Intraoperative normovolemic hemodilution

Comparison of Hemodynamic Changes After Acute Normovolemic Hemodilution Using Ringer’s Lactate Versus 5% Albumin in Patients on β-Blockers Undergoing Coronary Artery Bypass Surgery

OBJECTIVE

Acute normovolemic hemodilution (ANH) is used cautiously in coronary artery disease (CAD) patients because of concerns of compromised coronary blood flow. This study aimed to compare hemodynamic changes by using either Ringer's lactate or albumin for ANH in CAD patients receiving beta-blockers.

DESIGN

Prospective, randomized study.

SETTING

Postgraduate teaching hospital.

PARTICIPANTS

Thirty patients undergoing coronary artery bypass graft surgery (CABG) (hemoglobin >12 g/dL, on chronic beta-blocker therapy).

INTERVENTIONS

Monitoring, induction, and anesthesia followed a routine protocol for CABG surgery including pulmonary artery catheter placement. Patients were randomly included in group 1 (ANH by Ringer's lactate) or in group 2 (ANH by 5% albumin). A hemodynamic calculation software program was used for parameters recorded before and after ANH.

MEASUREMENTS AND MAIN RESULTS

ANH could not be completed in 5 patients (33%) in group 1 because of a fall in mean arterial pressure (MAP) of more than 25% from baseline. In both groups posthemodilution MAP, heart rate, systemic vascular resistance, and oxygen delivery index decreased, whereas stroke volume index, cardiac index, and tissue oxygen extraction increased significantly as compared to baseline values (p < 0.05). Hemodynamic parameters were better maintained during the study period in group 2 than group 1.

CONCLUSIONS

Hemodynamic stability was better maintained by 5% albumin than Ringer's lactate for ANH in chronic beta-blocked CAD patients. Despite an increase in cardiac index, systemic oxygen delivery was decreased irrespective of the hemodiluting fluid used. ANH to a hemoglobin value of 10 g/dL in chronically beta-blocked CAD patients was well tolerated.

Physiologic aspects of anemia

The most important adaptive responses from a physiological stance involved the cardiovascular system, consisting in particular of elevation of the cardiac output and its redistribution to favor the coronary and cerebral circulations, at the expense of the splanchnic vascular beds. The evidence regarding these physiological responses, especially in experimental studies that permit the control of many variables, is particularly powerful and convincing. On the other hand, there is a remarkable lack, in quality and quantity, of clinical studies addressing how normal physiological adaptive responses may be affected by a variety of diseases and conditions that often accompany and may complicate anemia, and interactions with other such compounding variables as age and different patient populations. For these reasons, it is not possible to offer guidelines on how to increase, maintain, or even to determine optimal DO2 in high-risk patients and how best transfusion strategies might be used under these conditions. From the brief review of physiological principles and the strong consensus in the literature, it is evident that cardiac function must be a central consideration in decisions regarding transfusion in anemia, because of the critical role it plays in assuring adequate oxygen supply of all vital tissues. Particular attention should be paid to the possible presence of CAD or incipient or cardiac failure, as these conditions may require careful transfusions to improve DO2 at levels that may not necessitate such interventions when cardiac disease is absent. Although the cerebral circulation also serves an obligate aerobic organ unable to tolerate significant hypoxia, there is little convincing evidence to support the notion that cerebral ischemia is aggravated by anemia and that this can be prevented by improved DO2 through rapid correction of anemia. Consequently, the arguments favoring transfusions in the presence of ischemic heart disease do not appear to apply to occlusive cerebrovascular disease. Because firm evidence is lacking on the interactions of concurrent diseases and anemia in various patient populations, understanding of the physiological consequences of anemia, and of the diseases concerned, is useful but not fully sufficient to provide firm and rational guidance to transfusion practice in specific complex clinical instances. A good deal of clinical and experimental investigation is required to support fully rational and comprehensive guidelines. In the meantime, prudent and conservative management, based on awareness of risks and sound understanding of the normal and pathological physiology, must remain the guiding principle.

Diaspirin crosslinked hemoglobin enables extreme hemodilution beyond the critical hematocrit

BACKGROUND

Normovolemic hemodilution is an effective strategy to limit perioperative homologous blood transfusions. The reduction of hematocrit related to hemodilution results in reduced arterial oxygen content, which initially is compensated for by an increase in cardiac output and oxygen extraction ratio. To increase the efficacy of hemodilution, a low hematocrit should be aimed for; however, this implies the risk of myocardial ischemia and tissue hypoxia.

