Fluid and Electrolytes Flashcards
Cations
Na+, K+, Mg+, Ca2+
Anions
: Cl-, HCO3-, PO43- (and other phosphates), and negatively charged proteins.
Osmolality
Osmolarity
Osmolality: Concentration of a solution expressed as the total number of solute particles per kilogram.
Osmolarity: Concentration of a solution expressed as the total number of solute particles per liter.
Because a liter of H2O weighs one kilogram, these two terms are sometimes used interchangeably.
Molecular diffusion.
Osmotic pressure gradient.
Molecular diffusion: the spontaneous movement of molecules from areas of high concentration to areas of low concentration.
If you have two solutions of different concentrations that are separated by a semipermeable membrane, the tendency of those solutions to equalize their concentration by moving across the membrane is called the osmotic pressure gradient.
The rate of osmosis is influenced by many factors
The concentration of each solution (the greater the difference, the greater the osmotic pull).
Temperature.
Surface area to volume ratio.
The permeability of the membrane (if more permeable, water will diffuse faster than solutes
There are two kinds of solutes (aka osmoles)
Tonicity Def=
Effective osmoles, which DO NOT freely move across a membrane (e.g., electrolytes).
Ineffective osmoles, which DO freely move (e.g., urea, ethanol, methanol).
The concentration of a solution, minus ineffective osmoles, is called tonicity
The 3 types of tonicity.
Isotonic (270-300 mOsm/L): no osmotic activity.
Hypertonic (>300 mOsml/L): pulls fluid from cell. The red blood cell will shrink
Hypotonic (<270 mOsm/L): fluid goes into cell. The red blood cell will swell.
The different fluid compartments?
Intracellular fluid (ICF): water contained within cell membranes. [~30L, ~40% of body weight]
Extracellular fluid (ECF): water contained outside cell membranes. [~14L, ~20% of body weight]
Interstitial [~9L, ~15% of body weight]
Intravascular [~5L, ~5% of body weight]
Composition of fluids. Intracellular-Interstitial-Intravascular Na+ K+ Cl- HCO3- Proteins
Na+ mostly Interstitial and Intravascular
K+ mostly Intracellular,
Cl- mostly Interstitial and Intravascular
HCO3- mostly Interstitial and then Intravascular
Proteins mostly Intracellular, and then Intravascular
How do fluids leave the body and what amounts?
800-1500ml in urine
0-250ml in stool
600-900ml through skin and lungs
What makes us thirsty?
In the hypothalamus, osmoreceptors trigger thirst when ECF is hypertonic (i.e, we’ve lost water but held on to our electrolytes).
The renin-angiotensin system triggers thirst with baroreceptors in response to hypovolemia.
Oropharyngeal dryness
Psychological factors
What can increase fluid loss?
GI: vomiting, diarrhea Renal: diuresis Vascular: hemorrhage Skin: burns, fever Lungs: tachypnea, mechanical ventilation
What can cause fluid overload?
Heart failure
Liver failure
Renal failure
Iatrogenic
What is Cholera?
What can it do to you?
An infection of the small intestine by Vibrio cholerae.
Vomiting and watery diarrhea (losing 10 to 20 liters a day).
Mortality in untreated patients is 50-60%.
Normal Fluid Requirements for average size adults
For an average-sized adult, the daily requirement of water is about 2 to 3 liters.
Humans require 1500ml of water for every square meter of surface area.
An average adult has a surface area of about 1.7 square meters. 1.7 x 1500 = 2.55 liters a day.
Thus, an adult needs around 100-125 ml/hr of IV fluid to meet his or her daily fluid requirements.
Daily fluid requirements for pediatric pts
0-10 kg - (100ml per kg)
11-20 kg - (1000ml PLUS 50ml per kg over 10kg)
21-70 kg - (1500ml PLUS 20ml per kg over 20kg)
71+ kg = 2500ml (adult rate)
Daily fluid requirements for the elderly?
1500ml PLUS 10-15ml per kg over 20
Daily elecrolyte requirements?
Sodium: 1-2 mEq/kg (~140mEq)
Potassium: 0.5-1 mEq/kg (~70 mEq)
Glucose: ~500 kcal
Glucose provides calories vital for brain, renal, and RBC function. Also will reduce the risk of the body going into “starvation mode,” thus protecting the body’s stores of protein.
Your patient is a 28-year-old man who is admitted at 6:00am to the pre-op area for an elective hernia repair. Since he is NPO, what should his maintenance fluid order look like?
D5NS with 20mEq KCl at 125ml/hr
What are Crystalloids?
Crystalloid fluids are aqueous solutions of mineral salts.
They are administered as maintenance fluids in NPO patients, used for hypovolemic resuscitation in trauma, used to maintain intravascular volume in sepsis patients, etc.
They are relatively cheap, and generally well tolerated.
D5NS
LR
NaCl
What are Colloids?
When not to give them?
Who do they work for?
Fluids that, in addition to mineral salts, also have large proteins. For example, albumin contains a protein that has a molecular weight of 69,000.
The proteins are too big to move out of the intravascular space, so they remain there and keep it hypertonic, drawing fluid from the ICF compartment. They expand plasma volume better, and are less likely than crystalloids to cause edema.
Whole Blood
PRBC’s
WBC’s
Platelets
FFP
5% Albumin
(HEAD INJURIES?
DON’T GIVE COLLOIDS!!!!!!!)
There appear to be only a small group of patients who can benefit from administration of colloids; e.g. elderly patients who cannot tolerate high volume resuscitation, severe diarrhea with low serum albumin, nephrotic syndrome, etc.
Stick with crystalloids unless instructed otherwise.
