotoxic particles are dimers, products of oxidative inactivation of the chains of unmodified hemoglobin. In our study, creatinine values were not different between the two patient groups; therefore, the previous fear of acute renal failure with acellular hemoglobin solutions may be unfounded for the doses of HBOC-201 used in the present study. In a recent study by LaMuraglia et al. (25), increases in serum creatinine in patients receiving HBOC-201 and LR were similar (average increases, 0.41 and 0.28 in the HBOC-201 and LR groups, respectively; difference not significant). These mild creatinine increases might be attributable to aortic aneurysm reconstruction, which is sometimes associated with alteration of kidney function. However, LaMuraglia et al. (25) found that blood urea nitrogen values significantly increased in patients receiving HBOC-201, presumably because of the HBOC-201-associated high protein load. The absence of hemoglobin in the urine in our study further indicates that HBOC-201 is not eliminated by the kidneys. In fact, primary excretion of HBOC-201 occurs through metabolism in the liver and reticuloendothelial system (21).
Transient skin discoloration occurred rarely and only after the administration of HBOC-201 at larger doses. Possibly, this benign dermatologic effect results from dose-dependent HBOC-201 extravasation into the areas injured by manipulation (shaving, adhesive tapes), because similar occurrences were not reported with exposure to LR solution. Furthermore, neither occasional skin discoloration nor discoloration of serum by HBOC-201 caused problems with pulse oximetry monitoring. The unimpeded ability to monitor pulse oximetry with HBOC-201 in the serum was confirmed previously by Hughes et al. (19).
Circulating methemoglobin in healthy humans is the result of a balance between methemoglobin production (from auto-oxidation and oxidation) and hemoglobin reduction. Methemoglobin, an oxidized form of hemoglobin, is unable to bind oxygen and therefore effectively decreases the oxygen-carrying capacity of hemoglobin. Because enzymes within intact erythrocytes maintain hemoglobin in a reduced state, methemoglobinemia is a concern whenever acellular hemoglobin solutions are given. Mild methemoglobinemia has been described in patients receiving bovine hemoglobin solutions (26). In the present study, the administration of HBOC-201 was followed by an increase in the percent of plasma methemoglobin. Interestingly, the percent of methemoglobin was not high immediately after HBOC-201 infusion but rather had a delayed onset and reached maximal value (mean of all study groups, 3.66%) by POD 3 (Table 3). However, in patients who received the 2.5 g/kg dose of HBOC-201, the mean methemoglobin concentration was 7.1% (Fig. 2). OHara et al. (27) demonstrated a somewhat shorter delay, 8 to 12 hours, in maximal methemoglobin concentrations after the infusion of diaspirin cross-linked human hemoglobin. This result indicated that the methemoglobin load was not administered with HBOC-201 but rather was gradually generated by oxidation of plasma hemoglobin. Linberg et al. (28) found that methemoglobin levels below 10% did not significantly alter the delivery of oxygen to organs; consequently, the levels measured in our study probably have little clinical significance. However, the delayed onset of methemoglobinemia coincident with declining concentrations of plasma hemoglobin resulting from the short half-life of HBOC-201 also might decrease the blood oxygen-carrying capacity. The sum of these unwanted effects needs to be closely monitored in patients who are receiving large doses of HBOC-201.
LaMuraglia et al. (25) found small increases in systemic blood pressure in patients who underwent aortic surgery and received HBOC-201. Similarly, in our study, we observed slightly increased blood pressure readings at the end of surgery and the time of discharge from the recovery room in patients who received HBOC-201 (Table 5). This increase was not considered clinically significant, and the mechanism remains obscure. Although nitric oxide binding by the hemoglobin was postulated to be a mechanism of the increase in blood pressure, several recent investigations found that products exhibiting the greatest nitric oxide affinity resulted in the least increase in blood pressure (29). Therefore, another unidentified mechanism may be responsible for the changes in blood pressure occasionally seen after the administration of acellular hemoglobin solutions. It is possible that the improved hemodynamics after HBOC-201 administration are attributable to high intravascular expanding properties of HBOC-201 based on its high colloid-oncotic properties.
There was no difference in estimated blood loss between the two groups, and total hemoglobin concentrations were not different at any measured points between the patients receiving HBOC-201 and those receiving LR. However, the disproportionally large total hemoglobin concentration in relation to the hematocrit on POD 2 in the HBOC-201 group (Fig. 1) may be consistent with one of the following: 1. Patients who received HBOC-201 had more bleeding (lower hematocrit), and the addition of polymerized hemoglobin in the HBOC-201 group may have served to equalize the total hemoglobin levels between the two groups. 2. Patients who received HBOC-201 experienced better intravascular volume expansion than the patients receiving LR. HBOC-201 has high colloid-oncotic pressure (17 mm Hg), which can attract fluid from the interstitial space and lead to a dilutional decrease in hematocrit.
Our study did not show that the use of HBOC-201 reduced the use of blood during the entire hospitalization, primarily, we believe, because of the study design, that is, relatively small single doses in some patients and restriction of the consecutive administration of HBOC-201 when oxygen-carrying capacity was needed postoperatively. The results of another recently published multicenter study demonstrated that HBOC-201 decreased the intraoperative requirements for allogeneic blood transfusion during aortic reconstructive surgery (25). That protocol, the same as ours, did not allow additional HBOC-201 infusion, which resulted in an increased requirement for allogeneic blood transfusion later during the hospitalization. The ultimate result was that the HBOC-201 did not reduce the median allogeneic blood requirements (25).
In conclusion, the intraoperative administration of HBOC-201 to our patients undergoing surgery was generally well tolerated, and even the dose-dependent methemoglobinemia, which reached maximal values by POD 3, did not have a clinically significant impact. The administration of a single dose of HBOC-201 also did not reduce the intraoperative allogeneic blood requirements.
| Acknowledgments |
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| Footnotes |
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TGM is presently affiliated with the University of Florida College of Medicine, Gainesville, FL.
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