Acute normovolemic hemodilution L.
STEHLING AlYD H.L.
UUDER
reduced. For example, the patient with a hematocrit (Hct) of 45 percent (0.45)who intraoperatively loses a liter of blood loses 450 mL of RBCs. If the Hct is 25 percent (0.25),the RBC loss is only 250 mL. In addition, ANH provides the only practical means of obtaining fresh autologous whole blood for transfusion. Reviewing a wide variety of surgical procedures using ANH, Martin and associates’ reported a decrease of 18 to 90 percent in the use of homologous blood. Two other groups2*’ found that 60 to 90 percent of patients who had open heart surgery received no homologous blood when ANH was combined with the transfusion of shed mediastinal blood. Using extreme hemodilution (Hct 15% [0.15]),Martin and OtP decreased the mean homologous transfusion requirement from 4370 mL to 750 mL in a randomized study of 26 patients who underwent the placement of Harrington instrumentation for scoliosis. Comparing patients who underwent hemodilution with historic controls, Kafer et al.5 reported a decrease in the need for RBCs from 8.6 & 1.6 to 1 2 0 units in similar groups of patients undergoing spinal instrumentation placement. The ANH patients required no additional component therapy, unlike the control group who received 1.8 f 0.7 units of fresh-frozen plasma and 1.2 & 0.8 units of platelets. Sejourne and associates6 reported a significant decrease in the use of homologous blood components following hepatic resection when patients had undergone hemodilution. Once again, a comparison was made with a historic control group, although the patient population, technique, and surgical procedures were said to be comparable. In a randomized study of 21 patients having major colon surgery, Rose and Coutsoftides’ found that those who underwent hemodilution to an average Hct of 22 percent (0.22) required 2.4 fewer units of homologous blood than did the control group. RosbergB reported a decreased use of 1.2 units when patients for total hip arthroplasty underwent hemodilution. It should be noted that the hemoglobin level in the control group immediately after operation was 12.8 f 1.6 g per dL (128 f 16 g/L), while that in the ANH group was 10.8 f 1.6 (108 ? 16 g/L). With the current “transfusion trigger,” the former group would probably not have been transfused, which would have eliminated the difference. Barbier-Bohm and associates9also found that ANH or the combination of ANH and deliberate hypotension markedly decreased the need for homologous blood in patients undergoing hip arthroplasty.
Programs designed to eliminate or decrease the use of homologous blood transfusion in the surgical patient should include several components: preoperative blood donation, intraoperative and postoperative blood salvage, acute normovolemic hemodilution (ANH), the use of pharmacologic agents to decrease blood loss, and meticulous surgical hemostasis. Successful programs have been built around two or three of these components. Scheduling difficulties in urgent or emergent cases may preclude the use of preoperative blood donation or intraoperative blood salvage, but ANH should always be available for suitable patients. ANH or acute isovolemic hemodilution entails the removal of blood from a patient, either immediately before or shortly after induction of anesthesia, and the simultaneous replacement with acellular fluid, that is, crystalloid or colloid. While ANH is usually the purview of the anesthesiologist, transfusion medicine specialists have become involved with the technique with increasing frequency as part of comprehensive autologous blood programs. They certainly must be involved in the approval of protocols, the technical aspects of blood collection and storage, and quality assurance. Under many circumstances, it is desirable for a member of the transfusion service to be available in the operating room to assist with the procedure. This review is designed to acquaint these clinicians with the rationale upon which this technique is based, as well as the indications for and the contraindications to its use. Advantages of Hemodilution The avoidance of disease transmission and transfusion reactions is an advantage of all autologous transfusion techniques. With ANH, red blood cell (RBC) loss is Abbreviations: ANH = acute normovolemlc hernodilution; Ca,, rrterial oxygen content; Ca,-Cv, = arteriovenow oxygen content dUfercncc; CBF = coronary blood flow; CO = cardiac output; D ,, = oxygen delivery; EBV = utimrted blood volume; EDV = end-dtrstolic volume; ESV = end-systolicvolume; H, = rverage hematocrit; Hb = hcmoglobln; Hct = hematocrit; Hr = desired hematocrit; H. = Initial hematocrit; LAD = left anterior descending; n = Viscosity; Pa, = arterial oxygen tension; Pv, = mlxed venow oxygen tension; R = total peripheral resistance; RBC(s) = red ceil(s); V = volume to be removed, Z = arteriolar tone or vascular hindrance. From Blood Systems, Inc., Scottsdale, Arizona, and the Carl Hayden Veterans Affairs Medical Center, Phoenix, Arizona. Received for publication January 10, 1991; revision received May 10. 1991, and accepted May 22, 1991.
