Lecture 21 11/25/24 Flashcards
How does body water relate to body weight?
-total body water equals 60-70% of body weight
-intracellular fluid volume equals approx. 40% body weight
-extracellular fluid volume equals approx. 20% body weight
What is the principle extracellular cation?
sodium
What is the principle intracellular cation?
potassium
What are the characteristics of plasma proteins?
-net negative charge
-important role in vascular volume
What are the characteristics of osmosis?
-process by which water is drawn across a semi-permeable membrane in response to presence of osmotically active particles
-impacted by sodium, potassium, chloride, and glucose
What is osmotic pressure?
theoretical pressure that would have to be applied against the semipermeable membrane to prevent movement of water by osmosis
What is osmolality?
number of osmoles of solute per KG of solvent
What is osmolarity?
number of osmoles of solute per L of solution
What is the normal ECF osmolality?
300 mOsm/kg
Which molecules contribute 95% of total osmolality of plasma?
-sodium
-potassium
-chloride
-bicarb.
-urea
-glucose
What are the characteristics of tonicity?
-measure of osmotic pressure gradient between two solutions
-influenced only by solutes unable to cross semipermeable membrane
-used to categorize fluids as hypotonic, isotonic or hypertonic based on how they compare with plasma tonicity
What are effective osmoles?
molecules unable to cross the semipermeable membrane
What are the characteristics of transcapillary fluid movement?
-fluid shifts between interstitial and intravascular compartments maintain the intravascular fluid volume
-balance between hydrostatic pressure and oncotic pressure favors or opposes fluid movement between compartments
What are the characteristics of hydrostatic pressure?
-independent of osmotic and oncotic pressures within blood vessels
-hydrostatic pressure is higher than that of the ISF compartment at the arterial end of a capillary; fluid is forced from intravascular to interstitium
-hydrostatic pressure is lower at the venous end of the capillary; fluid is not forced out of the vessel
What are the characteristics of osmotic pressure?
-exerted by proteins in plasma, namely albumin
-pulls/maintains fluid into intravascular space
-opposing force to hydrostatic pressure
-important for the maintenance of intravascular volume
What is the consequence of hypoproteinemia?
fluid can be shifted into the interstitium, resulting in edema
What is normal for the vascular endothelium?
selective permeability to larger molecules such as proteins
What are the characteristics of the endothelial glycocalyx layer?
-intraluminal hydrated gel in the vascular endothelium layer consists of glycoproteins, polysaccharides, and proteoglycans
-protective barrier between vessel wall and moving blood
-has a main role in transvascular fluid exchanges
-permeable to electrolytes and fluids but not larger molecules like albumin
What can perturb the endothelial glycocalyx layer?
-trauma
-sepsis
-diabetes/hyperglycemia
-electrolyte imbalance
-surgery
-overzealous fluid management
Why is fluid therapy an important component of anesthesia?
-optimize and maintain cardiac output and tissue perfusion
-maintain electrolyte conc. and acid-base balance
-replace fluids not being gained due to reduced intake
-replace ongoing fluid losses
-replace fluids lost to surgical bleeding/hemorrhage
-expand intravascular volume to offset vasodilation caused by anesthetic agents
-maintain intravenous catheter patency
-improve blood pressure
-maintain caloric balance
-address fluid resuscitation
-correct dehydration
What are the steps of goal-directed fluid therapy?
-recognize which fluid compartment deficit/s exist
-understand which fluid type and admin. route will best replace each deficit
-calculate fluid dose and admin. rate
-monitor patients for response to therapy and signs of complications
What is the order for addressing patient fluid deficits?
-treat hypovolemia/intravascular fluid space
-treat dehydration/interstitial fluid space
-treat free-water deficit/intracellular fluid space
How are intravascular fluid space deficits assessed?
*patient history: trauma, V+, D+, decreased water intake, fever
*perfusion parameters: mentation, HR, CRT, MM color, extremity temp., pulse quality
*BP: hypotension
*ECG: arrhythmias
*labs: hyperlactatemia, metabolic acidosis, decreased PCV/TS
*imaging: microcardia, small/collapsable vena cava
What is absolute hypovolemia?
