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Anesth Analg 2004;99:528-535
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000136769.65960.D1

CRITICAL CARE AND TRAUMA

Jukka Takala Section Editor

Increased Cerebral Tissue Oxygen Tension After Extensive Hemodilution with a Hemoglobin-Based Oxygen Carrier

Gregory M. T. Hare, MD PhD, FRCPC*, Kathryn M. Hum*, Steve Y. Kim*, Aiala Barr, PhD{dagger}, Andrew J. Baker, MD FRCPC*, and C. David Mazer, MD FRCPC*

Departments of *Anesthesia and {dagger}Public Health, University of Toronto, St. Michael’s Hospital, Toronto, Ontario, Canada

Address correspondence and reprint requests to C. David Mazer, MD, FRCPC, Department of Anesthesia, University of Toronto, St. Michael’s Hospital, 30 Bond St., Toronto, Ontario, M5B 1W8, Canada. Address e-mail to mazerd{at}smh.toronto.on.ca


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Transfusion of anemic patients with hemoglobin-based oxygen carriers (HBOCs) may improve cerebral oxygen delivery. Conversely, cerebral vasoconstriction, associated with HBOC transfusion, could limit optimal cerebral tissue oxygenation. We hypothesized that hemodilution with a HBOC would maintain cerebral tissue oxygenation, despite the occurrence of cerebral vasoconstriction. Isoflurane-anesthetized rats (100% oxygen) underwent direct measurement of mean arterial blood pressure (MAP), caudate tissue oxygen tension (PBrO2), and regional cortical cerebral blood flow (rCBF) before and after 50% of the estimated blood volume (30 mL/kg) was exchanged with either an HBOC (hemoglobin raffimer; HemolinkTM) or pentastarch (n = 6). Hemodilution with hemoglobin raffimer caused a transient increase in PBrO2 from 24.9 ± 13.3 mm Hg to 32.2 ± 19.1 mm Hg (P < 0.05), a sustained increase in MAP, and no change in rCBF. Arterial blood oxygen content was maintained despite an increase in methemoglobin and reduced oxygen saturation. Hemodilution with pentastarch caused a transient increase in MAP, no change in PBrO2, and a sustained increase in rCBF (P < 0.05), whereas the hemoglobin concentration and oxygen content were significantly reduced. Hemodilution with hemoglobin raffimer augmented PBrO2 and prevented the increase in rCBF observed after similar hemodilution with pentastarch. These data suggest that transfusion with hemoglobin raffimer may help to maintain cerebral oxygenation during severe anemia.

IMPLICATIONS: This study demonstrates that cerebral tissue oxygen tension is increased after exchange transfusion with a hemoglobin-based oxygen carrier (hemoglobin raffimer), despite evidence of cerebral vasoconstriction and an increase in methemoglobin concentration in isoflurane-anesthetized rats.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Although moderate hemodilutional anemia is generally well tolerated, severe acute hemodilution has been associated with cardiovascular morbidity (1–3) and cognitive impairment (4). Furthermore, chronically reduced hematocrit has been associated with increased mortality (5). These studies suggest that severe hemodilution eventually leads to reduced tissue oxygen delivery, possibly resulting in hypoxic organ injury. However, treatment of acute anemia with allogeneic blood transfusions has also been associated with increased morbidity and mortality (6,7), thus supporting the continuing development and assessment of safe and effective red blood cell substitutes. Currently, two different types of red blood cell substitutes are being developed: fluorocarbon emulsions and hemoglobin-based oxygen carriers (HBOCs) (8–10).

Severe isovolemic hemodilution with starch solutions causes tissue hypoxia in skin (11), muscle (12), and brain (13). Although experimental studies have demonstrated the ability of HBOCs to carry oxygen and to maintain global tissue oxygen delivery (11,12,14–27), their effect on specific tissue oxygenation has not been fully elucidated. Standl et al. (12) demonstrated that isovolemic hemodilution with an HBOC augmented muscle tissue oxygen levels. However, Tsai (11) was unable to demonstrate similar results in skin vascular beds. When used to resuscitate animals from hemorrhagic shock, HBOCs were capable of restoring tissue oxygen levels in muscle, liver, and brain (21,25,26). However, the effect of severe normotensive isovolemic hemodilution with a HBOC on cerebral tissue oxygen tension has not been previously reported.