OBJECTIVE

To assess whether hemodilution can be extended to lower hematocrit values by the use of a hemoglobin-based artificial oxygen carrier solution.

DESIGN

Prospective, randomized, controlled.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Twelve anesthetized, mechanically ventilated pigs.

INTERVENTIONS

Isovolemic hemodilution was performed with either 10% diaspirin crosslinked hemoglobin (DCLHb Baxter Healthcare, Boulder, CO; n = 6) or 8% human albumin solution (HSA, oncotically matched to DCLHb, Baxter Healthcare; n = 6) to a hematocrit of 15%, 8%, 4%, 2%, and 1%.

MEASUREMENTS AND MAIN RESULTS

In both groups, measurements were performed at baseline at the previously mentioned preset hematocrit values and at the onset of myocardial ischemia characterized by critical hematocrit (significant ST-segment depression >0.1 mV and/or arrhythmia). To determine peripheral tissue oxygenation and myocardial perfusion and function, the following variables were evaluated: total body oxygen transport variables, tissue oxygen partial pressure (tPo2, MDO-Electrode, Eschweiler Kiel, Germany) on the surface of the skeletal muscle, coronary perfusion pressure, left ventricular (LV) end-diastolic pressure, global and regional myocardial contractility (maximal change in pressure over time, LV segmental shortening, microsonometry method), LV myocardial blood flow (fluorescent microsphere technique), LV oxygen delivery, and the ratio between LV subendocardial and subepicardial myocardial perfusion. In the HSA group, critical hematocrit was found at 6.1 (1.8)% (hemoglobin, 2 g x dL(-1)), whereas all DCLHb-treated animals survived hemodilution until hematocrit 1.2 (0.2)% (hemoglobin, 4.7 g x dL(-1)) was achieved without signs of hemodynamic instability. Although arterial oxygen content was higher in the DCLHb group at 1.2% hematocrit than in the HSA group at critical hematocrit (i.e., hematocrit, 6.1%; hemoglobin, 2 g.dL-1) neither oxygen delivery and oxygen uptake nor median tPo2 and hypoxic tPo2 values on the skeletal muscle were different between groups. In contrast, subendocardial ischemia was absent in DCLHb-diluted animals until 1.2% hematocrit was achieved. This was attributable to a higher coronary perfusion pressure (65 (22) mm Hg vs. 19 (8) mm Hg; p <.05), higher subendocardial perfusion (4.1 (2.6) mL.min-1.g-1 vs. 1.2 (0.4) mL x min(-1) x g(-1)), and subendocardial oxygen delivery (5.7 (2) mL x min(-1) x g(-1), p <.05) in DCLHb-diluted animals, resulting in superior myocardial contractility reflected by maximal change in pressure over time (3829 (1914) vs. 1678 (730); p <.05) and higher regional myocardial contractility (11 (8)% vs. 6 (2)%; p <.05). An increased LV end-diastolic pressure reflected LV myocardial pump failure in HSA-diluted animals but was unchanged in DCLHb-diluted animals. In the DCLHb group, systemic vascular resistance index remained at baseline values throughout the protocol, whereas coronary vascular resistance decreased. In contrast, both variables decreased in HSA-diluted animals.

CONCLUSION

DCLHb as a diluent allowed for hemodilution beyond the hematocrit value, determined "critical" after hemodilution with HSA (6.1% (1.8)%). Even at 1.2% hematocrit (hemoglobin, 4.7 g x dL(-1)) myocardial perfusion and function were maintained, although at the expense of peripheral tissue oxygenation. This discrepancy in regional oxygenation might be caused by a redistribution of blood flow favoring the heart, which is related to a disproportionate decrease of coronary vascular resistance index during hemodilution with DCLHb.

