Renal Pharmacology & The Urinary System, Pt. 5 Flashcards
How much of the body weight is made up of water? What are the 2 major compartments?
TBW = 60%
- ECF (20%) - plasma (5%), IF (15%), TCF (1% - aqueous humor, pleural/abdominal fluid)
- ICF (40%)
What membranes separate body fluid compartments?
semipermeable capillary membranes (plasma/IF) and cell membranes (IF/ICF)
(increased osmotic pressure attracts water to move between compartments)
What is responsible for maintaining fluid compartments? How? What are the 2 major responses?
osmoreceptors in the hypothalamus detect significant changes in ECF composition or volume and trigger endocrine response of the pituitary to secrete ADH, aldosterone, ANGII, or ANP
- urinary excretion of water
- dietary absorption of water
What are the 5 major functions of electrolytes?
- maintain cell metabolism
- contribute to body structure
- facilitate the osmotic movement of water between body compartments (sodium)
- maintain hydrogen ion concentration (acid-base balance) required for normal cellular function (bicarbonate, chloride, phosphate)
- production and maintenance of membrane potentials and action potentials (hydrogen, potassium, sodium)
What are the major cations and anions found in the extracellular and intracellular fluids?
EXTRACELLULAR - Na+, Ca++, Cl-, HCO3
INTRACELLULAR - K+, Mg++, P, protein
(both compartments are electroneutral)
How is plasma osmolality calculated? What is the normal value?
plasma osmolality = 2[Na] + (glucose/18) + (BUN/2.8)
~290-300 mOsm/kg
(approximation, for accuracy an osmometer is used in the lab)
What are the 4 most common causes of hypernatremia?
- excessive loss of water with inadequate replacement, causing the ECF to become concentrated
- DISEASES: diabetes insipidus (PU), fever, diarrhea, vomiting
- IATROGENIC: administration of hypertonic saline or sodium bicarbonate solution
- ACCIDENTAL: heat stroke, salt poisoning (sea water ingestion)
What is hypervolemic hypernatremia? What are 4 causes? How is it treated?
impermeable solute gains with fluid overload and hypertonic urine
- excessive salt intake (sea water, salt lick)
- hypertonic fluid administration
- hyperaldosteronism
- hyperadrenocorticism
diuretics and 5% dextrose solution
What is isovolemic hypernatremia? What are 4 causes? How is it treated?
pure water loss with absent to minimal dehydration and normal to hypotonic urine
- diabetes insipidus
- fever
- stroke
- inadequate water intake
5% dextrose solution, correct water deficit, desmopressin for diabetes insipidus centralis
What is hypovolemic hypernatremia? What are the extrarenal and renal causes? How is it treated?
hypotonic fluid loss with moderate to severe dehydration
- EXTRARENAL = concentrated urine; GI disease (vomiting, diarrhea), third-space loss
- RENAL = dilute urine; osmotic diuresis (DM, mannitol), diuretics, post-obstructive diuresis, renal insufficiency
balanced electrolyte solution or normal saline, with hypotonic saline as required to reduce serum sodium
What are the 3 common causes of hyponatremia?
excess water in the ECF caused by…
- hypovolemia: GI loss, hypoadrenocorticism
- hypervolemia: CHF, nephrotic syndrome, heaptic disease
- iatrogenic: administration of hypotonic fluids or mannitol infusions
What is hyperosmolar hyponatremia? What are 2 causes? How is it treated?
initial normovolemia with a plasma osmolality > 310 mOsm/kg
- hyperglycemia
- mannitol infusion
manage underlying disease causing elevates glucose (DM), discontinue infusion
What is normosmolar hyponatremia? What are 2 causes? How is it treated?
normovolemia or pseudohyponatremia with a plasma osmolality = 290-310 mOsm/kg
- hyperlipidemia
- severe hyperproteinemia
(artefactual displacement of ions)
manage underlying case of elevated lipids or proteins
What is hypoosmolar hyponatremia? What are the hypervolemic, normovolemic, and hypovolemic causes?
varied volume status with a plasma osmolality < 290 mOsm/kg
- HYPERVOLEMIC: hepatic disease, CHF, nephrotic syndrome, renal disease
- NORMOVOLEMIC: inappropriate ADH secretion, antidiuretic drugs, hypothyroidism, hypotonic fluids, psychogenic PD
- HYPOVOLEMIC: GI loss, third space loss, hypoadrenocorticism, diuretics
How are asymptomatic and symptomatic hypoosmolar hyponatremia treated?
ASYMPTOMATIC: water restriction and serum sodium monitoring
SYMPTOMATIC: conventional crystalloids (LRS, saline) for slow correction
(manage underlying disease)
What organs are responsible for adjusting pH?
LUNGS - respirate CO2
KIDNEYS - secrete H+ and HCO3-
How is acid-base status calculated? What causes respiratory and metabolic differences?
pH = 6.1 + logHCO3 (0.03PCO2) —> log (renal function) x ventilation
RESPIRATORY:
- increased CO2 = decreased pH = acidosis
- decreased CO2 = increased pH = alkalosis
METABOLIC:
- increased HCO3 = increased pH = alkalosis
- decreased HCO3 = decreased pH = acidosis
What happens when pH changes?
alters cell metabolism and physiology
What 4 parameters are used to analyze acid-base status?