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858
TRANSFUSION Vol. 31, No. 9-1991
STEHLING AND ZAUDER
Admittedly, carefully controlled randomized studies of ANH are few and far between. Ethical and moral considerations make it unlikely that they will ever be carried out. Any decrease in the use of homologous blood would make such studies extremely difficult to justify. The decrease in viscosity of blood resulting from ANH usually leads to improved tissue perfusion. While this latter benefit is difficult to quantitate, it may be most important in patients with peripheral vascular and cerebrovascular disease. Some persons with religious objections to homologous transfusion agree to ANH as long as the blood is maintained in a closedcircuit system with continuous flow.1° Clinical Applications
Although some clinicians limit use of the technique to healthy adults, ANH has been employed extensively in small childrenl0-lZand the e l d e r l ~ . ~The J ~ technique is used most often in cardiac surgery but is becoming more popular for a wide variety of noncardiac procedures. Cardiac surgery In the early days of cardiopulmonary bypass, oxygenators were primed with fresh, heparinized blood. Large demands were made upon blood banks, transmission of disease was common, and the so-called “homologous blood syndrome,” characterized by hepatic and pulmonary congestion, portal hypertension, coagulation defects, renal failure, and cerebral insufficiency, was said to be common. These changes were thought to be due to the pooling of blood in the splanchnic circulati~n.’~ In 1959, Panic0 and Neptunels reported the use of normal saline as a prime. Some 2 years later, Cooley and assoCiates16 detailed the use of 5-percent dextrose in water as the prime in 100 patients. As a result of the use of “clear” prime for heart-lung bypass machines, hemodilution has become the standard of care during open heart surgery in most a d u l t ~ . ~ ~InJ *a further attempt to decrease the use of homologous blood, ANH is often As employed, along with an acellular pump with noncardiac surgery, blood can be withdrawn after placement of intravascular cannulae, immediately before or just after induction of anesthesia, and before surgical incision. However, in patients with severe coronary artery disease or aortic stenosis who may be unable to compensate for major fluid shifts, it is preferable to wait until the patient is heparinized and cannulated and then to draw the blood from the tubing to the oxygenator before the blood makes a first pass through the roller pump. With this technique, alterations in pump flow can be used to compensate for any hemodynamic instability associated with blood removal. The quality of the blood may be inferior to that removed prior to heparinization,
as heparin is thought by some investigators?3*23to have a detrimental effect on platelet function. In the cardiac surgical patient, when ANH is properly performed, the incidence of perioperative complications is no greater in those undergoing hemodilution than it is in those not so treated.” Although the decrease in viscosity associated with ANH should significantly increase blood flow to the tissues during hypothermic cardiopulmonary bypass, conclusive evidence has not been put forth to support this concept. There is some evidence indicating that hemodilution does minimize bleeding after the surgical correction of congenital heart disease.= Noncardiac swgery Having long been commonly used in Europe, ANH is now gaining acceptance in the United States as a tool for decreasing the use of homologous blood in noncardiac surgical procedures. The use of hemodilution should be considered in adults with Hct >34 percent (>0.34) who are expected to lose more than 1 L of blood intraoperatively. The technique has been employed most extensively in patients undergoing total joint replacements and spine However, there is experience with the use of ANH for general7and vascular surgeryz628 as well as urologic, gynecologic, and radical cancer procedures.6 Patients presenting for virtually any type of surgery associated with significant blood loss may be appropriate candidates for ANH. Contraindications Anemia is the major contraindication to ANH. Because hemoglobin (Hb) decreases by approximately 1 g per dL (10 g/L) for each unit of blood removed, it is usually inappropriate to employ the technique when the Hb is
STEHLING AlYD H.L.