ACUTE NORMOVOLEMIC HEMODILUTION IN PATIENTS UNDERGOING ELECTIVE MAJOR SURGERY

Efficacy of acute normovolemic hemodilution in patients undergoing elective major surgery was studied with the aim to evaluate optimum technique, safety and utility in the service. Forty adult patients undergoing elective major surgery, who were in ASA GD I with preoperative haemoglobin more than 10.0g% were included in this study after a detailed explanation of the procedure and obtaining consent. 350-700 ml of patients' blood was collected before induction of anaesthesia and was kept in the operation theatre at room temperature. This was followed by rapid infusion of crystalloid calculated at the rate of 3ml for every ml of blood withdrawn. Intraoperative blood loss, serial haemoglobin assessment, change in pulse rate, blood pressure, SpO₂ and urine output were carefully monitored. The blood was reinfused once haemostasis was secured at the end of surgery. All the vital parameters were maintained within normal limits throughout the procedure. This simple, easy and inexpensive technique was found to be very useful in obviating the necessity of other forms of blood transfusion and preventing all transfusion related hazards. It was found that this method has an important role in patients with uncommon blood groups and has an excellent patient acceptability. This technique has an important role in peripheral service hospitals, where formal blood bank facilities do not exist.

Acute normovolemic hemodilution and nitroglycerin-induced hypotension: comparative effects on tissue oxygenation and allogeneic blood transfusion requirement in total hip arthroplasty

STUDY OBJECTIVES

To study the comparative effects of acute normovolemic hemodilution and nitroglycerin-induced hypotension on tissue oxygenation and blood transfusion requirement.

DESIGN

Prospective, randomized study.

PATIENTS

30 ASA physical status I and II patients scheduled for primary total hip arthroplasty.

INTERVENTIONS

Patients were randomized to one of three groups of 10 patients each, to receive acute normovolemic hemodilutin (Group 1) or nitroglycerin-based hypotension (Group 2); Group 3 served as the control group. In Group 1, 2 U of blood was collected and replaced with an equal volume of hydroxyethyl starch (200/0.56%) immediately after anesthesia induction. In Group 2, nitroglycerin was infused at a rate sufficient to reduce mean arterial pressures to 60 to 65 mmHg before initiation of surgery. When hematocrit was reduced to 25%, at first autologous blood and then, if necessary, allogeneic blood was transfused to Group 1, and allogeneic blood was transfused to the other two groups, until hematocrit reached 30% for 5 days postoperatively.

MEASUREMENTS AND MAIN RESULTS

Total transfused allogeneic units of blood were determined by the fifth postoperative day. Arterial oxygen content (CaO2), venous oxygen content (CvO2), and oxygen extraction ratios (EO2) were calculated by standard formulas. The mean allogeneic transfusion requirement was significantly lower in Group 1 (1.3 +/- 0.8 U) than in Group 2 (2.3 +/- 0.8 U) or Group 3 (2.7 +/- 1.1 U) (p < 0.05). In Group 1, CaO2 and CvO2 were decreased at all times, but EO2 was significantly increased from 15 +/- 3.9% to 33.3 +/- 5.3% (p < 0.001). As for the other two groups, although CaO2 and CvO2 were decreased, EO2 was not significantly increased.

CONCLUSIONS

Acute normovolemic hemodilution is more effective than nitroglycerin-induced hypotension in reducing allogeneic blood transfusion requirement in total hip replacement surgery, without significant metabolic changes.

Does acute normovolemic hemodilution reduce perioperative allogeneic transfusion? A meta-analysis. The International Study of Perioperative Transfusion

The objective of this study was to systematically review the literature and to statistically summarize the evidence evaluating acute normovolemic hemodilution (ANH). Prospective, randomized, controlled trials of ANH that reported either the proportion of patients exposed to allogeneic blood or the units of allogeneic blood transfused were included. All types and languages of publication were eligible. Of 1573 identified publications, 24 trials (containing a total of 1218 patients) were included in the meta-analysis. When all trials were pooled, ANH reduced the likelihood of exposure to allogeneic blood (odds ratio [OR] 0.31, 95% confidence interval [CI] 0.15, 0.62) and the total units of allogeneic blood transfused (weighted mean difference [WMD] -2.22 U, 95% CI -3.57, -0.86). However, there was marked heterogeneity of the results. In trials using a protocol to guide perioperative transfusion, ANH failed to reduce either the likelihood of transfusion (OR 0.64, 95% CI 0.31, 1.31) or the units administered (WMD -0.25 U, 95% CI -0.60, 0.10). Adverse events were incompletely reported. It is possible that biased experimental design is, in part, responsible for the reported efficacy of this technique.

IMPLICATIONS

after a systematic literature review, 24 randomized trials examining the role of acute normovolemic hemodilution were identified, pooled, and summarized using statistical techniques. Many studies reported an impressive reduction in blood transfused. Closer examination suggests that these reductions in blood exposure may be due to flawed study design.

