Perflubron Emulsion Delays Blood Transfusions in Orthopedic Surgery 

The study was performed in 11 centers in six European countries in 147 of 290 formally screened patients reaching randomization between January 1996 and February 1997. The protocol was approved by all local ethics committees. Patients of either sex undergoing unilateral (first-time or revision) hip replacement or first-time spinal surgery with an expected blood transfusion requirement of 2–6 units of packed red cells were eligible for this study.

Additional inclusion criteria were a preoperative hemoglobin concentration between 11 and 16 g/dl; use of general, balanced anesthesia (isoflurane in oxygen and air with fentanyl and vecuronium) as opposed to spinal or epidural anesthesia; consent for insertion of a pulmonary artery catheter; acute normovolemic hemodilution (ANH) to a target hemoglobin concentration of 9 g/dl; an arterial oxygen partial pressure ≥ 360 mmHg after a 5-min ventilatory trial at an inspiratory fraction of oxygen (FI^O2) of 1.0; and the ability to achieve a mixed venous oxygen partial pressure (Pv^O2) of ≥ 40 mmHg after ANH at an FI^O2of 0.40. This Pv^O2was measured between the end of ANH and the beginning of surgery and was not always identical with the Pv^O2measured immediately after ANH.

Exclusion criteria were pregnancy or lactation; refusal of allogeneic blood transfusions; erythropoietin therapy within 21 days before surgery; hypersensitivity to constituents of the perflubron emulsion (e.g. , egg yolk allergy); surgical procedure expected to last longer than 8 h; expected transfusion requirements greater than 6 units; spinal or epidural anesthesia (alone or as adjunct to general anesthesia); preoperative blood transfusions; congestive heart failure greater than New York Heart Association class II; baseline electrocardiogram with nonassessable ST segments (left bundle branch block, duration of QRS complex > 0.12 s, preexisting ST-segment depression); severe chronic obstructive pulmonary disease necessitating regular use of bronchodilators or corticosteroids; American Society of Anesthesiologists class > 3; platelet count < 150,000/μl; significant hepatic disease (aspartate aminotransferase or alanine aminotransferase > twice upper limit of normal); significant impairment of renal function (creatinine concentration > 180 μM); body weight > 175% of that recommended by Metropolitan Life Height and Weight tables for patient's height; use of preoperative oral anticoagulation; treatment with aspirin, fibrinolytic drugs, or antifibrinolytics; history of bleeding disorder; immunosuppression; local or systemic infection; history of malignancy within past 5 yr; and alcohol or drug abuse within the past year. Preoperative autologous blood donation was allowed, as well as fractionated low molecular weight heparin for the prophylaxis of postoperative deep vein thrombosis. Emulsion-based drugs other than perflubron emulsion were not administered in the perioperative period.

This was a prospective, multinational, multicenter, randomized, controlled, single-blind, parallel group study. Perflubron emulsion (Oxygent, Alliance Pharmaceutical, San Diego, CA) was provided by the manufacturer, and the study was sponsored by the R. W. Johnson Pharmaceutical Research Institute (Zürich, Switzerland, and Raritan, New Jersey). Perflubron emulsion has an oxygen solubility of 7.6 mM (19.3 vol%) and a carbon dioxide solubility of 61.6 mM (157 vol%) at 37°C and one atmosphere ambient pressure.

A peripheral venous cannula was inserted and anesthesia was induced. The anesthesia induction agent was not specified by the protocol. Anesthesia was maintained with isoflurane and fentanyl and patients were paralyzed with vecuronium. Patients were ventilated with oxygen-enriched air without nitrous oxide. No epidural or spinal anesthesia was allowed, either as a primary anesthesia or as an adjunct to general anesthesia.

Patients were monitored with radial artery and pulmonary artery catheters. After anesthesia induction, ANH to a target hemoglobin concentration of 9 g/dl was performed by blood withdrawal and simultaneous colloid replacement (gelatin, hydroxyethyl starch 200 kDa/0.5 M, or human serum albumin). After ANH a first set of hemodynamic measurements was performed at an FI^O2of 0.40, including heart rate, systemic and pulmonary artery pressures, pulmonary capillary wedge pressure (PCWP), cardiac output (thermodilution), arterial and mixed venous blood-gas analyses, and hemoglobin concentration (HemoCue, AB Leo Diagnostics, Helsinborg, Sweden). The individual PCWP after ANH, measured in the position in which the operation was performed, served as an estimate of normovolemia in a given patient. During the subsequent operation, by protocol, PCWP was required to be kept at least at this posthemodilution level with crystalloid and colloid infusions. FI^O2was maintained at 0.4 until randomization (fig. 1).