- pH of blood at 37 degrees C and temperature corrected
- pCO2 at 37 degrees C and temperature corrected
- standard bicarbonate - measured bicarbonate concentration in blood standardized to a pCO2 of 40 mmHg and normal body temperature
- base excess - amount of acid or alkali needed to return the blood to normal pH (all bases over the normal)
What law is used by to calculate the ion gap? What electrolytes are normally measured in blood biochemistry? What anions calculated in the anion gap?
electroneutrality - concentrations of anions and cations and plasma must be equal (under normal conditions, there is no anion gap)
Na+, K+, Cl-, HCO3-
sulfates, phosphates, proteinates, organic acids
How is anion gap calculated? What should it equal?
anion gap = [Na+] - ([HCO3-] + [Cl-])
12 +/- 4 —> anything higher than 16 suggests that the unmeasured anions have increased, decreasing HCO3- and Cl-
What 4 situations commonly result in respiratory alkalosis?
- overzealous mechanical ventilation during anesthesia
- high altitude
- damage to respiratory centers
- emotional excitement
What 4 situations commonly result in respiratory acidosis?
- alveolar hypoventilation due to damage or depression of respiratory centers in SNC
- fractured ribs
- bloated abdomen
- respiratory obstructive diseases
What 4 situations commonly result in metabolic alkalosis?
- vomiting
- torsion of abomasum in ruminants
- hypokalemia
- hypoparathyroidism (low PTH inhibits HCO3- reabsorption)
What are some common causes of metabolic acidosis?
- renal failure
- hyperkalemia
- hyperparathyroidism
- diarrhea
- fistulas (pancreatic duct)
- mineralization of bone, CaCl2 infusion
- lactate formation (anaerobic glycolysis, severe exercise, tumors)
- starvation, DM, increased fat mobilization
- protein-rich diet
- rumen acidosis
What 6 questions should be asked regarding fluid therapy?
- When should it be instituted?
- What solution should be used?
- How much?
- How fast?
- What route of administration?
- How should results be evaluated?
What is the main purpose of fluid therapy? What are some other purposes?
correct fluid, electrolyte, or acid-base imbalances
- parenteral nourishment
- stimulate organ function
- drug administration
How is replacement fluid volume calculated? What maintenance fluids are given to mature and immature animals?
volume (L) = body weight x % dehydration
- MATURE = 40-65 mL/kg/day
- IMMATURE = 130 mL/kg/day
What are the 6 manifestations of dehydration? When are each present?
- loss of skin elasticity - 5%
- tacky oral MM - 6-7%
- prolonged CRT - 6-8%
- persisting skin tenting - 8-10%
- eyes sink into orbit - 10%
- cool extremities, early shock - 10-12%
What are common routes of adminstration of fluids?
- PO/nasogastric
- per-rectum
- IV
- SQ
- IP
- intraosseous
When is per-rectum, SQ, IP, and intraosseous administration of fluids useful?
PER-RECTUM = young animals - good for water, K+, Na+, and Cl- absorption
SQ = correcting mild to moderate deficits in small animals using isotonic solutions
IP = large volumes of electrolyte and water absorption for large animals
IO = catheter into long bone reaches rich capillary beds good for tiny animals where vessels are hard to find
What must be done before IV fluid administration? In what patients does this tend to be difficult?
- check osmolality and rate of administration
- maintain asepsis
small or severely ill patients
How does lactate/acetate act as an alkylating agent?
lactate is an acid produced from pyruvate during anaerobic respiration and it can cause the animal to utilize protons to convert it back into pyruvate
What are crystalloids? What are the 2 types and their usage?
isotonic fluids containing small particles, where it is high in Na+ and low in K+
- ALKALINIZING - metabolic acidosis resulting from diarrhea, renal disease, pre and post-surgical support, trauma, and shock (LRS, Normosol-R, Plasma-Lyte A)
- ACIDIFYING - metabolic alkalosis (saline, Ringer’s, 2.5% dextrose/water in saline)
What 3 molecules do most alkalinizing crystalloid fluids contain? Where are they metabolized?
- lactate - liver
- acetate - muscle
- gluconate - various tissues
(dictates usage - liver disease = no LRS)
What are colloid fluids? What are the 2 types?
fluids composed of large particles that are retained within the vascular space more readily than crystalloids by increasing colloid osmotic pressure (Gibbs-Donnan effect - charged plasma proteins attract positively charged particles)
- NATURAL - whole blood, plasma, albumin
- SYNTHETIC - dextran 40/70, hetastarch, pentastarch, oxypolygelatin
What are the 4 most common uses of colloid fluids?
- perfusion deficits
- hypooncotic states
- deficiency in blood components
- systemic inflammatory response syndrome (SIRS) - increased permeability moves fluid into other tissues
When is colloid fluid usage contraindicated? What are some possible adverse reactions?
oliguric or anuric renail failure due to rapid volume expansion
- anaphylaxis to starch or dextran
- impairment of coagulation (dilution!) - high colloid osmotic pressure move fluid into the intravascular space
What is the traditional usage of hypertonic solutions? How does it work?
resuscitation efforts for rapid plasma volume expansion
increases cardiac output, releases catecholamines, and increases oxygen delivery to the heart
What are the common concentrations of hypertonic solutions? What are 6 common uses?
5%, 7%, 7.7%
- shock associated with hemorrhage
- trauma
- GDV
- acute pancreatitis
- sepsis
- head injury (mannitol effect)
(effects transient - commonly combined with colloids (7% HSS in 6% dextran 70)
When are hypertonic fluids contraindicated?
hypernatremia
