Fluids and Electrolytes Flashcards
What initiates the thirst mechanism
Secretion of antidiuretic hormone (vasopressin)
Osmolality and the osmolal gap
Iso-osmolar: 280-295
Hypo-osmolar: <280
Hyper-osmolar: >295
Typically there is no difference between the measured and calculated osmolality but a difference of more than 10 suggests an osmolal gap
—OG = measured serum osmolality - calculated
Osmol gaps are used as a screening tool to identify toxins
–alcohols
–sugars: Mannitol, sorbitol
–lipids: triglycerides
–Proteins
Understanding water balances
Starling’s Principle:
The movement of water between intracellular fluid and extracellular fluid happens via osmosis
–Na maintains the osmotic balance of the ECF
–K maintains the osmotic balance of the ICF
Hyponatremia: Delineated into 3 groups
Where water goes, sodium follows
Euvolemic:
-SIADH - retain water because there is a lot of ADH - tend not to be taking in much water
-Hypothyroidism
-Addison’s Disease
-Psychogenic Polydipsia - pt drinks lots of water but also urinates a lot
-Beer Potomania
Hypovolemic:
-Extrarenal losses:
—-Diarrhea
—-Third spacing: pancreatitis, peritonitis, burns, effusions
-Renal losses:
—-Diuretics: loops, thiazides
—-Renal disorders - renal tubular acidosis
—-Addison’s disease
—-Osmotic diuresis - hyperglycemia
—-Cerebral salt wasting: increased intracranial pressure that stops ADH secretion - ICH, meningitis
Hypervolemic: (all are edematous)
-CHF
-Cirrhosis
-Renal disorders - Chronic renal failure, nephrotic syndrome
Considerations when treating hyponatremia
Treatment should focus on finding the underlying cause
Sodium deficit = (140-serum sodium) x total body water
total body water = kg body weight x 0.6
Mild, asymptomatic: treat with adequate solute intake and fluid restriction of 500mL/day
Moderate, symptomatic: treated by raising sodium level by 0.5-1/hr for a total of 8 during the first day with the use of lasix and replacing sodium and K losses with NS
Severe (confusion, convulsion, coma): consider hypertonic saline (3%) but can lead to rapid dilute diuresis and fall in the serum sodium. Contraindicated in hypervolemic hypoNa
Treatment of hypernatremia
If hypovolemic, give 0.45% saline slowly (target correction to 0.5-1 every 4 hours)
If euvolemic, should treat with D5W (free water)
If hypervolemic, use diuretics
Lowering the Na too quickly will cause cerebral edema
Causes of hypo and hyperkalemia
HypoK:
-Most commonly the result of medications - Diuretics
-GI losses: NG suction, emesis, diarrhea
-insulin excess
-alkalosis - hyperventilation
-B12 therapy
-Beta agonist (albuterol)
HyperK
-Increased intake of medications: NSAIDs, ACE-I, bactrim
-Decreased urinary excretion (most common cause) - CKD, Adrenal insufficiency, lupus, sickle cell
- Shifts from intracellular to extracellular
—Insulin deficiency (DKA)
—Metabolic acidosis
—Cell lysis (tumor lysis syndrome)
—Digitalis toxicity
Treatment of hypoK
Since Mg is a cofactor of retention in K in the kidney, you should check Mg and replete this before you replete K
Generally K will increase by 0.25 for every 20mEq given
Oral is preferred
Treatment of hyperK
Perform an EKG immediately
Give calcium gluconate 2g IV if stable (give calcium chloride 2g IV if arresting)
Dextrose 50% 50mL IV
Insulin (regular) 10 units IV
Sodium bicarbonate 50mEq IV
IV hydration
Consider dialysis
Kayexelate is sometimes used but it takes several hours to work and only has variable success
Magnesium usually goes hand in hand with _____
Potassium
What EKG changes can occur in hypoMg
Prolonged QT which can lead to Torsades des Pointes
Torsades is treated with Mg
How is calcium regulated and where is it stored?
Balance is controlled by parathyroid hormone and calcitonin
Ionized calcium can be measured in the blood and is more accurate in really calculating the calcium available
99% is stored in the bones
Treatment for hypercalcemia
Fluids and diuretics (forced diuresis)
—Furosemide can be given to permit continued large volume IV salt and water replacement while minimizing the risk of blood volume overload and pulmonary edema
Can also give bisphosphonates and calcitonin
–pamidronate and zoledronate for those with good kidneys
—if they have kidney disease, give Calcitonin
When should you be paying attention to calcium levels?
Blood transfusions can cause hypoCa, therefore you want to be checking ionized calcium after every few units of pRBC
Refeeding syndrome
Metabolic disturbances that occur as a result of reinstitution of nutrition in patients that are starved
Occurs during the initial 4-7 days after resuming eating
Because of starvation, the body stores of electrolytes were exhausted
Once the body starts to break down food again, electrolytes (specifically phos, K and Mg) are needed to break down the food
The body has no stores to do this, so the serum levels drop even further
Therefore if the phos drops below 2 after 2-3 days of restarting food, you should feed them less and give them cofactors