Most of the transfusion triggers were based on post-ANH hemodynamic measurements and are termed physiologic transfusion triggers  here. These physiologic transfusion triggers were prospectively defined in the protocol as tachycardia (heart rate > 125% of post-ANH heart rate or > 110 beats/min, whichever came first), hypotension (mean arterial pressure < 75% of post-ANH mean arterial pressure or ≤ 60 mmHg), high cardiac output (>150% of post-ANH cardiac output) or low Pv^O2(<38 mmHg). A hemoglobin concentration < 6 g/dl before reaching any of these physiologic transfusion triggers or electrocardiographic signs of myocardial ischemia (new ST-segment depression ≥ 0.1 mV or new ST-segment elevations ≥ 0.2 mV) prevented randomization and mandated retransfusion of autologous blood collected during ANH. If the patient had been randomized and one of the treatments had been given, a hemoglobin concentration < 6 g/dl or electrocardiographic signs of myocardial ischemia were considered additional triggers for subsequent blood transfusions.

Investigators were instructed to accept tachycardia and hypotension as physiologic transfusion triggers only after hypovolemia was excluded, as evidenced by a PCWP at or above the individual post-ANH PCWP level, and if an adequate depth of anesthesia was assured. This meant that increasing heart rates were to be treated first by fentanyl, and decreasing blood pressure by lowering isoflurane administration.

During surgery, the hemodynamic and blood-gas measurements were repeated at 30-min intervals or performed if a transfusion trigger was detected by continuous monitoring. After a transfusion trigger was reached, patients were randomized into one of four treatment groups based on a computer-generated randomization schedule using permuted blocks and stratification by center. Treatment groups were (1) a standard-of-care group, in which 450 ml of autologous blood (last complete unit removed during ANH) was transfused at an FI^O2of 0.40 (the AB group);(2) a low-dose perflubron emulsion group, in which 0.9 g perfluorochemical per kilogram (1.5 ml/kg) and colloid added to a total volume of 450 ml were administered in conjunction with changing FI^O2to 1.0 (the P^0.9group);(3) a high-dose perflubron emulsion group, in which 1.8 g perfluorochemical per kilogram (3.0 ml/kg) and colloid added to a total volume of 450 ml were administered in conjunction with changing FI^O2to 1.0 (the P^1.8group); and (4) a colloid group, in which 450 ml of colloid was infused in conjunction with changing FI^O2to 1.0 (the COL group)(fig. 1).

After completion of treatment and every 15 min thereafter, all previously mentioned hemodynamic and blood-gas measurements, including samples for perflubron concentration in the perflubron emulsion groups, were performed until a second transfusion trigger was reached. Upon reaching the second transfusion trigger all patients received a unit (450 ml) of autologous blood harvested during ANH (if available) or one unit of packed red cells (autologous or allogeneic) with ventilation at an unchanged FI^O2according to treatment-group assignment. Cell salvage was allowed during the operation. The protocol mandated retransfusion of autologous blood, in the order of blood collected during ANH, cell saver blood, and blood from preoperative autologous donation, before using allogeneic blood. After the second treatment, hemodynamic and blood-gas measurements, including perflubron concentration in the perflubron emulsion groups, were performed at 60-min intervals or upon reaching the next transfusion trigger when autologous blood collected during ANH or one unit of packed red blood cells (autologous or allogeneic) was given. After initiation of wound closure, the hemoglobin concentration was adjusted to ≥ 8 g/dl by gradual transfusion of all remaining autologous blood before allogeneic blood had to be used.

Patients underwent follow-up evaluation from enrollment to postoperative day 28. Besides vital signs and general aspects of well-being, blood was collected 4 h after the first treatment and at postoperative days 1, 2, 3, 4, 7, 14 and 28 for the determination of laboratory profiles (hematology, blood coagulation, and chemistry). All adverse and serious adverse events were recorded during the first 28 postoperative days. Treatment-emergent events were defined as those that were new in onset (e.g. , new onset of hypertension) or aggravated in frequency or severity following dosing (e.g. , known hypertension requiring more intense treatment). In addition, any pathologic finding that was new in occurrence or exacerbated compared with the subject's status at study entry was considered a treatment-emergent adverse event if it required medical intervention.

