Intravenous fluids are used to correct dehydration, restore blood volume, and deliver medication. Dextrose 5% in Lactated Ringer’s (D5LR) is one such solution, combining sugar, water, and electrolytes. The term “bolus” refers to the rapid, large-volume infusion of fluid intended to quickly expand the circulating blood volume in an emergency. D5LR is generally not the appropriate fluid choice for this rapid administration technique.
Defining D5LR and Rapid Infusion
D5LR is a compound intravenous solution containing 5 grams of dextrose (a form of glucose) per 100 milliliters of fluid, mixed with Lactated Ringer’s (LR) solution. The LR component provides necessary electrolytes, including sodium, chloride, potassium, calcium, and lactate, which closely resemble the composition of blood plasma. A bolus involves delivering a significant fluid volume, often 500 to 1,000 milliliters, over a very short time to treat conditions like shock or severe dehydration. The primary goal of a volume bolus is immediate and sustained expansion of the fluid volume within the blood vessels.
In the intravenous bag, D5LR has a high calculated osmolarity of approximately 530 milliosmoles per liter (mOsm/L), which technically classifies it as a hypertonic solution. However, this classification is misleading when considering its effect on the body after rapid infusion, as the fluid’s effectiveness for volume expansion depends on the fate of the dextrose molecule once it enters the bloodstream.
The Physiological Concerns of Bolusing Dextrose
The most significant physiological concern with bolusing D5LR is the rapid metabolism of the dextrose component, which dramatically changes the fluid’s behavior inside the body. Dextrose is a simple sugar, and the body’s cells quickly absorb and metabolize the 5% concentration, converting it into carbon dioxide and water. This rapid utilization effectively removes the solute (dextrose) that contributed to the fluid’s initial concentration. Once the sugar is metabolized, the remaining fluid becomes hypotonic relative to the body’s plasma. This conversion creates a dangerous osmotic gradient, causing water to shift rapidly out of the blood vessels (intravascular space) and into the body’s cells (intracellular space).
This intracellular fluid shift can lead to generalized cell swelling. If a large volume is infused quickly, the resulting rapid change in the fluid concentration outside the cells can lead to severe complications, most notably cerebral edema, or swelling of the brain cells. The brain is encased in the skull, and swelling can quickly increase intracranial pressure, leading to symptoms like confusion, seizures, and potentially coma. Furthermore, a rapid influx of dextrose can overwhelm the body’s ability to process glucose, leading to severe hyperglycemia (high blood sugar) and a dangerous state known as hyperosmolar hyperglycemic state.
Appropriate Clinical Applications for D5LR
D5LR is not intended for rapid volume resuscitation but serves a valuable role as a maintenance fluid, administered slowly over many hours. Its design addresses the daily requirements for water, electrolytes, and minimal caloric intake for patients who cannot eat or drink. The slow, controlled infusion rate allows the body to metabolize the dextrose gradually, preventing the osmotic shifts that occur with a bolus. The 5% dextrose provides a small amount of calories, approximately 170 kilocalories per liter, which is sufficient to prevent the body from entering starvation ketosis. The LR portion ensures hydration and replaces baseline fluid and electrolyte losses, making D5LR suitable for routine hydration and electrolyte support.
Standard Fluids for Volume Resuscitation
When a rapid fluid bolus is required to treat shock or severe volume depletion, the standard of care involves using isotonic crystalloid solutions that lack dextrose. These fluids are designed to remain primarily within the extracellular fluid compartment, maximizing the volume expansion effect. The two primary fluids used for volume resuscitation are Normal Saline (0.9% Sodium Chloride) and Lactated Ringer’s solution (without dextrose).
Normal Saline is a straightforward solution of salt and water, with a sodium concentration similar to plasma, making it isotonic. Lactated Ringer’s is also isotonic and is considered a “balanced” solution because its electrolyte composition more closely mimics that of the blood, reducing the risk of metabolic disturbances like hyperchloremic acidosis.