Does acute normovolemic hemodilution reduce perioperative allogeneic transfusion? A meta-analysis. The International Study of Perioperative Transfusion

The objective of this study was to systematically review the literature and to statistically summarize the evidence evaluating acute normovolemic hemodilution (ANH). Prospective, randomized, controlled trials of ANH that reported either the proportion of patients exposed to allogeneic blood or the units of allogeneic blood transfused were included. All types and languages of publication were eligible. Of 1573 identified publications, 24 trials (containing a total of 1218 patients) were included in the meta-analysis. When all trials were pooled, ANH reduced the likelihood of exposure to allogeneic blood (odds ratio [OR] 0.31, 95% confidence interval [CI] 0.15, 0.62) and the total units of allogeneic blood transfused (weighted mean difference [WMD] -2.22 U, 95% CI -3.57, -0.86). However, there was marked heterogeneity of the results. In trials using a protocol to guide perioperative transfusion, ANH failed to reduce either the likelihood of transfusion (OR 0.64, 95% CI 0.31, 1.31) or the units administered (WMD -0.25 U, 95% CI -0.60, 0.10). Adverse events were incompletely reported. It is possible that biased experimental design is, in part, responsible for the reported efficacy of this technique.

IMPLICATIONS

after a systematic literature review, 24 randomized trials examining the role of acute normovolemic hemodilution were identified, pooled, and summarized using statistical techniques. Many studies reported an impressive reduction in blood transfused. Closer examination suggests that these reductions in blood exposure may be due to flawed study design.

Combined hemodilution and hypotension monitored with jugular bulb oxygen saturation, EEG, and ECG decreases transfusion volume and length of ICU stay for major orthopedic surgery

STUDY OBJECTIVE

To assess the efficacy and safety of hemodilution combined with induced hypotension during surgery.

DESIGN

Randomized, nonblinded, controlled study.

SETTING

Operating room suite and intensive care unit (ICU) at a university hospital.

PATIENTS

16 ASA physical status I and II patients who underwent general or general plus epidural anesthesia for major orthopedic surgery.

INTERVENTIONS

In Group 1 (n = 10), mean arterial blood pressure (MAP) was decreased to 50 mmHg by increasing the inspired concentration of isoflurane and injecting 75 mg of 0.5% bupivacaine into the epidural catheter. Hematocrit was decreased to 20% by phlebotomy and simultaneous infusion of crystalloid and colloid. In Group 2 (n = 6), isoflurane was adjusted to maintain MAP within 20% of baseline values, and no phlebotomy or hemodilution was used.

MEASUREMENTS AND MAIN RESULTS

Efficacy of hemodilution combined with induced hypotension (Group 1) was compared to standard management of blood volume and pressure (Group 2) by measuring transfusion volume and length of ICU stay. Safety of hemodilution/hypotension was determined by measuring the electroencephalogram, internal jugular venous oxygen saturation, the electrocardiogram, and central venous oxygen saturation. In Group 1, both the volume of homologous blood (225 +/- 150 ml) and total blood (1440 +/- 286 ml) was significantly less than the volume of homologous blood transfused in Group 2 (2650 +/- 878 ml). No patients in Group 1, but all patients in Group 2 required ICU admission (3.5 +/- 1.6 days) for treatment to prevent sequelae from, or progression of, moderate-severe tissue edema and metabolic acidosis. Cerebral and myocardial measures were not significantly different between groups.

CONCLUSIONS

Hemodilution combined with induced hypotension was safe and may reduce the need for transfusion and ICU admission.

The physiology of oxygen transport

Adequate organ function requires adequate provision of cells with oxygen (O2). The driving force for O2-diffusion from ambient air to its site of consumption in cell mitochondria is the oxygen partial pressure (pO2) gradient along this pathway. After uptake in the lungs, O2 transport in blood is achieved (1) through binding to haemoglobin and (2) through physical dissolution in plasma. While the sum of O2 in these two transport states defines total oxygen content of blood, the delivery of O2 to different organs is determined by cardiac output and arterial O2 content, being the product of both parameters. In the case of anaemia, intravascular volume and cardiac compensatory mechanisms determine the degree of O2 content reduction allowable prior tissue hypoxia and lactacidosis occur. When intravascular volume is preserved (e.g. normovolemic dilutional anaemia), reductions in O2 content are tolerated to a much higher degree than in hypovolemic anaemia (e.g. haemorrhagic shock).

