Theory Midterm (2) Flashcards
What is the role of an ET tube
Transfer anesthetic gases directly from the anesthetic machine into the patients lungs.
Why do we use an ET tube
Maintain open airway
Decrease anatomical dead space
Allow precise administration anesthetics 02
Prevent pulmonary aspiration of stomach content, blood, and other material
Allow anesthetics to accurately monitor and control patient respiration
What are the advantages to PVC endotracheal tubes
Less porous than rubber, thus resists cracking
What are the disadvantages to PVC endotracheal tube
Less flexible than rubber and becomes stiff with age
What are the advantages to red rubber endotracheal tube
Relatively inexpensive
What are the disadvantages to red rubber endotracheal tubes
May absorb disinfectant solutions, causing drying and cracking after prolonged use.
Flexible so kinking or collapse may occur
Spiral or anode contain a coil of metal or nylon in a tube which resists kinking and collapse
What are the advantages to Silicone rubber tubes
Expensive
Smooth, Flexible, Nonporous, less irritating to tissues
What is the cuff of an ET tube
Balloon like inflatable structure at the extremity of the tube, and when it is inflated with air.
What are the advantages to having a cuff
Prevent leakage of waste gas around the tube and into operating room
Reduces risk of aspiration of blood, saliva, vomitus, etc.
Helps to maintain appropriate anesthetic depth by preventing room air coming into lungs
Disadvantage of cuffs includes:
Pressure may cause local necrosis, particularly after prolonged use
Primary functions of an anesthetic machine:
- Designed to deliver a volatile gaseous anesthetic to and from a patient by means of a circuit of corrugated tubing.
- Anesthetic is contained within a carrier gas (either O2 alone or with N2O)
- Must be able to achieve the following:
deliver O2 at a controlled flow rate
vaporize a designated concentration of a liquid anesthetic, mix it with O2 (+/- N2O) and deliver the resulting mixture to patient
move exhaled gases away from patient and dispose of via scavenging system or reuse after removing CO2. - May be used as a means of delivering O2 to hypoxic patients
List the 4 distincts systems of the anesthetic machine:
Compressed gas supply
Anesthetic vaporizer
Breathing circuit
Scavenging system
What is the function of O2 Compressed Gas cylinders
Provides up to 100% O2 (room air is 20%), alveolus 13% and down from there
Desirable because:
Anesthetized animal has higher metabolic requirement for O2 than normal
Anesthetized animal has reduced tidal volume relative to normal. This may result in hypoxia without the higher concentration of O2
Tidal volume; complete inspiration.
O2 also carries the anesthetic to the patient. No anesthetic can be carried to the patient without O2 flow as carrier
How do you calculate volume of a compressed gas cylinder,
Volume: comes in a compressed form (psi = pounds per square inch) in a cylinder or tank in varying sizes
What is a tank pressure gauge used for ,
Can figure amount of O2 in liters in the tank based on capacity of tank and psi read on tank pressure gauge;
What is the Pressure- reducing valve (P regulator) used for
Pressure is reduced by a pressure regulator as it moves from the tank into the anesthetic machine resulting in a constant flow of O2 at 40-50 psi
What are the 02 flow meters used for
- allows the anesthetist to set the gas flow rate (L/min of O2)
see p.126 for discussion of O2 flow rates - must have separate flowmeters for N2O and O2
3.the center of the ball should be read for flow rate (or the top of the rotor)
4.the flowmeter indicates actual flow of gas to patient rather than tank pressure gauge - flowmeter further reduces pressure from 50psi (345 kPa) to 15 psi (100 kPa) which is slightly above atmospheric pressure
What is the oxygen flush valve used for
Delivers a large volume of pure O2 at a flow rate of 35 to 75 L/min directly from the line exiting the P-reducing valve into
The common gas outlet or
Into the breathing circuit of a rebreathing system (between the flutter valves)
… bypassing the vaporizer and flow meter
What is the Description and function of the anesthetic vaporizer
converts liquid anesthetic to a gas state in controlled amounts in the carrier gas(es)
O2 exists flow meter → inlet port → vaporizer → fresh gas (O2 + anesthetic mixture) exit the outlet port → fresh gas inlet → rebreathing circuit
What is a vaporizer out of circle
Vaporizer out of circle (VOC) = vaporizer not located within the breathing circuit (O2 from the flow meter flows into the vaporizer before entering the breathing circuit: PRECISION VAPORIZER ARE POSITIONED IN A VOC CONFIGURATION SO WE USE VOC SINCE ARE ONLY PRECISION VAPORIZERS.
What is a vaporizer in circle
vaporizer located in the breathing circuit: nonprecision vaporizer are positioned this way
What are the factors affecting vaporizer output
may be keyed to prevent use with the wrong anesthetic
if wrong anesthetic is put in, drain, flush with O2 and air overnight
Concentration delivered depends upon: temperature, carrier gas flow rate, RR and depth, back pressure
Most modern models compensate for all of the factors and deliver the appropriate concentration with little or no error
How do you calculate % isoflurane concentration
Induction rate for Iso: 3-5% Maintenance rate for Iso : 1-5% - 2.5% This is approximately 1.5 x the MAC (minimal alveolar concentration) of Isoflurane . This results in a moderate depth of anesthesia MAC of Isoflurane in dogs: 1.3% MAC of Isoflurane in cats: 1.63%
What is the function of the vaporizer inlet port
point where O2 enter vaporizer from the flow meters
What is the description of the Vaporizer outlet port:
point where O2 + inhalant anesthetic exit the vaporizer on the way to the breathing circuit.
