Veterinary Anesthesia Pre- Medications Quiz

Practice Quiz Answers

• Acepromazine is a tranquilizing drug without a reversal agent, and causes enlargement of the spleen.
• Midazolam is a water-soluble benzodiazepine safe for IM administration.
• Methadone is an opioid with effects as an NMDA antagonist.
• Atropine is an anticholinergic drug used quickly in emergent situations.
• Atipamezole (antisedan) is the reversal agent for dexmedetomidine.
• Xylazine is a shorter-acting alpha-2 agonist commonly used in equine practice.
• Butorphanol is a kappa agonist and mu antagonist that blocks the mu receptor without binding.
• Acepromazine is an Alpha 1 antagonist, with its MOA causing vasodilation and potential hypotension.
• Benzodiazepines do not cause reliable sedation in dogs and cats, mainly providing pain relief.
• Simbadol, containing Butorphanol, is FDA-approved for cats and labeled for SQ use every 24 hours.

Benefits of Pre-Medications

• Combining drugs has a synergistic effect, leading to better results with fewer drugs needed later.

Neuroleptanalgesia

• Neuroleptanalgesia is a combination of a sedative and an analgesic drug.
• Examples include acepromazine + Fentanyl, and dexmedetomidine, butorphanol, & ketamine ("kitty magic").

FARAD

• FARAD is the best resource for veterinarians to determine meat and milk withdrawal times in food animals.

Species-Specific Induction Drug Considerations

• Greyhounds metabolize Propofol differently, resulting in prolonged recovery time.
• Use Propofol cautiously in cats, as it can cause hyperthermia with Hydromorphone.

Ketamine and Etomidate

• Ketamine is normally administered with a benzodiazepine which includes diazepam or midazolam.
• Use Etomidate cautiously with patients that have Addison's or are highly stressed.

Anesthesia Administration: Inhalation vs. TIVA vs. PIVA

• Inhalants are administered as vapors, examples are ISO and SEVO
• Equipment includes oxygen containers, CO2 absorption canisters, and ETT tubes
• Compared to SEVO, ISO is less reactive, more potent, has a lower MAC, and causes more respiratory depression, hypotension, hypoventilation, and noxious odor
• SEVO has lower blood-gas parturition, travels faster to the brain, gives a quicker recovery, lower potency, higher MAC, and offers good muscle relaxation, but can trigger malignant hyperthermia
• SEVO generates compound A when degraded by CO2 absorbents
• Both ISO and SEVO decrease cerebral metabolic rate and ventilation, and increase CO2, CO, and BP.
• TIVA is total intravenous anesthesia.
• TIVA is limited to 1 hour due to prolonged recovery times, and still needs supplemental O2.
• An example of TIVA includes a triple drip with ketamine, xylazine, and guaifenesin for equine castration.
• IV automatic flow meters, catheters, fluids, and syringes are used with TIVA.
• PIVA is partial intravenous anesthesia
• MLK with reduced ISO is used for canine TPLO as an example of PIVA.
• IV automatic flow meters, catheters, fluids, and syringes are used for PIVA.

Properties Determining Administration Method

• Important factors of determining the administration method include:
  • Boiling point
  • Liquid density
  • Vapor pressure
• Vapor pressure shows the ability to evaporate
• ISO is unsafe to smell directly and needs a vaporizer for clinical use.
• Vapor pressure is temperature-dependent and unique for each agent.
• Increased temperature raises the amount of molecules liquid and gas phase and increases VP.
• Vaporizers control the amount of anesthetic delivered via bypass and vaporizing chamber.

Properties Determining Kinetics in a Patient

• These depends on Gas solubility
• Low blood/gas partition means it reaches the brain faster
• SEVO has low gas solubility
• High blood/gas partition means it takes longer for it to reach the brain
• A higher anesthetic absorption in the blood increases the induction period.
• High oil/gas partition means drug "likes" to be in a fatty environment
• This leads to it easily crossing the BBB and increasing potency.
• Low oil/gas partition means drug is less soluble in oil
• A higher concentration to reach the brain is needed
• The higher the temperature leads to the less gas dissolving in the solvent.

