Efficacy and Safety of Heparinase I versus Protamine in Patients Undergoing Coronary Artery Bypass Grafting with and without Cardiopulmonary Bypass
Stafford-Smith, Mark M.D.*; Lefrak, Edward A. M.D.†; Qazi, Anjum G. M.D.‡; Welsby, Ian J. M.D.§; Barber, Linda M.S.N.∥; Hoeft, Andreas M.D.#; Dorenbaum, Alejandro M.D.*ast;; Mathias, Jasmine M.S.††; Rochon, James J. Ph.D.‡‡; Newman, Mark F. M.D.‡‡; Members of the Global Perioperative Research Organization
Background: Hemodynamic protamine reactions with heparin reversal during cardiac surgery are common and associated with adverse outcomes. As an alternative to protamine, the authors examined heparinase I reversal of heparin after aortocoronary bypass graft surgery.
Methods: In a randomized, double-blind, double-dummy trial, 167 on- and off-pump aortocoronary bypass graft surgery patients received either heparinase I (maximum 35 μg/kg) or protamine (maximum 650 mg) for heparin reversal, monitored by activated clotting time values and clinical assessment. Hemodynamic parameters were recorded electronically; safety evaluation was to 30 days postoperatively. Noninferiority was predefined as 400 ml or less median 12-h chest tube drainage from intensive care unit arrival for heparinase I patients, after risk adjustment. Hemodynamic instability was defined as systemic hypotension (≥ 30 mmHg decrease) and/or pulmonary hypertension (≥ 40 mmHg with an increase ≥ 10mmHg) within 30 min of heparin reversal initiation.
Results: Patient enrollment was terminated on advisement of the Data Safety Monitoring Board. Although heparinase I was noninferior for 12-h chest tube drainage, protamine had a superior safety profile. Overall, heparinase I subjects had longer hospital stays (P = 0.04), were more likely to experience a serious adverse event (P = 0.01), and were less likely to avoid transfusion (P = 0.006). A composite morbidity score was not different (P = 0.24), and similar rates of hemodynamic instability were observed between groups. Findings were consistent in analyses stratified by on- and off-pump surgery.
Conclusions: Heparinase I reverses heparin anticoagulation after aortocoronary bypass graft surgery but is not equivalent to protamine because of its inferior safety profile.
THE anticoagulant effect of heparin must be reversed after coronary artery bypass graft (CABG) surgery to avoid excess bleeding. Protamine, the only drug currently available for this purpose, binds tightly by the ionic attraction of its polycationic structure to the polyanionic structure of heparin. However, the safety of protamine has been questioned because of reactions ranging from minor hemodynamic instability to fatal cardiovascular collapse.1–5
Although catastrophic reactions are rare,5
protamine-related adverse events, including significant hemodynamic instability and respiratory complications, occur in 2.6% of cardiac surgeries3
and are highly associated with postoperative outcome.4,6
Recently, the relation between hemodynamic protamine reactions and mortality risk has been confirmed, even in the lowest observed range of values for both systemic hypotension and pulmonary hypertension.7
After the formation of protamine–heparin complexes, clinical and biochemical effects have been noted, including vasodilation,8
systemic hypotension, increases in pulmonary arterial pressure,10–12
platelet dysfunction, and leukocyte sequestration.15,16
However, in the absence of a safer replacement, undesirable effects related to protamine are outweighed by its utility as the only available heparin-reversal agent.
Heparinase I (Neutralase; BioMarin Pharmaceutical Inc., Novato, CA) is a potential alternative to protamine. Heparinase I, a specific heparin-degrading enzyme with a therapeutic half-life ranging from 5.5 to 18 min in cardiac surgery patients,17
is naturally synthesized by the bacterium Flavobacterium heparinum
and deactivates heparin through a different mechanism. Heparinase I causes rapid reversal of heparin as measured by point-of-care tests such as the activated clotting time, Hepcon (Medtronic, Minneapolis, MN), Thromboelastograph (Haemoscope Corp., Niles, IL), and activated partial thromboplastin time test. Heparinase I catalyzes cleavage of selected 1-4 glycosidic linkages within heparin; the resulting di-, tetra-, hexa-, and oligosaccharide fragments do not inhibit Factor IIa activity18
but retain 10–20% of the anti–Factor Xa activity of intact heparin.19,20
Although unmeasurable by standard testing, this residual anticoagulant activity clears over a 6–12 h period; low-level postprocedure antihemostatic effects have been associated with improved outcomes after percutaneous coronary intervention21
and CABG surgery.22
Two previous double-blind, double-dummy studies compared heparinase I with protamine23
; findings from these studies support further evaluation of heparinase I. As an alternative to protamine, heparinase I may avoid or attenuate the pathophysiology of protamine reactions and even improve outcomes. Therefore, we used a noninferiority clinical trial design to test the hypothesis that heparinase I is effective (noninferior to protamine) in the reversal of heparin after CABG surgery. In addition, we compared hemodynamic stability and safety profiles for the two heparin-reversal therapies.
Materials and Methods
General Study Design
This was a prospective randomized, double-blind, active-controlled, double-dummy noninferiority clinical trial of patients undergoing CABG surgery, with the study medication (heparinase I) or standard care (protamine) randomized in a 1:1 ratio, stratified by on- or off-pump CABG surgery. After institutional approval and written informed consent were obtained, 167 subjects received study drug at 46 centers (range, 1–26 patients/site) in the United States, Canada, and Germany from February through September 2003 (appendix 2
Inclusion and Exclusion Criteria
Eligible patients were aged 18–85 yr old and received heparin as part of a primary nonemergent on- or off-pump CABG surgery. Exclusion criteria were concomitant surgical procedures, hematologic disease including heparin-induced thrombocytopenia, preoperative platelet count less than 150,000/mm3, an international normalized ratio exceeding 1.5 within 48 h of surgery, severe liver dysfunction, serum creatinine greater than 2.0 mg/dl, ejection fraction of 20% or less, and allergy to heparin or protamine. Patients receiving preoperative heparin infusion were eligible; however, those receiving eptifibatide (Integrilin; Millennium Pharmaceuticals, Inc., Cambridge, MA and Schering Corporation, Kenilworth, NJ) within 12 h, clopidogrel (Plavix; Bristol-Myers Squibb/Sanofi Pharmaceuticals Partnership, New York, NY) or low-molecular-weight heparin within 3 days, abciximab (ReoPro; Centocor, Inc., Malvern, PA) or ticlopidine (Ticlid; Roche Laboratories, Inc., Nutley, NJ) within 7 days of surgery, or with another condition that compromised surgical hemostasis or patient safety were also excluded. Patients whose procedure changed from on- to off-pump after randomization remained in the trial if the decision to switch was unrelated to patient safety or bleeding. These patients (3% of total) were grouped by performed rather than scheduled procedure and were included for analysis. To minimize the need for readministration of heparin after study drug, intraoperative eligibility criteria included confirmation of clinical stability by the attending physicians immediately before heparin reversal (i.e., no major intraoperative concerns).
