Hemodilution -- new clothes for an anemic emperor

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

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

Difficulties in demonstrating efficacy of blood substitutes

Currently, the fear of infectious disease transmission by allogenic blood transfusions has spurred interest in developing a blood substitute FDA approval requires that a sponsor demonstrate that the substitute is effective. The challenge in designing efficacy studies in man is proving that the substitute offers significant advantages over conventional therapies for acute blood loss. This task is complicated by the oxygen reserve and the response to hemodilution following treatment of acute blood loss in man. Paradoxically, the technique that relies on these protective physiologies-isovolemic perioperative hemodilution-many offer the best experimental model to establish efficacy of a blood substitute in man.

Effects of acute isovolemic hemodilution and anesthesia on regional function in left ventricular myocardium with compromised coronary blood flow

The effects of progressive, isovolemic hemodilution using Dextran 70 and the effect of halothane (0.7, 0.9, 1.1, and 1.3% end-tidal, administered randomly at each level of hemodilution) on global cardiovascular and regional LV contractile functions were investigated in 24 dogs with induced critical constriction of the left anterior descending coronary artery (LAD). Two additional groups of six dogs each (with and without LAD stenosis) not undergoing hemodilution served as time controls. Regional LV contractile function was assessed by sonomicrometry in the flow-compromised apical LAD territory, as well as in three non-compromised LV areas supplied by the left circumflex coronary artery. Regional myocardial function was found to be stable throughout the study period of 4-5 h in both time control groups. Mean arterial and coronary perfusion pressures as well as LV dP/dtmin decreased (P < 0.01) during hemodilution. LV dP/dtmax remained unchanged, and heart rate and LVEDP increased slightly (P < 0.05). Systolic shortening (SS) in the LAD territory was unchanged at a hematocrit (HCT) of 33.5 +/- 0.3% (mean +/- s.e. mean), and decreased marginally at an HCT of 24.2 +/- 0.1% (SS of 17.4 +/- 1.0% as compared to 20.2 +/- 1.6% at critical constriction (CC), P < 0.05). No increase in post-systolic shortening (PSS) occurred in the compromised area. Severe LAD dysfunction was observed in the LAD territory at an HCT of 14.9 +/- 0.1%, as systolic shortening decreased (11.8 +/- 1.1%, P < 0.01 vs CC) and PSS increased (31.2 +/- 3.4%, P < 0.01 vs CC). The effects of hemodilution on global cardiovascular and regional myocardial functions were unaffected by halothane.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen transport by a modified haemoglobin solution (PPSFH) in a dog model of acute anaemia following hypovolaemia

Polymerised pyridoxylated stroma free haemoglobin (PPSFH) is a potential red cell substitute. We compared PPSFH to Succinylated Gelatin (SG) and autologous fresh blood (AFB) in a dog model. Three groups of dogs were subjected to a period of fluctuating hypovolaemia. Eight received AFB and had a final haematocrit (Hct) of 54% and total active haemoglobin level (WBod Hb) of 16.5 g/dl. Eight received SG, had a final Hct of 20% and WBod Hb of 5.6 g/dl. Eight received PPSFH, had a final Hct of 20% and a WBod Hb of 10.4 g/dl. Those dogs receiving AFB responded to the hypovolaemic stress by raising oxygen consumption by 27%, whereas in both those receiving SG and PPSFH, oxygen consumption fell by 15% (p = 0.007). In the PPSFH group the PPSFH carried 43% of oxygen consumed. Thus, although PPSFH provided a higher circulating haemoglobin level than SG and carried a high proportion of oxygen consumed, it did not confer any advantage in terms of bulk oxygen transport.

Cardiovascular responses, hemodynamics and oxygen transport to tissue during moderate isovolemic hemodilution in pigs

In conclusion, in contrast to many reports obtained from dogs, in pigs the rise in CO during moderate isovolemic hemodilution is, besides the increased venous return, more induced by increased work performance of the heart and less by a decreased SVR. The rise in CO did not compensate for the decrease in oxygen transport capacity. Our results confirm most of the reported findings in humans at the same stage of hemodilution. Besides changes in hemodynamics, in our study a gradual decreased oxygen affinity of hemoglobin could be observed. That the pig animal model for studying hemodilution and oxygen transport to the tissue is more appropriate than the dog model is open to discussion.

