Fetal oxygen content is restored after maternal hemorrhage and fluid replacement with polymerized bovine hemoglobin, but not with hetastarch, in pregnant sheep

Resuscitative efficacy of hemoglobin vesicles for severe postpartum hemorrhage in pregnant rabbits

We aimed to investigate the resuscitative efficacy of hemoglobin vesicles (HbVs) as a red blood cell (RBC) substitute for the initial treatment of severe postpartum hemorrhage (PPH). Twenty-five pregnant rabbits underwent cesarean section; uncontrolled hemorrhage was induced by transecting the right uterine artery to establish a severe PPH model. During the first 30 min, all rabbits were administered 6% hydroxyethyl starch (HES) of an equivalent volume to the hemorrhage every 5 min. Thereafter, they received any of the following three isovolemic fluids for resuscitation every 5 min: RBCs with platelet-poor plasma (RBC/PPP) (n = 8), 6% HES (n = 7), or HbVs with 25% human serum albumin (n = 10). After surgical hemostasis at 60 min, survival was monitored until 12 h. No rabbits receiving only HES infusion survived beyond 6 h, whereas all rabbits receiving RBC/PPP transfusion survived. The rabbits receiving HbV infusion showed significantly higher mean arterial pressure and hemoglobin levels than the HES-receiving rabbits, and 8 of 10 rabbits survived for 6 h. The HbV group showed significantly higher survival than the HES group but worse survival than the RBC/PPP group. In conclusion, HbV infusion for severe PPH effectively prevents lethal hemorrhagic shock in a pregnant rabbit model.

Colloids Yes or No? - a "Gretchen Question" Answered

Colloid solutions, both natural and synthetic, had been widely accepted as having superior volume expanding effects than crystalloids. Synthetic colloid solutions were previously considered at least as effective as natural colloids, as well as being cheaper and easily available. As a result, synthetic colloids (and HES in particular) were the preferred resuscitation fluid in many countries. In the past decade, several cascading events have called into question their efficacy and revealed their harmful effects. In 2013, the medicines authorities placed substantial restrictions on HES administration in people which has resulted in an overall decrease in their use. Whether natural colloids (such as albumin-containing solutions) should replace synthetic colloids remains inconclusive based on the current evidence. Albumin seems to be safer than synthetic colloids in people, but clear evidence of a positive effect on survival is still lacking. Furthermore, species-specific albumin is not widely available, while xenotransfusions with human serum albumin have known side effects. Veterinary data on the safety and efficacy of synthetic and natural colloids is limited to mostly retrospective evaluations or experimental studies with small numbers of patients (mainly dogs). Large, prospective, randomized, long-term outcome-oriented studies are lacking. This review focuses on advantages and disadvantages of synthetic and natural colloids in veterinary medicine. Adopting human guidelines is weighed against the particularities of our specific patient populations, including the risk-benefit ratio and lack of alternatives available in human medicine.

Efficacy of resuscitative infusion with hemoglobin vesicles in rabbits with massive obstetric hemorrhage

BACKGROUND

Hemoglobin vesicles have been developed as artificial oxygen carriers, and they have the potential to serve as a substitute for red blood cell transfusion.

OBJECTIVE

This study aimed to evaluate the efficacy of hemoglobin vesicle infusion for the initial treatment instead of red blood cell transfusion in rabbits with massive obstetric hemorrhage.

STUDY DESIGN

Pregnant New Zealand white rabbits (28th day of pregnancy; normal gestation period, 29-35 days) underwent uncontrolled hemorrhage to induce shock by transecting the right midartery and concomitant vein in the myometrium. Subsequently, rabbits received isovolemic fluid resuscitation through the femoral vein with an equivalent volume of hemorrhage every 5 minutes. Resuscitative infusion regimens included 5% human serum albumin (n=6), stored washed red blood cells with plasma (vol/vol=1:1; n=5), and hemoglobin vesicle with 5% human serum albumin (vol/vol=4:1; n=5). A total of 60 minutes after the start of bleeding, rabbits underwent surgical hemostasis by ligation of the bleeding vessels and then were monitored for survival within 24 hours.

