Regional blood flow during dextran-induced normovolemic hemodilution in the dog

Preoperative Haemoglobin Levels

It is a common practice in many anaesthetic centres throughout the world to require a minimum preoperative haemoglobin level of 10g/100 ml of blood or more, but very few references are quoted by writers on this subject. A search of relevant medical literature has been made in an attempt to establish the origin and significance of the preoperative haemoglobin requirements recommended.

Doppler ultrasonographic changes in the canine kidney during normovolaemic anaemia

The haemodynamics of the canine left renal artery (LRA) and interlobar artery (ILA) were evaluated in eleven fasted, healthy, conscious beagles with severe acute (haematocrit [Hct] 16%), moderate chronic (Hct 26%) and mild chronic (Hct 34%) normovolaemic anaemia using Doppler ultrasound. Heart rate, peak systolic velocity (PSV), end diastolic velocity (EDV), time-averaged mean velocity (TAVmean), pulsatility index (PI) and resistive index (RI) were recorded. Doppler values in the dogs following the induction of anaemia states were compared with corresponding values in the same dogs prior to the induction of anaemia. Left renal artery mean PSV, mean PI and mean RI were significantly higher and the mean EDV was significantly lower in severe acute anaemia. No significant change was seen in mean values of the same parameters in moderate or mild chronic anaemia. There was no significant change in TAVmean of the LRA or mean PI and mean RI of the ILA in any grade of anaemia. Acute, severe normovolaemic anaemia significantly altered LRA Doppler parameters in resting dogs without influencing those of the ILA. Moderate or mild chronic anaemia had no effect on any renal Doppler parameter.

INFLUENCE OF NORMOVOLEMIC ANEMIA ON DOPPLER-DERIVED BLOOD VELOCITY RATIOS OF ABDOMINAL SPLANCHNIC VESSELS IN CLINICALLY NORMAL DOGS

Doppler spectra of the abdominal aorta (AAo), cranial mesenteric artery (CMA), celiac artery (CA), and left renal artery (LRA) were obtained from 11 fasted, clinically healthy, conscious Beagles before and after inducing severe acute normovolemic anemia (mean +/- standard deviation hematocrit 16.0 +/- 0.77%). Peak systolic, end diastolic, and time-averaged mean velocities were measured. The different vessels were compared with each other. Peak systolic velocity ratio and time-averaged mean velocity ratio of splanchnic vessels to corresponding variables of the AAo were computed and compared between and within vessels during physiologic and anemic states. There was no difference between LRA and AAo, CMA or CA regarding time-averaged mean velocity, time-averaged mean velocity ratio, or end diastolic velocity during the physiological state. During the anemic state, LRA mean time-averaged mean velocity (P < or = 0.008) and mean end diastolic velocity (P < or = 0.041) were significantly lower than those of AAo, CMA, and CA. Mean time-averaged mean velocity ratio of the LRA was also significantly (P < or = 0.004) lower than the CMA and CA ratios, and significantly (P = 0.014) lower during anemic state than physiologic state of the same vessel. End diastolic and time-averaged mean velocities of the AAo, CMA, and CA increased proportionally during anemia, but there was a relatively less increase in the same variables of the LRA, suggesting less increase in blood flow. Doppler-ratios allowed a noninvasive comparison between splanchnic and aortic hemodynamics. Velocity ratios might be useful for clinical detection of relative hemodynamic changes between different vessels.

Influence of normovolemic anemia on Doppler characteristics of the abdominal aorta and splanchnic vessels in Beagles

OBJECTIVE

To ultrasonographically evaluate hemodynamics in the abdominal aorta (AAo) and splanchnic vessels in dogs with experimentally induced normovolemic anemia.

ANIMALS

11 healthy Beagles.

PROCEDURE

The AAo, cranial mesenteric artery (CMA), celiac artery (CA), hilar splenic artery (HSA), and main portal vein (MPV) were evaluated in conscious dogs immediately before and after experimental induction of severe normovolemic anemia (Hct, 16%) and during recovery from moderate and mild anemia (Hct, 26% and 34%, respectively). Peak systolic velocity (PSV) or peak velocity (PV), time-averaged mean velocity (TAVmean), pulsatility index (PI), resistive index (RI), blood flow, congestion index (CI), and heart rate (HR) were recorded. Results were compared for anemic and control states.

