[Mechanisms and prediction of hemorrhagic complications during surgery of thoraco-abdominal aortic aneurysms]

[Blood transfusion via the cardiopulmonary bypass circuit: the anesthesiologist point of view]

Cardiac surgery frequently requires blood transfusion. The use of transfusion should be restricted due to side effects. Blood transfusion via the cardiopulmonary bypass (CPB) circuit is easy and allows a fast transfusion. The administration of packed red cells is relatively frequent because of the CPB-induced hemodilution and of the higher rate of postoperative complications when the haematocrit during CPB decreases below 20%. This transfusion of packed red cells does not seem to be associated with complications during CPB. Platelet transfusion during bypass is illogical because of the destruction of platelets during CPB and must be avoided. Fresh frozen plasma transfusion during CPB is seldom indicated but is possible. It could reverse heparin resistance.

Coagulation Disorders and Blood Product Use in Patients Undergoing Thoracoabdominal Aortic Aneurysm Repair

Repair of thoracoabdominal aortic aneurysms (TAAA) is associated with major blood loss, often exceeding the patient's intravascular volume, and complex intraoperative and postoperative coagulopathies necessitating large-volume transfusion of blood products. Abnormalities sufficient to cause thrombocytopenia or clinically important prolongation of clotting parameters are rarely present before surgery in elective aneurysms but are more common with ruptured aneurysms. The finding of intraoperative and postoperative deficiencies of clotting factors, along with thrombin generation and activation of the thrombolytic system, is reflective of massive blood losses, visceral ischemia, and massive transfusions. An aggressive strategy of transfusion of blood products is critical to the prevention of clinically significant coagulopathy during surgery. Adjuncts to reduce blood losses and blood product use include low-dose aprotinin or epsilon -aminocaproic acid, intraoperative blood salvaging, and acute normovolemic hemodilution. In TAAA repair, an average blood loss of 5000 to 6000 mL and average transfusion of allogeneic blood products of 50 to 60 U are to be anticipated.

Activation of fibrinolytic pathways is associated with duration of supraceliac aortic cross-clamping

PURPOSE

The cause of the coagulopathy seen with supraceliac aortic cross-clamping (SC AXC) is unclear. SC AXC for 30 minutes results in both clotting factor consumption and activation of fibrinolytic pathways. This study was undertaken to define the hemostatic alterations that occur with longer intervals of SC AXC.

METHODS

Seven pigs underwent SC AXC for 60 minutes. Five pigs that underwent infrarenal aortic cross-clamping (IR AXC) for 60 minutes and 11 pigs that underwent SC AXC for 30 minutes served as controls. No heparin was used. Blood samples were drawn at baseline, 5 minutes before release of the aortic clamp, and 5, 30, and 60 minutes after unclamping. Prothrombin time, partial thromboplastin time, platelet count, and fibrinogen concentration were measured as basic tests of hemostatic function. Thrombin-antithrombin complexes were used to detect the presence of intravascular thrombosis. Fibrinolytic pathway activation was assessed with levels of tissue plasminogen activator antigen and tissue plasminogen activator activity, plasminogen activator inhibitor-1 activity, and alpha2-antiplasmin activity. Statistical analysis was performed with the Student t test and repeated measures of analysis of variance.

RESULTS

Prothrombin time, partial thromboplastin time, and platelet count did not differ between groups at any time. Fibrinogen concentration decreased 5 minutes (P =.005) and 30 minutes (P =.006) after unclamping in both SC AXC groups, but did not change in the IR AXC group. Thrombin-antithrombin complexes increased in both SC AXC groups, but were not significantly greater than in the IR AXC group. SC AXC for both 30 and 60 minutes produced a significant increase in tissue plasminogen activator antigen during clamping and 5 minutes after clamping. This increase persisted for 30 and 60 minutes after clamp release in the 60-minute SC AXC group. Tissue plasminogen activator activity, however, increased only in the 60-min SC AXC group during clamping (P =.02), and 5 minutes (P =.05) and 30 minutes (P =.06) after unclamping, compared with both control groups.

CONCLUSIONS

Thirty and 60 minutes of SC AXC results in similar degrees of intravascular thrombosis and fibrinogen depletion. Although SC AXC for both 30 and 60 minutes leads to activation of fibrinolytic pathways, only 60 minutes of SC AXC actually induces a fibrinolytic state. Fibrinolysis appears to be an important component of the coagulopathy associated with SC AXC, and is related to the duration of aortic clamping.

CLINICAL RELEVANCE

The coagulopathy frequently associated with thoracoabdominal aortic aneurysm repair is thought to revolt visceral ischemia-reperfusion. The nature of this coagulopathy is controversial. The current study demonstrates that the major hemostatic alteration associated with supraceliac aortic cross-clamping is activation of fibrinolytic pathways. The magnitude of this fibrinolytic response is directly related to the duration of supraceliac aortic occlusion. Future efforts to treat this coagulopathy may well include judicious use of autofibrinolytic agents.

A cohort study of coagulation parameters and the use of blood products in surgery of the thoracic and thoracoabdominal aorta

OBJECTIVES

We sought to study the hemostatic profile and the use of blood products in patients undergoing thoracic and thoracoabdominal aortic aneurysm repair.

