# Situation: A 40-year-old man with dengue is admitted on the fourth day of illness; his fever subsided this morning. He weighs 60 kg and has no history of heart or kidney disease. He is receiving intravenous (IV) fluids through a 20-gauge catheter in his left forearm. His fluid is an isotonic crystalloid. Why is 5% dextrose in water (D5W) a poor choice to support his circulating volume?

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> subject: Nursing Practice III — Care of Clients with Problems in Surgery, Oxygenation, Fluid and Electrolytes, Infectious, Inflammatory and Immunologic Response, Cellular Aberrations

## 문제

Situation: A 40-year-old man with dengue is admitted on the fourth day of illness; his fever subsided this morning. He weighs 60 kg and has no history of heart or kidney disease. He is receiving intravenous (IV) fluids through a 20-gauge catheter in his left forearm.

His fluid is an isotonic crystalloid. Why is 5% dextrose in water (D5W) a poor choice to support his circulating volume?

## 보기

1. Once its dextrose is used, the free water enters the cells **✔ 정답**
2. Its dextrose draws water out of the vessels into the tissues
3. Its high osmolality irritates the vein and causes phlebitis
4. It is hypertonic, so it pulls water out of the body's cells

**정답: 1**

## 해설

D5W is isotonic in the bag, but the dextrose is quickly metabolized, leaving free water that distributes into all compartments, mostly into cells. Very little stays in the vessels, so D5W is not a volume expander. Isotonic crystalloids such as 0.9% sodium chloride stay in the extracellular space.

## 심화 해설

Why D5W fails as a volume expander

5% dextrose in water (D5W) is classified as an isotonic crystalloid when it sits in the IV bag, but that label is misleading once the fluid enters the body. The dextrose component is rapidly metabolized by insulin-independent cellular uptake, leaving behind free water. That free water then follows osmotic gradients and distributes across the total body water compartments — approximately two-thirds moves into the intracellular space and only about one-third remains in the extracellular space. Of that extracellular third, only a small fraction stays within the intravascular volume. Because so little of the infused D5W remains inside the vessels, it cannot effectively support circulating volume or blood pressure in a dengue patient who is at risk for plasma leakage.

This explains why option 1 is correct: once the dextrose is metabolized, the free water enters the cells. The other options misstate the mechanism. D5W does not draw water out of vessels into tissues through dextrose-mediated osmosis (option 2); it is not primarily a phlebitis risk due to high osmolality (option 3); and it is not hypertonic in vivo in a way that pulls water out of cells (option 4). In fact, the free water generated after dextrose metabolism makes D5W functionally hypotonic in its distribution behavior.

Key point! D5W is isotonic in the bag but behaves as free water in the body. It is a maintenance fluid, not a volume expander.

Volume kinetics: crystalloids distribute beyond the vessel

The population-based volume kinetics study by Yi and colleagues [1] directly compared Ringer's lactate and D5W in healthy volunteers using nonlinear mixed-effects modeling. Their work reinforces that crystalloid solutions distribute into a central fluid space and then equilibrate with a peripheral compartment. For D5W, the effective volume-expanding capacity is even smaller than for balanced crystalloids because the metabolized dextrose leaves water that crosses cell membranes freely. In contrast, Ringer's lactate remains largely confined to the extracellular fluid volume for a longer period, which is why isotonic saline-based solutions are preferred when the goal is to restore intravascular volume.

Hahn and colleagues  showed that crystalloid fluid requires approximately 30 minutes for complete distribution throughout the extracellular fluid space and tends to cause long-standing peripheral edema. This finding applies to Ringer's acetate, but the principle is relevant here: even the best crystalloid volume expanders leave the intravascular space relatively quickly. D5W is even less effective because its distribution is not limited to the extracellular compartment — the free water enters cells as well.

Watch out! A dengue patient on day 4 of illness is entering the critical phase when plasma leakage peaks. Using D5W as the primary resuscitation fluid would leave most of the infused volume outside the vessels, worsening intravascular depletion.

Clinical comparison: D5W versus isotonic saline

| Fluid | Tonicity in bag | Behavior after infusion | Primary distribution | Role in volume resuscitation |
| --- | --- | --- | --- | --- |
| D5W | Isotonic | Dextrose metabolized; free water remains | Intracellular (about two-thirds) | Poor; maintenance only |
| 0.9% sodium chloride | Isotonic | Remains as sodium and chloride in ECF | Extracellular (interstitial + intravascular) | Good; expands circulating volume |
| Ringer's lactate | Isotonic | Balanced electrolytes remain in ECF | Extracellular | Good; preferred balanced crystalloid |

The study by Ernest and colleagues  in septic patients compared normal saline and 5% albumin and measured their distribution within the extracellular fluid volume. Normal saline expanded the extracellular compartment, including the plasma volume, to a measurable degree. D5W was not studied in that trial, but the physiological principle is clear: a fluid that distributes into the intracellular space cannot preferentially support the intravascular space. Morgan's review  further clarifies that crystalloid interstitial expansion is unavoidable, but the goal of resuscitation is to maximize the fraction that remains in the plasma volume. D5W fails this goal because its free water distributes into all compartments, with the largest share entering cells.

Why this matters for the dengue patient

The patient weighs 60 kg and is on day 4 of dengue illness, with fever subsiding that morning. In dengue, defervescence often marks the onset of the critical phase, when increased capillary permeability causes plasma to leak into the interstitial space. The circulating volume can drop rapidly even while total body water appears adequate. The priority is to keep fluid inside the vessels, which requires an isotonic crystalloid such as 0.9% sodium chloride or Ringer's lactate — not D5W. If D5W were infused, the free water would follow osmotic gradients into cells and the interstitial space, providing minimal intravascular support at the time the patient needs it most.

Key point! In dengue with plasma leakage, choose a fluid that stays in the extracellular space. D5W distributes into cells and is not a volume expander.References (research sources)

- [1]Population-based volume kinetics of crystalloids and colloids in healthy volunteers.Research articleYi JM, Bang JY, Choi B, Cho C, Lee YH, Lee EK (2019) · DOI: 10.1038/s41598-019-55171-1

## 임상 시나리오

D5W Is Not a Volume ExpanderIsotonic in the bag, free water in the body
In dengue with plasma leakage, choose an isotonic crystalloid such as 0.9% sodium chloride to keep fluid in the extracellular space.

D5W is isotonic in the IV bag, but dextrose is rapidly metabolized, leaving free water. About two-thirds of that free water moves into cells, and very little remains in the vessels.

CautionDo not use D5W to support circulating volume in dengue. It behaves as functionally hypotonic fluid and cannot maintain blood pressure during plasma leakage.

## 핵심 개념

- **D5W** — 5% dextrose in water; isotonic in the bag but becomes free water after dextrose metabolism, so it is a maintenance fluid, not a volume expander.
- **Isotonic crystalloid** — A fluid with the same osmolality as plasma that stays mainly in the extracellular space, such as 0.9% sodium chloride.
- **Free water** — Water without solutes that distributes across total body water, mostly into the intracellular space.
- **Volume expander** — A fluid that remains in the intravascular space to support circulating volume and blood pressure.
- **Plasma leakage** — A dengue complication in which fluid shifts from vessels into tissues, reducing effective circulating volume.

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