Fluid therapy Flashcards
What percentage of body weight does water constitute in the adult dog or cat?
60%
What are the two major compartments of total body water distribution?
Intracellular and extracellular
What is the osmolarity of the intracellular and extracellular body compartments?
290 to 310 mOsm/L
What is the distribution of total body water between the extracellular and intracellular compartments?
What is the function of the Na+-K+/ATPase cell membrane protein?
Removes Na+ from the cell and transports K+ into the cell consuming ATP in the process
What is the major cation in the intracellular fluid?
K+
What are the major anions in the intracellular fluid?
PO4-2 and polyionic charges of the intracellular proteins
What is the primary cation of the extracellular fluid?
Na+
What are the major anions of the extracellular fluid?
Cl-, HCO3
What is the glycocalyx?
A negatively charged layer of glycoproteins and proteoglycans that creates part of the endothelial barrier
What determines oncotic pressure?
The ratio of proteins between the intravascular and interstitial space
What is the primary component of osmotic pressure?
Albumin
What is the maximum rate that sodium concentration can be increased or decreased in the blood?
Should not be increased by more than 0.5 mEq/h or decreased by more than 1 mEq/h.
What is the formula for determining the volume of replacement fluids required in a patient?
Body weight in kg x percent dehydration PLUS estimated ongoing losses PLUS maintenance
What formula can be used to estimate maintenance fluid requirements in a patient?
What are the physical examination findings in dehydrated patients (based on % dehydration)?
What are the factors that determine oxygen delivery to tissues (DO2)?
What is the result of insufficient DO2?
Conversion from aerobic to anaerobic metabolism and decreased ATP production. Compromise of NaK/ATPase pump leads to disruption of cell membrane and exposure of subendothelial collagent. This causes activation of platelets, the clotting cascade, fibrinolytic system, and bacterial translocation.
What is the goal of hypotensive resuscitation?
Mean arterial pressure of 60 mmHg or systolic BP of 90 mmHg
What are the key recommendations of the 2012 surviving sepsis guidelines?
Early quantitative resuscitation, early sample collection for C&S, administration of ABs within 1 hour, and early administration of norEpi as first line vasopressor
What are the current fluid rate recommendations for dogs and cats under anesthesia?
Dogs: 5 ml/kg
Cats: 3 ml/kg
What is an isotonic fluid?
A fluid with the same osmolarity as the extracellular space
What is a balanced fluid?
A fluid with similar electrolytes to the extracellular space
Is isotonic saline (0.9% NaCl) a balanced or unbalanced fluid?
Unbalanced - contains higher concentrations of Na+ (154 meq/L) and Cl- (154 meq/L) than normal plasma
During rapid equilibration of isotonic crystalloids, what percentage of fluids remain in the intravascular space after 20-30 mins?
25% remain in the vascular space, 75% redistributes to the interstitial space
What is the typical dose of replacement fluids used to maintain hydration?
2-4 ml/kg/hr
What is the most appropriate fluid for resuscitation of a surgical patient with head trauma?
0.9% NaCl - least likely to cause decreases in osmolarity and movement of water in the brain interstitium
What is the most appropriate fluid for patients with severe hyponatremia or hypernatremia?
Crystalloid fluid most closely matched to the patients sodium concentration to prevent rapid changes in osmolarity and central pontine myelinolysis or cerebral edema
What is the most appropriate fluid for a patient with hypochloremic metabolic alkalosis?
0.9% NaCl (highest concentration of Cl)
What is the most appropriate fluid for a patient with severe metabolic acidosis?
Crystalloid with a buffer agent (not NaCl as this is acidifying)
Is a maintenance solution hypotonic, isotonic or hypertonic?
Hypotonic - obligate fluid losses in the normal animal are hypotonic and low in sodium but contain relatively more potassium. Maintenance fluids are designed to replace these losses.
Should maintenance fluids be administered as a bolus?
No - can lead to a rapid decrease in osmolarity and subsequent cerebral edema.
How can free water by safely administered?
Combine with 5% dextrose to yield an osmolarity of 252 mOsm/L
What can occur when rates of hypertonic fluid administration exceed 1 ml/kg/min?