RESULTS

Severe anemia caused significant increases in HR (25% to 70%), PSV (AAo, 45.8%; CMA, 56.1%; and CA, 41.9%), PV (MPV, 84.2%), and TAVmean, (AAo, 69.4%, CMA, 64.3%; CA, 29.7%; and MPV, 76.9%) and significant decreases in PI (AAo, 26.1%; HSA, 19.3%) and Cl (MPV, 45.2%). There was no significant change in PI of the CMA or CA, portal blood flow, or RI of any artery. Significantly higherTAVmean persisted in all vessels during moderate anemia, but higher PSV persisted only in the CMA; PI (CMA and CA) and RI (CA) decreased significantly, but portal blood flow increased significantly. Significant increase in TAVmean (AAo and CMA) persisted during mild anemia, and PI (AAo, CMA, and HSA) and RI (CMA) were significantly lower.

CONCLUSIONS AND CLINICAL RELEVANCE

Doppler ultrasonography revealed hyperdynamic circulation in the AAo and splanchnic vessels in dogs with experimentally induced normovolemic anemia.

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.

Isovolemic hemodilution and skeletal muscle function during ischemia and reperfusion

Hemodilution has previously been shown to improve microcirculation in skeletal muscle after ischemia. We have studied the effects of isovolemic hemodilution with dextran on the function of anterior tibial muscle in the rabbit. Hemodiluted (hematocrit 28%) and nonhemodiluted animals were compared. Hemodilution led to an immediate increase in femoral blood flow. Flow normalized within 1-2 h, possibly due to flow redistribution. Hemodilution increased muscle force by 10%, which can reflect alterations in blood chemical composition or an improved microcirculation. Unilateral hindlimb ischemia induced by arterial occlusion inhibited muscle force to less than 15% in 150 min. Force and blood flow recovered almost completely after ischemia. After longer ischemia (170-300 min) when force was <5%, muscles did not recover. Hemodilution did not alter the muscle force or the extent or rate of force recovery after ischemia, which shows that the increased blood flow and improved microcirculation are not directly associated with changes in the sensitivity of muscle function to ischemia.

Effects of hypertonic saline-dextran solution on regional blood flow and thrombogenicity in PTFE grafts in the vena cava of the rabbit

OBJECTIVES

to study the effects of hypervolaemic haemodilution with hypertonic saline-dextran solution (HSD) on regional blood flow and thrombogenicity of small diameter polytetrafluoroethylene (PTFE) grafts.

DESIGN

blood flow in rabbit aorta, vena cava and femoral, renal and ear arteries was determined in five groups: controls, isovolaemic haemodilution with dextran-70 (10 ml/kg body weight (b.w. )), hypervolaemic haemodilution (10 ml/kg b.w.) with either dextran-70, 7.5% NaCl or a combination of dextran and NaCl (HSD). In a second series PTFE grafts were inserted into the vena cava of rabbits treated with hypervolaemic haemodilution with dextran, hypertonic saline or HSD and examined after two days.

RESULTS

blood flow increased in aorta, vena cava and femoral artery after haemodilution. The increase was transient in animals treated with hypertonic NaCl alone but sustained in the dextran-70 groups. The grafts from animals treated with hypertonic saline alone had a lower thrombus mass and higher blood flow compared to those from rabbits haemodiluted with dextran-70 only, indicating that both dextran and NaCl have antithrombotic effects. Superior results were obtained with HSD solution.

CONCLUSIONS

HSD solution has a strong flow-promoting action in several vascular beds and beneficial effects on the patency of small diameter vessel grafts.

Cerebral oxygenation during cardiopulmonary bypass measured by near-infrared spectroscopy: effects of hemodilution, temperature, and flow

OBJECTIVE

To determine the effects of hemodilution, PaCO2, PaO2, arterial pressure, and temperature on cerebral oxygenation during mild hypothermic cardiopulmonary bypass (CPB).

PARTICIPANTS

Fourteen patients electively scheduled for cardiac surgery.

INTERVENTIONS

Oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), hemoglobin differential (Hb-diff = HbO2-Hb), and oxidized cytochrome aa3 (CtO2) were measured with near-infrared spectroscopy (NIRS) during CPB.

RESULTS

With onset of CPB, a significant decrease in HbO2 (median, -4.55 micromol/L; 25th to 75th percentile, -5.5 to -3.1; p < 0.05), Hb-diff (median, -3.88 micromol/L; 25th to 75th percentile, -4.7 to -1.9; p < 0.05), and CtO2 (median, -0.05 micromol/L; 25th to 75th percentile, -0.15 to 0; p < 0.001) occurred. The simultaneous decrease in arterial hemoglobin concentration (from 11.7 to 8.5 g/100 mL, p < 0.005) correlated significantly with changes in HbO2 (r2 = 0.71; p < 0.001), Hb-diff (r2 = 0.59; p < 0.005), and CtO2 (r2 = 0.57; p < 0.005). After 24 minutes of CPB, the largest decline in HbO2 (-5.03 micromol/L) and Hb-diff (-5.68 micromol/L) was recorded, whereas CtO2 showed no changes during cooling. During CPB, Hb and Hb-diff significantly correlated with the duration of CPB, PaO2 and PaCO2.

