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