-decreased fluid volume within the vascular space
-often due to hemorrhage
What is relative hypovolemia?
-inappropriate fluid redistribution
-due to pathological vasodilatory state, inhalant anesthesia, or vasodilatory drugs
Which parameters are used to assess interstitial fluid space deficits?
-decreased skin turgor
-decreased mucus membrane moisture
-increased PCV
-increased TP
-increased BUN
-increased urine osmolality
-increased USG
What are the characteristics of dehydration?
-typically a loss of interstitial space fluid
-water from intracellular space will also be reduced
-hypovolemia occurs in severe cases
What are the clinical signs of the different stages of dehydration?
-<5%: not detectable
-5-6%: some change in skin turgor
-6-8%: mild decreased skin turgor, dry mucous membranes
-8-10%: obvious decreased skin turgor, retracted globes within orbits
-10-12%: persistent skin tent due to complete loss of skin elasticity, dull corneas, evidence of hypovolemia
->12%: hypovolemic shock, death
How are intracellular fluid space deficits assessed?
-patient sodium conc.
-solute-free water deficit/free water deficit
What are the characteristics of crystalloids?
-long term correction of dehydration
-used most frequently
-water based solutions w/ small molecules permeable to capillary membrane
-interstitial compartment replacement solutions
-treat dehydration, electrolyte imbalances, hypovolemic shock, and free water deficits
-only 10-25% of crystalloids volume persists in vasculature 30-60 mins after admin
Which fluids most closely resemble extracellular fluid?
-isotonic
-high in sodium
-low in potassium
What are the characteristics of buffered isotonic crystalloids?
-commonly used
-composition resembles that of extracellular fluid
-ideal to replace ongoing losses, isotonic dehydration, treat hypovolemic shock, and correct electrolyte imbalances
-alkalinizing solutions
Which compounds may be added to form balanced electrolyte solutions?
-KCl
-Ca
-MgSO4
Which compounds should not be administered in the same port as calcium?
-whole blood
-HCO3-
What are the characteristics of NaCl 0.9%?
-isotonic but unbalanced
-compatible with many drugs, blood products, and anticoags
-large IV volumes can produce hyperchloremic metabolic acidosis and predispose to post-op vomiting
-indicated in metabolic alkalosis
What are the characteristics of hypotonic crystalloids?
-contain excess water
-administered in slow infusion
-used in hypertonic dehydration or maintenance/daily requirements in patients with inadequate intake
What are the characteristics of dextrose solutions?
-isotonic only as administered
-dextrose is metabolized to provide energy, leaving behind “free water” and a hypotonic solution
-hypertonic when administered with other balanced electrolyte solutions and approaches isotonicity as dextrose is metabolized
What are the characteristics of hypertonic crystalloids?
-used in emergencies such as hypovolemia/shock
-given in 4-6 ml/kg IV bolus to rapidly restore circulating volume
-draws extravascular fluids into intravascular space
-followed by isotonic solutions to maintain circulating volume and replenish interstitial and intracellular volumes
-avoid in severely dehydrated/hypernatremic patients
What are the characteristics of colloids?
-water based solutions with both small/permeable and large/impermeable molecules
-intravascular volume replacement solutions
-natural colloids include plasma, blood, albumin, and oxyhemoglobin
-synthetic colloids include large molecules in NaCl 0.9%
What are the characteristics of hydroxyethyl starch?
-immediate/sustained increase in hemodynamics with comparatively lower risk of fluid overload
-100% of infused volume still in vessels one hours post-admin
-followed by crystalloid therapy
-cons include interference with cross-matching, interfering with hemostasis, expensive
Which blood/blood products are natural colloids?
-fresh whole blood
-packed red cells
-fresh plasma/fresh frozen plasma
-human serum albumin
-oxyglobin
-cell-free crosslinked bovine hemoglobin
-canine albumin
What are the characteristics of IV fluid admin?
-patients under anesthesia
-patients with severe fluids/perfusion deficits or acute fluid losses
-patients NPO
-safe delivery of large fluid volumes/hypertonic fluids
-risk of infection and phlebitis
What are the characteristics of intraosseous fluid therapy?