CONCLUSIONS

In early stages of CPB, a diminished cerebral oxygen supply was found, which may be caused by acute hemodilution. Despite an increased extraction of oxygen as demonstrated by the decrease in Hb-diff, cerebral energy balance reflected by CtO2 was maintained within a safe range during cooling. Because NIRS measures regional cerebral oxygenation, it is useful as an adjunct to global measures in the early noninvasive detection of cerebral hypoxia.

Pulmonary gas exchange capacity is reduced during normovolaemic haemodilution in healthy human subjects

PURPOSE

To test the hypothesis that a physiological compensatory mechanism maintains respiratory gas exchange during normovolaemic haemodilution.

METHODS

Pulmonary gas exchange capacity was evaluated in seven healthy subjects by measuring the lung diffusion of carbon monoxide (DLCO). During the measurement, various breath-holding times, inspiratory volumes, and sitting or supine positions, were randomly selected in an attempt to alter pulmonary capillary perfusion. KCO was calculated as the percentage of theoretical values of the ratio of DLCO by alveolar volume and normalized by sex, age, and height. Normovolaemic haemodilution (NH) was performed by bleeding an average blood volume of 1 L with simultaneous Dextran 60 replacement to obtain an haematocrit below 35%.

RESULTS

After NH, haemoblogin concentration [Hb] decreased from 14.94 +/- 0.96 to 12.5 +/- 0.98 g.dl-1 (P < 0.001). KCO decreased (P < 0.02) but remained closely correlated to [Hb] at every lung volume (P < 0.02). Breathholding time and body position had no effect.

CONCLUSION

Moderate NH impairs pulmonary gas exchange capacity in awake, resting healthy subjects. There is no evidence of any compensatory mechanism since the KCO vs [Hb] relationship is unchanged.

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.

Distribution of ecto-5'-nucleotidase in the rat liver: effect of anaemia

In the kidney a striking parallel exists between the expression of ecto-5'-nucleotidase and of erythropoietin by renal fibroblasts. It was therefore hypothesized that the expression of ecto-5'-nucleotidase in fibroblasts might be controlled by oxygen tension. In order to test this hypothesis, we examined the distribution of the enzyme in a tissue which displays a defined zonation in respect to oxygen tension, namely in the liver; anaemia was used in order to exaggerate this zonation. The distribution of ecto-5'-nucleotidase was investigated by light and electron microscopy using enzyme and immunohistochemical methods in the livers of healthy and of anaemic rats. Anaemia was produced by haemolysis combined with X-ray irradiation. The enzyme was detected in the bile canaliculi, in the connective tissue of the portal triads and of the central veins, and in fat-storing cells probably corresponding to a special form of fibroblasts. In healthy animals the perisinusoidal ecto-5'-nucleotidase activity was slightly higher in the pericentral than in the periportal area of the acinus whereas the inverse was observed for the staining of bile canaliculi. Anaemia provoked an increase of ecto-5'-nucleotidase in fat-storing cells in the pericentral zone of the acinus and in fibroblasts around the central veins, resulting in steepended gradients along the sinusoids. The intralobular gradient of ecto-5'-nucleotidase in perisinusoidal cells and the effect thereon of anaemia suggest that the expression of the ecto-5'-nucleotidase might be directly or indirectly controlled by local oxygen tension.

Effects of acute normovolemic anemia on gastric mucosal blood flow in rats: role of nitric oxide