What is the outlet port used for
Connected directly to the breathing circuit via a hose OR
Connected to the common gas outlet (Fig. 4-32) which connects directly to the breathing circuit via a second hose.
The common gas outlet is the area where fresh gaseous anesthetic mixture enter the circuit (rebreathing or non-rebreathing circuit)
This mixture never return to vaporizer region
For non-rebreathing system (bain): fresh gas enters 1st through reservoir bag
For rebreathing or circle system: fresh gas enters just upstream from the inspiratory unidirectional flutter valve and downstream from the CO2 absorber.
Explain the Rebreathing systems (Circle systems):
- Use only with patients larger than 7 kg
- Fresh O2 + anesthetic enter circuit from fresh gas inlet and mix with the patient’s exhaled gases.
- May be closed (total) rebreathing systems with pop-off nearly closed OR partial semiclosed (partial) rebreathing systems with pop-off partially open
- O2 rate higher with partial rebreathing than total rebreathing
Safety concerns include:
CO2 accumulation may occur, especially if not efficient scavenger in place
Less likely in semiclosed system
Increased pressure in the anesthetic circuit may occur, making it difficult for animal to exhale
Less likely in semiclosed system
What is the function of Unidirectionnal Valves (flutter valves)
Control direction of gas flow through the rebreathing circuit
What is the pathway of unidirectional valves
Patient inhales
The inspiratory (Inhalation) unidirectional valve opens and allows the fresh gas to only flow in one direction (towards the patient)
Gases travel through the inspiratory breathing tube (hose)
….and travel toward the patient
Gases pass through the Y piece and
….into the ET tube or mask/chamber
O2 and anesthetics molecules are absorbed by the lungs
…and enter bloodstream
At the same time, CO2 and anesthetic molecules are released from the bloodstream, enter alveoli…..
….and are exhaled gases on the next breath
Exhaled gases travel through ET tube, then Y-piece
..then through expiratory breathing tube
….to reenter the anesthetic machine through the expiratory (exhalation) unidirectional expiratory valve (also one-way)
Then into the reservoir bab (bag inflates)
And pass directly into the CO2 (CO2 is removed from the expired gas before it returns to the patient)
What is the function of the pop off valves
Point of exit of anesthetic gases from the breathing circuit.
Main function:
allow excess carrier and anesthetic gases to exit from the breathing circuit and enter the scavenger system.
Allows waste gases to exit anesthetic circuit, preventing build-up of excessive pressure or volume within the circuit
Valve can be fully opened, partly opened or fully closed, allowing vary amounts of gas to exit. WE KEEP FULLY OPEN!
what is the description of the reservoir bag
rubber bag which gradually inflates as gases enter the circuit between the expiratory valve and the CO2 absorber and deflates as the patient breathes in
reflexes patient’s respirations
What are the functions of the reservoir bag
1.allows anesthetist to observe animal’s respirations:
minimal movement may indicate leakage around cuff (breathing room air) or decreased tidal volume
indicates that ET tube is properly within the trachea and not the esophagus
2.May confirm proper ET TUBE placement
Allows delivery of anesthetic gases to the patient by “bagging” – gently squeezing the bag, causing the patient’s chest to rise slightly by forcing O2 (+/- anesthetic) into the lungs
helps prevents atelectasis (collapsed alveoli) by reinflating alveoli
Normalize gas exchange; flushes airways, decreasing the CO2 (prevent hypercarbia) content and increasing O2 (prevent hypoxemia) (+/- anesthetic) in lungs
Normalize the RR
Also: lifesaving in the case of respiratory arrest and to check for gas leak around ET tube
What is the function dioxide absorber canister
Exhaled Gases that do not exit via pop-off valve go through CO2 absorber canister prior to returning to system
Absorbing ingredient (granules) is:
Ca(OH)2 (calcium hydroxide)
water
Na hydroxide, K hydroxide, Ca chloride, Ca sulfate
These react with CO2 to form Ca carbonate and other. Heat + H20 are produced and pH ↓
Explain how granules in the C02 work
If use exhausted granules, may lead to hypercapnia
Absorber granules contain a pH indicator when saturated, most frequently with to blue or purple.
Chemical rxn→ heat , H20 (captured in a trap below) and color change
The color change does not last more than several hours so remove soon after noticed (especially with Isoflurane)
Fresh granules: soft and crumble easily / white
Exhausted granules: hard and brittle / off-white to violet
What is the function of the pressure manometer
Indicates P inside machine and patient lungs In cm H20 or mmHg
Usually present in both type of circuit. For the rebreathing circuit = on top of CO2 absorber canister
when bagging an animal to determine the P being exerted on the animal’ lungs when the anesthetist squeeze the reservoir bag.
Should read 0 to 2cm of H20 at all time!!!
