The effects of acute normovolemic hemodilution on coagulation and blood utilization in major surgery

Validating the Physiologic Model HumMod as a Substitute for Clinical Trials Involving Acute Normovolemic Hemodilution

BACKGROUND

Blood conservation strategies and transfusion guidelines remain a heavily debated clinical topic. Previous investigational trials have shown that acute isovolemic hemodilution does not limit adequate oxygen delivery; however, a true critical hemoglobin level has never been investigated or defined due to safety concerns for human volunteers. Validated physiologic modeling may be useful to investigate hemodilution at critical hemoglobin levels without the ethical or safety hazards of clinical trials. Our hypothesis is that HumMod, an integrative physiological model, can replicate the cardiovascular and metabolic findings of previous clinical studies of acute isovolemic hemodilution and use coronary blood flow and coronary oxygen delivery in extreme hemodilution to predict a safety threshold.

METHODS

By varying cardiovascular and sizing parameters, unique individuals were generated to simulate a population using HumMod, an integrative mathematical model of human physiology. Hemodilution was performed by simultaneously hemorrhaging 500 mL aliquots of blood while infusing equal volumes of hetastarch, 5% albumin balanced salt solution, or triple volumes of lactated Ringer's solution over 10 minutes. Five hemodilution protocols reported over 3 studies were directly replicated with HumMod to compare and validate essential cardiovascular and metabolic responses to hemodilution in moderately healthy, awake adults. Cardiovascular parameters, mental status, arterial and mixed venous oxygen content, and oxyhemoglobin saturation were recorded after the removal of each aliquot. The outputs of this simulation were considered independent variables and were stratified by hemoglobin concentration at the time of measurement to assess hemoglobin as an independent predictor of hemodynamic and metabolic behavior.

RESULTS

The published reports exhibited discrepancies: Weiskopf saw increased heart rate and cardiac index, while Jones and Ickx saw no change in these variables. In HumMod, arterial pressure was maintained during moderate hemodilution due to decreases in peripheral resistance opposing increases in cardiac index. HumMod showed preserved ventilation through moderate hemodilution, compensated for by an increased oxygen extraction similar to the studies of Jones and Ickx. The simulation results qualitatively followed the clinical studies, but there were statistical differences. In more extreme hemodilution, HumMod had a lesser increase in cardiac index, which led to deficiencies in oxygen delivery and low venous saturation. In the simulations, coronary blood flow and oxygen delivery increase up to a critical hemoglobin threshold of 55-75 g/L in HumMod. In this range, coronary blood flow and oxygen delivery fell, leading to cardiac injury. The allowable amount of hemodilution before reaching the critical point is most closely correlated with nonmuscle mass (r = 0.69) and resting cardiac output (r = 0.67).

CONCLUSIONS

There were significant statistical differences in the model population and the clinical populations, but overall, the model responses lay within the clinical findings. This suggests our model is an effective replication of hemodilution in conscious, healthy adults. A critical hemoglobin range of 5.5-7.5 g/L was predicted and found to be highly correlated with nonmuscle mass and resting cardiac output.

Fresh-frozen plasma transfusion strategy in trauma with massive and ongoing bleeding. Common (sense) and sensibility

During trauma resuscitation involving massive transfusion, the best fresh-frozen plasma to packed red blood cells ratio is unknown. No randomised controlled trial (RCT) is available on this subject, although there are plenty of observational studies suggesting that the ratio should be about 1:1. This ratio also makes more physiological sense, and we suggest that in patients with massive and ongoing bleeding, it is a sensible strategy with which to start resuscitation.

Are we giving enough coagulation factors during major trauma resuscitation?

Hemorrhage is a major cause of trauma deaths. Coagulopathy exacerbates hemorrhage and is commonly seen during major trauma resuscitation, suggesting that current practice of coagulation factor transfusion is inadequate. Reversal of coagulopathy involves normalization of body temperature, elimination of the causes of disseminated intravascular coagulation (DIC), and transfusion with fresh-frozen plasma (FFP), platelets, and cryoprecipitate. Transfusion should be guided by clinical factors and laboratory results. However, in major trauma, clinical signs may be obscured and various factors conspire to make it difficult to provide the best transfusion therapy. Existing empiric transfusion strategies for, and prevailing teachings on, FFP transfusion appear to be based on old studies involving elective patients transfused with whole blood and may not be applicable to trauma patients in the era of transfusion with packed red blood cells (PRBCs). Perpetuation of such concepts is in part responsible for the common finding of refractory coagulopathy in major trauma patients today. In this review, we argue that coagulopathy can best be avoided or reversed when severe trauma victims are transfused with at least the equivalent of whole blood in a timely fashion.

