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*Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina;
Department of Anesthesiology, The Mount Sinai Medical Center, New York, New York; and Departments of
Haematology and
§Anaesthesia, University College London Hospitals, London, England
Address correspondence and reprint requests to T. J. Gan, MB, FRCA, Department of Anesthesiology, Duke University Medical Center, Box 3094, Durham, NC 27710. Address e-mail to gan00001{at}mc.duke.edu
| Abstract |
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Implications: Hextend® (BioTime, Inc., Berkeley, CA) is a new plasma volume expander containing 6% hetastarch, balanced electrolytes, a lactate buffer, and a physiological level of glucose. It is as effective as 6% hetastarch in saline for the treatment of hypovolemia but has a more favorable side effects profile in volumes of up to 5 L compared with 6% hetastarch in saline.
| Introduction |
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Hextend® (BioTime, Inc., Berkeley, CA), a new preparation of hydroxyethyl starch, is composed of 6% hetastarch (mean molecular weight 550 kD) in a solution of electrolytes (Na+, K+, Ca2+, Mg2+, Cl-), physiological levels of glucose (90 mg/dL), and a lactate buffer that is more likely to provide a more favorable acid-base balance. Preclinical use of Hextend® in shock models was associated with an improvement in outcome compared with alternatives such as albumin or lactated Ringer's solution (11). Recent in vitro studies of the effects of Hextend® in human plasma have shown that, at dilutions of up to 75% Hextend® and 25% human plasma, there were no adverse effects on hemostatic variables except those expected by hemodilution (12). Immediately before the main study, six patients received Hextend® in an open-labeled study. Volumes of up to 3000 mL (1385 ± 1116, mean ± SD) were infused with no adverse effects related to the study drug (13).
In a prospective, randomized, double-blinded trial, we tested the hypothesis that the intraoperative administration of Hextend® to patients undergoing major elective surgery is as safe and effective as 6% hetastarch in saline when used for the treatment of hypovolemia.
| Methods |
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Patients were premedicated with midazolam and fentanyl. Before the induction of anesthesia, an IV bolus of 7 mL/kg lactated Ringer's solution was administered, followed by an IV infusion of lactated Ringer's solution at a rate of 5 mL · kg-1 · h-1, which was continued for the duration of anesthesia. Anesthesia was induced by an IV technique and maintained with a balanced inhalational technique incorporating isoflurane, nitrous oxide, and oxygen with neuromuscular blockade supplied by IV vecuronium. Ventilation was adjusted to maintain PaCO2 at 3540 mm Hg, and temperature was maintained >35.5°C throughout surgery. If an epidural catheter was placed as part of the patient's postoperative care, a 3-mL test dose consisting of lidocaine 1.5% with 1:200,000 epinephrine was administered, and no epidural local anesthetic drugs were administered intraoperatively. Anesthesia was maintained at a constant level as judged by standard clinical criteria.
In addition to the standard monitoring, direct arterial and central venous pressures were also monitored. All cardiovascular variables and urine flow were monitored and recorded during general anesthesia. Postoperatively, heart rate (HR), blood pressure, and urinary volumes were recorded every hour for 4 h, then every 4 h until 24 h after surgery. Types and volumes of all fluids administered intra- and postoperatively (including but not limited to crystalloid solutions, blood, and blood products) were recorded, as were the volumes and doses of any drugs given during general anesthesia and an estimation of blood loss.
Laboratory tests including hematocrit, platelet count, serum electrolytes and creatinine, colloid oncotic pressure, coagulation tests (e.g., prothrombin time, activated partial thromboplastin time), Factor VIIIc, and von Willebrand factors were measured before induction, at the end of surgery, and on the day after surgery.
Patients at one center (DUMC) had a blood sample drawn before induction and at the end of the surgical procedure for thromboelastographic (TEG) analysis, which provides a bedside dynamic measure of clot formation and takes into account the presence of coagulation factors and cofactors (e.g., calcium) (14). Whole blood is placed in a cuvette, which is rotated back and forth. A piston is suspended in the blood, and as coagulation proceeds, fibrin strands form between the walls of the cuvette and the piston. The piston thus becomes increasingly coupled to the motion of the cuvette; hence, the shearing elasticity of the evolving blood clot is detected to yield the TEG trace. The TEG variables for patients receiving <20 mL/kg or
20 mL/kg of study solution are described in Figure 1.
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15 mm Hg, hypovolemia was a less likely cause of the abnormal hemodynamics; thus, consideration was given to further monitoring (i.e., inserting a pulmonary artery catheter) or circulatory support with vasoactive drugs. In addition, patients received 6% hetastarch in saline or Hextend® in volumes equivalent to that judged to be lost as a result of surgical hemorrhage. If the hematocrit was
21%, then blood was administered for the treatment of hypovolemia instead of 6% hetastarch in saline or Hextend®. However, the clinicians administered blood to a patient with a hematocrit >21% if clinically indicated; for example, if there was evidence of myocardial ischemia and anemia was thought to be a contributory cause.
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For the treatment of bleeding of a nonsurgical etiology, the protocol called for the administration of blood products (platelets, fresh-frozen plasma, cryoprecipitate, or fibrinogen) when clinically indicated and supported by the laboratory evidence of abnormal coagulation: platelet count <100,000/L, prothrombin time >1.5 times control, activated partial thrombin time >1.5 times control, and/or fibrinogen <100 mg/dL. Patients were extubated, either in the operating room or postoperatively, when they fulfilled standard clinical criteria. They were visited daily in the immediate postoperative period for a maximum of 5 days, until discharge or death. Patients who remained in the hospital for >5 days were visited again on the day of discharge. All adverse events and postoperative length of stay were recorded. In addition, adverse events were deemed coagulation-related if, in the judgement of the investigators, abnormal laboratory values were associated with a nonsurgical bleeding.
