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
How does the body compensate for respiratory vs metabolic acid-base changes
If the cause of acidosis or alkalosis is respiratory, the kidneys will compensate by altering HCO3 retention or excretion
-retention for acidosis, excretion for alk
If the cause of the acidosis or alk is renal or metabolic, the lungs will compensate by altering CO2 retention or exretion
What could cause a metabolic acidosis with a high anion gap?
MUDPILES
Methanol poisoning
Uremia (acute renal failure)
DKA
Polypropylene glycol poisoning
Isoniazid poisoning
Lactic acidosis
Ethanol
Salicylate poisoning
If you see a high AG, check a osmolal gap - likely toxic alcohols
Quick fix for acidosis
If the patient is acidotic and acutely unstable, it is not unreasonable to give exogenous bicarb, but overcorrection can be just as dangerous
Usually giving IVF is effective in correcting the acidosis as it increases the renal excretion of hydrogen and in the lungs, it tips the equilibrium away from carbonic acid
If in a pinch and pt is unable to tolerate IVF or is in acute renal failure, can give exogenous bicarb
If pt is on a vent, increase minute volume and they will just blow it off
What are three diagnostics that should be completed in the assessment of the hyponatremic patient to determine cause of hypoNa
Urine sodium (10-20 mEq/L)
Serum osmolality (usually 2xNa) 275-285
Clinical status
If urine sodium >20: Renal salt wasting (problem with the kidneys)
If urine sodium <10: Renal retention of sodium to compensate for extrarenal fluid losses (problem other than the kidneys)
Causes of hypovolemic hyponatremia with urine Na <10
Dehydration
Diarrhea (C. diff)
Vomiting
Causes of hypovolemic hypoNa with urine sodium >20
Low volume and kidneys cannot conserve Na
Diuretics
ACE inhibitors
Mineralocorticoids deficiency
Causes of hypervolemic, hypotonic hyponatremia
Need to water restrict
Edematous states
Congestive heart failure
Liver disease
Advanced renal failure
What would be the cause of a patient having hyponatremia but a high serum osm
Hyperglycemia: Usually from HHNK
Hyperosmotic hyperglycemic nonketotic state
What would you do if the patient is symptomatic and is notably hyponatremic
Give NS with a loop diuretic
If CNS symptoms, give 3%NS with loop diuretic
Any time that you give 3%, you want to make sure it is slow and calculated
-Can cause cerebral edema
Laboratory/Diagnostics findings for patients with hypokalemia
Decreased amplitude on EKG
Broad T waves
Prominent U waves
PVCs, ventricular tachycardia, ventricular fibrillation
What can an acidotic state do to the potassium
hyperkalemia
Symptoms of hypocalcemia
Increased deep tendon reflexes
Muscle/abd cramps
Trousseau’s Sign - blood pressure cuff causes asterixis
Chvostek’s Sign - cheek
Prolonged QT interval
Convulsions
Treatment of hypocalcemia
Acute: IV calcium gluconate
Chronic: Oral supplements, Vit D, aluminum hydroxide
Symptoms of hypercalcemia
Fatiguability
Muscle weakness
Depression
Anorexia
Nausea/vomiting
Constipation
In severe cases - coma or death
What causes respiratory acidosis
Decreased alveolar ventilation
The patient is not breathing
Respiratory component is pCO2
How do you treat respiratory acidosis
Improve ventilation, intubate if necessary
If already intubated, increase the rate in order to blow of pCO2
What causes respiratory alkalosis?
Hyperventilation
Low pCO2 because you are blowing it off
Symptoms of respiratory alkalosis
Think hyperventilation
Lightheadedness
Anxiety
Paresthesia
Stocking/glove tingling
tetany if very severe
What is the formula to measure Anion Gap
Anion Gap = [Na + K] - [Bicarb + Cl]
What can cause an increased Anion Gap metabolic acidosis
DKA
Alcoholic ketoacidosis
Lactic acidosis
What can cause a normal anion gap metabolic acidosis
Simple Diarrhea
Ileostomy
Renal tubular acidosis - intra-renal problem
Recovery from DKA
Treatment of metabolic acidosis
Treat underlying cause
Fluid rescuscitation
Causes of metabolic alkalosis
Saline responsive (volume down) most common
Post-hypercapnia alkalosis
NG Suctioning
Vomiting
Diuretics
Treatment of metabolic alkalosis
Correct volume deficit with NaCl and KCl
Discontinue diuretics
Acetazolamide if volume replacement is contraindicated