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.

A comparative study of the postoperative allogeneic blood-sparing effect of tranexamic acid versus acute normovolemic hemodilution after total knee replacement

Both acute normovolemic hemodilution (NVHD) and tranexamic acid (TA) are potentially useful allogeneic blood conservation strategies after total knee replacement. However, the relative efficacy of these blood-sparing techniques is unknown. Therefore, to compare the postoperative allogeneic blood sparing of NVHD and TA after total knee replacement, we investigated 40 patients in a prospective, single-blinded study protocol. In Group TA, 30 min before deflating the limb tourniquet, an IV infusion of TA, 15 mg/kg, was administered over a 30-min period. Thereafter, a constant IV infusion of 10 mg x kg(-1) x hr(-1) was administered until 12 h after deflation of the limb tourniquet. Before induction of anesthesia, NVHD patients were bled to a target hematocrit of approximately 28%. Intravascular blood volume was maintained with lactated Ringer's solution. All autologous blood was transfused at the end of the surgery. Postoperatively, hematocrit was measured daily. In all cases, a hematocrit <27% was the postoperative transfusion trigger. Before discharge, deep vein thrombosis was excluded by Echo Doppler. Three months after surgery, the incidence of delayed thromboembolic events was assessed. The two groups were demographically comparable. In Group NVHD, 843 mL+/-289 of autologous blood was removed. Despite autologous blood transfusion, during the early postoperative period and until the third postoperative day, the NVHD group had significantly (P < 0.01) lower mean hematocrits when compared with the TA group. Thereafter, because of a significantly (P < 0.0008) greater allogeneic blood requirement in the NVHD group, no statistically significant difference in mean hematocrit recordings was noted among the groups. Blood accumulation in the surgical drain 12 h postoperatively, was significantly (P < 0.0008) higher in the NVHD group (259 mL+/-156) when compared with the TA group (110 mL+/-62). Significantly (P < 0.0008) more allogeneic blood was transfused in the NVHD group (19 U/13 patients) when compared with the TA group (2 U/2 patients). No abnormal Echo Doppler studies were reported. During the 3-mo follow-up period, a deep vein thrombosis and pulmonary embolus were documented in one patient in the NVHD group. We conclude that perioperative hemodynamic stability and allogeneic blood sparing is superior after tranexamic acid administration when compared with normovolemic hemodilution.

IMPLICATIONS

For total knee replacement, when compared with normovolemic hemodilution, tranexamic acid administration is associated with superior perioperative hemodynamic stability and allogeneic blood sparing.

Differential effects of serial hemodilution with hydroxyethyl starch, albumin, and 0.9% saline on whole blood coagulation

STUDY OBJECTIVES

To determine by thrombelastography assessed coagulation, the effects of progressive hemodilution with three intravascular volume expanders.

DESIGN

Prospective, controlled, whole blood, volumetric ex vivo hemodilution study.

SETTING

University of Pennsylvania Medical Center Operating Rooms.

PATIENTS

60 ASA physical status I and II patients; phlebotomy prior to administration of IV fluids or medications.

INTERVENTIONS

Analysis of whole blood clotting determined by six thrombelastographic channels for control and five volumetric hemodilutions (11%, 25%, 33%, 50%, and 75%) with 0.9% saline, 5% albumin, and 6% hydroxyethyl starch (n = 20 for each diluent group).

MEASUREMENTS AND MAIN RESULTS

Thrombelastographic parameters R (minutes), angle alpha (degree), MA (mm), and lysis (%) were measured and compared to the sample control for each dilution of the same specimen. There was no significant difference between control groups in any thrombelastographic variable (R, angle alpha, MA, or lysis). No changes were seen in any variable from any diluent at 11% hemodilution. Seventy-five percent hemodilution caused significantly hypocoagulable changes from control for all thrombelastographic parameters for all three diluents. Thrombelastographic indices differed significantly from controls at intermediate hemodilutions. Both colloids caused decreases in measured angle alpha and MA at lower hemodilution than did 0.9% saline. Albumin 5% caused significant hypocoagulable changes from control values at lower hemodilution than did either 0.9% saline or 6% hydroxyethyl starch for all thrombelastographic parameters. Saline 0.9% increased angle alpha significantly at 50% hemodilution. Abnormal lysis did not occur at any dilution. Differing ex vivo effects of three different intravascular fluids thrombelastography assessed coagulation are found.

