2.3 Fluids and Electrolytes
Key Features
Appropriate fluid balance perioperatively can be estimated from established formulas.
Attention to fluids and electrolytes is especially important in the patient who is not capable of maintaining normal oral intake.
Surgical patients, especially head and neck cancer patients, may be incapable of adequate oral intake. Often, intravenous (IV) fluids are needed for a short period before postoperative oral intake can resume. In other cases, longer-term NPO (nothing by mouth) status is required, such as when a pharyngeal closure must heal or a fistula is resolving. An important rule is that if the gut is available and functional, it should be used; for example, if oral swallowing is not functional, intake should still be provided via a nasogastric (NG) tube or percutaneous endoscopic gastrostomy (PEG) tube rather than by total parenteral nutrition (TPN) or peripheral IV nutrients. A summary of important considerations for fluid management is provided here.
Functional Compartments
Total Body Water (TBW)
Normal total body water is 60% (adult males), 50% (adult females) of ideal body weight (IBW).
Intracellular Fluid (ICF)
ICF comprises 35% of IBW or 60% of TBW. This is the principal potassium-containing space.
Extracellular Fluid (ECF)
ECF constitutes 25% of IBW or 40% of TBW; subdivided into interstitial fluid (ISF) and blood volume (BV is ~8% of total volume weight). This is the principal sodium-containing space.
Daily Electrolyte Requirements
Sodium: 2 to 3 mEq/kg per day
Potassium: 1 to 2 mEq/kg per day
Chloride: 2 to 3 mEq/kg per day
See Table 2.20 .
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