-emergency route when IV access is not possible
-like a large central vein but without the collapse
-risk of infection and fracture
What are the characteristics of SQ fluid therapy?
-no evidence-based info for volume, frequency. or adverse side effects
-not effective in edematous and hypo-perfused patients
-should be avoided in euhydrated patients
-good for outpatient fluid therapy
-avoid excessive tissue distention
What are the characteristics of oral fluid therapy?
-should be used whenever possible
-can use feeding tubes if animal is anorexic
-can be used to correct mild dehydration or to supplement parenteral routes
-useful in dehydrated patients that cannot tolerate IV fluids
What are the components of total fluid requirement?
-resuscitation rate
-rehydration rate
-maintenance rate
What is the resuscitation rate for different species?
-given over 15 minutes
-cats: 5-10 ml/kg
-dogs and horses: 10-20 ml/kg
What are the characteristics of ongoing fluid loss replacement?
-done over 24 hours
-calculate dehydration vol. in L by taking dehydration % x BW in kg
-replaces losses due to GI loss, wounds, kidney disease, and inadequate intake
What are the daily fluid needs?
-total of 50-65 ml/kg/day
-approx. 20 ml/kg/day lost in urine
-approx. 10 ml/kg/day lost in feces
-approx. 20 ml/kg/day lost to skin/respiration
-40-60 ml/kg/24h is the maintenance rate
What are the fluid losses that must be accounted for during anesthesia?
-insensible water loss: 0.5 ml/kg/h
-extravasation due to surgical trauma: 1 ml/kg/h
-sensible loss: 0.5-1 ml/kg/h
What are the characteristics of hypoglycemia?
-must be accounted for in hypoglycemic patients and pediatric toy breeds
-corrected with 2.5% dextrose solution
What are the characteristics of acute surgical blood loss?
-fluid rate up to 10 ml/kg/hr while surgically correcting tissue
-3X crystalloid volume to replace 1X volume of blood lost
-colloid can aid perfusion if blood products are unavailable and patient’s perfusion is compromised
What are the characteristics of hypoproteinemia?
-canine albumin used when TS = 2.0 g/dL
-colloid followed by crystalloid used when TS = 4.0 g/dL
-fresh frozen/frozen plasma should be used when available
What are the characteristics of patients with renal disease?
-correct dehydration prior to anesthesia
-optimize cardiac output with appropriate anesthetic protocol
-closely monitor and manage blood pressure
-avoid rectifying hypotension with excessive fluid infusion rates
What should be monitored when a patient is on fluid therapy?
-pulse rate/quality, BP, pulse ox
-CRT, MM, skin turgor
-resp rate/effort, lung sounds
-body weight
-urine output, USG
-mental status
-extremities temp.
-venous and arterial blood gases
-PCV/TS/lactate/creatinine/electrolytes
What aspects of the fluids should be considered in monitoring?
-duration of anesthesia
-total vol. of IV fluids
-max of 20 ml/kg per single anesthetic episode
-do not exceed rate of 5 ml/kg/h for extended periods unless significant blood loss occurs
-calc. daily maintenance rate volume to determine total fluid admin. per anesthetic event
What are the signs of fluid overload?
-weight greater than 10% from baseline admission
-gallop sound/new murmur
-tachypnea
-pulmonary crackles
-low SpO2
-peripheral tissue swelling or chemosis
-clear nasal discharge
-pleural effusion/ascites
-electrolyte or acid-base disturbance
-hemorrhage exacerbation
-hemodilution
What should be done if fluid overload occurs?
-stop fluid admin.
-use furosemide in patients with pulmonary edema or pleural effusion development
What are the consequences of fluid overload?
-pulmonary edema
-cerebral edema
-myocardial edema
-increased renal venous pressure
-renal interstitial edema
-gut edema
-tissue edema
-impaired lymphatic drainage
-microcirculatory derangements
What are the takeaways of anesthesia fluid therapy?
-do not withhold water pre-op
-most animals do not require fluids post-op
-return patients to normal eating and drinking asap
-anorexic patients may need post-op fluids and SQ fluids at home
-all patients need IV catheter
-administer balanced isotonic crystalloid fluids
-assess fluid deficits
-maintain MAP > 60 mmHg to maintain perfusion
