General Anesthesia Flashcards
What proportion of anesthesia or sedation related deaths occur for the following taxa: humans, dogs/cats, small mammals, reptiles, birds, wildlife?
What is bispectral analysis?
In people, what are the established levels of hypnosis with bispectral analysis? (0-100)
At what point is anesthesia occuring?
How are these devices set up to monitor?
Fowler 7 Ch 19 - Depth of Anesthesia Monitoring by Bispectral Analysis in Zoo Animals
Depth of anesthesia (DoA)
- Monitoring under general anesthesia- variety of tests nervous responses
- HR, RR, BP, SpO2
- Monitoring depth of anesthesia
- Measurement of reactions to nonphysiologic positions such as dorsal recumbency (righting reflex), corneal and pupillary reflexes, and toe pinch stimulation
- Human anesthesia– avoid occurrence of awareness
- Veterinary- safety reasons, lower than necessary DoA chosen
- Prolongs recovery
- Increases dose-dependent cardiopulmonary impairment
- Results in increase of postanesthetic morbidity and mortality
- Anesthesia/sedation related deaths
- Sm mammals 1.4-3.6%
- Birds 1.8-16.3%
- Reptiles 1.5%
- Dogs/cats 0.1-0.2%
- Humans 0.02-0.01%
- Wildlife up to 3% (keep below 2%)
- Monitors – process level of corticocerebral activation into a signal to reflect DoA
- Bispectral index (BIS)
- Narcotrend index
- EEG - State and response entropy
BIS
- Index of level of hypnosis in humans
- 0- corticol silence, aka dead
- 20- increasing burse suppression
- 37- deep hypnotic state
- 48- general anesthesia
- 65- deep sedation
- 83- light hypnotic state
- 100 (awake)
- In humans, anesthesia 40-60
- Equipment: monitor, digital signal processing cable, 3 electrodes with sensors
- Monitor trends
- Hook up w/ needles on head similar to ECG (center of head and around eye, see pic pg 149)
- Impedances: sensor 1 & 3- <7.5 kΩ; sensor 2 <30 kΩ
- Suppression ratio – proportion of signals over last 63sec period for which EEG signals are considered to be suppressed or inactive (0 – no suppression, 100 – maximal suppression)
- Lower the value, the better the signal
Bispectral analysis has been used in a varety of zoological species.
How has this been used in reptiles? How can this be helpful in a critical case?
How has this been used in birds?
How about its use in primates?
What about bears?
What about dolphins?
What about rhinos and elephants?
Reptiles
- Hermann’s tortoises (Testudo hermanni)
- Premed butorph/midaz, propofol anesthes
- BIS from 15-60 – may be an adaption to avoid brain damage during brumation
- BIS not helpful in chelonians
- Boa constrictor & Iguana iguana
- IV propofol initially 70-90
- Isoflurane to inc depth anesth, BIS 20-30
- Could safely extubate at BIS >60 (still needs close monitoring)
- Gila monster (Heloderma suspectum)- venomous
- Mean values BIS 53 (no info on type of anesth)
- May help to determine if patient is dead during anesthesia (and when to stop CPR) – example of bearded dragon
- Animal went to cardiac arrest, but BIS remained high, CPR continued for over 20 minutes as BIS increased from 80 to 90
- At that point hear started beating again, started breathing spontan, and recovered fully
- In another case that was being euthanized for other reasons- 10 minutes after soln given, BIS decreased to 3
- Animal went to cardiac arrest, but BIS remained high, CPR continued for over 20 minutes as BIS increased from 80 to 90
Birds
- Chickens (Gallus gallus)
- Range of BIS 1.75, 1.5, 1.25, 1, 0.75 depending on depth of anesthesia
- Extubated at BIS 70
- These results using similar protocols have been used clinical in many orders (Anseriformes, Ciconiiformes, Psittaciformes, Falconiformes, and Strigiformes)
- Red kite (Milvus milvus) – able to determine bird was feigning death
- BIS 44 to 57 during anesthesia
- Extubation at 59
- Bird remained not moving despite BIS increasing to 85- conscious and feigning death
- Animal quickly moved once perched
Mammals
- Gelada baboons (Theropithecus gelada)
- BIS 30 to 65 with ket/medetomidine combo, quickly increased to 97 after reversal coinciding with blinking and face twitches
- Orangutan (Pongo pygmaeus)- similar results with ket/xylazine combo
- Spectacled bears (Tremarctos ornatus) – telazol/medetomidine
- BIS not reliable for hypnosis (suspected d/t telazol)- during anesthesia, BIS remained above 65
- However, bear that was euthanized had a low BIS reading (5)
- So, BIS may be usually if different drug combo (w/out telazol)
- European otter (Lutra lutra) BIS useful
- BIS 40-65 under anesthesia during surgery; 74 at end of anesthesia
- BN dolphin (Tursiops truncates) – BIS used to monitor interhemispheric asymmetry
- E Black rhino – anesth w/ etorphine, butorph, detom
- BIS 85-97 in fully anesthetized animal
- Suspect etorphine effect on brain may explain hi BIS
- Awake Asian elephant- BIS of 95 by applying sensors onto skin
What types of darting systems are available?