Activation of pulmonary C-fibers, resulting in vagally mediated hypotension, bradycardia, and bronchoconstriction
How long does intravascular volume expansion last following hypertonic fluid administration?
<30 minutes due to osmotic diuresis and rapid redistribution of sodium. Additional fluid therapy should be administered to maintain intravascular volume
What is the difference between the weight average or number average molecular weight when describing synthetic colloid solutions?
Weight average: arithmetic mean
Number average: median (more accurate).
Ratio of the weight and number average is known as the polydispersity index.
What is the most common type of synthetic colloid used in veterinary medicine?
Hydroxyethyl starches
Are high or low molecular weight colloids more likely to interfere with coagulation?
High
How do colloids affect coagulation?
They decrease factor VIII and vWF, impair platelet function, interfere with the stability of clots.
What should be monitored during synthetic colloid administration?
APTT, platelet count and function, and viscoelastic measurement of clotting
What dose of colloids can be administered to patients in hypovolemic shock not responsive to crystalloid therapy alone?
Dogs: 5-20 ml/kg
Cats: 2.5-10 ml/kg
What is acute normovolemic hemodilution?
Blood is collected immediately pre-operative and then replaced with colloids or 3 x volume of crystalloids. Blood lost during surgery is subsequently lower in protein and RBC levels and can be replaced with collected blood if needed.
NOTE: Expensive and minimally beneficial!
What is the rate of pRBC or FFP administration?
10-15 ml/kg
What is the rate of fresh whole blood administration?
20-25 ml/kg
What is the formula for blood transfusion in dogs and cats?
What are the components in fresh whole blood?
All clotting factors and platelets, although platelets are best used within 8-hours and are no longer present after 24-hours. Clotting factors are also non-functional after 24-hours (stored whole blood).
What is the typical hematocrit and storage time of PRBCs?
Hematocrit: 80%
Storage: Shelf life of 20 days at 4 degrees celsius. Extended to 35 days with additive solutions.
What are the advantages of PRBC administration?
Ready availability, low risk for volume overload, reduced exposure to plasma antigens.
What happens with prolonged storage of PRBCs?
Decreased ATP and 2,3-DPG concentrations, increased ammonia, nitric oxide scavenging, oxidative damage, red blood cell deformability, increased procoagulant properties.
What are the components of FFP?
Contains clotting factors, proteins, albumins and globulins.
What is the definition of FFP?
Plasma that is frozen within 6 hours of collection and stored at a temperature below 20 degrees C for less than 1 year.
What are the components of frozen plasma (stored)?
Once stored for more than 1 year, FFP no longer contains labile coagulation factors V, VIII and vWF.
What are the components of cryoprecipitate?
Factor VIII, vWF, fibronectin, fibrinogen
What are the components of cryosupernatant?
Contains all the serine protease clotting factors (including vitamin K-dependent factors II, VII, IX, X), anticoagulant and fibrinolytic factors, albumin and globulin
What are the most common sources of platelet transfusions?
Platelet rich plasma, fresh whole blood, or lyophilized and cryopreserved platelets
What do you need to monitor if blood products are administered rapidly?
Calcium levels as citrate containing products may cause chelation.
What is the dose of desmopressin for perioperative administration in VW patients?
1 mcg/kg subcutaneous
How many canine erythrocyte antigens are known?
Eight. Although clinically significant reactions generally only occur after previous transfusions with dog erythrocyte antigen (DEA) 1 and 7.
How many feline erythrocyte antigens are known?
Two. Type A (most common), type B (Scottish fold, Birman, Himalayan, Somali, Persian, Cornish and Devon Rex, British shorthair).
What anticoagulant should be used for blood storage?
Citrate phosphate dextrose adenine (CPDA-1)
What size filter should be used for blood product administration?
170 um pores
What are the two most common types of transfusion reaction in dogs and cats?
- Transfusion associated circulatory overload (TACO)
- Nonhemolytic febrile reaction (increase in body temp by 1 degree within 30-60 minutes of transfusion, lasting up to 20 hours)
What is transfusion related acute lung injury (TRALI)?
Onset of respiratory distress within 24-hours of transfusion.
Does auto-transfused blood contain clotting factors?