Hemodilution--possibilities and safety aspects

Normovolemic hemodilution is an essential part of the overall strategy to avoid exposure of patients to the hazards of homologous blood transfusions. It includes beneficial effects on the flow properties and flow conditions of blood. A hematocrit of 30% can be regarded as an optimal compromise between the fluidity and the oxygen content of the blood. Compensatory responses such as increased cardiac output and stroke volume occur following hemodilution. In patients with compromised coronary reserve the degree of hemodilution that is tolerated has to be carefully considered. Therefore specific selection criteria for patients to be preoperatively hemodiluted are needed. For reasons of safety, efficiency and practicability colloid solutions rather than crystalloid solutions should be used for intentional hemodilution.

Preoperative haemodilution

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

Effect of cardiac index and hematocrit changes on oxygen consumption in resuscitated patients

Oxygen consumption (Vo2) has been found to depend on oxygen delivery (Do2) following resuscitation from hemorrhage in both humans and animals. The relative influence of blood flow and arterial oxygen (O2) content, the components of Do2, has not been separately assessed. To determine the relative contribution of content and flow, we determined Do2 and Vo2 while making systematic changes in cardiac index (CI) and hematocrit (HCT). Fourteen patients were studied within 36 hr of hypotension from which they were resuscitated to a HCT of 27.9 +/- 0.4% (mean +/- SEM). Following initial hemodynamic measurements, CI was manipulated by changing end expiratory pressure by increments of +/- 5 cm H2O and measurements were repeated. Patients were then transfused overnight to raise their HCT to 36.7 +/- 0.5% and measurements were repeated, varying CI in the same manner. The increase in HCT resulted in significant (P less than 0.05) increases in O2 delivery (+ 130 +/- 33 ml/min/m2), arterial O2 content (+ 3.9 +/- 0.3 vol%), and mixed venous O2 content (+ 3.7 +/- 0.4 vol%). O2 extraction decreased by 6 +/- 1% from 30 +/- 2%. The change in HCT did not alter Vo2 (143 +/- 7 ml/min/m2), CI (3.6 +/- 0.2 L/min/m2), or intrapulmonary shunt (18.1 +/- 1.7%). However, as CI was changed at both levels of HCT, there were changes in Vo2 directly dependent on Do2. We conclude that oxygen consumption in patients resuscitated from hemorrhage may be influenced by oxygen delivery and that this influence is related more to flow than to arterial content.

Controversial and changing trends in blood transfusion

Advances in techniques of blood and plasma donation, cell separation and preservation as well as new methods for plasma fractionation have made component therapy available in countries with an advanced transfusion service. This has broadened the evergreen subject of use and abuse of whole blood with problems emerging from the clinical use of blood products. Without any attempt to cover this endless subjects, this paper will be focused on some controversial and changing trends in the use of cell concentrates.

Effect of transfusion regime on erythropoietin levels in refractory hypoplastic anemia

Erythropoietin measurements were performed in 2 patients with refractory hypoplastic anaemia who required regular blood transfusion. Erythropoietin levels varied inversely with the haemoglobin level consistent with the accepted role of erythropoietin in reflecting the adequacy of tissue oxygenation. A particularly step rise in erythropoietin occurred when the haemoglobin concentration fell below 8.0 g/dl. This coincided with the deterioration in clinical symptoms necessitating imminent admission for transfusion. Change from a regime involving a 5--6 unit transfusion every 6 weeks to that involving a regular 2 unit per 2 weeks transfusion resulted in a lower and more stable pattern of erythropoietin levels and was also associated with a considerable improvement in general well being.

Should autologous blood transfusion be rediscovered?

With a greater appreciation and understanding of reactions to homologous blood transfusion there has been a renewed interest in autologous blood transfusion. The techniques and indications for preoperative banked autologous blood, perioperative haemodilution and recycled salvaged autologous blood transfusion are described. When circumstances permit, autologous blood transfusion is a safe, economical and efficient alternative to homologous blood.