The primary endpoint was the duration of reversal of changes in protocol-specified transfusion triggers, that is, the time from the start of the first treatment to the start of the second treatment or the end of surgery (initiation of wound closure), whichever occurred sooner. Secondary endpoints included percentage of patients achieving complete reversal of physiologic transfusion triggers; the need for allogeneic blood transfusions; oxygen dynamics including calculated oxygen content, oxygen consumption, oxygen delivery, and oxygen extraction (see Appendix 2), assessment of a dose response (low vs.  high perflubron dose); and safety evaluation in the postoperative period until postoperative day 28 including vital signs, laboratory profiles (hematology, blood coagulation, and chemistry), and adverse event data.

All analyses were performed on an intent-to-treat basis. The primary efficacy variable was duration of transfusion-trigger reversal. Subjects who did not reach a second transfusion trigger before the end of surgery were treated as censored observations, and the time interval from the start of the first treatment to the end of surgery (initiation of wound closure) was used as an estimate of the duration of transfusion-trigger reversal. The cumulative distribution of the primary efficacy variable of each treatment group was estimated by using the method of Kaplan–Meier. 21Because subjects were comparable at baseline (see results), log-rank tests were performed to compare the distribution of the primary efficacy variable between groups using a step-down multiple-test comparison approach. 22The initial comparison was planned to be between the P^1.8group and the AB group. If that comparison was statistically significant (one-sided test, based on a significance level of 0.025), the P^0.9group was compared with the AB group. Comparisons between the perflubron emulsion groups and the COL group were performed exploratively.

Secondary efficacy variables included the proportion of subjects achieving complete reversal of their first transfusion triggers, the proportion of subjects requiring allogeneic blood transfusions and the units of allogeneic blood transfused. All secondary efficacy parameters were tested using the Fisher exact test (two-sided and based on a significance level of 0.05) and analysis of variance as appropriate.

Patient demographics and baseline characteristics, pre- and post ANH data, data before and after the first treatment, and allogeneic blood transfusion data were summarized for each treatment group. Continuous variables were compared among groups by analysis of variance and, if an overall significance was found, followed by the Scheffé multiple-comparison test. Categoric variables (e.g. , percentages) were compared among and between groups by Fisher's exact tests. Data before and after the first treatment were compared within groups using paired t  tests.

Two-hundred ninety patients were formally screened. Of these, 117 could not be enrolled because they violated one or more of the inclusion and exclusion criteria. Among these were 10 patients with post-ANH Pv^O2values < 40 mmHg. In addition, there were 26 patients who never reached a first transfusion trigger. Thus, a total of 147 patients were randomized, 38 patients to the COL group, 38 to the P^0.9group, 36 to the P^1.8group, and 35 to the AB group. Seven patients (5%) could not be evaluated at the 28-day follow up (COL, 2; P^0.9, 1; P^1.8, 2; AB, 2) but were included in the analysis of transfusion-trigger reversal and oxygen dynamics.

Patient baseline characteristics, type of surgical procedure, duration of surgery and anesthesia, and the percentage and volume of blood from preoperative autologous donation were similar among treatment groups (table 1). Hemoglobin levels before preoperative hemodilution were similar in all groups (COL, 11.7 ± 1.4 g/dl; P^0.9, 11.6 ± 1.3 g/dl; P^1.8, 11.7 ± 1.7 g/dl; AB, 11.7 ± 1.6 g/dl). The duration of preoperative hemodilution to a target hemoglobin level of 9 g/dl was also similar in all four groups (P = 0.09). During ANH, similar amounts of blood were removed with similar amounts of plasma expander replacement (table 2). This resulted in similar hemoglobin concentrations, hemodynamic parameters, and arterial and mixed venous blood-gas values after hemodilution (table 2). Times from skin incision to first transfusion trigger, hemoglobin concentration, and hemodynamics also were not different among treatment groups when reaching the first transfusion trigger (table 3).

