Chapter 7 Flashcards
ICF
2/3 TBW
ECF
1/3 TBW
Most clinically important fluid compartment
ECF, because the ECF includes the interstitial and intravascular spaces
Dominant extracellular osmole?
Sodium
Dominante intracellular osmole?
Potassium
How is 1L of dextrose IV solution dispersed?
1/3 ECF, 2/3 ICF
Of the 1/3 ECF from the 1L of dextrose IV solution, how much to interstitial and intravascular space?
2/3 Interstitial,1/3 intravascular
How is 0.9% NaCl (Isonic) solution dispersed? What is the clinical significiance?
100% to ECF, where 1/4 to intravascular, 3/4 to interstitial. To establish blood pressure as it is 3x more effective in expanding the intravascular space
1000 ml of dextrose solution, how much in intravascular space?
Approximately 83 ml
1000 ml of NaCl 0.9% isotonic solution, how much in intravascular space?
Approximately 250 ml
When is edema common?
Severe blood volume depletion, as it can cause capillary permeability to increase
Explain edema, after a reduction in blood volume.
Increased permeability of capillaries causes the leakage of albumin to interstitial space (still in ECF), reducing plasma oncotic pressure which further favours movement of fluid from the intravascular to interstitial space.
What is third spacing?
The accumulation of the excess fluid in the interstitial space (edema) or in the potential fluid spaces (effusion)
Why is water needed?
To support individuals LBM
Why should energy-based fluid calculations be avoided in those older than 65 years old?
To prevent dehydration
What does dehydration cause in the elderly?
Hypotension, confusion, extreme thirst and constipation
What are the three formulas that may be used for fluid calculations in the older adult?
1) Adj. Holliday-Segar
2) 30ml/kg, min of 1500 ml
3) 1500-2000 ml/day
Holliday-Segar formula?
1500 ml for first 20 kg, 15ml/kg for remaining BW
Why must obesity-adjusted weight be used when calculating fluid req?
We are hydrating lean mass, not adipose tissue
Obesity Adj. BW (lbs) =
[(ABW - IBW) x 0.25] + IBW
Give examples of increased fluid needs
- Severe diarrhea, emesis
- Large draining wounds
- High gastric fistula
- Ostomy outputs
- High fevers
- Lactating women
The more energy-dense a formula is, the lower ____
percentage of water volume
Heart failure patient fluid restriction?
20-25 ml/kg
Heart failure patient on fluid restriction, sodium restriction?
<2000 mg /day
In heart failure, what would not meeting the fluid restriction cause?
Contribute further respiratory decompensation, which would require diuresis and ICU transfer
How does fluid restriction help in HF?
Decreased O2 requirements, less stress on pumping blood through lungs
What else should HF patients be put on?
Loop diuretics
What is the normal range of serum osmolality?
280-295 mOSm/kg
What is elicited when serum osmolality changes?
Change in thirst and ADH secretion
When does volume depletion, or hypovolemia occur?
- GI hemorrhage
- Vomiting
- Diarrhea
- Diuresis
What are primary contributors to electrolyte balances?
- Losses from GI tract
- Abnormalities in renal excretion
What are the electrolytes found in the greatest amounts in the stomach, duodenum, ileum and bile
Cl, Na+
-More Cl in stomach compared to Na+
What are the predominant electrolytes in the pancreas?
Na+, HCO3-
What are the predominant electrolytes in the colon?
Na+, K+, Cl-
_____ trends in electrolytes are the most important, where acute electrolyte imbalance can be _____ if corrected too rapidly
- chronological
- harmful
When is IV electrolyte replacement preferred?
When patients have impaired GI tract absorption, nil os, and critically low electrolyte levels
When is conservative electrolyte replacement preferred?
In patients with impaired renal function, unles if they are receiving renal replacement therapy
(T/F) Magnesium should be repleted prior to correcting potassium levels
T
How can we correct hypokalemia and hypophosphatemia while minimizing electrolyte replacement?
potassium phosphate
Normal sodium
135-145 mEQ/L
Hyponatremia symptoms
Dizziness, headache, N/V, muscle cramps, lethargy
When electrolytes are above, how can we correct?
- Remove exogenous source
- Discontinue agents, meds
- Facilitate elimination
When electrolytes are below, how can we correct?
- IV
- Assess GI function for oral supplement
- Assess fluid status, renal function
- See if there are concurrent elect abnormalities
What is hypertonic hyponatremia?
- > 290 mOSm/L
- Caused by osmotically active substance other than sodium in the ECF
- Common causes is mannitol and hyperglycemia
What is isotonic hyponatremia?
- Serum osmolality is normal
- Fraction of serum compose of water is reduced
- Rare
What is hypotonic hyponatremia?