Randomization and Stratification
Eligible patients were stratified by study site and procedure (on- or off-pump CABG) and randomized preoperatively (1:1) to receive heparinase I or protamine. Unstable patients not receiving study drug were followed up postoperatively for safety criteria only.
Study Procedures before Drug Administration
Management of preoperative medications, anesthesia agents, antifibrinolytic therapy (for on-pump procedures), and cardiopulmonary bypass (CPB) management was per local practice. Although intraoperative heparin administration was carefully documented, there were no dosing guidelines, stipulations regarding type (porcine vs. bovine), or units of measure (International Units vs. United States Pharmacopeia Units). Performance of an activated clotting time test was required, in duplicate, for all time points when heparin effect was assessed. Because alternate point-of-care coagulation testing (Hepcon, Thromboelastograph) posed no risk of study drug unblinding, these tests were also permitted.
Administration of Study Drug
Study Drug Protocol.
A protocol was developed for heparin reversal. A total dose of up to 650 mg protamine or 35 μg/kg heparinase I was available. The protamine regimen represented a consensus from all study sites, and heparinase I dosing was based on previous safety, preclinical, and clinical data.17
Protocol development involved a high-fidelity simulation laboratory23,24
; a draft protocol was evaluated and refined using observations from CABG surgery scenarios resembling the typical complexity of heparin-reversal decisions, including mandatory and optional drug doses, activated clotting time values, clinical cues, and hemodynamic perturbations. For all doses, study drug was administered as a combination of bolus (heparinase I or saline placebo) and infusion (protamine or saline placebo) in a double-dummy fashion.
Two mandatory and two optional doses of study drug were available as part of the heparin-reversal protocol (table 1
). Dose 1 was a calculated mandatory initial dose, by body weight for heparinase I, and by cumulative intraoperative heparin dose for protamine. Dose 2 was an optional supplementary dose available 5–10 min after dose 1 as judged necessary by the clinical team. Dose 3 was a mandatory pump blood dose (for on-pump patients only) given after return of heparin-containing blood from the extracorporeal circuit; the protocol required blood return within 40 min of initiating heparin reversal. Dose 3 was not required if returned blood was washed by an autotransfusion device (e.g.
, Hemonetics Cell Saver, Braintree, MA), and was optional if blood return was completed within 5 min of dose 2. Dose 4 was an optional postoperative dose for use within 12 h of intensive care unit (ICU) arrival. If residual heparin effect was suspected after available doses of study drug were administered, investigators could use open-label protamine, and the treatment was considered a failure in that subject. To minimize any potential effect of inexperience on performance of this complex protocol, education for all study monitors and coordinators, in addition to the standard investigator meeting, included participation in a full-day course including involvement in several simulations of the final protocol in an operating room setting.24
Although guidelines to identify residual heparin effect requiring optional doses or open-label protamine were provided (e.g.
, persistent increased activated clotting time, “wet” surgical field), these decisions were left to the judgment of the clinical team. As a safety consideration, education was provided about the need for immediate unblinding of drug assignment if heparin readministration was required within 1 h of study drug, because of the special heparin dosing requirements for patients receiving heparinase I. In addition, immediate unblinding for study drug was available during the study, and individualized heparin dosing instructions for urgent anticoagulation were provided for each patient.
Efficacy and Assessment
Primary and Secondary Outcome Measures.
The primary efficacy measurement was postoperative hemorrhage, defined as the cumulative chest tube drainage during the first 12 h after ICU admission.25,26
Chest tube drainage was measured and recorded at hourly intervals, beginning with patient arrival in the ICU and continuing for 12 h, after which chest tube drainage was measured and recorded every 4 h until the 24th hour or until chest tubes were removed.
The secondary efficacy endpoint was hemodynamic stability, as determined by a composite of systolic arterial blood pressure decrease (> 30 mmHg) or pulmonary artery systolic pressure increase (> 40 mmHg with an increase of at least 10 mmHg from baseline) within 30-min of study drug dosing. Baseline hemodynamic parameters were the average values during the 5 min after CPB separation and before heparin reversal. Electronic data capture from an automated anesthesia record-keeping system was used to record minute-to-minute hemodynamic parameters. A freestanding laptop-based system (Saturn Information System; Draeger Medical Inc., Telford, PA) was provided if electronic data capture was not already available. Interventions to treat hemodynamic instability were also documented.
Tertiary measurements were used to derive a composite morbidity score reflecting the percentage of patients who died within 30 days of surgery or sustained at least one of the following severe adverse events known to be related to protamine reactions: congestive heart failure, catastrophic pulmonary hypertension or acute myocardial depression within 1 h of study drug, anaphylaxis, acute renal failure/dialysis, stroke/cerebral vascular accident, or encephalopathy/delirium.
Safety was assessed on the basis of adverse events and serious adverse events. Adverse events were recorded throughout the patients' hospitalization and summarized by severity and relation to study drug. Serious adverse events were recorded throughout the 30-day duration of the study. An independent Data Safety Monitoring Board, comprised of five individuals with expertise in the areas of cardiothoracic surgery, cardiovascular anesthesia, heparinization, and biostatistics, from around the United States reviewed safety analyses at regular scheduled intervals.
A statistical plan was developed before the start of the study and followed for this analysis. Unless otherwise noted, patients in the on-pump CABG stratum were analyzed separately from those in the off-pump CABG stratum.
The primary analysis included an as-treated data set and comprised all patients who received study drug. Preliminary analyses suggested that chest tube drainage was skewed toward higher values; therefore, statistical analysis was conducted using a natural logarithm scale. A regression model was developed for the ln (chest tube drainage) and included the treatment allocation and clinical center as predictors, as well as preidentified bleeding risk factors including age, sex, body weight, preoperative hemoglobin, total dose of heparin, and duration of CPB (in the on-pump CABG group only). From the characteristics of the log-normal distribution, the median chest tube drainage, adjusted for covariates, is the exponent of the adjusted mean on the natural logarithm scale. Medians were estimated separately by treatment arm, and the heparinase I minus protamine difference was derived. Bootstrap procedures were applied, and the empirical, one-sided, 95% confidence interval was derived.