UUDER
reduced. For example, the patient with a hematocrit (Hct) of 45 percent (0.45)who intraoperatively loses a liter of blood loses 450 mL of RBCs. If the Hct is 25 percent (0.25),the RBC loss is only 250 mL. In addition, ANH provides the only practical means of obtaining fresh autologous whole blood for transfusion. Reviewing a wide variety of surgical procedures using ANH, Martin and associates’ reported a decrease of 18 to 90 percent in the use of homologous blood. Two other groups2*’ found that 60 to 90 percent of patients who had open heart surgery received no homologous blood when ANH was combined with the transfusion of shed mediastinal blood. Using extreme hemodilution (Hct 15% [0.15]),Martin and OtP decreased the mean homologous transfusion requirement from 4370 mL to 750 mL in a randomized study of 26 patients who underwent the placement of Harrington instrumentation for scoliosis. Comparing patients who underwent hemodilution with historic controls, Kafer et al.5 reported a decrease in the need for RBCs from 8.6 & 1.6 to 1 2 0 units in similar groups of patients undergoing spinal instrumentation placement. The ANH patients required no additional component therapy, unlike the control group who received 1.8 f 0.7 units of fresh-frozen plasma and 1.2 & 0.8 units of platelets. Sejourne and associates6 reported a significant decrease in the use of homologous blood components following hepatic resection when patients had undergone hemodilution. Once again, a comparison was made with a historic control group, although the patient population, technique, and surgical procedures were said to be comparable. In a randomized study of 21 patients having major colon surgery, Rose and Coutsoftides’ found that those who underwent hemodilution to an average Hct of 22 percent (0.22) required 2.4 fewer units of homologous blood than did the control group. RosbergB reported a decreased use of 1.2 units when patients for total hip arthroplasty underwent hemodilution. It should be noted that the hemoglobin level in the control group immediately after operation was 12.8 f 1.6 g per dL (128 f 16 g/L), while that in the ANH group was 10.8 f 1.6 (108 ? 16 g/L). With the current “transfusion trigger,” the former group would probably not have been transfused, which would have eliminated the difference. Barbier-Bohm and associates9also found that ANH or the combination of ANH and deliberate hypotension markedly decreased the need for homologous blood in patients undergoing hip arthroplasty.
Programs designed to eliminate or decrease the use of homologous blood transfusion in the surgical patient should include several components: preoperative blood donation, intraoperative and postoperative blood salvage, acute normovolemic hemodilution (ANH), the use of pharmacologic agents to decrease blood loss, and meticulous surgical hemostasis. Successful programs have been built around two or three of these components. Scheduling difficulties in urgent or emergent cases may preclude the use of preoperative blood donation or intraoperative blood salvage, but ANH should always be available for suitable patients. ANH or acute isovolemic hemodilution entails the removal of blood from a patient, either immediately before or shortly after induction of anesthesia, and the simultaneous replacement with acellular fluid, that is, crystalloid or colloid. While ANH is usually the purview of the anesthesiologist, transfusion medicine specialists have become involved with the technique with increasing frequency as part of comprehensive autologous blood programs. They certainly must be involved in the approval of protocols, the technical aspects of blood collection and storage, and quality assurance. Under many circumstances, it is desirable for a member of the transfusion service to be available in the operating room to assist with the procedure. This review is designed to acquaint these clinicians with the rationale upon which this technique is based, as well as the indications for and the contraindications to its use. Advantages of Hemodilution The avoidance of disease transmission and transfusion reactions is an advantage of all autologous transfusion techniques. With ANH, red blood cell (RBC) loss is Abbreviations: ANH = acute normovolemlc hernodilution; Ca,, rrterial oxygen content; Ca,-Cv, = arteriovenow oxygen content dUfercncc; CBF = coronary blood flow; CO = cardiac output; D ,, = oxygen delivery; EBV = utimrted blood volume; EDV = end-dtrstolic volume; ESV = end-systolicvolume; H, = rverage hematocrit; Hb = hcmoglobln; Hct = hematocrit; Hr = desired hematocrit; H. = Initial hematocrit; LAD = left anterior descending; n = Viscosity; Pa, = arterial oxygen tension; Pv, = mlxed venow oxygen tension; R = total peripheral resistance; RBC(s) = red ceil(s); V = volume to be removed, Z = arteriolar tone or vascular hindrance. From Blood Systems, Inc., Scottsdale, Arizona, and the Carl Hayden Veterans Affairs Medical Center, Phoenix, Arizona. Received for publication January 10, 1991; revision received May 10. 1991, and accepted May 22, 1991.
