Ischemia-reperfusion injury of the spinal cord: the influence of normovolemic hemodilution and gradual reperfusion

Recent studies have suggested that oxygen-derived free radicals play an important role in ischemia-reperfusion injury of the spinal cord. In other organ systems, reperfusion injury has been reduced by limiting the availability of oxygen in the reperfusion phase. The purpose of this study was to test the effect of normovolemic hemodilution and gradual reperfusion on spinal cord function after aortic cross-clamping in 84 New Zealand White rabbits. All animals underwent 21 min of infrarenal aortic cross-clamping in the conscious state by means of a previously placed aortic occlusion device and were randomized to four groups. Group 1 animals were hemodiluted to a mean (s.e.m.) hematocrit of 28(2)% by extracting 25% of the effective blood volume and reinfusing the plasma component after centrifugation concurrently with a volume of normal saline three times that of the discarded red cells. Group 2 animals (controls) were bled similarly but both plasma and red cells were reinfused, resulting in a mean (s.e.m.) hematocrit of 38(2)%. In the next two groups, distal aortic flow was recorded via an implantable Doppler device. After cross-clamping, flow was returned gradually over 45 min in animals of group 3, and abruptly in group 4. Animals were observed for 5 days and neurologic function was graded by an independent observer. Paraplegia at 5 h after clamping occurred in 75% of animals in group 1 versus 32% in group 2 (P < 0.05), and in 33% of group 3 versus 28% in group 4 (not significant). Of those animals showing initial neurologic recovery, delayed-onset paraplegia was seen in 100% in group 1 versus 87% in group 4 (not significant), and in 50% of group 3 versus 92% of group 4 (P < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute normovolaemic haemodilution does not reduce the inflammatory process induced by facial surgery

The place of preoperative acute normovolaemic haemodilution (haematocrit = 28%-32%) in reducing postoperative inflammation was evaluated after facial surgery. Thirty-two patients scheduled for mandibular osteotomy were randomized to a nonhaemodiluted group or to a haemodiluted group. The degree of postoperative inflammation was evaluated: first by an x-ray technique (radiotelemetry) providing measurements of the tissue thickness (quantitation of facial oedema), and second by the measurement of four acute phase protein plasma concentrations during the first postoperative week. Throughout the study, no changes in facial oedema or in variation of acute phase proteins were detected after haemodilution. It is concluded that acute normovolaemic haemodilution has no effect on the intensity of facial oedema and the biological inflammation process after facial surgery.

Isovolemic hemodilution alters the ratio of whole-body to large-vessel hematocrit (F-cell ratio). A prospective, randomized study comparing the volume effects of hydroxyethyl starch 200,000/0.62 and albumin

OBJECTIVE

To evaluate potential changes in the ratio of whole-body/large-vessel hematocrit (f-cell ratio) during isovolemic hemodilution and to compare the volume effects of 2 different plasma exchange solutions (hydroxyethyl starch 200,000/0.62 6% and human albumin 5%).

DESIGN

Prospective, randomized, controlled trial.

SETTING

Operating theater in a university hospital.

PATIENTS

24 gynecological patients scheduled for elective surgery.

INTERVENTIONS

Isovolemic hemodilution was performed using 2 different plasma exchange solutions. Plasma volume was determined using dye dilution technique before and after hemodilution. The volume of withdrawn blood was measured from the change in weight of the blood bags taking into account the specific gravity of blood.

RESULTS

The volume of administered plasma exchange solutions exceeded the amount of withdrawn blood by 80 +/- 47 ml (p < 0.001). Plasma volume was 3,067 +/- 327 ml before and 3,517 +/- 458 ml after hemodilution. Using red cell volumes calculated from measured plasma volumes and peripheral hematocrit, a deficit of 249 +/- 133 ml (p < 0.0001) in red cells after hemodilution appeared with the measured withdrawn red cell volumes taken into account. This finding can be explained by a change in the f-cell ratio during isovolemic hemodilution. The volume effect of the exchange solutions was 1.05 for hydroxyethyl starch and 0.95 for albumin.

CONCLUSIONS

The results demonstrate that a change in the f-cell ratio occurs during isovolemic hemodilution. The estimation of red cell volume or plasma volume changes by using either the hematocrit or plasma or red cell volume determinations together with the hematocrit may lead to erroneous results.