The secondary efficacy endpoint was hemodynamic stability as described above (see Efficacy and Assessment). The tertiary efficacy endpoint was a composite morbidity score including all cause mortality, congestive heart failure, catastrophic pulmonary hypertension, acute myocardial depression, anaphylaxis, acute renal failure, stroke/cerebral vascular accident, and encephalopathy/delirium. The proportions of patients meeting these criteria were compared in a stratified analysis using the Cochran-Mantel-Haenszel procedure.
The incidences of adverse events and serious adverse events were compared using the Fisher exact test. Several endpoints were examined, including all adverse events, hemodynamic changes, 12-h chest tube drainage, safety variables (including death), reoperation, vital signs and physical examination, and open-label protamine use after study drug administration. Composite variables representing the need for intervention to stabilize the patient hemodynamically because of hypotension or pulmonary hypertension within 30 min after study drug administration were similarly examined. Changes from baseline values in laboratory tests and vital signs were compared using a one-way analysis of variance test.
Based on a review of the literature and a broad background of clinical experience, a group of clinicians were invited to develop a noninferiority bleeding threshold; the group included several experienced cardiac anesthesiologists, surgeons, and established clinician–scientist investigators in the field. The consensus opinion was that a difference in 12-h chest tube drainage of less than or equal to 400 ml after on-pump CABG surgery was clinically acceptable. Using previously published clinical data for estimates of 12-h chest tube drainage differences between patients receiving protamine and heparinase I for on-pump procedures,17
power and sample size calculations for 12-h chest tube drainage were performed separately for the on- and off-pump CABG strata. The 12-h chest tube drainage estimates for off-pump CABG patients were proportionately reduced 10% relative to the on-pump CABG stratum, based on published reports.27–34
Bootstrap procedures were performed 1,000 times for each strata, with empirical power defined as the proportion of the 1,000 simulations in which the one-sided 95% confidence interval for the difference between medians was less than or equal to the noninferiority margin. The sample size was then successively changed until 90% power was achieved. To achieve the minimum 90% power, a study sample size of 300 (150 in each group) for on-pump CABG patients and 150 (75 in each group) for off-pump CABG patients was required. To be conservative, the sample size was set at 600 total patients: 400 on-pump and 200 off-pump CABG. All summaries and statistical analyses were generated using statistical software (SAS version 8.2; SAS Institute, Cary, NC).
The 167 subjects undergoing CABG surgery received study drug between February and September 2003, including 46 off-pump (protamine/heparinase I, 23/23) and 131 on-pump (protamine/heparinase I, 64/57) patients. All patients receiving study drug were included in the final analysis, which represents just over a quarter of the expected final data set because of the early discontinuation of the study, an action based on a recommendation from the study Data Safety Monitoring Board.
Overall, patients receiving heparinase I were older (65.6 vs.
62.1 yr; P
= 0.04; table 2
), more likely to have a history of congestive heart failure (11.3 vs.
= 0.05; table 2
), had a higher baseline heart rate in the off-pump CABG group (68 ± 14 vs.
58 ± 10 beats/min; P
= 0.008), and were less likely to have a history of peripheral vascular disease in the on-pump CABG group (4 vs.
= 0.04). No substantial differences were noted in the preoperative characteristics between those patients who underwent on- or off-pump CABG surgery. The median total intraoperative heparin dose was 40,000 units (46,000 units for on-pump CABG patients, 20,500 units for off-pump CABG patients). Overall, 84% patients had two to four bypass grafts, and an internal mammary artery graft was used in 99% of all procedures. The mean operative time was 4.7 h, with the duration of CPB in the on-pump CABG group averaging 84 min. A total of 14 patients received open-label protamine, and 2 patients were unblinded because they required readministration of heparin anticoagulation after receiving study drug; both patients were in the protamine group.
In addition to the 167 who received study drug, 34 patients (16.5%) were randomized but withdrawn before receiving study drug; the most common reasons were meeting exclusion criteria or investigator withdrawal. During the drug administration period, 47% of patients received an optional dose 2, and 18% received an optional postoperative dose 4. In the on-pump CABG group, 80 of 131 patients received dose 3; washing of heparin-containing blood before return to the patient accounted for the majority of omitted dose 3s.
Primary Efficacy Measure: Twelve-hour Postoperative Chest Tube Drainage.
The use of heparinase I was associated with an increased level of chest tube drainage compared with protamine; however, this difference did not exceed the predefined noninferiority margin (table 3
). The adjusted heparinase I minus protamine difference in 12-h chest tube drainage was +181 ml (230 ml, one-sided 95% confidence interval) for on-pump CABG surgery and +310 ml (361 ml, one-sided 95% confidence interval) for off-pump CABG surgery.
Secondary and Tertiary Efficacy Measures.
There was no significant difference in the incidence of hemodynamic instability between the heparinase I and protamine groups (46.8% vs.
= 0.98; table 4
). Similarly, there were no major differences in the rate of intervention to treat hemodynamic changes. No significant differences were noted between the heparinase I and protamine groups, adjusted for procedure type, for a composite morbidity score including death, major organ dysfunction, and rehospitalization (55.0% vs.
= 0.24; table 5
Although efficacy analyses demonstrated noninferiority of heparinase I compared with protamine for heparin reversal, an inferior safety profile for heparinase I emerged when the study was approximately one quarter complete, prompting the Data Safety Monitoring Board to recommend discontinuation of the study. No patients were enrolled after the recommendation was issued; however, data collection was completed for all enrolled patients.
Adverse Events and Serious Adverse Events.
Adverse events and serious adverse events were common in both study groups; at least one adverse event or serious adverse event occurred in 93% and 99% of patients receiving protamine or heparinase I, respectively. Serious adverse events were more common in the heparinase I group compared with the protamine group (42.5 vs. 24.1%; P = 0.01). Although both the on- and off-pump strata demonstrated the same trend, the difference in serious adverse events between the protamine and heparinase I arms was more pronounced in the off-pump strata (off-pump: 13 vs. 43.5%; P = 0.02; on-pump: 28.1 vs. 42.1%; P = 0.11). No subset of complications grouped by body system was primarily responsible for this observation.
