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Hemodilution and Blood Conservation
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Hemodilution and Blood Conservation Glenn P. Gravlee Case Synopsis A 61-year-old, 80-kg man is scheduled for removal and replacement of a total hip prosthesis. He is concerned about blood transfusion and the transmission of infectious diseases, particularly human immunodeficiency virus (HIV). He requests that transfusion of homologous blood be avoided, if possible. He predonated 2 units of autologous blood. During surgery, blood loss is more than 2000 mL, and the hemoglobin level is 7.5 g/dL after both units of autologous blood are given. Vital signs and urine output remain within normal limits. An additional 500 mL of intraoperative blood loss is expected.
PROBLEM ANALYSIS
Complications arising from the transfusion of homologous (also called allogeneic) blood products have been recognized since the beginning of modern transfusion therapy. Bacterial blood contamination was fairly common before the introduction of refrigerated storage and sterile plastic bags. Subsequently, contamination with viruses (e.g., cytomegalovirus, hepatitis B and C, HIV, and human T-cell lymphotropic virus) became a source of greater morbidity. Now, West Nile virus and possibly variant Creutzfeldt-Jakob disease have been added to the list of viral diseases transmissible by blood transfusion. Fortunately, improvements in donor screening and blood component testing have reduced the risk of both HIV and hepatitis C transmission to less than 1 per 1 million units, and that for hepatitis B to about 1 per 137,000 units. Cytomegalovirus remains prevalent in the blood pool, but its transmission is generally not a problem in the absence of clinical immunosuppression. Nevertheless, many blood banks now routinely apply leukoreduction techniques to all cellular blood components before dispensing them, which has greatly reduced the risk of cytomegalovirus transmission. Thus, viral transmission by blood transfusion is now so rare that bacterial contamination once again poses the highest risk for infectious complications, which is 1 in 30,000 red blood cell (RBC) units and 1 in 2000 to 3000 platelet units. Blood group incompatibility and anaphylactic reactions remain rare.
Implications Considerable evidence supports immunosuppression as a significant consequence of blood transfusion. This increases the risk of cancer recurrence and of bacterial infection among transfusion recipients. Large blood loss and hemodilution also raise the question of what constitutes a reasonable minimum hemoglobin level in an anesthetized patient with acceptable intravascular
MANAGEMENT This section focuses on available techniques (Table 73-1) and a cost-benefit analysis of autotransfusion techniques that may reduce or avoid the need for homologous RBC or blood component therapy.
Autologous Predonation Patients can donate blood up to 42 days before operation, which constitutes the maximum storage period for modern
Table 73–1
■
Autotransfusion Techniques
Technique
Cost
Risk
Advisability*
Autologous predonation Acute normovolemic hemodilution Intraoperative salvage Postoperative salvage, unwashed Postoperative salvage, washed
Moderate Low
Low Low
Yes No
High Low
Low Moderate
Yes No
Moderate
Low
Yes
*For the patient described in the case synopsis.
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volume and vital signs. This is a surprisingly complex issue, but in general, healthy patients safely tolerate hemoglobin concentrations as low as 6 g/dL. Sicker patients may require hemoglobin concentrations as high as 10 g/dL. Assuming that the hypothetical patient described in the case synopsis is otherwise healthy, the limiting factor may be the rate and predictability of blood loss, because some margin of safety is desirable if sudden additional blood loss should occur. Also, one must consider the possibility of significant postoperative bleeding. Consequently, the patient’s hemoglobin concentration of 7.5 g/dL signals the possible need for homologous transfusion, unless shed blood is being effectively salvaged.
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anticoagulant and storage solutions. The frequency and amount of donation depend on the patient’s ability to tolerate serial phlebotomy while maintaining an adequate hemoglobin level. Typically, a patient donates 2 units of blood per week starting 2 to 4 weeks before surgery. The minimum recommended hemoglobin level for donation is 11 g/dL. To maintain this level, patients are routinely given iron supplementation. Erythropoietin can be used to increase hemoglobin levels during predonation, which enables patients to donate more units; this is quite expensive, however, costing approximately $800 per unit of erythropoietin “manufactured.” Erythropoietin augmentation of autologous predonation may be justified if some combination of the following factors exists: ● ●
● ●
The preoperative timeline is short (e.g., cancer resection). Homologous transfusion is not possible (e.g., Jehovah’s Witness). The patient is anemic. The anticipated surgical blood loss is large (>2000 mL).