METHODS

This is a cohort study comparing three groups of patients: 7 undergoing elective acute normovolemic hemodilution (ANH); 15 undergoing elective procedures without ANH (non-ANH); and 8 undergoing repair of ruptured thoracoabdominal aneurysms. A control group of 10 patients was used for comparison of preoperative hemostasis. The parameters studied were platelet concentration, partial thromboplastin time (PTT), and international normalized ratio (before and after surgery), packed red blood cells, fresh frozen plasma, platelets, cryoprecipitates, donor exposure, and use of desmopressin and epsilon-aminocaproic acid. Analysis of variance and multiple stepwise regression analysis were used.

RESULTS

Before operation the patients with aneurysms had PTTs prolonged compared with control subjects (P <.05). After operation the ANH group had higher platelet counts than the ruptured group (P =.001) and higher platelet counts (P =.05) and lower PTTs (P =.001) than the non-ANH group. The ANH group was transfused fewer platelets than the non-ANH group (P =.001) and less of every blood product than the ruptured group (P =.05); statistically significant differences were not observed for packed red blood cells, fresh frozen plasma, or platelets. The ANH group was exposed to an average of 65 donors fewer than the ruptured group (P <.001) and 34 fewer than the non-ANH group (P <.05). These differences could not be explained by baseline coagulation status or by the intraoperative use of desmopressin or epsilon-aminocaproic acid.

CONCLUSIONS

The coagulation abnormality identified before surgery is that of higher PTT values, suggesting a disturbance of the extrinsic coagulation pathway. Blood losses, donor exposure, and platelet use were highest in the ruptured group and lowest in the ANH group. After surgery the ruptured group exhibited the worst coagulation parameters, and the ANH group exhibited the best with higher platelet count and lower PTT values than the other groups. The ANH technique appears to be an useful adjunct in the anesthetic management of these patients.

[Preoperative evaluation of hemorrhagic risk]

Should we consider that haemostasis tests may help guide the anaesthesiologist's therapeutic choices when the patients is on the operating table and bleeds without evident explanation? The response is yes, provided that the results will be available rapidly. Haemostasis tests that are performed in laboratory wards distant from the surgery room often prove to be unuseful in emergency situations as haemostasis abnormalities usually occur in a shorter time than is required to get biological test results. Devices located in the vicinity of the surgery room should therefore be available to the anaesthesiologist. Furthermore, these devices should be able to perform not only platelet counts and haematocrit determination, but other blood tests that may be useful to get further insights in the patient's haemostasis function. Such devices are already available, allowing rapid haemostasis tests in the surgery room and prompt decision with regard to appropriate transfusion policy. However, the haemostasis laboratory is still useful, as it permits to refine coagulation profile and also offers quality controls for those tests that were done in the surgery room.

Aprotinin to decrease bleeding and intraoperative blood transfusion requirements during descending thoracic and thoracoabdominal aortic aneurysmectomy using cardiopulmonary bypass

The purpose of this retrospective study was to assess the efficacy of aprotinin, an antifibrinolytic agent, in reducing bleeding and blood transfusion requirements in patients undergoing descending thoracic or thoracoabdominal aortic aneurysmectomy using cardiopulmonary bypass (CPB). Sixty-nine consecutive patients underwent thoracic or thoracoabdominal aneurysmectomy using CPB in a 2-year period. None of the 29 patients operated on in 1990 (group 1) received aprotinin, whereas all 40 patients operated on in 1991 (group 2) were placed on a high-dose regimen of aprotinin. There were no significant differences between the two groups. Administration of aprotinin was associated with a decrease in CPB time (p = 0.02), surgical duration (p = 0.05) and intraoperative blood loss (p = 0.008) as well as a reduction in intraoperative packed red cells (p = 0.01), Cell-Saver units (p = 0.05), fresh-frozen plasma units (p = 0.002), and platelet concentrate (p = 0.01) requirements. These data suggest that aprotinin is effective in reducing bleeding and blood transfusion requirements during descending thoracic or thoracoabdominal aortic aneurysmectomy using CPB.

Intraoperative measurement of activated partial thromboplastin time and prothrombin time with a new compact monitor

A prospective study was conducted to evaluate a new compact portable coagulation monitor (Ciba-Corning Biotrack 512 Monitor), which enables the clinician to perform instantaneous activated partial thromboplastin time (APTT) and prothrombin time (PT). 126 patients scheduled for heparinized and nonheparinized vascular surgery, and gynaecological surgery, were included. A drop of capillary or venous whole blood was applied in disposable cartridges to successively perform APTT and PT, and the results of the tests were compared with conventional laboratory methods, performed in two different laboratories (Lab. A and B). Comparisons between Lab. A. and Lab. B. enables determination of the bias, precision, and percent of outliers (patients whose values differed more than 20%) in conventional methods. The reference value was defined as the mean of Lab. A. and Lab. B. values. For PT, there were no statistical differences between the capillary and venous samples performed with the portable monitor, and the reference value, for the bias, the precision and the proportion of outliers. For APTT, there were no statistical differences between the capillary and venous samples performed with the portable monitor, and the reference value, for the bias and the precision. The percent of outliers, however, was significantly greater with the venous sample of the compact monitor than with the reference (48 versus 22%), and even if it did not reach the statistical significance (P = 0.07) it was also higher with the capillary sample performed with the Ciba Monitor than with the reference (33%).(ABSTRACT TRUNCATED AT 250 WORDS)