What physical restraint devices are available?
What are conducted electrical weapons? How are they used in the field?
Fowler 8 Ch 79 Update on Remote Delivery and Restraint Equipment
History and background
- Remote injection invented in the 1950’s and hasn’t changed much since then
- These systems need to be efficient and reliable
- In a study on dart gun range and precision, none of the three remote injection systems apart from the Pneu-Dart X-Caliber attained the effective shooting range specific by manufacturers
- Trajectories remained stable up to a certain, rifle-specific pressure
- Newest dart gun - daninject double barrel rifle which makes it capable of propelling virtually all darts available for CO2 guns
- Darts
- Lighter 5 mL, 11 mm slow air injection darts–simplifies the use of larger volume darts
- Several producers now have very-high-frequency (VHF) transmitters available to facilitate tracking and recovery of the darted animal
- Pneu-Dart also has LED’s on darts to facilitate night captures
Physical restraint devices
- Net guns
- 2 types of handheld net guns available - either propelled by blanks or compressed gas cartridges
- Should be limited to situations in which chemical immobilization is not feasible
- Other equipment
- Newly developed catchpole allows for both instant enlarging of the noose and the quick release of the noose
Conducted electrical weapons (CEW)
- Used by human law enforcement agencies for short term incapacitation
- CEWs work with 2 gas propelled barbed darts connected to the main unit via wires that deliver pulsed electrical currents
- Numerous studies have examined pathophysiologic side effects, with little to no evidence of major side effects
- Use in animals
- The Taser company has developed commercially available product for use in wildlife, the TASER X3W Wildlife CEW
- For situations that require short term immobilization
- Has been successful in moose, brown bear, collared peccary, and deer as well as others
- Should only be used if other options are not possible
- Limited in that its maximal distance is about 11 meters
What are the advantages and disadvantages of inhalant anesthesia? Particularly for use in the field.
What does it mean when a vaporizer is calibrated?
Why do vaporizers have to be kept upright?
What is the temperature range vaporizers function well at?
How does altitude affect vaporizer delivery?
What are the indications, advantages, and disadvantages of circle systems?
What are the indications, advantages, and disadvantages of nonrebreathing systems?
How are the flow rates calculated for each system?
How do you calculate how much oxygen may be needed for a field project?
How should oxygen cylinders be transported or stored?
How can respiratory support be provided in the field?