No, it is not a reliable source of clotting factors
What are the primary mechanisms responsible for free water balance in the body?
Vasopressin (antidiuretic hormone) and thirst.
What is the function of the renin-angiotensin-aldosterone system?
If the juxtaglomerular apparatus of the kidney senses decreased extracellular fluid volume (reduced renal perfusion) it releases renin. This is converted to aldosterone (via angiotensin produced in the liver) and results in increased renal reabsorption of sodium and water.
What are clinical signs of hyponatremia?
CNS depression, ataxia, coma, seizures secondary to cerebral edema (occurs at Na+ concentrations less than 120 meq/L or with rates of decrease greater than 0.5 meq/K/hr)
What are the clinical signs of hypernatremia?
Typically seen at levels over 170 meq/L in dogs and 175 meq/L in cats. Severity related more to rapidity than degree. Clinical signs are due to neuronal dehydration and can result in vascular damage and hemorrhage within the brain (lethargy, vomiting, muscle weakness, ataxia, seizures, coma, death)
What is the formula for calculating free water deficit for correction of hypernatremia?
How is free water most commonly replaced?
5% dextrose in water intravenously
What cation is responsible for negative cell resting potential?
Potassium. Extracellular movement down concentration gradients maintains cell membrane potential at -90 mV
What causes intracellular potassium shifting?
Glucose, insulin, catecholamines, metabolic alkalosis.
What causes extracellular potassium shifting?
Metabolic acidosis or hyperosmolarity.
What are the clinical signs of hypokalemia?
Progressive weakness with eventual respiratory collapse at less than 2.0 meq/L
What ECG changes are seen with hypokalemia?
Increased amplitude of p-waves, ST segment depression, decreased amplitude of t-waves, prolonged PR intervals, arrhythmias
What effect does hypomagnesemia have on potassium?
Can cause refractor hypokalemia due to intracellular efflux of potassium and subsequent renal excretion.
What rate of potassium administration should you not exceed?
0.5 meq/kg/hr
What effect does hyperkalemia have on the resting potential of cardiac myocytes?
Resting potential becomes closer to the threshold potential, resulting in rate and rhythm disturbances
What ECG changes are seen with hyperkalemia?
Progressive loss of p-wave, spiked t-waves, shortened QT intervals, prolonged PR interval, and widening of the QRS.
What are potential treatments for hyperkalemia induced cardiotoxicity?
- Calcium gluconate 10% (raises the threshold membrane potential of the cardiac myocyte): 0.5 to 1 ml/kr over 10-20 minutes
- Intravenous dextrose (drives potassium intracellular): 0.5 - 1 g/kg +/- insulin 0.5 to 1 IU/kg.
- Sodium bicarbonate (drives potassium intracellular in exchange for hydrogen ions): 0.5 - 2 meq/kg IV over 15 minutes.
What percentage of calcium is found as hydroxyapatite in bone?
99%, with the remaining 1% divided between the extracellular and intracellular fluid components
What are the three biologic forms of calcium?
- Ionized (active form)
- Protein bound
- Chelated
Does hypoalbuminemia affect total or ionized calcium levels?
Total only
What are the three hormones that help to regulate calcium homeostasis?
- Parathyroid hormone - increases mobilization of calcium from bone.
- Vitamin D (cholecalciferol) - produced in the kidney and increases intestinal calcium absorption.
- Calcitonin - inhibits bone resorption.
What are the three general processes involved in hypocalcemia?
- Impaired parathyroid hormone release
- Impaired vitamin D synthesis
- Chelation/precipitation
What is the treatment for life-threatening hypocalcemia?
10% calcium gluconate (0.5 to 1.5ml/kg intravenous) over 15-30 minutes
What is the most common cause of hypercalcemia in dogs?
Malignancy due to paraneoplastic production of parathyroid hormone related pepite (PTH-rp).
What is the most common cause of hypercalcemia in cats?
Idiopathic.
What are treatment options for severe hypercalcemia?
- Intravenous fluid therapy with calcium free isotonic fluids
- Loop diuretic (furosemide) to promote diuresis
- Glucocorticoids, biphosphonates, calcitonin, sodium bicarb, low calcium diets, calcium channel blockers
What percentage of magnesium is found in the intracellular space?