Possible reasons of excess pressure:
Pop-off valve closed or not sufficiently open
O2 flow rate too high
Scavenger deficient
What is the function of the negative pressure relief valve
Valve that opens and admits room air to the circuit if negative pressure (vacuum) is detected in circuit
Not on all machine
When is the negative pressure relief valve engaged
Active scavenging system with excessive pressure
O2 tank runs out of O2
If O2 flow rate too low
Explain the non-rebreathing system
Patient
What are the advantages to the non-rebreathing system
minimal resistance to respiration
resistance offered is secondary to the tubing (ET and other) size rather than gas flow
less drag on patient
faster rate of anesthetic concentration change (although depth changes are secondary to concentration and solubility coefficients of anesthetic)
What are the disadvantages of the non-rebreathing system
much more expensive to use due to non-reuse of O2 and anesthetics
does not conserve heat and moisture of patient
produces much more waste gas
How do you make the choice between the rebreathing and the non-rebreathing system
Made on the basis of patient size because patient’s respiratory drive (force generated by the respiratory muscles during breathing) is directly related to BW
In small patient, this drive is insufficient to move gas through areas of resistance present in a rebreathing circuit
A non-rebreathing circuit offer little resistance to air movement
What do the oxygen flow rates depend on
Type of breathing system (rebreathing or Bain)
Period of anesthesia
When changing the anesthetic depth
What rate do you generally use with the semi-closed rebreathing system
Semi-closed rebreathing system: flow rates vary from:
relatively low rates when maintaining a patient at a desired anesthetic depth
…to relatively high rates during induction and recovery and when changing anesthetic depth.
What rate do you generally use with the non-rebreathing system
Non-rebreathing system: in general, high rates are used at all times regardless of the period of anesthesia
What rates do you use during chamber and mask induction
very high flow rates are required
it saturates the circuit, flushes out Nitrogen produced at the start of the anesthetic period
How do you determine the flow rate for the non-rebreathing system
High flow rates per unit BW is required during all periods of general anesthesia (induction, maintenance, recovery) because the removal of CO2 from the circuit is dependent on fresh gas flow
It is based on BW of patient
What is the class and function of Ketamine
Ketamine (salivation)
anticholinergic (minimize salivation)
What is the class and function of Halothane
Halothane: cardiac arrhythmias and bradycardia
anticholinergic (minimize salivation & bradycardia)
What is the class and function of Opioids
Opioids: bradycardia, vomiting, diarrhea and flatulence
anticholinergic (minimize bradycardia)
phenothiazines: anti-emetic
What are the uses of Preanesthetic Medications
- To calm or sedate excited, frigntened, vicious animal (but some not affected)
- To minimize adverse effects of concurrently administered drugs
- To reduce required dose of concurrently administered agents
- To produce smoother anesthetic inductions and recoveries
- To decreases pain and discomfort before, during, and after surgery
- To produce muscle relaxation
What are the 3 types of preanesthetic medications
Anticholinergics
Tranquilizers and Sedatives
Opioids
What do anticholinergics used for
Anticholinergic blocks binding of Ach at the muscarinic Rc
What is the function of the vagus nerve
provide PЄ innervations to numerous target organs
How is the vagus nerve stimulated
During surgery, vagus nerve may be stimulated by pulling, touching some organs, by the administration of some drugs , and common anesthetics.
When the muscarinic receptors are stimulated by acetylcholine what happens
bradycardia, bronchoconstriction, excess tear, and salivation, excess production of or respiratory system secretions, ↑ GI motility and pupil constriction
When do you administer Glyco or Atropine
20-30 mins before to allow time for peak effect, when to administer IM before anesthetic induction
What are the effects of glyco/atropine
prevent bradycardia
What are other effects of glyco/atropine
(+) ↓ resp. tract secretions. Less risk of airway obstruction
(+) ↓ GI tract secretions
(+)↓ salivary secretions
Mydriasis (esp. cats) and slows PLR
(-) Reduction of lacrimal secretions (risk of corneal drying, ulcer)
(-) Bronchodilation: increases diameter = increase in dead space = risk of hypoxemia.
What pre-anesthetic drugs promote vomiting
opioids
What two pre-anesthetic drugs promote production of saliva
Ketamine, Thiopental
What are the adverse effects of Glyco/Atropine
CV system: arrythmia, tachycardia.
Respiratory system: thickening of respiratory and salivary secretions in cats
Other Adverse effects: Inhibit intestinal peristalsis. Causes constipation
What patients do you avoid giving glyco/atropine
Patients with rapid RR, Cardiovascular disease, Geriatric, Hyperthyroid
Why is glycol preferred over atropine
Less arrhythmia, suppress salivation better, crosses the placental barrier less
What is atropine used for in an emergency
Treat bradycardia
What is the difference between tranquilizers and sedatives
Tranquilizers decrease anxiety, sedative decreases mental activity and sleepiness.
What are 3 classes of tranquilizers and sedatives
Phenothiazines
Benzodiazepines
Alpha2-Agonist
What are some precautions to take when using these medications
Never let the patient unattended on the table or in an open cage.
It relaxes tissues in pharynx so watch out with brachycephalic breeds
Also unusual behaviour possible.
What is the mode of action and Pharmacology of Phenothiazines
Depression of RAC of brain + Blockage of -adrenergic, dopamine, histamine Rc
Where are phenothiazines metabolized
By the liver
How quick is the onset of action of the phenothiazines
Onset of action : 15 min IM dogs) Peak: 30-60 minutes
What are the effects of phenothiazines on the major organ systems
CNS: Calming, sedation, reluctance to move, and decreased interest in the patient’s surroundings.
CV system
Peripheral vasodilatation = hypotension, reflexive ↑ heart rate, ↑ heat loss → hypothermia
↓cardiac output
Antiarrhythmic effect.
Respiratory system: don’t cause resp. depression
What are some other effects of phenothiazines
Antiemetic
Ataxia
Prolapse of 3rd eyelid
What are the adverse effects of phenothiazines
CNS system
reduce seizure threshold.
Occasionally acepromazine may induce excitement or aggression
CV system
Severe hypotension (especially if Iso is used as an inhalant anesthetic)
Decreased PCV
What patients should phenothiazines be avoided in
Patients with liver problems, hypotensive, small, geriatric patients, patients in shock
Why should patients be placed in a quiet location free from stimulation between administration and peak effect.