Chapter 28: Vaporizers and Field Anesthesia Equipment for Free-Ranging Wildlife
Sathya K. Chinnadurai
Introduction to Inhalant Anesthesia
- Capture- and anesthesia-related morbidity & mortality may occur w/ field immobilization regardless of anesthetic protocol used
- Injectable anesthesia often used in the field over inhalant
Inhalant Anesthesia
- Advantages: well-described techniques in literature for various species, able to adjust anesthetic depth precisely/rapidly
- Disadvantages: need to transport volatile fluids, expense/bulk of vaporizers, logistically transporting compressed gases
- May need to use inhalant anesthetize to avoid using tightly regulated controlled substances (esp. when crossing internat’l borders)
- Goal: achieve a partial pressure of anesthetic in brain/SC resulting in anesthesia
Vaporizers
- Most common inhalant anesthetics delivered by a vaporizer with some fresh gas source (except nitrous oxide - regulated by flowmeter)
- Most modern vaporizers care calibrated (out-of-circuit) to reduce user error, but be aware of nonprecision (uncalibrated, in-circuit) vaporizers in the field
- i.e. A calibrated vaporizer set to 3% delivers 3% ISO in 97% O2
- Noncalibrated, incircuit vaporizers do not deliver same % as on dial, varies w/ patient ventilation and fresh gas flow rate, would need a gas analyzer to measure delivered inhalant concentrations (not feasible)
- Keep vaporizers upright → tipped vaporizers will release high concentration of anesthetic (at or near saturated vapor concentration) which can be lethal
- Vaporizers may decompensate at extreme temperatures (most are OK between 15-35*C/59-95*F)
- Desflurane vaporizers are thermostatically controlled to stay at 39*C → limited use in the field d/t need for electricity
- Other methods:
- Mechanical vaporizer w/ syringe of liquid anesthetic delivered in a precise amt to achieve a desired concentration when mixed with pumped ambient air (lab animal med, modified field)
- “Open drop” method → cotton ball/gauze w/ anesthetic allowed to vaporize in a closed container → common in rodent anesthesia → usually exceeds lethal doses
Gas Anesthesia at Altitude
- Vaporizers calibrated at 20*C at sea level (1 atm or 760 mmHg barometric pressure)
- Higher altitude: ambient pressure <1 atm but vapor pressure is unchanged → increased delivered anesthetic concentration from vaporizer
- MAC as a partial pressure does not change w/ altitude
- MAC as a volume percentage changes w/ altitude
- Higher altitude: vaporizer releases higher volume percentage but same partial pressure
- Changes in ambient pressure can affect the accuracy of a flowmeter that is calibrated at sea level
Anesthesia Machines
- Compressed carrier gas (usu. O2), pressure regulator w/ integrated/separate flowmeter, vaporizer, breathing circuit, ETT, face mask
- Rebreathing systems need CO2 adsorbent and reservoir bag
- Custom-built machines can be made!
- Different pressure systems:
- High-pressure: 1900-2200 psi, O2 cylinder, yoke, regulator, pressure gauge
- Medium-pressure: 40-55 psi, lines from pressure regulator to flowmeter
- Low-pressure: 0.42 psi (30 cmH2O), flowmeter, vaporizer, anesthesia circuit; all pressures are transmitted directly to patient
- Circle (rebreathing) vs. nonrebreathing systems
- Circle: >7-10 kg, CO2 adsorbant (soda lime), 1-way valves, patient breathing circuit, reservoir bag, vaporizer, manometer, adjustable pressure limiting valve (pop-off valve)
- Advantages: conserves body heat, O2, & anesthetic gases
- Disadvantages: complex and bulky system compared to nonrebreathing
- Suggested flow rate = body weight (kg) * 30 mL/min
- Nonrebreathing: not physiologically appropriate for >30 kg (ideally do not use for >10kg)
- Advantages: simpler design, fewer parts, less potential for mechanical failure
- Disadvantages: higher O2 flow rate, expends more anesthetic agent
- Capnography important when using on larger animals
- Suggested flow rate = body weight (kg) * 300 mL/min
- Circle: >7-10 kg, CO2 adsorbant (soda lime), 1-way valves, patient breathing circuit, reservoir bag, vaporizer, manometer, adjustable pressure limiting valve (pop-off valve)
Field Oxygen Support
- Oxygen tank pressure correlates to gas volume
- Calculating how much oxygen you need = (number of animals) x (time in hours per animal) x (60 min/h) x (fresh gas flow rate in L/min)
- EXAMPLE: (3 fish) x (1 h/fish) x 60 min/h x (1.5 L/min) = 270 L of oxygen
Oxygen Safety
- Store cylinders on their side, transport using proper cars, avoid extreme temperatures (>54*C/130*F or -7*C/20*F), test all connections and fittings prior to transport
- Avoid dropping oxygen tanks or keeping near oxidizing/flammable agents
- Do not fill smaller oxygen tanks from larger ones too rapidly → high pressure causes smaller cylinder to heat up rapidly and can ignite
- Battery-powered, compact, portable oxygen concentrators can be used in the field
Field Ventilatory Support
- Bag-valve devices (AKA manual resuscitators) are self-inflating and can administer room air w/ or w/o O2 under positive pressure → often lightweight and consistent of a self-expanding bag, a 1-way valve, a reservoir bag, and a line for additional O2 supp.