RESULTS

During fluid resuscitation, hemoglobin vesicle infusion and red blood cell transfusion maintained a mean arterial pressure of >50 mm Hg and a hemoglobin concentration of >9 g/dL and prevented the elevation of plasma lactate. In contrast, resuscitation with 5% human serum albumin alone could not prevent hemorrhagic shock as evidenced by a low mean arterial pressure (40 mm Hg), a low hemoglobin concentration (2 g/dL), and a marked elevation of plasma lactate. All animals in the red blood cell group and the hemoglobin vesicle group survived more than 8 hours, whereas all animals in the 5% human serum albumin group died within 8 hours.

CONCLUSION

Hemoglobin vesicle infusion may be effective in the initial management of massive obstetric hemorrhage.

A hemoglobin-based oxygen carrier, bovine polymerized hemoglobin (HBOC-201) versus hetastarch (HEX) in a moderate severity hemorrhagic shock swine model with delayed evacuation

OBJECTIVE

To evaluate the efficacy of HBOC-201 for resuscitation of hemorrhagic shock in a swine model incorporating soft tissue injury and delayed evacuation.

METHODS

A muscle crush injury and 40% estimated blood volume controlled hemorrhage was completed in 24 Yucatan mini-pigs. Pigs were untreated or resuscitated with HBOC-201 or 6% hetastarch (HEX) at 20 min. Invasive hemodynamics and clinical variables were monitored for 4 h (pre-hospital phase) and subsequent fluid infusions were administered for severe hypotension or tachycardia. Animals were recovered from anesthesia and monitored non-invasively to 72 h (hospital phase).

RESULTS

100% (8/8) of HBOC-201-, 88% (7/8) of HEX-, and 63% (5/8) of non-resuscitated pigs, survived to 72 h (p=0.27). Mean arterial pressure, mean pulmonary arterial pressure and systemic vascular resistance index were higher in HBOC-201 pigs. By 90 min, cardiac index was restored to baseline in the HBOC-201 group and was 1.4-fold greater than baseline in the HEX group. HBOC-201 pigs had lower fluid requirements than HEX pigs (18.8+/-1.8 and 29.9+/-1.1 ml/kg, p<0.001) in the pre-hospital phase and required fewer blood transfusions (1.3+/-1.3 and 9.4+/-0.6 ml/kg, respectively, p<0.001) in the hospital phase. Urine output and blood creatinine were comparable in HBOC-201 and HEX pigs. Tissue oxygenation levels were highest in the HBOC-201 group.

CONCLUSIONS

As HBOC-201 restored hemodynamics and tissue oxygenation and decreased fluid requirements, in comparison with HEX, HBOC-201 was at least as efficacious and possibly a superior resuscitative fluid in a military-relevant delayed evacuation hemorrhagic shock swine model.

Colloid osmotic pressure after hemorrhage and replenishment with Oxyglobin Solution, hetastarch, or whole blood in pregnant sheep

OBJECTIVE

To compare plasma colloid osmotic pressure (COP) of both maternal and fetal blood, before and after hemorrhage, and replenishment with Oxyglobin Solution (Biopure Corporation, Cambridge, MA, USA), hetastarch or whole blood in pregnant ewes.

STUDY DESIGN

Prospective, randomized study.

ANIMALS

A total of 17 adult Rambouillet ewes at 131 (128-133) [median (minimum, maximum)] days gestation, weighing 56 (46, 63) kg.

METHODS

Ewes and fetuses were chronically instrumented with catheters in a maternal jugular vein, maternal carotid artery and fetal femoral artery. Twenty milliliters per kilograms of blood were removed from each ewe over 1 hour. The ewes were then given 20 mL kg(-1) of either Oxyglobin Solution (n = 5), hetastarch (n = 6), or autologous whole blood (n = 6) IV. Maternal plasma COP was measured before hemorrhage, after hemorrhage, after replenishment, and 1 and 2 hours later. Fetal plasma COP was measured after maternal hemorrhage and 2 hours after maternal volume replenishment.