Due to possible excitement
What breeds should phenothiazines be avoided in
Boxers, Giant breeds, Greyhounds
What are severe hypotension and bradycardia treated with
IV fluids
Why are phenothiazines used
To provide sedation
To ↓ dose of general aneshtic
To ease of induction and recovery
What is the mode of action and pharmacology of Benzodiazepines
Depression the CNS
Metabolized by the liver
Rapid onset of action and short duration
What patients should you avoid the use of benzodiazepines in
Patients with liver problems
What are the effects on major organ systems of benzodiazepines
CNS: antianxiety and calming effect (no sedation), in healthy young animals unless used in combination with other drugs such as ketamine or opioids.
much more effective in geriatric or debilitated animals
unreliable sedative effects (may instead produce dysphoria, excitement, ataxia, especially young, healthy animals)
enhances the sedation and analgesia of other agents
Anticonvulsant effect
also given as a tx for seizures
CV system and Respiratory system: few effects
What are the other effects of benzodiazepines
Other effects:
skeletal muscle relaxation (counteract rigidity seen with ketamine. Use in FUS patients, herniated disk patient.
Premed with diazepam ↓requirements of many general anesthetics including the inhalant agents
Appetite stimulation in cats
What are the adverse effects of benzodiazepines
CNS system:
young and healthy: more difficult to control
Dogs: disorientation, excitement
Cats: dysphoria, aggressivity
Is diazepam water soluble?
Not water soluable so it cannot be mixed with water soluble drugs because it will precipitate. Except with ketamine
Why should diazepam not be stored in a plastic container
Because it gets absorbed by plastic
Why is diazepam used in combination with other agents
their muscle relaxant
anticonvulsant,
and appetite-stimulating properties
What precaution must you take with ketval
It must be stored in a brown container or in a drawer
By what route is diazepam usually administered
IV mainly (avoid IM in dogs).
Why do you avoid giving diazepam IM in dogs
Because IM is painful and not as easily absorbed
What is the reversal agent for diazepam
Flumazenil
Mode of action and Pharmacology for alpha2-agonists
act on alpha2-adrenergic receptors of the S (Є) NS both within the CNS and peripherally, causing a decrease in the release of the neurotransmitter norepinephrine (NE)
Usually, the S (Є) NS → «fight-or flight response»
What effects do alpha 2 agonists cause
Sedation Analgesia Bradycardia Hypotension Hypothermia
What is the onset of action and duration of alpha2 agonists
IV: within 5 to 15 minutes
IM: 15 to 30 minutes
Duration: about 1 to 2 hours
Complete recovery: about 2 to 4 hours if the drug not reversed.
Where are alpha 2 agonists metabolized? and excreted?
Metabolized by liver, excreted by the urine.
What are the effects on major organs of alpha 2 agonists?
CNS: Potent sedatives
When combined with other agents, sedation may be sufficient for minor or even major surgical procedures
Analgesia? YES
CV system: Brief hypertension + reflex bradycardia. MM pale, arrythmias, ↓ co, hypotension, ↓ HR
Respiratory system: Minor at low dose, higher at high dose (↓ Tv, ↓ RR)
What are the other effects of alpha 2 agonists
Muscle relaxation Increased effects of other anesthetics. Vomiting (dogs, cats) Hyperglycemia Hypothermia
What are the adverse effects of alpha 2 agonists
CNS system: temporally behavior changes
CV system: profound CV depression.
Respiratory system: potential respiratory depression.
In which patients do you avoid using alpha 2 agonists
Heart Murmur patients, heart disease, geriatric , small patients, liver disease, diabetic, pregnant, paediatric
Describe medetomidine
good analgesia, excellent sedation
Approved only in dogs, usually mixed with opioids
Cats: kitty magic (refer to Lab notes (Lab #4)
Usually for minor procedure
Usually too awake for intubation (but give it a try)
For more extensive surgery: sedated animal most be intubated and maintained on inhalant anesthetic (but at much lower % concentration!)
What is the antagonist of xylazine
Yohimbine
What is the antagonist of Medetomidine
Atipamezole. Antisedan
What drug is a partial agonist of opioids
Buprenorphine
What drug is an opioid agonist-antagonist
Butorphanol
What is the antagonist of opioids
Naloxone
What is the mode of action and pharmacology of opioids
Analgesic and sedative effects
Action on Rx located in brain and spinal cord: stimulate receptors similar as do endogenous opiod (eg. Endorphins)
Duration: short to relatively short
What are the effects on Major Organ System of opioids
CNS:
1) Sedation: may cause CNS depression or excitement (dose, route, agent used, species, patient temperament, and pain status dependent)
dogs: predominant effect : sedation
cats may show bizarre behavior (use low dose and avoid IV)
Short acting (15 min after IM injection)
2) Analgesia: degree of analgesia varies among members of the class
severe pain: morphine, hydromorphone, fentanyl, oxy
Mild to Moderate pain: butorphanol, buprenorphine
Widely used in premedication (BAG, HAG)
CV system: bradycardia (especially if combined with the drugs that slow the heart rate such as? Alpha 2-Agonist
Respiratory system: potential to ↓ RR + Tv (but minimal in health patient). Panting in dogs.
What are the other effects of opioids
miosis in dogs, mydriasis in cats
Dogs: hypothermic as a result of resetting of the thermoregulatory center and panting.