- Oxygen demand valves: high-flow devices supplying 100% O2 at high pressure; equine model (160 L/min) vs. adult human model (40 L/min) → may need a specially-designed demand valve to meet needs to ventilating megavertebrates (can also use commercial leafblowers)
Patient Monitoring
- Be able to deal with hypoxia, hypotension, hypoventilation, hypothermia
- Ideally monitor SpO2, EtCO2, temperature, BP
- Basic monitoring: HR, RR, temperature
- Newer technology: ECGs sent to your phone
- Point-of-care analyzers: BG, lactate, blood gases (important for marine mammals or large ungulates to monitor prior to CPA)
What is cardiac output determined by?
How is CO estimated in a clinical setting?
How is HR monitored?
How is heart rhythm monitored?
What is bradycardia associated with? How is it treated?
What is tachycardia associated with? How is it treated?
Monitoring the Cardiovascular System: O2 delivery = CO x O2
- Cardiac output (CO) determined by intrinsic factors (HR, myocardial contractility) and extrinsic factors (preload, afterload)
- CO is estimated via HR, heart rhythm, arterial blood pressure, central venous pressure (CVP), MM color, CRT
- Monitoring Heart Rate
- Auscultation w/ external/esophageal stethoscope - not always feasible
- Palpation of a pulse - not always possible d/t extreme vasoconstriction or lack of easy access to externally palpable arteries
- Use pulse monitors (e.g. Doppler, pulse oximeter, arterial pressure waveform) - can provide HR information, other info may not be accurate
- Electrocardiogram
- Monitoring Heart Rhythm - electrocardiogram or electrocardiograph
- ECG is only indicator of electrical activity and does not quantitate CO; ECG can continue for minutes after circulation ceases
- Electrode gel/saline improves ECG lead contact; alcohol can be used but is flammable
- Bradycardia usually associated with decreased CO
- Anticholinergics (atropine) is nonspecific treatment - can be associated with ileus, increased salivation (ruminants); some spp (rabbits) have atropinases
- Sympathomimetics (dopamine) increase HR
- Antagonist (esp. when alpha-2 agonists are used; atipamizole) can be used instead of anticholinergic → results in arousal
- Address cause of bradycardia if known
- Hypothermia may contribute to bradycardia
- Tachycardia can decrease cardiac filling
- Ensure appropriate analgesia during noxious stimulation
- Non-specific therapies in domestic canines: beta blocks (esmolol 50-100 ug/kg), cholinesterase inhibitors (edrophonium 0.5 mg/kg titrated slowly)
- Alpha-2 agonists are valuable in otherwise healthy animals
How is blood pressure monitored during anesthesia?
What does pulse palpation tell you?
What are oscillometric measurements affected by? Which reading is most accurate?
When would you choose doppler monitoring over oscillometric monitoring?
What are some complications that can occur from oscillometric monitoring?
How is direct monitoring of blood pressure accomplished?
How do you balance a transducer?
What are some complications from monitoring BP directly?
What are the target ranges for blood pressure in various species?
How is hypotension managed?
How is hypertension managed?