With the first treatment, PCWP remained essentially unchanged (table 3). Hemoglobin concentration decreased in both perflubron emulsion and colloid groups because of ongoing surgical blood loss and colloid replacement and remained relatively unchanged in the AB group receiving a unit of blood collected during ANH. Mean arterial pressure was relatively stable in all groups but increased in the P^1.8group. Pulmonary artery pressure was unchanged in the COL and P^1.8groups and minimally increased in the P^0.9and AB groups. Heart rate remained relatively stable in all groups. Cardiac index increased in the P^0.9, P^1.8, and AB groups but was stable in the COL group. Arterial oxygen partial pressure increased (by protocol) in the COL, P^0.9, and P^1.8groups but remained unchanged in the AB group. Pv^O2and mixed venous oxygen saturation increased in all groups, but these measurements in the AB group were significantly lower after the first treatment compared with all other groups. Calculated arterial oxygen content increased only in the P^0.9and P^1.8groups and remained unchanged in the COL and AB groups. Mixed venous oxygen content increased in all groups. Oxygen delivery index increased in the P^0.9, P^1.8, and AB groups but remained unchanged in the COL group. Oxygen consumption index remained unchanged in all groups, and oxygen extraction decreased in all groups (table 3).

Percentage of complete transfusion-trigger reversal, that is reversal of all transfusion triggers (when multiple transfusion triggers were present), was highest in the P^1.8group, followed by the P^0.9, COL, and AB groups (P = 0.001). The differences between the P^1.8and AB (P < 0.001) and COL (P = 0.014) groups were statistically significant. Reversal of low Pv^O2was more frequent in the COL, P^0.9, and P^1.8groups compared with the AB group (table 4). Reversal of hypotension, tachycardia, and high cardiac output was not significantly different among groups (table 4). Duration of transfusion-trigger reversal (primary endpoint) was longest in the P^1.8group, followed by the P^0.9, AB, and COL groups (fig. 2and table 4). The differences in duration of reversal between the P^1.8and AB (P = 0.014) and COL (P < 0.001) groups and the difference between P^0.9and COL (P = 0.012) were statistically significant.

Tachycardia, high cardiac output, and a hemoglobin concentration < 6 g/dl occurred with similar incidences in all treatment groups as a second transfusion trigger (table 5). Hypotension occurred more often in the COL group (45%) than in the P^1.8group (11%), and a Pv^O2< 38 mmHg was recorded more often in the AB group compared with all other treatment groups.

There were no perioperative deaths through postoperative day 28. Allogeneic blood transfusion requirements were comparable in all treatment groups, and hemoglobin values at hospital discharge were similar (table 6).

No patient discontinued the study prematurely because of an adverse event. A total of 12 (COL, 6; P^0.9, 2; P^1.8, 2; AB, 2) patients experienced serious adverse events, all of which were assessed by the investigators as unlikely to be related to study treatment. A summary of adverse events is presented in table 7. The proportions of patients with any adverse events were 61% in the COL group, 53% in the P^0.9group, 69% in the P^1.8group, and 66% in the AB group. The majority of these were mild or moderate in severity, with no significant differences among groups. Platelet, bleeding, and clotting disorders were reported more frequently as adverse events in the P^0.9(11%; n = 4) and P^1.8(28%; n = 10) groups than in the COL (5%; n = 2) and AB (6%; n = 2) groups. These 14 adverse events in the perflubron emulsion groups included five cases of mild to moderate thrombocytopenia on the day of surgery, one case of thrombocytopenia (80,000/μl) on postoperative day 2, three cases of surgically induced bleeding, two cases of less intraoperative bleeding than expected, one elevated platelet count on postoperative day 13, and two cases with low coagulation parameters.

Postoperatively, platelet counts decreased in all groups as compared with baseline (fig. 3). An additional temporary decrease in platelet count between postoperative days 2 and 4 was observed in the P^1.8group compared with the AB, COL, and P^0.9groups (fig. 3). Platelet counts also were lower in the P^0.9group on postoperative days 2 and 3 compared with the COL group, whereas no difference from the AB group was detected. No differences among groups were observed from postoperative day 7 onward.

Routine laboratory parameters were similar during the study period of 28 days in all treatment groups (data not shown). Mean duration of hospitalization was also similar across groups (15–17 days;table 1).

This study demonstrates that infusion of a 1.8-g/kg dose of perflubron emulsion combined with ventilation with 100% oxygen was well tolerated in all patients and resulted in hemodynamics and oxygen delivery changes similar to those found with blood transfusions. There was a higher frequency of “reversal of transfusion trigger” and a longer duration of reversal, although these conclusions are the results of relatively small differences in various parameters.