Several parameters reflected a pattern of increased bleeding and transfusion in the heparinase I group (table 6
). Lowest hemoglobin values were lower in the heparinase I group at 24 h after surgery and before hospital discharge, and these patients were also more likely to have received a transfusion at these time points. In addition, the median duration of hospital stay was 1 day longer for patients in the heparinase I group than in the protamine group (6 vs.
5 days; P
= 0.04). Although similar patterns of increased bleeding, transfusion, and extended hospital stay were evident in both strata, more findings reached statistical significance in the off-pump CABG group, despite the smaller numbers in this group.
One patient in the protamine group having on-pump CABG surgery died within 30 days of surgery; death was attributed to saphenous vein graft thrombosis and occurred in the operating room.
As a potential alternate to protamine that deactivates heparin using a different mechanism, the current noninferiority study was designed to demonstrate that heparinase I reverses heparin anticoagulation safely and without excess bleeding. We found that heparinase I was associated with an increased level of chest tube drainage compared with protamine, although the difference in bleeding did not exceed the predefined noninferiority threshold. This finding was made in an analysis adjusted to account for a priori
identified bleeding risk factors; however, the findings were almost identical in an unadjusted analysis. The secondary efficacy endpoint was hemodynamic instability related to heparin reversal. Curiously, despite previous indications of benefit with heparinase I,16,35
we observed no difference in the frequency of hemodynamic instability between the two drugs in our study. Finally, the tertiary outcome was a composite morbidity index, reflecting the percentage of patients sustaining at least one major complication after their procedure. We found no difference between groups in this composite of all-cause mortality, rehospitalization, or major organ dysfunction. However, an overall inferior safety profile of heparinase I relative to protamine caused the study to be terminated on the advisement of the Data Safety Monitoring Board before complete enrollment. Although adverse events rates were similar, there were almost twice as many patients sustaining at least one serious adverse event in the heparinase I group (P
= 0.01). Heparinase I patients also had lower hemoglobin values (P
< 0.005) both at 24 h postoperatively and at hospital discharge, despite having greater transfusion rates (P
< 0.006). The median duration of hospital stay was 1 day longer for patients in the heparinase I group than in the protamine group (6 vs.
5 days; P
= 0.04). Therefore, our study does not support the use of heparinase I as a protamine replacement for elective CABG surgery.
Although no peer-reviewed studies have reported comparisons of protamine and heparinase I in cardiac surgery patients, some data exists on this subject. Heres et al.35
reported safety data in a dose-escalation study describing heparin reversal in 49 patients receiving between 5 and 20 μg/kg heparinase I; however, these treatments were not compared with protamine therapy. Two previous double-blind, double-dummy studies compared heparinase I with protamine17
; heparinase I was administered in smaller and differently timed doses compared with those used in the current study. The first involved 176 patients undergoing CABG surgery and found a single 7-μg/kg postbypass bolus dose of heparinase I for heparin reversal to be inferior to 1 mg protamine per 100 units heparin (infused over 10 min) with regard to bleeding. This study also demonstrated insufficient heparinase I dosing. The second trial, evaluating 10 and 15 μg/kg heparinase I with optional additional doses, was terminated early for business reasons. Analysis of 94 enrolled patients was not sufficiently powered to demonstrate statistically significant findings. However, substantial improvements in bleeding were evident as compared with the previous trial, with the 15-μg/kg dose performing better than the 10-μg/kg dose. Hemodynamic data from both studies indicated better hemodynamic stability in the heparinase I groups, but the dosing regimen provided only immediate post-CPB heparin reversal activity, without addressing the possibility of delayed heparin-reversal needs (e.g.
, return of pump blood, ICU reheparinization). Based on the findings of these two trials, the current study was designed to include a further significant increase in the dose of available heparinase I (up to 35 μg/kg) and match heparinase I dose timing to include all postbypass heparin reversal needs. However, despite modifications to address these concerns, our study regimen did not achieve efficacy without increased postoperative transfusion and lower hemoglobin concentrations. Given the short half-life of heparinase I, it is possible that our findings could be explained by residual heparin that was not degraded; however, we believe that the increased heparinase I dosing and the protocol requirement for return of pump blood (and contained heparin) within 40 min of initiation of heparin reversal assured adequate intraoperative heparinase I concentrations. In addition, we included an optional ICU dose to address the possibility of postoperative reheparinization. Although no differences in coagulation test results were evident between the two groups (table 6
), samples drawn for a substudy specifically to evaluate residual anti–Factor IIa and Xa activity were unfortunately not processed because of excessive cost. However, we believe that the observed excess transfusion and anemia in our study with heparinase I treatment is primarily due to the previously reported property of this agent to incompletely reverse anti–Factor Xa activity during heparin degradation17
and not related to residual uncorrected heparin activity.
Examination of the hourly chest tube drainage data (fig. 1
) highlights the differing patterns of bleeding between the two agents. Notably, heparinase I was associated with more chest tube effluent during the first 6 postoperative hours. This effect is particularly obvious in the off-pump CABG group, possibly because of the lack of antifibrinolytic therapy in this population, and is consistent with the known pattern of residual anti–Factor Xa anticoagulant activity after heparin degradation with heparinase I.17
A key aspect of the design of any noninferiority study is the predefined tolerable threshold for no difference. A panel of independent clinicians was gathered to develop the noninferiority bleeding threshold, including several experienced cardiac anesthesiologists, surgeons, and established clinician–scientist investigators in the field. Among the evidence they considered was data from two large outcomes databases with postoperative bleeding and transfusion records. A consensus was developed that less than or equal to 400 ml excess bleeding over the first 12 h after CABG surgery would be a tolerable difference in chest tube drainage if an alternate heparin-reversal agent had other potential advantages. This consensus was also accepted by regulatory authorities, institutional review boards, and study investigators and was used to perform power calculations to determine the necessary study size. Despite the smaller-than-anticipated number of study subjects enrolled in our study, this noninferiority bleeding threshold was easily achieved in both on- and off-pump groups. However, despite the consensus of numerous individuals regarding the reasonableness of the a priori
determined noninferiority boundary, successful avoidance of the boundary did not assure patient safety, and no benefits were apparent.