- Monitoring Arterial Blood Pressure
- Indirect (Riva-Rocci - “Return of flow”) or Noninvasive Methods
- Pulse palpation not accurate for BP but provides qualitative information about stroke volume (= difference between systolic & diastolic pressure)
- Oscillometric measurement accuracy affected by internal (programmed algorithms) and external (cuff size/placement) factors
- Systolic pressure determined at first detection of pulse oscillations (systolic pressure is most accurate)
- Determination of MAP increases accuracy
- Other values determined via proprietary algorithms and accuracy may vary
- Doppler: useful for monitoring trends, but nonautomated so monitoring can be limited
- Accuracy limited by species, cuff size, distance of monitoring site above/below level of right atrium or LVOT (d/t hydrostatic pressure gradient - pressures incr above, decr below)
- Subtract 0.73 mmHg from recorded value for each cm below the heart (or add if above)
- Generally, Doppler good for a wide range of animals but oscillometric best for patients w/ regular HR and heart rhythms w/in the stated “normal” range
- Complications: pain, venous stasis, compartment syndrome, peripheral neuropathy, petechiae/ecchymosis
- Direct Methods: aneroid manometer (mean arterial blood pressure)or a strain gauge/transducer (systolic, diastolic, mean pressure) requires arterial catheterization
- Transducer must be appropriately balanced (zeroed relative to atmospheric pressure)
- Zero reference level based on estimate of location of LVOT → use the point of the shoulder (or thoracic inlet) in dorsal recumbency, or midline for lateral recumbency
- Complications of arterial catheterization: infection, ischemia, hemorrhage
- Maintain MAP > 60 mmHg or systolic arterial pressure (SAP) > 90 mmHg (equines: 70-80 mmHg & >100 mmHg, respectively, to maintain adequate muscle/organ perfusion
- Hypotension - usually resolves w/ IV crystalloid or colloid fluid bolus and decrease dose of inhalation anesthetic
- Inotropes, vasopressors have dose-dependent and species-specific actions
- i.e. Dobutamine is preferred in horses but dopamine preferred in dogs/cats; rabbits have no change after dopamine or phenylephrine
- Titrated administration of calcium if iCa is low
- Inotropes, vasopressors have dose-dependent and species-specific actions
- Hypertension - not common except in adult cattle or w/ alpha-2 agonists
- Can be seen in diseased animals (renal, adrenal)
- Important to interpret hypertension in light of other drugs being used
- Hypertension more common w/ injectable drugs in exotic species
- Intervention: increased inhalant anesthesia to see if BP decrease, then provide analgesia if not improved
- Can consider vasodilators (hydralazine), sympatholytics/beta blocks (esmolol, propranolol)
- Transducer must be appropriately balanced (zeroed relative to atmospheric pressure)
- Indirect (Riva-Rocci - “Return of flow”) or Noninvasive Methods
- Monitoring Central Venous Pressure - CVP is measured in the thoracic vena cava
- Used as an indicator of adequate preload in patients w/ normal myocardial function
- Record at end of exhalation and in the absence of a positive end-expiratory pressure (PEEP)
- CVP monitoring not routine, but useful in high-risk patients
What is ventilation?
How does pH change with increase in CO2?
Where do most species maintain their ETCO2?
How would blood gas (PCO2) differ from capnography?
How does that change by species (birds, small animals, large animals)?
How is tidal volume calculated?
What changes for small mammals or birds?
- Ventilation = how the lung removes CO2 from the body
- pH decreases 0.05 unit for each 10 mmHg increase in PaCO2
- Most domestic species maintain between 35-45 mmHg
- Higher elevations: mammals tend to hyperventilate to maintain O2 tensions
- Hypothermia increases solubility of CO2 in blood and decreases partial pressure
- Blood Gas Analysis: venous values typically 3-5 mmHg higher than arterial
- Capnography:
- Mammals: EtCO2 is lower than alveolar or arterial CO2
- Birds: relationship between EtCO2 and alveolar/arterial CO2 not well-understood
- Small animals: EtCO2 and alveolar/arterial CO2 usually w/in 1-3 mmHg of each other when V/Q ratio well-maintained
- Large animals: variable differences of 10-20 mmHg may be observed
- 2 types of analyzers: sidestream (part of multiparameter physiologic monitoring) and mainstream (placed btwn ETT and breathing circuit → increases bulk and work of breathing)
- Can be used to confirm intubation
- Ventilometry and Clinical Assessment - “minute ventilation” (= tidal volume x RR over 1 minute) approximates 150-250 mL/kg/min
- TV: 10-20 mL/kg; defined as two-thirds to alveolar ventilation and one-third to dead space ventilation; can be estimated by excursions of rebreathing bag or quantitated by ventilometer/respirometer on expiratory limb of breathing circuit
- RR: 6-20 brpm
- Small mammals have higher RR, birds require larger volumes
How is FiO2 calculated in a clinical setting?
