Crystalloids

Introduction

A crystalloid fluids form a true solution meaning it can easily cross a semi permeable membrane and is distinguished by its ability to be crystallised. They can be classified as maintainance or replacement fluids. A replacement crystalloid often do not have high potassium concentrations allowing for rapid administration without potassium toxicity, where as maintainance crystalloids often have a higher potassium but lower sodium and chloride than a replacement crystalloid.

Types of Crystalloids

• 0.9% Sodium Chloride
• Hartmanns/Lactated Ringers Solution
• 5% Dextrose
• Hypertonic Saline (3%)

0.9% Sodium Chloride

Also known as normal saline, 0.9% sodium chloride is often used as a replacement solution. It contains no further electrolytes. It has a higher chloride concentration than plasma. This can lead to a hyperchloremic acidosis which is unlikely to cause any problems in healthy patients but may cause further issues in compromised patients.

Hartmanns/Lactated Ringers

Hartmanns or Lactated Ringers Solution (LRS) is a balanced electrolyte solution. It also contains lactate which aids correction of acidosis. It also contains potassium and calcium. It also has a lower sodium concentration than plasma. Due to the calcium, it is not possible to administer LRS with blood products or sodium bicarbonate as it leads to clot/crystal formation. It is commonly used as a maintenance solution.

5% Dextrose

5% Dextrose consists of dextrose in water, and no electrolytes. It is rarely indicated for use during surgeries. It should not be used in patients thought to have cerebral injuries due to the deterimental effects the glucose will have.

Hypertonic saline

Hypertonic saline is rarely used although it does have some benefits. It increases plasma volume by drawing fluid from outside the circulation (i.e. intersitial and intracellular fluid) due to the change in osmotic pressure between the two compartments. However, the consequence of this is that the patient will become dehydrated which can be detrimental to a patient and so hypertonic solutions should not be used long term.