Although the noninferiority threshold for heparinase I–related bleeding was achieved, the termination of the study before complete enrollment reduced the total number of study participants and diminished the power of our study to identify more subtle differences. It is possible that a hemodynamic advantage of heparinase I was missed in our study. In addition, data collection for the hemodynamic analysis at trial termination was incomplete, with 54% and 68% of computerized data available in the protamine and heparinase I groups, respectively. However, the incidence of systemic hypotension and/or pulmonary hypertension was almost identical between groups (table 4
). Our enrollment criteria selected for a low-risk study population, but these subjects were similar to others in whom differences in hemodynamic stability have previously been observed.17
One possible explanation is that slowly developing hemodynamic instability may be masked by corrective action; however, no striking differences in hemodynamic drug interventions were evident. It is also possible that hemodynamic reactions were muted by the slow rate of infusion of protamine; rapid administration predicts greater hemodynamic responses.36
Although patterns of protamine administration vary widely among clinicians, we believe it is not typical to complete a primary dose of protamine (dose 1) more rapidly than the 10 min in our study design. For similar reasons, it is also possible that a difference in the composite morbidity index, the percentage of patients with at least one major postoperative complication, was missed in our study. However, these data were captured for almost 100% of study participants as part of required study safety data. Data collection for other adverse event/serious adverse event and morbidity reporting was almost complete, exceeding 95% except for the incidence of dialysis in the protamine group (87%, 76/87).
Almost twice as many heparinase I patients had at least one serious adverse event. Closer examination of serious adverse events reveals a pattern of morbidity; serious adverse events related to bleeding (cardiac tamponade, pericardial effusion, pleural effusion, hemothorax, postprocedure hemorrhage, mediastinal hemorrhage, and hemorrhage) occurred more frequently in the heparinase I group (P
= 0.01 by log-linear model; table 7
). In addition, serious adverse events specifically or likely related to infectious complications (catheter site discharge, cellulitis, wound infection, staphylococcal infection, rectal abscess, sepsis, and multiorgan failure) were more common in the heparinase I group (P
= 0.05 by log-linear model; table 7
). Blood transfusions are associated with significant immunomodulatory effects that have been linked to increased postoperative infections,37–41
and transfusion and reoperation are strong independent predictors of extended hospital stay.38,42
The median hospital stay was 1 day longer in the heparinase I group. It is plausible that increased transfusion, infectious complications, and extended hospital stay in the heparinase I group are all consequences of the increased bleeding in this group. Bleeding and infectious-related serious adverse events represented 44% and 21% of total for heparinase I and protamine groups, respectively, and accounted for much of the excess in serious adverse event reporting in the heparinase I group. Although patterns of increased bleeding, transfusion, and extended hospital stay were evident in both strata, these findings were more statistically significant in the off-pump CABG group, despite the smaller numbers. Notably, off-pump patients did not receive antifibrinolytic therapy and, therefore, may have been predisposed to complications from residual anticoagulation; in this trial, we observed more bleeding and greater transfusion requirements in the off- than the on-pump surgery group.
When protamine is contraindicated (e.g.
, catastrophic protamine reactions, protamine allergy), no satisfactory approach is currently available. Ralley and De Varennes43
reported the successful use of heparinase I for cardiac surgery in a patient with protamine allergy. Heparinase I has not been evaluated as an alternative when a positive response to a protamine test dose raises concern that continued dosing may precipitate a full-blown reaction; current options are limited to tolerating the potential adverse consequences of residual heparin effect or continued protamine administration.44
Other therapeutic options that eliminate protamine include avoidance of heparin–protamine altogether (ancrod,45,46
) or heparin without protamine (reduced heparin dosing with heparin-coated CPB circuits,53
extracorporeal heparin adsorption54
). No comparisons exist among these approaches, although when compared with standard heparin–protamine therapy, as with the current study, they have been associated with excess bleeding and transfusion.45,47,49
Clearly, further trials are required to identify new strategies that avoid or attenuate the adverse events associated with protamine.
In summary, heparinase I for heparin reversal was associated with increased chest tube drainage after elective CABG surgery as compared with protamine, but the difference in bleeding did not exceed the predefined noninferiority threshold for 12-h cumulative mediastinal chest tube drainage. However, heparinase I demonstrated an inferior safety profile compared with protamine. Patients receiving heparinase I sustained more postoperative bleeding complications and had increased transfusion requirements and anemia, possibly because of residual anti–Factor Xa effects. Although all patients demonstrated the same trend, bleeding differences were less pronounced in the on-pump strata, possibly because of the use of antifibrinolytics in this group. The increased risk of infection and delayed hospital discharge observed with heparinase I may be secondary to increased bleeding. Postdrug hemodynamic stability and an index of major postoperative morbidity and mortality were not significantly different between the study groups. Heparinase I is not suitable as a replacement for protamine for nonemergent CABG surgery.
The authors thank Fiona Clements, M.D., Jeff Taekman, M.D., Melanie Wright, Ph.D., and Gene Hobbs, C.R.T. (Duke University Human Simulation and Patient Safety Center, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina), and Gaetano Paone, M.D. (Assistant Professor, Section of Cardiac Surgery, University of Michigan Medical Center, Crittenton Hospital Medical Center, Rochester, Michigan), for their assistance in developing and teaching the study protocol; and Elizabeth Schramm (Duke Clinical Research Institute, Duke University) and Cheryl Stetson, A.A.S. (Staff Assistant, Department of Anesthesiology, Duke University Medical Center), for assistance in manuscript preparation.
