|Gelatins are formed by hydrolysing collagen, creating a large soluble molecular weight protein. The earliest gelatins were very large molecules, which had a high oncotic effect, although they also had a high viscosity and could solidify at low temperatures. Now there are a newer generation of gelatins, of which there are three main groups:
• Succinylated or modified fluid gelatins (e.g. Isoplex®, Volplex® and Gelofusine®)
• Urea-cross-linked gelatins (e.g. Haemaccel®)
• Oxypolygelatins (e.g. Gelifundol®)
Within the UK, the most commonly used gelatins are the succinylated or modified fluid gelatins. Most are manufactured as a 4% solution with electrolytes. For example, Isoplex® 4% w/v Solution for Infusion contains the active ingredient succinylated gelatin 4%. The product is supplied in sterile flexible infusion bags (500 ml), which are overwrapped. Each 500 ml of Isoplex contains succinylated gelatin 20 g in 500 ml of water for injections, also containing electrolytes.
The electrolytes vary with each gelatin. In Volplex® and Gelofusine® the electrolytes consist of sodium (154 mmol/L) and chloride (125 mmol/L). Isoplex® contains sodium (145 mmol/L), chloride (105 mmol/L), potassium (4 mmol/L) and a buffer, lactate (25 mmol/L).1-3 The lower the chloride levels, the lower the risk of causing hyperchloraemic metabolic acidosis (HCMA).4 Also, products with a low calcium content can be given concomitantly with blood.
The half-life for the succinylated gelatins is around 4 hours, greater than a crystalloid, but shorter than a starch, and they lead to around 70% to 80% volume expansion.5
The main advantages of using a succinylated gelatin are:
• They are cost effective.
• There is a lot of experience in their use.
• There is no limit to the amount that can be infused, whereas starches and dextrans do have an upper infusion limit. When large volumes are given, suitable monitoring should be used to ensure that an adequate haematocrit is maintained and that dilutional effects upon coagulation are avoided.
• Gelatins are small-sized molecules compared with starches; they are therefore easily excreted renally, and have no effect on renal impairment.3
The main disadvantages are:
• Gelatins are associated with an increase in anaphylactoid reactions compared with natural colloids. However, the frequency of anaphylactoid reactions with common gelatins is rare, with an incidence level of between 1 in 6000 and 1 in 13,000 units.
 Gelofusine SPC, 2002
 Volplex SPC, 2010
3] Isoplex SPC, 2010
 Lobo DN et al. Effect of volume loading with 1 liter intravenous infusions of 0.9% saline, 4% succinylated gelatine (Gelofusine) and 6% hydroxyethyl starch (Voluven) on blood volume and endocrine responses: a randomized, three-way crossover study in healthy volunteers. Crit Care Med 2010; Vol 38: 464-470.
 Mitra S and Khandelwal P. Are all colloids same? How to select the right colloid? Indian J Anaesth 2009; 53: 592-607.
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