Hydroxyethyl starch solution attenuates blood-brain barrier disruption caused by intracarotid injection of hyperosmolar mannitol in rats

This study was performed to investigate whether a fraction of hydroxyethyl starch macromolecules, prepared from pentastarch and known as "Hes-Pz," with molecular weights of 100,000-1,000,000, protects against blood-brain barrier (BBB) disruption due to intracarotid injection of hyperosmolar mannitol. Rats were anesthetized with isoflurane, and retrograde catheterization of a unilateral eternal carotid artery was performed. Except for the Control group (n = 8), hemodilution was performed using lactated Ringer's solution LR group, n = 7), 6% hetastarch (HES group, n = 7), or 6% HES-Pz (HES-Pz group, n = 8) to reduce the hematocrit to about 23%. The BBB transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid was determined after a unilateral intracarotid injection of 25% mannitol. Blood pressure and hematocrit were similar in all groups. In the control group, Ki was increased significantly in the ipsilateral cortex (IC) where mannitol was injected (16.3 +/- 6.1 vs 4.1 +/- 1.4 microL.min-1) when compared with the contralateral cortex (CC). Ki was similar in the CC in all four groups. The Ki in the IC was significantly lower in the HES-Pz(6.4 +/- 3.5 microL.g-1.min-1) than in the Control, HES, or LR group (16.3 +/- 6.1, 19.0 +/- 12.9, 17.9 +/- 10.8 microL.g-1.min-1, respectively). Our data suggest that HES-Pz significantly attenuates disruption of the BBB caused by an injection of hyperosmolar mannitol.

Blood conservation strategies to minimize allogeneic blood use in urologic surgery

Analysis of the net costs, efficacy, and cost-effectiveness of preoperative autologous blood donation (PAD), versus acute normovolemic hemodilution (ANH), in patients undergoing radical prostatectomy is presented. Currently, PAD is a standard of care for patients undergoing radical prostatectomy. Comparison of PAD with ANH showed no differences in risks or outcome, but ANH was less expensive. Hemodilution is a simple, safe, convenient, and effective alternative to PAD. The use of recombinant human erthropoietin in conjunction with PAD and ANH has optimized perioperative hematocrits and further minimized exposure to allogeneic blood. Intraoperative blood salvage, lower transfusion triggers, and other blood conservation strategies are discussed. The most cost-effective techniques currently available for decreasing allogeneic blood transfusions appear to be avoidance of blood loss, increased tolerance for decreased HCT levels, and autologous blood procurement via ANH.

Intraoperative hemodilution and autologous platelet rich plasma collection: two techniques for collecting fresh autologous blood

Intraoperative hemodilution (IH) and autologous platelet rich plasma (APRP) collection are two techniques used to obtain autologous blood in the operating room. They have been used to reduce allogeneic blood exposure in patients undergoing both cardiac and non-cardiac surgery. Both components have the advantage of providing fresh blood not subject to the storage lesion. Whole blood (IH) or platelet rich plasma is removed from the patient as anesthesia is induced and replaced with acellular fluid. The blood is transfused back after bypass or major bleeding has ceased. Although used commonly, the data supporting the use of either technique are controversial. Methodologic problems which have confounded studies evaluating their utility include: poorly defined transfusion criteria, concommitant use of other blood conservation techniques (i.e. cell salvage, pharmacologic agents, hypothermia, controlled hypotension) and changing transfusion practices with greater tolerance of normovolemic anemia. Randomized controlled studies with well defined up to date transfusion criteria are needed to identify patients likely to benefit from these techniques.

Oxygen consumption and cardiovascular function in children during profound intraoperative normovolemic hemodilution

