Podcast
Questions and Answers
How is sodium excretion primarily regulated in the body?
How is sodium excretion primarily regulated in the body?
Sodium excretion is primarily regulated by aldosterone.
What is a common cause of sodium and water depletion in surgical patients?
What is a common cause of sodium and water depletion in surgical patients?
A common cause of sodium and water depletion in surgical patients is small intestinal obstruction.
What is the average daily requirement of potassium in the body?
What is the average daily requirement of potassium in the body?
The average daily requirement of potassium is 1 mmol/kg.
What percentage of total body water does a 70 kg young man comprise?
What percentage of total body water does a 70 kg young man comprise?
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Identify one reason for potassium depletion (hypokalemia).
Identify one reason for potassium depletion (hypokalemia).
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What are the three classifications of disturbances in body fluids?
What are the three classifications of disturbances in body fluids?
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What are the two main components of total body water?
What are the two main components of total body water?
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What is a common cause of extracellular fluid volume deficit in surgical patients?
What is a common cause of extracellular fluid volume deficit in surgical patients?
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What is the most appropriate fluid replacement for blood loss?
What is the most appropriate fluid replacement for blood loss?
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What happens to sodium excretion following trauma or surgery?
What happens to sodium excretion following trauma or surgery?
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Study Notes
Fluid Electrolyte and Acid-Base Imbalances in Surgical Patients
- Body Water: Total body water comprises 50-85% of body weight, varying with age and lean body mass. A 70kg young man is roughly 55-60% water. Females have lower water content (45-60%) due to higher fat. Neonates have higher water content (80-85%).
- Fluid Compartments: Body water is divided into intracellular (2/3) and extracellular (1/3) compartments. Extracellular fluid further divides into intravascular (plasma – 2/3 of ECF) and interstitial (1/3 of ECF).
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Fluid Volume Deficit (most common surgical problem): Loss isn't just water, but electrolytes in similar proportions to normal ECF.
- Causes: GI losses (vomiting, diarrhea, tubes, fistulas), soft tissue injuries/infections (burns), intra-abdominal/retroperitoneal inflammation (peritonitis).
- Clinical Features (severity dependent): Mild (5-10% loss): sleepiness, orthostatic hypotension. Severe (>15% loss): hypotension, stupor/coma, sunken eyeballs, dry mucosa, poor skin turgor.
- Treatment: Replace lost fluid and electrolytes using fluids similar to ECF (e.g., Ringer's Lactate, Normal Saline). Blood loss – replace with blood if needed.
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Electrolyte Disturbances: Sodium and potassium are most commonly affected.
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Sodium (Na+): Predominant extracellular cation. Post-trauma/surgery, sodium excretion can be suppressed for 48 hours. Serum sodium concentration doesn't directly equate to extracellular volume status (a severe volume deficit can exist with a normal serum sodium). Daily need ≈ 1 mmol/kg. Excretion is regulated by aldosterone.
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Hyponatremia Causes:
- Volume depletion (sodium and water loss – common in small intestinal obstruction, duodenal/biliary/pancreatic/high intestinal fistulas).
- Water intoxication (excess volume and edema – over-prescribing of 5% D/W, colorectal washouts with plain water).
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Hyponatremia Causes:
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Potassium (K+): Predominant intracellular cation. 98% of body potassium is intracellular, with ¾ in skeletal muscles. Daily need ≈ 1 mmol/kg.
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Hypokalemia (K+ < 3.5 mmol):
- Causes: GI losses (vomiting, diarrhea), potassium shift into cells (alkalosis), prolonged potassium-free IV fluids, excessive renal excretion (diuretics).
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Hypokalemia (K+ < 3.5 mmol):
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Sodium (Na+): Predominant extracellular cation. Post-trauma/surgery, sodium excretion can be suppressed for 48 hours. Serum sodium concentration doesn't directly equate to extracellular volume status (a severe volume deficit can exist with a normal serum sodium). Daily need ≈ 1 mmol/kg. Excretion is regulated by aldosterone.
Fluid and Electrolyte Intake/Output
- Total Output (estimated): Urine (1500mL), Insensible loss (1000mL, up to 1700mL in warm climate), Stool (200mL) which equates to 2700-3400mL total
- Input: Endogenous (200mL (from food oxidation) and Net requirement (2500-3200mL)
Fluid and Electrolyte Disturbances Classification
- Fluid volume disturbance
- Composition disturbance
- Acid-base balance disturbance
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Description
This quiz covers key concepts related to fluid electrolyte and acid-base imbalances commonly encountered in surgical patients. It includes discussions on body water composition, fluid compartments, and the impact of volume deficit due to various causes. Test your knowledge on these critical aspects of surgical care.
