Response to Injury, Fluids, and Nutrition

Fluid Balance

• Normal Fluid Balance: The normal fluid balance in a 70 kg man is comprised of 140 liters of total body water. This includes 28 liters of extracellular fluid (ECF) and 42 liters of intracellular fluid (ICF). The principal ECF cation is sodium (Na+). Potassium (K+), and magnesium (Mg2+) are the principal cations of the ICF.
• Stages of Dehydration:
  • Mild Dehydration (2-5% BW lost as water): Thirst, low urine volume, reduced sweating, and dry axilla and groin are common symptoms.
  • Moderate Dehydration (6-10% BW lost as water): These symptoms include severe thirst, nausea, tachycardia, orthostatic hypotension, severe oliguria, and thready pulse.
  • Severe Dehydration (11-15% BW lost as water): Stupor, severe oliguria, hypotension, shock, coma, and death are potential consequences.

Extracellular Volume Deficit vs. Excess

• Extracellular Volume Deficit:

  • The most common fluid disorder in surgical patients.
  • Acute volume deficit can lead to cardiovascular and central nervous system complications.
  • Chronic volume deficit is characterized by tissue signs such as decreased skin turgor and sunken eyes.
  • The most common cause of volume deficit in surgical patients is loss of GI fluids due to nasogastric suction, vomiting, diarrhea, or enterocutaneous fistula.
  • Third-space fluid losses can also contribute to massive volume deficits.

• Extracellular Volume Excess:

  • May be iatrogenic or secondary to renal dysfunction, congestive heart failure, or cirrhosis.
  • Results in an increase in both plasma and interstitial volumes.

Hypokalemia

• A serum potassium concentration below the normal range of 3.5-5 mEq/L.
• The severity of symptoms depends on the level of hypokalemia and the rate of decline.
• Mild cases typically present with minimal symptoms.
• Moderate to severe hypokalemia often manifests with fatigue, weakness, muscle cramps, and arrhythmias.
• Treatment: Potassium repletion, with the rate guided by the severity of symptoms.
  • Mild, asymptomatic hypokalemia: oral repletion is sufficient.
  • Moderate to severe hypokalemia: IV repletion is often necessary, with careful monitoring to avoid complications.

Hyperkalemia

• Serum potassium concentration above the normal range of 3.5-5 mEq/L.
• Can occur due to excessive K+ intake, increased release of K+ from cells, or impaired renal excretion.
• Clinical manifestations:
  • Primarily GI (nausea/vomiting, diarrhea), neuromuscular (weakness, paralysis), and cardiovascular (arrhythmia, arrest).
• Treatment: Calcium supplementation and correction of other contributing factors.

Hypocalcemia

• A serum ionized calcium level below 2.5 mg/dL.
• Can be caused by a variety of factors, including vitamin D deficiency, parathyroid disorders, chronic kidney disease, and certain medications.
• Neuromuscular symptoms and decreased cardiac contractility often present when the ionized calcium level is low.
• Treatment: Calcium supplementation and addressing the underlying cause of hypocalcemia.

Hypercalcemia

• A serum calcium concentration above the normal range (8.5-10.5 mg/dL).
• Often associated with hyperparathyroidism due to parathyroid adenoma.
• It can lead to:
  • Bone remineralization
  • Decreased bone density
  • Neuromuscular symptoms
• Treatment: Focused on managing the underlying condition (such as parathyroid adenoma removal).

Nutritional Assessment Criteria

• Nutritional Status:
  • BMI (Body Mass Index): Used to assess body weight relative to height.
  • WHO (World Health Organization) criteria:
    • Underweight: BMI ≤ 18.5 kg/m²
  • Asian criteria:
    • Underweight: BMI ≤ 18.5 kg/m²

Test your knowledge on fluid balance, normal hydration levels, and the stages of dehydration. This quiz will cover essential concepts related to extracellular and intracellular fluids, their roles, and symptoms of volume deficits. Prepare to explore critical information that is vital for understanding fluid management in health care.