117 terms

Veterinary Anesthesia

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Anesthesia
Loss of feeling or sensation
Premedication
Drugs administered to the patient before general anesthesia is induced
Anesthetic induction
The process of bringing a patient from a state of consciousness to general anesthesia usually by means of injectable anesthetic drugs
Anesthetic maintenance
The process used to keep patients under general anesthesia until the procedure is over
Local anesthesia
The loss of sensation in a localized body part or region without the loss of consciousness
Analgesia
A state without pain
Sedation
A state of calm or drowsiness
Tranquilization
A state of relaxation and reduction of anxiety (muscles are so relaxed they don't work anymore)
Neuroleptanalgesia
A state of profound sedation and analgesia produced by giving simultaneous administration of an opioid and tranquilizer
Objectives of anesthesia:
Produce a loss of sensation
Provide muscle relaxation
Provide analgesia
Alter consciousness
Balanced anesthesia
The process of using multiple different drugs that have complimentary effects (make it the best possible experience we can)
Steps of anesthesia:
Patient evaluation and preparation
Equipment and supplies
Preanesthetic medication
Induction
Maintenance
Recovery
When should a PE be performed by a DVM?
Before administering any drugs to the patient
Who is responsible for obtaining and recording a TPR, MM color, CRT, mentation, and weight?
LVT
ARA (anesthetic risk assessment)
Information collected via the physical exam and laboratory results will allow the DVM to formulate
ARA scale 1
Minimal risk, normal healthy patient undergoing an elective procedure (spay, neuter, declaw)
ARA scale 2
Low risk, patient with mild systemic disease. Neonatal, geriatric or obese patients. Patients with mild dehydration (procedures such as lump removal; may be an elective procedure)
ARA scale 3
Moderate risk, patient with severe systemic disease such as anemia, moderate dehydration, and compensated major organ disease
ARA scale 4
High risk, patient with severe systemmic disease that is a constant threat to life (ruptured bladder, internal hemorrhage, pneumothorax and pyometra)
ARA scale 5
Extreme risk, patient is moribund (on the way to death) that is not expected to live without the operation (severe head trauma, pulmonary embolus, GDV, and end-stage organ failure)
How are ET tubes placed?
Inside the trachea of an unconscious patient, attached to a breathing tube, and connected to the anesthetic machine
Benefits or ET tubes:
Allows an open airway, prevents aspiration of stomach contents and water and allows for manual ventilation if needed (breathing for patient)
What is used to measure ET tubes?
The internal diameter (ID)
Laryngoscope
Used to allow better visualization of the pharynx and larynx when placing ET tubes
Two parts to laryngoscopes:
Blade (with light)
Handle
What animal(s) are laryngoscopes NOT used on?
Cattle or horses
Masks
Cone shaped devices that allow you to deliver oxygen and/or anesthetic gases to the patient without intubating them
What do masks NOT do?
Maintain an open airway, prevent aspiration, nor allow you to manually ventilate for the patient
Induction chambers
Modified fish tank; allows you to provide the patient with O2 and/or anesthetic gas; very helpful in anesthetizing aggressive small animals such as cats and some dogs
Anesthetic machine
Used to deliver O2 and anesthetic gas to a patient which allows us to maintain them at a surgical plane of anesthesia
Oxygen source
Either attached to the machine or piped in
Vaporizer
Turns liquid anesthetic into vapor
Pressure regulator
Drops pressure down before it goes to machine; usually 50 psi
Flow meter
Controls the amount of gas (oxygen) flowing through vaporizer or to the patient; marked in liters per minute or ml/min
Soda lime granules
Canister that removes CO2
Scavenger unit
Passive OR
active: no charcoal
They remove excess anesthetic gas
Manometer
Tells us pressure of the anesthetic circuit
Pop off valve
Exit point where gas leaves machine
Unidirectional valves
Patient breathes in = oxygen and gas out --> goes to pop off valve
O2 flush valve
Puts pure oxygen into the circuit
Rebreathing bag
Extra safety thing; if they take in a deep breath; there's extra gas to give
Oxygen tanks
Green tanks; Legally must be anchored to the wall; in America (2200 psi) and should be changed when they contain 100-200 psi
Nitrous oxide tanks
Blue tanks; don't see too much in veterinary medicine anymore; 95% liquid (750 psi) >
E tanks
Smaller tanks connected directly to the machine; lasts for months depending on amount of surgery done
Delivery rate
Measured by the middle of the steel ball as it corresponds to the scale on the flow meter
What should you NEVER do to the flowmeter?