99%, with the remaining 1% in the intracellular space
What are the three forms of biologic magnesium?
- Ionized
- Protein bound
- Chelated
What determines serum magnesium concentrations?
Intestinal magnesium absorption and renal excretion.
What is the treatment for hypomagnesemia?
50% magnesium sulfate or chloride given at a dose of 0.25 to 1 meq/kg/day as a CRI in 5% dextrose in water
What is the treatment for hypermagnesemia?
Loop diuretics, calcium gluconate, anticholinesterases
What are the roles of phosphorous in the body?
Component of hydroxyapatite, energy for metabolic processes through ATP, maintaining cell membranes as phospholipids, oxygen delivery to tissues (2,3-DPG).
What is the distribution of total body phosphorous?
<1% in extracellular fluid, 15% in intracellular space, 85% as hydroxyapatite in bone.
What determines phosphorous balance?
Dietary intake, GI absorption, renal excretion (under influence of PTH), vitamin D, calcitonin.
What is the treatment for hypophosphatemia?
Potassium and sodium phosphate (0.01-0.06 mmol/kg/hr).
What is the treatment for hyperphosphatemia?
Volume expansion with IVF, glucose (+/- insulin) and phosphate binders (aluminium hydroxide)
Does hypochloremia result in metabolic acidosis or alkalosis?
Alkalosis
How is the chloride concentration evaluated in light of the free water balance of plasma?
What are the hormones involved in glucose regulation?
Insulin, glucagon, epinephrine, growth hormone, cortisol.
What is glycogenolysis?
The conversion of glycogen (stored glucose in the cells) to glucose in the liver during periods of hypoglycemia.
What is gluconeogenesis?
The formation of glucose from lactate and amino acids in the liver during periods of hypoglycemia.
Where is insulin produced?
Pancreatic beta cells in response to hyperglycemia
Where is glucagon produced?
Pancreatic alpha cells in response to hypoglycemia. Stimulates glycogenolysis.
What is Whipple’s triad?
Low blood glucose, clinical signs of hypoglycemia, resolution of clinical signs when blood glucose is normalized
What percentage of hepatic function must be lost before glucose levels are affected?
70%
What is the treatment of hypoglycemia?
Intravenous bolus of 50% dextrose (0.5 g/kg) diluted 1:1 to 1:4 to prevent phlebitis +/- CRI of 2.5-5% dextrose.
If hypoglycemia worsens following dextrose administration (suspect insulinoma), what should you do?
Administer glucagon bolus of 50 ng/kg, followed by CRI of 5-40 ng/kg/min
What is the Henderson-Hasselbalch equation?
Equation that demonstrates how the pH of blood is affected by the ratio of PaCO2 and HCO3-
What are the primary buffers in the body?
Extracellular: Bicarbonate
Intracellular: Phosphate
What does it mean when it says bicarbonate operates in an open buffering system?
As H+ is added to the buffering system more CO2 is produced (equation driven to left). CO2 is then able to be removed through alveolar ventilation to maintain pH.
What is paradoxical aciduria?
Loss of gastric fluid (containing K+, Na+ and HCl) leads to sodium and fluid retention in the kidneys. Due to low Cl the kidney must reabsorb sodium in exchange for K+ and H+. This worsens the metabolic alkalosis but results in aciduria.
What is the anion gap?
The difference between measured cations and anions created by the measurement of only certain particles (NOTE: This is artifactual, if all cations and anions were measured there would be electroneutrality).
What is a common cause of a normochloremic metabolic acidosis with an increased anion gap?
Lactic acidosis or ketoacidosis (because these unmeasured anions maintain electroneutrality without retention of chloride)
When should sodium bicarb therapy be considered?
If the underlying cause of metabolic acidosis cannot be readily corrected or is severe (pH <7.1 or 7.2)
What are the risks of sodium bicarb administration?
Hyperosmolar induced fluid shifts, electrolyte abnormalities, respiratory acidosis due to conversion to CO2, iatrogenic metabolic alkalosis
What is the goal of sodium bicarb administration?
Achieve a blood pH of 7.2
What is the formula for sodium bicarb administration?
