Week 8 - Fluids, Anesthetizing Specific Conditions

Why are fluids almost always necessary peri-operatively?

- Anesthetics result in "relative hypovolemia" due to myocardial depression, vasodilation, blunted SNS responsiveness, and ongoing obligatory losses

Total body water in a dog is _____________% of body weight. ___________% of body weight (1/3 of total water) is intravascular fluid and __________% of body weight (2/3 total water) is extravascular fluid.

- 60

- 20

- 40

What determines fluid distribution in the body?

- Presence of membranes that restrict/control movement of certain substances that can act as effective water barriers and pressures including the cell membrane between extravascular and intracellular space, and the capillary endothelium (and glycocalyx) between the intravascular and interstitial space

What are the effective "osmoles" in the following spaces?

A. Intracellular

B. Extracellular

C. Interstitium

- Na+

- K+

- Macromolecules (albumin)

What is osmolarity?

- Measure of the number of osmoles/liter of solution

What is tonicity?

- Measure of effective osmolarity dependent on semipermeable membrane, generally expressed relative to plasma tonicity

The tonicity of plasma is primarily the result of which electrolyte?

- Na+

Describe the movement of molecules between the vascular and extravascular space.

- Osmoles move freely between vascular & extravascular space (movement partially limited by cellular membranes)

- Colloid movement is limited by membranes (vascular walls) which creates oncotic pressure

Which electrolytes are higher in the ECF?

- Na+, Ca++, Cl-, HCO3-, Proteins, Glucose

Which electrolytes are higher in the ICF?

- K+, Mg++, Phosphate, other

What is the total osmolarity of the blood?

~290 mOsm/L

Describe how the Na/K gradient between the ECF and ICF is maintained.

- Na/K ATPase pump in cellular membranes

- Body spends a lot of energy maintaining cell membrane integrity (consider cases of shock)

Which "space" do we have access to for fluid administration?

- ECF

The only safe, effective osmole for extracellular administration is ___________.

- Na+

Define hypotonic solutions in regards to sodium and its distribution.

- [Na+] = 0 or < plasma [Na+]

- Distributes throughout all fluid compartments

Define isotonic solutions in regards to sodium and its distribution.

- [Na+] ≅ plasma [Na+]

- Distributes to the extracellular space

Define hypertonic solutions in regards to sodium and its distribution.

- Na+] > than plasma [Na+]

- Transiently increases intravascular space -> Redistributes throughout extracellular space -> May then draw fluid from intracellular space

What is a "colloid"?

- Large macromolecules impermeable to capillary membrane (Naturals include albumin and globulin while synthetics include sugars, starches, and proteins)

- Colloids are 'active' molecules that produce an effect by 'drawing' or 'pulling' water across a semipermeable membrane (eg, capillary membranes)

Without colloids, describe the distribution of water. What about colloids?

- Without colloids - water freely distributes out of vascular space

- With colloids - water is retained within the vascular space

What are the types of parenteral fluids? Briefly describe them.

- Crystalloids: Contains ions or solutes that may redistribute to all fluid compartments w/in the body

- Colloids: Contain large macromolecules that remain predominantly w/in the intravascular space and subsequently hold water in the intravascular space

What are indications for crystalloids? What are indications for colloids?

- Crystalloids: Ongoing fluid administration

- Colloids: Resuscitation, to maintain oncotic pressure

How are crystalloids classified?

1) Electrolyte composition

2) Tonicity

3) Effect on acid/base status (plasma pH)

What is the difference between crystalloid fluids used for replacement and crystalloid fluods used for maintenance in regards to electrolyte composition?

- Replacement: Electrolyte composition is similar to extracellular fluid or plasma

- Maintenance: Electrolyte composition is not the same as extracellular fluid (usually low Na+, high K+, and often contain glucose - effectively hypotonic relative to [Na+])

What is an example of an acidifying fluid?

- 0.9% NaCl -> Produces a hyperchloremic metabolic acidosis

What are some examples of alkalinizing fluids?

- LRS (lactate metabolized to HCO3- by the liver)

- Normosol/Plasmalyte (acetate metabolized by muscle to HCO3-)

- Normosol/Plasmalyte (gluconate metabolized to HCO3- by most cells)

What are "routes to the extracellular space"? Which are actually effective under anesthesia?