Avoiding allogeneic blood transfusions has become an important issue in the perioperative care of surgical patients 19,23because of a variety of risks and side effects such as transfusion reactions, 1alloimmunization, 2transmission of infectious agents, 3,4and immunosuppression. 5As a result, there is a growing number of patients demanding perioperative treatment without allogeneic blood transfusions. Thus, in recent years a variety of methods and procedures have been developed to minimize allogeneic blood transfusions. Artificial oxygen carriers such as modified hemoglobin solutions or perfluorocarbon emulsions 24could supplement these methods by providing additional oxygen delivery and oxygen unloading capacity and thereby enhancing patient safety during periods of intraoperative anemia.

The efficiency of perflubron emulsion in providing additional oxygen delivery and, more importantly, enhancing oxygen unloading capacity has been shown in experimental models of hemodilution and surgical blood loss 16,25and cardiopulmonary bypass. 26In these studies, animals treated with perflubron emulsion had a higher level of oxygen delivery because of an increased arterial oxygen content and the ability to maintain an increased cardiac output at low endogenous hemoglobin levels of 3 to 5 g/dl. 16,27,28The increased oxygen delivery enhanced tissue oxygenation 25,29–31and mixed venous oxygenation 16,26,27and tended to improve survival after cardiopulmonary bypass 26and after hemorrhagic shock with hypotensive resuscitation. 28 

Reversal of low mixed venous oxygen partial pressure in the present study in patients treated with perflubron emulsion and ventilation with an FI^O2of 1.0 (table 4) is in agreement with recent experimental data. 16,25,31,32Habler et al.  25found that mixed-venous oxygen partial pressure was higher in animals treated with perflubron emulsion after hemodilution to a hemoglobin of 3 g/dl than in control animals, and parameters of left-ventricular contractility were found to be improved at a hemoglobin level of 3 g/dl after perflubron emulsion administration. 31This may be the result of augmented oxygen delivery through very narrow microvascular channels that are more readily perfused with the tiny perflubron emulsion particles (< 0.2 μm in diameter) than relatively large red blood cells (7–8 μm in diameter). 33Enhanced convective oxygen transport may increase local tissue oxygenation, particularly in the myocardium, 34and thus contribute to maintaining blood pressure despite profound hemodilutional anemia. 25,27,31 

An increase in Pv^O2after the administration of perflubron emulsion was demonstrated previously in a pilot study in seven surgical patients. 35The present study demonstrates that the increased oxygen delivery to the peripheral tissues seems to have a clinically relevant physiologic consequence, namely, the reversal of transfusion triggers (fig. 2and table 4), although a similar calculated amount of additional oxygen-carrying capacity was provided by each treatment (COL, 0.78 ml/dl; P^0.9, 0.97 ml/dl; P^1.8, 1.16 ml/dl; AB, 1.21 ml/dl; see Appendix 2). This provides evidence of efficient oxygen unloading by the perflubron emulsion. Interestingly, the duration of trigger reversal was the longest with administration of high-dose perflubron emulsion (fig. 2). This is particularly noteworthy because with ongoing surgical blood loss and concomitant volume replacement to maintain normovolemia a significant portion of the administered perflubron emulsion was lost, whereas in the colloid and 100% oxygen ventilation groups the full potential of the treatment was preserved. This suggests that the treatment benefit originated from the administration of perflubron and not primarily from the increased FI^O2or the volume effect of the administered colloid.

We are aware of the complexity of using physiologic parameters such as individual tachycardia, hypotension, and low Pv^O2to indicate the need for a blood transfusion in anesthetized patients undergoing major surgery with significant blood loss. For this reason, a strict anesthesia and volume-replacement scheme was followed to differentiate, as much as possible, the manifestations of too much or too little anesthesia or hypovolemia from signs of compromised oxygen delivery resulting from normovolemic anemia. Thus, normovolemia was strictly mandated during the entire surgical procedure. In each patient normovolemia was achieved before and after ANH by an experienced anesthesiologist. The PCWP measured after ANH served as the best evidence of normovolemia and, by protocol, PCWP was maintained at or above this level during the entire surgical procedure. Evidence that this was indeed achieved included PCWP values 1–3 mmHg higher before the first treatment (table 3) than after ANH (table 2). Because normovolemia seems to have been well maintained during the operation, hypovolemia can be excluded as an important factor influencing the physiologic transfusion triggers.