Data were analyzed to compare all patients in the protocol group with all patients in the control group on an intent to treat basis. The groups were compared using a t-test or Wilcoxon rank-sum test as appropriate. The volumes of IV colloid and calcium administered to the two groups were compared by using a one-way analysis of covariance adjusted for each patient's estimated blood loss. Incidence of adverse events and intraoperative calcium administration were compared using a two-tailed Fisher's exact test. A P value <0.05 was considered statistically significant.
For estimation of sample size, the total volume of colloid (Hextend® or 6% hetastarch in saline) administered by the end of surgery was taken as the primary outcome. Analysis of data from 207 patients undergoing similar types of surgery and anesthesia revealed a mean ± SD colloid equivalent volume transfused during surgery of 1821 ± 540 mL. A sample size of 60 in each group was calculated to have at least 80% power to detect a difference in means of 30% given a common standard deviation of 540 mL using a two-group t-test with a 0.05 two-sided significance.
| Results |
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20 mL/kg), this difference was more pronounced in the 6% hetastarch group (Figure 1). Other TEG variables were similar between the two groups. | Discussion |
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The administration of colloid as plasma volume expander during the intraoperative period may be associated with an improved outcome. Mythen and Webb (3) demonstrated a reduction in the incidence of major complications and hospital stay in elective cardiac surgery patients who received perioperative plasma volume expansion with colloid. Similar results were shown by Sinclair et al. (4), who studied the effect of fluid optimization with colloid in elderly patients undergoing repair of a proximal femoral fracture. There was a 39% reduction in hospital stay in the colloid treatment group.
Although 6% hetastarch in saline is effective in expanding plasma volume, its use has been associated with side effects, notably coagulation abnormalities, when large volumes are used (15,16). This prompted a labeling statement cautioning the use of >20 mL · kg-1 · d-1. In this study, 35% of patients in the 6% hetastarch group and 42% of patients in the Hextend® group received more than the 20-mL/kg recommendation.
Numerous findings in this study suggest that Hextend® has a favorable side effect profile. Only one patient received parenteral calcium supplementation intraoperatively in the Hextend® group, versus six patients in the control group. There were trends toward there being less bleeding in the Hextend® group, as judged by estimated blood loss and the requirement for blood products. These trends were observed at both study sites for red blood cell, platelets, fresh-frozen plasma, and cryoprecipitate transfusions. Several of these differences became more pronounced in the subset of patients in which one would expect to observe a larger drug effect, i.e., patients receiving intraoperative blood transfusions and patients receiving >20 mL/kg study fluid. The Hextend®-treated group demonstrated a significantly better TEG dynamic clot formation (P < 0.05), which was more marked in the subgroup who received
20 mL/kg.
Based on the laboratory coagulation tests, there is no obvious explanation for the decreased blood loss, need for blood products, and coagulation-related adverse events noted in Hextend® patients. The difference in dose-dependent changes in factor VIII and von Willebrand factor previously observed with higher molecular weight starches (7) were not seen in either group. One possible explanation may lie in the differences in ionized calcium, as calcium is essential to the pathways underlying effective clot formation. Hextend® contains calcium levels similar to those normally found in blood (10 mg/dL), whereas 6% hetastarch in saline contains none. Moreover, this supposition is supported by the observation that, in patients who received red blood cell transfusions, there was a mean difference in estimated blood loss of approximately 1 L. The transfusion of citrated red blood cells may have been associated with a more profound but transient reduction in plasma calcium levels in the patients receiving large amounts of calcium-free 6% hetastarch in saline as opposed to Hextend® (17). A rapid (within 5 min) infusion of 750 mL of citrated red blood cells has been shown to induce up to a 41% acute decline in ionized calcium (18). This transient reduction in ionized calcium may have lead to less effective clotting at the cut tissue edge. Because Hextend® is also lower in chloride (which therefore reduces acidosis secondary to this chloride burden) and is buffered with lactate, a more favorable localized and acute acid-base balance may also prevail in these patients relative to controls, further facilitating clotting (19).
The TEG studies conducted at DUMC provided further evidence consistent with coagulation-related abnormalities in the patients given 6% hetastarch in saline. The r times were significantly increased during surgery in these patients compared with the Hextend® patients, which suggests that the onset of clot formation became delayed in the 6% hetastarch in saline group. This difference became more pronounced in the subgroup who received
20 mL/kg. The r time correlates with initial fibrin formation and is related to overall activity of clotting factors, which could be influenced by local calcium concentration (14).
Our findings in this study indicate that Hextend® is as effective as 6% hetastarch in saline when used for the treatment of hypovolemia. Numerous findings suggest that Hextend® has a favorable side effects profile. Furthermore, there were no serious adverse events related to the administration of Hextend® in volumes of up to 5 L. With its buffered, balanced electrolyte formulation, Hextend® seems to be a safe alternative to 6% hetastarch in saline.
| Acknowledgments |
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| Footnotes |
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1 J. V. Booth, MB, FRCA, D.S. Bronheim, MD, C. Robertson, MD, D. E. Feierman, MD, D. Kucmeroski, BS, G. V. Gabrielson, S. Dufore, RN, I. H. Sampson, MD, K. M. Robertson, MD, S. B. Scarola, MD, A. B. Hilton, MD, W. J. Winfree, BSN, R. L. Woolf, MB, FRCA, and I. J. Mackie, MRCPath. ![]()
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