Overtighten
Flow of O2 through the system:
Compressed gas (very high pressure)
Pressure regulator (takes pressure down to 50 psi)
Flow meter (precision control of gas delivered to vaporizer or patient)
Vaporizer color code:
Purple (isoflurane)
Yellow (sevoflurane)
Red (halothane)
Active scavengers
Use a mechanical fan to remove waste gas from the machine and places it in the outside environment
Passive scavengers
F/air canisters; removes waste anesthetic gas from the machine, cleans it using activated charcoal, and puts it into the room
How do you change a passive scavenger?
Weighing the canister and once it has reached the specified weight set by the manufacturer, discarding it and replacing with new charcoal
What colors do the soda lime granules change to when they work?
White (new
Blue (old)
How do clinics base the change of the soda lime granules?
- Amount of time used
- Color change
- By a set day (1 per month)
What is the pressure that the manometer should NEVER exceed?
20 cm/H2O
Cases of pulmonary atelectasis may go up to what pressure in the manometer?
40 cm/H2O
Rebreathing bag
A rubber bag that holds extra gas that allows the patient to recycle gas that was previously exhaled and cleaned of CO2 with the soda lime granules
How often should you administer manual breaths to the patient if they are undergoing a long procedure to prevent pulmonary atelectasis?
Once every 5-10 minutes
Always round ______________ to the next biggest size of rebreathing bags
Up
To calculate the bag needed we use a bag equivalent to ___________________ the patient's tidal volume
6 times
Tidal volume
10 ml/kg --> 60 mL's per kg
Rebreathing circuit
Require the patient to move the gas through the tubes while inhaling and exhaling
What is the most common type of rebreathign circuit?
Y-piece rebreather
Non-rebreathing circuits
Rely on higher pressures to move the gas and do not require the patient to move it (used on small patients)
Non-rebreathing circuits are generally used on small animals weight under ____________________________?
2.5-3 kg (5.5-6.6 lbs)
How do you leak check a machine?
1. Turn on O2
2. Attach breathing circuit and rebreathing bag
3. Completely close pop-off valve
4. Occlude patient end
5. Turn on flow meter to 2L/min and watch the manometer until it reaches 20cm/H2O
6. Turn flow meter down to 200ml/min
7. Watch manometer (if leak free it should stay at 20cm/H2O)
8. Check machine for leak and recheck if problem found
9. When completed, OPEN popoff valve
What are some common areas for leaks in the anesthetic machine?
Breathing circuit
Rebreathing bag
Soda lime granules
Functions of a preanesthetic:
- Calm the patient
- Aid in restraint
- Reduce pain and discomfort
- Decrease salivation
- Minimize vagal reflexes
- Smooth anesthetic induction and recovery
- Minimize doses of anesthetics required for induction and maintenance
Anticholinergics
Used to reduce or eliminate some of the undesirable effects of anesthesia (reduce secretinos, maintain adequate co)
Cardiac output
Stroke volume x heart rate
Opioids
Very potent analgesic often used in preanesthesia and post-op pain
Induction agents
Given to bring a patient from consciousness to unconsciousness
Minimum alveolar concentration
The lowest alveolar concentration required to prevent gross purposeful movement to a graded noxious stimulus (such as skin incision or tail clamp) in 50% of patients (least amount of gas needed in lungs that when we do something really painful; half of the patients won't move; potency of an anesthetic
The ______________ the MAC value the more potent the anesthetic
Lower
________________ MAC usually maintains surgical plane of anesthesia
1.5-2.0
Solubility
How an anesthetic is distributed between blood and gas and tissue and blood; expressed as a partition coefficient
The ________________ the blood-gas partition coefficient, the greater the uptake of anesthetic by blood
Greater; the higher the number the more soluble = takes longer to induce and recover
What is the goal during maintenance of anesthesia?