Understanding the specific effects of HBOCs on cerebral oxygen delivery is important because these compounds have been demonstrated to cause cerebral vasoconstriction (14–16). Such vasoconstriction can be partially attributed to nitric oxide (NO) binding by HBOCs (11,28). NO is an important regulator of cerebral blood flow (CBF) for a number of different stimuli, including hypoxia and hemodilution (29,30). Increased cerebral cortical neuronal nitric oxide synthase (nNOS) gene expression has recently been described in anemic animals (31), and this supports the potential role of nNOS/NO as an important mediator of CBF during anemia. Therefore, the potential for HBOCs to bind NO, initiate cerebral vasoconstriction, and thereby impair optimal cerebral tissue oxygen delivery must be more fully explored. Given the large cerebral metabolic requirement for oxygen, such vasoconstriction could paradoxically render the brain more susceptible to anemia-induced cerebral hypoxia, despite the increased oxygen-carrying capacity imparted by HBOCs.

Therefore, this study was designed to determine the effect of severe isovolemic hemodilution with an HBOC on CBF and cerebral tissue oxygen tension. An o-raffinose cross-linked human hemoglobin (Hemoglobin raffimer, HemolinkTM; Hemosol Inc., Mississauga, ON, Canada) was used to test the hypothesis that cerebral tissue oxygen tension would be maintained after extensive (50%) hemodilution with an HBOC, despite a possible cerebral vasoconstrictive response. This experimental study has relevance in the clinical setting with regard to intraoperative blood loss, because patients often experience a normovolemic reduction in hemoglobin concentration due to intravascular fluid resuscitation with crystalloid and colloid before blood transfusion.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
All animal protocols were approved by the Animal Care and Use Committee at St. Michael’s Hospital in accordance with the requirements of the Canadian Council on Animal Care. Anesthesia was induced in male Sprague-Dawley rats (Charles River, St. Constant, PQ, Canada), with ketamine/xylazine (100/7.5 mg/kg intraperitoneally; Parke-Davis/Bayer, Toronto, ON, Canada) and maintained with 1%–2% isoflurane (Abbott, St. Laurent, PQ, Canada) in 100% oxygen after tracheostomy, and ventilation was maintained with a pressure-controlled ventilator (Kent Scientific, Litchfield, CT). Ventilation was adjusted to achieve normocapnia and normoxia as determined by blood gas analysis (Radiometer ALB 500; London Scientific, London, ON, Canada). Ventilation was adjusted to minimize any changes in PaCO2 to control for any effect of CO2 on CBF and oxygenation. Cannulation of the right jugular vein (polyethylene 90) and tail artery (polyethylene 50) was performed to achieve vascular access for direct measurement of mean arterial blood pressure (MAP) and blood gases, and to perform acute hemodilution. Animals were then placed in a stereotaxic frame (ADI Instruments; Harvard Apparatus, Saint-Laurent, PQ, Canada), and the scalp was incised sagittally. Bilateral 5-mm-diameter burr holes were trephined at the level of the bregma, 2–3 mm lateral to the sagittal sinus, exposing the intact dura.

Bilateral calibrated polarographic oxygen-sensing microelectrodes with a maximal diameter of 500 µm and a maximal sensing aperture 1 mm in diameter (LICOX GMS; Harvard Apparatus) were then inserted approximately 6 mm past the dura into the region of the caudate nucleus, by using stereotaxic coordinates as previously described (31). The caudate nucleus was chosen because it is a large and relatively homogenous area of gray matter with a metabolic rate similar to that of the cerebral cortex, suitable for placement of an invasive oxygen electrode. This location for probe placement was also favored because the caudate nucleus represents a region of the brain with relatively limited collateral circulation that may be more susceptible to hypoxia (32). A corresponding temperature probe was placed at the same coordinates as the oximetry probe. Caudate tissue oxygen tension (PBrO2) is reported in millimeters of mercury.

Bilateral laser Doppler flowprobes (OxyFlo; Oxford Optronix, Oxford, UK) were positioned over the dura, avoiding any visible large dural vessels. Regional cortical CBF (rCBF) was measured by using a probe at the surface of the cerebral cortex and not in the caudate nucleus to minimize local tissue trauma that might alter PBrO2 measurements. Because laser Doppler flowmetry provides a relative measure of blood flow, values were normalized to baseline for each experiment and are reported as changes relative to baseline. A period of 30 min was used to establish a steady baseline while a heating pad and heating lamp were used to maintain the brain temperature near 37°C. Brain oxygenation (PBrO2), temperature, CBF, and MAP were recorded with a computerized data acquisition system (DASYLab 5.6; Kent Scientific).