Cats: hyperthermic for unknown reasons.
↑ responsiveness to noise.
What are the adverse effects of opioids
CNS: anxiety, disorientation, excitement, dysphoria, and ↑ motor activity
CV system: pronounced bradycardia: results from: vagal tone stimulation
Resp. system: respiratory depressor at high dose (except buthorphanol) or combined with tranquilizer or other drugs that are resp. depressant. an inhlant anesthetic respiratory depresssant: isoflurane
GI system: Salivation, V+
Initially ↑ peristaltic movement = D+, V+ , flatulence. Constipation.
What are the three uses of opioids
- Component of preanesthetic protocols
- As an induction agent
- Analgesia
Why are opioids used as a component of preanesthetic protocols
For high-risk patients, morphine or hydromorphone as the sole preanesthetic agent.
More commonly mixed with a tranquilizer (such as acepromazine, diazepam, or medetomidine) and/or an anticholinergic (atropine or glycopyrrolate) and given during the preanesthetic period.
Why are opioids used as an induction agent
(eg. Kitty magic IM in ferals cats: cats are then intubating and maintained at a low % concentration of Iso (0.5-1%)
Why are opioids used for analgesia
To prevent and treat postoperative pain
To achieve state of profound sedation and analgesia: opiods + tranquilizer = neuroleptanalgesia (will be discussed later if time permits)
What should the minimal data base include
Patient history, Physical examination, Preanesthetic diagnostic workup
What is involved in getting a patient history
Know how to get a good one. Don’t ask leading questions, get owners to describe.
know the procedure to be performed, reproductive status of animal (heat- more bleeding)
age of pet, vaccine status of animal
previous illnesses, and response to treatment (be aware of major diseases)
any illness in the past 24 hours (pathogens in hospital, higher risk)
how well the animal tolerates exercise (CVS or respiratory disease)
recent treatment with drugs or insecticides (alter effects of anesthetics)
history of allergies of drug reactions
patient authorization, informed consent, emergency number, and give estimate
What is part of the physical examination
vet techs are certified to perform GPE provided they are acting under the direct supervision of a licensed veterinarian
may reveal resp. or CVS disease, enlarged livers, small kidneys which all affect ability to detoxify or excrete drugs
ear mites, otitis, dental disease, overgrown nails, deciduous teeth, fleas, dewclaws that need to be taken care of during Sx
physical factors such as ‘the spay a male cat club’ registration, cryptorchids….
What is part of the signalment
species\breed (ie brachycephalics: airway problems, sighthounds: metabolism of drugs problems), weight and age ( neonates, pediatrics and geriatrics take special consideration)
What biological tests are usually done
Diagnostic tests: clinic dependent, and cost
The following will be discussed into the Hematology course:
CBC, PCV and TP
Urinalysis
Blood chemistry tests
Blood coagulation screens
How long should you fast animals before surgery
8-12hrs
What is the goal of anesthetic induction
take the patient from consciousness to stage III anesthesia smoothly and rapidly, so that an endotracheal tube can be placed.
Patient passes through the excitement stage and therefore may show signs of uncoordination or struggling, followed by progressive relaxation and unconsciousness.
What does excitement and struggling during induction cause
Excitement and struggling during induction hamper restraint, increase the risk of inadvertent perivascular drug injection, and predispose the patient to traumatic injury, vomiting, cardiac arrhythmias, and other adverse effects, and so should be minimized through administration of pre medications.
How can general anesthesia be achieved
IV induction Induction with Inhalant agents Mask induction Chamber induction IM induction
Describe IV induction
The volume is calculated based on a prescribed dose and drawn into a syringe.
The agent is then injected directly into the vein, or into a winged-infusion set or indwelling catheter to effect until:
the patient can be intubated OR until
the patient is at an adequate plane of anesthesia for completion of the planned procedure. It is given to effect.
Why is giving drugs to effect necessary
The amount of drug needed to induce or maintain anesthesia cannot be accurately predicted for a given patient.
What is the average duration of anesthesia with the commonly used IV injectable agents
10-20 mins
If you require more than 20 minutes anesthesia what must you do?
Maintain it with inhalant anesthetics, or administration of propofol by repeat boluses or CRI
What are the general disadvantages of mask induction
Fear (stage I) + excitement (stage II) → struggle → stimulate sympathethic system → release of epinephrine → arrhythmia, hypotension and others
MM color and refill time as well as ocular indicators of anesthetic depth are not as easily observed
Avoiding mask induction is preferable. We might have to use it in the lab, so you should have an idea how to proceed.Operator exposure to agent + wasteful of anesthetic agent
Slow induction time so not appropriate:
with patient with poor respiratory function.
with unfasted patients: non-fasted patients→ vomiting→ aspiration pneumonia because no ET tube
with patients at risk of vomiting during induction
What general anesthesia is induced by IM induction
neuroleptanalgesic combinations
variety of combinations of tranquilizers, dissociative, and opioids. Eg. Kitty magic
IM induction is useful for animals in which IV injections are difficult eg. Feral cats, wild animals
What is the maintenance period of general anesthesia
The period during which a stable level of anesthetic depth is achieved.
Most commonly achieved after anesthetic induction and ET intubation
Most commonly maintained with an inhalant agents delivered via an anesthetic machine
Most common: Isoflurane
What is the recovery period of general anesthesia
The period when the concentration of anesthetic in the brain begins to decrease.
Describe the general safety of general anesthesia
Vital centers may be affected, resulting in depression of the CV, respiratory and thermoregulation systems. Death may occur if these centers are not properly maintained and monitored.