Autologous predonation is most effective at avoiding homologous transfusion when used in combination with other autotransfusion techniques, such as intraoperative blood salvage. The cost-effectiveness of autologous donation varies widely, but it often fails to meet the usual standards of efficacy. For this reason, its popularity has dropped substantially over the past several years. The donation itself carries a hospitalization risk of approximately 1 in 17,000, which is 12 times that for community donations by healthy individuals. Even though the blood is autologous, its use still incurs some of the usual homologous transfusion risks, including bacterial contamination or clerical errors leading to incompatible blood transfusions. Compared with allogeneic blood units, autologous units typically require the same testing procedures but more complex storage and identification procedures, so the cost for each unit is higher.
drop in hemoglobin concentration could induce unanticipated end-organ ischemia if there is an undiagnosed condition such as critical stenosis of a coronary artery or carotid artery. Mathematical analyses strongly suggests that the blood loss savings are fairly minor unless this technique is used quite aggressively—for example, hemodilution from a starting hematocrit of 40% to one of 20% or lower. Typically, this would require withdrawing 6 to 10 500-mL bags of blood. One study found no difference in allogeneic transfusion exposure when 3 units of acute normovolemic hemodilution were compared with a similar volume of autologous predonation in patients undergoing total hip arthroplasty.
Postoperative Blood Salvage This technique involves the collection and reinfusion of blood shed postoperatively. The blood is collected through a relatively large filter and reinfused through a small-pore filter. This blood can be reinfused unmodified (“unwashed”), or it can be washed and concentrated in the same way as for intraoperative blood salvage. Reinfused blood typically contains very low concentrations of plasma coagulation factors and platelets. It also contains elevated levels of fibrin degradation products, free hemoglobin, and inflammatory products such as cytokines. With total hip arthroplasty, it might also contain fat and bone spicules. As a result, many clinicians elect to administer salvaged blood only after it has been washed. This somewhat controversial technique reduces the need for allogeneic blood only when postoperative blood losses are large (e.g., >1000 mL), because the hematocrit of blood shed postoperatively is typically in the 15% to 20% range.
Intraoperative Blood Salvage Acute Normovolemic Hemodilution Acute normovolemic hemodilution involves the removal of blood just before or after the induction of anesthesia, combined with volume replacement using crystalloid or colloid. The technique requires standard anesthesia monitors (electrocardiogram, blood pressure, pulse oximetry, and temperature) and large-bore intravenous access with a 14- or 16-gauge peripheral or central venous catheter. Blood is collected into standard citrate-phosphate-dextrose bags. Removed blood is then stored in anticoagulated sterile bags and returned to the patient intraoperatively or postoperatively. The rationale is that the patient will be losing fewer RBCs into the surgical field because shed blood has a lower hematocrit due to hemodilution. Assuming that the lowest hematocrit remains acceptable (>20%) and that intravascular volume also remains intact, tissue perfusion will be maintained (and perhaps enhanced). Also, oxygen delivery will be sufficient owing to reduced blood viscosity. Additional clinical advantages include low cost, simple storage, and ease of transportation and record keeping. Acute normovolemic hemodilution risks hypovolemia if volume replacement is inadequate. Further, the obligatory
This method involves using a suction apparatus to collect the patient’s blood as it is shed intraoperatively into the surgical field. An anticoagulant solution is added to the shed blood, and it is then stored in a filtered reservoir. Once an adequate amount of blood has been collected (typically >700 mL), it is washed and concentrated so that the final product usually has a hematocrit between 55% and 70%. Because intraoperative blood salvage conserves RBCs but not plasma or platelets, a dilutional coagulopathy should be anticipated if blood losses approach or exceed one blood volume. Otherwise, the risks of this technique are low if appropriate procedures and standards are followed and the blood is not contaminated with bacteria. The ability to conserve RBCs with this technique depends largely on the surgeon’s ability to capture shed blood using suction. In this regard, total hip arthroplasty is in an intermediate category between laparotomy for aortic aneurysm repair, where blood pools in a body cavity and is easily captured, and a more superficial procedure such as reduction mammaplasty, where blood typically runs off the surgical field onto the drapes or is absorbed by sponges.