The HBOC used in this study (hemoglobin raffimer; HemolinkTM) was manufactured by a process of pasteurization, chromatographic purification, viral filtration, and o-raffinose cross-linking from donated human blood that was collected from Food and Drug Administration-approved collection sites and was outdated (>42 days from donation). Size-exclusion high-performance liquid chromatography at the time of manufacture demonstrated a mixture of dimeric (32 kd, 3%), tetrameric (64 kd, 39%), and oligomeric (>64 kd, 58%) hemoglobin with a right-shifted oxyhemoglobin dissociation curve (33). The hemoglobin raffimer was stored according to the manufacturer’s recommendations in 100% nitrogen at –20°C in 20-mL aliquots. Immediately before hemodilution, hemoglobin raffimer was warmed to 37°C in an incubator, and a sample was extracted for cooximetry before infusion into each rat.

Three different groups of animals were studied (n = 6 rats per group). Control animals underwent acute isovolemic hemodilution by simultaneously exchanging 30 mL/kg of arterial blood (50% of the estimated blood volume) withdrawn from the tail artery with an equivalent volume of pentastarch (Pentaspan; DuPont Pharma, Mississauga, ON, Canada) infused via the jugular vein. The experimental group underwent a similar degree of hemodilution with hemoglobin raffimer. In both cases, volume exchange was performed over 10 min by using a programmable "push-pull" pump (PHD 2000; Harvard Apparatus). Tail artery cannulation was used for continuous MAP measurement before and after the exchange transfusion period. After completion of volume exchange, all variables were recorded for an additional 60 min before the animal was killed by anesthetic overdose (ketamine 100 mg IV; Parke-Davis). A third group consisted of animals that received an infusion of phenylephrine (40 µg/mL; n = 6) titrated from 2–3 µg · kg–1 · min–1 to increase the MAP to approximately 110 mm Hg (34). This MAP was chosen to match the increase in MAP observed after infusion of hemoglobin raffimer to determine the relative effect of different vasoconstricting drugs on PBrO2 and CBF.

For each group, arterial blood gas analysis (Radiometer ALB 500) and cooximetry (Radiometer OSM 3) were performed at baseline (10 min) and after hemodilution (or initiation of phenylephrine infusion) at 35, 45, 60, and 75 min. Brain temperature, PBrO2, and rCBF measurements from bilateral probes were averaged to provide a single value at each time point for each experimental animal. Individual laser Doppler flowmetry measurements were normalized to baseline and are presented as normalized values. Data were assessed with SAS (SAS Institute Inc., Cary, NC). All data were initially assessed for any time and group effect by using a two-way analysis of variance. Subsequently, between-group and within-group comparisons were performed by using Wilcoxon’s ranked sum and Wilcoxon’s signed rank test, respectively, at baseline (10 min) and after hemodilution or phenylephrine infusion at 40, 60, and 75 min. Statistical significance was assigned at a P value <0.05. Data are presented as mean ± SD.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
Before infusion into animals, the hemoglobin raffimer had a pH of 7.46 ± 0.08, a PaCO2 of 2.2 ± 0.1, and a PaO2 of 0.5 ± 0.5 mm Hg. The hemoglobin concentration of the hemoglobin raffimer was 108 ± 1 g/L, with a methemoglobin concentration of 4.8% ± 0.1% (n = 6). These values are within the expected manufacturer’s specifications for storage in an anoxic environment.

There were no differences in baseline blood gas or cooximetry values among any of the three experimental groups. Arterial blood gas values did not deviate significantly from baseline after hemodilution with pentastarch (Table 1). However, there was a significant reduction in the hemoglobin concentration from a baseline value of 137 ± 23 g/L to a minimum of 54 ± 7 g/L at 35 min, with a corresponding reduction in blood oxygen content from 8.4 ± 1.4 mmol/L to 3.4 ± 0.4 mmol/L (Table 1; P < 0.05). No significant changes in oxygen saturation or methemoglobin concentration were detected after hemodilution with pentastarch.