CONCLUSION

No differences were found after 11% hemodilution with any volume expanders. Hemodilution with up to 50% saline maintained thrombelastographic indices. Albumin produced early and profound hypocoagulable effects. Significant hypocoagulability occurred for all three diluents at 75% hemodilution. The study supports the use of albumin in patients at risk for thrombosis, and saline in patients with a need for normal hemostasis.

Profound normovolemic hemodilution: hemostatic effects in patients and in a porcine model

Previous systematic investigations of the hemostatic effects of normovolemic hemodilution (NHD) have not explored the influence of hematocrits less than 20% in humans or animals. However, clinical interest in maximizing the perioperative conservation of erythrocytes may involve profound NHD beyond traditionally accepted empiric end points. We report here on coagulation data in eight healthy adolescent patients undergoing profound NHD in concert with surgical correction of idiopathic scoliosis, and in 29 swine undergoing experimental stepwise NHD until death. Blood was replaced with 5% albumin in 0.9% saline in our patients, and with 5% albumin in lactated Ringer's solution in our pigs. A 75% blood volume exchange in our patients yielded a platelet count (PLT) of 158 +/- 26 x 10(3)/microL, fibrinogen concentration (FIB), 50 +/- 7 mg/dL, prothrombin time (PT), 25.4 +/- 2.6 s, activated partial thromboplastin time (aPTT), 87 +/- 15s, and a nadir hemoglobin of 2.8 +/- 0.2 g/dL; however, global oxygen delivery as assessed by body oxygen consumption remained adequate. Coagulation during the experimental porcine hemodilution was assessed by measuring PLT, FIB, PT, and aPTT, as well as by measurement of coagulation factor activities. In neither species did clinically significant thrombocytopenia (PLT < 100 x 10(3)/ microL) become manifest prior to clinical or other laboratory evidence of coagulopathy. Rather, a combined deficiency of coagulation factors explains the coagulopathy developing during NHD in both patients and swine. Abnormal hemostasis develops prior to compromise of global tissue oxygenation, assessed by mixed venous oxygen saturation and total body oxygen consumption, during NHD in healthy patients anesthetized as described. Therefore, NHD may be more limited by preservation of normal coagulation than of global oxygen delivery and consumption.

[Preoperative hemodilution by erythrocytapheresis with homologous blood saving in total hip arthroplasty]

OBJECTIVES

To compare three techniques for decreasing homologous blood requirements in total hip arthroplasty (THA), including preoperative autologous donation (PAD), preoperative acute normovolaemic haemodilution with erythrocytapheresis (erythro) and intraoperative normovolaemic haemodilution (haemo).

STUDY DESIGN

Prospective clinical trial.

PATIENTS

The study included 45 patients scheduled for THA, under general anaesthesia and operated on by the same surgeon. The patients were allocated into three groups of 15 each.

METHODS

Blood loss was assessed, during surgical procedure, by the weight of sponges and, the amount of blood collected in the suction bottles during and after surgery. The haemoglobin concentration was measured at the time of preoperative assessement (d-30), just prior to surgery (d-1), in the recovery room (d+3h), and 1, 3, and 8 days later (d8). The transfusion end-point in the three groups was to obtain a haemoglobin concentration of 100 g.L-1 from d+3h until d8. Every pack of red blood cells transfused was weighed and its haematocrit assessed to determine the accurate volume of red blood cells.

RESULTS

In the three groups haemoglobin concentration was similar from d+3h until d8. In the PAD group, no patient required homologous blood transfusion. There was no significant difference between the two other groups in the mean volume of homologous red blood cells required (308 +/- 197 mL in erythro group and 331 +/- 202 mL in the haemo group, respectively). The intraoperative blood loss was significantly higher (P = 0.001) in the erythro group: 914 +/- 305 mL vs 665 +/- 263 in the PAD group and 512 +/- 146 mL in the haemo group, respectively. There was an inverse correlation between haematocrit at d-1 and intraoperative bleeding (r = -0.7) (P = 0.0001). The distribution of the points was fitted as an exponential curve.

CONCLUSIONS

In THA, PAD is obviously the best technique to avoid homologous blood transfusion. However, when PAD is not feasible, removal of blood prior to surgery does not decrease requirements of homologous blood, as intraoperative blood loss is higher. Our results strongly question the use of major haemodilution during a surgical procedure exposing a major blood loss.