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Table 73–2
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297
Other Potential Blood-Conservation Techniques
Technique
Cost
Risk
Advisability*
Induced hypotension Prophylactic aprotinin Spinal or epidural anesthesia
Varies Expensive Low
Varies Low Low
Questionable; patient’s age is cause for some concern Unclear; reduces blood loss, but expensive Facilitates blood pressure control; reduces deep vein thrombosis
*For the patient described in the case synopsis.
PREVENTION Often, clinicians fail to appreciate how much blood loss can be safely tolerated by patients before the need for transfusion. This can be estimated using the following formula: ABL = V × (Hi – Hd)/Hm,
Autologous Predonation In retrospect, if one could have predicted the amount of blood loss experienced by the patient in the case synopsis based on the surgeon’s track record with reoperative hip arthroplasties, the patient should have been given supplemental iron therapy and predonated 3 or 4 units of autologous blood over 3 to 4 weeks before surgery. If the patient’s original hematocrit was less than 40%, supplementation with erythropoietin would have been reasonable, although health insurance policies often do not cover the cost of erythropoietin used for this purpose.
Acute Normovolemic Hemodilution Arguably, the most common application of this procedure is to withdraw 2 units in smaller patients (e.g., those <70 kg) and 3 units in larger ones. This saves 1 to 2 units of allogeneic packed RBCs if the intraoperative blood loss is between 3000 and 6000 mL, which crudely approximates one half to one normal blood volume. As blood losses exceed 6000 mL, the number of units saved gradually diminishes (to 0.5 to 1 unit) with this technique. Initially, one bag containing approximately 450 mL of blood is collected. As this is occurring, either 500 mL of colloid solution or about 1500 mL of crystalloid solution is infused into the patient to maintain intravascular volume. Hypotension or tachycardia suggests inadequate volume replacement. The exchange continues to the desired end point, as long as the patient tolerates the procedure. Checking the hematocrit or hemoglobin concentration periodically is
Intraoperative Blood Salvage In the case presented here, intraoperative blood salvage may offer the best chance of respecting the patient’s wish to avoid homologous blood. Further, effective use of this technique tends to override any theoretical benefits of acute normovolemic hemodilution. Alternatively, if the patient is otherwise completely healthy, one might “tough it out” to a hematocrit as low as 20%. Considering this patient’s age, however, reducing the hematocrit below that level is probably ill advised.
Postoperative Blood Salvage Because the cost of this technique is low and the likelihood of substantial postoperative bleeding is high in the patient described in the case synopsis, postoperative salvage is appropriate. Wound drainage contains various undesirable elements, however, so washing the product before reinfusion is advisable. Bacterial contamination can also occur, so this strategy should be avoided unless the drainage exceeds 500 mL over an 8-hour period. After this time, the collection device should be replaced if reinfusion is planned.
Alternative Blood Conservation Techniques Other potential blood-conserving options are listed in Table 73-2. Moderate deliberate hypotension is reasonable if the patient is otherwise healthy; for a patient in his 60s, however, setting a relatively conservative lower mean arterial pressure limit, in the range of 70 mm Hg for 1 to 2 hours, might be prudent.1 Another reasonable approach for deliberate hypotension might be to reduce the mean arterial pressure
1 Because our hypothetical patient is male and older than 60 years, and assuming no coronary artery disease or risk factors for it (hyperlipidemia, hypertension, or smoking history; see Chapter 38), another way to estimate the minimal acceptable pressure for deliberate hypotension (i.e., that required to maintain coronary perfusion pressure) is diastolic blood pressure – left ventricular end-diastolic pressure = 50 mm Hg. The value for adequate coronary perfusion pressure may be higher in patients with advanced age, diastolic heart failure, or a strong family history of coronary artery disease, hypertension, or other heart disease (all associated with some amount of elevated left ventricular end-diastolic pressure).
CARDIOTHORACIC & VASCULAR SURGERY
where ABL is allowable blood loss; V is blood volume; Hi and Hd are the initial and lowest desired hematocrit values, respectively; and Hm is the hematocrit average of Hi and Hd. Assuming a blood volume of 5600 mL (80 kg × 70 mL/kg), an Hi of 40%, and an Hd of 25%, the patient in the case synopsis can tolerate a blood loss of almost 2600 mL without transfusion therapy. Intraoperative RBC salvage increases this figure in direct proportion to the efficacy of salvage.
advisable to reassess the appropriateness of the calculated end point. The blood is then stored at room temperature if it will be used within 8 hours; otherwise, refrigerated storage is required.
