Dextran 70 and dextran 40
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Here is a comprehensive overview of Dextran 40 and Dextran 70:
Dextran 40 & Dextran 70
Chemistry & Basic Properties
Dextrans are heterogeneous polysaccharides synthesized by the bacterium Leuconostoc mesenteroides acting on sucrose. The numbers refer to their average molecular weights: dextran 40 = 40,000 Da, dextran 70 = 70,000 Da.
| Property | Dextran 40 (Rheomacrodex) | Dextran 70 (Macrodex) |
|---|---|---|
| Molecular weight | 40,000 Da | 70,000 Da |
| Concentration | 10% (hyperoncotic) | 6% (iso-oncotic) |
| Osmolality | ~308 mOsm/L | ~308 mOsm/L |
| Sodium | 154 mEq/L | 154 mEq/L |
| Duration of volume expansion | Shorter (rapidly excreted by kidney) | Up to 48 hours (large molecules retained) |
Volume Expansion
- Dextran 40 (10%) is hyperoncotic — it initially exerts a marked volume-expanding effect by drawing fluid into the intravascular space. However, because of its lower molecular weight, it is more rapidly excreted by the kidneys, so the effect is shorter-lived.
- Dextran 70 (6%) is not hyperoncotic. Volume expansion is somewhat greater than the volume infused, and because of its larger molecular size, the effect is maintained for up to 48 hours.
— Mulholland and Greenfield's Surgery, 7th ed.
Mechanisms of Action
Dextrans exert several physiological effects beyond simple volume expansion:
- Reduce blood viscosity (hemorheologic effect)
- Decrease platelet adhesiveness
- Decrease von Willebrand factor antigen and Factor VIII activity (Factor VII also affected)
- Interfere with fibrin network formation and increase fibrin degradation
- Reduce RBC aggregation
- Expand intravascular volume
— Morgan & Mikhail's Clinical Anesthesiology, 7th ed.; Cummings Otolaryngology
Clinical Uses
| Indication | Agent |
|---|---|
| Plasma volume expansion (hypovolemic shock) | Both (historically); dextran 70 preferred for sustained effect |
| Peripheral vascular disease / hyperviscosity syndromes | Dextran 40 (rapidly excreted, better hemorheology) |
| Microvascular surgery / free flap surgery | Dextran 40 (antiplatelet + antithrombotic effect) |
| Digit replantation | Dextran 40 (antithrombotic effect) |
| Hysteroscopy distension medium | Dextran 70 (hyperosmolar; volume must be kept < 300 mL) |
| Prevention of DVT/PE | Historically used (now largely replaced by LMWH) |
Adverse Effects
- Anaphylaxis / anaphylactoid reactions: incidence up to 5%; severe anaphylaxis ~0.6%. Dextran 1 (Promit) — a low-MW hapten — can be given before dextran 40 or 70 to bind circulating anti-dextran antibodies and prevent severe anaphylaxis.
- Coagulopathy: decreased platelet adhesion, reduced Factor VIII/vWF activity; doses > 20 mL/kg/day may prolong bleeding time.
- Acute kidney injury: dextran can precipitate in renal tubules, especially dextran 40; avoid in renal disease or at-risk patients.
- Volume overload / pulmonary edema: especially in elderly patients.
- Interference with blood typing/cross-matching at high doses.
- Nephrotoxicity and ARDS have been reported.
Dosing in Microvascular Surgery (Dextran 40)
Two common protocols:
- Johnson & Barker: 40 mL loading dose before clamp release → 25 mL/h infusion for 5 days
- Buckley et al.: 500 mL before anastomosis → 500 mL/day for 3 days
A test dose of < 5 mL of 10% dextran 40 is recommended before initiating therapy. — Cummings Otolaryngology
Key Comparison Summary
| Feature | Dextran 40 | Dextran 70 |
|---|---|---|
| MW | 40 kDa | 70 kDa |
| Concentration | 10% (hyperoncotic) | 6% (iso-oncotic) |
| Duration of action | Shorter | Longer (up to 48h) |
| Primary use | Hemorheology, microvascular surgery | Sustained volume expansion |
| Renal excretion | Faster | Slower |
| Coagulopathy risk | Both; dose-dependent |
Both are now used less commonly for shock resuscitation compared to crystalloids, and hydroxyethyl starch has largely supplanted them in many settings. Current evidence does not show a mortality benefit of colloids over crystalloids in hypovolemic shock.
Sources: Morgan & Mikhail's Clinical Anesthesiology 7e; Mulholland and Greenfield's Surgery 7e; Cummings Otolaryngology Head and Neck Surgery; Schwartz's Principles of Surgery 11e; Berek & Novak's Gynecology
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