From low hematocrit physiology to isovolemic hemodilution

The aim of this study, starting from some concepts of physiology, was to deal with the ever growing question of intentional anemia. Physiology suitably expresses the linear relationship between hematocrit and blood fluidity, and at the same time explains how viscosity and aggregability are important co-factors in the circulation, in disease and in thromboembolic complications. The need to understand how a low hematocrit level, compared to the volemia, is a fundamental requirement in surgery, and even more so in surgery with a high risk of embolism, like orthopedic traumatology surgery. Normovolemic hemodilution was analyzed both for the risks it involves and for how much it sticks to the changes induced by a similar situation on the various organs and apparatus. The authors, based on their experience in the field of anesthesiology, propose an operating schedule to safely perform intentional normovolemic hemodilution, describing the preoperative, intraoperative and finally the postoperative period. In conclusion, the authors advocate a wider use of this technique, confirming its safety in relation to volemia.

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.

Mathematical analysis of isovolemic hemodilution indicates that it can decrease the need for allogeneic blood transfusion

BACKGROUND

The implementation of acute isovolemic hemodilution prior to surgical blood loss is a strategy used in an attempt to diminish the need for or obviate allogeneic transfusion and to avert the potential, attendant complications. Studies examining the efficacy of this technique have produced conflicting results.

STUDY DESIGN AND METHODS

The present mathematical analysis was undertaken to resolve these conflicts by determining the efficacy of hemodilution and examining the influence of the variables affecting the outcome. Efficacy was defined as the volume of additional blood loss permitted and the volume and number of units of allogeneic blood saved from transfusion. A mathematical analysis evaluated the impact of circulating blood volume and initial and target hematocrits on the efficacy of isovolemic hemodilution. It was assumed that 1) hemodilution was completed before surgical blood loss; 2) transfusion of removed blood was begun when the target hematocrit was reached and lost surgical blood was replaced at a rate that maintained the target hematocrit; 3) allogeneic transfusion was begun after all autologous blood drawn was transfused; 4) normovolemia was maintained; and 5) a unit of allogeneic blood contains 175 mL of red cells.

RESULTS

The analysis showed that isovolemic hemodilution can result in substantial additional allowable surgical blood loss that can diminish the need for or obviate allogeneic transfusion of red cells. Larger circulating blood volume, higher initial hematocrits, and lower target hematocrits increase the efficacy of hemodilution. Removal and isovolemic replacement of 1 to 2 units of blood provide minimal potential savings, as does hemodilution to a circulating (target) hematocrit of 30 percent. The extension of hemodilution to a hematocrit of (or below) 20 percent allows a disproportionately greater surgical blood loss and diminishes the need for allogeneic transfusion. It allows, for example, an additional 4.5 L of surgical blood loss, which represents a savings of 4 units of allogeneic blood when a patient with an initial blood volume of 5.0 L and a hematocrit of 45 percent undergoes isovolemic hemodilution to a hematocrit of 15 percent.

CONCLUSION

Isovolemic hemodilution can diminish or in some circumstances eliminate the need for allogeneic transfusion.

Autologous blood transfusion: evaluation of an alternative strategy in reducing exposure to allogeneic blood transfusion

The perceived risk of transfusion-transmitted disease led to the rejuvenation of autologous blood transfusion (ABT). ABT, a process in which the blood donor and recipient are the same, is increasingly becoming an integral component of the elective surgical protocol in many institutions. Various methods of ABT are being utilized. These include: preoperative blood donation, in which the patient donates blood prior to surgery and the blood is stored for an expected need during or after surgery; acute normovolemic hemodilution, in which blood is collected immediately prior to surgery and replaced with cell free fluids and then returned to the patient upon need; intraoperative blood salvage in which blood is collected from the surgical field and is reinfused after being washed and finally, postoperative blood salvage in which collected shed blood from surgical drains is reinfused to the patient. Although ABT is known to reduce the risk of allogeneic blood transfusion, it is not risk free and should be evaluated in relation to the patient's clinical picture. The combination of various methods of ABT in addition to the proper utilization of blood may consequently lead to the elimination of patients' exposure to allogeneic blood transfusion in many surgical procedures.

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.