Maximum blood savings by acute normovolemic hemodilution

Acute normovolemic hemodilution (ANH) entails collecting blood from a patient immediately prior to surgery with concurrent fluid infusion to maintain intravascular volume constant. Blood collected during ANH is later reinfused to replace the red cell losses that occur during surgery. This technique is advocated as a means to reduce or eliminate homologous blood transfusion during surgery. Published guidelines for performing ANH vary, and the literature does not describe how to perform ANH to achieve the maximum benefit for a given patient. To evaluate how to save red blood cells as much as possible via ANH, and to determine the maximum benefit that can be expected, we developed a mathematic model of the process. Using the model, the net red cell mass savings possible when using ANH can be calculated given the patient's weight, initial hematocrit and minimum safe hematocrit. Results are reported to demonstrate the impact of the initial hematocrit and minimum safe hematocrit on the red cell savings possible with ANH. The data indicate that ANH does indeed save red blood cells that would otherwise be lost during surgery. However, the red cell savings possible when using ANH are not as much as typically published and, a degree of hemodilution more than that which is typically recommended is necessary to achieve even modest red cell savings.

Serial changes in hemostasis after intracranial surgery

We performed hemostatic studies on eight patients undergoing clipping of unruptured cerebral aneurysms to assess the influence of intracranial surgery itself on hemostasis. Blood samples were collected from each patient 10 times: before and after the induction of anesthesia and 6, 12, and 24 hours and 2, 3, 5, and 7 days immediately after surgery. The changes and our interpretation of them include the following: 1) the elevation of thrombin antithrombin III complex levels (activation of blood coagulation) was transient and monophasic; 2) the elevation of plasmin alpha 2-antiplasmin complex and D-dimer levels (activation of fibrinolysis) was biphasic, despite the monophasic elevation of tissue plasminogen activator or plasminogen activator inhibitor-1 levels; 3) the elevation of beta-thromboglobulin and platelet-factor-4 levels (activation of platelet) was also biphasic; 4) fibrinogen level and alpha 2-antiplasmin activity increased in the acute phase of the postoperative course (acute phase reaction); 5) the changes in hematocrit appeared to parallel those in various other parameters, especially platelet count, antithrombin III, and plasminogen levels for 1 or 2 days after surgery; 6) fibronectin appeared to be consumed in the acute phase of postoperative course; and 7) general anesthesia did not significantly affect hemostasis. These serial changes seem to be related to the activation of hemostatic systems after intracranial surgery and the subsequent acute phase reaction.

Acute normovolaemic haemodilution and idiopathic scoliosis surgery: effects on homologous blood requirements

After the introduction of acute normovolaemic haemodilution(NVHD) in our hospital, we prospectively studied 19 patients managed with moderate NVHD (mean haematocrit 0.28, SD 0.02) during idiopathic scoliosis surgery (mean angle 53.2, SD 16.7 degrees) with the Cotrel-Dubousset instrumentation (CDI). Our standard scoliosis anaesthetic technique was used. Intraoperatively, one patient received one unit of homologous blood. Postoperatively, seven patients received ten units of homologous blood. Homologous blood used was reduced by about 83% for this procedure in our institution. In the assessment of fluid and blood requirements we found physical signs reflecting tissue perfusion and oxygen supply more reliable than the estimated blood loss using the suction bottle and swabs. The similar postoperative complications (nine fever, five atelectasis/pneumonia, one urinary infection, one phlebitis), anaesthetic duration (mean 5.21, SD 1.13) hours, hospitalisation (mean 6.67, SD 1.19) days and return to normal activity (mean 8, SD 7.68) weeks indicate that the NVHD patients did just as well as with our previous regimen when only homologous blood was used.

[Effectiveness of the Cell Saver and salvage from ultrafiltered extracorporeal circulation in heart surgery]

The efficiency of two intraoperative techniques of blood saving were compared prospectively. During a period of eight months, in 120 adults patients undergoing heart surgery with a cardiopulmonary bypass (CPB). They all had blood removed before the start of CPB for isovolaemic haemodilution. They were randomly assigned to two groups (n = 60 for each): for group A patients, blood was salvaged during surgery before the start of the CPB, during cardioplegia, and from the CPB circuit at the end of surgery, using a Cell Saver 1V (Haemonetics), and returned to the patient in theatre or in intensive care; in group B patients, blood in the CPB circuit at the end of surgery was ultrafiltered and returned to the patient at the same time as 0.8 mg.kg-1 protamine sulfate. The same anaesthetic protocol was used in all the patients (flunitrazepam, phenoperidine and pancuronium bromide). There was no significant difference between the two groups in the volume of blood removed at the start of surgery (9.12 +/- 2.01 ml.kg-1 (A) vs. 8.85.2.22 ml.kg-1 (B)), in the amounts of replacement fluid (Haemaccel, 4% albumin) given to maintain volaemia, and in postoperative blood loss Red cell count, haemoglobin level and haematocrit were higher in the Cell Saver group at the third postoperative hour and on the first postoperative day, whereas fibrinogen levels and platelet count were higher in the ultrafiltration group at the same times. A mean of 1.02 +/- 1.71 homologous blood units were given to group A and 1.45 +/- 1.71 in group B (not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of isovolemic hemodilution on abdominal aortic aneurysmectomy in high risk patients