The present study investigates the effects of acute normovolemic anemia induced by isovolemic hemodilution on gastric mucosal blood flow (GMBF), measured by hydrogen gas clearance, and on the oxygen and hemoglobin content in the gastric mucosa, estimated by reflectance spectrophotometry. GMBF significantly increased after 3 and 6 mL of isovolemic hemodilution (from 50 +/- 5 to 70 +/- 7 and 77 +/- 6 mL.min-1.100 g-1, respectively; P less than 0.05) compared with basal values (50 +/- 5.mL-1.min-1.100 g-1; P less than 0.05). Oxygen content remained unchanged, whereas hemoglobin concentration decreased in parallel with the decrease in hematocrit. In a second set of experiments, the role of endogenous nitric oxide (NO) as a possible mediator of the gastric vascular changes induced by hemodilution was investigated by using the specific inhibitor of NO biosynthesis, NG-monomethyl-L-arginine (L-NMMA). The increase in GMBF induced by 3 mL of isovolemic hemodilution (delta 23 +/- 7 mL.min-1.100 g-1) was attenuated in a dose-related manner with L-NMMA, 6.25 mg/kg IV (delta 15 +/- 4 mL.min-1.100 g-1) or 50 mg/kg IV (delta 5 +/- 2 mL.min-1.100 g-1 g; P less than 0.05). The concurrent administration of L-arginine (the precursor of NO biosynthesis) abolished the effects of L-NMMA on GMBF changes. The current findings show that acute normovolemic anemia causes an increase in GMBF that is dependent on the endogenous formation of NO.

The effects of normovolemic hemodilution with dextran-40 on acute myocardial ischemia/reperfusion injury in rabbits

The effects of decreasing blood viscosity by normovolemic hemodilution with dextran-40 or normal saline (NS) on myocardial lipid peroxides, superoxide dismutase, infarct size and left ventricular function during acute myocardial ischemia/reperfusion were studied in rabbits. It was found that normovolemic hemodilution with dextran-40 could decrease the content of ischemic myocardial malondialdehyde and preserve ischemic myocardial superoxide dismutase activity after 1 h of coronary occlusion followed by 1 h of reperfusion. However, after administration of NS only a tendency in this aspect exhibited without statistical significance. Besides, hemodilution with dextran-40 reduced infarct size and improved left ventricular systolic function after 1 h of ischemia followed by 23 h of reperfusion. These results suggest that normovolemic hemodilution with dextran-40 may have anti-injury effect on acute myocardial ischemia/reperfusion to a certain degree.

[Normovolemic hemodilution]

Transfusion of homologous blood to surgical patients is not without risks. Thus, strategies to prevent blood loss must be considered. This article deals with one of them: normovolaemic haemodilution together with its advantages, physiological consequences and technical aspects. In particular, it is important to follow certain inclusion criteria. The technique is safe, effective and relatively easy to implement. In the future, it could be used in non-surgical patients, when it is necessary to increase tissue perfusion.

Effects of normovolemic hemodilution on blood flow in the rabbit ear

The effect of isovolemic hemodilution using dextran-60 on arterial blood flow in the rabbit ear was investigated. The animals were anesthetized and an electromagnetic flow probe was applied around the central artery of the ear. Isovolemic hemodilution was performed during a 15 min exchange period. Two degrees of hemodilution were investigated [8.5 and 17 ml dextran-60/kg body weight (b.w.)] and compared with a nontreated control group. The two levels of hemodilution induced reductions in hematocrit to 29 and 21%, respectively, from the control level of about 40%. In all groups, blood pressure maintained constant levels throughout each experiment, which lasted 240 min. In the controls, ear artery blood flow was unchanged or decreased slightly during the experiment. The lower level of hemodilution caused a slight increase of blood flow after 4 h. In the group treated with 17 ml/kg b.w. dextran, blood flow gradually increased after 90 min following hemodilution. After 240 min, flow rates had increased to two- or threefold the initial rate in this group. Although other possibilities exist, the increased blood flow following hemodilution may be interpreted as reflecting a decreased resistance to flow in the tissue due to the decreased viscosity of the blood.

Cerebral resuscitation after cardiac arrest using hetastarch hemodilution, hyperbaric oxygenation and magnesium ion

This study was done to investigate the effects of hemodilution, hyperbaric oxygenation, and magnesium sulfate on cerebral resuscitation. Sixteen mongrel dogs were anesthetized, and monitored via pulmonary artery catheter, arterial catheter and electrocardiogram. A left lateral thoracotomy was done. Ventricular fibrillation was obtained by application of a 6-volt AC current. Mechanical ventilation was stopped. Total arrest time was 12 min. All dogs were cardiac resuscitated within 6 min using internal massage, ventilation, bicarbonate, epinephrine and internal defibrillation. The animals were then randomized into three groups. Group I represented controls, and were not treated. Group II dogs received normvolemic hemodilution using hetastarch (Hespan) containing magnesium sulfate (2000 mg/l), resulting in a hematocrit of 20%-30%. Group III dogs received the above hemodilution plus compression in a hyperbaric oxygen chamber to 2 atmospheres absolute. Critical care management and hourly neurologic scoring was performed for 7 days by blinded observers. All dogs at the time of death underwent autopsies for gross study. Data analysis revealed no statistical difference among the three groups with respect to survival time, cardiac function or neurologic scoring.

