Fluid Rate

Fluid therapy frequently starts with the maintenance rate, or the volume of fluid necessary to keep the patient's fluid balance normal, whether it is administered during anesthesia or to a sick patient. Most fluid loss in healthy patients is caused by urine production. Patients who are not eating or drinking but do not exhibit volume depletion, hypotension, or continuing losses are candidates for maintenance fluid treatment.

Replacement fluids (for example, LRS) are designed to replenish lost body fluids and electrolytes. LRS and other isotonic polyionic replacement crystalloids can be used as replacement or maintenance fluids. Short-term maintenance fluid therapy with replacement solutions typically does not alter electrolyte balance. However, electrolyte imbalances can occur in patients with renal disease or those receiving long-term administration of replacement solutions for maintenance.

Because replacement solutions like LRS contain more sodium (Na) and less potassium (K) than the patient typically loses, administering them for maintenance puts the patient at risk for hypernatremia and hypokalemia. Patients who are well-hydrated and have normal renal function are usually able to excrete excess Na and do not develop hypernatremia. Because the kidneys do not very well conserve K, hypokalemia may develop in patients who receive replacement solutions for maintenance fluid therapy if they are either anorexic or have vomiting or diarrhea.

If a replacement crystalloid solution is being used for maintenance therapy, periodically check the serum electrolytes (e.g., q 24 hr). There are commercially available maintenance crystalloid solutions. Alternatively, due to the lower Na and higher K concentrations, fluid containing equal volumes of replacement solution and D5W supplemented with K (i.e., potassium chloride [KCl], 13-20 mmol/L, which is equivalent to 13-20 mEq/L) would be ideal for replacing typical ongoing losses. The use of 0.45% sodium chloride with 13–20 mmol/L KCl added is an additional option for a maintenance fluid solution.

Source: AAHA Guidelines