The clinically acceptable limit of acute normovolemic, normothermic hemodilution, a standard procedure in scoliosis surgery, is not yet well defined. Eight ASA class I patients undergoing idiopathic scoliosis correction were administered a standard anesthetic with 100% oxygen and controlled ventilation. Hemodilution was accomplished by exchanging whole blood for 5% albumin in 0.9% saline. Blood gases, acid-base status, and circulatory variables were recorded prior to and after hemodilution, and every 30 min throughout surgery. The impact of hemodilution was judged by mixed venous oxygen saturation which was maintained at > or = 60%, while intravascular volume was maintained with the 5% albumin solution. Reinfusion of the autologous blood was completed by the end of surgery. In the eight controlled cases in which normovolemic hemodilution was studied, hemoglobin levels decreased from 10.0 +/- 1.6 g/dL to 3.0 +/- 0.8 g/dL. Mixed venous oxygen saturation decreased from 90.8% +/- 5.4% to 72.3% +/- 7.8%. Oxygen extraction ratio increased from 17.3% +/- 6.2% to 44.4% +/- 5.9%. Oxygen delivery decreased from 532.1 +/- 138.1 mL.min-1.m-2 to 260.2 +/- 57.1 mL.min-1.m-2, while global oxygen consumption did not decrease and plasma lactate did not appreciably increase. Central venous pressure increased and peripheral resistance decreased during hemodilution. Cardiac index increased, heart rate remained essentially constant, and left ventricular stroke work index did not decrease significantly. No patients suffered clinically adverse outcomes. Global oxygen transport and myocardial work can be maintained at extreme normovolemic anemia. Our evidence suggests that stages of normovolemic hemodilution more severe than previously reported may be clinically acceptable for young, healthy patients during normocarbic anesthesia.

Preoperative haemodilution

In preoperative haemodilution, blood is withdrawn before surgery while normovolaemia is maintained by infusion of cell free fluid. A surgical bleeding then entails a smaller loss of red cells. Reinfusion of the saved blood maintains normovolaemia, raises hematocrit and decreases the need for donor blood. Dilutional anaemia may endanger the oxygenation of the tissues. Tissue oxygenation can be upheld by an augmented and redistributed cardiac output and by a raised oxygen extraction. These compensatory mechanisms are less efficient in the presence of vascular stenosis, in particular in the myocardium which relies virtually exclusively on coronary vasodilatation. Major contraindications to preoperative haemodilution are, apart from coronary insufficiency, ventricular failure and valvular disease. Deleterious increases in cardiac oxygen consumption and/or heart rate may result from e.g. hypovolaemia, arterial desaturation and painful stimuli. The haemodilution procedure requires knowledge and vigilance in all involved personnel and gives best results if combined with other blood saving measures, like blood predeposit and intraoperative red blood cell salvage.

Major childhood tumor resection using normovolemic hemodilution anesthesia and hetastarch

Acute normovolemic hemodilution is a safe technique for minimizing operative blood loss during major tumor resection in children. Based on our experience using hemodilution anesthesia in 14 successful extensive tumor resections, we conclude the following: (1) this is an effective means of reducing use of bank blood and thus avoiding the risks of multiple transfusions; (2) it facilitates surgical dissection due to increased visibility with dilute blood, and decreased bleeding due to controlled hypotension; (3) this technique is acceptable for Jehovah's Witnesses; (4) hetastarch is an effective, inexpensive colloid hemodiluent which minimized perioperative edema compared to crystalloid hemodilution.

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.

The effects of hemodilution during pulmonary edema in dogs

Because of their multiple medical problems, patients with the adult respiratory distress syndrome (ARDS) often develop anemia. In order to determine the effects of a low hemoglobin concentration on gas exchange in such patients, the authors studied the effects of isovolemic hemodilution in the dog oleic acid model of ARDS. Twelve splenectomized dogs with oleic acid-induced pulmonary edema and a consequent venous admixture of 31% +/- 5% (mean +/- SEM) (FIO2 = 0.21) underwent two-stage isovolemic hemodilution with Hetastarch followed by retransfusion of the withdrawn red cells. This resulted in hemoglobin levels at each stage of 12.7 +/- 0.7 g/100 ml, 9.1 +/- 0.6 g/100 ml, 6.5 +/- 0.5 g/100 ml, and 10.1 +/- 0.5 g/100 ml (mean +/- SEM). Oxygen transport fell from 363 +/- 25 ml/kg/min to 219 +/- 17 ml/kg/min (p less than 0.001) at maximum hemodilution during air ventilation and from 383 +/- 79 ml/kg/min to 292 +/- 91 ml/kg/min (p less than 0.001) during oxygen ventilation. Since oxygen consumption remained constant throughout the hemoglobin range studied, decreased hemoglobin resulted in declines in P-VO2. Hemodilution with Hetastarch did not affect intrapulmonary shunt or venous admixture despite the significant increase in cardiac output associated with hemodilution.