Binding of hydroxyethyl starch molecules to the platelet surface

The effects of colloid solutions on hemostasis

PURPOSE

Colloid solutions are widely used to prevent or to correct hypovolemia in surgical patients. Although more efficacious than crystalloids, they are more expensive and can be associated with adverse effects, in particular when they interfere with the hemostatic system.

METHODS

This narrative review focuses on the effects of albumin and synthetic colloids on the biological markers of coagulation and their clinical consequences.

RESULTS

All colloidal plasma substitutes interfere with the physiological mechanisms of hemostasis either through a non-specific effect correlated to the degree of hemodilution or through specific actions of these macromolecules on platelet function, coagulation proteins, and the fibrinolytic system. Albumin has the least effect, while high molecular weight (Mw) dextrans and hydroxyethyl starches (HES) have the most significant effects. Gelatins and medium Mw HES with a low molar substitution ratio have moderate and, probably, comparable effects. The use of dextrans and high in vivo Mw HES may be associated with increased bleeding, while gelatins and low in vivo Mw HES are unlikely to have such an effect.

CONCLUSIONS

In most cases, the clinical consequences of the biological effects of colloids on hemostasis are limited, provided that safety considerations are observed (maximum daily dosage, duration of treatment, patient's hemostatic status, clinical conditions). The implications may be different in patients with hemostatic disorders, either inherited or related to preoperative antiplatelet or anticoagulant treatment. In these patients, crystalloids, gelatins or even albumin solutions should be preferred when hemodilution exceeds 30% of the circulating blood volume.

Molar substitution and C2/C6 ratio of hydroxyethyl starch: influence on blood coagulation

BACKGROUND

Development of hydroxyethyl starches (HES) with a low impact on blood coagulation but a long intravascular persistence is of clinical interest. A previous in vitro study showed that low substituted high molecular weight HES does not compromise blood coagulation more than medium molecular weight HES. In the present study we assessed the individual effects on blood coagulation of molar substitution and C2/C6 ratio of a high molecular weight HES.

METHODS

Blood was obtained from 30 healthy patients undergoing elective surgery and mixed with six high molecular weight (700 kDa) HES solutions differing in their molar substitution (0.42 and 0.51) and C2/C6 ratio (2.7, 7 and 14) to achieve 20, 40 and 60% dilution. Blood coagulation was assessed by Thrombelastograph analysis (TEG) and plasma coagulation tests. Data were compared using a three-way analysis of variance model with repeated measures on the three factors.

RESULTS

Higher molar substitution compromised blood coagulation most (for all TEG parameters, P<0.05). The lowest C2/C6 ratio was associated with the lowest effect on blood coagulation; r (P<0.001), angle alpha (P=0.003) and coagulation index (P<0.001). No effect on k and maximum amplitude was observed (P for both >0.50). The higher molar substitution was associated with a lesser increase in PT (P=0.007) and a greater decrease in factor VIII (P=0.010). PTT, functional and antigenic von Willebrand factors were not significantly influenced by molar substitution (P for all >0.20). No significant differences between solutions with the same molar substitution but different C2/C6 ratios were found in plasma coagulation parameters (P for all >0.05).

CONCLUSIONS

TEG analysis indicates that high molecular HES with a molar substitution of 0.42 and a C2/C6 ratio of 2.7 has the lowest effect on in vitro human blood coagulation.

In vitro effects of gelatin solutions on platelet function: a comparison with hydroxyethyl starch solutions

The aim of this study was to investigate the effects of various gelatin and hydroxyethyl starch solutions on platelet reactivity. Citrated whole blood was obtained from 20 healthy volunteers. Expression of glycoprotein (GP) IIb-IIIa and p-selectin were determined using whole blood flow cytometry on both resting and agonist-activated platelets before and after in vitro haemodilution (20% and 40%) using oxypolygelatin, modified gelatin, urea-linked gelatin, hydroxyethyl starch (HES) 130 (mean molecular weight in kDa), HES 200, HES 450 and HES 550. High degrees of haemodilution using oxypolygelatin had no significant effect, similar to HES 130, whereas modified gelatin inhibited GP IIb-IIIa expression, similar to HES 200 and HES 450. Urea-linked gelatin significantly increased the expression of GP IIb-IIIa, similar to HES 550. p-selectin expression remained unchanged in all samples. The present in vitro study indicates that chemical characteristics of colloidal solutions modulate their influence on platelet reactivity.