What is PaO2 measured clinically?
How is SaO2 measured clinically?
What si the relationship between SaO2 & PaO2?
- Oxygenation
- [Oxygen content (mL/dL) = (1.36 x Hemoglobin concentration x %Sat/100) + PO2 x 0.003)]
- 1.36 = oxygen-binding capacity of 1 g of hemoglobin when well-saturated
- Hemoglobin expressed in terms of grams per 100 mL of blood; PCV/3 is clinical estimate
- %Sat = relative saturation of hemoglobin; measured w/ oximeter or estimated from hemoglobin dissociation curve after measuring PaO2 (if PaO2 > 150, consider %Sat=100%)
- PaO2 = partial pressure generated by dissolved O2 (0.003 = solubility of O2 in the blood at 37*C, i.e. 0.003 mL O2 will be dissolved in each 100 mL of blood per mmHg PO2)
- 1.36 = oxygen-binding capacity of 1 g of hemoglobin when well-saturated
- Alveolar gas equation: PA = (PB - H2Ovap) x FiO2 - PaCO2/0.8
- PB = barometric pressure
- H2Ovap = water vapor pressure
- FiO2 = inspired oxygen
- Need to calculate alveolar pressure of O2 to derive PaO2: normal alveolar (A) to arterial (a) gradient of 10 (room air) to 100 (100% oxygen) mmHg may exist
- SIMPLE WAY: multiple FiO2 by 5 (at sea level) and by 4 (if 1 mile high/barometric pressure ~640 mmHg)
- Measurement of PaO2 - arterial sample collected anaerobically in heparinized syringe, run immediately or keep on ice and run w/in 1 hour
- PaO2 values increased w/ excess heparin or air contamination
- Increase the PaO2 value for room air, decrease for high FiO2
- Measurement of SaO2 - pulse oximeter, most accurate for saturations 80-95%
- Relationship of SaO2 and PaO2 - sigmoid curve relationship between Hg saturation and PaO2
- PaO2 > 80 mmHg or SaO2 > 95% are acceptable
- SaO2 = 90% under anesthesia indicates hypoxemia
- SaO2 = 100% (maximum hemoglobin saturation) can reflect a PaO2 of 100-500 mmHg, so very limiting if goal is to assess pulmonary fxn in face of high FiO2
- [Oxygen content (mL/dL) = (1.36 x Hemoglobin concentration x %Sat/100) + PO2 x 0.003)]
How is body temperature affected by anesthesia?
What are the physiologic effects of hypothermia?
What are the physiologic effects of hyperthermia?
Monitoring Body Temperatures
- Controlled by thermoregulatory centers in the brain - affected by anesthesia
- Heat generation decreased by decreased metabolic rate induced by anesthetic sleep state
- Hypothermia: can alter blood viscosity and coagulation, increased risk of myocardial fibrillation, affected anesthetic dose requirements (reduced MAC) and rate of clearance of anesthetic drugs
- Malignant hyperthermia - hyperdynamic metabolic state that is fatal without intervention
What is the optimal pH for mammals?
What values of bicarbonate (HCO3) are expected for carnivores and herbivores?
How does an increase in bicarb relate to the metabolic processes going on?
What are expected values for Base Excess for carnivores and herbivores?
What does a negative or a positive BE indicate?