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  		Table 1. Arterial Blood Gas and Co-oximetry Data for Rats Hemodiluted with Pentastarch or Hemoglobin Raffimer, or after Infusion of Phenylephrine
 
Hemodilution with hemoglobin raffimer resulted in a slight increase in PaO2 relative to baseline at 45 min, without any other significant changes in arterial blood gases (Table 1; P < 0.05). After hemodilution, the hemoglobin concentration decreased at 45 min (95 ± 17 g/L) relative to baseline but remained significantly higher than the pentastarch group at 35, 60, and 75 min (Table 1; P < 0.05). After hemodilution with the HBOC, the arterial oxygen saturation was significantly reduced from 99.1% ± 0.7% to 90.3% ± 1.5% at 35 min and remained reduced for the duration of the experiment (Table 1; P < 0.05). Concurrently, the methemoglobin concentration increased from 0.8% ± 0.2% to a maximum of 4.9% ± 1.5% at 45 min and remained increased for the duration of the experiment (Table 1; P < 0.05). Unlike in the pentastarch group, the arterial oxygen content was not significantly reduced after hemodilution with hemoglobin raffimer (Table 1). No significant changes in blood gas or cooximetry measurements were observed after phenylephrine infusion.

There were no significant differences among baseline brain measurement values for all three experimental groups. After hemodilution with pentastarch, there was a sustained increase in brain temperature from a baseline value of 35.3°C ± 1.1°C to 36.9°C ± 0.7°C at 40 min (P < 0.05). A similar increase was observed in the phenylephrine group, but not after hemodilution with hemoglobin raffimer. After pentastarch hemodilution, the MAP increased transiently from a baseline value of 83.4 ± 5.6 mm Hg to 95.4 ± 4.7 mm Hg at 40 min before returning to baseline. After hemodilution with hemoglobin raffimer, there was a sustained increase in MAP from 77.3 ± 7.6 mm Hg to 108.2 ± 26.2 mm Hg at 40 min. The MAP remained increased for the duration of the experiment. The MAP in the phenylephrine group followed a similar pattern, increasing from 76.0 ± 12.5 mm Hg to 107.6 ± 10.7 mm Hg at 40 min (Fig. 1, upper row; P < 0.05). After hemodilution with pentastarch, the PBrO2 did not change from its baseline value of 20.2 ± 2.2 mm Hg (Fig. 1; middle row, left column). Hemodilution with hemoglobin raffimer resulted in a transient increase in PBrO2 relative to baseline (24.9 ± 8.9 mm Hg) to a maximum value of 32.3 ± 9.0 mm Hg at 40 min (Fig. 1, middle row, middle column; P < 0.05). Phenylephrine infusion resulted in a sustained increase in PBrO2 from 40 to 75 min; this reached a peak value of 44.5 ± 18.9 mm Hg at 75 min (Fig. 1; middle row, right column). Normalized rCBF increased from a baseline value of 0.98 ± 0.05 to 1.32 ± 0.25, 1.48 ± 0.13, and 1.57 ± 0.38 at 40, 60 and 75 min after hemodilution with pentastarch (Fig. 1, bottom row, left column; P < 0.05). After hemodilution with the hemoglobin raffimer, no increase in rCBF was observed (Fig. 1; bottom row, middle column). Phenylephrine infusion also caused a progressive increase in rCBF, and this reached a peak value of 1.83 ± 0.26 at 75 min (Fig. 1, bottom row, right column; P < 0.05).



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  		Figure 1. Hemodilution with pentastarch ({downarrow}) resulted in a transient increase in mean arterial blood pressure (MAP). Caudate tissue oxygen tension was maintained at baseline in association with a sustained increase in regional cerebral blood flow (rCBF) (left column). Hemodilution with hemoglobin raffimer ({downarrow}) caused a sustained increase in MAP and a transient increase in caudate tissue oxygen tension without any increase in rCBF (middle column). Infusion of phenylephrine ({downarrow}) caused a sustained increase in MAP that was comparable to that in the hemoglobin raffimer group. There were sustained progressive increases in caudate tissue oxygen tension and rCBF (right column).

 
Between-group analysis demonstrated that the MAP was increased in the phenylephrine group relative to the pentastarch group at 60 and 75 min (Fig. 2, top; P < 0.05). PBrO2 was increased significantly in the phenylephrine group relative to the pentastarch group at 40 min (Fig. 2, middle; P < 0.05). The rCBF in the hemoglobin raffimer group was significantly less than that of the other groups at 60 and 75 min (Fig. 2, bottom; P < 0.05).