The question remains whether the depth of anesthesia could be responsible for reaching physiologic transfusion triggers. We do not believe that this was likely, based on the anesthesia technique used and the fact that investigators were instructed to first assess and adjust depth of anesthesia if a physiologic transfusion trigger occurred. Anesthesia consisted of isoflurane, fentanyl, and vecuronium with ventilation with oxygen-enriched air without nitrous oxide. No epidural or spinal anesthesia was allowed, either as a primary anesthesia or as an adjunct to general anesthesia. Investigators were instructed to initially treat tachycardia with additional fentanyl, and hypotension with a reduction of isoflurane. Only if anesthesia adjustments to correct these changes were unsuccessful were they considered to be physiologic transfusion triggers.

The transfusion triggers used in this study can be criticized as being too liberal, that is, not representing critical values. However, for the purpose of this study, the exact values selected for the individual transfusion triggers are not critical to the evaluation of the drug's activity or efficacy of the four treatments because transfusion triggers were the same in all groups, and patients were randomized only after the first transfusion trigger was reached. More importantly, all groups were essentially identical at the point at which they reached the first transfusion trigger (table 3). However, the effects of the four treatments were different (fig. 2and tables 3 and 4).

Particularly important is the finding that duration of transfusion-trigger reversal in the high-dose perflubron emulsion group was the longest despite this group having the highest incidence of censored observations (table 4). Censored observations occurred in patients who did not reach a second transfusion trigger before the end of surgery. In 53% of patients treated with 1.8 g/kg perflubron emulsion at the first transfusion trigger, the time difference between the start of first treatment and end of surgery had to be used as an estimate for the duration of trigger reversal rather than the true duration, which always would have been longer. In addition, a hemoglobin level < 6 g/dl was set by the protocol as a second transfusion trigger. Hence, patients with no physiologic transfusion triggers who reached a hemoglobin level < 6 g/dl had to be transfused with one unit of autologous blood, thereby truncating the potential duration of transfusion-trigger reversal further. Both factors result in an underestimation of the total potential duration of transfusion-trigger reversal in the high-dose perflubron emulsion treatment group, because censored observations occurred significantly more frequently in this group compared with the COL and AB control groups (table 4).

Hypotension was recorded as a second transfusion trigger (table 5) more often in the COL group than in the P^1.8group, the only treatment group in which an increase in mean arterial pressure was observed resulting from the first treatment (table 3). A low mixed venous oxygen tension occurred most often in the AB group, the group in which the lowest Pv^O2was measured after the first treatment. Distribution of second transfusion triggers therefore mirrored the initially observed treatment effect on physiologic parameters.

Allogeneic blood transfusion requirements were comparable among treatment groups (table 6). It must be stressed that this was not the primary goal of this study, and the design of the study essentially precluded the showing of any significant differences in transfusion outcome, because patients from all groups were managed at similar hemoglobin levels throughout the perioperative period. Hemoglobin levels were nearly identical at screening (table 1), before and after ANH (table 2), when reaching the first transfusion trigger (table 3), and after the first treatment (table 3), and patients in all groups were transfused to reach a hemoglobin level ≥ 8 g/dl after initiation of wound closure and were ultimately discharged from the hospital with similar hemoglobin levels (table 6). If there is bleeding at similar hemoglobin levels, it is to be expected that similar amounts of red blood cells will be lost, resulting in similar requirements for allogeneic blood transfusions. To show a reduction in allogeneic transfusion requirement requires future pivotal studies in which patients treated with perflubron emulsion are taken to lower hemoglobin levels to minimize the loss of red blood cells during surgical blood loss.

In conscious subjects, a delayed febrile response (6–8 h after dosing) along with flu-like symptoms and a moderate decrease in platelet count (3–4 days after dosing) have been described as side effects of perflubron administration. 33,36In the present study, febrile responses were observed in 5 of 74 patients, compared with 1 of 73 in the groups not treated with perflubron emulsion (table 7). All other categories of adverse events were reported with similar incidences among treatment groups. Postoperative platelet counts were lower in perflubron emulsion–treated patients in the present study, with full recovery by postoperative day 7 (fig 3). This was not associated with any detectable adverse clinical event. This effect on platelet counts should continue to be investigated in future studies, particularly if redosing is allowed or if higher doses of perflubron emulsion are administered.