Effect of isovolemic hemodilution with dextran and albumin on thrombus formation in artificial vessel grafts inserted into the abdominal aorta of the rabbit

The effects of isovolemic hemodilution with dextran-70 and albumin on thrombus formation in artificial arterial grafts were investigated. A polytetrafluoroethylene graft (PTFE, length 13 mm, inner diameter 3 mm) was inserted into the abdominal aorta of rabbits. Three groups of animals were studied; 1) animals receiving isovolemic hemodilution with dextran-70 (10 ml/kg body weight), 2) animals receiving isovolemic hemodilution with albumin (10 ml/kg body weight), and 3) nonhemodiluted controls. The blood flow increased by about 70% and 60% after the hemodilution with dextran and albumin, respectively, and remained high in the hemodiluted animals, after insertion of the graft. After 2 days, the vessel graft was removed and weighed. The thrombus mass was separately weighed. The results suggest that isovolemic hemodilution with both albumin and dextran is associated with a marked increase in blood flow in the rabbit. Hemodilution with dextran also reduced the amount of thrombus formation on the inner wall of the graft.

Randomized controlled trial of Ringer solution versus serum for partial exchange transfusion in neonatal polycythaemia

We tested whether crystalliod solutions could be used instead of colloid solutions for partial exchange transfusions (PET) in polycythaemic neonates because crystalloid solutions are cheap, carry no risk of anaphylactic reactions and can be sterilized. We randomly assigned 20 term neonates with venous haematocrit (Hct) > 0.65 l/l to PET with either a serum preparation (BISEKO) or Ringer solution. Plasma volume (PV) was measured with Evans blue dilution. Blood volume (BV) and red cell mass were calculated from PV and venous Hct. Before PET both serum and Ringer groups had the same Hct (0.69 (0.66-0.76) vs 0.69 (0.66-0.71) l/l; median (range)) and BV (108 (81-116) versus 96 (68-121) ml/kg. During PET an equivalent amount of blood was withdrawn stepwise (19 (14-26) versus 17 (13-25) ml/kg and replaced by either serum or Ringer solution. More of the Ringer solution (median 77%) than of the serum (median 36%) given left the intravascular space within 4 h after PET (P = 0.016); but there was no significant difference in Hct after Ringer-PET compared to serum-PET (median 0.58 vs 0.56 l/l). No infant required repeat PET. Ringer-PET reduced BV from high to normal values (from median 96 to 83 ml/kg; P = 0.005), whereas after serum-PET BV remained high (from median 108 to 98 ml/kg; not significant).

CONCLUSION

PET with Ringer solution resulted in a haemodilution comparable to PET with serum and a correction of hypervolaemia.

[Artificial blood substitutes ]

The most important function of blood is gas transport. In the attempt to replace this function, two lines of investigation were followed. Gas transport using of hemoglobin involves saturable physicochemical mechanisms. The affinity of human "stroma-free" hemoglobin for oxygen is too high, hampering the release of oxygen in tissue. The binding of oxygen to stroma-free hemoglobin can be improved by coupling of hemoglobin to pyridoxal phosphate. By cross-linking with, for example, dialdehydes (particularly glutaraldehyde) the production of hemoglobin molecules of higher molecular weight and greater stability is possible. However, first trials in humans using these preparations fall short of expectations. The stability of the polymers and of the preparations was not as good as expected. Another possibility is the use of water-insoluble fluorocarbons (perfluorocarbons), which have a high capacity for physical gas transport. The disadvantage of using emulsions of these substances is the necessity for high partial oxygen pressure to attain sufficient gas transport. The complete insolubility in water impedes the use of the metabolic inert fluorocarbons, because they can only be eliminated via the lungs. Despite these problems the fluorocarbons have been extensively used in humans. In the USA the use of some emulsions is allowed for special indications. Extended clinical use of fluorocarbons and of hemoglobin derivates cannot be expected in the near future. Substitution of the blood hydrocolloid albumin has been practiced for many years, synthetic hydrocolloids being used to replace the colloid osmotic pressure of albumin and also to decrease the blood viscosity by hemodilution and hence improve flow. In Germany hydroxyethyl starch (HES) is the most-used hydrocolloid with the least side effects. Anaphylactic reactions restrict the use of dextran, and gelatin derivatives, because of their short half-life, are not of clinical importance in Germany. Hydrocolloids with a half-life of 3-6 h (dextran 40, middle-substituted HES) are preferred, while those with a half-life of about 20-30 h (dextran 60/70, highly substituted HES) are infrequently used.

[Hemodynamics during hypervolemic hemodilution (HH) technique]

In order to avoid blood transfusion in patient, we have been carrying out hypervolemic hemodilution (HH) with HES and Ringer's lactate without blood withdrawal. We studied the hemodynamics during hypervolemic hemodilution in adult mongrel dogs. The dogs were divided into two groups; control group (group C) and nitroglycerin group (group N) in which nitroglycerin was administrated at 1 microgram.kg-1.min-1. During HH, CVP, PAP, PCWP increased remarkably, and they were lower in group N than in group C, and CO increased in group N more than in group C. Though by the acute hemodilution Hct decreased to 30%, PaO2/FIO2, pH, and SvO2 remained within normal ranges. We conclude that HH is a very useful technique to avoid blood transfusion. However, during HH the excessive volume loading is associated with significant increase in CVP and PCWP, and the vasodilating therapy is effective to reduce the volume overloading.

