Perioperative approaches to coagulation defects

Coagulopathy After Ruptured Abdominal Aortic Aneurysm

Although potentially treatable, coagulopathy is often included among the predictors of a poor outcome after ruptured abdominal aortic aneurysm (rAAA). The purpose of this review was to define the incidence of coagulopathy among patients presenting with rAAA and to identify the factors contributing to its development.

The medical records of 89 consecutive patients presenting with a rAAA were retrospectively reviewed. Laboratory results (international normalized ratio [INR], partial thromboplastin time [aPTT], platelet count, fibrinogen, and fibrin degradation products [D-dimer]) measured on admission and perioperatively were recorded and related to features of the patients' prehospital and hospital course.

At least one admission coagulation study was obtained in 70 of 89 patients. All measured coagulation values were within the normal range in only 10 (14%) patients, whereas at least one value was in the coagulopathic bleeding range in 17 patients (24%). Profound abnormalities of the INR (> 2.0) were present in 24%, of the aPTT (> 60 sec) in 12%, and of the platelet count (< 50) in 7% of patients. In a multivariate model, hematocrit was the only significant predictor of an INR > 2.0, while hematocrit and degree and duration of hypotension predicted an aPTT > 60 sec. Fluid volume prior to admission did not independently predict either the INR or aPTT, although it was the only significant predictor of a platelet count <50. Admission D-dimer levels were elevated in 79% of patients and were not significantly associated with either the degree of hemorrhage or volume resuscitation. All coagulation studies showed deterioration following admission, with profound abnormalities observed in 90% and 52% of patients intraoperatively and postoperatively, respectively. Mortality was 74% among those undergoing operation and was significantly associated with advanced age and lowest systolic blood pressure, but not with admission INR or aPTT.

The majority of rAAA patients present with disordered coagulation, profound abnormalities being more related to the degree of hemorrhage than to the volume of fluid resuscitation. Evidence of intravascular fibrinolysis is even more common and may be more closely related to the aneurysm itself than to acute hemorrhage.

Use of Aprotinin in the Control of Bleeding During Cardiopulmonary Bypass Surgery: Current Status

Excessive bleeding is one of the major complica tions of cardiac surgery with cardiopulmonary bypass (CPB). This complication is related to the operation and the defects in hemostasis induced by extracorporeal circulation. The system atic effects of CPB are called whole body inflammatory reac tion. Heparin, platelet dysfunctions, and fibrinolysis are the major causes of bleeding problems associated with CPB. Dif ferent pharmacological approaches have been used to reduce bleeding and the need for blood transfusions in patients under going cardiac surgery. The most effective is aprotinin, a serum protease inhibitor that is an antifibrinolytic with a platelet- preserving action. It inhibits the activation of the intrinsic co agulation system. Aprotinin therapy effectively reduces blood loss and donor blood requirements. According to most reports, it does not increase the risk of acute myocardial infarction, renal dysfunction, and mortality.

Age and left ventricular impairment predict reopening for bleeding

Statistical analysis of data collected prospectively from all patients undergoing surgery under cardiopulmonary bypass from September 1994 to November 1998 (group 1) was performed to identify preoperative risk factors for reopening for bleeding. Multiple logistic regression analysis of 19 preoperative variables was carried out with reoperation for bleeding as the endpoint. The protocol for intraoperative use of aprotinin was then changed to include high-risk patients. Data collected from all subsequent patients from May 1999 to March 2002 (group 2) were analyzed. Subgroup analyses on primary isolated coronary artery surgery were also performed. Data were obtained from 1,946 patients aged 22 to 88 years (mean, 62.5 years). Older age, severe left ventricular impairment, redo surgery, and chronic renal failure were the independent predictors of reopening for bleeding in group 1. There were no independent predictors of reopening in group 2. Older age and chronic renal failure were the predictors of reexploration for bleeding in patients undergoing primary isolated coronary artery grafting. Prophylactic measures to prevent excessive bleeding should be used in elderly patients and those with severe left ventricular impairment, redo surgery, and chronic renal failure.

Desmopressin does not reduce bleeding and transfusion requirements in congenital heart operations

BACKGROUND

Desmopressin (DDAVP) has been evaluated in many randomized clinical trials as a means to reduce blood loss and transfusion of allogeneic blood in cardiac operation requiring cardiopulmonary bypass. Desmopressin reduces blood loss in adult patients with excessive bleeding after cardiac operation. Its usefulness in patients undergoing complex congenital heart repair with cardiopulmonary bypass is unproved.