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by about 20% below the patient’s preoperative baseline level, which could probably be safely sustained for several hours if necessary. Aprotinin and its lysine analogues (e.g., tranexamic acid) can also reduce blood loss in hip replacement surgery with a low risk of complications, but the high cost of aprotinin must be considered.
Further Reading American Association of Blood Banks: All about blood (2004). Available at www.aabb.org/All_About_Blood. American Society of Anesthesiologists Task Force on Blood Component Therapy: Practice guidelines for blood component therapy. Anesthesiology 84:732-747, 1996. Birkmeyer JD, Goodnough LT, AuBuchon JP, et al: The cost effectiveness of preoperative autologous blood donation for total hip and knee replacement. Transfusion 33:544-551, 1993.
Goodnough LT: Red blood cell support in the perioperative setting. In Simon TL, Dzik WH, Snyder EL, et al (eds): Rossi’s Principles of Transfusion Medicine, 3rd ed. Philadelphia, JB Lippincott–Williams & Wilkins, 2002, pp 590-601. Goodnough LT, Despotis GJ, Merkel K, Monk TG: A randomized trial comparing acute normovolemic hemodilution and preoperative autologous blood donation in total hip arthroplasty. Transfusion 40:1054-1057, 2000. Goodnough LT, Monk TG, Brecher ME: Autologous blood procurement in the surgical setting: Lessons learned in the last 10 years. Vox Sang 71:133-141, 1996. Jacobs MR, Palavecino E, Yomtovian R: Don’t bug me: The problem of bacterial contamination of blood components—challenges and solutions. Transfusion 41:1331-1334, 2001. Wu W-C, Rathore SS, Wang Y, et al: Blood transfusion in elderly patients with acute myocardial infarction. N Engl J Med 345:1230-1236, 2001.
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Hemodilution and Blood Conservation Glenn P. Gravlee Case Synopsis A 61-year-old, 80-kg man is scheduled for removal and replacement of a total hip prosthesis. He is concerned about blood transfusion and the transmission of infectious diseases, particularly human immunodeficiency virus (HIV). He requests that transfusion of homologous blood be avoided, if possible. He predonated 2 units of autologous blood. During surgery, blood loss is more than 2000 mL, and the hemoglobin level is 7.5 g/dL after both units of autologous blood are given. Vital signs and urine output remain within normal limits. An additional 500 mL of intraoperative blood loss is expected.
PROBLEM ANALYSIS
Complications arising from the transfusion of homologous (also called allogeneic) blood products have been recognized since the beginning of modern transfusion therapy. Bacterial blood contamination was fairly common before the introduction of refrigerated storage and sterile plastic bags. Subsequently, contamination with viruses (e.g., cytomegalovirus, hepatitis B and C, HIV, and human T-cell lymphotropic virus) became a source of greater morbidity. Now, West Nile virus and possibly variant Creutzfeldt-Jakob disease have been added to the list of viral diseases transmissible by blood transfusion. Fortunately, improvements in donor screening and blood component testing have reduced the risk of both HIV and hepatitis C transmission to less than 1 per 1 million units, and that for hepatitis B to about 1 per 137,000 units. Cytomegalovirus remains prevalent in the blood pool, but its transmission is generally not a problem in the absence of clinical immunosuppression. Nevertheless, many blood banks now routinely apply leukoreduction techniques to all cellular blood components before dispensing them, which has greatly reduced the risk of cytomegalovirus transmission. Thus, viral transmission by blood transfusion is now so rare that bacterial contamination once again poses the highest risk for infectious complications, which is 1 in 30,000 red blood cell (RBC) units and 1 in 2000 to 3000 platelet units. Blood group incompatibility and anaphylactic reactions remain rare.