1. Weiss ME, Nyhan D, Peng ZK, Horrow JC, Lowenstein E, Hirshman C, Adkinson Jr NF: Association of protamine IgE and IgG antibodies with life-threatening reactions to intravenous protamine. N Engl J Med 1989; 320:886–92
2. Weiler JM, Gellhaus MA, Carter JG, Meng RL, Benson PM, Hottel RA, Schillig KB, Vegh AB, Clarke WR: A prospective study of the risk of an immediate adverse reaction to protamine sulfate during cardiopulmonary bypass surgery. J Allergy Clin Immunol 1990; 85:713–9
3. Kimmel SE, Sekeres MA, Berlin JA, Goldberg LR, Strom BL: Adverse events after protamine administration in patients undergoing cardiopulmonary bypass: Risks and predictors of under-reporting. J Clin Epidemiol 1998; 51:1–10
4. Kimmel SE, Sekeres M, Berlin JA, Ellison N: Mortality and adverse events after protamine administration in patients undergoing cardiopulmonary bypass. Anesth Analg 2002; 94:1402–8
5. Panos A, Orrit X, Chevalley C, Kalangos A: Dramatic post-cardiotomy outcome, due to severe anaphylactic reaction to protamine. Eur J Cardiothorac Surg 2003; 24:325–7
6. Michaels IA, Barash PG: Hemodynamic changes during protamine administration. Anesth Analg 1983; 62:831–5
7. Welsby IJ, Newman MF, Phillips-Bute B, Messier RH, Stafford-Smith M: Hemodynamic changes after protamine administration: Association with mortality after coronary artery bypass surgery. Anesthesiology 2005; 102:308–14
8. Sealy WC, Brown Jr, IW Young Jr WG: A report on the use of both extracorporeal circulation and hypothermia for open heart surgery. Ann Surg 1958; 147:603–13
9. Del Re MR, Ayd JD, Schultheis LW, Heitmiller ES: Protamine and left ventricular function: A transesophageal echocardiography study. Anesth Analg 1993; 77:1098–103
10. Carr JA, Silverman N: The heparin-protamine interaction: A review. J Cardiovasc Surg (Torino) 1999; 40:659–66
11. Morel DR, Zapol WM, Thomas SJ, Kitain EM, Robinson DR, Moss J, Chenoweth DE, Lowenstein E: C5a and thromboxane generation associated with pulmonary vaso- and broncho-constriction during protamine reversal of heparin. Anesthesiology 1987; 66:597–604
12. Lowenstein E, Zapol WM: Protamine reactions, explosive mediator release, and pulmonary vasoconstriction. Anesthesiology 1990; 73:373–5
13. Porsche R, Brenner ZR: Allergy to protamine sulfate. Heart Lung 1999; 28:418–28
14. Gupta SK, Veith FJ, Ascer E, Wengerter KR, Franco C, Amar D, el-Gaweet, ES, Gupta A: Anaphylactoid reactions to protamine: An often lethal complication in insulin-dependent diabetic patients undergoing vascular surgery. J Vasc Surg 1989; 9:342–50
15. Mochizuki T, Olson PJ, Szlam F, Ramsay JG, Levy JH: Protamine reversal of heparin affects platelet aggregation and activated clotting time after cardiopulmonary bypass. Anesth Analg 1998; 87:781–5
16. Ammar T, Fisher CF: The effects of heparinase 1 and protamine on platelet reactivity. Anesthesiology 1997; 86:1382–6
17. Heft R, Broughton R: Chapter 32: Comparative pharmacology of the investigational agent Neutralase (heparinase I) and protamine in the reversal of heparin, Thrombosis Research and Treatment: Bench to Bedside. Edited by Vossoughi J, Fareed J, Mousa S, Karanian J. Washington, D.C., Medical and Engineering Publishers, 2004, pp 565–94
18. Langer R, Linhardt RJ, Hoffberg S, Larsen AK, Cooney CL, Tapper D, Klein M: An enzymatic system for removing heparin in extracorporeal therapy. Science 1982; 217:261–3
19. Larsen AK, Hetelekidis S, Langer R: Disposition and anticoagulant activity of biologically active heparin fragments in the rat. J Pharmacol Exp Ther 1984; 231:373–8
20. Linhardt RJ, Grant A, Cooney CL, Langer R: Differential anticoagulant activity of heparin fragments prepared using microbial heparinase. J Biol Chem 1982; 257:7310–3
21. Steinhubl SR, Berger PB, Mann III, JT Fry, ET, DeLago A, Wilmer C, Topol EJ: Early and sustained dual oral antiplatelet therapy following percutaneous coronary intervention: A randomized controlled trial. JAMA 2002; 288:2411–20
22. Mangano DT: Aspirin and mortality from coronary bypass surgery. N Engl J Med 2002; 347:1309–17
23. Wright MC, Taekman JM, Barber L, Newman MF, Stafford-Smith M: The role of simulation in the development of clinical research protocols (abstract). Anesthesiology 2004; 101:A1248
24. Taekman J, Hobbs G, Barber L, Phillips-Bute B, Wright M, Newman M, Stafford-Smith M: Preliminary report on the use of high-fidelity simulation in the training of study coordinators conducting a clinical research protocol. Anesth Analg 2004; 99:521–7
25. Horrow JC, Van Riper, DF, Strong MD, Grunewald KE, Parmet JL: The dose–response relationship of tranexamic acid. Anesthesiology 1995; 82:383–92
26. Kozek-Langenecker SA, Wanzel O, Berger R, Kettner SC, Coraim F: Increased anticoagulation during cardiopulmonary bypass by prostaglandin E1. Anesth Analg 1998; 87:985–8
27. Ascione R, Williams S, Lloyd CT, Sundaramoorthi T, Pitsis AA, Angelini GD: Reduced postoperative blood loss and transfusion requirement after beating-heart coronary operations: A prospective randomized study. J Thorac Cardiovasc Surg 2001; 121:689–96
28. Cartier R, Robitaille D: Thrombotic complications in beating heart operations. J Thorac Cardiovasc Surg 2001; 121:920–2
29. Cox CM, Ascione R, Cohen AM, Davies IM, Ryder IG, Angelini GD: Effect of cardiopulmonary bypass on pulmonary gas exchange: A prospective randomized study. Ann Thorac Surg 2000; 69:140–5
30. Arom KV, Flavin TF, Emery RW, Kshettry VR, Janey PA, Petersen RJ: Safety and efficacy of off-pump coronary artery bypass grafting. Ann Thorac Surg 2000; 69:704–10
31. Kshettry VR, Flavin TF, Emery RW, Nicoloff DM, Arom KV, Petersen RJ: Does multivessel, off-pump coronary artery bypass reduce postoperative morbidity? Ann Thorac Surg 2000; 69:1725–30
32. Brasil LA, Gomes WJ, Salomao R, Buffolo E: Inflammatory response after myocardial revascularization with or without cardiopulmonary bypass. Ann Thorac Surg 1998; 66:56–9
