Fluids And Electrolytes Flashcards
The pathophysiology of metabolic alkalosis is divided into 2 factors
A particularly important maintenance factor is?
- Generating
- Maintenance
Renal response to hypovolemia
Target blood glucose to lower mortality
180 mg/dL
Factors that generate metabolic ALKALOSIS are (2)
- Vomiting
2. Diuretic administration
Treatment of metabolic alkalosis(2)
- Expansion of intravascular volume
2. Potassium administration
This most rapidly corrects life threatening metabolic alkalosis
0.1 N hydrochloric acid
Administered through a central vein to prevent tissue damage
Metabolic acidosis, what anion gap occurs when bicarbonate is lost externally.
Normal anion gap (< 13 mEq/L)
Metabolic acidosis, what anion gap occurs because of excess production or decreased excretion of organic acids or ingestion of one of several toxic compounds.
High anion gap
How much is ICV of total body weight?
60%
How much is ECV of total body weight?
20%
The primary mechanism of controlling water intake
Thirst
Final osmolality of tubular fluid
1200 mOsm/kg
Daily adult requirement for
Na
K
75 meqs
40 meqs
Number of osmotically active particles per LITER of solvent
Osmolarity
Number of osmotically active particles per KILOGRAM
Osmolality
This volume is determined by the rates of capillary filtration and lymphatic drainage.
IFV (interstitial fluid volume)
Because of the influence of the glycocalyx, theoretical rates of fluid filtration usually substantially exceed actual filtration rates, a phenomenon termed as
Low lymph flow paradox
What is a positive tilt test?
A positive tilt test defined as an increase in heart rate of at least 20 beats per minute and a decrease in systolic blood pressure of 20 mmHg or more when the subject assumes the upright position.
How many % of nephrons must be dysfunctional before serum creatinine exceeds the normal range.
40 to 50%
Requirement of PPV (4)
- Direct arterial monitoring
- Mechanical ventilation
- Vt of 8 mL/kg
- No cardiac arrhythmia
In esophageal doppler assessment of iop blood volume
A corrected flow time of 0.35 suggests
A corrected flow time of 0.40 suggests
Volume expansion should improve CO
Further volume expansion will be ineffective
In high risk surgical patients, these parameters has been associated with improved outcomes (3)
- DO2I of 600 mL/m2/min (equivalent to a cardiac index of 3)
- Hgb of 14 g/dL
- 98% oxyhgb
Disorders of total body sodium are affected by two factors
- ECV
2. PV
Is the most common electrolyte problem in hospitalized patients
Hyponatremia
Plasma sodium DECREASES approximately how much for each 100 mg/dL rise in glucose concentration
2.4 mEq/L
The vasopressin-regulated water channel
Aquaporin 2
Diagnosis of SIADH (6)
- Hyponatremia (low plasma osmolality)
- Urinary osmolality > plasma osmolality
- Renal sodium excretion > 20 mmol/L
- Absence of hypotension, hypovolemia & edematous states
- Normal renal & adrenal functions
- Absence of drugs that affect renal water & sodium handling
Cornerstone of SIADH
Free water restriction (0.5 - 1L per day)
Elimination of cause
As long as GFR is above this level, potassium intake can be excreted.
8 mL/min
2 most important regulators of potassium excretion
- Plasma K
2. Aldosterone
Hallmark of hypocalcemis
Increased neuronal membrane irritability and tetany
Low or normal phosphate concentrations imply 2 things
- Vitamin D deficiency
2. Magnesium deficiency
High phosphate concentration suggests (2)
- Renal failure
2. Hypoparathyroidism
Enzyme responsible for conversion of calcidiol to calcitriol
1a hydroxylase
Treatment of hypocalcemia
Treat cause
Symotomatic hypocalcemia occurs when serum ionized calcium is?
Less than 0.7 mM
Correction of this electrolyte abnormality without treating hypocalcemia may provoke tetany
Hypokalemia
Has been called an enogenous calcium antagonist
Magnesium
How does Magnesium function in potassium metabolism?
Regulating Na K ATPase enzyme especially in potassium depleted states, and controls reabsorption of potassium
Absorption of most Mg
Thick ascending loop of Henle
An electrolyte that may block the NMDA receptor
Mg
1 gram of magnesium sulfate provides approximately how much mmol, meqs and mg of elemental mg?
4 mmol
8 meqs
98 mg
Symptomatic hypomagnesemia should be treated with?
MgSO4 1 to 2 grams IV for 1 hour
Then 2 to 4 meqs/hr infusion
Infusion should not exceed 1 meq/min
Most cases of hypermagnesemia are due to?