METHODS

Sixty patients younger than 40 years of age scheduled for complex congenital heart operation (44 redo, 16 primary) were enrolled in this prospective, randomized, double-blind trial. Desmopressin 0.3 microg/kg or placebo was administered 10 minutes after protamine administration. Transfusion requirements and postoperative blood loss were recorded. Differences were analyzed using analysis of variance with a p value of 0.05 or less used to denote statistical significance.

RESULTS

There were no differences in demographic or surgical characteristics between the DDAVP or placebo groups. There was no difference in blood loss and transfusion requirements between the DDAVP and placebo groups. During the intraoperative postinfusion time period, the median blood loss for redo patients was 343 versus 357 mL/m2 for placebo versus DDAVP, respectively, and for primary patients, the median blood loss was 277 versus 228 mL/m2.

CONCLUSIONS

The prophylactic use of DDAVP to reduce excessive bleeding or transfusion requirements in patients undergoing complex congenital heart operations is not warranted.

The effect of three different doses of tranexamic acid on blood loss after cardiac surgery with mild systemic hypothermia (32 degrees C)

OBJECTIVE

Prophylactic administration of tranexamic acid (TA), an antifibrinolytic agent, decreases bleeding after cardiac surgery with systemic hypothermia (25 degrees C to 29 degrees C). Warmer systemic temperatures during cardiopulmonary bypass (CPB) may reduce bleeding and thus alter the requirement for TA. The effect of three different doses of TA on bleeding after cardiac surgery with mild systemic hypothermia (32 degrees C) is evaluated.

DESIGN

Double-blind, prospective, randomized study.

SETTING

University hospital.

PARTICIPANTS

One hundred fifty adult patients undergoing aortocoronary bypass or valvular cardiac surgery.

INTERVENTIONS

Patients received TA, 50 (n = 50), 100 (n = 50), or 150 (n = 50) mg/kg intravenously before CPB with mild systemic hypothermia.

MEASUREMENTS AND MAIN RESULTS

Blood loss through chest drains over 6, 12, and 24 hours after surgery and total hemoglobin loss were measured. Autotransfused blood, transfused banked blood and blood products, and coagulation profiles were measured. Analysis of variance on log-transformed data for blood loss and confidence intervals (CIs) of 0.95 were calculated and transformed to milliliters of blood. No patient was re-explored for bleeding. Blood loss at 6 hours was statistically greater in the 50-mg/kg group compared with the other two groups (p = 0.03; p = 0.02). Total hemoglobin loss was statistically greater in the 50-mg/kg group compared with the 150-mg/kg group (p = 0.04). There was no statistical difference in blood tranfusion rate or coagulation profiles among the three groups. However, preoperative hemoglobin level was statistically lower in the 150-mg/kg group compared with the other two groups (p = 0.01).

CONCLUSION

Of the three doses of TA studied, the most efficacious and cost-effective dose to reduce bleeding after cardiac surgery with mild hypothermic systemic perfusion is 100 mg/kg.

epsilon-Aminocaproic acid plasma levels during cardiopulmonary bypass

epsilon-Aminocaproic acid (EACA) concentrations achieved during cardiopulmonary bypass (CPB) have not been previously reported. It is unknown whether plasma concentrations reported to inhibit fibrinolysis in vitro (130 microg/mL) are achieved or whether differences in these levels relate to variability in postoperative bleeding. EACA (total intraoperative dose 270 mg/kg) was administered to 27 patients undergoing cardiac reoperation. The plasma EACA concentration was measured by using high-pressure liquid chromatography: 1) 30 min after initiation of drug administration (baseline); 2) 30 min (CPB + 30) after initiation of CPB; 3) 90 min after initiation of CPB. (CPB + 90); and 4) at cardiopulmonary bypass termination (end CPB). Plasma EACA concentrations (microg/mL, min - max, mean +/- SD) were 276-998, 593 +/- 154 at baseline; 147-527, 302 +/- 95 at CPB + 30; 112-500, 314 +/- 100 at CPB + 90; and 84-537, 317 +/- 100 at end CPB. Twenty-four-hour postoperative thoracic drainage and allogeneic red blood cell transfusions were not associated with plasma levels at any time. Although plasma EACA concentrations greater than 130 microg/mL were consistently achieved, we observed a marked variability (more than sixfold) in plasma concentrations and bleeding outcomes despite the use of a weight-based dosing regimen. This variability in drug levels appears to have little relevance to bleeding outcomes, possibly since mean plasma levels exceeded 130 microg/mL during CPB, and nearly all patients (26 of 27) achieved that target level.

