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How many stages are there in general anesthesia?
When does stage l start and stop?
- Begins as soon as anesthetic drug enters body
- Ends with loss of consciousness (can't wake them up just by stimulating them)
Describe the patient during stage l.
- Conscious, disoriented
- Normal reflexes
- Reduced sensitivity to pain
- Vocalization (crying)
- Normal HR & RR
What is another name for stage l?
When does stage ll start and stop?
- Begins with loss of consciousness
- Ends when patient starts to relax
What is another name for stage ll?
What does "excitement stage" mean?
No longer awake but body is still fighting.
Describe how the body is still fighting during stage ll.
Cry, struggle, howl, thrash, bite, fall off table, paddle legs, vomit
Why do the patients get excited during stage ll?
- Excitement due to lack of inhibition and voluntary control
- Selective depression of inibition centers in brain
How can we minimize excitment during stage ll?
Use preanesthetic drugs
Describe the patient's vitals during stage ll.
- Reflexes: present, variable, may be exaggerated
- HR & RR: decrease as patient goes deeper
- Respiration: irregular
- Pupils: dilated, respond to light
What are the dangers of stage ll?
- Cardiopulmonary arrest
- Aspirate vomit
- Injury to patient or people
What is a "stormy recovery"?
Whatever the patient goes through going down, they go back through waking up.
What is another name for stage lll?
How many planes is stage lll divided into?
Describe the patients vitals during stage lll, plane 1.
- Respiration: regular
- Eyes: start to rotate ventrally (partial miosis)
- Reflexes: palpebral reflex present, less swallowing, patient will react to pain
Can you intubate dogs during stage lll, plane 1? Cats?
What is stage lll, plane 2 called?
Can you intubate cats during stage lll, plane 2?
Describe the patient's respiration during stage lll, plane 2.
Describe the patient's eyes during stage lll, plane 2.
- Slight mydriasis, usually rotated
- Rotated wtih halothane, isoflurane, sevoflurane
- Central with methoxyflurane
Describe the patient's reflexes during stage lll, plane 2.
- Most are lost
- Palpebral reflex gone
- Laryngeal reflex still present in come cats (laryngospasm)
- Tail reflex in cats gone
Describe the patients heart in stage lll, plane 2.
- slightly decreased HR & BP
- Good pulse
What is stage lll, plane 3 called?
When is stage lll, plane 3 necessary?
Surgeries where we need them very relaxed or the surgery requires a lot of stimulation that we don't want them to wake up for (example: spinal surgery)
Describe the patient's respiration during stage lll, plane 3.
Describe the patient's eyes during stage lll, plane 3.
central, moderate mydriasis
Describe the patient's reflexes during stage lll, plane 3.
flaccid (no reflexes)
Describe the patient's heart during stage lll, plane 3.
- decrease HR & BP
- weaker pulse
- CRT > 2 seconds
What is stage lll, plane 4 called?
very deep anesthesia - too deep for any surgery
Describe the patient's respiration during stage lll, plane 4.
Describe the patient's eyes during stage lll, plane 4.
- fully dilated pupils
- central position
- no pupillary light reflex
Describe the patient's reflexes during stage lll, plane 4.
none - flaccid
Describe the patient's heart during stage lll, plane 4.
- seriously decreased HR & BP
- Cardiopulmonary arrest (CPA)
Describe the patient during stage lV.
- almost dead
- respiratory arrest then cardia arrest and then they die
- time to perform CPR
What is general anesthesia?
state of controlled and reversible unconsciousness
What are the characteristics of general anesthesia?
- loss of reflexes
What is the short-acting barbiturate?
What are the ultra short acting barbiturates?
What are the cyclohexamines?
- tiletamine (Telazol)
What are the different inhalation anesthetics?
- diethyl ether
- nitrous oxide
- halogenated compounds
What are the different halogenated compounds?
What is "balanced anesthesia"?
- combination of preanesthetics and anesthetic drugs
- decrease doses of each
- decrease side effects
- increase patient safety
What do we need to take into consideration when choosing the anesthesia protocol?