- Oral

- IO - Effective under anesthesia

- Intraperitoneal

- SubQ

- IV- Effective under anesthesia

What are anesthetic fluid maintenance rates for dogs, cats, and large animals?

- Dogs: 5 mls/kg/hr

- Cats: 3 mls/kg/hr

- Large animal: 3-5 mls/kg/hr

What are shock dose fluid rates in dogs, cats, and large animals (These are essentially obsolete now)?

- Dogs: 90 mls/kg/hr

- Cats: 60 mls/kg/hr

- LA: 45 mls/kg/hr

When are fluids recommended to mitigate hypotension?

- If the patient has an absolute fluid deficiency (otherwise there is risk of fluid overloading)

What is the appropriate rate/dose for a fluid bolus?

- 3 to 5 ml/kg

- ¼ shock dose over 15 minutes

Which electrolyte is cardiotoxic when given at high rates?

- Potassium

What is the recommended maximum rate for potassium containing fluids?

- 0.5 mEq/kg/hr

What are some albumin containing products?

- Whole blood

- Plasma

- Packed RBCs (only if re-suspended in a colloid)

What are some synthetic colloid containing/complex CHO solutions?

- Dextrans

- Hetastarch

- Pentastarch

What are indications for colloid fluids?

- Whole blood product therapy

- Colloidal therapy (Hypoproteinemia and hypoalbuminemia)

- Hypotension mitigation

- Volume replacement

What are some side effects of colloidal fluid therapy?

- Anaphylaxis to whole blood products

- Anaphylaxis to synthetic colloids

- Renal injury (sepsis)

- Fluid overload with cardiac failure patients

- Coagulopathy (platelet dysfunction)

Colloidal fluid therapy is given at _____________ the rate of crystalloid fluid therapy.

- 1/3

The larger the molecular weight of a colloidal therapy, the...

- Longer it lasts and more potential side effects there are

What are the maximum doses for colloidal fluid therapy?

- Cats: 5 -10 mls/kg/24 hrs

- Dogs, horses: 10 - 20 mls/kg/24 hrs

- Maximum of 3 days

What blood products are available?

- Whole blood (Fresh vs. stored)

- Packed RBCs

- Fresh frozen plasma

- Platelet concentrates

- Frozen or stored plasma

What are some indications for blood products?

- Hypovolemia due to acute hemorrhage

- Anemia, hemoglobinemia (normovolemic, hypovolemic)

- Coagulation disorders

- Hypoproteinemia

- PCV < 20% or TPP <4 mg/dL

If you detect a blood transfusion reaction, what should you do?

- Stop the transfusion

- Antihistamines/steroids?

What are the "big 3" clinically important electrolytes that have direct effects and impact on patient management under anesthesia?

- Calcium

- Magnesium

- Potassium

In order for fluids to remain intravascular they must have a ____________ component.

- Colloid

Describe the relative cost associated with crystalloid vs. colloid fluids.

- Crystalloid fluids: Cheap

- Colloid fluids: Expensive

Resistance to fluid flow rate/administration is proportional to what?

- The radius of the catheter (Maximal rate of administration limited by vascular access, so you may need to place a second catheter in the event of a hypotensive crisis)

What is the number one cause of hypotension under anesthesia?

- Too much anesthesia

What is the effect of many/most anesthetics on the cardiovascular system?

- Hypotension

- Bradycardia (cats are HR dependent and dogs with DCM are HR dependent)

- Decreased contractility

- Decrease vascular tone (relative hypovolemia, after preload/afterload)

What is fundamental to to anesthetizing a patient with cardiovascular complications?

- Adequate delivery of oxygen (Tissue hypoxia is a hallmark of shock and heart failure)

Patients with pre-existing cardiovascular disease have decreased _________________ ______________ and are therefore less able to compensate for anesthetic-induced changes.

- Reserve capacity

What do heart murmurs indicate?

- There is turbulent flow through the heart (could be neonate-innocent murmur, could be viscosity related, not necessarily pathophyiologic)

What laboratory data may be abnormal in a patient with cardiovascular abnormalities?

- Increased BUN/creatinine

- Increased liver enzymes

- Polycythemia/anemia

- Electrolyte abnormalities (diuretic therapy)

What is an essential method for evaluating cardiac enlargement on thoracic radiographs?