Maintenance of therapeutic plasma aprotinin levels during prolonged cardiopulmonary bypass using a large-dose regimen

Aprotinin concentrations in the range of 127-191 kallikrein inactivator units (KIU)/mL at the end of cardiopulmonary bypass (CPB) (< 2 h duration) reduce transfusion requirements. It has been suggested that prolonged CPB may require higher infusion rates which significantly increase cost. We tested the hypothesis that large-dose aprotinin maintains therapeutic plasma levels during prolonged periods of CPB (< 2 h). Aprotinin was administered as follows: 2 x 10(6) KIU upon skin incision; 0.5 x 10(6) KIU/h x 4-h infusion on initiation of CPB; and 2 x 10(6) KIU added to the CPB prime solution. Aprotinin activity was measured 1) 30 min after initiation of drug administration (Pre-CPB); 2) 30 min after initiation of CPB (CPB + 30); 3) 90 min after initiation of CPB (CPB + 90); and 4) at CPB termination (End CPB). CPB duration (mean +/- SD) was 158 +/- 51 min. Plasma aprotinin concentrations (KIU/mL, mean +/- SD) were: 234 +/- 30 at Pre-CPB; 229 +/- 35 at CPB + 30; 184 +/- 27 at CPB + 90; and 179 +/- 22 at End CPB. In all patients, aprotinin levels at the completion of CPB were in the range previously reported to be effective. The authors conclude that large-dose regimen limited to 6 x 10(6) KIU maintained therapeutic plasma aprotinin concentrations during prolonged CPB.

Aprotinin

OBJECTIVE

To review the clinical pharmacology of aprotinin in patients undergoing surgical procedures involving major blood loss, namely, coronary artery bypass graft (CABG).

DATA SOURCES

A MEDLINE search was used to identify French- and English-language publications on aprotinin using the indexing terms aprotinin, cardiothoracic surgery, and hemorrhage. The MEDLINE search was supplemented by review of article bibliographies. Data also were obtained from the approved Canadian and US product labels.

STUDY SELECTIONS

All abstracts and uncontrolled and controlled clinical trials were reviewed.

DATA EXTRACTION

Study design, population, results, and safety information were retained. Efficacy conclusions were drawn from controlled trials.

DATA SYNTHESIS

Aprotinin, a serine protease inhibitor isolated from bovine lung tissue, decreases bleeding after cardiac surgery by mechanisms including antifibrinolytic activity and preservation of platelet function. Several trials have shown that aprotinin reduced blood loss and transfusion requirements in patients undergoing CABG. Its use in other surgical procedures involving major blood loss has been reported. Aprotinin is well tolerated, with minor allergic reactions being the most frequently reported adverse effect. Although unsubstantiated, the possibility that aprotinin could create a prothrombic state leading to early graft occlusion and formation of microthrombi in renal and coronary vasculatures is of concern.

CONCLUSIONS

Aprotinin is an effective hemostatic agent in CABG. Clear definitions of indications, dosing, safety, and repeated use remain to be investigated thoroughly.

Factors influencing haemostasis and blood transfusion in cardiac surgery

To find out the risk factors influencing perioperative bleeding and use of blood products in cardiac surgery so that appropriate interventions can be selected for blood conservation, risk factors were analysed in 343 cardiac surgical patients, retrospectively, by multiple regression technique. The results showed that the factors related to postoperative bleeding were male gender, Higgins score, cardiopulmonary bypass (CPB) time, operation procedures, intraoperative blood loss and use of internal mammary artery (IMA) graft. Factors related to perioperative homologous blood transfusions were emergency surgery, preoperative haemoglobin level, Higgins score, intraoperative blood loss, operation time and operation procedures. The geometric mean of postoperative bleeding in the entire series was 1085 ml and the mean packed red cell, plasma and platelet transfusions were 3.29 +/- 0.4, 1.96 +/- 0.39 and 0.21 +/- 0.05 units respectively. The incidence of homologous blood transfusion during the hospital stay was 58.9% for the entire series and 54.5% in the nonrevision patients. Emergency patients received significantly more blood transfusion (p = 0.0001). Perioperative blood loss and transfusions are still problems in cardiac surgery and certain patient groups in this study were identified as high risk; available blood conservation techniques, therefore, are recommended in these patients.