RESULTS

Median COP of all ewes before hemorrhage was 20 (16, 24) mm Hg and after hemorrhage (p < 0.05), decreased to 16 (11, 19) mm Hg. After volume replenishment, the COP of the Oxyglobin Solution group was 22 (21, 25) mm Hg, the autologous whole blood group was 17 (16, 22) mm Hg and the hetastarch group was 20 (17, 21) mm Hg. The COP of the Oxyglobin Solution group was significantly greater (p < 0.05) than the COP of the hetastarch group immediately and 60 minutes after volume replenishment, and greater (p < 0.05) than that of the autologous whole blood group at 60 minutes after volume replenishment. The COP of all the fetuses after maternal hemorrhage was 16 (12, 19) mm Hg and at 120 minutes after maternal volume replenishment was 15 (11, 18) mm Hg. There were no differences in COP between or within any of the fetal groups.

CONCLUSIONS

When used to treat blood loss, Oxyglobin Solution increases plasma COP more than an equal volume of hetastarch in the first hour following administration. Maternal administration of Oxyglobin Solution did not alter fetal COP.

CLINICAL RELEVANCE

Oxyglobin Solution is a more potent colloid than hetastarch. Oxyglobin Solution did not appear to translocate fluid from the fetal to maternal circulation.

Systemic and microvascular responses to hemorrhagic shock and resuscitation with Hb vesicles

A phospholipid vesicle encapsulating hemoglobin (Hb vesicle, HbV) has been developed to provide O(2)-carrying capacity to plasma expanders. Its ability to restore systemic and microcirculatory conditions after hemorrhagic shock was evaluated in the dorsal skinfold window preparation of conscious hamsters. The HbV was suspended in 8% human serum albumin (HSA) at Hb concentrations of 3.8 g/dl [HbV(3.8)/HSA] and 7.6 g/dl [HbV(7.6)/HSA]. Shock was induced by 50% blood withdrawal, and mean arterial pressure (MAP) at 40 mmHg was maintained for 1 h by the additional blood withdrawal. The hamsters receiving either HbV(3.8)/HSA or HbV(7.6)/HSA suspensions restored MAP to 93 +/- 14 and 93 +/- 10 mmHg, respectively, similar with those receiving the shed blood (98 +/- 13 mmHg), which were significantly higher by comparison with resuscitation with HSA alone (62 +/- 12 mmHg). Only the HSA group tended to maintain hyperventilation and negative base excess after the resuscitation. Subcutaneous microvascular blood flow reduced to approximately 10-20% of baseline during shock, and reinfusion of shed blood restored blood flow to approximately 60-80% of baseline, an effect primarily due to the sustained constriction of small arteries A(0) (diameter 143 +/- 29 microm). The HbV(3.8)/HSA group had significantly better microvascular blood flow recovery and nonsignificantly better tissue oxygenation than of the HSA group. The recovery of base excess and improved tissue oxygenation appears to be primarily due to the increased oxygen-carrying capacity of HbV fluid resuscitation.

Blood substitutes

Blood substitutes are solutions intended to replace transfusion of banked red blood cells. Several variations of products based on either hemoglobin (animal or human) or perfluorocarbon emulsions are in advanced stages of clinical development. The need for such products is pressing as shortages of banked blood worsen and awareness of the dangers of blood transfusion increases. Animal and human studies with these cell-free oxygen carriers have led to new concepts of how oxygen is delivered to tissue and how the microcirculation is regulated. Although development of products is exciting and timely, understanding how they function to perfuse and oxygenate tissue could be at least as important. Because cell-free oxygen carriers will perfuse every organ of the body, their effects are far-reaching, and the transition from the laboratory to the bedside can be expected to be slow and deliberate. Comparison of oxygen carriers with more traditional starch-based products provides new insight into the interaction of oxygen transport, microvascular perfusion, and blood volume expansion.