[Hypervolemic hemodilution as a means of preventing homologous blood transfusion. A simple alternative to acute normovolemic hemodilution]

PROBLEM

Acute normovolenic hemodilution (ANH) is timeconsuming and complicated, and has only a small effect in reducing the need for homologous blood. A simpler procedure is hypervolemic hemodilution (HHD). In the present prospective, randomized study, HHD is compared with ANH for its blood-saving effect.

STUDY DESIGN

Forty-nine patients undergoing total hip replacement were admitted. Group I (ANH): Withdrawal of 15 ml/kg bodyweight autologous blood and isovolemic replacement by hydroxyethyl starch (200/0.5). Group II (HHD): Infusion of 15 ml/kg bodyweight hydroxyethyl starch (200/0.5).

RESULTS

No significant differences were found between the groups in terms of Hb, hematocrit and coagulation. The blood loss (intra-operative+drainage losses) was comparable in the two groups at 1274 +/- 310 ml (HHD) and 130 +/- 335 ml (ANH). During the period under investigation, 66% of the patients in the HHD group and 57% in the ANH group required no homologous blood.

CONCLUSION

HHD is just as effective as ANH for reducing homologous blood requirements, and is much simpler to apply.

[Strategies for minimizing homologous blood transfusion in elective interventions]

The risks associated with homologous blood transfusion necessitates the development of strategies for reducing the need for it. The most effective method is certainly preoperative donation of autologous blood, which leads to an increase in the absolute numbers of erythr789789 by the time surgery is performed. Depending on the type of preparation and storage, erythrocytes may be viable for between 49 days (liquid storage) and many years (deep frozen). By employing preoperative plasmapheresis, high-quality autologous fresh frozen plasma can be made available for use during surgery. Donation of autologous blood and plasmapheresis are preoperative measures that need to be organized. Another possibility is the use of a cell separator to recycle blood lost during surgery, and may be applied intra-operatively (aspiration from the surgical wound) or postoperative (drainage). Hemodilution has but little effect in reducing homologous blood requirements. Instead of the technically complex and time-consuming acute normovolemic hemodilution (ANH), the simpler hypervolemic alternative version (HHD) should be employed. Applying all the measures described above, an appreciable reduction in the need for homologous blood can be achieved. A prerequisite, however, is close cooperation between the surgeon an anaesthesiologist.

The effect of haemodilution and hypercapnia on the recovery of cerebral function from experimental focal ischaemia

The direct cortical response (DCR) and associated local cerebral blood flow was recorded from the primate cerebral cortex during a period of focal ischaemia induced by middle cerebral artery occlusion (MCAO). The DCR was lost when local blood flow fell below 20 ml/100 g/min but began to recover as collateral flow increased. Hypercapnia demonstrated a loss of local vascular reactivity following MCAO, but isovolaemic haemodilution still proved effective in increasing blood flow to these areas. The reduction in blood oxygen content induced by haemodilution did not impair cerebral function but the reduction in whole blood viscosity did exacerbate cerebral susceptibility to hypercapnia-induced intra-cerebral steal.

[Non-arteritic anterior ischemic optic neuropathy: long-term results after hemodilution therapy]

BACKGROUND

In patients with nonarteritic anterior ischemic optic neuropathy (AION) we investigated the long-term effect of hemodilution on functional results, recurrence rate in the affected and involvement of the second eye.

PATIENTS AND METHODS

In a retrospective study we reviewed 24 patients ranging in age from 62 to 92 years (mean 77 years) with AION. The duration of follow-up was between 8-51 months (mean 24.8 months). All patients received iso- (Hct > 40%) or hypervolemic (Hct < or = 40%) hemodilution over 8-10 days with daily infusion of 10% hydroxyethyl-starch 200/0.5. The hematocrit decreased significant (p < 0.001) from 43.4 +/- 3.8% to 37.8 +/- 3.5% after this 10-day hemodilution treatment.

