Fluids and Electrolytes Flashcards
What are the two major body fluid compartments?
- Intracellular
2. Extracellular
What are the two sub compartments of extracellular fluid?
- Interstitial
2. Intravascular
What percentage of body weight is in fluid?
60%
What percentage of body fluid is intracellular?
66%
What percentage of body fluid is extracellular?
33%
On average, what percentage of body weight does blood account for in adults?
7%
How many liters of blood are in a 70-kg man?
5 liters
What is the daily water requirement?
30-35 mL/kg
What is the daily potassium requirement?
1 mEq/kg
What is the daily chloride requirement?
1.5 mEq/kg
What is the daily sodium requirement?
1-2 mEq/kg
What are the levels and sources of normal daily water loss?
Urine: 1200-1500 mL (25-30 mL/kg)
Sweat: 200-400 mL
Respiratory losses: 500-700 mL
Feces: 100-200 mL
What are the levels and sources of normal daily electrolyte loss?
Sodium and potassium: 100 mEq
Chloride: 150 mEq
What are the levels of sodium and chloride in sweat?
40 mEq/L
What is the major electrolyte in colonic feculent fluid?
Potassium: 65 mEq/L
What is the physiologic response to hypovolemia?
Sodium/water retention via renin/aldosterone; water retention via ADH; vasoconstriction via angiotensin II and sympathetics; low urine output and tachycardia (early), hypotension (late)
What is third spacing?
Fluid accumulation in the interstitial of tissues, as in edema (e.g. loss of fluid into the interstitium and lumen of a paralytic bowel following surgery)
When does third-spacing occur postoperatively?
Third-spaced fluid tends to mobilize back into the intravascular space around POD #3 (switch to hypotonic fluid and decrease IV rate)
What are the classic signs of third spacing?
Tachycardia, decreased urine output
What is the treatment for third spacing?
IV hydration with isotonic fluids
What are the surgical causes of metabolic acidosis?
Loss of bicarbonate (e.g. diarrhea, ileus, fistula, high-output ileostomy, carbonic anhydrase inhibitors).
Increase in acids (e.g. lactic acidosis from ischemia, ketoacidosis, renal failure, necrotic tissue).
What are the surgical causes of hypochloremic alkalosis?
NGT suction, loss of gastric HCl through vomiting/NGT
What are the surgical causes of metabolic alkalosis?
Vomiting, NG suction, diuretics, alkali ingestion, mineralocorticoid excess
What are the surgical causes of respiratory acidosis?
Hypoventilation (e.g. CNS depression, drugs, PTX, pleural effusion, parenchymal lung disease, acute airway obstruction)
What are the surgical causes of respiratory alkalosis?
Hyperventilation (e.g. anxiety, pain, fever, wrong ventilator settings)
What is the classic acid-base finding with significant vomiting or NGT suctioning?
Hypokalemic hypochloremic metabolic alkalosis
Why hypokalemia with NGT suctioning?
Loss of HCl causes alkalosis, driving K into cells
What is the treatment for hypokalemic hypochloremic metabolic alkalosis?
IVF, Cl/K replacement
What is paradoxic alkalotic aciduria?
Seen in severe hypokalemic, hypovolemic, hypochloremic metabolic alkalosis with paradoxic metabolic alkalosis of serum and acidic urine
How does paradoxic alkalotic aciduria occur?
H is lost in the urine in exchange for Na in an attempt to restore volume
With paradoxic alkalotic aciduria, why is H preferentially lost?
H is exchanged preferentially into the urine instead of K because of the low concentration of K
What can be followed to assess fluid status?
Urine output, base deficit, lactic acid, vital signs, weight changes, skin turgor, JVD, mucosal membranes, rales, central venous pressure, PCWP, CXR
With hypovolemia, what changes occur in vital signs?
Tachycardia, tachypnea, initial rise in diastolic BP because of peripheral vasoconstriction with subsequent decrease in both systolic and diastolic BP
What are the insensible fluid losses?
Loss of fluid not measured: feces, breathing (increased with fever, tachypnea), sweat (increased with fever)
What quantity of bile is secreted daily?
1000 mL
What quantity of gastric secretions are secreted daily?
2000 mL
What quantity of pancreatic secretions are secreted daily?
600 mL
What quantity of small intestinal secretions are secreted daily?
3000 mL
What quantity of saliva is secreted daily?
1500 mL
What comprises NS?
154 mEq of Cl
154 mEq of Na
What comprises 1/2 NS?
77 mEq of Cl
77 mEq of Na
What comprises 1/4 NS?
39 mEq of Cl
39 mEq of Na
What comprises lactated Ringer’s?
130 mEq of Na 109 mEq of Cl 28 mEq lactate 4 mEq K 3 mEq Ca
What comprises D5W?
5% dextrose (50 g) in water
What accounts for tonicity?
Mainly electrolytes (thus NS and LR are both isotonic)
What happens to the lactate in LR in the body?
Converted into bicarbonate, thus LR cannot be used as a maintenance fluid because patients would become alkalotic
What is the IVF replacement for gastric fluid loss (NGT)?
D5 1/2 NS + 20 KCl
What is the IVF replacement for biliary fluid loss?
LR +/- sodium bicarbonate
What is the IVF replacement for pancreatic fluid loss?
LR +/- sodium bicarbonate
What is the IVF replacement for small bowel fluid loss (ileostomy)?
LR
What is the IVF replacement for colonic fluid loss (diarrhea)?
LR +/- sodium bicarbonate
What is the 100/50/20 rule?
Maintenance IV fluids for a 24-hour period:
100 mL/kg for the first 10 kg
50 mL/kg for the next 10 kg
20 mL/kg for every kg over 20
What is the 4/2/1 rule?
Maintenance IV fluids for hourly rate:
4 mL/kg for the first 10 kg
2 mL/kg for the next 10 kg
1 mL/kg for every kg over 20
What is the maintenance for a 70-kg man?
110 mL/hr
What is the common adult maintenance fluid?
D5 1/2 NS with 20 mEq KCl/L
What is the common pediatric maintenance fluid?
D5 1/4 NS with 20 mEq KCl/L (children have decreased ability to concentrate urine)
Why should sugar be added to maintenance fluid?
To inhibit muscle breakdown
What is the best way to assess fluid status?
Urine output (unless the patient has cardiac or renal dysfunction, in which case central venous pressure or wedge pressure is often used)
What is the minimal urine output for an adult on maintenance IV fluids?
30 mL/hr (0.5 mL/kg/hr)
What is the minimal urine output for an adult trauma patient?
50 mL/hr
How many mL are in 12 oz?
356 mL
How many mL are in 1 oz?
30 mL
How many mL are in 1 tsp?
5 mL
What are common isotonic fluids?
NS, LR
What is a bolus?
Volume of fluid given IV rapidly.
Used for increasing intravascular volume, and isotonic fluids should be used.
Why not combine bolus fluids with dextrose?
Hyperglycemia may result
What is the possible consequence of hyperglycemia in the patient with hypovolemia?
Osmotic diuresis