Intraoperative isovolemic hemodilution might increase blood flow and tissue oxygenation in the periphery but there is concern that acute anemia may have deleterious effects on myocardium in patients with coronary artery disease. This study investigates the effects of intraoperative isovolemic hemodilution on morbidity, mortality and hemodynamics in 32 patients with significant cardiovascular disease undergoing elective abdominal aortic aneurysmectomy. The average hematocrit was lowered intraoperatively from 43% to 31% by withdrawing blood and replacing volumes with 1:3 Ringer's lactate. In ten patients myocardial function was evaluated during aortic cross-clamping and declamping in the face of hemodilution. There were two deaths: one myocardial infarction and one multiple organ failure. Aortic cross clamping did not change heart rate, vascular pressures (VP), vascular resistance (SVR), cardiac output (CO), and left ventricular stroke work (LVSW). Following declamping, VP, CO and LVSW decreased and SVR increased momentarily (p less than 0.05), but the myocardial function did not change. Isovolemic hemodilution had no apparent adverse effects on morbidity, mortality and cardiovascular performance in these patients.

The advantages of hemodilution anesthesia for major liver resection in children

Since 1977, eight children have had major liver resections with the aid of normovolemic hemodilution anesthesia. Five children were 7 months of age or less; the other three were 3 1/2, 8, and 12 years old. This includes three operations for hepatoblastoma, three for hepatoma, and two for mesenchymal hamartoma. There were three right lobectomies, two trisegmentectomies, two extended left lobectomies, and one standard left lobectomy. With the use of this method, operative blood loss has been greatly reduced and operating technique significantly improved. After abdominal exploration and initial liver mobilization, whole blood is removed from the patient and simultaneously replaced with three times the volume of Ringer's lactate solution to maintain adequate intravascular volume. After the major blood loss has ceased, the patient is reinfused with his own blood and a simultaneous diuresis is induced with LASIX to remove the previously administered crystalloid solution. Metabolic demand is reduced by allowing the patient's temperature to drift down to 32 degrees C. Blood loss is further reduced by a Halothane-induced hypotension to a mean arterial pressure of 40 to 50 torr. The diluted blood lost during surgery has a low red blood cell volume per cc; therefore, each cc of blood lost depletes the total red cell volume by a lesser amount. This results in a nearly bloodless operative field which facilitates the ease, speed, and safety of the dissection. Use of this technique can avoid the need for massive intra-operative transfusions and the threat of cardiac arrest due to extensive blood loss during major liver resection in children.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodilution anesthesia: a valuable aid to major cancer surgery in children

Since 1974, 25 children had 27 major cancer operations with the aid of hemodilution anesthesia. This includes operations for Wilms' tumors, liver tumors, adrenal tumors, pancreatic tumors, ovarian tumors, and resection of metastatic thoracoabdominal tumors. With the use of this method, operative blood loss has been greatly reduced and operative technique improved. At the beginning of surgery, whole blood is removed from the patient and replaced with three times the volume of a balanced electrolyte solution to maintain intravascular volume. After the time of significant blood loss has ceased, the patient's own blood is returned and diuresis stimulated with furosimide to remove the infused electrolyte solution. Hypothermia, allowing the temperature to drift down to just below 32 degrees C, helps protect vital organs against hypoxia and arterial hypotension to a mean of 50 torr systolic pressure is well tolerated and further reduces blood loss. Adequate tissue oxygenation can be maintained safely during hemodilution to a hematocrit value of 14 percent. Use of bank blood transfusion was necessary in only 6 of 25 patients. It was given when the calculated postoperative hematocrit value would be less than 30 percent. The diluted blood lost during surgery has a low red blood cell volume per milliliter and each milliliter lost depletes the total red blood cell volume by a lesser amount. Also, the ease and speed of surgery may be facilitated by the nearly bloodless operative field. Provided respiratory support is maintained, these children showed only minor clinical effects from this large fluid infusion. The majority of patients who are Jehovah's Witnesses accept this technique with the modification that we keep the blood moving and in direct contact with the patient's vascular system. Carefully planned and meticulously applied short-term hemodilution anesthesia provides a safe method for minimizing operative blood loss and reduces the difficulty of major cancer surgery in children.