=
857
858
TRANSFUSION Vol. 31, No. 9-1991
STEHLING AND ZAUDER
Admittedly, carefully controlled randomized studies of ANH are few and far between. Ethical and moral considerations make it unlikely that they will ever be carried out. Any decrease in the use of homologous blood would make such studies extremely difficult to justify. The decrease in viscosity of blood resulting from ANH usually leads to improved tissue perfusion. While this latter benefit is difficult to quantitate, it may be most important in patients with peripheral vascular and cerebrovascular disease. Some persons with religious objections to homologous transfusion agree to ANH as long as the blood is maintained in a closedcircuit system with continuous flow.1° Clinical Applications
Although some clinicians limit use of the technique to healthy adults, ANH has been employed extensively in small childrenl0-lZand the e l d e r l ~ . ~The J ~ technique is used most often in cardiac surgery but is becoming more popular for a wide variety of noncardiac procedures. Cardiac surgery In the early days of cardiopulmonary bypass, oxygenators were primed with fresh, heparinized blood. Large demands were made upon blood banks, transmission of disease was common, and the so-called “homologous blood syndrome,” characterized by hepatic and pulmonary congestion, portal hypertension, coagulation defects, renal failure, and cerebral insufficiency, was said to be common. These changes were thought to be due to the pooling of blood in the splanchnic circulati~n.’~ In 1959, Panic0 and Neptunels reported the use of normal saline as a prime. Some 2 years later, Cooley and assoCiates16 detailed the use of 5-percent dextrose in water as the prime in 100 patients. As a result of the use of “clear” prime for heart-lung bypass machines, hemodilution has become the standard of care during open heart surgery in most a d u l t ~ . ~ ~InJ *a further attempt to decrease the use of homologous blood, ANH is often As employed, along with an acellular pump with noncardiac surgery, blood can be withdrawn after placement of intravascular cannulae, immediately before or just after induction of anesthesia, and before surgical incision. However, in patients with severe coronary artery disease or aortic stenosis who may be unable to compensate for major fluid shifts, it is preferable to wait until the patient is heparinized and cannulated and then to draw the blood from the tubing to the oxygenator before the blood makes a first pass through the roller pump. With this technique, alterations in pump flow can be used to compensate for any hemodynamic instability associated with blood removal. The quality of the blood may be inferior to that removed prior to heparinization,
as heparin is thought by some investigators?3*23to have a detrimental effect on platelet function. In the cardiac surgical patient, when ANH is properly performed, the incidence of perioperative complications is no greater in those undergoing hemodilution than it is in those not so treated.” Although the decrease in viscosity associated with ANH should significantly increase blood flow to the tissues during hypothermic cardiopulmonary bypass, conclusive evidence has not been put forth to support this concept. There is some evidence indicating that hemodilution does minimize bleeding after the surgical correction of congenital heart disease.= Noncardiac swgery Having long been commonly used in Europe, ANH is now gaining acceptance in the United States as a tool for decreasing the use of homologous blood in noncardiac surgical procedures. The use of hemodilution should be considered in adults with Hct >34 percent (>0.34) who are expected to lose more than 1 L of blood intraoperatively. The technique has been employed most extensively in patients undergoing total joint replacements and spine However, there is experience with the use of ANH for general7and vascular surgeryz628 as well as urologic, gynecologic, and radical cancer procedures.6 Patients presenting for virtually any type of surgery associated with significant blood loss may be appropriate candidates for ANH. Contraindications Anemia is the major contraindication to ANH. Because hemoglobin (Hb) decreases by approximately 1 g per dL (10 g/L) for each unit of blood removed, it is usually inappropriate to employ the technique when the Hb is