- type of patient (species, age)
- condition of patient (healthy, ill, injured)
- type of procedure
What is preanesthesia?
time immediately before anesthesia
What do we need to do during the preanesthesia stage?
- collect data
- fasts patient
- give preanesthetic drugs
What are the steps of induction?
- give pre-op drugs
- give inducing drug (injectable or inhalation)
- +/- intubate patient
What is maintenance?
stable depth of anesthesia
The longer the patient stays in maintenance...
the more relaxed, more loss of reflexes, more respiratory & cardiovascular depression
When does recovery begin?
drug starts to leave the brain (patient starts to wake up)
How does a patient recover from injectables?
- drug is removed from the blood
- blood levels become to low to effect the brain
How are injectables metabolized & excreted?
metabolized by the liver & excreted by the kidneys
How are inhalants excreted?
from the lungs
How do the inhalants leave the lungs?
breathed off (exhaled)
Which is a quicker recovery, inhalants or injectables?
What are the reversing agents for injectables?
What is a reversing agent of general anesthesia?
Why do we give preanesthetic drugs?
- prevent bradycardia
- reduce dose of general anesthetic drug
What should you "double check"?
- label syringes
What does it mean to "give to effect"?
use minimum amount of drug
What does "titrate" mean?
give small amounts until you get what you want
What are the three safety mottoes?
- better light than dead
- a little paranoia is a good thing
- breathing is a good sign
Name the advantages of using an inhalant.
safer for critically ill patients because the depth can be changed rapidly
Name the disadvantages of using an inhalant.
Necessity to physically restrain the patient during induction which may take 10 minutes or more, too slow for patients with respiratory compromise, waste gas escape into room air, may allow prolonged excitement period
Name the advantages of inhalant by induction chamber.
good for very fractious patients that can not be physically restrained
Name the disadvantages of inhalant by induction chamber.
- small patients only
- limited ability to monitor
- lots of waste contamination
Name the advantages of induction by IM injection
good for patients not handled easily
Name the disadvantages of induction by IM injection.
- requires larger dose
- slower onset versus IV
- cannot titrate dose to effect
- longer recovery
Name the advantages to induction by oral dose.
appropriate when you can't get drug in any other way
Name the disadvantages to induction by oral dose.
- unknown and variable
- few agents work this way
- none work well enough for induction this way alone
Name the advantages of induction by an IV injection.
- usually the preferred method
- rapid induction
- can "give to effect"
- smaller total dose
- recovery time faster than IM but slower than inhalation
Name disadvantages to inductions by an IV injection.
requires access to a vein
Why is an endotracheal tube used during anesthesia?
- maintain control of airway for manual ventilation if necessary
- prevent aspiration of vomit
- more efficient delivery of anesthetic gas, with less waste
- reduces anatomic dead space
What is anatomic dead space?
all parts of the respiratory system containing gas, but where gas exchange does not take place
What is equipment dead space?
part of the anesthesia circuit, or the endotracheal tube containing gas that the animal must move in order to get fresh gas to the alveoli
Why is it important to minimize dead space?
because anesthesia depresses both respiratory rate and depth, making it more difficult to move gas, possibly leading to hypoxia
The endotracheal tube should go from where to where? How do you measure on an awake patient?
should go from just rostral to the incisor teeth to mid-trachea. approximate length from the tip of the nose to the point of the shoulder
What if the tube is too long?
increases dead space, danger of placing tube into just one lung, thus reducing the volume of gas delivered by half.
What is laryngospasm? In what species is it usually a problem? What do you do about it?
Cats tend to have this problem of intense reflex closure of the laryngeal cartilages, blocking the airway and attempts to pass a tube. Desensitizing with a drop of lidocaine on each cartilage helps.
Why are cuffed endotracheal tubes used? What is the danger of overinflating the cuff?
to seal the space between the tube & the tracheal wall, preventing aspiration & escape of anesthetic gases. overinflation can lead to ischemic damage to the trachea, possibly to necrosis & stricture
What is the only way to know for sure that an endotracheal tube is properly placed in the trachea and not the esophagus?
Seeing it passing through the laryngeal cartilages. Less reliable means are seeing condensation appear on exhalation, movement of the valves in the anesthetic circuit, palpating the larynx.