33. Bull DA, Neumayer LA, Stringham JC, Meldrum P, Affleck DG, Karwande SV: Coronary artery bypass grafting with cardiopulmonary bypass versus off-pump cardiopulmonary bypass grafting: Does eliminating the pump reduce morbidity and cost? Ann Thorac Surg 2001; 71:170–3
34. Arom KV, Emery RW, Flavin TF, Petersen RJ: Cost-effectiveness of minimally invasive coronary artery bypass surgery. Ann Thorac Surg 1999; 68:1562–6
35. Heres EK, Horrow JC, Gravlee GP, Tardiff BE, Luber Jr, J Schneider, J, Barragry T, Broughton R: A dose-determining trial of heparinase-I (Neutralase) for heparin neutralization in coronary artery surgery. Anesth Analg 2001; 93:1446–52
36. Kien ND, Quam DD, Reitan JA, White DA: Mechanism of hypotension following rapid infusion of protamine sulfate in anesthetized dogs. J Cardiothorac Vasc Anesth 1992; 6:143–7
37. Houbiers JG, van de Velde CJ, van de Watering LM, Hermans J, Schreuder S, Bijnen AB, Pahlplatz P, Schattenkerk ME, Wobbes T, de Vries JE, Klementschitsch P, van de Maas, AH, Brand A: Transfusion of red cells is associated with increased incidence of bacterial infection after colorectal surgery: A prospective study. Transfusion 1997; 37:126–34
38. Blumberg N: Allogeneic transfusion and infection: Economic and clinical implications. Semin Hematol 1997; 34:34–40
39. Klein HG: Immunomodulatory aspects of transfusion: A once and future risk? Anesthesiology 1999; 91:861–5
40. Blumberg N, Heal JM: Immunomodulation by blood transfusion: An evolving scientific and clinical challenge. Am J Med 1996; 101:299–308
41. Kaplan J, Sarnaik S, Gitlin J, Lusher J: Diminished helper/suppressor lymphocyte ratios and natural killer activity in recipients of repeated blood transfusions. Blood 1984; 64:308–10
42. Unsworth-White MJ, Herriot A, Valencia O, Poloniecki J, Smith EE, Murday AJ, Parker DJ, Treasure T: Resternotomy for bleeding after cardiac operation: A marker for increased morbidity and mortality. Ann Thorac Surg 1995; 59:664–7
43. Ralley FE, De Varennes B: Use of heparinase I in a patient with protamine allergy undergoing redo myocardial revascularization. J Cardiothorac Vasc Anesth 2000; 14:710–1
44. Panos A, Orrit X, Chevalley C, Kalangos A: Dramatic post-cardiotomy outcome, due to severe anaphylactic reaction to protamine. Eur J Cardiothorac Surg 2003; 24:325–7
45. Zulys VJ, Teasdale SJ, Michel ER, Skala RA, Keating SE, Viger JR, Glynn MF: Ancrod (Arvin) as an alternative to heparin anticoagulation for cardiopulmonary bypass. Anesthesiology 1989; 71:870–7
46. Teasdale SJ, Zulys VJ, Mycyk T, Baird RJ, Glynn MF: Ancrod anticoagulation for cardiopulmonary bypass in heparin-induced thrombocytopenia and thrombosis. Ann Thorac Surg 1989; 48:712–3
47. Westphal K, Martens S, Strouhal U, Matheis G, Lindhoff-Last E, Wimmer-Greinecker G, Lischke V: Heparin-induced thrombocytopenia type II: Perioperative management using danaparoid in a coronary artery bypass patient with renal failure. Thorac Cardiovasc Surg 1997; 45:318–20
48. Koster A, Kuppe H, Hetzer R, Sodian R, Crystal GJ, Mertzlufft F: Emergent cardiopulmonary bypass in five patients with heparin-induced thrombocytopenia type II employing recombinant hirudin. Anesthesiology 1998; 89:777–80
49. Kwapisz MM, Schindler E, Muller M, Akinturk H: Prolonged bleeding after cardiopulmonary bypass with recombinant hirudin in heart transplantation. Eur J Cardiothorac Surg 1999; 16:256–7
50. Vasquez JC, Vichiendilokkul A, Mahmood S, Baciewicz Jr FA: Anticoagulation with bivalirudin during cardiopulmonary bypass in cardiac surgery. Ann Thorac Surg 2002; 74:2177–9
51. Davis Z, Anderson R, Short D, Garber D, Valgiusti A: Favorable outcome with bivalirudin anticoagulation during cardiopulmonary bypass. Ann Thorac Surg 2003; 75:264–5
52. Koster A, Spiess B, Chew DP, Krabatsch T, Tambeur L, DeAnda A, Hetzer R, Kuppe H, Smedira NG, Lincoff AM: Effectiveness of bivalirudin as a replacement for heparin during cardiopulmonary bypass in patients undergoing coronary artery bypass grafting. Am J Cardiol 2004; 93:356–9
53. Mukadam ME, Pritchard P, Riddington D, Wilkes M, Graham TR, Horrow JC, Spiess BD: Case 7-2001: Management during cardiopulmonary bypass of patients with presumed fish allergy. J Cardiothorac Vasc Anesth 2001; 15:512–9
54. Zwischenberger JB, Vertrees RA, Brunston Jr, RL Tao W, Alpard SK, Brown Jr PS: Application of a heparin removal device in patients with known protamine hypersensitivity. J Thorac Cardiovasc Surg 1998; 115:729–31
Appendix 1: Global Perioperative Research Group Faculty
Mark F. Newman, M.D., Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina; Lee Fleischer, M.D., Department of Anesthesiology, University of Pennsylvania, Philadelphia, Pennsylvania. Study Principal Investigator:
Mark Stafford-Smith, M.D., F.R.C.P.C., Department of Anesthesiology, Duke University Medical Center. Quality Assurance:
Michael Cuffe, M.D., Department of General Medicine, Duke University Medical Center. Study Coordination:
Linda Barber, M.S.N., Duke Clinical Research Institute, Duke University; Nancy Newark, B.S.N., Duke Clinical Research Institute, Duke University; Tammy Reece, M.S., Duke Clinical Research Institute, Duke University. Human Simulation Laboratory:
Jeffrey Taekman, M.D., Department of Anesthesiology, Duke University Medical Center; Melanie Wright, Ph.D., Department of Anesthesiology, Duke University Medical Center; Gene Hobbs, C.R.T., Department of Anesthesiology, Duke University Medical Center; Fiona Clements, M.D., Department of Anesthesiology, Duke University Medical Center. Analysis Group:
James Rochon, Ph.D., Biostatistics and Bioinformatics, Duke University; Jasmine Mathias, M.S., Duke Clinical Research Institute, Duke University; Christina Sigmon, M.A., Duke Clinical Research Institute, Duke University. Cited Here...