RESULTS

After the longterm follow-up 29.1% of the patients had an improvement of the central vision by two or more lines, 16.7% had a deterioration, 54.2% remained unchanged. The resulting visual acuity was between 0.5-1.0 in 37.5%, between 0.4-0.1 in 41.7% and worse than 0.1 in 20.8%. Neither visual fields nor the VECP were significant changed by hemodilution. After the mean follow-up period of 24.8 months no recurrence occurred in the affected eye and the second eye as never involved.

CONCLUSION

Hemodilution therapy has no significant longterm effect on visual acuity and visual fields, but it seems to have a beneficial influence on the recurrence rate in the affected and on the involvement of the second eye.

Transesophageal echocardiographic monitoring of preoperative acute hypervolemic hemodilution

BACKGROUND

Preoperative acute hypervolemic hemodilution is used in anesthesia to reduce the loss of blood cells during intraoperative bleeding. Indications for use of the technique might be broadened if it can be shown to be safe in older as well as younger patients. Few data are available describing heart function in humans subjected to hypervolemic hemodilution.

METHODS

Nineteen anesthetized Jehovah's Witnesses (ages 22-70 yr) without evidence of heart disease had hypervolemic hemodilution before surgery in three stages, each consisting of an infusion of 500 ml dextran 40 (50 g/l) and 500 ml Ringer's lactate over a 10-min period. After each stage, the size and function of the left ventricle were recorded by transesophageal cross-sectional echocardiography in the short-axis view. Simultaneously heart rate, arterial blood pressure, pulmonary arterial and wedge pressures and cardiac output were recorded, to compare the echocardiographic and hemodynamic data.

RESULTS

No complications occurred. Hypervolemic hemodilution resulted in an increased cardiac output by increasing the stroke volume from 48 ml in basal conditions to 67, 71, and 72 ml over the three stages, whereas heart rate did not increase. There was an initial increase in end-diastolic volume of the left ventricle, as assessed from the cross-sectional end-diastolic area from 12.9 to 15.5, 16.6, and 16.9 cm2 followed by a decrease in the in cross-sectional end-systolic area from 6.3 to 6.8, 6.0, and 5.7 cm2. The increase in wedge pressures (from 5.9 to 12.4, 17.9, and 22.6 mmHg) did not lead to progressive cardiac dilation. There was a curvilinear relation between wedge pressure and cross-sectional end-diastolic area. Stroke volume did not decrease, nor did cross-sectional end-systolic area increase; instead, a decrease in end-systolic area was a common observation.

CONCLUSIONS

The described regimen of acute hypervolemic hemodilution is well tolerated during anesthesia by patients without heart disease and does not lead to cardiac failure. It leads to an increase in stroke volume that is generated initially from an increase in end-diastolic volume, followed in many patients by a decrease in end-systolic volume, the mechanism of which is as yet unclear.

Ischemic stroke: today and tomorrow

OBJECTIVE

To review selected aspects of the current treatment of acute ischemic stroke and provide an overview of basic neuroscience research in cerebral ischemia that may be applicable to future therapies.

DATA SOURCES

Selected recent references dealing with current therapy of acute stroke and basic neuroscience developments in cerebrovascular disease from the past several years.

STUDY SELECTION/DATA EXTRACTION

Whenever possible, recommendations concerning treatment were based on results of clinical trials; when such data were lacking, the authors present possible treatment approaches.

DATA SYNTHESIS

Acute stroke is a heterogeneous process involving different etiologic mechanisms. Different types of stroke, however, may produce a similar cascade of physiologic and biochemical events leading to tissue damage. Calcium flux, glutamate excitotoxicity, platelet and leukocyte activation, free radical formation, and nitric oxide metabolism may be crucial focal points of future stroke therapy.

CONCLUSIONS

Recent clinical trials have given scientific basis for some of our treatment approaches to ischemic stroke. Future treatments for stroke will likely focus on factors which modulate biochemical events occurring as a final common pathway to all forms of cerebral ischemia.

Cardiovascular effects of moderate normovolaemic haemodilution during enflurane-nitrous oxide anaesthesia in man