Implications Considerable evidence supports immunosuppression as a significant consequence of blood transfusion. This increases the risk of cancer recurrence and of bacterial infection among transfusion recipients. Large blood loss and hemodilution also raise the question of what constitutes a reasonable minimum hemoglobin level in an anesthetized patient with acceptable intravascular
MANAGEMENT This section focuses on available techniques (Table 73-1) and a cost-benefit analysis of autotransfusion techniques that may reduce or avoid the need for homologous RBC or blood component therapy.
Autologous Predonation Patients can donate blood up to 42 days before operation, which constitutes the maximum storage period for modern
Table 73–1
■
Autotransfusion Techniques
Technique
Cost
Risk
Advisability*
Autologous predonation Acute normovolemic hemodilution Intraoperative salvage Postoperative salvage, unwashed Postoperative salvage, washed
Moderate Low
Low Low
Yes No
High Low
Low Moderate
Yes No
Moderate
Low
Yes
*For the patient described in the case synopsis.
295
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Definition, Recognition, and Risk Assessment
volume and vital signs. This is a surprisingly complex issue, but in general, healthy patients safely tolerate hemoglobin concentrations as low as 6 g/dL. Sicker patients may require hemoglobin concentrations as high as 10 g/dL. Assuming that the hypothetical patient described in the case synopsis is otherwise healthy, the limiting factor may be the rate and predictability of blood loss, because some margin of safety is desirable if sudden additional blood loss should occur. Also, one must consider the possibility of significant postoperative bleeding. Consequently, the patient’s hemoglobin concentration of 7.5 g/dL signals the possible need for homologous transfusion, unless shed blood is being effectively salvaged.
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anticoagulant and storage solutions. The frequency and amount of donation depend on the patient’s ability to tolerate serial phlebotomy while maintaining an adequate hemoglobin level. Typically, a patient donates 2 units of blood per week starting 2 to 4 weeks before surgery. The minimum recommended hemoglobin level for donation is 11 g/dL. To maintain this level, patients are routinely given iron supplementation. Erythropoietin can be used to increase hemoglobin levels during predonation, which enables patients to donate more units; this is quite expensive, however, costing approximately $800 per unit of erythropoietin “manufactured.” Erythropoietin augmentation of autologous predonation may be justified if some combination of the following factors exists: ● ●
● ●
The preoperative timeline is short (e.g., cancer resection). Homologous transfusion is not possible (e.g., Jehovah’s Witness). The patient is anemic. The anticipated surgical blood loss is large (>2000 mL).
Autologous predonation is most effective at avoiding homologous transfusion when used in combination with other autotransfusion techniques, such as intraoperative blood salvage. The cost-effectiveness of autologous donation varies widely, but it often fails to meet the usual standards of efficacy. For this reason, its popularity has dropped substantially over the past several years. The donation itself carries a hospitalization risk of approximately 1 in 17,000, which is 12 times that for community donations by healthy individuals. Even though the blood is autologous, its use still incurs some of the usual homologous transfusion risks, including bacterial contamination or clerical errors leading to incompatible blood transfusions. Compared with allogeneic blood units, autologous units typically require the same testing procedures but more complex storage and identification procedures, so the cost for each unit is higher.
drop in hemoglobin concentration could induce unanticipated end-organ ischemia if there is an undiagnosed condition such as critical stenosis of a coronary artery or carotid artery. Mathematical analyses strongly suggests that the blood loss savings are fairly minor unless this technique is used quite aggressively—for example, hemodilution from a starting hematocrit of 40% to one of 20% or lower. Typically, this would require withdrawing 6 to 10 500-mL bags of blood. One study found no difference in allogeneic transfusion exposure when 3 units of acute normovolemic hemodilution were compared with a similar volume of autologous predonation in patients undergoing total hip arthroplasty.
Postoperative Blood Salvage This technique involves the collection and reinfusion of blood shed postoperatively. The blood is collected through a relatively large filter and reinfused through a small-pore filter. This blood can be reinfused unmodified (“unwashed”), or it can be washed and concentrated in the same way as for intraoperative blood salvage. Reinfused blood typically contains very low concentrations of plasma coagulation factors and platelets. It also contains elevated levels of fibrin degradation products, free hemoglobin, and inflammatory products such as cytokines. With total hip arthroplasty, it might also contain fat and bone spicules. As a result, many clinicians elect to administer salvaged blood only after it has been washed. This somewhat controversial technique reduces the need for allogeneic blood only when postoperative blood losses are large (e.g., >1000 mL), because the hematocrit of blood shed postoperatively is typically in the 15% to 20% range.