Factors Affecting Alveolar Anesthetic Tension

• Increased alveolar delivery:
  • Increased inspiration
  • Increased concentration vapor
  • Increased vapor dial
  • Increased O2 flow rate
  • Decreased gas volume of P breathing circuit to reduce mechanical dead spaces from the Y-piece, adaptors, ETT tube, etc
• Increased alveolar ventilation:
  • Increased minute ventilation (reservoir bag TV calc)
  • Decreased dead space ventilation
• Decreased alveolar removal makes it easier for anesthesia to change because the patient stays asleep
• Decreased alveolar removal is caused by decreased blood solubility which includes SEVO, decreased CO, and alveolar-venous anesthetic gradient from the alveoli compared to blood in veins returning to lungs, and takes longer for blood to move from alveoli back into lungs

Gauifenesin

• Gauifenesin should not be administered outside the vein due to the potential for tissue necrosis
• Always administer drug using IVC

Inhalant Anesthetic Metabolism

• HALO is metabolized 20-46%
• SEVO is metabolized 2-5%
• ISO id metabolized 0.2%
• Rest is eliminated through lungs

MAC

• Minimum alveolar concentration (MAC) is the minimum alveolar concentration of inhaled anesthetic at 1 atm that results in immobility in 50% of patients exposed to supramaximal noxious stimulus
• MAC has an inverse relationship with potency
• Higher potency results in decreased MAC, allowing for less drug use, like HALO
• Pre-medications should not be included in the calculation of MAC
• ED95 lies between 1.2-1.4 (95% patients anesthetized)
• Multiple inhalant by 1.5 to get Surgical anesthesia
• Preferred level of ISO is 1.3
• The SEVO level is 2.3

MAC Affecting Factors

• MAC increases with hyperthermia, drugs with increased CNS stimulation, and increased metabolic rate/stress (Cushing's, hyperthyroidism)
• MAC decreases with hypothermia and caution must be taken when a patient is getting too deep, drugs with CNS depression, geriatric patients, pregnancy, hyponatremia, and BP < 50 mmHg.

Loading Dose

• The amount of the drug is increased to reach the therapeutic window, and concentration of the drug stays elevated
• No need to give continuous boluses

MDR1/ABCB1 Gene Mutation

• Mutation in gene code affects herding-breed dogs for P-glycoprotein
• This defect allows drugs (Butorphanol & Acepromazine) to penetrate the BBB, recovers proloned in affected animals
• Adjustments are made by decreasing normal doses by 25-50%

Balanced and Multimodal Anesthesia

• Balanced anesthesia utilizes multiple drugs and techniques to produce anesthesia at the same time.
• Multimodal analgesia uses over 2 drugs or techniques to manage pain
• Morphine, lidocaine, ketamine, and MLK significantly decreased ISO needed. Dexmedetomidine, MLK, and DMLK decreased MAC values.

Risks With Combining Drugs

• Never give glucocorticoids at the same time as NSAIDS, this could cause increased stomach bleeding, ulcers, a synergistic effect and added side effects, steroids decrease immune system which could cause harm to the GI tract lining from NSAIDS

Lidocaine In Horses

• Used to treat ileus, impactions, inflammation, laminitis, post-opt pain, etc.
• Given for 1-3 days and carefully monitored due to potential overdose

Alpha 2 Induced Bradycardia

Alpha 2 induced bradycardia due to increased systemic vascular resistance (SVR) in periphery where BP initially increases, decreased sympathetic tone b/c decreased NE / catecholamines in CNS and vasodilation

• ex) Xylazine, detomidine, dexmedetomidine.

Fluid Variation By Species

• Kangaroo rats don't need to drink water and can consume increased foods that have it, however cats are more susceptible to fluid overload.

Fluid Therapy Origins

• Fluid therapy originated from the Cholera epidemic.

Spleen in Horses

• The spleen autoinjects 2-3 liters of blood into the vascular system where half of the water is contained and can last longer (8-9 days) without water.

Calculating Fluid Overload

• In patients its over 10% of body weight, this can be used to identify its importance when administering fluids.

Plasma

• 95% plasma without RBCs is equal to H2O

Organ Response to Fluid Overload

• Result in:
  • Pulmonary edema due to impaired gas exchange and increased muscle use
  • Gut edema specifically found in ruminants with chronic fluid overload
  • Cerebral, myocardial, and tissue edema
  • Hepatic congestion
  • Increased renal venous pressure and impaired lymphatic drainage

Blood Volume and Fluid Flux

• Blood volume is 8% of body weight
• Aspects of transvascular fluid flux:
  • Capillary colloid osmotic pressure: pressure exerted by proteins (albumin) to pull water into circulation, value changes and is limited by molecular size so people can have greater influence when making fluid bags
  • Capillary hydrostatic pressure

Endothelial Glycocalyx

• Acts as "gatekeeper" for fluid that is present on blood vessel walls, prevents leaking, maintains fluid balance, prevents edema, and maintains vascular permeability

Interstitium Fluid Dynamics

• Interstitium refers to a fluid-filled space made of flexible connective tissue that stretches with increased fluid volume and condenses with decreased volume
• Normal ranges of 2 to -3 mmHg
• Inflammation with increased tension from -10 to -20 mmHg, this usually signifies a regulatory mechanisim issue
  • ex) kidney/gut function
• Dynamic space is associated with IV fluids and helps reduce hypotension when using excess fluid
• Dynamic space presents "over-stretching" of interstitium during distribution