In conclusion, this study indicates that administration of perflubron emulsion combined with 100% oxygen ventilation is at least as effective as autologous blood in reversing physiologic transfusion triggers and thereby may represent a safe temporary alternative to conventional blood transfusion.

D. R. Spahn, Ch. Rippmann (Institute of Anesthesiology, University Hospital, Zurich, Switzerland); E. Vandermeersch, R. van Brempt, L. Veeckman, R. Vranckx (Department of Anesthesiology, University Hospital Leuven, Belgium); H. van Aken, G. Theilmeier, T. Prien, K. Singbartl, N. Mertes, C. Schneider (Department of Anesthesiology and Intensive Care Medicine, University Hospital Münster, Germany); G. Hempelmann, J. P. Reibold, P. von Rosen, K. Wulf (Department of Anesthesiology, University Hospital, Giessen, Germany); K. Messmer, M. Welte, O. Habler, A. Hagemann, M. Kleen (Institute for Surgical Research and Department of Anesthesiology, Grosshadern Hospital, Munich, Germany); S. de Lange, L. Berry, P. de Laat, F. A. Kwinten, C. D. Punt (Department of Anesthesiology, Academisch Ziekenhuis Maastricht, The Netherlands); P. Musto (Department of Anesthesiology, Leicester General Hospital, Leicester, U.K.); D. M. Albrecht, M. Ragaller, M. Gama de Abreu (Department of Anesthesiology and Intensive Care, University Hospital Dresden, Germany); K. van Ackern, K. Waschke, W. Segiet, T. Frietsch (Department of Anesthesiology and Intensive Care, Hospital Mannheim, Germany); E. W. G. Weber, R. Slappendeel, J. J. de Hoog (Department of Anesthesiology, Sint Martinskliniek, Nijmwegen, The Netherlands); F. Mercuriali, G. Inghilleri, A. d'Aloia, R. Coluccia (Istituto Ortopedico Gaetano Pini, Milano, Italy).

where Ca^O2denotes arterial oxygen content (ml/dl), Ca^O2TOTALdenotes total Ca^O2, Ca^O2Hbdenotes hemoglobin-bound Ca^O2, Ca^O2PL is the plasma-contained Ca^O2, and Ca^O2PERFLis the perflubron emulsion transported oxygen level.

where Sa^O2and Sv^O2denote arterial and mixed venous oxygen saturations [%]; Pa^O2and Pv^O2denote arterial and mixed venous oxygen partial pressures (mmHg);[PERFL] denotes perflubron concentration (g/dl); 1.34 is the oxygen carrying capacity of hemoglobin (ml O²/g Hb); 0.003 is the solubility coefficient of oxygen in plasma (ml O²/mmHg P^O2); 0.53 is the solubility of oxygen (ml O²) in 1 ml perflubron at one atmosphere (760 mmHg) and 37°C; and 1.92 is the density of perflubron (g/ml).

where V^O2Idenotes oxygen consumption index and CI denotes cardiac index (cardiac output/body surface area)(l · min⁻¹· m⁻²).

where D^O2Idenotes oxygen delivery index.

where O^2Exoveralldenotes overall oxygen extraction ratio (%).

where O^{2Exhemoglobin}denotes hemoglobin oxygen extractionratio (%).

These formulae do not take into account the small volume of the fluorocrit after perflubron emulsion application. However, fluorocrit was not measured, and the theoretically expected correction factor is 1.2 ± 0.4% for a 1.8-g/kg perflubron emulsion dose.

To compute the theoretical amount of additional oxygen carrying capacity initially offered by the four treatments the following assumptions were made: a pretreatment arterial oxygen partial pressure of approximately 160 mmHg at an FI^O2of 0.4 and a posttreatment pressure of approximately 420 mmHg at an FI^O2of 1.0 (except for the AB group)(table 3), a body weight of 70 kg, an estimated blood volume of 5,000 ml, and a hemoglobin concentration of 10 g/dl (with a protocol-defined ANH hemoglobin target of 9 g/dl).

Perflubron concentration in whole-blood samples was dertermined by gas-chromatographic headspace analysis, in which a sample of the gas phase from a closed blood sample vial is injected and analyzed by gas chromatography and then compared with a standard curve generated by spiking whole blood with known quantities of perflubron emulsion.