- <275 mOsm/L
- Can be hypervolemic or hypovolemic
- More serious
Hypovolemic hypotonic hyponatremia?
- More sodium loss than water, but water also decreases
- Treat with isotonic fluids to expand ECF volume
Hypervolemic hypotonic hyponatremia?
- Retain more water than sodium, but sodium is also retained
- May cause edema forming states and renal failure
- Treat with fluid and sodium restriction
Why sodium restriction in hypervolemic hypotonic hyponatremia?
To avoid further water retention, as there is already more water retained than sodium
Euvolemic hypotonic hyponatremia?
- sodium remains the same, while total body water increases
- urine osmolality > serum osmolality, which indicates that the kidneys are inappropriately concentrating urine
- Treat with fluid restriction
What is euvolemic hypotonic hyponatremia usually associated with?
SIAD (Syndrome of innappropriate diuresis), where there are excessive levels of ADH
What is more common, hypo or hypernatremia?
Hypo, but hyper has a lower threshold to see clinical manifestations
What is euvolemic hypernatremia?
Diabetes insipidus, where water losses exceed sodium losses
Hypovolemic hypernatremia?
- Total body water decreases more that total body sodium
- Treat with volume expansion with isotonic saline
Euvolemic hypernatremia?
- Total body sodium unchanged, total body water decreases
- Treat with water replacement
Hypervolemic hypernatremia?
- Total body sodium increases, total body water remains unchanged
- Treat with diuretics, water replacement
Hypokalemia?
When serum potassium less than 3.6 mEQ/L
What often causes hypokalemia?
Loss of potassium in urine or stool, less often caused by trans-cellular shift or inadequate dietary intake
What can cause trans cellular shift of K+ into cells?
- Catecholamines
- Metabolic alkalosis
- Insulin increase
Hypokalemia and hypo___ are often seen together
magnesemia
In the presence of metabolic acidosis, what potassium salt is used to treat hypoK? Why?
Potassium acetate instead of potassium chloride, because acetate is converted to bicarbonate
Why should dextrose solutions be avoided within the context of hypokalemia?
insulin facilitates trans-cellular shift of K+ to intracellular space
What can hypomagnesemia result in?
Refractory hypokalemia
Clinical manifestations of hyperK?
Changes in neuromuscular and cardiac function
What is the most common context of hyperK?
Chronic kidney disease
Extracellular shifts of K+ are relatively commonn, and due to what?
- Metabolic acidosis
- Tissue catabolism
- PseudohyperK
Explain why we see HyperK in metabolic acidosis
ECF flux of K+ to maintain electroneutrality due to excess of H+ ions (remember that outside the cell is usually more positive)
How can those with HyperK have their membrane excitability be restored to normal (making K+ shift back intracellularly?)
- IV calcium gluconate
- Insulin, dextrose
- Sodium bicarbonate
- Loop diuretics
Normal mg? where is it found?
1.8-2.8 mg/dl, mostly found in ICF, and up to 60% in bone
Where does most Mg absorption take place?
In the distal jejunum and ileum
What is the primary symptom of mg deficiency?
Neuromuscular hyper-excitability
What must be corrected prior to correcting mg?
Calcium and potassium
What is hypomg’s impact on CHO and lipid metabolism?
- Reduce insulin sensitivity and secretion and glucose cellular uptake
- Reduce LPL
When may hypomg occur?
- Alcoholism
- PEM
- Ileostomy, colostomy
- Short bowel syndrome
- Reduced mg intake, mg-free IV fluids or TPN
When can intra-cellular shifts of mg be seen?
- Refeeding
- Diabetic ketoacidosis
- Hyperthryoidism
- MI
Normal serum calcium?
8.6-10.2 mg/dl
Most abundant cation in the body?
Calcium, accounts for 1-2% of total body weight
Metabolically active form of calcium? Is it impacted by hypoalbuminemia?
- Ionized calcium
- NO
Low serum calcium stimulates ___ high serum calcium stimulates ___
PTH
Calcitonin
For each 1 g/dl decrease in albumin below 4 g/dl, there is an decrease of total serum calcium of ___
0.8 mg/dl
Direct measurement of ____ is the most critical in the ICU patient
ionized calcium
Hypocalcemia is not usually clinically significant if the _____ remains the same
ionized calcium
Options to correct hypocalcemia?
- IV calcium gluconate
- Calcium chloride table
What calcium supplement may cause tissue necrosis if exacerbation occurs?
CaCl, 3 x more elemental calcium than IV calcium gluconate
When does hypercalcemia occure?
- Hyperparathyroidism
- Cancer w/ bone mestases
- Vit A or Vit D toxicity
- CaCl and renal insufficiency
How should hypercalcemia be treated?
Isotonic solution, as it often causes volume depletion
What is the main intracellular anion?
Phosphorous
Normal range of phosphorous?