What strategies can you employ to maximize anesthetic safety
Usage of preanesthetic drugs (anticholinergics, tranquilizers, sedatives)
Injectable drugs: Double check all dosage calculations and verify that the labeled concentration on vials is the same as that used for the drug calculations. Label all premade syringes.
Inducing/Maintenance: Use the minimum dose of drug needed to achieve the desired level of anesthesia. (Give only to effect or titration of dose.)
Recovery observation: Vomiting, laryngospasm, hypothermia and convulsions may complicate recovery. CR arrest is also possible.
What is stage 1 of general anesthesia
Immediately after administration of an inhalation or injectable agent
begins to lose consciousness
fear, excitement, disorientation, and struggling
HR and RR increase
patient may pant, urinate, or defecate
difficult to handle
Near the end of stage I, the patient loses the ability to stand and becomes recumbent.
What is stage 2 of general anesthesia
excitement stage
the patient loses voluntary control (loss of consciousness)
breathing becomes irregular (may hold its breath)
characterized by involuntary reactions: vocalizing, struggling, paddling, chewing, swallowing, yawning)
HR and RR are often elevated
pupils are dilated but responsive to light
muscle tone is marked
reflexes are present and in fact may appear exaggerated
appear to be “fighting” the anesthesia, but actions are not under conscious control (should get through this stage rapidly)
Stage II ends when the animal shows signs of muscle relaxation, slower RR, and decreased reflex activity.
What is special about stage 2 of general anesthesia
**This stage is unpleasant and potentially hazardous for both the animal and hospital personnel.
risk of epinephrine release and the possibility of cardiac arrhythmias or arrest. The struggling patient may injure itself, the restrainer, or the anesthetist
What is special about stage 1-2 in premedicated animals
Premedicated animals may pass directly from consciousness to stage III if induced rapidly.
Stages I and II are often very pronounced in animals in which anesthesia is mask or chamber induced without premedication
What is stage 3 of general anesthesia
subdivided into four planes
patient is unconscious and progresses gradually from light to deep surgical anesthesia
characterized by progressive muscle relaxation, ↓ HR and RR, and loss of reflexes
pupils gradually dilate, tear production ↓, and the PLR is lost
The increase in HR, BP, and RR seen in response to surgical stimulation during light anesthesia is also gradually lost.
What is stage 3 plane 1 of general anesthesia
Respirations become regular
Limb movements cease
Eyes rotate ventrally
pupillary response to bright light is ↓
Gagging and swallowing decreased (time to ET tube → A.machine
Palpebral and other reflexes decreased but present
Still responds to painful stimuli (HR, RR, resp. depth, BP would ↑ if in pain)
This plane is inadequate for surgery.
What is stage 3 plane 2 of general anesthesia
Suitable for most surgical procedures. Pain may induce slight increased HR, RR but no movement
The PLR is sluggish, and the pupil size is moderate.
Respirations: regular but shallow
RR, HR, and BP are mildly ↓
Relaxed skeletal muscle tone
pedal and swallowing reflexes are absent
laryngeal and palpebral reflexes are diminished or lost.
So loss of the pedal and swallowing reflexes marks entry into plane 2, and ventromedial eye rotation also generally occurs at this time.
What is stage 3 plane 3 of general anesthesia
Too deep for most surgical procedures. Significant ↓in HR RR, BP (even with surgical stimulation)
Dog, cat = RR
What is stage 3 plane 4 of general anesthesia
Abdominal breathing recognized by a “Rocking boat” respirations.
Spasmodic, jerky, uncoordinated respirations
Fully dilated pupil with no light reflex
eyes may be dry because of an absence of lacrimal secretions.
Muscle tone is flaccid.
Obvious drop in HR, BP
Pale mm and ↑ CRT
Too deep for safety: imminent cardiac and respiratory arrest.
What is stage 4 of general anesthesia
Cessation of respiration
Total circulatory collapse and death unless immediate resuscitation
What are the objectives of surgical anesthesia
Maintain anesthesia at the lightest level possible while ensuring the patient does not move, is not aware, and does not feel pain
How often should an evaluation of the patient be done during surgery
Every 3-5 minutes
What parameters are examined during the evaluation of a patient done during surgery
RR depth and character. MM color and CRT. HR. Pulse strength, Palpebral and pedal reflex activity, o2 flow rate, IV catheter placement, Temperature
What are the indicators of circulation
heart rate, heart rhythm, CRT, BP
How can you check the heartbeat
palpation of the apical pulse through the thoracic wall,
palpation of a peripheral pulse
auscultation with a stethoscope
in conjunction with pulse strength to determine adequate blood flow.
ausculation with a esophageal stethoscope
ECG
Pulse oximeter
BP monitor (Doppler blood flow detector or oscillometric monitor)
+/- intraarterial line attached to a transducer.
Drugs of which class are particularly likely to cause bradycardia
Opioids and Alpha 2 agonist, barbituates
What can cause bradycardia
Adverse effects of certain drugs
Excessive surgical stimulation
Excessive anesthetic depth
What causes tachycardia
Inadequate anesthetic depth Pain during light surgical stimulation Hypotension Bloodloss Shock Hypoxemia Hypercapnia
What is the most common HR rhythm in normal dogs and cats
Normal sinus rhythm.