An In Vitro Study Comparing the Effects of Hextend, Hespan, Normal Saline, and Lactated Ringer’s Solution on Thrombelastography and the Activated Partial Thromboplastin Time

OBJECTIVE

The purpose of this study was to determine if 6% HES 450/0.7 (hydroxyethyl starch 450/0.7) in normal saline (Hespan) and 6% HES 450/0.7 in lactated Ringer's solution (Hextend) have the same inhibition of the intrinsic coagulation pathway and platelet function. Multiple studies have suggested that 6% Hespan inhibits coagulation and increases chest tube drainage and transfusion requirements in cardiac surgical patients. There have been few studies of the effects of 6% Hextend, a relatively new plasma volume expander, on coagulation and the results thus far have been mixed.

DESIGN

A prospective in vitro study.

SETTING

A large academic medical center.

PARTICIPANTS

Blood was collected from 30 healthy volunteers. Interventions : The blood was fractionated and diluted by 30% with Hextend, Hespan, normal saline, and lactated Ringer's solutions, with a native sample for a control.

MEASUREMENTS AND MAIN RESULTS

Primary outcome measures were thromboelastography and activated partial thromboplastin time (APTT). For each of the TEG parameters, there was no difference between samples diluted with Hextend compared with Hespan (p > or = 0.112 in all cases). APTT did not differ significantly between samples diluted with Hextend compared with Hespan (p = 0.562).

CONCLUSIONS

This prospective in vitro study suggests that Hextend and Hespan, hydroxyethyl starch 450/0.7 in different base solutions, exhibit the same effect on platelet function as measured by the TEG.

Molecular weight of hydroxyethyl starch: is there an effect on blood coagulation and pharmacokinetics? ‡ ‡Declaration of interest. This study was funded in part by B. Braun, of which MB and AF are employees and DS is a paid consultant. B. Braun has funded other research in this department in the past, as have other competitor companies

BACKGROUND

The development of hydroxyethyl starches (HES) with low impact on blood coagulation but higher volume effect compared with the currently used HES solutions is of clinical interest. We hypothesized that high molecular weight, low-substituted HES might possess these properties.

METHODS

Thirty pigs were infused with three different HES solutions (20 ml kg(-1)) with the same degree of molar substitution (0.42) but different molecular weights (130, 500 and 900 kDa). Serial blood samples were taken over 24 h and blood coagulation was assessed by Thromboelastograph analysis and analysis of plasma coagulation. In addition, plasma concentration and in vivo molecular weight were determined and pharmacokinetic data were computed based on a two-compartment model.

RESULTS

Thromboelastograph analysis and plasma coagulation tests did not reveal a more pronounced alteration of blood coagulation with HES 500 and HES 900 compared with HES 130. In contrast, HES 500 and HES 900 had a greater area under the plasma concentration-time curve [1542 (142) g min litre(-1), P<0.001, 1701 (321) g min litre(-1), P<0.001] than HES 130 [1156 (223) g min litre(-1)] and alpha half life (t(alpha)(1/2)) was longer for HES 500 [53.8 (8.6) min, P<0.01] and HES 900 [57.1 (12.3) min, P<0.01] than for HES 130 [39.9 (10.7) min]. Beta half life (t(beta)(1/2)), however, was similar for all three types of HES [from 332 (100) to 381 (63) min].

CONCLUSIONS

In low-substituted HES, molecular weight is not a key factor in compromising blood coagulation. The longer initial intravascular persistence of high molecular weight low-substituted HES might result in a longer lasting volume effect.

The Effects of High Molecular Weight Hydroxyethyl Starch Solutions on Platelets

Physicochemical characteristics of hydroxyethyl starch (HES) molecules determine their side effects on hemostasis. Our aim in the present experiments was to test the antiplatelet effect of novel high molecular weight HES. Citrated whole blood was hemodiluted in vitro (0% and 20%) with either HES 550 (Hextend), HES 600 (6%Hetastarch-Baxter), HES 200 (Elohäst), or the solvent of Hextend in its commercially available solution. The availability of glycoprotein IIb-IIIa was assessed on nonstimulated and on agonist-induced platelets using flow cytometry. Glycoprotein IIb-IIIa availability increased significantly after hemodilution with Hextend and its solvent by 23% and 24%, respectively, but decreased in the presence of 6% Hetastarch-Baxter and Elohäst by 18% and 15%, respectively, with no significant difference between the latter two colloids. This study shows that Hextend does not inhibit platelet function as anticipated by its high molecular weight and degree of substitution. The unexpected platelet stimulating effect of Hextend is unique among the currently available HES preparations and may, at least in part, be induced by its solvent containing calcium chloride dihydrate (2.5 mmol/L). The platelet-inhibiting effect of 6%Hetastarch-Baxter was not significantly different from that of medium molecular weight HES 200.