2.7-4.5 mg/Dl, reflects less than 1% of total body phosphorous
What causes intracellular shifts of phosphorus?
- CHO and insulin administration
- Catecholamine
- Alkalosis
When is hypophophatemia observed?
- Chronic alcoholism
- Critically ill
- Diabetic ketoacidosis
When is hypophosphatemia likely to be caused?
After administration of CHO load or PN without phosphate, especially in the context of a malnourished patient (refeeding)
What can agressive feeding in malnourished patients cause?
major shifts of potassium, magnesium and phosphorus into the intracellular space
How should nutrition support be administered to avoid re-feeding?
500 kcal/day, increase by 150% per day if OK, and add thiamine supplementation to aid in CHO metabolism
____ should be corrected prior to nutritional therapy
Electrolyte imbalances
When does hyperphosphatemia occur?
CKD usually, trauma, cytoxic agents, metabolic acidosis
When can the administration of high quantities of phosphate containing laxatives cause severe hyperphospatemia and end-organ damage?
In the elderly
What is the most serious complication of hyperphosphatemia?
Soft tissue and vascular calcification
pH for acidemia of blood?
<7.35
pH for alkalemia of blood?
> 7.45
What are the three ways the body regulates H+?
1) Buffering through ECF and ICF
2) PCO2, by changing breathing
3) HCO3- changes through kidneys
What is the principle buffer system?
H2CO3 –> HCO3-
What is the principle role of the lungs?
Maintain acid-base balance by regulating the pressure of dissolved CO2 gas in the blood –> when the respiratory system is compromised, we risk acid-base balance
What is the slowest mechanism to regulate H+?
Excretion of H+ and reabsorption of HCO3- by the kidneys
What is the only organ that can regulate alkaline substances and eliminate metabolic acids?
The kidneys
What are arterial blood gases? (ABGs)
Ability of lungs to oxygenate the blood
What are venous blood gases (VBGs)
Reflect tissue oxygenation
PCO2 indicated what?
Lungs ability to excrete CO2
Increased PCO2?
Acidosis
Decreased PCO2?
Alkalosis
PO2 indicates what?
Ability of hemoglobin to carry oxygen
The PO2 values is directly related to __
O2 saturation
Increase HCO3-?
alkalosis
Decreased HCO3-?
Acidosis
Steps to analyze acid base disorder?
1) Measure pH
2) Assess PCO2 to see if resp. disorder
3) Assess serum HCO3- to see if met. disorder
4) Calculate anion gap to see if metabolic acidosis is present
What is resp. acidosis characterized by?
- Decreased pH
- Increased PCO2
- Variable increase in HCO3-
What is resp. acidosis caused by?
Decreased alveolar ventilation
What is resp. alkalosis characterized by?
- Increased pH
- Decreased PCO2
- Variable decrease in HCO3-
Whet is resp. alkalosis caused by?
Effective alveolar ventilation is increased beyond the level necessary to eliminated metabolically produced CO2
What is metabolic acidosis?
- Reduced pH
- Reduced serum HCO3-
- Compensatory hyperventilation, causing decreased PCO2
How can met. acidosis be induced?
- Inability of kidneys to excrete H+ load
- Increase in the generation of H+ by addition of H+ or loss of HCO3-
Anion gap equation?
(serum Na+) - (Serum Cl-) + (Serum HCO3-)
What affects anion gap? What must be added?
- Hypoalbuminemia
- 2.5 mEQ/L of anion gap added for each 1 g/dL decrease
What does the anion gap distinguish between?
Normal and elevated anion gap acidosis
What is normal anion gap acidosis?
Replacement with HCO3- by Cl-, thus anion gap does not change as sum remains constant
How is elevated anion gap resolved?
Arises from the increased endogenous acid production
What should the PN formula for patient with high output ileostomy be in the context of metabolic acidosis?
-Maximum amounts of acetate salts, the acetate will be converted into bicarbonate in the functioning liver
What should the PN formula for patient with high output ileostomy be in the context of avoiding refeeding?
start at 500 kcal/day, then increase. Correct electrolyte abnormalities before
What should the PN formula for patient with high output ileostomy be in the context of ileostomy output?
Should be at an isotonic solution 0.9% which is the same as the ileostomy fluid
Why are those with high-output ileostomy at risk for acid-base disturbances?
Anatomical changes
May require fluid replacement
What is metabolic alkalosis characterized by?
- Elevated pH
- Increase in serum HCO3-
- Compensatory hypoventilation, increased PCO2
How can metabolic alkalosis occur?
- Loss of HCL through vomiting and diarrhea
- Nasogastric suction
- Diuretic use
- Hypokalemia, H+ shifts
What is usually required for metabolic alkalosis to occur ?Why?
Some degree of renal impairment, as the kidney can usually excrete HCO3-