- Vertebral heart score

Describe the classes for mitral insufficiency.

- A: A patient who is predisposed (i.e., a poodle)

- B1: Murmur

- B2: Radiographic changes + murmur

- C: In failure

- D: Going to die soon

What diagnostic provides the best information about patients with cardiovascular complications?

- Echocardiography

What are ideal characteristics for anesthetic agents in a patient with cardiovascular complications?

- Minimal cardiovascular effects

- Short duration of action

- Reversible

What are ways to support cardiovascular and respiratory functions during anesthesia in a patient with cardiovascular complications?

- Inotropes (dobutamine)

- Chronotropes (anticholinergics)

- Pressors (norepinephrine)

- Antiarrhythmics

- IPPV

- Fluids

Patients with cardiovascular complications are susceptible to volume _________________.

- Overload

What is an appropriate maintenance fluid rate for patients with cardiovascular complications?

- Maintenance rates reduced (3-5 mls/kg/hr)

What are some good options for pre-anesthetic sedation of SA patients with cardiovascular complications?

- Opioids +/- benzodiazepines

- Acepromazine

- Zenalpha (Alpha-2 agonist with vasodilating agent (no afterload))

- Use anticholinergics with caution/judiciously

True or false: The use of alpha-2 adrenergic agonists should be avoided in SA patients with cardiovascular patients. Why?

- True (except for in cats with HCM)

- Dexmedetomidine dilates the ventricle and slows down the HR (Improves CO in cats with HCM)

- Note: Ketamine is contra-indicated in cats with HCM (speeds up HR -> Drops CO)

What are some good options for IV anesthetic induction of SA patients with cardiovascular complications?

- Alfaxalone

- Propofol

- Ketamine?

- Etomidate

What are some options for anesthetic maintenance of SA patients with cardiovascular complications?

- Isoflurane or sevoflurane

- TIVA/PIVA (Alfaxalone)

- + Opioid (i.e., Fentanyl CRI)

- + local anesthetics if appropriate

What are some good anesthetic options for cats when you don't know whether they have a valvular insufficiency or HCM?

- Alfaxalone with an opioid IM pre-medication

What are some good anesthetic options for dogs when you are unsure of their exact cardiovascular pathophysiology?

- Alphaxalone and possibly Acepromazine

What is a good pre-anesthetic option for large animals with cardiovascular complications?

- Low dose alpha-2 adrenergic agonist and high dose opioid

- Avoid acepromazine

What is a good option for anesthetic induction of large animals with cardiovascular complications?

- Ketamine and benzodiazepine and/or guifenesin

What is a good option for anesthetic maintenance of large animals with cardiovascular complications?

- Isoflurane or Sevoflurane

Methadone is a mu agonist, but also an NDMA antagonist. Ketamine is also an NDMA antagonist. Why is methadone safer for the heart?

- Ketamine increases the HR, meaning it is usually contraindicated in patients with cardiovascular complications.

- Methadone is not the same as the dissociative NDMA antagonists and does not increase the HR

What is a challenge of preliminary evaluation of patients with respiratory disease?

- Physical exam & obtaining laboratory data may be difficult w/o significant stress (may need sedation and/or anesthesia - a dilemna)

What diagnostic is the best way to evaluate ventilatory function and oxygenation?

- Arterial blood gas

What values on an arterial blood gas indicate the following?

A. Hypoxemia

B. Hyperventilation

C. Hypoventilation

A. PaO2 < 60 mm Hg

B. PaCO2 < 30-40 mm Hg

C. PaCo2 > 50-60 mm Hg

Why may arrhythmias occur in a patient with respiratory disease?

- Secondary to hypoxia, hypercarbia

- Primary

- Can be related to thoracic trauma

Describe how to appropriately induce a patient with pre-existing respiratory disease.

- This has the potential to be the most catastrophic of all inductions

- Be prepared (Assortment of ETT, stylets, tracheotomy kit, suction, laryngoscope, plenty of light, monitors)

- Pre-oxygenate

- Rapid induction with goal of rapid control of airway

What are some SA pre-anesthetic options for patients with pre-existing respiratory disease?

- Acepromazine/Benzodiazepines/low dose opioids

- Alpha 2 agonists - low dose

What are some SA induction techniques for patients with pre-existing respiratory disease?