Appendix 2: The Cohort of the Global Perioperative Research Organization Biomarin Neutralase Study Group Who Participated in This Study
The Global Perioperative Research Organization is an academic research organization representing a strategic collaboration between the International Anesthesia Research Society and the Duke Clinical Research Institute. These investigators are listed in alphabetical order with their medical centers.
Edwin Avery, M.D., Instructor in Anesthesia, Department of Anesthesia and Critical Care Medicine, Massachusetts General Hospital, Boston, Massachusetts; Richard Baillot, M.D., Quebec Heart Institute, Laval Hospital, Sainte Foy, Quebec, Canada; Denis Bouchard, M.D., Department of Surgery, Montreal Heart Institute, Montreal, Quebec, Canada; Steven W. Boyce, M.D., Cardiac Surgery, Washington Hospital Center, Washington, D.C.; Luis A. Dibos, M.D., Department of Surgery, Union Memorial Hospital, Baltimore, Maryland; H. Muhammad Ghotbi, M.D., Department of Anesthesiology, Kaiser Foundation Hospital, San Francisco, California; N. Martin Giesecke, M.D., Clinical Assistant Professor, Department of Cardiovascular Anesthesiology, Texas Heart Institute, Houston, Texas; Richard Hall, M.D., Pharmacology/Critical Care/Anesthesiology, Capital Health Center for Clinical Research, Halifax, Nova Scotia, Canada; John Harlan, M.D., Cardio-Thoracic Surgeons, Medical Center East, Birmingham, Alabama; Andreas Hoeft, M.D., Chairman, Department of Anesthesiology and Intensive Care Medicine, Universitatsklinkiken Bonn, Bonn, Germany; Marc Kanchuger, M.D., Associate Professor, Department of Anesthesiology, New York University Medical Center, New York, New York; Charles T. Klodell, M.D., Assistant Professor, Department of Surgery, University of Florida Health Science Center, Gainesville, Florida; Irving L. Kron, M.D., Professor and Chief, Department of Surgery, University of Virginia Medical Center, Charlottesville, Virginia; Edward A. Lefrak, M.D., Chief, Cardiac Surgery, Inova Fairfax Hospital, Falls Church, Virginia; Andrew Maitland, M.D., Cardiac Surgery, Foothills Medical Centre, Calgary, Alberta, Canada; David Marsh, M.D., Associate Director, San Diego Cardiac Center, San Diego, California; Nancy Nussmeier, M.D., Clinical Associate Professor, Cardiovascular Anesthesiology, Texas Heart Institute, Houston, Texas; Anjum G. Qazi, M.D., Cardiac Surgery, Washington Adventist Hospital, Takoma Park, Maryland; Scott T. Reeves, M.D., Professor, Department of Anesthesiology and Perioperative Medicine, Medical University of South Carolina Hospital, Charleston, South Carolina; Mohan R. Sarabu, M.D., Cardiac Surgery, Westchester Medical Center, Valhalla, New York; Linda Shore-Lesserson, M.D., Associate Professor, Department of Anesthesiology, Mount Sinai School of Medicine, New York, New York; Norman Silverman, M.D., Chief, Cardiothoracic Surgery, Henry Ford Hospital, Detroit, Michigan; Victor E. Tedesco, M.D., Touro Infirmary, New Orleans, Louisiana; Serge G. Tyler, M.D., Department of Anesthesia, John Stroger Hospital, Chicago, Illinois; Felipe Urdaneta, M.D., Assistant Professor, Department of Anesthesiology, V.A. Medical Center, Gainesville, Florida; Hugo Van Aken, M.D., Department of Anesthesiology and Intensive Care Medicine, University Hospital of Muenster, Muenster, Germany; Michael T. Weaver, M.D., Pendleton Memorial Methodist Hospital, New Orleans, Louisiana; Thorsten Wahlers, M.D., Klinikdirektor Prof., Klinikum der Friedrich Schiller, Universitat Jena, Jena, Germany; Ian J. Welsby, M.B.B.S., Assistant Professor, Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina; Michael Zenz, M.D., Department of Anesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital Bergmannsheil, Bochum, Germany. Cited Here...
This article has been cited 12 time(s).
Journal of Thrombosis and HaemostasisA chemically-modified inactive antithrombin as a potent antagonist of fondaparinux and heparin anticoagulant activityJournal of Thrombosis and Haemostasis
Clinics in Liver DiseaseHeparin-like Effect in Liver Disease and Liver TransplantationClinics in Liver Disease
Basic & Clinical Pharmacology & ToxicologySerious anaphylactic reactions due to protamine sulfate: A systematic literature reviewBasic & Clinical Pharmacology & Toxicology
Anesthesia and AnalgesiaThe Right Ventricle in Cardiac Surgery, a Perioperative Perspective: II. Pathophysiology, Clinical Importance, and ManagementAnesthesia and Analgesia
Contemporary Clinical TrialsThe use of high-fidelity human patient simulation as an evaluative tool in the development of clinical research protocols and proceduresContemporary Clinical Trials
Perfusion-UkDoes an allergy to fish pre-empt an adverse protamine reaction? A case report and a literature reviewPerfusion-Uk
Transfusion Medicine ReviewsAnticoagulants and their reversalTransfusion Medicine Reviews
Perfusion-UkAnticoagulation management in patients undergoing open heart surgery by activated clotting time and whole blood heparin concentrationPerfusion-Uk
Hematology-Oncology Clinics of North AmericaRegulation of thrombin activity - Pharmacologic and structural aspectsHematology-Oncology Clinics of North America
Thrombosis and HaemostasisHeparanase modulates heparinoids anticoagulant activities via non-enzymatic mechanismsThrombosis and Haemostasis
Anesthesia and AnalgesiaThe Effect of Epsilon-Aminocaproic Acid and Aprotinin on Fibrinolysis and Blood Loss in Patients Undergoing Primary, Isolated Coronary Artery Bypass Surgery: A Randomized, Double-Blind, Placebo-Controlled, Noninferiority TrialAnesthesia and Analgesia
European Journal of PharmacologyReversal of heparin-induced increases in aPTT in the rat by PM102, a novel heparin antagonistEuropean Journal of Pharmacology
© 2005 American Society of Anesthesiologists, Inc.
Publication of an advertisement in Anesthesiology Online does not constitute endorsement by the American Society of Anesthesiologists, Inc. or Lippincott Williams & Wilkins, Inc. of the product or service being advertised.