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  		Figure 2. Between-group analysis demonstrated a significant increase in mean arterial blood pressure (MAP) in the phenylephrine group at 60 and 75 min (top). Caudate tissue oxygen tension was increased in the phenylephrine group only at 40 min (middle). Cerebral blood flow did not increase in the hemoglobin raffimer group relative to the pentastarch group at 60 and 75 min (bottom).

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
This study demonstrates that PBrO2 is transiently increased after 50% isovolemic hemodilution with an HBOC in anesthetized rats ventilated with 100% oxygen. Such an increase in PBrO2 did not occur in the pentastarch group. This is the first report that cerebral tissue oxygen tension is increased after extensive isovolemic hemodilution with hemoglobin raffimer. Lee et al. (26) have recently demonstrated that brain tissue hypoxia, secondary to hemorrhage and hypotension, improved after resuscitation with infusion of 6 mL/kg of a bovine-derived HBOC. Resuscitation with the HBOC restored the blood pressure and caused the brain oxygen tension to increase above baseline values. This study differs, in that it assessed the effect of human hemoglobin raffimer on anesthetized rats in the absence of hypovolemia or hypotension. This setting more closely resembles conditions of steady, but not catastrophic, blood loss in patients undergoing major surgery. Normovolemia and normotension are usually maintained in these patients by the administration of intravascular crystalloid and colloid. However, these patients may eventually require a blood transfusion to prevent anemia-induced tissue hypoxia. In experimental animals, severe isovolemic hemodilution has been demonstrated to cause cerebral hypoxia (13,31). In these situations, the administration of an HBOC might maintain adequate cerebral tissue oxygen delivery while reducing the need for allogeneic blood transfusions. Although PBrO2 increased after hemodilution with hemoglobin raffimer, no relative increase in PBrO2 was observed in the pentastarch group. This suggests that oxygen delivery to the brain may be improved during severe hemodilution with hemoglobin raffimer. These data are consistent with clinical evidence of improved neurological function in a severely anemic child transfused with 500 mL of hemoglobin raffimer (35). They also support the potential for the intraoperative use of HBOCs, which have been shown to be effective in reducing the need for transfusion of allogeneic blood (36,37). However, one clinical trial that used diaspirin-cross-linked hemoglobin in trauma patients was terminated because of significant mortality in the HBOC group, emphasizing the need for continuing assessment of these oxygen therapeutics (38).

After hemodilution with pentastarch, the expected increase in cortical rCBF was observed (39). The concurrent increase in caudate temperature after hemodilution with pentastarch also provides indirect evidence of a global increase in CBF. This increase in CBF is known to be proportional to the reduction in arterial oxygen content and occurs by both passive changes in blood rheology and actively mediated cerebrovascular vasodilation (30,39). The hemodilutional increase in CBF may be a cerebral protective mechanism directed at augmenting cerebral oxygen delivery during anemia, as supported by a recent study in rats (31). As has been previously reported, no increase in rCBF or caudate temperature was observed after hemodilution with HBOCs (14–16). Increased cerebral oxygen delivery and/or HBOC-induced cerebral vasoconstriction likely contributed. Because cerebral hypoxia stimulates a regulated increase in CBF (29), the lack of increased blood flow after hemodilution with the hemoglobin raffimer may provide further evidence of improved cerebral oxygen delivery. Although vasoconstriction has been reported with hemoglobin raffimer, it is reportedly of lesser magnitude than with other HBOCs (33). Evidence of systemic vasoconstriction was demonstrated by the significant increase in MAP in the HBOC group.

Cerebral vasoconstriction observed after hemodilution with hemoglobin raffimer may be partially caused by modulation of endogenous vasoactive molecules such as NO. However, enhanced delivery of oxygen to the tissue may have also led to vasoconstriction. Therefore, hemoglobin raffimer-induced vasoconstriction may be due to both pharmacological ef-fects and physiologic mechanisms. This differs from the effect of phenylephrine, which caused a more pronounced increase in PBrO2 and rCBF, suggesting that the increased perfusion pressure may have over-whelmed autoregulatory mechanisms for maintaining CBF. Alternatively, phenylephrine may have caused more profound vasoconstriction in the systemic circulation relative to the cerebral vasculature, leading to an increase in CBF and oxygenation. This suggestion is supported by the finding that phenyl-ephrine has been demonstrated to increase CBF in awake rats (34).