To keep the patient at a surgical plane of anesthesia and to ensure adequate tissue perfusion
Anesthetic stages:
Stage 1: Amnesia
Stage 2: Excitement or delirium
Stage 3: Anesthesia
Anesthetic planes:
Plane 1: light anesthesia
Plane 2: Surgical anesthesia
Plane 3: deep anesthesia
Plane 4: overdosage
Plane 5: terminal
What stage/plane do we want to keep our patients in?
Stage 3, plane 2; surgical anesthesia
Excitatory phase
Lasts about 15-30 seconds; patient may begin to thrash around and begin moving their legs in a running fashion
Palpebral reflex
When the eyelids are touched and the eyelids close
Corneal reflex
Best used with eye drop solution (want to see eye retract slightly)
Pupillary light response
Shining of light into eye
Pedal reflex
Firmly pinch skin between toes; if animal pulls back they are too light.
What color should MM color be?
Pink
The eyes of an anesthetized dog should rotate ___________________?
Ventrally; if the eyes are looking right at you they are either too deep or too light
Pulse oximeter
Evaluate the level of oxygen saturation in the blood by evaluating the amount of hemoglobin saturation
Normally when breathing pure O2, hemoglobin in the lungs is at least ______________?
97%
The lowest acceptable reading of pulse oximeter is what?
95% with 100% ideal
Readings of pulse oximeter below 90% indicates what condition?
90%
Readings of pulse oximeter below _______ for more than ___________________ is a medical emergency
85%; 30 seconds
Capnograph
Used to measure CO2 content of inspired and expired air
How often should you monitor an anesthetized animal's temperature?
Every 15-30 minutes
Direct BP measurement:
Require an arterial catheter; rarely used
Indirect BP measurement
Can be taken with a sphygmomanometer and doppler monitor
The width of a sphygmomanometer should be ___________________ the circumference of the patient's leg
30-50%
Where is the cuff of the oscillometric unit placed?
Foreleg, metatarsals, metacarpals, or tail base
What may a tech use to wipe away blood from the periphery of a surgical site?
Hydrogen peroxide (H2O2)
Why should hydrogen peroxide not be used on the action incision site?
It delays wound healing
The patient should swallow ___________________ before removing their ET tube
Twice
Procedure to follow if an animal starts to regurgitate under anesthesia:
1. Notify DVM
2. Immediately move patient so that their head is off the table and pointing to the ground (gravity works in our favor)
3. May need to lavage oral cavity
Hypovolemia
A decrease in the volume of circulating blood. Should be corrected by a DVM (i.e. blood transfusion or IV fluids)
Hypothermia
Decreased body temp. Should be corrected by warming the patient. Ideally a warm water re-circulating blanket. Can use heating pads with extreme caution. Should always be kept on low, with a towel between the patient and the pad
Hypoventilation
Decrease in ventilation. Can be corrected by breathing for the patient, administering Doxapram (with DVM permission) or turning down the vaporizer and allowing patient to breath O2
Hypotension
Decrease in blood pressure. Can be corrected by increasing IV fluid rate, or turning down vaporizer
Hypoexmia
Decrease in amount of O2 in peripheral blood. Can be corrected by breathing fresh O2 for patient, or by turning down/off vaporizer
Procedure to follow if patient wakes up on surgery table:
1. Start at the patient. Is the ET tube placed correctly?
2. Check the anesthetic machine. Is there liquid anesthetic in the vaporizer? Is the percent too low?
Is there oxygen
flowing (check flow meter)?
Is the machine hooked up properly?
Procedure to follow if patient goes into cardiac arrest:
1. Alert DVM
2. Check ABC's (airway breathing circulation)
3. Locate emergency drug box
4. If needed begin CPR. If ET tube is placed breath for the patient and have someone perform chest compressions
5. If DVM requests, get epinephrine from the refrigerator and administer as directed
Stage 1 of anesthesia
Amnesia
Stage 2 of anesthesia
Excitement or delirium
Stage 3 of anesthesia
Anesthesia
Plane 1 of anesthesia
Light anesthesia
Plane 2 of anesthesia
Surgical anesthesia
Plane 3 of anesthesia
Deep anesthesia
Plane 4 of anesthesia
Overdosage
Plane 5 of anesthesia
Terminal
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