23-22: Fluid Management

Daily parenteral maintenance fluids and electrolytes for an average adult of 70 kg would include at least 2 L of water in the form of 0.45% saline with 20 mEq/L of potassium chloride. Patients with hypoglycemia, starvation ketosis, or ketoacidosis being treated with insulin may require 5% dextrose-containing solutions. Guidelines for GI fluid losses are shown in Table 23–17.

Weight loss or gain is the best indication of water balance. Insensible water loss should be considered in febrile patients. Water loss increases by 100–150 mL/day for each degree of body temperature over 37°C.

In patients requiring maintenance and possibly replacement of fluid and electrolytes by parenteral infusion, the total daily ration should be administered continuously over 24 hours to ensure optimal utilization.

If intravenous fluids are the only source of water, electrolytes, and calories for longer than a week, parenteral nutrition containing amino acids, lipids, trace metals, and vitamins may be indicated. (See Part 31.)

Balanced crystalloid solutions, such as Ringer lactate, have become the resuscitation fluid of choice, due to concern for metabolic acidosis and reduced GFR associated with normal saline (see Part 14). However, studies are conflicting and have not established superiority of one fluid over another, which may reflect an overall paradigm shift favoring conservative fluid administration and earlier use of vasopressors. Excessive fluid resuscitation and maintenance are complications in hospitalized patients, especially those with critical illness or AKI. These complications have been associated with worsened outcomes, such as prolonged mechanical ventilation, dependence on dialysis, and longer hospitalization with increased mortality.