In this study, animals receiving hemoglobin raffimer did not exhibit any evidence of metabolic acidosis secondary to reduced oxygen delivery associated with systemic vasoconstriction, as assessed by arterial blood gas analysis up to approximately one hour after transfusion. Although Tsai (11) demonstrated reduced skin tissue oxygen levels after hemodilution with an HBOC, Standl et al. (12) demonstrated an increase in muscle tissue oxygenation after similar exchange transfusion with an HBOC. Our data suggest that cerebral tissue oxygenation is improved after hemodilution with hemoglobin raffimer, despite evidence of significant systemic vasoconstriction, suggesting that oxygen delivery to brain tissue is favored. Improved cognitive function in an anemic child after receiving hemoglobin raffimer provides further anecdotal evidence of improved cerebral tissue oxygen delivery (35). Further study is required to assess the longer-term effects of HBOCs on the balance between systemic vasoconstriction and optimization of oxygen delivery.

Laser Doppler flowmetry has been used in a variety of experimental studies to assess rCBF. It was used in this study to facilitate the concurrent measurements of CBF and tissue oxygenation in an attempt to determine the overall effect on tissue oxygen delivery. Several previous reports have validated the use of laser Doppler flowmetry to assess changes in CBF. Measurements of changes in CBF during hemodilution and hemorrhage resuscitation by using hydrogen clearance and labeled microsphere methodologies have been correlated with CBF measurements obtained by laser Doppler flowmetry (40,41). Furthermore, Rebel et al. (15) have used labeled microsphere techniques to measure rCBF after hemodilution with colloid and HBOC solutions. They demonstrated changes in CBF in the cerebral cortex and caudate nucleus that were comparable to the changes in CBF measured in this study. In this study, concurrent measurements of CBF and PBrO2 suggested that cerebral oxygen delivery was maintained or augmented despite significant cerebral vasoconstriction.

After hemodilution with hemoglobin raffimer, the PBrO2 increased despite a significant increase in methemoglobin concentration and a reduction in arterial oxygen saturation. The increase in methemoglobin occurs because of oxidation of the heme iron in the hemoglobin molecule. Because methemoglobin does not carry oxygen, this could limit the oxygen-carrying capacity of the blood. Despite this, no statistically significant reduction in blood oxygen content was calculated after hemodilution with hemoglobin raffimer. The increase in methemoglobin concentration and the reduction in arterial oxygen saturation were not associated with a significant reduction in arterial oxygen content, suggesting that the hemoglobin raffimer was able to deliver adequate amounts of oxygen to the brain. This reduction in hemoglobin saturation and the right-shifted oxyhemoglobin dissociation curve of hemoglobin raffimer suggest that high levels of inspired oxygen should be used to optimize cerebral oxygen delivery.

There are some limitations to this study. These experiments were performed in animals with an intact blood-brain barrier. In the normal situation, the brain cells are protected from the possible toxic effects of hemoglobin by two barriers—the red blood cell membrane and the blood-brain barrier. Although pressor-related filtration of diaspirin-cross-linked hemoglobin into lung and soft tissue lymph has been described (42), it is unknown whether filtration of HBOCs occurs across the cerebral microvasculature. The effect of HBOCs in clinical situations with blood-brain barrier disruption, such as in traumatic brain injury or stroke, remains to be determined.

In summary, extensive hemodilution with the HBOC hemoglobin raffimer resulted in a transient increase in PBrO2, which was not observed after hemodilution with pentastarch. This increase occurred in association with an increase in MAP, a decrease in arterial oxygen saturation, an increase in methemoglobin concentration, and an unchanging oxygen content. The lack of an increase in rCBF suggests cerebral vasoconstriction had occurred. The balance of effects favors oxygen delivery to the brain. Improved tissue oxygen delivery in the absence of significant cerebral vasodilation may be especially relevant for clinical situations in which an increase in CBF may be potentially detrimental.


   Acknowledgments
 
Supported in part by the Canadian Anesthesiologists’ Society, the Physicians’ Services Incorporated Foundation, the Anemia Institute for Research and Education, and Hemosol Inc.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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Accepted for publication February 25, 2004.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press