When reviewing body systems in conjunction with a physical assessment, the nurse should listen carefully to the patient’s description of the chief complaint. Many fluid and electrolyte imbalances are insidious and require careful history taking and monitoring to prevent further problems. If the patient has suffered an injury, the type and degree of injury should be ascertained because injury may affect the patient’s fluid and electrolyte balance (Table 22-1).

Patients should be questioned to determine whether they suffer from any illness or condition that affects fluid and electrolyte balance. For example, in heart failure the patient is at risk for fluid volume excess. Metabolic aberrations, such as diabetes mellitus, can put the patient at risk for metabolic acidosis and fluid volume deficits. Episodes of acute pancreatitis can result in calcium deficits. Conditions such as emphysema cause a respiratory acidosis that results from the patient’s inability to exchange carbon dioxide. Some tumors interfere with the use or uptake of calcium, leading to calcium excess. Prolonged immobilization of a patient may cause calcium excess caused by loss of calcium from the bone into the extracellular fluid. A patient who drinks excessive amounts of plain water may wash out electrolytes, causing potassium or sodium deficits or metabolic alkalosis if the condition is not corrected (Table 22-2).

A thorough medication history should be obtained because any medications or therapeutic regimens, such as steroids or parenteral nutrition, can disrupt fluid or electrolyte balance. For example, potassium-depleting diuretics may cause potassium deficit. Conversely, potassium-sparing diuretics may cause potassium excess, the opposite of problems anticipated with diuretics. Overuse of laxatives may also result in potassium deficits.

The nurse must ascertain whether the patient has experienced a large loss of body fluids from vomiting, diarrhea, or lack of intake. An assessment of dietary alterations or medically imposed dietary restrictions should be made. Questions are asked of the patient to try to elicit any discrepancies in intake and output. Is the patient producing copious amounts of urine, or is the patient drinking large amounts of plain water? Has the patient experienced any draining wounds or high-output fistulas that would cause a discrepancy between intake and output? The answers to these questions must be examined carefully when the history is analyzed and must be kept in mind as the clinical assessment is begun.

An accurate body weight is one of the initial clinical assessment parameters. Changes in body weight accurately reflect fluid loss or gain. An accurate determination of change in weight provides important information and is sometimes easier to obtain than an accurate intake and output record. Rapid changes in the patient’s body weight can reflect problems with the fluid balance status. One way to approximate the amount of fluid gain or loss is to compare the equivalent between kilograms and liters of fluid. One kilogram, or 2.2 pounds of body weight, is approximately equivalent to the gain or loss of 1 L of fluid. Expressed in pounds, a gain or loss of 1 pound is equivalent to 500 mL of fluid.

This gain or loss is usually rapid. It is typically compared with what is called the dry weight of an individual. Even under conditions of starvation, a person will lose no more than one third to one half of a pound of dry weight a day. When monitoring for rapid weight gain or loss (and therefore fluid gain or loss), it is important to assess weight daily. Fluid gains or losses are categorized as mild, moderate, or severe, as described in Table 22-3.

The phenomenon of third spacing may complicate the fluid balance picture. Third spacing occurs when a patient has a fluid volume deficit of the extracellular space. Body weight is basically unchanged because the fluid loss is from the extracellular space to other body compartments.

To ensure that accurate weights are obtained, the patient should be weighed at the same time every day, preferably in the morning before breakfast and after voiding. The same scale should be used for each weighing, and the patient should wear the same or similar-weight clothing. It is also important to ensure that the scale is accurate. This requires verifying the scale reading at regular intervals as recommended by the manufacturer.