Iatrogenic causes
Criteria for SIADH (6)
- Hyponatremia, low plasma osmolality
- Urinary greater than plasma osmolality
- Renal sodium excretion > 20 mmol/L
- No hypotension, hypovolemia & edema
- Normal renal & adrenal functions
- Absence of drugs affecting renal & sodium handling
Is a class of drugs that inhibit the action of AVP
Vassopressin receptor blocking agents
Is a vassopressin receptor blocking agent that inhibits both V1a and V1b. However, there are potential decreases of blood pressure when V1a is blocked.
Conivaptan
This drug only blocks the V2 receptor
Tolvaptan
This is indicated for hyponatremic patients who experience seizures
Hypertonic 3% saline (1 to 2 mL/kg/hr or 1 to 2 meqs/L/hr)
NO MORE THAN 4 to 8 meqs/L/day
Principal determinants of neurological injury in Na replacement therapy (2)
- Severity & chronicity of hyponatremia
2. Rate of correction
Osmotic demyelination is more common if hyponatremia persisted for how many hours
48 hours
Rate of hyponatremia should be at?
It should not exceed for how much rate?
Above 1 to 2 meqs/L in an hour
No more than 8 meqs/L/day
Why are geriatric patients at risk for hypernatremia
Because of decreased renal concentrating ability
Criteria diagnostic of DI (3)
- Hypertonicity
- Polyuria
- Hypotonic urine (<150 mOsm/kg)
Central DI drug treatment (2)
- Desmopressin (DDAVP), 10-20 ug intranasally, 2-4 ug SC
- Aqueous vasopressin (5 U q2-4H IM or SC)
DDAVP: longer duration without VASOCONSTRICTOR EFFECTS
TBW deficit is the first step in treating hypernatremia
What is the formula.
TBW deficit = 0.6 x body weight x [(Na - 140)/140)]
Water deficit should be replaced over 24 to 48 hours
Should not exceed 1 to 2 meq/L/hr
If present for 2 days, no more than 10 meqs/L/day
Is a drug that potentiates the renal effects of vasopressin, ang carbamazepine, which enhances vasopressin excretion.
Chlorpropramide
Potassium concentration
- Intracellular?
- Extracellular?
150 meqs/L
3.5 to 5 meqs/L
As long as GFR is above this rate, potassium can be excreted
8 mL/min
Major site at which potassium excretion is regulated
DCT
Two most important regulators of potassium
- Plasma K
2. Aldosterone
As a general rule, a chronic decrement of 1 meq/L in plasma potassium corresponds to a total body deficit of how much?
200 to 300 meqs
Read
Cardiac rhythm disturbances are among the most dangerous complications of potassium deficiency. Acute hypokalemia causes HYPERPOLARIZATION of the cardiac cell and may lead to ventricular escape activity, re-entrant phenomena, ectopic tachycardias, and delayed conduction.
This drug increases its binding capacity into the myocardium if associated with hypokalemia
Digoxin
Aldosterone primarily controls this electrolyte reabsorption and not potassium excretion.
Sodium reabsorption
Read
Potassium is usually replaced as the chloride salt because coexisting chloride deficiency may limit the ability of the kidney to conserve potassium.
Ascending muscle weakness appears when plasma K is?
7 meqs/L
If hyponatremia exists with hypokalemia what organ should be evaluated?
Adrenals
Drugs that may contribute to hyperkalemia (5)
- NSAIDs
- ACEi
- Cyclosporine
- Potassium-sparing diuretics
- Triamterene
Salbutamol decreases potassium acutely by how much?
1 meq/L
What are the two most important regulators of calcium?
PTH
Calcitriol
Hallmark of hypocalcemia is?
Increased neuronal membrane irritability and tetany
Read
In renal insufficiency, reduced phosphorus excretion results in hyperphosphatemia, which downregulates the 1a hydroxylase responsible for the conversion of calcidiol to calcitriol.
Symptomatic hypocalcemia usually occurs when ionized calcium is less than?
0.7 mM
What 2 electrolyte abnormalities potentiate hyocalcemic induced cardiac and neuromuscular irritability?
- Hyperkalemia
- Hypomagnesemia
Therefore correction of hypokalemia without correction of hypocalcemia may provoke tetany.
Oral calcium can be substituted once serum calcium is at what level?
4 to 5 mg/dL
In hypoalbuminemic patients, total serum calcium can be estimated by assuming an increase of how much?
0.8 mg/dL for every 1 g/dL of albumin concentration below 4 g/dL