- Propofol - Alphaxalone - Etomidate (fastest and etomidate has the least respiratory depressant)

- Ketamine/Diazepam (slower, poorer intubation quality, little respiratory depression)

- Mask, neuroleptanalgesic techniques (slowest, usually a poor choice)

What are options for maintenance of anesthesia in patients with pre-existing respiratory disease?

- Inhalant of choice

- Supplement with local anesthetic techniques if applicable

- TIVA/PIVA, especially for BAL

What are the big 3 respiratory diseases we anesthetize patients with?

- Brachycephalic syndrome

- Lar par

- Thoracic neoplasia

How does one assess hepatic function?

- Bile acid assay

- Baseline ammonia

- Ammonia tolerance

What do liver enzymes indicate about hepatic function?

- Not much; Can have extraordinarily high enzymes with okay liver function

What blood values are we particularly interested in with patients with liver diseases?

- Glucose

- BUN

- Albumin

- Coagulation

- Bilirubin

- Cholesterol

What values on a serum chemistry can be non-specific indicators of hepatic/biliary damage (not hepatic function)?

-AST, ALT, GGT

Is there a family of anesthetic drugs that completely bypass the liver? Is there a family of anesthetic drugs that almost nearly bypass the liver?

- No

- Yes -> Inhalant anesthetics

Is there a "liver safe" anesthetic protocol?

- No

- If only liver enzymes are elevated, usually no problem anesthetizing them; With liver insufficiency, some drugs are not recommended

What are some consequences of hepatic disease?

- Hypoglycemia

- Encephalopathy

- Ammonia

- Colloid oncotic pressure reduction due to hypovolemia -> Edema formation and sensitivity to vasodilators

- Coagulopathies

- Ascites

- Portal hypertension

What is an important PK alteration in patients with hepatic disease?

- Increased free drug (active drug) due to decreased protein binding

What are some pre-operative prepatory steps to take in patients with hepatic disease?

- Glucose supplementation if BG < 60-70

- Consider lactate/lactate metabolism and avoid LRS, use Norm-R

- Evaluate coagulation profile

- Provide colloidal support (plasma/albumin/vetstarch/hetastarch) if albumin is less than 1.5

What are some drugs which are problematic for the liver?

- Acepromazine

- NSAIDs

- Benzodiazepines

- Propylene glycol

What are some "good liver drugs"?

- Opioids

- Alpha-2 adrenergic agonists

- Propofol

- Alfaxalone

- Ketamine (?)

- Local anesthetics

- Inhalant anesthetics

What makes a drug a "good liver drug"?

- Easy hepatic biodegradation

- Extra-hepatic biodegradation

- Little to no hepatic biodegradation

- Reversible

What are some good pre-medication options in patients with hepatic disease?

- Opioid alone

- Alpha-2 agonist

- Alfaxalone

What are some good induction options in patients with hepatic disease?

- Propofol or alphaxalone

- Inhalant

What blood value should one consider monitoring intra-operatively in a patient with hepatic disease?

- Blood glucose

True or false: In patients with hepatic disease, lower doses of drugs are important. Use the lowest dose possible to effect.

- True

What change is common post-correction of a PSS in surgery?

- Portal hypertension

What are some renal functions?

- Regulation of extracellular water balance

- Regulation of electrolyte balance (resorption, excretion)

- Regulation of acid/base balance (long term maintenance)

- Excrete nitrogenous waste

- Metabolize and excrete various drugs

- Hormone production (EPO)

What are some consequences of renal disease?

- Unpredictable intravascular volume (hypervolemic in anuric renal failure and hypovolemic in polyuric renal failure)

- Azotemia (alters BBB - increased CNS sensitivity, interferes with platelet function)

- Hyperkalemia (inability to excrete K+ which is worsened by acidosis; Movement of H+ ions intracellularly results in movement of K+ ions extracellularly)

What values on a chemistry profile and CBC should be particularly paid attention to in patients with renal disease?

- BUN, creatinine

- Hyperkalemia

- Hyperphosphatemia

- Anemia

Both urea and creatinine are excreted primarily by glomerular filtration in the kidneys, but _____________ has a steady state release into circulation while ____________ is influenced by many non-renal parameters.

- Creatinine

- Urea

There must be an over _________% reduction in GFR before creatinine/urea concentrations rise due to the kidney's significant reserve capacity.

- 75