Intraoperative Blood Salvage Acute Normovolemic Hemodilution Acute normovolemic hemodilution involves the removal of blood just before or after the induction of anesthesia, combined with volume replacement using crystalloid or colloid. The technique requires standard anesthesia monitors (electrocardiogram, blood pressure, pulse oximetry, and temperature) and large-bore intravenous access with a 14- or 16-gauge peripheral or central venous catheter. Blood is collected into standard citrate-phosphate-dextrose bags. Removed blood is then stored in anticoagulated sterile bags and returned to the patient intraoperatively or postoperatively. The rationale is that the patient will be losing fewer RBCs into the surgical field because shed blood has a lower hematocrit due to hemodilution. Assuming that the lowest hematocrit remains acceptable (>20%) and that intravascular volume also remains intact, tissue perfusion will be maintained (and perhaps enhanced). Also, oxygen delivery will be sufficient owing to reduced blood viscosity. Additional clinical advantages include low cost, simple storage, and ease of transportation and record keeping. Acute normovolemic hemodilution risks hypovolemia if volume replacement is inadequate. Further, the obligatory
This method involves using a suction apparatus to collect the patient’s blood as it is shed intraoperatively into the surgical field. An anticoagulant solution is added to the shed blood, and it is then stored in a filtered reservoir. Once an adequate amount of blood has been collected (typically >700 mL), it is washed and concentrated so that the final product usually has a hematocrit between 55% and 70%. Because intraoperative blood salvage conserves RBCs but not plasma or platelets, a dilutional coagulopathy should be anticipated if blood losses approach or exceed one blood volume. Otherwise, the risks of this technique are low if appropriate procedures and standards are followed and the blood is not contaminated with bacteria. The ability to conserve RBCs with this technique depends largely on the surgeon’s ability to capture shed blood using suction. In this regard, total hip arthroplasty is in an intermediate category between laparotomy for aortic aneurysm repair, where blood pools in a body cavity and is easily captured, and a more superficial procedure such as reduction mammaplasty, where blood typically runs off the surgical field onto the drapes or is absorbed by sponges.
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Table 73–2
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297
Other Potential Blood-Conservation Techniques
Technique
Cost
Risk
Advisability*
Induced hypotension Prophylactic aprotinin Spinal or epidural anesthesia
Varies Expensive Low
Varies Low Low
Questionable; patient’s age is cause for some concern Unclear; reduces blood loss, but expensive Facilitates blood pressure control; reduces deep vein thrombosis
*For the patient described in the case synopsis.
PREVENTION Often, clinicians fail to appreciate how much blood loss can be safely tolerated by patients before the need for transfusion. This can be estimated using the following formula: ABL = V × (Hi – Hd)/Hm,
Autologous Predonation In retrospect, if one could have predicted the amount of blood loss experienced by the patient in the case synopsis based on the surgeon’s track record with reoperative hip arthroplasties, the patient should have been given supplemental iron therapy and predonated 3 or 4 units of autologous blood over 3 to 4 weeks before surgery. If the patient’s original hematocrit was less than 40%, supplementation with erythropoietin would have been reasonable, although health insurance policies often do not cover the cost of erythropoietin used for this purpose.
Acute Normovolemic Hemodilution Arguably, the most common application of this procedure is to withdraw 2 units in smaller patients (e.g., those <70 kg) and 3 units in larger ones. This saves 1 to 2 units of allogeneic packed RBCs if the intraoperative blood loss is between 3000 and 6000 mL, which crudely approximates one half to one normal blood volume. As blood losses exceed 6000 mL, the number of units saved gradually diminishes (to 0.5 to 1 unit) with this technique. Initially, one bag containing approximately 450 mL of blood is collected. As this is occurring, either 500 mL of colloid solution or about 1500 mL of crystalloid solution is infused into the patient to maintain intravascular volume. Hypotension or tachycardia suggests inadequate volume replacement. The exchange continues to the desired end point, as long as the patient tolerates the procedure. Checking the hematocrit or hemoglobin concentration periodically is
Intraoperative Blood Salvage In the case presented here, intraoperative blood salvage may offer the best chance of respecting the patient’s wish to avoid homologous blood. Further, effective use of this technique tends to override any theoretical benefits of acute normovolemic hemodilution. Alternatively, if the patient is otherwise completely healthy, one might “tough it out” to a hematocrit as low as 20%. Considering this patient’s age, however, reducing the hematocrit below that level is probably ill advised.