Why use it? Whole Blood PRBC's WBC's Platelets FFP 5% Albumin
Whole Blood:Increases volume and oxygen carrying capacity
PRBC’s:Increases oxygen carrying capacity
WBC’s:Sepsis with granulocytopenia
Platelets:Bleeding due to thrombocytopenia
FFP:Bleeding due to factor deficiencies
5% Albumin:Volume replacement
As a general rule…
it is safe to assume that a patient just leaving the OR is going to be down 1 to 2 liters of fluid.
Whats important when Assessing Fluid Status?
Review history (procedure, I & Os, PMH, pre-op weight)
Review BP, HR, RR, skin turgor, cap refill, lung sounds.
Check urine output, blood tests, CVP, chest X-ray
Hyponatremia can happen in the presence of?
What do you check in order o manage it?
What can lead to it?
Can happen in the presence of hypertonicity, hypotonicity, or isotonicity. Checking serum osmolality is required to manage hyponatremia. If patient is hypotonic (<280 mOsm), you must also determine fluid status.
May be chronic (“reset osmostat”) or acute (water intoxication, loss of potassium, syndrome of inappropriate ADH secretion (SIADH)).
Hyponatremia:The Symptoms
Symptoms are primarily neurologic, due to the hypo-osmolality in the intracellular compartment. Water rushed into the cells, causing cerebral edema.
Lethargy, confusion, nausea, vomiting, seizures, coma.
Hyponatremia:The Solution
What can cause Isotonic and hypertonic hyponatremia. What do you treat.
If hypotonic and hypovolemic.
If hypotonic and isovolemic or hypervolemic.
Isotonic and hypertonic hyponatremia can be caused by hyperlipidemia, hyperglycemia, excessive infusion of isotonic or hypotonic fluids, or post-TURP syndrome. Treatment is by treating the underlying cause.
If hypotonic and hypovolemic, administer NS
If hypotonic and isovolemic or hypervolemic, try water restriction first. If no response, replace Na+ deficit with 250ml of 3% NaCL and recheck Na+
Hypernatremia:What causes it? What can else can it be?
Typically from the loss of water, but not always. Hypernatremia is always hypertonic, but may be hypovolemic, isovolemic, or hypervolemic
Hypernatremia:The Symptoms
Primarily neurologic, and include lethargy, weakness, irritability, leading to fasciculations, seizures, coma, and irreversible neurologic damage.
Hypernatremia:The Solution
Hypovolemic: correction of fluid deficits with either free water PO or hypotonic IVF (e.g., 1/2NS).
Hypervolemic: most commonly iatrogenic, due to administration of fluids and medicine with excess Na+.
Isovolemic: Commonly due to hypotonic losses replaced with isotonic fluid. Less commonly may be diabetes insipidus, if accompanied by high output of hypotonic urine.
Hypokalemia:What causes it?
Potassium is the major intracellular cation
Generally caused by GI depletion (e.g., vomiting, NG suctioning, diarrhea) renal dysfunction (e.g., diuretics), or cutaneous losses (i.e., burns
May also be due to acute intracellular uptake of K+ due to MI, excess insulin, DTs, hypothermia, and more).
Often accompanied by hypomagnesemia; both deficits must be corrected
Hypokalemia:The Symptoms
Generally cardiovascular, and may be seen on EKG.
Ectopy, T-wave depression, prominent U-waves.
Severe hyponatremia increases susceptibility to arrhythmias.
Hypokalemia:The Solution
In mild hypokalemia (>3.0), may replace orally with 40-100 mmol of KCl elixir.
If severe, replace via IV. Concentrations should be no more than 40 mmol/L, and should not be infused faster than 20 mmol/hr.
Hyperkalemia:The EKG
Elevated levels of potassium are associated with EKG abnormalities, including peaked T-waves, reduced P-wave voltage, and widening of the QRS complex. In more severe cases, the EKG will show a sine-wave pattern,
Hyperkalemia:Caused by?
Can be due to renal failure, rhabdomyolysis, cell lysis (after chemotherapy), acidemia, digitalis intoxication, reperfusion of ischemic limbs, and succinylcholine administration.
Hyperkalemia:The Solution
Mild: reduce K+ intake and give a loop diuretic.
In severe cases, use rapid-acting agents that drive K+ back into the cells: IV NaHCO3, infusion of dextrose with insulin, inhaled beta agonists, and IV calcium gluconate
Hypocalcemia:What causes it?
Generally occurs with calcium sequestration of vitamin D deficiency. Can occur after thyroidectomy
Whats the formula for Corrected Ca?
Corrected Ca2+ = (0.8 x (4.o-pt. albumin)) + serum Ca2+
Hypocalcemia:The Symptoms
Tetany. Patients will have a Chvostek’s sign (facial muscle spasm elicited by tapping over branches of the facial nerve).
May also have QT-interval prolongation and ventricular arrhythmias.
Hypocalcemia:The Solution
Asymptomatic patients with mild or moderate hypocalcemia (6.0-8.5) can take 1000-2000mg calcium PO daily.
Symptomatic patients get a bolus of 10% calcium gluconate (10-20ml), then an infusion of 1-2mg/kg/hr of calcium for 6-12 hours.
Hypercalcemia:What causes it?
Causes include malignancy, hyperparathyroidism, hyperthyroidism, thiazide diuretics, vitamin D intoxication, granulomatous disease (e.g., sarcoidosis).
Hypercalcemia:The symptoms
Symptoms include nephrolithiasis, altered mental status, diffuse weakness, dehydration, ileus, nausea, vomiting, severe constipation, as well as QT-interval shortening and arrhythmias.
Hypercalcemia:The Solution
Mild: restrict calcium intake and treat underlying disorder.
Severe: NS infusion with loop diuretics, salmon calcitonin, pamidronate disodium