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

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

[Effects of hemodilution on the ventricular function of the coronary patient]

Ten patients (9 males and 1 female: mean age: 64.8 +/- 7 yr) were studied. They were all stabilized coronary heart disease patients free of cardiac failure who where to undergo normovolaemic haemodilution as medical treatment of lower limb arteritis. Ventricular function was assessed by a radioisotope method: myocardial perfusion (thallium-201 and dipyridamole scintillation scan) and left ventricular contraction by technetium-99m angiography. Blood volume was measured by iodine-131 marked albumin. The following parameters were also measured: plasma viscosity, blood viscosity at seven different speeds, red blood cell aggregation index and filtration index. These were all measured before and 24 h after normovolaemic haemodilution which was carried out with à 5% albumin solution. This haemodilution was well tolerated: 1,062 +/- 335 ml of blood were sampled, the same volume of albumin being transfused, thus reducing the mean haematocrit from 0.42 +/- 0.05 to 0.32 +/- 0.02 (p less than 0.01). Normovolaemia was respected. Blood viscosity was reduced, especially at low speeds and the red blood cell aggregation index was also reduced. Ventricular contraction did not vary. Moreover, the basal myocardial state as assessed by the thallium scintillation count was not modified by the haemodilution, even being improved in three cases. The dipyridamole perfusion (the equivalent of an effort test) gave no changes in seven patients, resolved the ischaemic signs in two patients and slightly increased ischaemia in one case.

[Hemodilution and tissue oxygenation]

In a healthy person, when the haematocrit decreases in acute moderate haemodilution, oxygen delivery and oxygen pressures are preserved or improved by increasing the cardiac output. With a haematocrit of about 0.32, oxygen transport is maximum if the patient's heart function is normal, with no coronary heart disease. If the haematocrit falls below 0.25, there is a risk of anoxic anaemia, by splanchnic and cutaneous vasoconstriction and by a limitation of coronary blood flow adaptation to an increase in cardiac output. If oxygen requirements are increased by muscle exercise, fever, other stresses or when respiratory hypoxaemia occurs, extreme haemodilution is rapidly responsible for an oxygen debt. In all situations, the tissue oxygenation is compromised in the case of hypovolaemia.

[Intentional normovolemic hemodilution in the medical treatment of lower limb arteritis]

Thirty patients suffering from arterial occlusive disease (stages II, III or IV of Fontaine's classification) were treated by isovolaemic haemodilution (IDH). Most of these patients received conventional medical treatment without success (negative selection). Angiography was performed on all patients prior to treatment. 500 ml of whole blood was withdrawn from each patient. 250 ml of dextran 40 mixed with 250 ml of 5% albumin solution was injected intravenously to avoid hypovolaemia. This procedure, carried out three or four times, was repeated until a haematocrit of 0.30 was reached. This haematocrit level of 0.30-0.35 was maintained for 60 days. The measurement of ankle systolic pressure, systolic index at rest, treadmill performance and lower limb thallium-201 muscular scintigraphy were used to assess laboratory efficiency. On the sixtieth day, 14 patients (46%) showed clinical improvement, nine were stable and arterial occlusive disease worsened in seven patients. Clinical improvement persisted for several months (15 months in one case). Clinically, it seemed that patients treated by IHD showed improvement of their arterial occlusive disease. However, the prediction of the chances of success of IHD, as well as the quantification of results by common laboratory examination, were difficult. Muscular scintigraphy with thallium-201 gave a good assessment as well as a quantifiable analysis of results.

Circulatory effects of haemorrhage during sodium nitroprusside induced hypotension. A study in the rat

The haemodynamic changes induced by acute moderate blood loss were investigated in rats during normotensive halothane anaesthesia and during sodium-nitroprusside-induced hypotensive anaesthesia, respectively. Following haemorrhage in the normotensive group, mean arterial blood pressure, heart rate and left cardiac work decreased. Cardiac output was reduced non-significantly. Blood flow was redistributed to favour cerebral, coronary, renal and hepatic circulation, mainly at the expense of blood flow to the carcass. Following haemorrhage in the hypotensive group, cardiac output increased significantly. Mean arterial pressure, heart rate and left cardiac work were unchanged. Absolute values for cerebral, coronary, renal and hepatic blood flow were maintained or even increased, while blood flow to the carcass was unchanged.