Functions of Fluids

• Treat dehydration greater than 5% of body weight, acidosis and hyperkalemia begins
• Prevent hypovolemia to over 15-20%
• Main hydration 30-60 mL/kg a day
• Treat hypotension when under 60 mmHg, and decrease anesthetic dept with analgesics or ultrasound guided nerve blocks, dynamic monitoring, vasoactive drugs, and fluid pre-load
• Maintain acid-base balance, electrolytes and calories around 50-100 Cal/kg a day since it provides good access to vein

Caution For Fluid Treatment

• Exercise caution with excess fluid treatment for initial dehydrated patients to avoid excess fluid in cells
• Rehydrate slowly (16-36 hrs) with NaCl and colloids

Issues Seen With Anesthesia on Dogs

• Arousal and breaks through from pain at 15%
• Hypoventilation at 14%
• Hypotension at 10-15% is measure of 'quality anesthetic care' is a result with disturbing normal drugs and normal homeostatic
• Can also be due to hypothermia, hypercarbia, acidemia, hyperkalemia, arrhythmia, and sepsis

Mechanism of Hypotension

• Hypotension is caused by increasing circulation from the arteries to the veins that creates relative hypovolemia
• Normally veins carry a larger blood volume, 70%, and the arterial system holding 10%

Compensation

• Compensation include decreased pressure and stimulation, altered blood gases that removes chemoreceptor reflex and there is a loss of lympathic return
• Treatment with potassium at the golden hour to prevent death from the the likely chance of medical or surgical use like splenic entrapment in horses with the use of alpha-1 agonist
• If at 45 mmHg, the circulatory system begins turning off organ functions to save the animal ex. kidneys

Classifications of Volume Loss

• Decreased circulating volume that's sympathetically driven
• Loss of 10-15%, animal looses the ability but healthy animals have some compensation
• Loss of 15-30% and causes a danger zone of hypovolemia, hypotension, high HR and BP but organ use is maintained -Loss of 30-40% is an uncopensated class III blood loss

Blood Volume Loss

• Losing over 50% can decrease the survival rate by 50%
• Tonicity depends on the plasma where it moves from inside and outside of a cell effectively through osmosis and stay within the compartment to prevent fluid shift

Colloid Osmotic Pressure

• Colloid pressure uses soluble molecules that stay in tissue and avoid inadequate fluids to allow the molecules from entering and leaving
• Not routinely use in human medicine as toxic colloids contain allergic reactions that create renal failure

Fluids As Drugs

• Body recognizes fluids as drugs that effectively change their electrotype, osmolarity, viscosity, or change pH values
• Fluid type are a saline group of NaCl, K and Cl electrolytes that have their glucose level like blood cells, and use animal buffer and are not electrolytic balance

Fluid Products

• Invented by Hartmen the Lacted ringers consist of NaCl, K, Ca, 29 that converted to HCO3 buffers, can also use donor that mimic electrolytes and the balance balance in ECV that produced vascular output
• They can retain their size and rate while the fluid is in circulation depends what is in it as well

Fluid Distribution

• Most tissues have around 60% of the tissue volume.

Bolus

The fastest to receive are muscle and vessels which allow a low pressure of output and they dont do anything for fluids

Considerations for Medication

• Determine choice, rate, time, volume, and length for their treatment to increase the pressure

Fluid Therapy

• Fluid therapy can reach 40-60 mL/kg/hr, 60 being the max dose and risk for death and edema because its NOT actively being used for nurishment

Arterial and Venous Pressure

• Maintaining a certain pressure level will not prevent fluid overload
• Can read fluid, or saturation with pluses that may determine variability

Fluid Resistance

• May see 25-75% of animals be resistant with heart failure and anesthetic shock

Most Common Pain Therapy

• ICE slows down pain receptors by using conduction.

Pain Defined

• Pain is unpleasant and emotional experience with actual or potential tissues and detection from mechanism with stimuli/ feeling its effects

Nociception Pathway

• Pathway moves through skin and effects the brain, nervous system has a coding system and may have a tissue or nontissue that will stimulate receptor and channel with a protective system when the removal and sensitive touch with receptors

Pain in Detail

• Pain that causes for injury depends on a response with mechanical thermal injury with certain fibers that cause dull pain which causes mediators with cells and is also very common with patients due to increased rates with changes

Limbic System

• Affects cortex, hipocampus, and amygdala, with pain and some drugs will target for its pain

Pain Sensitivty

Some cause amplification that cause state depending with spinal and nerves for sensitivty that increase rates and create inflammation due in the gliael cells that may cause