Postoperative Blood Salvage Because the cost of this technique is low and the likelihood of substantial postoperative bleeding is high in the patient described in the case synopsis, postoperative salvage is appropriate. Wound drainage contains various undesirable elements, however, so washing the product before reinfusion is advisable. Bacterial contamination can also occur, so this strategy should be avoided unless the drainage exceeds 500 mL over an 8-hour period. After this time, the collection device should be replaced if reinfusion is planned.
Alternative Blood Conservation Techniques Other potential blood-conserving options are listed in Table 73-2. Moderate deliberate hypotension is reasonable if the patient is otherwise healthy; for a patient in his 60s, however, setting a relatively conservative lower mean arterial pressure limit, in the range of 70 mm Hg for 1 to 2 hours, might be prudent.1 Another reasonable approach for deliberate hypotension might be to reduce the mean arterial pressure
1 Because our hypothetical patient is male and older than 60 years, and assuming no coronary artery disease or risk factors for it (hyperlipidemia, hypertension, or smoking history; see Chapter 38), another way to estimate the minimal acceptable pressure for deliberate hypotension (i.e., that required to maintain coronary perfusion pressure) is diastolic blood pressure – left ventricular end-diastolic pressure = 50 mm Hg. The value for adequate coronary perfusion pressure may be higher in patients with advanced age, diastolic heart failure, or a strong family history of coronary artery disease, hypertension, or other heart disease (all associated with some amount of elevated left ventricular end-diastolic pressure).
CARDIOTHORACIC & VASCULAR SURGERY
where ABL is allowable blood loss; V is blood volume; Hi and Hd are the initial and lowest desired hematocrit values, respectively; and Hm is the hematocrit average of Hi and Hd. Assuming a blood volume of 5600 mL (80 kg × 70 mL/kg), an Hi of 40%, and an Hd of 25%, the patient in the case synopsis can tolerate a blood loss of almost 2600 mL without transfusion therapy. Intraoperative RBC salvage increases this figure in direct proportion to the efficacy of salvage.
advisable to reassess the appropriateness of the calculated end point. The blood is then stored at room temperature if it will be used within 8 hours; otherwise, refrigerated storage is required.
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by about 20% below the patient’s preoperative baseline level, which could probably be safely sustained for several hours if necessary. Aprotinin and its lysine analogues (e.g., tranexamic acid) can also reduce blood loss in hip replacement surgery with a low risk of complications, but the high cost of aprotinin must be considered.
Further Reading American Association of Blood Banks: All about blood (2004). Available at www.aabb.org/All_About_Blood. American Society of Anesthesiologists Task Force on Blood Component Therapy: Practice guidelines for blood component therapy. Anesthesiology 84:732-747, 1996. Birkmeyer JD, Goodnough LT, AuBuchon JP, et al: The cost effectiveness of preoperative autologous blood donation for total hip and knee replacement. Transfusion 33:544-551, 1993.
Goodnough LT: Red blood cell support in the perioperative setting. In Simon TL, Dzik WH, Snyder EL, et al (eds): Rossi’s Principles of Transfusion Medicine, 3rd ed. Philadelphia, JB Lippincott–Williams & Wilkins, 2002, pp 590-601. Goodnough LT, Despotis GJ, Merkel K, Monk TG: A randomized trial comparing acute normovolemic hemodilution and preoperative autologous blood donation in total hip arthroplasty. Transfusion 40:1054-1057, 2000. Goodnough LT, Monk TG, Brecher ME: Autologous blood procurement in the surgical setting: Lessons learned in the last 10 years. Vox Sang 71:133-141, 1996. Jacobs MR, Palavecino E, Yomtovian R: Don’t bug me: The problem of bacterial contamination of blood components—challenges and solutions. Transfusion 41:1331-1334, 2001. Wu W-C, Rathore SS, Wang Y, et al: Blood transfusion in elderly patients with acute myocardial infarction. N Engl J Med 345:1230-1236, 2001.