Effects of prenalterol and volume loading with dextran on haemodynamics and oxygen consumption in dogs during high epidural block with special reference to the splanchnic region

High lumbar epidural block was induced in seven dogs, causing a fall in mean arterial blood pressure (AP) from 24.5 +/- 2.9 to 12.0 +/- 3.1 kPa owing to reductions in cardiac output (QT) and systemic vascular resistance (SVR) to 67% and 68% of the pre-epidural values. Volume loading with dextran 10 ml X kg-1 b.w. increased QT nearly to the pre-epidural value. SVR decreased further to 61% of the pre-epidural value and AP was only slightly increased to 14.9 +/- 2.7 kPa. Subsequent administration of prenalterol 20 micrograms X kg-1 b.w. caused a further increase in QT to 17% above the pre-epidural value due to an increase in heart rate of 51 beats/min. AP did not change since SVR decreased further to 49% of the pre-epidural value. The hepatic arterial blood flow (QHA) was essentially unchanged during epidural block as well as during volume loading, while the portal venous blood flow (Qpv) was changed concurrently with (QT). In spite of the decrease in SVR, the preportal and hepatic arterial vascular resistances were not diminished following prenalterol. The increase in OT must therefore have favoured other vascular beds. Hepatic and pre-portal tissue oxygen uptakes were unchanged during the experimental procedure, while whole-body oxygen uptake decreased by 20% following the epidural block and increased nearly to the pre-epidural level following volume loading in combination with prenalterol.

Myocardial blood flow, oxygen uptake and carbon dioxide release of the human heart during hemodilution

Myocardial blood flow, oxygen consumption and carbon dioxide release were studied before and during hemodilution in man. Dextran 70 was used as the dilutional agent to reduce hematocrit values from 37 to 28% (mean). The decrease of oxygen content in arterial blood after hemodilution was compensated by an increase of cardiac output. The myocardial blood flow increased proportionally more than the cardiac output, resulting in a virtually unchanged oxygen tension in coronary sinus blood. The metabolism of the heart was not affected as the respiratory quotient remained unchanged. This investigation suggests that blood losses up to 20% of the total blood volume can be replaced by dextran solutions, without a significant decrease of myocardial oxygen supply.

Intravascular aggregation after acute intracranial hypertension by epidural balloon compression in cats

The authors have studied the effect of acute intracranial hypertension produced by placement of an epidural balloon (control group) in cats, on cerebral perfusion, evoked responses, and hematological parameters. These elements were measured in similarly injured animals which underwent isovolemic hemodilution with dextran 75, after relief of intracranial hypertension. Four hours after balloon deflation, perfusion was markedly impaired in 30% of the control group, and was reduced to 11% in the dextran-infused group. The suppressed N1 amplitude of somatosensory evoked responses on the compression side, the reduced platelet aggregability, and the erythrocyte-deformability by intracranial hypertension were all significantly more restored in the dextran-infused group after decompression. The percentage of platelets with volumes between 21.75 and 48.75 cu mu (normal 9.75 to 12.75 cu mu) significantly increased after decompression. Activation of platelets during intracranial hypertension leads to an increase in platelet volume from platelet aggregation, and correlates with a decrease in platelet aggregability. It was also suggested that reduction of erythrocyte deformability was not caused by erythrocyte aggregation. The authors emphasize the role of intravascular factors such as vascular obstruction by platelet aggregates, and difficulty in passage of erythrocytes through capillaries due to reduced deformability, in the disturbance of the microcirculation following acute intracranial hypertension. The protective effect of dextran 75 by inhibition of platelets as well as hemodilution is stressed.

Hemodilution -- new clothes for an anemic emperor

This review deals with the rationale for the use of hemodilution in patients not subjected to open heart surgery. The claim for an optimum of circulatory oxygen transport at 30% hematocrit has been disproved; hemodilution thus simply means acute normovolemic anemia. Accordingly, it generates a cardiovascular strain and particularly jeopardizes cerebral and myocardial oxygen supply. Potentially serious clinical side effects have been reported. Hemodilution should therefore not be carried beyong the lower normal range for the hemoglobin or hematocrit level, i.e. 12--12.5 g% or 35--36%.