What are arrhythmias caused by
Certain drugs, Anticholinergic, Ketamine, Thiopental
What instruments are used to monitor HR and Rhythm
Stethoscope
Esophageal stethoscope
ECG: read by the vet but tech must be able to set up the ECG and recognize normal from abnormal rhythm based on auscultation and palpation of pulse
What is a CRT
CRT > 2secs indicates that tissues in the area tested have reduced blood perfusion
Normal CRT may be present in the face of abnormal circulation so not infallible.
What are the possible reasons for slow CRT
Possible reasons:
vasoconstriction caused by epinephrine release.
low BP caused by anesthetic drugs (including acepromazine, alpha2-agonists, propofol, and inhalation agents)
hypothermia
cardiac failure
excessive anesthetic depth
blood loss or shock.
reduced temperature of the affected part.
What is blood pressure
force exerted by flowing blood on arterial walls
What is the pulse strength
rough indicator of BP ( lingual (dog), dorsal pedal arteries, femoral)
What is a normal pulse strength
strong and should occur shortly after each apical beat or S1 heart sound.
What are indirect methods of measuring blood pressure
can be done with external device using pressure cuff and device to note return of blood flow.
Doppler blood flow detector
Oscillometric BP monitor (eg. Cardell®)
What are the indicators of oxygenation
MM color, pulse Oximeter, Blood gas analysis Objective: to ensure adequate oxygenation of the patient’s arterial blood.”
What is MM color
Usually the gingiva but if pigmented look at tongue, conjunctiva or MM of prepuce or vulva.
Provide only a crude assessment of both oxygenation and tissue perfusion (since other factors affect MM color
What are the causes of pale MM color
blood loss, anemia, poor capillary perfusion (eg. vasoconstriction, excessive anesthetic depth, or prolonged anesthesia).
What is SaO2
Oxygen saturation
What is PaO2
partial pressure of O2 in arterial blood. Measures the unbound O2 molecules dissolved on plasma (only 1.5% of the total amount of O2 available to tissue)
What does a pulse oximeter do
estimates the saturation of hemoglobin (So2), expressed as a % of the total binding sites of Hb molecules occupied by O2 molecules
What are the indicators of ventilation
RR, Tv, Respiratory character, Capnograph. Blood gas analysis
How do you monitor RR
Watching the chest wall movements
observing the rebreathing movement
Mechanically with an apnea monitor or capnograph.
What typically occurs with the RR in anaesthetized animals
During anesthesia, there is normally a decrease in the RR.
isoflurane (inhalant) anesthetics, opioids, and alpha2 agonists are particularly likely to cause respiratory depression.
Propofol and thiopental sodium typically cause bradypnea or apnea during induction, especially if given quickly or at higher doses.
What does true tachypnea cause
Hypercapnia
Excess CO2 in the circuit
pulmonary disease,
or a response to a mild surgical stimulus.
(((progression from moderate to light anesthesia (one of the first signs of arousal from anesthesia) ))))
(((((Some patients (particularly obese dogs) breathe rapidly even at a moderate depth of anesthesia.))))
What is tidal volume
Amount of air inhaled in a breath
How do you monitor tidal volume
watching the chest wall movements
observing the rebreathing movement
What is atelectasis
partial collapse of some alveoli
How often do you bag an animal
Every 5-10 minutes
What is respiratory character
Effort required to breathe, the relative length of inhalation and exhalation and regularity
What is hyperventilation
Increased tidal volume, may result from hypercapnia or surgical stimulation.
How do you monitor respiratory character
By watching chest wall
If an animal is gasping, having difficult or laboured breathing during surgery what can this mean
Airway blockage, respiratory disease, pressure buildup, hypoxemia
If an animal is anesthetized with Ketamine, what can the animals exhibit
Apneustic respiratory pattern in which there is a prolonged pause between inspiration and expiration.
What are the reflexes that indicate anesthetic depth
Swallowing reflex Laryngeal reflex Palpebral reflex Pedal reflex Corneal Reflex Pupillary Light reflex
What do spontaneous mvt indicate
light plane of anesthesia, and imminent arousal
What does muscle tone indicate
Light: marked
Medium: moderate
Deep: flaccid
What does eye position indicate
Light anesthesia: central
medium anesthesia: ventromedial
deep anesthesia: central
Describe pupil size in relation to anesthetic depth
Stage 2 anesthesia: dilated
Stage 1: Constricted
What is referred pain?
felt in a body part other than that in which it is situated
What is Hyperesthesia
increase sensitivity to touch, heat, cold
What is pain?
Pain is an aversive sensory and emotional experience that elicits protective motor actions, results in learned avoidance, and may modify species-specific behavior
Different for every individual animal, although similarities exist within a species
What is multimodal therapy?
Multiple receptors and mechanisms have been identified that are responsible for pain and the development of windup.
An analgesic plan for moderate to severe pain should make use of several drugs, each having a different mechanism of action.
What is the purpose of pain assessment tools
help determine how much pain the animal is in and to assess response to treatment.
How often do you assess animals Response to Therapy:
Animals undergoing major surgery: assess hourly or possibly more frequently in the first few hours of the postoperative period
patients with chronic pain: less frequently
What are The benefits of multimodal analgesic therapy
each individual drug dose is reduced,
overall anesthetic drug requirement is reduced,
and therefore the risk of toxicity and adverse effects is decreased.
What is the purpose of premedication
offers an opportunity to administer analgesia before surgery (i.e., preemptively)
animals having received preanesthetics appear less painful than those who receive none (helps to prevent windup)
Those who get “wound up” need more post-op analgesia
Also note that less general anesthetic is needed for surgery (im morphine pre-op, can keep Iso % lower).
