Metabolic Disorders

NORMAL FLUID AND ELECTROLYTE REQUIREMENTS

Normal body homeostasis requires careful regulation of fluid volume and the concentration of electrolytes within the fluid. Volume regulation is primarily under the control of aldosterone, whereas tonicity is regulated by antidiuretic hormone (ADH). Volume has priority over tonicity when the protective mechanisms conflict.

Body Fluid Compartment	% Body Weight (kg)
Total body water	60
Intracellular fluid	40
Extracellular fluid	20
Blood (plasma 4% + RBCs 3%)	7

Maintenance Requirements

The normal daily maintenance requirements for fluid and electrolytes in an essentially healthy individual include the following:

Water	2 L/day
NaCl	75 mEq/day
K⁺	40 mEq/day

Minimum daily water requirement for the body is based on the following needs:

At least 600 mL urine is needed to keep the normal daily load of solutes in solution (1,000 mL in hypermetabolic, critically ill patients).
Approximately 1,000 mL is needed to replace daily insensible water loss (i.e., from the respiratory tract and skin). These losses will increase with fever.
Abnormal water losses include fluid loss in nasogastric suction, vomiting, diarrhea, fistula drainage, and third space sequestration (e.g., ascites, bowel obstruction, retroperitoneal edema, and operative trauma).

Saline Solutions	Na mEq/L
Normal saline (0.9% NaCl)	154
Half normal saline (0.45% NaCl)	77

Maintenance carbohydrate replacement of 100 to 150 g/day is necessary; 5% dextrose in water (D5W) contains 50 g/L glucose. A reasonable intravenous maintenance fluid for the uncomplicated hospitalized patient who is taking nothing by mouth would be D5 0.5 NS with 20 mEq KCl/L at 100 mL/hour. Replacement of any abnormal fluid losses should be added to this maintenance.

Abnormal Fluid Loss Replacements

Gastric fluid is isotonic and high in K⁺. Replacement: 0.5 NS with 40 mEq KCl/L.
Fever or osmotic diuresis (as in diabetics or after hyperalimentation) results in hypotonic fluid loss (free water). Replacement: 0.5 NS.

Pediatric Intravenous Fluid Replacement

Weight	mL/kg/day
First 10 kg (0-10)	100+
Second 10 kg (10-20)	50+
Each additional kg	20

ABNORMAL FLUID DISTURBANCES

Hypotonic Dehydration

Hypotonic dehydration occurs because of loss of isotonic fluid such as blood (hemorrhage), plasma (burns, pancreatitis, peritonitis), or gastrointestinal fluid (diarrhea) with secondary free water retention, because of the increased ADH release with stress. Treatment—use normal saline for all fluid needs for a few days.

Hypotonic Overhydration

Only gold members can continue reading. Log In or Register to continue