Optimal hematocrit for canine skeletal muscle during rhythmic isotonic exercise

Contractile power, blood flow, O2-uptake, and O2-extraction during isotonic, rhythmic exercise were determined in the isolated canine gastrocnemius muscle during perfusion with blood with hematocrits between 0.21 and 0.81. The results obtained in 36 measurements on nine muscles showed that maximal O2-delivery to the muscle if found at hematocrits between 0.5 and 0.6. Both in the range of hemodilution, and in the range of extreme hemoconcentration, O2-delivery decreases significantly. O2-consumption and contractile power of the muscles are almost unaffected in the hematocrit range between 0.4 and 0.7; beyond and below this hematocrit range both parameters decrease. O2-extraction is virtually constant in the hematocrit range between 0.3 and 0.6, but increase both below and above these hematocrit levels. It is concluded that due to reduced vasodilatory reserve in working skeletal muscle compared to resting muscle the optimal hematocrit is shifted to higher values.

Regional lung function and central hemodynamics following normovolemic hemodilution in the dog

Regional lung function, using xenon 133-radiospirometry, and central hemodynamics were studied following normovolemic hemodilution with dextran 70. Normovolemic hemodilution to hermatocrit values of 25% increased cardiac output and pulmonary blood volume significantly. The systemic oxygen transport and mixed venous oxygen tension were unchanged. The acute hemodilution did not significantly change the distribution of ventilation or prefusion within the lungs. It is hypothesised that a tendency to an increase in arterial oxygenation is due to a reduced interstitial pressure in the basal region of the lungs, resulting from water absorption by the hyperoncotic dextran used for hemodilution.

The effect of hemodilution on regional myocardial function in the presence of coronary stenosis

Hemodilution decreases blood viscosity and circulatory input impedance and thus reduces afterload. Its use in treatment of LV power failure has been advocated, but the safe limits of isovolemic hemodilution are not known. Compensation of the reduced O2-capacity of the blood was therefore studied with normal and impaired coronary reserve. In 20 dogs the LAD was stenosed to a degree just not affecting the supplied region and central and coronary hemodynamics were studied. Regional myocardial function was assessed by ultrasound transit time between transducers implanted in the LV wall. Lowering the hematocrit to 15% by isovolumic exchange of blood for Dextran 60 increased CVP (18%), PAP (47%), LAP (64%), LVedP (46%), CO (67%), and flow to the intact area (LCA: 211%). Flow in the stenosed LAD increased slightly. Enddiastolic length (EDL) of LAD dependent muscle segments rose to 120% and their contraction amplitude deltaL was decreased by 46%. Whereas non-ischemic segments showed compensatory rise in deltaL (38%) at almost constant EDL (+9%). After release of the LAD stenosis EDL and deltaL returned to normal. During progressive anemia myocardial O2-demand is not adequately met if coronary reserve capacity is depleted. Reversion of hypokinesia after removal of the stenosis shows unimpaired myocardial function at a hematocrit as low as 15% provided the coronary circulation is intact.

Hemodilution

The dilution of whole blood leads to a significant improvement of its rheologic properties based on a decrease in hematocrit and, hence, blood viscosity. Under conditions of normovolemia and an adequate response of the cardiorespiratory system, the acute dilution of blood will enhance the venous return to the heart and thereby improve total and capillary blood flow significantly. In the hematocrit range of 25 to 30 per cent (limited hemodilution), this increase in flow rate is able to compensate fully for the diminished oxygen content of the blood. Changes in oxygen extraction or in oxygenhemoglobin affinity are only encountered at hematocrits below 20 per cent or if hemodilution is associated with hypovolemia. Since normovolemia is the condition sine qua non for the heart to increase its output compensatorily, intentional hemodilution should preferably be performed with colloid solutions which are capable of maintaining the colloid osmotic pressure of plasma and the circulating volume in normal limits. Limited normovolemic hemodilution with its beneficial effects on microcirculatory flow and tissue nutrition is emphasized for the treatment of impaired microcirculation as occurring in shock and low flow states, polycythemia, and high viscosity syndromes. Acute preoperative hemodilution is a means of reducing the use of bank blood and of avoiding the risks of blld transfusions in patients undergoing major elective surgery. Extreme hemodilution and total body washout in hypothermia appear to be effective clinical tools.