The cardiovascular effects of mild normovolaemic haemodilution during enflurane-nitrous oxide anaesthesia were studied in 20 patients with normal cardiac function before, during and after total hip replacement. After induction of anaesthesia, patients were randomly allocated to one control group (C), or one haemodiluted group (H) where Hct was decreased to 30% by replacement of blood volume by an identical volume of hydroxyethyl starch 200/05. Each patient was monitored with a pulmonary artery catheter allowing the measurement of right ventricular ejection fraction. During haemodilution, stroke index and right ventricular end-diastolic volume index increased from 33.1 +/- 7.9 to 39.3 +/- 7.1 ml.M-2 and from 73.8 +/- 20.3 to 94.9 +/- 18.5 ml.M-2 respectively (mean +/- s.d., both P < 0.05). However, heart rate decreased so that cardiac index did not change. O2 delivery decreased significantly (from 389 +/- 70 to 311 +/- 63 ml.min-1.m-2; P < 0.05), but was not different to the control group. O2 consumption was maintained by an increase in O2 extraction. During the surgical procedure, cardiac index was higher in the haemodiluted group than in the control group, so that O2 delivery was similar in the two groups. O2 consumption tended to be greater in the haemodiluted group. In patients with normal cardiac function, enflurane-nitrous oxide anesthesia could alter the normal physiologic response to mild normovolaemic haemodilution.

Cardiovascular and coronary physiology of acute isovolemic hemodilution: a review of nonoxygen-carrying and oxygen-carrying solutions

Acute isovolemic hemodilution is used increasingly to avoid the potentially serious side effects of homologous blood transfusions. Cardiovascular physiology during hemodilution is characterized by a marked increase in cardiac output and organ blood flow to compensate for the decrease in arterial oxygen-carrying capacity. During advanced hemodilution an increased oxygen extraction is also observed, such that oxygen consumption generally is maintained even during advanced hemodilution. The increase in cardiac output is related mainly to a decrease in blood viscosity and an enhanced sympathetic tone resulting in stimulation of the heart. The magnitude and the mechanisms involved in the increase depend upon species, state of awareness (awake versus anesthetized), type of anesthesia, type of exchange solution, and condition of the heart prior to hemodilution. Recent laboratory findings, as well as clinical practice in cardiac surgery, suggest that moderate hemodilution to hematocrit values of approximately 25% is well tolerated in single vessel coronary artery disease which should thus not be regarded as an absolute contraindication for moderate hemodilution. An integral concept to minimize homologous blood transfusions consists of preoperative autologous blood donation, preoperative isovolemic hemodilution, meticulous (asanguineous) surgical technique, and acceptance of minimum hemoglobin levels during the entire hospitalization. The incidence of homologous blood transfusions will be reduced using acute isovolemic hemodilution. This incidence will be further reduced once hemoglobin solutions become clinically available for specific indications. At present, research activities are concentrated on defining the critical level of hemodilution in various pathologic conditions and to investigate pharmacology and physiology of the new hemoglobin solutions. Finally, several chemically modified hemoglobin-based oxygen-carrying solutions devoid of renal toxicity will be available in the future. The cardiovascular physiology and pharmacology of these hemoglobin solutions have been studied. Cardiac output is generally constant and oxygen extraction is increased to maintain oxygen consumption during hemodilution with hemoglobin solutions. In most studies, some vasoconstriction was observed also, which might result from interaction of the hemoglobin molecule with the EDRF/NO system. However, with enhanced purification, chemical modification or microencapsulation of the hemoglobin molecule, vasoconstriction can be limited.

Microcirculatory long-term effects after hypervolaemic and isovolaemic haemodilution in patients with intermittent claudication

OBJECTIVE

The aim of the present study was to clarify the possible long term effects in the course of different haemodilution regimes according to the tissue oxygen supply in the lower limb muscle of patients with intermittent claudication.

METHODS

In order to simulate the situation of intermittent claudication muscle tissue pO2 measurements were performed before and after a standardized pedal ergometric test. Muscle tissue pO2 readings were performed using micro-pt-needle electrodes at a work load of 5.7 +/- 0.2 Watt. We performed hypervolaemic haemodilution as well as isovolaemic haemodilution intraindividually and in order to compare these different regimes we have chosen the situation, when the haematocrit had returned to the pretreatment values.

RESULTS

Observing 4 weeks after the end of isovolaemic haemodilution the red blood cell aggregation is significantly decreased, whereas the other haemorrheological variables remained unchanged. Furthermore muscle tissue pO2 values are increased at rest without improvement of the exercise-induced muscle tissue pO2. In contrast there is no effect on haemorrheological variables as well as muscle tissue oxygen supply at rest and after pedal ergometric exercise test after the end of hypervolaemic haemodilution.

CONCLUSIONS

Our results suggest no benefit in the course of a long-term hypervolaemic haemodilution therapy in patients with intermittent claudication. In contrast after isovolaemic haemodilution there was found an increase in muscle tissue oxygen supply at rest without changing of the exercise-induced pattern. In our opinion isovolaemic haemodilution is to prefer in the course of long-term haemodilution therapy.