What are expected values and lactate and blood glucose?
Laboratory Parameters
- pH range well-described for mammals (7.35-7.45)
- Bicarbonate: lower for carnivores (17-24 for cats), higher for herbivores (24-32 for horses)
- Indicates metabolic contribution to pH (high = metabolic alkalosis, low = metabolic acidosis)
- Influenced by CO2: increases in PaCO2 of 10 mmHg increases bicarbonate by 1-3 mEq/L
- Base excess: more negative in carnivores (-7 to +3), more positive in herbivores (0 to +4)
- Negative value indicates metabolic acidosis, positive value indicates metabolic alkalosis
- Interpret lactate, blood glucose based on typical normal ranges (lactate >2 mmol/L indicates aerobic metabolism; BG < 60 mg/dL is hypoglycemia)
- Electrolyte values vary slightly between species but tend to hold tight ranges
- Ionized potassium/calcium influenced by pH (low pH falsely elevates both)
- PCV/TP useful in anemic animals or if at risk of hemorrhage
Describe the use of BAM anesthesia.
What species has it been used in?
What are its pros and cons?
Butorphanol-Azaperone-Medetomidine Combinations (BAM)
BAM USA and BAM South Africa
Species used = Bears, large felids, bison, ruminants, standing sedation for elephants
Pros:
* Provides deep sedation for minor manipulative and surgical procedures
* Wide safety range w/ limited side effects (good if estimating weight)
* Smooth inductions; lasts ~ 1 hour
* Quick reversal with naltrexone and atipamezole
Cons:
* Can override medetomidine if stress or provoked
* Give extra 5 mins before approaching animal given medetomidine
* Bradycardia, hypoxemia, muscle twitching
* Muscle twitching is from antidopaminergic effect of azaperone (NOT light plane of sedation)
* Equids and canids may get dysphoric with azaperone
* Muscle tremors, sweating, salivation
What species has nalbuphine-azaperone-medetomidine been used in?
What are some pros and cons of this protocol?
Nalbuphine-Azaperone-Medetomidine Combination
Species used = beavers, bison, elk, pigs
Pros: Smooth induction and recovery
Cons
* Respiratory depression and hypoxemia
* Variable levels of sedation
* Reversible with naltrexone and atipamezole
What species are butorphanol-medetomidine-midazolam combinations used in?
What are pros and cons of this protocol?
Butorphanol-Medetomidine- Midazolam Combination
- Species used = wild predators and primates
Pros
- Works synergistically, so individual doses reduced
- Fully reversible – naltrexone, atipamezole, flumazenil
- Fast inductions, stable anesthesia, good analgesia, muscle relaxation
- Lasts ~40 mins
- Can also use dexmedetomidine instead of medetomidine
Cons
- Sometimes need to add hyaluronidase to increase absorption of darted drugs (done in African lion)
- Some hypoxemia (via SpO2) and hypertension
What species are ketamine-butorphanol-medetomidine combinations used in?
What are some advantages and disadvantages of this protocol?
How can the ketamine dose be modified to affect induction and recovery?
Ketamine-Butorphanol-Medetomidine Combinations
- Species used = felids, canids
Pros
- Medetomidine counteracts ketamine-induced HR increase; improves muscle relaxation
- Butorphanol + ketamine 🡪 increased analgesia
- Smooth inductions
- Can also stage ketamine
Cons
- Hypertension, hypoxemia, hypercapnia, hypothermia can occur
- Shorter DOA compared to BMM (<30 min procedures)
Lower ketamine dose 🡪 longer induction, but shorter recovery
Higher ketamine dose 🡪 shorter induction, but longer recovery
Describe the advantages and disadvantages of using alfaxalone for anesthesia
Alfaxalone
Pros
* Multiple routes of administration
* Synergistic effects with other sedatives
* Smooth inductions with Med-Azap-Alfax combination – less resp depression than ketamine and medetomidine in bighorn sheep
Cons
* High volume
* Hypoventilation 🡪 hypoxemia, arrhythmias in some deer
* No analgesia
* Not reversible