Effect of increased blood fluidity through hemodilution on coronary circulation at rest and during exercise in dogs

Coronary flow and myocardial oxygen consumption were measured in conscious dogs at rest and during two levels of submaximal treadmill exercise (3 and 7 km/h at 15% grade, respectively) during adaptation to progressive hemodilution with dextran 60. At rest coronary flow increased to more than seven-fold with diminishing hematocrit to 12.5% in order to cover myocardial oxygen consumption which increased from 6.5 +/- 0.3 ml/min with 100 g at hematocrit 47.5% to 13.5 +/- 0.8 ml/min with 100 g at hematocrit 12.5%. The dilatory capacity of the coronary vessels, estimated from the reactive hyperemia after a 12 sec occlusion of the left circumflex coronary artery, dropped from 602% at control to 45% at lowest hematocrit levels. During the superimposed stress of exercise coronary flow and myocardial oxygen consumption increased further, so that the dilatory capacity of the coronaries was exhausted at hematocrit levels between 16 and 22%. Myocardial oxygen consumption per unit of oxygen delivered to peripheral tissues increased substantially with progressive hemodilution. In the presence of the reduced arterial oxygen content the augmented myocardial oxygen demand limits the overall adaptability to hemodilution by an exhaustion of the coronary dilatory capacity.

Effect of increased blood fluidity through hemodilution on general circulation at rest and during exercise in dogs

During progressive normovolemic hemodilution with dextran-60, circulatory functions (cardiac output, oxygen delivery to tissues, arterial pressure and mixed venous oxygen saturation) and total body oxygen consumption were studied in conscious dogs at rest and during two levels of submaximal treadmill exercise. At rest, cardiac output rose continuously with progressive hemodilution. This increase, however, was not sufficient to compensate for the reduced arterial oxygen content. Consequently oxygen delivery fell significantly from 23.3 +/- 1.8 ml/min with kg at hematocrit 47.5% to 15.7 +/- 0.9 ml/min with kg at hematocrit 12.5%. The constant oxygen consumption was maintained by a simultaneous increase in oxygen extraction from blood. During the superimposed stress of exercise, a constant oxygen consumption was maintained between hematocrit ranges of 50 to 15 or 25%, respectively. Again, the increase of cardiac output due to hemodilution did not compensate for the reduced arterial oxygen content and consequently oxygen extraction rate was increased. These data demonstrate that at rest (and even more during submaximal treadmill exercise) the reduced whole blood viscosity or improved fluidity during hemodilution does not initiate an increase in cardiac output that is sufficient to maintain a constant oxygen delivery to the tissues.

[Neurological complications of heart surgery. Review of their pathogenesis and bases for their treatment]

São relatadas as complicações neurológicas assinaladas em 320 pacientes submetidos a cirurgias cardíacas, com uma incidência de 7,8%. As etiologias mais comuns encontradas foram a embolia aérea (4,0%) e isquemia cerebral após hipotensão sistêmica (2,4%). Os autores analisam a patogenia das complicações cerebrais e tentam correlacioná-las com o fluxo sangüíneo cerebral, com o metabolismo cerebral e com a dinâmica dos pequenos vasos cerebrais. Uma revisão a respeito dos métodos para tratamento da isquemia cerebral é apresentada.

Regional circulatory adjustments to moderate and severe chronic anemia in conscious dogs at rest and during exercise

The successive changes in regional blood flows and resistances due to moderate and severe anemia were studied serially in nine conscious dogs after they recovered from implantation of ultrasonic Doppler transducers or electromagnetic flow probes on the left circumflex coronary, the mesenteric, the renal, and the iliac arteries and pressure gauges or catheters in the aorta. Anemia was induced by progressive phlebotomy and volume replacement over a period of 2-4 weeks. In moderate anemia (average hematocrit 22%) heart rate increased from 73 beats/min to 105 beats/min, and mean arterial pressure fell from 98 mm Hg to 94 mm Hg. Flow increased to the coronary bed by 75% and to the iliac bed by 45%, but flow to the mesenteric bed was not significantly affected and renal flow fell by 9%. Coronary and iliac resistances fell by 45% and 32%, respectively, but mesenteric and renal resistances were not significantly affected. In severe anemia (hematocrit 14%) heart rate increased to 129 beats/min, and mean arterial pressure was at control levels; coronary flow increased by 227%, iliac flow by 102%, mesenteric flow by 29%, and renal flow by 20%. Resistance decreased in the coronary bed by 69%, in the iliac bed by 52%, in the mesenteric bed by 23%, and in the renal bed by 19%. Exercise during severe anemia increased heart rate to 224 beats/min, mean arterial pressure to 114 mm Hg, coronary flow by 34%, and iliac flow by 215%; it reduced mesenteric flow by 59% and renal flow by 48%. Thus, blood flow increased and resistance decreased to all beds studied, indicating that in the resting conscious dog compensatory reduction of visceral flow is not a feature of the cardiovascular response to severe anemia at rest, although a redistribution of regional blood flow does occur. However, the added stress of exercise during severe anemia results in substantial reductions in mesenteric and renal blood flows.