What is another method of preemptive analgesia
Application of fentanyl patch 6-12hrs before surgery
Whats an opioids mechanism of pain relief
Works at brain and spinal cord level
What is an NSAID mechanism of pain relief
Works at tissue level, reducing PG production, also at level of brain
What is an alpha 2 adrenergic agonist’s mechanism of pain relief
Activate alpha 2 adrenergic receptors both centrally and in the peripherally
What is ketamine’s mechanism of pain relief
Blocks the NMDA receptors in the CNS at the level of the spinal cord
What is a corticosteroid’s mechanism of pain relief
tissue level, reducing prostaglandin production
What is tramadol’s mechanism of pain relief
at brain level + inhibition of NE and serotonin uptake
What are a tranquilizer’s mechanism of pain relief
Potentiate the effects of opioids in some patients
How do you choose what analgesic you’re going to give
The choice of analgesic is governed by the severity and type of pain and the animal’s general condition.
The veterinarian also selects the route of delivery, which may include injection SC, IM, IV, intraarticular, epidural, local infiltration, oral administration, or transdermal patch.
How can pharmacologic analgesia be achieved
Opioid agents
NSAID’s
Other Analgesic Agents: Local anesthetics, Alpha 2 adrenoreceptor agonists, Ketamine, Corticosteroids, Tramadol, Tranquilizers
What is the general disadvantage to opioid agents
Relatively short duration of action when given by injection, necessitating repeat injections which can be expensive.
Also have potential for several side effects
All opiods cross the placental barrier in significant amount
Why don’t you cut or trim the fentanyl patch
It splits unevenly
What are the advantages of inhalant anesthesia
The depth of anesthesia is constantly altered by varying the amount entering the lungs. It is impossible to vary the amount of injectable agent other than injecting increasing amounts of drug.
Elimination of injectable agents is via bloodstream to the rest of the body, liver metabolism and/or renal excretion. Inhalation agents are eliminated via the lung and thus, are less dependent upon patient metabolism and organ function.
Inhalation anesthesia allows high concentrations of O2 (almost 100%) to be delivered to the patient vs. 20% O2 in room air.
Usually patients using inhalation anesthesia are intubated allowing relatively easy access to mechanical ventilation if needed.
What are the disadvantages to inhalant anesthesia
Inhalation anesthesia requires the use of an expensive anesthetic machine. Once purchased, this is relatively economical to use however.
Inhalation anesthesia may become waste anesthetic gas which increases operating room pollution – increasing operating room personnel’s risks for various health related problems – also environmental pollution.
What are the characteristics of an ideal inhalant anesthetic agent
Minimal toxicity – especially to the cardiovascular, respiratory, hepatic, renal and nervous systems.
Minimal toxicity of waste gas to operating room personnel
Ease of administration
Rapid and smooth induction and recovery
Anesthetic depth easily controlled and altered
Good muscle relaxation
Post-operative analgesia
Low cost
Adequate potency (to achieve surgical anesthetic plane)
Nonflammable and nonexplosive (safe to handle)
Inexpensive equipment required
What is the class of Isoflurane
Halogenated Organic Compounds
What is special about Isoflurane, sevoflurane, and desflurane
have low lipid solubility: little retention in boy fat stores, little hepatic metabolism and little renal excretion
What are the Effects on Major Organ Systems of isoflurane
CNS:
Dose-related, reversible depression of the CNS
depress temperature-regulating center, leading to hypothermia
CVS: depress cardiovascular function (vasodilation, ↓ CO, ↓BP, ↓tissue perfusion)
Respiratory system: depress ventilation in a dose-dependent manner (↓ Tv and RR = hypoventilation)
What are the adverse effects of isoflurane
CNS adverse effects: minimal with the currently used halogenated anesthetic
CVS adverse effects: ↓ BP so potential to ↓ renal blood flow (significant in renal patients, or patients receiving nephrotoxic drugs
Respiratory adverse effects: hypoventilation: ↑ risk of hypercapnia + resp. acidosis
What is the minimum alveolar concentration
The MAC is the lowest alveolar concentration that will produce no response from 50% of the patients exposed to a painful stimulus; thus, indicating the presence of the anesthetic agent.
What is the rough guideline for the MAC of an animal
ROUGH GUIDELINE:
1 x MAC = light anesthesia,
1.5 x MAC = surgical anesthesia
2 x MAC = deep anesthesia
What are the physical and chemical properties of isoflurane
high vapor pressure, requiring a precision vaporizer
low blood-gas solubility coefficient (1.46)
= rapid induction and recovery
anesthetist will see response to changes in anesthetic depth within 1 to 2 minutes of adjusting level
Ok then for mask or chamber induction (induce rapid induction) (but irritating and smelly!)
MAC is higher (1.3% to 1.63%) than the older inhalant thus requiring higher levels of anesthetic (1.5 - 2.5% for maintenance) (lower potency)
Low rubber solubility (no absorption of iso through the rubber) so decreased waste gas potential
Stable at room temperature
What are the effects and adverse effects of isoflurane
~~Little effects on HR, does not sensitive heart muscle to epinephrine-induced arrhythmias
~~depresses respiration (greater than halothane but less than methoxyflurane)
~~eliminated through lungs once vap turned off
~~low fat solubility, so little retention in fat, little hepatic metabolism, and little renal excretion of the metabolites occurs (preferred anesthetic for animals with compromised hepatic or renal function, including neonates and geriatrics)
induce good muscle relaxation
~~no post-operative analgesia so post-operative analgesics is advisable
~~Irritants to the respiratory tract
